[PATCH 00/24] netfs: Read/write improvements

[PATCH 00/24] netfs: Read/write improvements

[David Howells]

Hi Christian, Steve, Willy,

This set of patches includes one fscache fix and one cachefiles fix

 (1) Fix a cookie access race in fscache.

 (2) Fix the setxattr/removexattr syscalls to pull their arguments into
     kernel space before taking the sb_writers lock to avoid a deadlock
     against mm->mmap_lock.

A couple of adjustments to the /proc/fs/netfs/stats file:

 (3) All the netfs stats lines begin 'Netfs:'.  Change this to something a
     bit more useful.

 (4) Add a couple of stats counters to track the numbers of skips and waits
     on the per-inode writeback serialisation lock to make it easier to
     check for this as a source of performance loss.

Some miscellaneous bits:

 (5) Reduce the number of conditional branches in netfs_perform_write().

 (6) Move the CIFS_INO_MODIFIED_ATTR flag to the netfs_inode struct and
     remove cifs_post_modify().

 (7) Move the max_len/max_nr_segs members from netfs_io_subrequest to
     netfs_io_request as they're only needed for one subreq at a time.

 (8) Add an 'unknown' source value for tracing purposes.

 (9) Remove NETFS_COPY_TO_CACHE as it's no longer used.

(10) Set the request work function up front at allocation time.

(11) Use bh-disabling spinlocks for rreq->lock as cachefiles completion may
     be run from block-filesystem DIO completion in softirq context.

Then there's the main performance enhancing changes:

(12) Define a structure, struct folio_queue, and a new iterator type,
     ITER_FOLIOQ, to hold a buffer as a replacement for ITER_XARRAY.  See
     that patch for questions about naming and form.

(13) Make cifs RDMA support ITER_FOLIOQ.

(14) Add a function to reset the iterator in a subrequest.

(15) Use folio queues in the write-side helpers instead of xarrays.

(16) Simplify the write-side helpers to use sheaves to skip gaps rather than
     trying to work out where gaps are.

(17) In afs, make the read subrequests asynchronous, putting them into work
     items to allow the next patch to do progressive unlocking/reading.

(18) Overhaul the read-side helpers to improve performance.

(19) Remove fs/netfs/io.c.

(20) Fix the caching of a partial block at the end of a file.

(21) Allow a store to be cancelled.

Then some changes for cifs to make it use folio queues instead of xarrays
for crypto bufferage:

(22) Use raw iteration functions rather than manually coding iteration when
     hashing data.

(23) Switch to using folio_queue for crypto buffers.

(24) Remove the xarray bits.

David

David Howells (23):
  cachefiles: Fix non-taking of sb_writers around set/removexattr
  netfs: Adjust labels in /proc/fs/netfs/stats
  netfs: Record contention stats for writeback lock
  netfs: Reduce number of conditional branches in netfs_perform_write()
  netfs, cifs: Move CIFS_INO_MODIFIED_ATTR to netfs_inode
  netfs: Move max_len/max_nr_segs from netfs_io_subrequest to
    netfs_io_stream
  netfs: Reserve netfs_sreq_source 0 as unset/unknown
  netfs: Remove NETFS_COPY_TO_CACHE
  netfs: Set the request work function upon allocation
  netfs: Use bh-disabling spinlocks for rreq->lock
  mm: Define struct folio_queue and ITER_FOLIOQ to handle a sequence of
    folios
  cifs: Provide the capability to extract from ITER_FOLIOQ to RDMA SGEs
  netfs: Use new folio_queue data type and iterator instead of xarray
    iter
  netfs: Provide an iterator-reset function
  netfs: Simplify the writeback code
  afs: Make read subreqs async
  netfs: Speed up buffered reading
  netfs: Remove fs/netfs/io.c
  cachefiles, netfs: Fix write to partial block at EOF
  netfs: Cancel dirty folios that have no storage destination
  cifs: Use iterate_and_advance*() routines directly for hashing
  cifs: Switch crypto buffer to use a folio_queue rather than an xarray
  cifs: Don't support ITER_XARRAY

Max Kellermann (1):
  fs/netfs/fscache_cookie: add missing "n_accesses" check

 fs/9p/vfs_addr.c             |   5 +-
 fs/afs/file.c                |  29 +-
 fs/afs/fsclient.c            |   9 +-
 fs/afs/write.c               |   4 +-
 fs/afs/yfsclient.c           |   9 +-
 fs/cachefiles/io.c           |  19 +-
 fs/cachefiles/xattr.c        |  34 +-
 fs/ceph/addr.c               |  72 ++--
 fs/netfs/Makefile            |   3 +-
 fs/netfs/buffered_read.c     | 677 ++++++++++++++++++++++++-----------
 fs/netfs/buffered_write.c    | 309 ++++++++--------
 fs/netfs/direct_read.c       | 147 +++++++-
 fs/netfs/fscache_cookie.c    |   4 +
 fs/netfs/internal.h          |  33 +-
 fs/netfs/io.c                | 647 ---------------------------------
 fs/netfs/iterator.c          |  50 +++
 fs/netfs/main.c              |   6 +-
 fs/netfs/misc.c              |  94 +++++
 fs/netfs/objects.c           |  16 +-
 fs/netfs/read_collect.c      | 540 ++++++++++++++++++++++++++++
 fs/netfs/read_retry.c        | 256 +++++++++++++
 fs/netfs/stats.c             |  23 +-
 fs/netfs/write_collect.c     | 243 ++++---------
 fs/netfs/write_issue.c       |  92 ++---
 fs/nfs/fscache.c             |  19 +-
 fs/nfs/fscache.h             |   7 +-
 fs/smb/client/cifsencrypt.c  | 144 +-------
 fs/smb/client/cifsglob.h     |   3 +-
 fs/smb/client/cifssmb.c      |   6 +-
 fs/smb/client/file.c         |  71 ++--
 fs/smb/client/smb2ops.c      | 218 ++++++-----
 fs/smb/client/smb2pdu.c      |  10 +-
 fs/smb/client/smbdirect.c    |  82 +++--
 include/linux/folio_queue.h  | 138 +++++++
 include/linux/iov_iter.h     | 104 ++++++
 include/linux/netfs.h        |  44 ++-
 include/linux/uio.h          |  18 +
 include/trace/events/netfs.h | 140 ++++++--
 lib/iov_iter.c               | 229 +++++++++++-
 lib/kunit_iov_iter.c         | 259 ++++++++++++++
 lib/scatterlist.c            |  69 +++-
 41 files changed, 3175 insertions(+), 1707 deletions(-)
 delete mode 100644 fs/netfs/io.c
 create mode 100644 fs/netfs/read_collect.c
 create mode 100644 fs/netfs/read_retry.c
 create mode 100644 include/linux/folio_queue.h

[PATCH 01/24] fs/netfs/fscache_cookie: add missing "n_accesses" check

[David Howells]

From: Max Kellermann <max.kellermann@ionos.com>

This fixes a NULL pointer dereference bug due to a data race which
looks like this:

  BUG: kernel NULL pointer dereference, address: 0000000000000008
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: 0000 [#1] SMP PTI
  CPU: 33 PID: 16573 Comm: kworker/u97:799 Not tainted 6.8.7-cm4all1-hp+ #43
  Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 10/17/2018
  Workqueue: events_unbound netfs_rreq_write_to_cache_work
  RIP: 0010:cachefiles_prepare_write+0x30/0xa0
  Code: 57 41 56 45 89 ce 41 55 49 89 cd 41 54 49 89 d4 55 53 48 89 fb 48 83 ec 08 48 8b 47 08 48 83 7f 10 00 48 89 34 24 48 8b 68 20 <48> 8b 45 08 4c 8b 38 74 45 49 8b 7f 50 e8 4e a9 b0 ff 48 8b 73 10
  RSP: 0018:ffffb4e78113bde0 EFLAGS: 00010286
  RAX: ffff976126be6d10 RBX: ffff97615cdb8438 RCX: 0000000000020000
  RDX: ffff97605e6c4c68 RSI: ffff97605e6c4c60 RDI: ffff97615cdb8438
  RBP: 0000000000000000 R08: 0000000000278333 R09: 0000000000000001
  R10: ffff97605e6c4600 R11: 0000000000000001 R12: ffff97605e6c4c68
  R13: 0000000000020000 R14: 0000000000000001 R15: ffff976064fe2c00
  FS:  0000000000000000(0000) GS:ffff9776dfd40000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000008 CR3: 000000005942c002 CR4: 00000000001706f0
  Call Trace:
   <TASK>
   ? __die+0x1f/0x70
   ? page_fault_oops+0x15d/0x440
   ? search_module_extables+0xe/0x40
   ? fixup_exception+0x22/0x2f0
   ? exc_page_fault+0x5f/0x100
   ? asm_exc_page_fault+0x22/0x30
   ? cachefiles_prepare_write+0x30/0xa0
   netfs_rreq_write_to_cache_work+0x135/0x2e0
   process_one_work+0x137/0x2c0
   worker_thread+0x2e9/0x400
   ? __pfx_worker_thread+0x10/0x10
   kthread+0xcc/0x100
   ? __pfx_kthread+0x10/0x10
   ret_from_fork+0x30/0x50
   ? __pfx_kthread+0x10/0x10
   ret_from_fork_asm+0x1b/0x30
   </TASK>
  Modules linked in:
  CR2: 0000000000000008
  ---[ end trace 0000000000000000 ]---

This happened because fscache_cookie_state_machine() was slow and was
still running while another process invoked fscache_unuse_cookie();
this led to a fscache_cookie_lru_do_one() call, setting the
FSCACHE_COOKIE_DO_LRU_DISCARD flag, which was picked up by
fscache_cookie_state_machine(), withdrawing the cookie via
cachefiles_withdraw_cookie(), clearing cookie->cache_priv.

At the same time, yet another process invoked
cachefiles_prepare_write(), which found a NULL pointer in this code
line:

  struct cachefiles_object *object = cachefiles_cres_object(cres);

The next line crashes, obviously:

  struct cachefiles_cache *cache = object->volume->cache;

During cachefiles_prepare_write(), the "n_accesses" counter is
non-zero (via fscache_begin_operation()).  The cookie must not be
withdrawn until it drops to zero.

The counter is checked by fscache_cookie_state_machine() before
switching to FSCACHE_COOKIE_STATE_RELINQUISHING and
FSCACHE_COOKIE_STATE_WITHDRAWING (in "case
FSCACHE_COOKIE_STATE_FAILED"), but not for
FSCACHE_COOKIE_STATE_LRU_DISCARDING ("case
FSCACHE_COOKIE_STATE_ACTIVE").

This patch adds the missing check.  With a non-zero access counter,
the function returns and the next fscache_end_cookie_access() call
will queue another fscache_cookie_state_machine() call to handle the
still-pending FSCACHE_COOKIE_DO_LRU_DISCARD.

Fixes: 12bb21a29c19 ("fscache: Implement cookie user counting and resource pinning")
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: stable@vger.kernel.org
---
 fs/netfs/fscache_cookie.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/netfs/fscache_cookie.c b/fs/netfs/fscache_cookie.c
index bce2492186d0..d4d4b3a8b106 100644
--- a/fs/netfs/fscache_cookie.c
+++ b/fs/netfs/fscache_cookie.c
@@ -741,6 +741,10 @@ static void fscache_cookie_state_machine(struct fscache_cookie *cookie)
 			spin_lock(&cookie->lock);
 		}
 		if (test_bit(FSCACHE_COOKIE_DO_LRU_DISCARD, &cookie->flags)) {
+			if (atomic_read(&cookie->n_accesses) != 0)
+				/* still being accessed: postpone it */
+				break;
+
 			__fscache_set_cookie_state(cookie,
 						   FSCACHE_COOKIE_STATE_LRU_DISCARDING);
 			wake = true;

[PATCH 02/24] cachefiles: Fix non-taking of sb_writers around set/removexattr

[David Howells]

Unlike other vfs_xxxx() calls, vfs_setxattr() and vfs_removexattr() don't
take the sb_writers lock, so the caller should do it for them.

Fix cachefiles to do this.

Fixes: 9ae326a69004 ("CacheFiles: A cache that backs onto a mounted filesystem")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Gao Xiang <xiang@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-erofs@lists.ozlabs.org
cc: linux-fsdevel@vger.kernel.org
---
 fs/cachefiles/xattr.c | 34 ++++++++++++++++++++++++++--------
 1 file changed, 26 insertions(+), 8 deletions(-)

diff --git a/fs/cachefiles/xattr.c b/fs/cachefiles/xattr.c
index 4dd8a993c60a..7c6f260a3be5 100644
--- a/fs/cachefiles/xattr.c
+++ b/fs/cachefiles/xattr.c
@@ -64,9 +64,15 @@ int cachefiles_set_object_xattr(struct cachefiles_object *object)
 		memcpy(buf->data, fscache_get_aux(object->cookie), len);
 
 	ret = cachefiles_inject_write_error();
-	if (ret == 0)
-		ret = vfs_setxattr(&nop_mnt_idmap, dentry, cachefiles_xattr_cache,
-				   buf, sizeof(struct cachefiles_xattr) + len, 0);
+	if (ret == 0) {
+		ret = mnt_want_write_file(file);
+		if (ret == 0) {
+			ret = vfs_setxattr(&nop_mnt_idmap, dentry,
+					   cachefiles_xattr_cache, buf,
+					   sizeof(struct cachefiles_xattr) + len, 0);
+			mnt_drop_write_file(file);
+		}
+	}
 	if (ret < 0) {
 		trace_cachefiles_vfs_error(object, file_inode(file), ret,
 					   cachefiles_trace_setxattr_error);
@@ -151,8 +157,14 @@ int cachefiles_remove_object_xattr(struct cachefiles_cache *cache,
 	int ret;
 
 	ret = cachefiles_inject_remove_error();
-	if (ret == 0)
-		ret = vfs_removexattr(&nop_mnt_idmap, dentry, cachefiles_xattr_cache);
+	if (ret == 0) {
+		ret = mnt_want_write(cache->mnt);
+		if (ret == 0) {
+			ret = vfs_removexattr(&nop_mnt_idmap, dentry,
+					      cachefiles_xattr_cache);
+			mnt_drop_write(cache->mnt);
+		}
+	}
 	if (ret < 0) {
 		trace_cachefiles_vfs_error(object, d_inode(dentry), ret,
 					   cachefiles_trace_remxattr_error);
@@ -208,9 +220,15 @@ bool cachefiles_set_volume_xattr(struct cachefiles_volume *volume)
 	memcpy(buf->data, p, volume->vcookie->coherency_len);
 
 	ret = cachefiles_inject_write_error();
-	if (ret == 0)
-		ret = vfs_setxattr(&nop_mnt_idmap, dentry, cachefiles_xattr_cache,
-				   buf, len, 0);
+	if (ret == 0) {
+		ret = mnt_want_write(volume->cache->mnt);
+		if (ret == 0) {
+			ret = vfs_setxattr(&nop_mnt_idmap, dentry,
+					   cachefiles_xattr_cache,
+					   buf, len, 0);
+			mnt_drop_write(volume->cache->mnt);
+		}
+	}
 	if (ret < 0) {
 		trace_cachefiles_vfs_error(NULL, d_inode(dentry), ret,
 					   cachefiles_trace_setxattr_error);

[PATCH 03/24] netfs: Adjust labels in /proc/fs/netfs/stats

[David Howells]

Adjust the labels in /proc/fs/netfs/stats that refer to netfs-specific
counters.  These currently all begin with "Netfs", but change them to begin
with more specific labels.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/stats.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/netfs/stats.c b/fs/netfs/stats.c
index 0892768eea32..95ed2d2623a8 100644
--- a/fs/netfs/stats.c
+++ b/fs/netfs/stats.c
@@ -42,39 +42,39 @@ atomic_t netfs_n_wh_write_failed;
 
 int netfs_stats_show(struct seq_file *m, void *v)
 {
-	seq_printf(m, "Netfs  : DR=%u RA=%u RF=%u WB=%u WBZ=%u\n",
+	seq_printf(m, "Reads  : DR=%u RA=%u RF=%u WB=%u WBZ=%u\n",
 		   atomic_read(&netfs_n_rh_dio_read),
 		   atomic_read(&netfs_n_rh_readahead),
 		   atomic_read(&netfs_n_rh_read_folio),
 		   atomic_read(&netfs_n_rh_write_begin),
 		   atomic_read(&netfs_n_rh_write_zskip));
-	seq_printf(m, "Netfs  : BW=%u WT=%u DW=%u WP=%u\n",
+	seq_printf(m, "Writes : BW=%u WT=%u DW=%u WP=%u\n",
 		   atomic_read(&netfs_n_wh_buffered_write),
 		   atomic_read(&netfs_n_wh_writethrough),
 		   atomic_read(&netfs_n_wh_dio_write),
 		   atomic_read(&netfs_n_wh_writepages));
-	seq_printf(m, "Netfs  : ZR=%u sh=%u sk=%u\n",
+	seq_printf(m, "ZeroOps: ZR=%u sh=%u sk=%u\n",
 		   atomic_read(&netfs_n_rh_zero),
 		   atomic_read(&netfs_n_rh_short_read),
 		   atomic_read(&netfs_n_rh_write_zskip));
-	seq_printf(m, "Netfs  : DL=%u ds=%u df=%u di=%u\n",
+	seq_printf(m, "DownOps: DL=%u ds=%u df=%u di=%u\n",
 		   atomic_read(&netfs_n_rh_download),
 		   atomic_read(&netfs_n_rh_download_done),
 		   atomic_read(&netfs_n_rh_download_failed),
 		   atomic_read(&netfs_n_rh_download_instead));
-	seq_printf(m, "Netfs  : RD=%u rs=%u rf=%u\n",
+	seq_printf(m, "CaRdOps: RD=%u rs=%u rf=%u\n",
 		   atomic_read(&netfs_n_rh_read),
 		   atomic_read(&netfs_n_rh_read_done),
 		   atomic_read(&netfs_n_rh_read_failed));
-	seq_printf(m, "Netfs  : UL=%u us=%u uf=%u\n",
+	seq_printf(m, "UpldOps: UL=%u us=%u uf=%u\n",
 		   atomic_read(&netfs_n_wh_upload),
 		   atomic_read(&netfs_n_wh_upload_done),
 		   atomic_read(&netfs_n_wh_upload_failed));
-	seq_printf(m, "Netfs  : WR=%u ws=%u wf=%u\n",
+	seq_printf(m, "CaWrOps: WR=%u ws=%u wf=%u\n",
 		   atomic_read(&netfs_n_wh_write),
 		   atomic_read(&netfs_n_wh_write_done),
 		   atomic_read(&netfs_n_wh_write_failed));
-	seq_printf(m, "Netfs  : rr=%u sr=%u wsc=%u\n",
+	seq_printf(m, "Objs   : rr=%u sr=%u wsc=%u\n",
 		   atomic_read(&netfs_n_rh_rreq),
 		   atomic_read(&netfs_n_rh_sreq),
 		   atomic_read(&netfs_n_wh_wstream_conflict));

[PATCH 04/24] netfs: Record contention stats for writeback lock

[David Howells]

Record statistics for contention upon the writeback serialisation lock that
prevents racing writeback calls from causing each other to interleave their
writebacks.  These can be viewed in /proc/fs/netfs/stats on the WbLock line,
with skip=N indicating the number of non-SYNC writebacks skipped and wait=N
indicating the number of SYNC writebacks that waited.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Steve French <sfrench@samba.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/internal.h    |  2 ++
 fs/netfs/stats.c       |  5 +++++
 fs/netfs/write_issue.c | 10 +++++++---
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 7773f3d855a9..9e6e0e59d7e4 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -117,6 +117,8 @@ extern atomic_t netfs_n_wh_upload_failed;
 extern atomic_t netfs_n_wh_write;
 extern atomic_t netfs_n_wh_write_done;
 extern atomic_t netfs_n_wh_write_failed;
+extern atomic_t netfs_n_wb_lock_skip;
+extern atomic_t netfs_n_wb_lock_wait;
 
 int netfs_stats_show(struct seq_file *m, void *v);
 
diff --git a/fs/netfs/stats.c b/fs/netfs/stats.c
index 95ed2d2623a8..5fe1c396e24f 100644
--- a/fs/netfs/stats.c
+++ b/fs/netfs/stats.c
@@ -39,6 +39,8 @@ atomic_t netfs_n_wh_upload_failed;
 atomic_t netfs_n_wh_write;
 atomic_t netfs_n_wh_write_done;
 atomic_t netfs_n_wh_write_failed;
+atomic_t netfs_n_wb_lock_skip;
+atomic_t netfs_n_wb_lock_wait;
 
 int netfs_stats_show(struct seq_file *m, void *v)
 {
@@ -78,6 +80,9 @@ int netfs_stats_show(struct seq_file *m, void *v)
 		   atomic_read(&netfs_n_rh_rreq),
 		   atomic_read(&netfs_n_rh_sreq),
 		   atomic_read(&netfs_n_wh_wstream_conflict));
+	seq_printf(m, "WbLock : skip=%u wait=%u\n",
+		   atomic_read(&netfs_n_wb_lock_skip),
+		   atomic_read(&netfs_n_wb_lock_wait));
 	return fscache_stats_show(m);
 }
 EXPORT_SYMBOL(netfs_stats_show);
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 9258d30cffe3..e7d4f39b8fdc 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -503,10 +503,14 @@ int netfs_writepages(struct address_space *mapping,
 	struct folio *folio;
 	int error = 0;
 
-	if (wbc->sync_mode == WB_SYNC_ALL)
+	if (!mutex_trylock(&ictx->wb_lock)) {
+		if (wbc->sync_mode == WB_SYNC_NONE) {
+			netfs_stat(&netfs_n_wb_lock_skip);
+			return 0;
+		}
+		netfs_stat(&netfs_n_wb_lock_wait);
 		mutex_lock(&ictx->wb_lock);
-	else if (!mutex_trylock(&ictx->wb_lock))
-		return 0;
+	}
 
 	/* Need the first folio to be able to set up the op. */
 	folio = writeback_iter(mapping, wbc, NULL, &error);

[PATCH 05/24] netfs: Reduce number of conditional branches in netfs_perform_write()

[David Howells]

Reduce the number of conditional branches in netfs_perform_write() by
merging in netfs_how_to_modify() and then creating a separate if-statement
for each way we might modify a folio.  Note that this means replicating the
data copy in each path.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/buffered_write.c    | 299 ++++++++++++++++-------------------
 include/trace/events/netfs.h |   2 -
 2 files changed, 134 insertions(+), 167 deletions(-)

diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index 4726c315453c..fba5b238455b 100644
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -13,91 +13,22 @@
 #include <linux/pagevec.h>
 #include "internal.h"
 
-/*
- * Determined write method.  Adjust netfs_folio_traces if this is changed.
- */
-enum netfs_how_to_modify {
-	NETFS_FOLIO_IS_UPTODATE,	/* Folio is uptodate already */
-	NETFS_JUST_PREFETCH,		/* We have to read the folio anyway */
-	NETFS_WHOLE_FOLIO_MODIFY,	/* We're going to overwrite the whole folio */
-	NETFS_MODIFY_AND_CLEAR,		/* We can assume there is no data to be downloaded. */
-	NETFS_STREAMING_WRITE,		/* Store incomplete data in non-uptodate page. */
-	NETFS_STREAMING_WRITE_CONT,	/* Continue streaming write. */
-	NETFS_FLUSH_CONTENT,		/* Flush incompatible content. */
-};
-
-static void netfs_set_group(struct folio *folio, struct netfs_group *netfs_group)
+static void __netfs_set_group(struct folio *folio, struct netfs_group *netfs_group)
 {
-	void *priv = folio_get_private(folio);
-
-	if (netfs_group && (!priv || priv == NETFS_FOLIO_COPY_TO_CACHE))
+	if (netfs_group)
 		folio_attach_private(folio, netfs_get_group(netfs_group));
-	else if (!netfs_group && priv == NETFS_FOLIO_COPY_TO_CACHE)
-		folio_detach_private(folio);
 }
 
-/*
- * Decide how we should modify a folio.  We might be attempting to do
- * write-streaming, in which case we don't want to a local RMW cycle if we can
- * avoid it.  If we're doing local caching or content crypto, we award that
- * priority over avoiding RMW.  If the file is open readably, then we also
- * assume that we may want to read what we wrote.
- */
-static enum netfs_how_to_modify netfs_how_to_modify(struct netfs_inode *ctx,
-						    struct file *file,
-						    struct folio *folio,
-						    void *netfs_group,
-						    size_t flen,
-						    size_t offset,
-						    size_t len,
-						    bool maybe_trouble)
+static void netfs_set_group(struct folio *folio, struct netfs_group *netfs_group)
 {
-	struct netfs_folio *finfo = netfs_folio_info(folio);
-	struct netfs_group *group = netfs_folio_group(folio);
-	loff_t pos = folio_pos(folio);
-
-	_enter("");
-
-	if (group != netfs_group && group != NETFS_FOLIO_COPY_TO_CACHE)
-		return NETFS_FLUSH_CONTENT;
-
-	if (folio_test_uptodate(folio))
-		return NETFS_FOLIO_IS_UPTODATE;
-
-	if (pos >= ctx->zero_point)
-		return NETFS_MODIFY_AND_CLEAR;
-
-	if (!maybe_trouble && offset == 0 && len >= flen)
-		return NETFS_WHOLE_FOLIO_MODIFY;
-
-	if (file->f_mode & FMODE_READ)
-		goto no_write_streaming;
-
-	if (netfs_is_cache_enabled(ctx)) {
-		/* We don't want to get a streaming write on a file that loses
-		 * caching service temporarily because the backing store got
-		 * culled.
-		 */
-		goto no_write_streaming;
-	}
+	void *priv = folio_get_private(folio);
 
-	if (!finfo)
-		return NETFS_STREAMING_WRITE;
-
-	/* We can continue a streaming write only if it continues on from the
-	 * previous.  If it overlaps, we must flush lest we suffer a partial
-	 * copy and disjoint dirty regions.
-	 */
-	if (offset == finfo->dirty_offset + finfo->dirty_len)
-		return NETFS_STREAMING_WRITE_CONT;
-	return NETFS_FLUSH_CONTENT;
-
-no_write_streaming:
-	if (finfo) {
-		netfs_stat(&netfs_n_wh_wstream_conflict);
-		return NETFS_FLUSH_CONTENT;
+	if (unlikely(priv != netfs_group)) {
+		if (netfs_group && (!priv || priv == NETFS_FOLIO_COPY_TO_CACHE))
+			folio_attach_private(folio, netfs_get_group(netfs_group));
+		else if (!netfs_group && priv == NETFS_FOLIO_COPY_TO_CACHE)
+			folio_detach_private(folio);
 	}
-	return NETFS_JUST_PREFETCH;
 }
 
 /*
@@ -177,13 +108,10 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 		.range_end	= iocb->ki_pos + iter->count,
 	};
 	struct netfs_io_request *wreq = NULL;
-	struct netfs_folio *finfo;
-	struct folio *folio, *writethrough = NULL;
-	enum netfs_how_to_modify howto;
-	enum netfs_folio_trace trace;
+	struct folio *folio = NULL, *writethrough = NULL;
 	unsigned int bdp_flags = (iocb->ki_flags & IOCB_NOWAIT) ? BDP_ASYNC : 0;
 	ssize_t written = 0, ret, ret2;
-	loff_t i_size, pos = iocb->ki_pos, from, to;
+	loff_t i_size, pos = iocb->ki_pos;
 	size_t max_chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER;
 	bool maybe_trouble = false;
 
@@ -213,15 +141,14 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 	}
 
 	do {
+		struct netfs_folio *finfo;
+		struct netfs_group *group;
+		unsigned long long fpos;
 		size_t flen;
 		size_t offset;	/* Offset into pagecache folio */
 		size_t part;	/* Bytes to write to folio */
 		size_t copied;	/* Bytes copied from user */
 
-		ret = balance_dirty_pages_ratelimited_flags(mapping, bdp_flags);
-		if (unlikely(ret < 0))
-			break;
-
 		offset = pos & (max_chunk - 1);
 		part = min(max_chunk - offset, iov_iter_count(iter));
 
@@ -247,7 +174,8 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 		}
 
 		flen = folio_size(folio);
-		offset = pos & (flen - 1);
+		fpos = folio_pos(folio);
+		offset = pos - fpos;
 		part = min_t(size_t, flen - offset, part);
 
 		/* Wait for writeback to complete.  The writeback engine owns
@@ -265,71 +193,52 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 			goto error_folio_unlock;
 		}
 
-		/* See if we need to prefetch the area we're going to modify.
-		 * We need to do this before we get a lock on the folio in case
-		 * there's more than one writer competing for the same cache
-		 * block.
+		/* Decide how we should modify a folio.  We might be attempting
+		 * to do write-streaming, in which case we don't want to a
+		 * local RMW cycle if we can avoid it.  If we're doing local
+		 * caching or content crypto, we award that priority over
+		 * avoiding RMW.  If the file is open readably, then we also
+		 * assume that we may want to read what we wrote.
 		 */
-		howto = netfs_how_to_modify(ctx, file, folio, netfs_group,
-					    flen, offset, part, maybe_trouble);
-		_debug("howto %u", howto);
-		switch (howto) {
-		case NETFS_JUST_PREFETCH:
-			ret = netfs_prefetch_for_write(file, folio, offset, part);
-			if (ret < 0) {
-				_debug("prefetch = %zd", ret);
-				goto error_folio_unlock;
-			}
-			break;
-		case NETFS_FOLIO_IS_UPTODATE:
-		case NETFS_WHOLE_FOLIO_MODIFY:
-		case NETFS_STREAMING_WRITE_CONT:
-			break;
-		case NETFS_MODIFY_AND_CLEAR:
-			zero_user_segment(&folio->page, 0, offset);
-			break;
-		case NETFS_STREAMING_WRITE:
-			ret = -EIO;
-			if (WARN_ON(folio_get_private(folio)))
-				goto error_folio_unlock;
-			break;
-		case NETFS_FLUSH_CONTENT:
-			trace_netfs_folio(folio, netfs_flush_content);
-			from = folio_pos(folio);
-			to = from + folio_size(folio) - 1;
-			folio_unlock(folio);
-			folio_put(folio);
-			ret = filemap_write_and_wait_range(mapping, from, to);
-			if (ret < 0)
-				goto error_folio_unlock;
-			continue;
-		}
-
-		if (mapping_writably_mapped(mapping))
-			flush_dcache_folio(folio);
-
-		copied = copy_folio_from_iter_atomic(folio, offset, part, iter);
-
-		flush_dcache_folio(folio);
-
-		/* Deal with a (partially) failed copy */
-		if (copied == 0) {
-			ret = -EFAULT;
-			goto error_folio_unlock;
+		finfo = netfs_folio_info(folio);
+		group = netfs_folio_group(folio);
+
+		if (unlikely(group != netfs_group) &&
+		    group != NETFS_FOLIO_COPY_TO_CACHE)
+			goto flush_content;
+
+		if (folio_test_uptodate(folio)) {
+			if (mapping_writably_mapped(mapping))
+				flush_dcache_folio(folio);
+			copied = copy_folio_from_iter_atomic(folio, offset, part, iter);
+			if (unlikely(copied == 0))
+				goto copy_failed;
+			netfs_set_group(folio, netfs_group);
+			trace_netfs_folio(folio, netfs_folio_is_uptodate);
+			goto copied;
 		}
 
-		trace = (enum netfs_folio_trace)howto;
-		switch (howto) {
-		case NETFS_FOLIO_IS_UPTODATE:
-		case NETFS_JUST_PREFETCH:
-			netfs_set_group(folio, netfs_group);
-			break;
-		case NETFS_MODIFY_AND_CLEAR:
+		/* If the page is above the zero-point then we assume that the
+		 * server would just return a block of zeros or a short read if
+		 * we try to read it.
+		 */
+		if (fpos >= ctx->zero_point) {
+			zero_user_segment(&folio->page, 0, offset);
+			copied = copy_folio_from_iter_atomic(folio, offset, part, iter);
+			if (unlikely(copied == 0))
+				goto copy_failed;
 			zero_user_segment(&folio->page, offset + copied, flen);
-			netfs_set_group(folio, netfs_group);
+			__netfs_set_group(folio, netfs_group);
 			folio_mark_uptodate(folio);
-			break;
-		case NETFS_WHOLE_FOLIO_MODIFY:
+			trace_netfs_folio(folio, netfs_modify_and_clear);
+			goto copied;
+		}
+
+		/* See if we can write a whole folio in one go. */
+		if (!maybe_trouble && offset == 0 && part >= flen) {
+			copied = copy_folio_from_iter_atomic(folio, offset, part, iter);
+			if (unlikely(copied == 0))
+				goto copy_failed;
 			if (unlikely(copied < part)) {
 				maybe_trouble = true;
 				iov_iter_revert(iter, copied);
@@ -337,16 +246,53 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 				folio_unlock(folio);
 				goto retry;
 			}
-			netfs_set_group(folio, netfs_group);
+			__netfs_set_group(folio, netfs_group);
 			folio_mark_uptodate(folio);
-			break;
-		case NETFS_STREAMING_WRITE:
+			trace_netfs_folio(folio, netfs_whole_folio_modify);
+			goto copied;
+		}
+
+		/* We don't want to do a streaming write on a file that loses
+		 * caching service temporarily because the backing store got
+		 * culled and we don't really want to get a streaming write on
+		 * a file that's open for reading as ->read_folio() then has to
+		 * be able to flush it.
+		 */
+		if ((file->f_mode & FMODE_READ) ||
+		    netfs_is_cache_enabled(ctx)) {
+			if (finfo) {
+				netfs_stat(&netfs_n_wh_wstream_conflict);
+				goto flush_content;
+			}
+			ret = netfs_prefetch_for_write(file, folio, offset, part);
+			if (ret < 0) {
+				_debug("prefetch = %zd", ret);
+				goto error_folio_unlock;
+			}
+			/* Note that copy-to-cache may have been set. */
+
+			copied = copy_folio_from_iter_atomic(folio, offset, part, iter);
+			if (unlikely(copied == 0))
+				goto copy_failed;
+			netfs_set_group(folio, netfs_group);
+			trace_netfs_folio(folio, netfs_just_prefetch);
+			goto copied;
+		}
+
+		if (!finfo) {
+			ret = -EIO;
+			if (WARN_ON(folio_get_private(folio)))
+				goto error_folio_unlock;
+			copied = copy_folio_from_iter_atomic(folio, offset, part, iter);
+			if (unlikely(copied == 0))
+				goto copy_failed;
 			if (offset == 0 && copied == flen) {
-				netfs_set_group(folio, netfs_group);
+				__netfs_set_group(folio, netfs_group);
 				folio_mark_uptodate(folio);
-				trace = netfs_streaming_filled_page;
-				break;
+				trace_netfs_folio(folio, netfs_streaming_filled_page);
+				goto copied;
 			}
+
 			finfo = kzalloc(sizeof(*finfo), GFP_KERNEL);
 			if (!finfo) {
 				iov_iter_revert(iter, copied);
@@ -358,9 +304,18 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 			finfo->dirty_len = copied;
 			folio_attach_private(folio, (void *)((unsigned long)finfo |
 							     NETFS_FOLIO_INFO));
-			break;
-		case NETFS_STREAMING_WRITE_CONT:
-			finfo = netfs_folio_info(folio);
+			trace_netfs_folio(folio, netfs_streaming_write);
+			goto copied;
+		}
+
+		/* We can continue a streaming write only if it continues on
+		 * from the previous.  If it overlaps, we must flush lest we
+		 * suffer a partial copy and disjoint dirty regions.
+		 */
+		if (offset == finfo->dirty_offset + finfo->dirty_len) {
+			copied = copy_folio_from_iter_atomic(folio, offset, part, iter);
+			if (unlikely(copied == 0))
+				goto copy_failed;
 			finfo->dirty_len += copied;
 			if (finfo->dirty_offset == 0 && finfo->dirty_len == flen) {
 				if (finfo->netfs_group)
@@ -369,17 +324,25 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 					folio_detach_private(folio);
 				folio_mark_uptodate(folio);
 				kfree(finfo);
-				trace = netfs_streaming_cont_filled_page;
+				trace_netfs_folio(folio, netfs_streaming_cont_filled_page);
+			} else {
+				trace_netfs_folio(folio, netfs_streaming_write_cont);
 			}
-			break;
-		default:
-			WARN(true, "Unexpected modify type %u ix=%lx\n",
-			     howto, folio->index);
-			ret = -EIO;
-			goto error_folio_unlock;
+			goto copied;
 		}
 
-		trace_netfs_folio(folio, trace);
+		/* Incompatible write; flush the folio and try again. */
+	flush_content:
+		trace_netfs_folio(folio, netfs_flush_content);
+		folio_unlock(folio);
+		folio_put(folio);
+		ret = filemap_write_and_wait_range(mapping, fpos, fpos + flen - 1);
+		if (ret < 0)
+			goto error_folio_unlock;
+		continue;
+
+	copied:
+		flush_dcache_folio(folio);
 
 		/* Update the inode size if we moved the EOF marker */
 		pos += copied;
@@ -401,6 +364,10 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 		folio_put(folio);
 		folio = NULL;
 
+		ret = balance_dirty_pages_ratelimited_flags(mapping, bdp_flags);
+		if (unlikely(ret < 0))
+			break;
+
 		cond_resched();
 	} while (iov_iter_count(iter));
 
@@ -421,6 +388,8 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 	_leave(" = %zd [%zd]", written, ret);
 	return written ? written : ret;
 
+copy_failed:
+	ret = -EFAULT;
 error_folio_unlock:
 	folio_unlock(folio);
 	folio_put(folio);
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index da23484268df..fc5dbd19f120 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -128,7 +128,6 @@
 	E_(netfs_sreq_trace_put_terminated,	"PUT TERM   ")
 
 #define netfs_folio_traces					\
-	/* The first few correspond to enum netfs_how_to_modify */	\
 	EM(netfs_folio_is_uptodate,		"mod-uptodate")	\
 	EM(netfs_just_prefetch,			"mod-prefetch")	\
 	EM(netfs_whole_folio_modify,		"mod-whole-f")	\
@@ -138,7 +137,6 @@
 	EM(netfs_flush_content,			"flush")	\
 	EM(netfs_streaming_filled_page,		"mod-streamw-f") \
 	EM(netfs_streaming_cont_filled_page,	"mod-streamw-f+") \
-	/* The rest are for writeback */			\
 	EM(netfs_folio_trace_cancel_copy,	"cancel-copy")	\
 	EM(netfs_folio_trace_clear,		"clear")	\
 	EM(netfs_folio_trace_clear_cc,		"clear-cc")	\

[PATCH 06/24] netfs, cifs: Move CIFS_INO_MODIFIED_ATTR to netfs_inode

[David Howells]

Move CIFS_INO_MODIFIED_ATTR to netfs_inode as NETFS_ICTX_MODIFIED_ATTR and
then make netfs_perform_write() set it.  This means that cifs doesn't need
to implement the ->post_modify() hook.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/buffered_write.c | 10 ++++++++--
 fs/smb/client/cifsglob.h  |  1 -
 fs/smb/client/file.c      |  9 +--------
 include/linux/netfs.h     |  1 +
 4 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/fs/netfs/buffered_write.c b/fs/netfs/buffered_write.c
index fba5b238455b..7ecae5392a1f 100644
--- a/fs/netfs/buffered_write.c
+++ b/fs/netfs/buffered_write.c
@@ -372,8 +372,14 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 	} while (iov_iter_count(iter));
 
 out:
-	if (likely(written) && ctx->ops->post_modify)
-		ctx->ops->post_modify(inode);
+	if (likely(written)) {
+		/* Set indication that ctime and mtime got updated in case
+		 * close is deferred.
+		 */
+		set_bit(NETFS_ICTX_MODIFIED_ATTR, &ctx->flags);
+		if (unlikely(ctx->ops->post_modify))
+			ctx->ops->post_modify(inode);
+	}
 
 	if (unlikely(wreq)) {
 		ret2 = netfs_end_writethrough(wreq, &wbc, writethrough);
diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 8e86fec7dcd2..85e6495dc440 100644
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -1573,7 +1573,6 @@ struct cifsInodeInfo {
 #define CIFS_INO_DELETE_PENDING		  (3) /* delete pending on server */
 #define CIFS_INO_INVALID_MAPPING	  (4) /* pagecache is invalid */
 #define CIFS_INO_LOCK			  (5) /* lock bit for synchronization */
-#define CIFS_INO_MODIFIED_ATTR            (6) /* Indicate change in mtime/ctime */
 #define CIFS_INO_CLOSE_ON_LOCK            (7) /* Not to defer the close when lock is set */
 	unsigned long flags;
 	spinlock_t writers_lock;
diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index b2405dd4d4d4..fd9f82ff44b8 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -286,12 +286,6 @@ static void cifs_rreq_done(struct netfs_io_request *rreq)
 		inode_set_atime_to_ts(inode, inode_get_mtime(inode));
 }
 
-static void cifs_post_modify(struct inode *inode)
-{
-	/* Indication to update ctime and mtime as close is deferred */
-	set_bit(CIFS_INO_MODIFIED_ATTR, &CIFS_I(inode)->flags);
-}
-
 static void cifs_free_request(struct netfs_io_request *rreq)
 {
 	struct cifs_io_request *req = container_of(rreq, struct cifs_io_request, rreq);
@@ -338,7 +332,6 @@ const struct netfs_request_ops cifs_req_ops = {
 	.clamp_length		= cifs_clamp_length,
 	.issue_read		= cifs_req_issue_read,
 	.done			= cifs_rreq_done,
-	.post_modify		= cifs_post_modify,
 	.begin_writeback	= cifs_begin_writeback,
 	.prepare_write		= cifs_prepare_write,
 	.issue_write		= cifs_issue_write,
@@ -1362,7 +1355,7 @@ int cifs_close(struct inode *inode, struct file *file)
 		dclose = kmalloc(sizeof(struct cifs_deferred_close), GFP_KERNEL);
 		if ((cfile->status_file_deleted == false) &&
 		    (smb2_can_defer_close(inode, dclose))) {
-			if (test_and_clear_bit(CIFS_INO_MODIFIED_ATTR, &cinode->flags)) {
+			if (test_and_clear_bit(NETFS_ICTX_MODIFIED_ATTR, &cinode->netfs.flags)) {
 				inode_set_mtime_to_ts(inode,
 						      inode_set_ctime_current(inode));
 			}
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 5d0288938cc2..2d438aaae685 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -73,6 +73,7 @@ struct netfs_inode {
 #define NETFS_ICTX_ODIRECT	0		/* The file has DIO in progress */
 #define NETFS_ICTX_UNBUFFERED	1		/* I/O should not use the pagecache */
 #define NETFS_ICTX_WRITETHROUGH	2		/* Write-through caching */
+#define NETFS_ICTX_MODIFIED_ATTR 3		/* Indicate change in mtime/ctime */
 #define NETFS_ICTX_USE_PGPRIV2	31		/* [DEPRECATED] Use PG_private_2 to mark
 						 * write to cache on read */
 };

[PATCH 07/24] netfs: Move max_len/max_nr_segs from netfs_io_subrequest to netfs_io_stream

[David Howells]

Move max_len/max_nr_segs from struct netfs_io_subrequest to struct
netfs_io_stream as we only issue one subreq at a time and then don't need
these values again for that subreq unless and until we have to retry it -
in which case we want to renegotiate them.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/afs/write.c           |  4 +++-
 fs/cachefiles/io.c       |  5 +++--
 fs/netfs/io.c            |  4 ++--
 fs/netfs/write_collect.c | 10 +++++-----
 fs/netfs/write_issue.c   | 14 +++++++-------
 fs/smb/client/file.c     | 15 ++++++++-------
 include/linux/netfs.h    |  4 ++--
 7 files changed, 30 insertions(+), 26 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index e959640694c2..34107b55f834 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -89,10 +89,12 @@ static const struct afs_operation_ops afs_store_data_operation = {
  */
 void afs_prepare_write(struct netfs_io_subrequest *subreq)
 {
+	struct netfs_io_stream *stream = &subreq->rreq->io_streams[subreq->stream_nr];
+
 	//if (test_bit(NETFS_SREQ_RETRYING, &subreq->flags))
 	//	subreq->max_len = 512 * 1024;
 	//else
-	subreq->max_len = 256 * 1024 * 1024;
+	stream->sreq_max_len = 256 * 1024 * 1024;
 }
 
 /*
diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index a91acd03ee12..5b82ba7785cd 100644
--- a/fs/cachefiles/io.c
+++ b/fs/cachefiles/io.c
@@ -627,11 +627,12 @@ static void cachefiles_prepare_write_subreq(struct netfs_io_subrequest *subreq)
 {
 	struct netfs_io_request *wreq = subreq->rreq;
 	struct netfs_cache_resources *cres = &wreq->cache_resources;
+	struct netfs_io_stream *stream = &wreq->io_streams[subreq->stream_nr];
 
 	_enter("W=%x[%x] %llx", wreq->debug_id, subreq->debug_index, subreq->start);
 
-	subreq->max_len = MAX_RW_COUNT;
-	subreq->max_nr_segs = BIO_MAX_VECS;
+	stream->sreq_max_len = MAX_RW_COUNT;
+	stream->sreq_max_segs = BIO_MAX_VECS;
 
 	if (!cachefiles_cres_file(cres)) {
 		if (!fscache_wait_for_operation(cres, FSCACHE_WANT_WRITE))
diff --git a/fs/netfs/io.c b/fs/netfs/io.c
index c93851b98368..27dbea0f3867 100644
--- a/fs/netfs/io.c
+++ b/fs/netfs/io.c
@@ -469,9 +469,9 @@ netfs_rreq_prepare_read(struct netfs_io_request *rreq,
 			goto out;
 		}
 
-		if (subreq->max_nr_segs) {
+		if (rreq->io_streams[0].sreq_max_segs) {
 			lsize = netfs_limit_iter(io_iter, 0, subreq->len,
-						 subreq->max_nr_segs);
+						 rreq->io_streams[0].sreq_max_segs);
 			if (subreq->len > lsize) {
 				subreq->len = lsize;
 				trace_netfs_sreq(subreq, netfs_sreq_trace_limited);
diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index 426cf87aaf2e..e105ac270090 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -231,7 +231,7 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 			__set_bit(NETFS_SREQ_RETRYING, &subreq->flags);
 			stream->prepare_write(subreq);
 
-			part = min(len, subreq->max_len);
+			part = min(len, stream->sreq_max_len);
 			subreq->len = part;
 			subreq->start = start;
 			subreq->transferred = 0;
@@ -271,8 +271,6 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 			subreq = netfs_alloc_subrequest(wreq);
 			subreq->source		= to->source;
 			subreq->start		= start;
-			subreq->max_len		= len;
-			subreq->max_nr_segs	= INT_MAX;
 			subreq->debug_index	= atomic_inc_return(&wreq->subreq_counter);
 			subreq->stream_nr	= to->stream_nr;
 			__set_bit(NETFS_SREQ_RETRYING, &subreq->flags);
@@ -286,10 +284,12 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 			to = list_next_entry(to, rreq_link);
 			trace_netfs_sreq(subreq, netfs_sreq_trace_retry);
 
+			stream->sreq_max_len	= len;
+			stream->sreq_max_segs	= INT_MAX;
 			switch (stream->source) {
 			case NETFS_UPLOAD_TO_SERVER:
 				netfs_stat(&netfs_n_wh_upload);
-				subreq->max_len = min(len, wreq->wsize);
+				stream->sreq_max_len = umin(len, wreq->wsize);
 				break;
 			case NETFS_WRITE_TO_CACHE:
 				netfs_stat(&netfs_n_wh_write);
@@ -300,7 +300,7 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 
 			stream->prepare_write(subreq);
 
-			part = min(len, subreq->max_len);
+			part = umin(len, stream->sreq_max_len);
 			subreq->len = subreq->transferred + part;
 			len -= part;
 			start += part;
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index e7d4f39b8fdc..2f4f795124a8 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -156,8 +156,6 @@ static void netfs_prepare_write(struct netfs_io_request *wreq,
 	subreq = netfs_alloc_subrequest(wreq);
 	subreq->source		= stream->source;
 	subreq->start		= start;
-	subreq->max_len		= ULONG_MAX;
-	subreq->max_nr_segs	= INT_MAX;
 	subreq->stream_nr	= stream->stream_nr;
 
 	_enter("R=%x[%x]", wreq->debug_id, subreq->debug_index);
@@ -168,10 +166,12 @@ static void netfs_prepare_write(struct netfs_io_request *wreq,
 
 	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
 
+	stream->sreq_max_len	= UINT_MAX;
+	stream->sreq_max_segs	= INT_MAX;
 	switch (stream->source) {
 	case NETFS_UPLOAD_TO_SERVER:
 		netfs_stat(&netfs_n_wh_upload);
-		subreq->max_len = wreq->wsize;
+		stream->sreq_max_len = wreq->wsize;
 		break;
 	case NETFS_WRITE_TO_CACHE:
 		netfs_stat(&netfs_n_wh_write);
@@ -288,13 +288,13 @@ int netfs_advance_write(struct netfs_io_request *wreq,
 		netfs_prepare_write(wreq, stream, start);
 	subreq = stream->construct;
 
-	part = min(subreq->max_len - subreq->len, len);
-	_debug("part %zx/%zx %zx/%zx", subreq->len, subreq->max_len, part, len);
+	part = umin(stream->sreq_max_len - subreq->len, len);
+	_debug("part %zx/%zx %zx/%zx", subreq->len, stream->sreq_max_len, part, len);
 	subreq->len += part;
 	subreq->nr_segs++;
 
-	if (subreq->len >= subreq->max_len ||
-	    subreq->nr_segs >= subreq->max_nr_segs ||
+	if (subreq->len >= stream->sreq_max_len ||
+	    subreq->nr_segs >= stream->sreq_max_segs ||
 	    to_eof) {
 		netfs_issue_write(wreq, stream);
 		subreq = NULL;
diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index fd9f82ff44b8..c1d8c5d2ac71 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -49,6 +49,7 @@ static void cifs_prepare_write(struct netfs_io_subrequest *subreq)
 	struct cifs_io_subrequest *wdata =
 		container_of(subreq, struct cifs_io_subrequest, subreq);
 	struct cifs_io_request *req = wdata->req;
+	struct netfs_io_stream *stream = &req->rreq.io_streams[subreq->stream_nr];
 	struct TCP_Server_Info *server;
 	struct cifsFileInfo *open_file = req->cfile;
 	size_t wsize = req->rreq.wsize;
@@ -73,7 +74,7 @@ static void cifs_prepare_write(struct netfs_io_subrequest *subreq)
 		}
 	}
 
-	rc = server->ops->wait_mtu_credits(server, wsize, &wdata->subreq.max_len,
+	rc = server->ops->wait_mtu_credits(server, wsize, &stream->sreq_max_len,
 					   &wdata->credits);
 	if (rc < 0) {
 		subreq->error = rc;
@@ -92,7 +93,7 @@ static void cifs_prepare_write(struct netfs_io_subrequest *subreq)
 
 #ifdef CONFIG_CIFS_SMB_DIRECT
 	if (server->smbd_conn)
-		subreq->max_nr_segs = server->smbd_conn->max_frmr_depth;
+		stream->sreq_max_segs = server->smbd_conn->max_frmr_depth;
 #endif
 }
 
@@ -149,11 +150,11 @@ static void cifs_netfs_invalidate_cache(struct netfs_io_request *wreq)
 static bool cifs_clamp_length(struct netfs_io_subrequest *subreq)
 {
 	struct netfs_io_request *rreq = subreq->rreq;
+	struct netfs_io_stream *stream = &rreq->io_streams[subreq->stream_nr];
 	struct cifs_io_subrequest *rdata = container_of(subreq, struct cifs_io_subrequest, subreq);
 	struct cifs_io_request *req = container_of(subreq->rreq, struct cifs_io_request, rreq);
 	struct TCP_Server_Info *server = req->server;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(rreq->inode->i_sb);
-	size_t rsize = 0;
 	int rc;
 
 	rdata->xid = get_xid();
@@ -166,8 +167,8 @@ static bool cifs_clamp_length(struct netfs_io_subrequest *subreq)
 						     cifs_sb->ctx);
 
 
-	rc = server->ops->wait_mtu_credits(server, cifs_sb->ctx->rsize, &rsize,
-					   &rdata->credits);
+	rc = server->ops->wait_mtu_credits(server, cifs_sb->ctx->rsize,
+					   &stream->sreq_max_len, &rdata->credits);
 	if (rc) {
 		subreq->error = rc;
 		return false;
@@ -183,11 +184,11 @@ static bool cifs_clamp_length(struct netfs_io_subrequest *subreq)
 			      server->credits, server->in_flight, 0,
 			      cifs_trace_rw_credits_read_submit);
 
-	subreq->len = min_t(size_t, subreq->len, rsize);
+	subreq->len = umin(subreq->len, stream->sreq_max_len);
 
 #ifdef CONFIG_CIFS_SMB_DIRECT
 	if (server->smbd_conn)
-		subreq->max_nr_segs = server->smbd_conn->max_frmr_depth;
+		stream->sreq_max_segs = server->smbd_conn->max_frmr_depth;
 #endif
 	return true;
 }
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 2d438aaae685..aada40d2182b 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -136,6 +136,8 @@ static inline struct netfs_group *netfs_folio_group(struct folio *folio)
 struct netfs_io_stream {
 	/* Submission tracking */
 	struct netfs_io_subrequest *construct;	/* Op being constructed */
+	size_t			sreq_max_len;	/* Maximum size of a subrequest */
+	unsigned int		sreq_max_segs;	/* 0 or max number of segments in an iterator */
 	unsigned int		submit_off;	/* Folio offset we're submitting from */
 	unsigned int		submit_len;	/* Amount of data left to submit */
 	unsigned int		submit_max_len;	/* Amount I/O can be rounded up to */
@@ -179,14 +181,12 @@ struct netfs_io_subrequest {
 	struct list_head	rreq_link;	/* Link in rreq->subrequests */
 	struct iov_iter		io_iter;	/* Iterator for this subrequest */
 	unsigned long long	start;		/* Where to start the I/O */
-	size_t			max_len;	/* Maximum size of the I/O */
 	size_t			len;		/* Size of the I/O */
 	size_t			transferred;	/* Amount of data transferred */
 	refcount_t		ref;
 	short			error;		/* 0 or error that occurred */
 	unsigned short		debug_index;	/* Index in list (for debugging output) */
 	unsigned int		nr_segs;	/* Number of segs in io_iter */
-	unsigned int		max_nr_segs;	/* 0 or max number of segments in an iterator */
 	enum netfs_io_source	source;		/* Where to read from/write to */
 	unsigned char		stream_nr;	/* I/O stream this belongs to */
 	unsigned long		flags;

[PATCH 08/24] netfs: Reserve netfs_sreq_source 0 as unset/unknown

[David Howells]

Reserve the 0-valued netfs_sreq_source to mean unset or unknown so that it
can be seen in the trace as such rather than appearing as
download-from-server when it's going to get switched to something else.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 include/linux/netfs.h        | 1 +
 include/trace/events/netfs.h | 1 +
 2 files changed, 2 insertions(+)

diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index aada40d2182b..5e623e52e5a2 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -43,6 +43,7 @@ static inline void folio_start_private_2(struct folio *folio)
 #define NETFS_BUF_PAGECACHE_MARK XA_MARK_1	/* - Page needs wb/dirty flag wrangling */
 
 enum netfs_io_source {
+	NETFS_SOURCE_UNKNOWN,
 	NETFS_FILL_WITH_ZEROES,
 	NETFS_DOWNLOAD_FROM_SERVER,
 	NETFS_READ_FROM_CACHE,
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index fc5dbd19f120..bd4f6f1f1040 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -59,6 +59,7 @@
 	E_(netfs_rreq_trace_write_done,		"WR-DONE")
 
 #define netfs_sreq_sources					\
+	EM(NETFS_SOURCE_UNKNOWN,		"----")		\
 	EM(NETFS_FILL_WITH_ZEROES,		"ZERO")		\
 	EM(NETFS_DOWNLOAD_FROM_SERVER,		"DOWN")		\
 	EM(NETFS_READ_FROM_CACHE,		"READ")		\

[PATCH 09/24] netfs: Remove NETFS_COPY_TO_CACHE

[David Howells]

Remove NETFS_COPY_TO_CACHE as it isn't used anymore.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/main.c              | 3 +--
 include/linux/netfs.h        | 3 +--
 include/trace/events/netfs.h | 3 +--
 3 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/netfs/main.c b/fs/netfs/main.c
index 5f0f438e5d21..1ee712bb3610 100644
--- a/fs/netfs/main.c
+++ b/fs/netfs/main.c
@@ -37,11 +37,10 @@ static const char *netfs_origins[nr__netfs_io_origin] = {
 	[NETFS_READAHEAD]		= "RA",
 	[NETFS_READPAGE]		= "RP",
 	[NETFS_READ_FOR_WRITE]		= "RW",
-	[NETFS_COPY_TO_CACHE]		= "CC",
+	[NETFS_DIO_READ]		= "DR",
 	[NETFS_WRITEBACK]		= "WB",
 	[NETFS_WRITETHROUGH]		= "WT",
 	[NETFS_UNBUFFERED_WRITE]	= "UW",
-	[NETFS_DIO_READ]		= "DR",
 	[NETFS_DIO_WRITE]		= "DW",
 };
 
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 5e623e52e5a2..daaa6eae3a9f 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -208,11 +208,10 @@ enum netfs_io_origin {
 	NETFS_READAHEAD,		/* This read was triggered by readahead */
 	NETFS_READPAGE,			/* This read is a synchronous read */
 	NETFS_READ_FOR_WRITE,		/* This read is to prepare a write */
-	NETFS_COPY_TO_CACHE,		/* This write is to copy a read to the cache */
+	NETFS_DIO_READ,			/* This is a direct I/O read */
 	NETFS_WRITEBACK,		/* This write was triggered by writepages */
 	NETFS_WRITETHROUGH,		/* This write was made by netfs_perform_write() */
 	NETFS_UNBUFFERED_WRITE,		/* This is an unbuffered write */
-	NETFS_DIO_READ,			/* This is a direct I/O read */
 	NETFS_DIO_WRITE,		/* This is a direct I/O write */
 	nr__netfs_io_origin
 } __mode(byte);
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index bd4f6f1f1040..b5a30d9a0d20 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -34,11 +34,10 @@
 	EM(NETFS_READAHEAD,			"RA")		\
 	EM(NETFS_READPAGE,			"RP")		\
 	EM(NETFS_READ_FOR_WRITE,		"RW")		\
-	EM(NETFS_COPY_TO_CACHE,			"CC")		\
+	EM(NETFS_DIO_READ,			"DR")		\
 	EM(NETFS_WRITEBACK,			"WB")		\
 	EM(NETFS_WRITETHROUGH,			"WT")		\
 	EM(NETFS_UNBUFFERED_WRITE,		"UW")		\
-	EM(NETFS_DIO_READ,			"DR")		\
 	E_(NETFS_DIO_WRITE,			"DW")
 
 #define netfs_rreq_traces					\

[PATCH 10/24] netfs: Set the request work function upon allocation

[David Howells]

Set the work function in the netfs_io_request work_struct when we allocate
the request rather than doing this later.  This reduces the number of
places we need to set it in future code.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/internal.h    | 1 +
 fs/netfs/io.c          | 4 +---
 fs/netfs/objects.c     | 9 ++++++++-
 fs/netfs/write_issue.c | 1 -
 4 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 9e6e0e59d7e4..f2920b4ee726 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -29,6 +29,7 @@ int netfs_prefetch_for_write(struct file *file, struct folio *folio,
 /*
  * io.c
  */
+void netfs_rreq_work(struct work_struct *work);
 int netfs_begin_read(struct netfs_io_request *rreq, bool sync);
 
 /*
diff --git a/fs/netfs/io.c b/fs/netfs/io.c
index 27dbea0f3867..874bbf2386a4 100644
--- a/fs/netfs/io.c
+++ b/fs/netfs/io.c
@@ -278,7 +278,7 @@ static void netfs_rreq_assess(struct netfs_io_request *rreq, bool was_async)
 	netfs_rreq_completed(rreq, was_async);
 }
 
-static void netfs_rreq_work(struct work_struct *work)
+void netfs_rreq_work(struct work_struct *work)
 {
 	struct netfs_io_request *rreq =
 		container_of(work, struct netfs_io_request, work);
@@ -584,8 +584,6 @@ int netfs_begin_read(struct netfs_io_request *rreq, bool sync)
 	// TODO: Use bounce buffer if requested
 	rreq->io_iter = rreq->iter;
 
-	INIT_WORK(&rreq->work, netfs_rreq_work);
-
 	/* Chop the read into slices according to what the cache and the netfs
 	 * want and submit each one.
 	 */
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index f4a642727479..1dbcd7f44eca 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -52,9 +52,16 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 	INIT_LIST_HEAD(&rreq->io_streams[0].subrequests);
 	INIT_LIST_HEAD(&rreq->io_streams[1].subrequests);
 	INIT_LIST_HEAD(&rreq->subrequests);
-	INIT_WORK(&rreq->work, NULL);
 	refcount_set(&rreq->ref, 1);
 
+	if (origin == NETFS_READAHEAD ||
+	    origin == NETFS_READPAGE ||
+	    origin == NETFS_READ_FOR_WRITE ||
+	    origin == NETFS_DIO_READ)
+		INIT_WORK(&rreq->work, netfs_rreq_work);
+	else
+		INIT_WORK(&rreq->work, netfs_write_collection_worker);
+
 	__set_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags);
 	if (cached) {
 		__set_bit(NETFS_RREQ_WRITE_TO_CACHE, &rreq->flags);
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 2f4f795124a8..6e835670dc58 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -107,7 +107,6 @@ struct netfs_io_request *netfs_create_write_req(struct address_space *mapping,
 
 	wreq->contiguity = wreq->start;
 	wreq->cleaned_to = wreq->start;
-	INIT_WORK(&wreq->work, netfs_write_collection_worker);
 
 	wreq->io_streams[0].stream_nr		= 0;
 	wreq->io_streams[0].source		= NETFS_UPLOAD_TO_SERVER;

[PATCH 11/24] netfs: Use bh-disabling spinlocks for rreq->lock

[David Howells]

Use bh-disabling spinlocks when accessing rreq->lock because, in the
future, it may be twiddled from softirq context when cleanup is driven from
cache backend DIO completion.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/write_collect.c | 4 ++--
 fs/netfs/write_issue.c   | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index e105ac270090..5f504b03a1e7 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -466,7 +466,7 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 
 		cancel:
 			/* Remove if completely consumed. */
-			spin_lock(&wreq->lock);
+			spin_lock_bh(&wreq->lock);
 
 			remove = front;
 			list_del_init(&front->rreq_link);
@@ -482,7 +482,7 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 				}
 			}
 
-			spin_unlock(&wreq->lock);
+			spin_unlock_bh(&wreq->lock);
 			netfs_put_subrequest(remove, false,
 					     notes & SAW_FAILURE ?
 					     netfs_sreq_trace_put_cancel :
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 6e835670dc58..0354c992467b 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -189,7 +189,7 @@ static void netfs_prepare_write(struct netfs_io_request *wreq,
 	 * the list.  The collector only goes nextwards and uses the lock to
 	 * remove entries off of the front.
 	 */
-	spin_lock(&wreq->lock);
+	spin_lock_bh(&wreq->lock);
 	list_add_tail(&subreq->rreq_link, &stream->subrequests);
 	if (list_is_first(&subreq->rreq_link, &stream->subrequests)) {
 		stream->front = subreq;
@@ -200,7 +200,7 @@ static void netfs_prepare_write(struct netfs_io_request *wreq,
 		}
 	}
 
-	spin_unlock(&wreq->lock);
+	spin_unlock_bh(&wreq->lock);
 
 	stream->construct = subreq;
 }

[PATCH 12/24] mm: Define struct folio_queue and ITER_FOLIOQ to handle a sequence of folios

[David Howells]

Define a data structure, struct folio_queue, to represent a sequence of
folios and a kernel-internal I/O iterator type, ITER_FOLIOQ, to allow a
list of folio_queue structures to be used to provide a buffer to
iov_iter-taking functions, such as sendmsg and recvmsg.

The folio_queue structure looks like:

	struct folio_queue {
		struct folio_batch	vec;
		u8			orders[PAGEVEC_SIZE];
		struct folio_queue	*next;
		struct folio_queue	*prev;
		unsigned long		marks;
		unsigned long		marks2;
	};

It does not use a list_head so that next and/or prev can be set to NULL at
the ends of the list, allowing iov_iter-handling routines to determine that
they *are* the ends without needing to store a head pointer in the iov_iter
struct.

A folio_batch struct is used to hold the folio pointers which allows the
batch to be passed to batch handling functions.  Two mark bits are
available per slot.  The intention is to use at least one of them to mark
folios that need putting, but that might not be ultimately necessary.
Accessor functions are used to access the slots to do the masking and an
additional accessor function is used to indicate the size of the array.

The order of each folio is also stored in the structure to avoid the need
for iov_iter_advance() and iov_iter_revert() to have to query each folio to
find its size.

With careful barriering, this can be used as an extending buffer with new
folios inserted and new folio_queue structs added without the need for a
lock.  Further, provided we always keep at least one struct in the buffer,
we can also remove consumed folios and consumed structs from the head end
as we without the need for locks.

[Questions/thoughts]

 (1) To manage this, I need a head pointer, a tail pointer, a tail slot
     number (assuming insertion happens at the tail end and the next
     pointers point from head to tail).  Should I put these into a struct
     of their own, say "folio_queue_head" or "rolling_buffer"?

     I will end up with two of these in netfs_io_request eventually, one
     keeping track of the pagecache I'm dealing with for buffered I/O and
     the other to hold a bounce buffer when we need one.

 (2) Should I make the slots {folio,off,len} or bio_vec?

 (3) This is intended to replace ITER_XARRAY eventually.  Using an xarray
     in I/O iteration requires the taking of the RCU read lock, doing
     copying under the RCU read lock, walking the xarray (which may change
     under us), handling retries and dealing with special values.

     The advantage of ITER_XARRAY is that when we're dealing with the
     pagecache directly, we don't need any allocation - but if we're doing
     encrypted comms, there's a good chance we'd be using a bounce buffer
     anyway.

     This will require afs, erofs, cifs, orangefs and fscache to be
     converted to not use this.  afs still uses it for dirs and symlinks;
     some of erofs usages should be easy to change, but there's one which
     won't be so easy; ceph's use via fscache can be fixed by porting ceph
     to netfslib; cifs is using xarray as a bounce buffer - that can be
     moved to use sheaves instead; and orangefs has a similar problem to
     erofs - maybe orangefs could use netfslib?

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: Steve French <sfrench@samba.org>
cc: Ilya Dryomov <idryomov@gmail.com>
cc: Gao Xiang <xiang@kernel.org>
cc: Mike Marshall <hubcap@omnibond.com>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
cc: linux-afs@lists.infradead.org
cc: linux-cifs@vger.kernel.org
cc: ceph-devel@vger.kernel.org
cc: linux-erofs@lists.ozlabs.org
cc: devel@lists.orangefs.org
---
 include/linux/folio_queue.h | 138 +++++++++++++++++++
 include/linux/iov_iter.h    |  57 ++++++++
 include/linux/uio.h         |  12 ++
 lib/iov_iter.c              | 229 ++++++++++++++++++++++++++++++-
 lib/kunit_iov_iter.c        | 259 ++++++++++++++++++++++++++++++++++++
 lib/scatterlist.c           |  69 +++++++++-
 6 files changed, 760 insertions(+), 4 deletions(-)
 create mode 100644 include/linux/folio_queue.h

diff --git a/include/linux/folio_queue.h b/include/linux/folio_queue.h
new file mode 100644
index 000000000000..52773613bf23
--- /dev/null
+++ b/include/linux/folio_queue.h
@@ -0,0 +1,138 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Queue of folios definitions
+ *
+ * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#ifndef _LINUX_FOLIO_QUEUE_H
+#define _LINUX_FOLIO_QUEUE_H
+
+#include <linux/pagevec.h>
+
+/*
+ * Segment in a queue of running buffers.  Each segment can hold a number of
+ * folios and a portion of the queue can be referenced with the ITER_FOLIOQ
+ * iterator.  The possibility exists of inserting non-folio elements into the
+ * queue (such as gaps).
+ *
+ * Explicit prev and next pointers are used instead of a list_head to make it
+ * easier to add segments to tail and remove them from the head without the
+ * need for a lock.
+ */
+struct folio_queue {
+	struct folio_batch	vec;		/* Folios in the queue segment */
+	u8			orders[PAGEVEC_SIZE]; /* Order of each folio */
+	struct folio_queue	*next;		/* Next queue segment or NULL */
+	struct folio_queue	*prev;		/* Previous queue segment of NULL */
+	unsigned long		marks;		/* 1-bit mark per folio */
+	unsigned long		marks2;		/* Second 1-bit mark per folio */
+#if PAGEVEC_SIZE > BITS_PER_LONG
+#error marks is not big enough
+#endif
+};
+
+static inline void folioq_init(struct folio_queue *folioq)
+{
+	folio_batch_init(&folioq->vec);
+	folioq->next = NULL;
+	folioq->prev = NULL;
+	folioq->marks = 0;
+	folioq->marks2 = 0;
+}
+
+static inline unsigned int folioq_nr_slots(const struct folio_queue *folioq)
+{
+	return PAGEVEC_SIZE;
+}
+
+static inline unsigned int folioq_count(struct folio_queue *folioq)
+{
+	return folio_batch_count(&folioq->vec);
+}
+
+static inline bool folioq_full(struct folio_queue *folioq)
+{
+	//return !folio_batch_space(&folioq->vec);
+	return folioq_count(folioq) >= folioq_nr_slots(folioq);
+}
+
+static inline bool folioq_is_marked(const struct folio_queue *folioq, unsigned int slot)
+{
+	return test_bit(slot, &folioq->marks);
+}
+
+static inline void folioq_mark(struct folio_queue *folioq, unsigned int slot)
+{
+	set_bit(slot, &folioq->marks);
+}
+
+static inline void folioq_unmark(struct folio_queue *folioq, unsigned int slot)
+{
+	clear_bit(slot, &folioq->marks);
+}
+
+static inline bool folioq_is_marked2(const struct folio_queue *folioq, unsigned int slot)
+{
+	return test_bit(slot, &folioq->marks2);
+}
+
+static inline void folioq_mark2(struct folio_queue *folioq, unsigned int slot)
+{
+	set_bit(slot, &folioq->marks2);
+}
+
+static inline void folioq_unmark2(struct folio_queue *folioq, unsigned int slot)
+{
+	clear_bit(slot, &folioq->marks2);
+}
+
+static inline unsigned int __folio_order(struct folio *folio)
+{
+	if (!folio_test_large(folio))
+		return 0;
+	return folio->_flags_1 & 0xff;
+}
+
+static inline unsigned int folioq_append(struct folio_queue *folioq, struct folio *folio)
+{
+	unsigned int slot = folioq->vec.nr++;
+
+	folioq->vec.folios[slot] = folio;
+	folioq->orders[slot] = __folio_order(folio);
+	return slot;
+}
+
+static inline unsigned int folioq_append_mark(struct folio_queue *folioq, struct folio *folio)
+{
+	unsigned int slot = folioq->vec.nr++;
+
+	folioq->vec.folios[slot] = folio;
+	folioq->orders[slot] = __folio_order(folio);
+	folioq_mark(folioq, slot);
+	return slot;
+}
+
+static inline struct folio *folioq_folio(const struct folio_queue *folioq, unsigned int slot)
+{
+	return folioq->vec.folios[slot];
+}
+
+static inline unsigned int folioq_folio_order(const struct folio_queue *folioq, unsigned int slot)
+{
+	return folioq->orders[slot];
+}
+
+static inline size_t folioq_folio_size(const struct folio_queue *folioq, unsigned int slot)
+{
+	return PAGE_SIZE << folioq_folio_order(folioq, slot);
+}
+
+static inline void folioq_clear(struct folio_queue *folioq, unsigned int slot)
+{
+	folioq->vec.folios[slot] = NULL;
+	folioq_unmark(folioq, slot);
+	folioq_unmark2(folioq, slot);
+}
+
+#endif /* _LINUX_FOLIO_QUEUE_H */
diff --git a/include/linux/iov_iter.h b/include/linux/iov_iter.h
index 270454a6703d..a223370a59a7 100644
--- a/include/linux/iov_iter.h
+++ b/include/linux/iov_iter.h
@@ -10,6 +10,7 @@
 
 #include <linux/uio.h>
 #include <linux/bvec.h>
+#include <linux/folio_queue.h>
 
 typedef size_t (*iov_step_f)(void *iter_base, size_t progress, size_t len,
 			     void *priv, void *priv2);
@@ -140,6 +141,60 @@ size_t iterate_bvec(struct iov_iter *iter, size_t len, void *priv, void *priv2,
 	return progress;
 }
 
+/*
+ * Handle ITER_FOLIOQ.
+ */
+static __always_inline
+size_t iterate_folioq(struct iov_iter *iter, size_t len, void *priv, void *priv2,
+		      iov_step_f step)
+{
+	const struct folio_queue *folioq = iter->folioq;
+	unsigned int slot = iter->folioq_slot;
+	size_t progress = 0, skip = iter->iov_offset;
+
+	if (slot == folioq_nr_slots(folioq)) {
+		/* The iterator may have been extended. */
+		folioq = folioq->next;
+		slot = 0;
+	}
+
+	do {
+		struct folio *folio = folioq_folio(folioq, slot);
+		size_t part, remain, consumed;
+		size_t fsize;
+		void *base;
+
+		if (!folio)
+			break;
+
+		fsize = folioq_folio_size(folioq, slot);
+		base = kmap_local_folio(folio, skip);
+		part = umin(len, PAGE_SIZE - skip % PAGE_SIZE);
+		remain = step(base, progress, part, priv, priv2);
+		kunmap_local(base);
+		consumed = part - remain;
+		len -= consumed;
+		progress += consumed;
+		skip += consumed;
+		if (skip >= fsize) {
+			skip = 0;
+			slot++;
+			if (slot == folioq_nr_slots(folioq) && folioq->next) {
+				folioq = folioq->next;
+				slot = 0;
+			}
+		}
+		if (remain)
+			break;
+	} while (len);
+
+	iter->folioq_slot = slot;
+	iter->folioq = folioq;
+	iter->iov_offset = skip;
+	iter->count -= progress;
+	return progress;
+}
+
 /*
  * Handle ITER_XARRAY.
  */
@@ -249,6 +304,8 @@ size_t iterate_and_advance2(struct iov_iter *iter, size_t len, void *priv,
 		return iterate_bvec(iter, len, priv, priv2, step);
 	if (iov_iter_is_kvec(iter))
 		return iterate_kvec(iter, len, priv, priv2, step);
+	if (iov_iter_is_folioq(iter))
+		return iterate_folioq(iter, len, priv, priv2, step);
 	if (iov_iter_is_xarray(iter))
 		return iterate_xarray(iter, len, priv, priv2, step);
 	return iterate_discard(iter, len, priv, priv2, step);
diff --git a/include/linux/uio.h b/include/linux/uio.h
index 7020adedfa08..845d110acadc 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -11,6 +11,7 @@
 #include <uapi/linux/uio.h>
 
 struct page;
+struct folio_queue;
 
 typedef unsigned int __bitwise iov_iter_extraction_t;
 
@@ -25,6 +26,7 @@ enum iter_type {
 	ITER_IOVEC,
 	ITER_BVEC,
 	ITER_KVEC,
+	ITER_FOLIOQ,
 	ITER_XARRAY,
 	ITER_DISCARD,
 };
@@ -66,6 +68,7 @@ struct iov_iter {
 				const struct iovec *__iov;
 				const struct kvec *kvec;
 				const struct bio_vec *bvec;
+				const struct folio_queue *folioq;
 				struct xarray *xarray;
 				void __user *ubuf;
 			};
@@ -74,6 +77,7 @@ struct iov_iter {
 	};
 	union {
 		unsigned long nr_segs;
+		u8 folioq_slot;
 		loff_t xarray_start;
 	};
 };
@@ -126,6 +130,11 @@ static inline bool iov_iter_is_discard(const struct iov_iter *i)
 	return iov_iter_type(i) == ITER_DISCARD;
 }
 
+static inline bool iov_iter_is_folioq(const struct iov_iter *i)
+{
+	return iov_iter_type(i) == ITER_FOLIOQ;
+}
+
 static inline bool iov_iter_is_xarray(const struct iov_iter *i)
 {
 	return iov_iter_type(i) == ITER_XARRAY;
@@ -273,6 +282,9 @@ void iov_iter_kvec(struct iov_iter *i, unsigned int direction, const struct kvec
 void iov_iter_bvec(struct iov_iter *i, unsigned int direction, const struct bio_vec *bvec,
 			unsigned long nr_segs, size_t count);
 void iov_iter_discard(struct iov_iter *i, unsigned int direction, size_t count);
+void iov_iter_folio_queue(struct iov_iter *i, unsigned int direction,
+			  const struct folio_queue *folioq,
+			  unsigned int first_slot, unsigned int offset, size_t count);
 void iov_iter_xarray(struct iov_iter *i, unsigned int direction, struct xarray *xarray,
 		     loff_t start, size_t count);
 ssize_t iov_iter_get_pages2(struct iov_iter *i, struct page **pages,
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 4a6a9f419bd7..f410b4b50b16 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -527,6 +527,39 @@ static void iov_iter_iovec_advance(struct iov_iter *i, size_t size)
 	i->__iov = iov;
 }
 
+static void iov_iter_folioq_advance(struct iov_iter *i, size_t size)
+{
+	const struct folio_queue *folioq = i->folioq;
+	unsigned int slot = i->folioq_slot;
+
+	if (!i->count)
+		return;
+	i->count -= size;
+
+	if (slot >= folioq_nr_slots(folioq)) {
+		folioq = folioq->next;
+		slot = 0;
+	}
+
+	size += i->iov_offset; /* From beginning of current segment. */
+	do {
+		size_t fsize = folioq_folio_size(folioq, slot);
+
+		if (likely(size < fsize))
+			break;
+		size -= fsize;
+		slot++;
+		if (slot >= folioq_nr_slots(folioq) && folioq->next) {
+			folioq = folioq->next;
+			slot = 0;
+		}
+	} while (size);
+
+	i->iov_offset = size;
+	i->folioq_slot = slot;
+	i->folioq = folioq;
+}
+
 void iov_iter_advance(struct iov_iter *i, size_t size)
 {
 	if (unlikely(i->count < size))
@@ -539,12 +572,40 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
 		iov_iter_iovec_advance(i, size);
 	} else if (iov_iter_is_bvec(i)) {
 		iov_iter_bvec_advance(i, size);
+	} else if (iov_iter_is_folioq(i)) {
+		iov_iter_folioq_advance(i, size);
 	} else if (iov_iter_is_discard(i)) {
 		i->count -= size;
 	}
 }
 EXPORT_SYMBOL(iov_iter_advance);
 
+static void iov_iter_folioq_revert(struct iov_iter *i, size_t unroll)
+{
+	const struct folio_queue *folioq = i->folioq;
+	unsigned int slot = i->folioq_slot;
+
+	for (;;) {
+		size_t fsize;
+
+		if (slot == 0) {
+			folioq = folioq->prev;
+			slot = folioq_nr_slots(folioq);
+		}
+		slot--;
+
+		fsize = folioq_folio_size(folioq, slot);
+		if (unroll <= fsize) {
+			i->iov_offset = fsize - unroll;
+			break;
+		}
+		unroll -= fsize;
+	}
+
+	i->folioq_slot = slot;
+	i->folioq = folioq;
+}
+
 void iov_iter_revert(struct iov_iter *i, size_t unroll)
 {
 	if (!unroll)
@@ -576,6 +637,9 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll)
 			}
 			unroll -= n;
 		}
+	} else if (iov_iter_is_folioq(i)) {
+		i->iov_offset = 0;
+		iov_iter_folioq_revert(i, unroll);
 	} else { /* same logics for iovec and kvec */
 		const struct iovec *iov = iter_iov(i);
 		while (1) {
@@ -603,6 +667,9 @@ size_t iov_iter_single_seg_count(const struct iov_iter *i)
 		if (iov_iter_is_bvec(i))
 			return min(i->count, i->bvec->bv_len - i->iov_offset);
 	}
+	if (unlikely(iov_iter_is_folioq(i)))
+		return !i->count ? 0 :
+			umin(folioq_folio_size(i->folioq, i->folioq_slot), i->count);
 	return i->count;
 }
 EXPORT_SYMBOL(iov_iter_single_seg_count);
@@ -639,6 +706,36 @@ void iov_iter_bvec(struct iov_iter *i, unsigned int direction,
 }
 EXPORT_SYMBOL(iov_iter_bvec);
 
+/**
+ * iov_iter_folio_queue - Initialise an I/O iterator to use the folios in a folio queue
+ * @i: The iterator to initialise.
+ * @direction: The direction of the transfer.
+ * @folioq: The starting point in the folio queue.
+ * @first_slot: The first slot in the folio queue to use
+ * @offset: The offset into the folio in the first slot to start at
+ * @count: The size of the I/O buffer in bytes.
+ *
+ * Set up an I/O iterator to either draw data out of the pages attached to an
+ * inode or to inject data into those pages.  The pages *must* be prevented
+ * from evaporation, either by taking a ref on them or locking them by the
+ * caller.
+ */
+void iov_iter_folio_queue(struct iov_iter *i, unsigned int direction,
+			  const struct folio_queue *folioq, unsigned int first_slot,
+			  unsigned int offset, size_t count)
+{
+	BUG_ON(direction & ~1);
+	*i = (struct iov_iter) {
+		.iter_type = ITER_FOLIOQ,
+		.data_source = direction,
+		.folioq = folioq,
+		.folioq_slot = first_slot,
+		.count = count,
+		.iov_offset = offset,
+	};
+}
+EXPORT_SYMBOL(iov_iter_folio_queue);
+
 /**
  * iov_iter_xarray - Initialise an I/O iterator to use the pages in an xarray
  * @i: The iterator to initialise.
@@ -765,12 +862,19 @@ bool iov_iter_is_aligned(const struct iov_iter *i, unsigned addr_mask,
 	if (iov_iter_is_bvec(i))
 		return iov_iter_aligned_bvec(i, addr_mask, len_mask);
 
+	/* With both xarray and folioq types, we're dealing with whole folios. */
 	if (iov_iter_is_xarray(i)) {
 		if (i->count & len_mask)
 			return false;
 		if ((i->xarray_start + i->iov_offset) & addr_mask)
 			return false;
 	}
+	if (iov_iter_is_folioq(i)) {
+		if (i->count & len_mask)
+			return false;
+		if (i->iov_offset & addr_mask)
+			return false;
+	}
 
 	return true;
 }
@@ -835,6 +939,9 @@ unsigned long iov_iter_alignment(const struct iov_iter *i)
 	if (iov_iter_is_bvec(i))
 		return iov_iter_alignment_bvec(i);
 
+	/* With both xarray and folioq types, we're dealing with whole folios. */
+	if (iov_iter_is_folioq(i))
+		return i->iov_offset | i->count;
 	if (iov_iter_is_xarray(i))
 		return (i->xarray_start + i->iov_offset) | i->count;
 
@@ -887,6 +994,51 @@ static int want_pages_array(struct page ***res, size_t size,
 	return count;
 }
 
+static ssize_t iter_folioq_get_pages(struct iov_iter *iter,
+				     struct page ***ppages, size_t maxsize,
+				     unsigned maxpages, size_t *_start_offset)
+{
+	const struct folio_queue *folioq = iter->folioq;
+	struct page **pages;
+	unsigned int slot = iter->folioq_slot;
+	size_t extracted = 0;
+
+	maxpages = want_pages_array(ppages, maxsize, iter->iov_offset & ~PAGE_MASK, maxpages);
+	if (!maxpages)
+		return -ENOMEM;
+	*_start_offset = iter->iov_offset & ~PAGE_MASK;
+	pages = *ppages;
+
+	for (;;) {
+		struct folio *folio = folioq_folio(folioq, slot);
+		size_t offset = iter->iov_offset, fsize = folioq_folio_size(folioq, slot);
+		size_t part = PAGE_SIZE - offset % PAGE_SIZE;
+
+		part = umin(part, umin(maxsize - extracted, fsize - offset));
+		iter->count -= part;
+		iter->iov_offset += part;
+		extracted += part;
+
+		*pages++ = folio_page(folio, offset % PAGE_SIZE);
+		maxpages--;
+		if (maxpages == 0 || extracted >= maxsize)
+			break;
+
+		if (offset >= fsize) {
+			iter->iov_offset = 0;
+			slot++;
+			if (slot == folioq_nr_slots(folioq) && folioq->next) {
+				folioq = folioq->next;
+				slot = 0;
+			}
+		}
+	}
+
+	iter->folioq = folioq;
+	iter->folioq_slot = slot;
+	return extracted;
+}
+
 static ssize_t iter_xarray_populate_pages(struct page **pages, struct xarray *xa,
 					  pgoff_t index, unsigned int nr_pages)
 {
@@ -1034,6 +1186,8 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
 		}
 		return maxsize;
 	}
+	if (iov_iter_is_folioq(i))
+		return iter_folioq_get_pages(i, pages, maxsize, maxpages, start);
 	if (iov_iter_is_xarray(i))
 		return iter_xarray_get_pages(i, pages, maxsize, maxpages, start);
 	return -EFAULT;
@@ -1118,6 +1272,11 @@ int iov_iter_npages(const struct iov_iter *i, int maxpages)
 		return iov_npages(i, maxpages);
 	if (iov_iter_is_bvec(i))
 		return bvec_npages(i, maxpages);
+	if (iov_iter_is_folioq(i)) {
+		unsigned offset = i->iov_offset % PAGE_SIZE;
+		int npages = DIV_ROUND_UP(offset + i->count, PAGE_SIZE);
+		return min(npages, maxpages);
+	}
 	if (iov_iter_is_xarray(i)) {
 		unsigned offset = (i->xarray_start + i->iov_offset) % PAGE_SIZE;
 		int npages = DIV_ROUND_UP(offset + i->count, PAGE_SIZE);
@@ -1398,6 +1557,68 @@ void iov_iter_restore(struct iov_iter *i, struct iov_iter_state *state)
 	i->nr_segs = state->nr_segs;
 }
 
+/*
+ * Extract a list of contiguous pages from an ITER_FOLIOQ iterator.  This does
+ * not get references on the pages, nor does it get a pin on them.
+ */
+static ssize_t iov_iter_extract_folioq_pages(struct iov_iter *i,
+					     struct page ***pages, size_t maxsize,
+					     unsigned int maxpages,
+					     iov_iter_extraction_t extraction_flags,
+					     size_t *offset0)
+{
+	const struct folio_queue *folioq = i->folioq;
+	struct page **p;
+	unsigned int nr = 0;
+	size_t extracted = 0, offset, slot = i->folioq_slot;
+
+	if (slot >= folioq_nr_slots(folioq)) {
+		folioq = folioq->next;
+		slot = 0;
+		if (WARN_ON(i->iov_offset != 0))
+			return -EIO;
+	}
+
+	offset = i->iov_offset & ~PAGE_MASK;
+	*offset0 = offset;
+
+	maxpages = want_pages_array(pages, maxsize, offset, maxpages);
+	if (!maxpages)
+		return -ENOMEM;
+	p = *pages;
+
+	for (;;) {
+		struct folio *folio = folioq_folio(folioq, slot);
+		size_t offset = i->iov_offset, fsize = folioq_folio_size(folioq, slot);
+		size_t part = PAGE_SIZE - offset % PAGE_SIZE;
+
+		if (offset < fsize) {
+			part = umin(part, umin(maxsize - extracted, fsize - offset));
+			i->count -= part;
+			i->iov_offset += part;
+			extracted += part;
+
+			p[nr++] = folio_page(folio, offset / PAGE_SIZE);
+		}
+
+		if (nr >= maxpages || extracted >= maxsize)
+			break;
+
+		if (i->iov_offset >= fsize) {
+			i->iov_offset = 0;
+			slot++;
+			if (slot == folioq_nr_slots(folioq) && folioq->next) {
+				folioq = folioq->next;
+				slot = 0;
+			}
+		}
+	}
+
+	i->folioq = folioq;
+	i->folioq_slot = slot;
+	return extracted;
+}
+
 /*
  * Extract a list of contiguous pages from an ITER_XARRAY iterator.  This does not
  * get references on the pages, nor does it get a pin on them.
@@ -1618,8 +1839,8 @@ static ssize_t iov_iter_extract_user_pages(struct iov_iter *i,
  *      added to the pages, but refs will not be taken.
  *      iov_iter_extract_will_pin() will return true.
  *
- *  (*) If the iterator is ITER_KVEC, ITER_BVEC or ITER_XARRAY, the pages are
- *      merely listed; no extra refs or pins are obtained.
+ *  (*) If the iterator is ITER_KVEC, ITER_BVEC, ITER_FOLIOQ or ITER_XARRAY, the
+ *      pages are merely listed; no extra refs or pins are obtained.
  *      iov_iter_extract_will_pin() will return 0.
  *
  * Note also:
@@ -1654,6 +1875,10 @@ ssize_t iov_iter_extract_pages(struct iov_iter *i,
 		return iov_iter_extract_bvec_pages(i, pages, maxsize,
 						   maxpages, extraction_flags,
 						   offset0);
+	if (iov_iter_is_folioq(i))
+		return iov_iter_extract_folioq_pages(i, pages, maxsize,
+						     maxpages, extraction_flags,
+						     offset0);
 	if (iov_iter_is_xarray(i))
 		return iov_iter_extract_xarray_pages(i, pages, maxsize,
 						     maxpages, extraction_flags,
diff --git a/lib/kunit_iov_iter.c b/lib/kunit_iov_iter.c
index 27e0c8ee71d8..13e15687675a 100644
--- a/lib/kunit_iov_iter.c
+++ b/lib/kunit_iov_iter.c
@@ -12,6 +12,7 @@
 #include <linux/mm.h>
 #include <linux/uio.h>
 #include <linux/bvec.h>
+#include <linux/folio_queue.h>
 #include <kunit/test.h>
 
 MODULE_DESCRIPTION("iov_iter testing");
@@ -62,6 +63,9 @@ static void *__init iov_kunit_create_buffer(struct kunit *test,
 		KUNIT_ASSERT_EQ(test, got, npages);
 	}
 
+	for (int i = 0; i < npages; i++)
+		pages[i]->index = i;
+
 	buffer = vmap(pages, npages, VM_MAP | VM_MAP_PUT_PAGES, PAGE_KERNEL);
         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buffer);
 
@@ -362,6 +366,179 @@ static void __init iov_kunit_copy_from_bvec(struct kunit *test)
 	KUNIT_SUCCEED(test);
 }
 
+static void iov_kunit_destroy_folioq(void *data)
+{
+	struct folio_queue *folioq, *next;
+
+	for (folioq = data; folioq; folioq = next) {
+		next = folioq->next;
+		for (int i = 0; i < folioq_nr_slots(folioq); i++)
+			if (folioq_folio(folioq, i))
+				folio_put(folioq_folio(folioq, i));
+		kfree(folioq);
+	}
+}
+
+static void __init iov_kunit_load_folioq(struct kunit *test,
+					struct iov_iter *iter, int dir,
+					struct folio_queue *folioq,
+					struct page **pages, size_t npages)
+{
+	struct folio_queue *p = folioq;
+	size_t size = 0;
+	int i;
+
+	for (i = 0; i < npages; i++) {
+		if (folioq_full(p)) {
+			p->next = kzalloc(sizeof(struct folio_queue), GFP_KERNEL);
+			KUNIT_ASSERT_NOT_ERR_OR_NULL(test, p->next);
+			folioq_init(p->next);
+			p->next->prev = p;
+			p = p->next;
+		}
+		folioq_append(p, page_folio(pages[i]));
+		size += PAGE_SIZE;
+	}
+	iov_iter_folio_queue(iter, dir, folioq, 0, 0, size);
+}
+
+static struct folio_queue *iov_kunit_create_folioq(struct kunit *test)
+{
+	struct folio_queue *folioq;
+
+	folioq = kzalloc(sizeof(struct folio_queue), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, folioq);
+	kunit_add_action_or_reset(test, iov_kunit_destroy_folioq, folioq);
+	folioq_init(folioq);
+	return folioq;
+}
+
+/*
+ * Test copying to a ITER_FOLIOQ-type iterator.
+ */
+static void __init iov_kunit_copy_to_folioq(struct kunit *test)
+{
+	const struct kvec_test_range *pr;
+	struct iov_iter iter;
+	struct folio_queue *folioq;
+	struct page **spages, **bpages;
+	u8 *scratch, *buffer;
+	size_t bufsize, npages, size, copied;
+	int i, patt;
+
+	bufsize = 0x100000;
+	npages = bufsize / PAGE_SIZE;
+
+	folioq = iov_kunit_create_folioq(test);
+
+	scratch = iov_kunit_create_buffer(test, &spages, npages);
+	for (i = 0; i < bufsize; i++)
+		scratch[i] = pattern(i);
+
+	buffer = iov_kunit_create_buffer(test, &bpages, npages);
+	memset(buffer, 0, bufsize);
+
+	iov_kunit_load_folioq(test, &iter, READ, folioq, bpages, npages);
+
+	i = 0;
+	for (pr = kvec_test_ranges; pr->from >= 0; pr++) {
+		size = pr->to - pr->from;
+		KUNIT_ASSERT_LE(test, pr->to, bufsize);
+
+		iov_iter_folio_queue(&iter, READ, folioq, 0, 0, pr->to);
+		iov_iter_advance(&iter, pr->from);
+		copied = copy_to_iter(scratch + i, size, &iter);
+
+		KUNIT_EXPECT_EQ(test, copied, size);
+		KUNIT_EXPECT_EQ(test, iter.count, 0);
+		KUNIT_EXPECT_EQ(test, iter.iov_offset, pr->to % PAGE_SIZE);
+		i += size;
+		if (test->status == KUNIT_FAILURE)
+			goto stop;
+	}
+
+	/* Build the expected image in the scratch buffer. */
+	patt = 0;
+	memset(scratch, 0, bufsize);
+	for (pr = kvec_test_ranges; pr->from >= 0; pr++)
+		for (i = pr->from; i < pr->to; i++)
+			scratch[i] = pattern(patt++);
+
+	/* Compare the images */
+	for (i = 0; i < bufsize; i++) {
+		KUNIT_EXPECT_EQ_MSG(test, buffer[i], scratch[i], "at i=%x", i);
+		if (buffer[i] != scratch[i])
+			return;
+	}
+
+stop:
+	KUNIT_SUCCEED(test);
+}
+
+/*
+ * Test copying from a ITER_FOLIOQ-type iterator.
+ */
+static void __init iov_kunit_copy_from_folioq(struct kunit *test)
+{
+	const struct kvec_test_range *pr;
+	struct iov_iter iter;
+	struct folio_queue *folioq;
+	struct page **spages, **bpages;
+	u8 *scratch, *buffer;
+	size_t bufsize, npages, size, copied;
+	int i, j;
+
+	bufsize = 0x100000;
+	npages = bufsize / PAGE_SIZE;
+
+	folioq = iov_kunit_create_folioq(test);
+
+	buffer = iov_kunit_create_buffer(test, &bpages, npages);
+	for (i = 0; i < bufsize; i++)
+		buffer[i] = pattern(i);
+
+	scratch = iov_kunit_create_buffer(test, &spages, npages);
+	memset(scratch, 0, bufsize);
+
+	iov_kunit_load_folioq(test, &iter, READ, folioq, bpages, npages);
+
+	i = 0;
+	for (pr = kvec_test_ranges; pr->from >= 0; pr++) {
+		size = pr->to - pr->from;
+		KUNIT_ASSERT_LE(test, pr->to, bufsize);
+
+		iov_iter_folio_queue(&iter, WRITE, folioq, 0, 0, pr->to);
+		iov_iter_advance(&iter, pr->from);
+		copied = copy_from_iter(scratch + i, size, &iter);
+
+		KUNIT_EXPECT_EQ(test, copied, size);
+		KUNIT_EXPECT_EQ(test, iter.count, 0);
+		KUNIT_EXPECT_EQ(test, iter.iov_offset, pr->to % PAGE_SIZE);
+		i += size;
+	}
+
+	/* Build the expected image in the main buffer. */
+	i = 0;
+	memset(buffer, 0, bufsize);
+	for (pr = kvec_test_ranges; pr->from >= 0; pr++) {
+		for (j = pr->from; j < pr->to; j++) {
+			buffer[i++] = pattern(j);
+			if (i >= bufsize)
+				goto stop;
+		}
+	}
+stop:
+
+	/* Compare the images */
+	for (i = 0; i < bufsize; i++) {
+		KUNIT_EXPECT_EQ_MSG(test, scratch[i], buffer[i], "at i=%x", i);
+		if (scratch[i] != buffer[i])
+			return;
+	}
+
+	KUNIT_SUCCEED(test);
+}
+
 static void iov_kunit_destroy_xarray(void *data)
 {
 	struct xarray *xarray = data;
@@ -677,6 +854,85 @@ static void __init iov_kunit_extract_pages_bvec(struct kunit *test)
 	KUNIT_SUCCEED(test);
 }
 
+/*
+ * Test the extraction of ITER_FOLIOQ-type iterators.
+ */
+static void __init iov_kunit_extract_pages_folioq(struct kunit *test)
+{
+	const struct kvec_test_range *pr;
+	struct folio_queue *folioq;
+	struct iov_iter iter;
+	struct page **bpages, *pagelist[8], **pages = pagelist;
+	ssize_t len;
+	size_t bufsize, size = 0, npages;
+	int i, from;
+
+	bufsize = 0x100000;
+	npages = bufsize / PAGE_SIZE;
+
+	folioq = iov_kunit_create_folioq(test);
+
+	iov_kunit_create_buffer(test, &bpages, npages);
+	iov_kunit_load_folioq(test, &iter, READ, folioq, bpages, npages);
+
+	for (pr = kvec_test_ranges; pr->from >= 0; pr++) {
+		from = pr->from;
+		size = pr->to - from;
+		KUNIT_ASSERT_LE(test, pr->to, bufsize);
+
+		iov_iter_folio_queue(&iter, WRITE, folioq, 0, 0, pr->to);
+		iov_iter_advance(&iter, from);
+
+		do {
+			size_t offset0 = LONG_MAX;
+
+			for (i = 0; i < ARRAY_SIZE(pagelist); i++)
+				pagelist[i] = (void *)(unsigned long)0xaa55aa55aa55aa55ULL;
+
+			len = iov_iter_extract_pages(&iter, &pages, 100 * 1024,
+						     ARRAY_SIZE(pagelist), 0, &offset0);
+			KUNIT_EXPECT_GE(test, len, 0);
+			if (len < 0)
+				break;
+			KUNIT_EXPECT_LE(test, len, size);
+			KUNIT_EXPECT_EQ(test, iter.count, size - len);
+			if (len == 0)
+				break;
+			size -= len;
+			KUNIT_EXPECT_GE(test, (ssize_t)offset0, 0);
+			KUNIT_EXPECT_LT(test, offset0, PAGE_SIZE);
+
+			for (i = 0; i < ARRAY_SIZE(pagelist); i++) {
+				struct page *p;
+				ssize_t part = min_t(ssize_t, len, PAGE_SIZE - offset0);
+				int ix;
+
+				KUNIT_ASSERT_GE(test, part, 0);
+				ix = from / PAGE_SIZE;
+				KUNIT_ASSERT_LT(test, ix, npages);
+				p = bpages[ix];
+				KUNIT_EXPECT_PTR_EQ(test, pagelist[i], p);
+				KUNIT_EXPECT_EQ(test, offset0, from % PAGE_SIZE);
+				from += part;
+				len -= part;
+				KUNIT_ASSERT_GE(test, len, 0);
+				if (len == 0)
+					break;
+				offset0 = 0;
+			}
+
+			if (test->status == KUNIT_FAILURE)
+				goto stop;
+		} while (iov_iter_count(&iter) > 0);
+
+		KUNIT_EXPECT_EQ(test, size, 0);
+		KUNIT_EXPECT_EQ(test, iter.count, 0);
+	}
+
+stop:
+	KUNIT_SUCCEED(test);
+}
+
 /*
  * Test the extraction of ITER_XARRAY-type iterators.
  */
@@ -761,10 +1017,13 @@ static struct kunit_case __refdata iov_kunit_cases[] = {
 	KUNIT_CASE(iov_kunit_copy_from_kvec),
 	KUNIT_CASE(iov_kunit_copy_to_bvec),
 	KUNIT_CASE(iov_kunit_copy_from_bvec),
+	KUNIT_CASE(iov_kunit_copy_to_folioq),
+	KUNIT_CASE(iov_kunit_copy_from_folioq),
 	KUNIT_CASE(iov_kunit_copy_to_xarray),
 	KUNIT_CASE(iov_kunit_copy_from_xarray),
 	KUNIT_CASE(iov_kunit_extract_pages_kvec),
 	KUNIT_CASE(iov_kunit_extract_pages_bvec),
+	KUNIT_CASE(iov_kunit_extract_pages_folioq),
 	KUNIT_CASE(iov_kunit_extract_pages_xarray),
 	{}
 };
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 7bc2220fea80..473b2646f71c 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -11,6 +11,7 @@
 #include <linux/kmemleak.h>
 #include <linux/bvec.h>
 #include <linux/uio.h>
+#include <linux/folio_queue.h>
 
 /**
  * sg_next - return the next scatterlist entry in a list
@@ -1261,6 +1262,67 @@ static ssize_t extract_kvec_to_sg(struct iov_iter *iter,
 	return ret;
 }
 
+/*
+ * Extract up to sg_max folios from an FOLIOQ-type iterator and add them to
+ * the scatterlist.  The pages are not pinned.
+ */
+static ssize_t extract_folioq_to_sg(struct iov_iter *iter,
+				   ssize_t maxsize,
+				   struct sg_table *sgtable,
+				   unsigned int sg_max,
+				   iov_iter_extraction_t extraction_flags)
+{
+	const struct folio_queue *folioq = iter->folioq;
+	struct scatterlist *sg = sgtable->sgl + sgtable->nents;
+	unsigned int slot = iter->folioq_slot;
+	ssize_t ret = 0;
+	size_t offset = iter->iov_offset;
+
+	BUG_ON(!folioq);
+
+	if (slot >= folioq_nr_slots(folioq)) {
+		folioq = folioq->next;
+		if (WARN_ON_ONCE(!folioq))
+			return 0;
+		slot = 0;
+	}
+
+	do {
+		struct folio *folio = folioq_folio(folioq, slot);
+		size_t fsize = folioq_folio_size(folioq, slot);
+
+		if (offset < fsize) {
+			size_t part = umin(maxsize - ret, fsize - offset);
+
+			sg_set_page(sg, folio_page(folio, 0), part, offset);
+			sgtable->nents++;
+			sg++;
+			sg_max--;
+			offset += part;
+			ret += part;
+		}
+
+		if (offset >= fsize) {
+			offset = 0;
+			slot++;
+			if (slot >= folioq_nr_slots(folioq)) {
+				if (!folioq->next) {
+					WARN_ON_ONCE(ret < iter->count);
+					break;
+				}
+				folioq = folioq->next;
+				slot = 0;
+			}
+		}
+	} while (sg_max > 0 && ret < maxsize);
+
+	iter->folioq = folioq;
+	iter->folioq_slot = slot;
+	iter->iov_offset = offset;
+	iter->count -= ret;
+	return ret;
+}
+
 /*
  * Extract up to sg_max folios from an XARRAY-type iterator and add them to
  * the scatterlist.  The pages are not pinned.
@@ -1323,8 +1385,8 @@ static ssize_t extract_xarray_to_sg(struct iov_iter *iter,
  * addition of @sg_max elements.
  *
  * The pages referred to by UBUF- and IOVEC-type iterators are extracted and
- * pinned; BVEC-, KVEC- and XARRAY-type are extracted but aren't pinned; PIPE-
- * and DISCARD-type are not supported.
+ * pinned; BVEC-, KVEC-, FOLIOQ- and XARRAY-type are extracted but aren't
+ * pinned; DISCARD-type is not supported.
  *
  * No end mark is placed on the scatterlist; that's left to the caller.
  *
@@ -1356,6 +1418,9 @@ ssize_t extract_iter_to_sg(struct iov_iter *iter, size_t maxsize,
 	case ITER_KVEC:
 		return extract_kvec_to_sg(iter, maxsize, sgtable, sg_max,
 					  extraction_flags);
+	case ITER_FOLIOQ:
+		return extract_folioq_to_sg(iter, maxsize, sgtable, sg_max,
+					    extraction_flags);
 	case ITER_XARRAY:
 		return extract_xarray_to_sg(iter, maxsize, sgtable, sg_max,
 					    extraction_flags);

[PATCH 13/24] cifs: Provide the capability to extract from ITER_FOLIOQ to RDMA SGEs

[David Howells]

Make smb_extract_iter_to_rdma() extract page fragments from an ITER_FOLIOQ
iterator into RDMA SGEs.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Tom Talpey <tom@talpey.com>
cc: Enzo Matsumiya <ematsumiya@suse.de>
cc: linux-cifs@vger.kernel.org
---
 fs/smb/client/smbdirect.c | 71 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 68 insertions(+), 3 deletions(-)

diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
index d74e829de51c..52acead63d9d 100644
--- a/fs/smb/client/smbdirect.c
+++ b/fs/smb/client/smbdirect.c
@@ -6,6 +6,7 @@
  */
 #include <linux/module.h>
 #include <linux/highmem.h>
+#include <linux/folio_queue.h>
 #include "smbdirect.h"
 #include "cifs_debug.h"
 #include "cifsproto.h"
@@ -2463,6 +2464,8 @@ static ssize_t smb_extract_bvec_to_rdma(struct iov_iter *iter,
 		start = 0;
 	}
 
+	if (ret > 0)
+		iov_iter_advance(iter, ret);
 	return ret;
 }
 
@@ -2519,6 +2522,65 @@ static ssize_t smb_extract_kvec_to_rdma(struct iov_iter *iter,
 		start = 0;
 	}
 
+	if (ret > 0)
+		iov_iter_advance(iter, ret);
+	return ret;
+}
+
+/*
+ * Extract folio fragments from a FOLIOQ-class iterator and add them to an RDMA
+ * list.  The folios are not pinned.
+ */
+static ssize_t smb_extract_folioq_to_rdma(struct iov_iter *iter,
+					  struct smb_extract_to_rdma *rdma,
+					  ssize_t maxsize)
+{
+	const struct folio_queue *folioq = iter->folioq;
+	unsigned int slot = iter->folioq_slot;
+	ssize_t ret = 0;
+	size_t offset = iter->iov_offset;
+
+	BUG_ON(!folioq);
+
+	if (slot >= folioq_nr_slots(folioq)) {
+		folioq = folioq->next;
+		if (WARN_ON_ONCE(!folioq))
+			return -EIO;
+		slot = 0;
+	}
+
+	do {
+		struct folio *folio = folioq_folio(folioq, slot);
+		size_t fsize = folioq_folio_size(folioq, slot);
+
+		if (offset < fsize) {
+			size_t part = umin(maxsize - ret, fsize - offset);
+
+			if (!smb_set_sge(rdma, folio_page(folio, 0), offset, part))
+				return -EIO;
+
+			offset += part;
+			ret += part;
+		}
+
+		if (offset >= fsize) {
+			offset = 0;
+			slot++;
+			if (slot >= folioq_nr_slots(folioq)) {
+				if (!folioq->next) {
+					WARN_ON_ONCE(ret < iter->count);
+					break;
+				}
+				folioq = folioq->next;
+				slot = 0;
+			}
+		}
+	} while (rdma->nr_sge < rdma->max_sge || maxsize > 0);
+
+	iter->folioq = folioq;
+	iter->folioq_slot = slot;
+	iter->iov_offset = offset;
+	iter->count -= ret;
 	return ret;
 }
 
@@ -2563,6 +2625,8 @@ static ssize_t smb_extract_xarray_to_rdma(struct iov_iter *iter,
 	}
 
 	rcu_read_unlock();
+	if (ret > 0)
+		iov_iter_advance(iter, ret);
 	return ret;
 }
 
@@ -2590,6 +2654,9 @@ static ssize_t smb_extract_iter_to_rdma(struct iov_iter *iter, size_t len,
 	case ITER_KVEC:
 		ret = smb_extract_kvec_to_rdma(iter, rdma, len);
 		break;
+	case ITER_FOLIOQ:
+		ret = smb_extract_folioq_to_rdma(iter, rdma, len);
+		break;
 	case ITER_XARRAY:
 		ret = smb_extract_xarray_to_rdma(iter, rdma, len);
 		break;
@@ -2598,9 +2665,7 @@ static ssize_t smb_extract_iter_to_rdma(struct iov_iter *iter, size_t len,
 		return -EIO;
 	}
 
-	if (ret > 0) {
-		iov_iter_advance(iter, ret);
-	} else if (ret < 0) {
+	if (ret < 0) {
 		while (rdma->nr_sge > before) {
 			struct ib_sge *sge = &rdma->sge[rdma->nr_sge--];
 

[PATCH 14/24] netfs: Use new folio_queue data type and iterator instead of xarray iter

[David Howells]

Make the netfs write-side routines use the new folio_queue struct to hold a
rolling buffer of folios, with the issuer adding folios at the tail and the
collector removing them from the head as they're processed instead of using
an xarray.

This will allow a subsequent patch to simplify the write collector.

The primary mark (as tested by folioq_is_marked()) is used to note if the
corresponding folio needs putting.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/internal.h          |  9 +++-
 fs/netfs/misc.c              | 76 ++++++++++++++++++++++++++++++++
 fs/netfs/objects.c           |  1 +
 fs/netfs/stats.c             |  4 +-
 fs/netfs/write_collect.c     | 84 +++++++++++++++++++-----------------
 fs/netfs/write_issue.c       | 28 ++++++------
 include/linux/netfs.h        |  8 ++--
 include/trace/events/netfs.h |  1 +
 8 files changed, 150 insertions(+), 61 deletions(-)

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index f2920b4ee726..e1149e05a5c8 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -7,6 +7,7 @@
 
 #include <linux/slab.h>
 #include <linux/seq_file.h>
+#include <linux/folio_queue.h>
 #include <linux/netfs.h>
 #include <linux/fscache.h>
 #include <linux/fscache-cache.h>
@@ -64,6 +65,10 @@ static inline void netfs_proc_del_rreq(struct netfs_io_request *rreq) {}
 /*
  * misc.c
  */
+int netfs_buffer_append_folio(struct netfs_io_request *rreq, struct folio *folio,
+			      bool needs_put);
+struct folio_queue *netfs_delete_buffer_head(struct netfs_io_request *wreq);
+void netfs_clear_buffer(struct netfs_io_request *rreq);
 
 /*
  * objects.c
@@ -120,6 +125,7 @@ extern atomic_t netfs_n_wh_write_done;
 extern atomic_t netfs_n_wh_write_failed;
 extern atomic_t netfs_n_wb_lock_skip;
 extern atomic_t netfs_n_wb_lock_wait;
+extern atomic_t netfs_n_folioq;
 
 int netfs_stats_show(struct seq_file *m, void *v);
 
@@ -153,7 +159,8 @@ struct netfs_io_request *netfs_create_write_req(struct address_space *mapping,
 						loff_t start,
 						enum netfs_io_origin origin);
 void netfs_reissue_write(struct netfs_io_stream *stream,
-			 struct netfs_io_subrequest *subreq);
+			 struct netfs_io_subrequest *subreq,
+			 struct iov_iter *source);
 int netfs_advance_write(struct netfs_io_request *wreq,
 			struct netfs_io_stream *stream,
 			loff_t start, size_t len, bool to_eof);
diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c
index 83e644bd518f..1700849491a0 100644
--- a/fs/netfs/misc.c
+++ b/fs/netfs/misc.c
@@ -8,6 +8,82 @@
 #include <linux/swap.h>
 #include "internal.h"
 
+/*
+ * Append a folio to the rolling queue.
+ */
+int netfs_buffer_append_folio(struct netfs_io_request *rreq, struct folio *folio,
+			      bool needs_put)
+{
+	struct folio_queue *tail = rreq->buffer_tail;
+	unsigned int slot, order = folio_order(folio);
+
+	if (WARN_ON_ONCE(!rreq->buffer && tail) ||
+	    WARN_ON_ONCE(rreq->buffer && !tail))
+		return -EIO;
+
+	if (!tail || folioq_full(tail)) {
+		tail = kmalloc(sizeof(*tail), GFP_NOFS);
+		if (!tail)
+			return -ENOMEM;
+		netfs_stat(&netfs_n_folioq);
+		folioq_init(tail);
+		tail->prev = rreq->buffer_tail;
+		if (tail->prev)
+			tail->prev->next = tail;
+		rreq->buffer_tail = tail;
+		if (!rreq->buffer) {
+			rreq->buffer = tail;
+			iov_iter_folio_queue(&rreq->io_iter, ITER_SOURCE, tail, 0, 0, 0);
+		}
+		rreq->buffer_tail_slot = 0;
+	}
+
+	rreq->io_iter.count += PAGE_SIZE << order;
+
+	slot = folioq_append(tail, folio);
+	/* Store the counter after setting the slot. */
+	smp_store_release(&rreq->buffer_tail_slot, slot);
+	return 0;
+}
+
+/*
+ * Delete the head of a rolling queue.
+ */
+struct folio_queue *netfs_delete_buffer_head(struct netfs_io_request *wreq)
+{
+	struct folio_queue *head = wreq->buffer, *next = head->next;
+
+	if (next)
+		next->prev = NULL;
+	netfs_stat_d(&netfs_n_folioq);
+	kfree(head);
+	wreq->buffer = next;
+	return next;
+}
+
+/*
+ * Clear out a rolling queue.
+ */
+void netfs_clear_buffer(struct netfs_io_request *rreq)
+{
+	struct folio_queue *p;
+
+	while ((p = rreq->buffer)) {
+		rreq->buffer = p->next;
+		for (int slot = 0; slot < folioq_nr_slots(p); slot++) {
+			struct folio *folio = folioq_folio(p, slot);
+			if (!folio)
+				continue;
+			if (folioq_is_marked(p, slot)) {
+				trace_netfs_folio(folio, netfs_folio_trace_put);
+				folio_put(folio);
+			}
+		}
+		netfs_stat_d(&netfs_n_folioq);
+		kfree(p);
+	}
+}
+
 /**
  * netfs_dirty_folio - Mark folio dirty and pin a cache object for writeback
  * @mapping: The mapping the folio belongs to.
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index 1dbcd7f44eca..9d2563d4dab8 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -151,6 +151,7 @@ static void netfs_free_request(struct work_struct *work)
 		}
 		kvfree(rreq->direct_bv);
 	}
+	netfs_clear_buffer(rreq);
 
 	if (atomic_dec_and_test(&ictx->io_count))
 		wake_up_var(&ictx->io_count);
diff --git a/fs/netfs/stats.c b/fs/netfs/stats.c
index 5fe1c396e24f..5065289f5555 100644
--- a/fs/netfs/stats.c
+++ b/fs/netfs/stats.c
@@ -41,6 +41,7 @@ atomic_t netfs_n_wh_write_done;
 atomic_t netfs_n_wh_write_failed;
 atomic_t netfs_n_wb_lock_skip;
 atomic_t netfs_n_wb_lock_wait;
+atomic_t netfs_n_folioq;
 
 int netfs_stats_show(struct seq_file *m, void *v)
 {
@@ -76,9 +77,10 @@ int netfs_stats_show(struct seq_file *m, void *v)
 		   atomic_read(&netfs_n_wh_write),
 		   atomic_read(&netfs_n_wh_write_done),
 		   atomic_read(&netfs_n_wh_write_failed));
-	seq_printf(m, "Objs   : rr=%u sr=%u wsc=%u\n",
+	seq_printf(m, "Objs   : rr=%u sr=%u foq=%u wsc=%u\n",
 		   atomic_read(&netfs_n_rh_rreq),
 		   atomic_read(&netfs_n_rh_sreq),
+		   atomic_read(&netfs_n_folioq),
 		   atomic_read(&netfs_n_wh_wstream_conflict));
 	seq_printf(m, "WbLock : skip=%u wait=%u\n",
 		   atomic_read(&netfs_n_wb_lock_skip),
diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index 5f504b03a1e7..1521a23077c3 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -74,42 +74,6 @@ int netfs_folio_written_back(struct folio *folio)
 	return gcount;
 }
 
-/*
- * Get hold of a folio we have under writeback.  We don't want to get the
- * refcount on it.
- */
-static struct folio *netfs_writeback_lookup_folio(struct netfs_io_request *wreq, loff_t pos)
-{
-	XA_STATE(xas, &wreq->mapping->i_pages, pos / PAGE_SIZE);
-	struct folio *folio;
-
-	rcu_read_lock();
-
-	for (;;) {
-		xas_reset(&xas);
-		folio = xas_load(&xas);
-		if (xas_retry(&xas, folio))
-			continue;
-
-		if (!folio || xa_is_value(folio))
-			kdebug("R=%08x: folio %lx (%llx) not present",
-			       wreq->debug_id, xas.xa_index, pos / PAGE_SIZE);
-		BUG_ON(!folio || xa_is_value(folio));
-
-		if (folio == xas_reload(&xas))
-			break;
-	}
-
-	rcu_read_unlock();
-
-	if (WARN_ONCE(!folio_test_writeback(folio),
-		      "R=%08x: folio %lx is not under writeback\n",
-		      wreq->debug_id, folio->index)) {
-		trace_netfs_folio(folio, netfs_folio_trace_not_under_wback);
-	}
-	return folio;
-}
-
 /*
  * Unlock any folios we've finished with.
  */
@@ -117,13 +81,25 @@ static void netfs_writeback_unlock_folios(struct netfs_io_request *wreq,
 					  unsigned long long collected_to,
 					  unsigned int *notes)
 {
+	struct folio_queue *folioq = wreq->buffer;
+	unsigned int slot = wreq->buffer_head_slot;
+
+	if (slot >= folioq_nr_slots(folioq)) {
+		folioq = netfs_delete_buffer_head(wreq);
+		slot = 0;
+	}
+
 	for (;;) {
 		struct folio *folio;
 		struct netfs_folio *finfo;
 		unsigned long long fpos, fend;
 		size_t fsize, flen;
 
-		folio = netfs_writeback_lookup_folio(wreq, wreq->cleaned_to);
+		folio = folioq_folio(folioq, slot);
+		if (WARN_ONCE(!folio_test_writeback(folio),
+			      "R=%08x: folio %lx is not under writeback\n",
+			      wreq->debug_id, folio->index))
+			trace_netfs_folio(folio, netfs_folio_trace_not_under_wback);
 
 		fpos = folio_pos(folio);
 		fsize = folio_size(folio);
@@ -148,9 +124,25 @@ static void netfs_writeback_unlock_folios(struct netfs_io_request *wreq,
 		wreq->cleaned_to = fpos + fsize;
 		*notes |= MADE_PROGRESS;
 
+		/* Clean up the head folioq.  If we clear an entire folioq, then
+		 * we can get rid of it provided it's not also the tail folioq
+		 * being filled by the issuer.
+		 */
+		folioq_clear(folioq, slot);
+		slot++;
+		if (slot >= folioq_nr_slots(folioq)) {
+			if (READ_ONCE(wreq->buffer_tail) == folioq)
+				break;
+			folioq = netfs_delete_buffer_head(wreq);
+			slot = 0;
+		}
+
 		if (fpos + fsize >= collected_to)
 			break;
 	}
+
+	wreq->buffer = folioq;
+	wreq->buffer_head_slot = slot;
 }
 
 /*
@@ -181,9 +173,12 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 			if (test_bit(NETFS_SREQ_FAILED, &subreq->flags))
 				break;
 			if (__test_and_clear_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags)) {
+				struct iov_iter source = subreq->io_iter;
+
+				iov_iter_revert(&source, subreq->len - source.count);
 				__set_bit(NETFS_SREQ_RETRYING, &subreq->flags);
 				netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
-				netfs_reissue_write(stream, subreq);
+				netfs_reissue_write(stream, subreq, &source);
 			}
 		}
 		return;
@@ -193,6 +188,7 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 
 	do {
 		struct netfs_io_subrequest *subreq = NULL, *from, *to, *tmp;
+		struct iov_iter source;
 		unsigned long long start, len;
 		size_t part;
 		bool boundary = false;
@@ -220,6 +216,14 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 			len += to->len;
 		}
 
+		/* Determine the set of buffers we're going to use.  Each
+		 * subreq gets a subset of a single overall contiguous buffer.
+		 */
+		source = from->io_iter;
+		iov_iter_revert(&source, subreq->len - source.count);
+		iov_iter_advance(&source, from->transferred);
+		source.count = len;
+
 		/* Work through the sublist. */
 		subreq = from;
 		list_for_each_entry_from(subreq, &stream->subrequests, rreq_link) {
@@ -242,7 +246,7 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 				boundary = true;
 
 			netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
-			netfs_reissue_write(stream, subreq);
+			netfs_reissue_write(stream, subreq, &source);
 			if (subreq == to)
 				break;
 		}
@@ -309,7 +313,7 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 				boundary = false;
 			}
 
-			netfs_reissue_write(stream, subreq);
+			netfs_reissue_write(stream, subreq, &source);
 			if (!len)
 				break;
 
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 0354c992467b..d581fd8a568b 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -211,9 +211,11 @@ static void netfs_prepare_write(struct netfs_io_request *wreq,
  * netfs_write_subrequest_terminated() when complete.
  */
 static void netfs_do_issue_write(struct netfs_io_stream *stream,
-				 struct netfs_io_subrequest *subreq)
+				 struct netfs_io_subrequest *subreq,
+				 struct iov_iter *source)
 {
 	struct netfs_io_request *wreq = subreq->rreq;
+	size_t size = subreq->len - subreq->transferred;
 
 	_enter("R=%x[%x],%zx", wreq->debug_id, subreq->debug_index, subreq->len);
 
@@ -221,27 +223,20 @@ static void netfs_do_issue_write(struct netfs_io_stream *stream,
 		return netfs_write_subrequest_terminated(subreq, subreq->error, false);
 
 	// TODO: Use encrypted buffer
-	if (test_bit(NETFS_RREQ_USE_IO_ITER, &wreq->flags)) {
-		subreq->io_iter = wreq->io_iter;
-		iov_iter_advance(&subreq->io_iter,
-				 subreq->start + subreq->transferred - wreq->start);
-		iov_iter_truncate(&subreq->io_iter,
-				 subreq->len - subreq->transferred);
-	} else {
-		iov_iter_xarray(&subreq->io_iter, ITER_SOURCE, &wreq->mapping->i_pages,
-				subreq->start + subreq->transferred,
-				subreq->len   - subreq->transferred);
-	}
+	subreq->io_iter = *source;
+	iov_iter_advance(source, size);
+	iov_iter_truncate(&subreq->io_iter, size);
 
 	trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
 	stream->issue_write(subreq);
 }
 
 void netfs_reissue_write(struct netfs_io_stream *stream,
-			 struct netfs_io_subrequest *subreq)
+			 struct netfs_io_subrequest *subreq,
+			 struct iov_iter *source)
 {
 	__set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
-	netfs_do_issue_write(stream, subreq);
+	netfs_do_issue_write(stream, subreq, source);
 }
 
 static void netfs_issue_write(struct netfs_io_request *wreq,
@@ -255,7 +250,7 @@ static void netfs_issue_write(struct netfs_io_request *wreq,
 
 	if (subreq->start + subreq->len > wreq->start + wreq->submitted)
 		WRITE_ONCE(wreq->submitted, subreq->start + subreq->len - wreq->start);
-	netfs_do_issue_write(stream, subreq);
+	netfs_do_issue_write(stream, subreq, &wreq->io_iter);
 }
 
 /*
@@ -420,6 +415,9 @@ static int netfs_write_folio(struct netfs_io_request *wreq,
 		trace_netfs_folio(folio, netfs_folio_trace_store_plus);
 	}
 
+	/* Attach the folio to the rolling buffer. */
+	netfs_buffer_append_folio(wreq, folio, false);
+
 	/* Move the submission point forward to allow for write-streaming data
 	 * not starting at the front of the page.  We don't do write-streaming
 	 * with the cache as the cache requires DIO alignment.
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index daaa6eae3a9f..f8ca28d476c3 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -38,10 +38,6 @@ static inline void folio_start_private_2(struct folio *folio)
 	folio_set_private_2(folio);
 }
 
-/* Marks used on xarray-based buffers */
-#define NETFS_BUF_PUT_MARK	XA_MARK_0	/* - Page needs putting  */
-#define NETFS_BUF_PAGECACHE_MARK XA_MARK_1	/* - Page needs wb/dirty flag wrangling */
-
 enum netfs_io_source {
 	NETFS_SOURCE_UNKNOWN,
 	NETFS_FILL_WITH_ZEROES,
@@ -234,6 +230,8 @@ struct netfs_io_request {
 	struct netfs_io_stream	io_streams[2];	/* Streams of parallel I/O operations */
 #define NR_IO_STREAMS 2 //wreq->nr_io_streams
 	struct netfs_group	*group;		/* Writeback group being written back */
+	struct folio_queue	*buffer;	/* Head of I/O buffer */
+	struct folio_queue	*buffer_tail;	/* Tail of I/O buffer */
 	struct iov_iter		iter;		/* Unencrypted-side iterator */
 	struct iov_iter		io_iter;	/* I/O (Encrypted-side) iterator */
 	void			*netfs_priv;	/* Private data for the netfs */
@@ -255,6 +253,8 @@ struct netfs_io_request {
 	short			error;		/* 0 or error that occurred */
 	enum netfs_io_origin	origin;		/* Origin of the request */
 	bool			direct_bv_unpin; /* T if direct_bv[] must be unpinned */
+	u8			buffer_head_slot; /* First slot in ->buffer */
+	u8			buffer_tail_slot; /* Next slot in ->buffer_tail */
 	unsigned long long	i_size;		/* Size of the file */
 	unsigned long long	start;		/* Start position */
 	atomic64_t		issued_to;	/* Write issuer folio cursor */
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index b5a30d9a0d20..8d14715422c0 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -151,6 +151,7 @@
 	EM(netfs_folio_trace_mkwrite,		"mkwrite")	\
 	EM(netfs_folio_trace_mkwrite_plus,	"mkwrite+")	\
 	EM(netfs_folio_trace_not_under_wback,	"!wback")	\
+	EM(netfs_folio_trace_put,		"put")		\
 	EM(netfs_folio_trace_read_gaps,		"read-gaps")	\
 	EM(netfs_folio_trace_redirtied,		"redirtied")	\
 	EM(netfs_folio_trace_store,		"store")	\

[PATCH 15/24] netfs: Provide an iterator-reset function

[David Howells]

---
 fs/netfs/internal.h      |  4 +---
 fs/netfs/misc.c          | 18 ++++++++++++++++++
 fs/netfs/write_collect.c |  3 +--
 fs/netfs/write_issue.c   |  6 +++---
 4 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index e1149e05a5c8..21a3c7d13585 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -69,6 +69,7 @@ int netfs_buffer_append_folio(struct netfs_io_request *rreq, struct folio *folio
 			      bool needs_put);
 struct folio_queue *netfs_delete_buffer_head(struct netfs_io_request *wreq);
 void netfs_clear_buffer(struct netfs_io_request *rreq);
+void netfs_reset_iter(struct netfs_io_subrequest *subreq);
 
 /*
  * objects.c
@@ -161,9 +162,6 @@ struct netfs_io_request *netfs_create_write_req(struct address_space *mapping,
 void netfs_reissue_write(struct netfs_io_stream *stream,
 			 struct netfs_io_subrequest *subreq,
 			 struct iov_iter *source);
-int netfs_advance_write(struct netfs_io_request *wreq,
-			struct netfs_io_stream *stream,
-			loff_t start, size_t len, bool to_eof);
 struct netfs_io_request *netfs_begin_writethrough(struct kiocb *iocb, size_t len);
 int netfs_advance_writethrough(struct netfs_io_request *wreq, struct writeback_control *wbc,
 			       struct folio *folio, size_t copied, bool to_page_end,
diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c
index 1700849491a0..a9baa46a17ff 100644
--- a/fs/netfs/misc.c
+++ b/fs/netfs/misc.c
@@ -84,6 +84,24 @@ void netfs_clear_buffer(struct netfs_io_request *rreq)
 	}
 }
 
+/*
+ * Reset the subrequest iterator to refer just to the region remaining to be
+ * read.  The iterator may or may not have been advanced by socket ops or
+ * extraction ops to an extent that may or may not match the amount actually
+ * read.
+ */
+void netfs_reset_iter(struct netfs_io_subrequest *subreq)
+{
+	struct iov_iter *io_iter = &subreq->io_iter;
+	size_t remain = subreq->len - subreq->transferred;
+
+	if (io_iter->count > remain)
+		iov_iter_advance(io_iter, io_iter->count - remain);
+	else if (io_iter->count < remain)
+		iov_iter_revert(io_iter, remain - io_iter->count);
+	iov_iter_truncate(&subreq->io_iter, remain);
+}
+
 /**
  * netfs_dirty_folio - Mark folio dirty and pin a cache object for writeback
  * @mapping: The mapping the folio belongs to.
diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index 1521a23077c3..801a130a0ce1 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -219,9 +219,8 @@ static void netfs_retry_write_stream(struct netfs_io_request *wreq,
 		/* Determine the set of buffers we're going to use.  Each
 		 * subreq gets a subset of a single overall contiguous buffer.
 		 */
+		netfs_reset_iter(from);
 		source = from->io_iter;
-		iov_iter_revert(&source, subreq->len - source.count);
-		iov_iter_advance(&source, from->transferred);
 		source.count = len;
 
 		/* Work through the sublist. */
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index d581fd8a568b..520be44d132e 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -259,9 +259,9 @@ static void netfs_issue_write(struct netfs_io_request *wreq,
  * we can avoid overrunning the credits obtained (cifs) and try to parallelise
  * content-crypto preparation with network writes.
  */
-int netfs_advance_write(struct netfs_io_request *wreq,
-			struct netfs_io_stream *stream,
-			loff_t start, size_t len, bool to_eof)
+static int netfs_advance_write(struct netfs_io_request *wreq,
+			       struct netfs_io_stream *stream,
+			       loff_t start, size_t len, bool to_eof)
 {
 	struct netfs_io_subrequest *subreq = stream->construct;
 	size_t part;

[PATCH 16/24] netfs: Simplify the writeback code

[David Howells]

Use the new folio_queue structures to simplify the writeback code.  The
problem with referring to the i_pages xarray directly is that we may have
gaps in the sequence of folios we're writing from that we need to skip when
we're removing the writeback mark from the folios we're writing back from.

At the moment the code tries to deal with this by carefully tracking the
gaps in each writeback stream (eg. write to server and write to cache) and
divining when there's a gap that spans folios (something that's not helped
by folios not being a consistent size).

Instead, the folio_queue buffer contains pointers only the folios we're
dealing with, has them in ascending order and indicates a gap by placing
non-consequitive folios next to each other.  This makes it possible to
track where we need to clean up to by just keeping track of where we've
processed to on each stream and taking the minimum.

Note that the I/O iterator is always rounded up to the end of the folio,
even if that is beyond the EOF position, so that the cache can do DIO from
the page.  The excess space is cleared, though mmapped writes clobber it.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/write_collect.c     | 146 ++++++-----------------------------
 fs/netfs/write_issue.c       |  36 +++++----
 include/linux/netfs.h        |   1 -
 include/trace/events/netfs.h |  33 +-------
 4 files changed, 45 insertions(+), 171 deletions(-)

diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index 801a130a0ce1..0116b336fa07 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -15,15 +15,11 @@
 
 /* Notes made in the collector */
 #define HIT_PENDING		0x01	/* A front op was still pending */
-#define SOME_EMPTY		0x02	/* One of more streams are empty */
-#define ALL_EMPTY		0x04	/* All streams are empty */
-#define MAYBE_DISCONTIG		0x08	/* A front op may be discontiguous (rounded to PAGE_SIZE) */
-#define NEED_REASSESS		0x10	/* Need to loop round and reassess */
-#define REASSESS_DISCONTIG	0x20	/* Reassess discontiguity if contiguity advances */
-#define MADE_PROGRESS		0x40	/* Made progress cleaning up a stream or the folio set */
-#define BUFFERED		0x80	/* The pagecache needs cleaning up */
-#define NEED_RETRY		0x100	/* A front op requests retrying */
-#define SAW_FAILURE		0x200	/* One stream or hit a permanent failure */
+#define NEED_REASSESS		0x02	/* Need to loop round and reassess */
+#define MADE_PROGRESS		0x04	/* Made progress cleaning up a stream or the folio set */
+#define BUFFERED		0x08	/* The pagecache needs cleaning up */
+#define NEED_RETRY		0x10	/* A front op requests retrying */
+#define SAW_FAILURE		0x20	/* One stream or hit a permanent failure */
 
 /*
  * Successful completion of write of a folio to the server and/or cache.  Note
@@ -78,10 +74,10 @@ int netfs_folio_written_back(struct folio *folio)
  * Unlock any folios we've finished with.
  */
 static void netfs_writeback_unlock_folios(struct netfs_io_request *wreq,
-					  unsigned long long collected_to,
 					  unsigned int *notes)
 {
 	struct folio_queue *folioq = wreq->buffer;
+	unsigned long long collected_to = wreq->collected_to;
 	unsigned int slot = wreq->buffer_head_slot;
 
 	if (slot >= folioq_nr_slots(folioq)) {
@@ -110,12 +106,6 @@ static void netfs_writeback_unlock_folios(struct netfs_io_request *wreq,
 
 		trace_netfs_collect_folio(wreq, folio, fend, collected_to);
 
-		if (fpos + fsize > wreq->contiguity) {
-			trace_netfs_collect_contig(wreq, fpos + fsize,
-						   netfs_contig_trace_unlock);
-			wreq->contiguity = fpos + fsize;
-		}
-
 		/* Unlock any folio we've transferred all of. */
 		if (collected_to < fend)
 			break;
@@ -373,7 +363,7 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 {
 	struct netfs_io_subrequest *front, *remove;
 	struct netfs_io_stream *stream;
-	unsigned long long collected_to;
+	unsigned long long collected_to, issued_to;
 	unsigned int notes;
 	int s;
 
@@ -382,28 +372,21 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 	trace_netfs_rreq(wreq, netfs_rreq_trace_collect);
 
 reassess_streams:
+	issued_to = atomic64_read(&wreq->issued_to);
 	smp_rmb();
 	collected_to = ULLONG_MAX;
-	if (wreq->origin == NETFS_WRITEBACK)
-		notes = ALL_EMPTY | BUFFERED | MAYBE_DISCONTIG;
-	else if (wreq->origin == NETFS_WRITETHROUGH)
-		notes = ALL_EMPTY | BUFFERED;
+	if (wreq->origin == NETFS_WRITEBACK ||
+	    wreq->origin == NETFS_WRITETHROUGH)
+		notes = BUFFERED;
 	else
-		notes = ALL_EMPTY;
+		notes = 0;
 
 	/* Remove completed subrequests from the front of the streams and
 	 * advance the completion point on each stream.  We stop when we hit
 	 * something that's in progress.  The issuer thread may be adding stuff
 	 * to the tail whilst we're doing this.
-	 *
-	 * We must not, however, merge in discontiguities that span whole
-	 * folios that aren't under writeback.  This is made more complicated
-	 * by the folios in the gap being of unpredictable sizes - if they even
-	 * exist - but we don't want to look them up.
 	 */
 	for (s = 0; s < NR_IO_STREAMS; s++) {
-		loff_t rstart, rend;
-
 		stream = &wreq->io_streams[s];
 		/* Read active flag before list pointers */
 		if (!smp_load_acquire(&stream->active))
@@ -415,26 +398,10 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 			//_debug("sreq [%x] %llx %zx/%zx",
 			//       front->debug_index, front->start, front->transferred, front->len);
 
-			/* Stall if there may be a discontinuity. */
-			rstart = round_down(front->start, PAGE_SIZE);
-			if (rstart > wreq->contiguity) {
-				if (wreq->contiguity > stream->collected_to) {
-					trace_netfs_collect_gap(wreq, stream,
-								wreq->contiguity, 'D');
-					stream->collected_to = wreq->contiguity;
-				}
-				notes |= REASSESS_DISCONTIG;
-				break;
+			if (stream->collected_to < front->start) {
+				trace_netfs_collect_gap(wreq, stream, issued_to, 'F');
+				stream->collected_to = front->start;
 			}
-			rend = round_up(front->start + front->len, PAGE_SIZE);
-			if (rend > wreq->contiguity) {
-				trace_netfs_collect_contig(wreq, rend,
-							   netfs_contig_trace_collect);
-				wreq->contiguity = rend;
-				if (notes & REASSESS_DISCONTIG)
-					notes |= NEED_REASSESS;
-			}
-			notes &= ~MAYBE_DISCONTIG;
 
 			/* Stall if the front is still undergoing I/O. */
 			if (test_bit(NETFS_SREQ_IN_PROGRESS, &front->flags)) {
@@ -476,15 +443,6 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 			front = list_first_entry_or_null(&stream->subrequests,
 							 struct netfs_io_subrequest, rreq_link);
 			stream->front = front;
-			if (!front) {
-				unsigned long long jump_to = atomic64_read(&wreq->issued_to);
-
-				if (stream->collected_to < jump_to) {
-					trace_netfs_collect_gap(wreq, stream, jump_to, 'A');
-					stream->collected_to = jump_to;
-				}
-			}
-
 			spin_unlock_bh(&wreq->lock);
 			netfs_put_subrequest(remove, false,
 					     notes & SAW_FAILURE ?
@@ -492,10 +450,13 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 					     netfs_sreq_trace_put_done);
 		}
 
-		if (front)
-			notes &= ~ALL_EMPTY;
-		else
-			notes |= SOME_EMPTY;
+		/* If we have an empty stream, we need to jump it forward
+		 * otherwise the collection point will never advance.
+		 */
+		if (!front && issued_to > stream->collected_to) {
+			trace_netfs_collect_gap(wreq, stream, issued_to, 'E');
+			stream->collected_to = issued_to;
+		}
 
 		if (stream->collected_to < collected_to)
 			collected_to = stream->collected_to;
@@ -504,36 +465,6 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 	if (collected_to != ULLONG_MAX && collected_to > wreq->collected_to)
 		wreq->collected_to = collected_to;
 
-	/* If we have an empty stream, we need to jump it forward over any gap
-	 * otherwise the collection point will never advance.
-	 *
-	 * Note that the issuer always adds to the stream with the lowest
-	 * so-far submitted start, so if we see two consecutive subreqs in one
-	 * stream with nothing between then in another stream, then the second
-	 * stream has a gap that can be jumped.
-	 */
-	if (notes & SOME_EMPTY) {
-		unsigned long long jump_to = wreq->start + READ_ONCE(wreq->submitted);
-
-		for (s = 0; s < NR_IO_STREAMS; s++) {
-			stream = &wreq->io_streams[s];
-			if (stream->active &&
-			    stream->front &&
-			    stream->front->start < jump_to)
-				jump_to = stream->front->start;
-		}
-
-		for (s = 0; s < NR_IO_STREAMS; s++) {
-			stream = &wreq->io_streams[s];
-			if (stream->active &&
-			    !stream->front &&
-			    stream->collected_to < jump_to) {
-				trace_netfs_collect_gap(wreq, stream, jump_to, 'B');
-				stream->collected_to = jump_to;
-			}
-		}
-	}
-
 	for (s = 0; s < NR_IO_STREAMS; s++) {
 		stream = &wreq->io_streams[s];
 		if (stream->active)
@@ -544,43 +475,14 @@ static void netfs_collect_write_results(struct netfs_io_request *wreq)
 
 	/* Unlock any folios that we have now finished with. */
 	if (notes & BUFFERED) {
-		unsigned long long clean_to = min(wreq->collected_to, wreq->contiguity);
-
-		if (wreq->cleaned_to < clean_to)
-			netfs_writeback_unlock_folios(wreq, clean_to, &notes);
+		if (wreq->cleaned_to < wreq->collected_to)
+			netfs_writeback_unlock_folios(wreq, &notes);
 	} else {
 		wreq->cleaned_to = wreq->collected_to;
 	}
 
 	// TODO: Discard encryption buffers
 
-	/* If all streams are discontiguous with the last folio we cleared, we
-	 * may need to skip a set of folios.
-	 */
-	if ((notes & (MAYBE_DISCONTIG | ALL_EMPTY)) == MAYBE_DISCONTIG) {
-		unsigned long long jump_to = ULLONG_MAX;
-
-		for (s = 0; s < NR_IO_STREAMS; s++) {
-			stream = &wreq->io_streams[s];
-			if (stream->active && stream->front &&
-			    stream->front->start < jump_to)
-				jump_to = stream->front->start;
-		}
-
-		trace_netfs_collect_contig(wreq, jump_to, netfs_contig_trace_jump);
-		wreq->contiguity = jump_to;
-		wreq->cleaned_to = jump_to;
-		wreq->collected_to = jump_to;
-		for (s = 0; s < NR_IO_STREAMS; s++) {
-			stream = &wreq->io_streams[s];
-			if (stream->collected_to < jump_to)
-				stream->collected_to = jump_to;
-		}
-		//cond_resched();
-		notes |= MADE_PROGRESS;
-		goto reassess_streams;
-	}
-
 	if (notes & NEED_RETRY)
 		goto need_retry;
 	if ((notes & MADE_PROGRESS) && test_bit(NETFS_RREQ_PAUSE, &wreq->flags)) {
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 520be44d132e..10ff2bd290cb 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -105,7 +105,6 @@ struct netfs_io_request *netfs_create_write_req(struct address_space *mapping,
 	if (test_bit(NETFS_RREQ_WRITE_TO_CACHE, &wreq->flags))
 		fscache_begin_write_operation(&wreq->cache_resources, netfs_i_cookie(ictx));
 
-	wreq->contiguity = wreq->start;
 	wreq->cleaned_to = wreq->start;
 
 	wreq->io_streams[0].stream_nr		= 0;
@@ -156,6 +155,7 @@ static void netfs_prepare_write(struct netfs_io_request *wreq,
 	subreq->source		= stream->source;
 	subreq->start		= start;
 	subreq->stream_nr	= stream->stream_nr;
+	subreq->io_iter		= wreq->io_iter;
 
 	_enter("R=%x[%x]", wreq->debug_id, subreq->debug_index);
 
@@ -211,22 +211,15 @@ static void netfs_prepare_write(struct netfs_io_request *wreq,
  * netfs_write_subrequest_terminated() when complete.
  */
 static void netfs_do_issue_write(struct netfs_io_stream *stream,
-				 struct netfs_io_subrequest *subreq,
-				 struct iov_iter *source)
+				 struct netfs_io_subrequest *subreq)
 {
 	struct netfs_io_request *wreq = subreq->rreq;
-	size_t size = subreq->len - subreq->transferred;
 
 	_enter("R=%x[%x],%zx", wreq->debug_id, subreq->debug_index, subreq->len);
 
 	if (test_bit(NETFS_SREQ_FAILED, &subreq->flags))
 		return netfs_write_subrequest_terminated(subreq, subreq->error, false);
 
-	// TODO: Use encrypted buffer
-	subreq->io_iter = *source;
-	iov_iter_advance(source, size);
-	iov_iter_truncate(&subreq->io_iter, size);
-
 	trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
 	stream->issue_write(subreq);
 }
@@ -235,8 +228,15 @@ void netfs_reissue_write(struct netfs_io_stream *stream,
 			 struct netfs_io_subrequest *subreq,
 			 struct iov_iter *source)
 {
+	size_t size = subreq->len - subreq->transferred;
+
+	// TODO: Use encrypted buffer
+	subreq->io_iter = *source;
+	iov_iter_advance(source, size);
+	iov_iter_truncate(&subreq->io_iter, size);
+
 	__set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
-	netfs_do_issue_write(stream, subreq, source);
+	netfs_do_issue_write(stream, subreq);
 }
 
 static void netfs_issue_write(struct netfs_io_request *wreq,
@@ -247,10 +247,8 @@ static void netfs_issue_write(struct netfs_io_request *wreq,
 	if (!subreq)
 		return;
 	stream->construct = NULL;
-
-	if (subreq->start + subreq->len > wreq->start + wreq->submitted)
-		WRITE_ONCE(wreq->submitted, subreq->start + subreq->len - wreq->start);
-	netfs_do_issue_write(stream, subreq, &wreq->io_iter);
+	subreq->io_iter.count = subreq->len;
+	netfs_do_issue_write(stream, subreq);
 }
 
 /*
@@ -462,10 +460,11 @@ static int netfs_write_folio(struct netfs_io_request *wreq,
 		if (choose_s < 0)
 			break;
 		stream = &wreq->io_streams[choose_s];
+		wreq->io_iter.iov_offset = stream->submit_off;
 
+		atomic64_set(&wreq->issued_to, fpos + stream->submit_off);
 		part = netfs_advance_write(wreq, stream, fpos + stream->submit_off,
 					   stream->submit_len, to_eof);
-		atomic64_set(&wreq->issued_to, fpos + stream->submit_off);
 		stream->submit_off += part;
 		stream->submit_max_len -= part;
 		if (part > stream->submit_len)
@@ -476,6 +475,8 @@ static int netfs_write_folio(struct netfs_io_request *wreq,
 			debug = true;
 	}
 
+	wreq->io_iter.iov_offset = 0;
+	iov_iter_advance(&wreq->io_iter, fsize);
 	atomic64_set(&wreq->issued_to, fpos + fsize);
 
 	if (!debug)
@@ -524,10 +525,10 @@ int netfs_writepages(struct address_space *mapping,
 	netfs_stat(&netfs_n_wh_writepages);
 
 	do {
-		_debug("wbiter %lx %llx", folio->index, wreq->start + wreq->submitted);
+		_debug("wbiter %lx %llx", folio->index, atomic64_read(&wreq->issued_to));
 
 		/* It appears we don't have to handle cyclic writeback wrapping. */
-		WARN_ON_ONCE(wreq && folio_pos(folio) < wreq->start + wreq->submitted);
+		WARN_ON_ONCE(wreq && folio_pos(folio) < atomic64_read(&wreq->issued_to));
 
 		if (netfs_folio_group(folio) != NETFS_FOLIO_COPY_TO_CACHE &&
 		    unlikely(!test_bit(NETFS_RREQ_UPLOAD_TO_SERVER, &wreq->flags))) {
@@ -671,6 +672,7 @@ int netfs_unbuffered_write(struct netfs_io_request *wreq, bool may_wait, size_t
 		part = netfs_advance_write(wreq, upload, start, len, false);
 		start += part;
 		len -= part;
+		iov_iter_advance(&wreq->io_iter, part);
 		if (test_bit(NETFS_RREQ_PAUSE, &wreq->flags)) {
 			trace_netfs_rreq(wreq, netfs_rreq_trace_wait_pause);
 			wait_on_bit(&wreq->flags, NETFS_RREQ_PAUSE, TASK_UNINTERRUPTIBLE);
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index f8ca28d476c3..c47753a24623 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -258,7 +258,6 @@ struct netfs_io_request {
 	unsigned long long	i_size;		/* Size of the file */
 	unsigned long long	start;		/* Start position */
 	atomic64_t		issued_to;	/* Write issuer folio cursor */
-	unsigned long long	contiguity;	/* Tracking for gaps in the writeback sequence */
 	unsigned long long	collected_to;	/* Point we've collected to */
 	unsigned long long	cleaned_to;	/* Position we've cleaned folios to */
 	pgoff_t			no_unlock_folio; /* Don't unlock this folio after read */
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index 8d14715422c0..065fa168f964 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -510,33 +510,6 @@ TRACE_EVENT(netfs_collect,
 		      __entry->start + __entry->len)
 	    );
 
-TRACE_EVENT(netfs_collect_contig,
-	    TP_PROTO(const struct netfs_io_request *wreq, unsigned long long to,
-		     enum netfs_collect_contig_trace type),
-
-	    TP_ARGS(wreq, to, type),
-
-	    TP_STRUCT__entry(
-		    __field(unsigned int,		wreq)
-		    __field(enum netfs_collect_contig_trace, type)
-		    __field(unsigned long long,		contiguity)
-		    __field(unsigned long long,		to)
-			     ),
-
-	    TP_fast_assign(
-		    __entry->wreq	= wreq->debug_id;
-		    __entry->type	= type;
-		    __entry->contiguity	= wreq->contiguity;
-		    __entry->to		= to;
-			   ),
-
-	    TP_printk("R=%08x %llx -> %llx %s",
-		      __entry->wreq,
-		      __entry->contiguity,
-		      __entry->to,
-		      __print_symbolic(__entry->type, netfs_collect_contig_traces))
-	    );
-
 TRACE_EVENT(netfs_collect_sreq,
 	    TP_PROTO(const struct netfs_io_request *wreq,
 		     const struct netfs_io_subrequest *subreq),
@@ -608,7 +581,6 @@ TRACE_EVENT(netfs_collect_state,
 		    __field(unsigned int,	notes		)
 		    __field(unsigned long long,	collected_to	)
 		    __field(unsigned long long,	cleaned_to	)
-		    __field(unsigned long long,	contiguity	)
 			     ),
 
 	    TP_fast_assign(
@@ -616,12 +588,11 @@ TRACE_EVENT(netfs_collect_state,
 		    __entry->notes	= notes;
 		    __entry->collected_to = collected_to;
 		    __entry->cleaned_to	= wreq->cleaned_to;
-		    __entry->contiguity = wreq->contiguity;
 			   ),
 
-	    TP_printk("R=%08x cto=%llx fto=%llx ctg=%llx n=%x",
+	    TP_printk("R=%08x col=%llx cln=%llx n=%x",
 		      __entry->wreq, __entry->collected_to,
-		      __entry->cleaned_to, __entry->contiguity,
+		      __entry->cleaned_to,
 		      __entry->notes)
 	    );
 

[PATCH 17/24] afs: Make read subreqs async

[David Howells]

Perform AFS read subrequests in a work item rather than in the calling
thread.  For normal buffered reads, this will allow the calling thread to
copy data from the pagecache to the application at the same time as the
demarshalling thread is shovelling data from skbuffs into the pagecache.

This will also allow the RA mark to trigger a new read before we've
finished shovelling the data from the current one.

Note: This would be a bit safer if the FS.FetchData RPC ops returned the
metadata (including the data version number) before returning the data.
This would allow me to flush the pagecache before installing the new data.

In future, it may be possible to asynchronously flush the pagecache either
side of the region being read.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-afs@lists.infradead.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/afs/file.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/afs/file.c b/fs/afs/file.c
index c3f0c45ae9a9..addb106dba4c 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -304,8 +304,9 @@ int afs_fetch_data(struct afs_vnode *vnode, struct afs_read *req)
 	return afs_do_sync_operation(op);
 }
 
-static void afs_issue_read(struct netfs_io_subrequest *subreq)
+static void afs_read_worker(struct work_struct *work)
 {
+	struct netfs_io_subrequest *subreq = container_of(work, struct netfs_io_subrequest, work);
 	struct afs_vnode *vnode = AFS_FS_I(subreq->rreq->inode);
 	struct afs_read *fsreq;
 
@@ -324,6 +325,12 @@ static void afs_issue_read(struct netfs_io_subrequest *subreq)
 	afs_put_read(fsreq);
 }
 
+static void afs_issue_read(struct netfs_io_subrequest *subreq)
+{
+	INIT_WORK(&subreq->work, afs_read_worker);
+	queue_work(system_long_wq, &subreq->work);
+}
+
 static int afs_symlink_read_folio(struct file *file, struct folio *folio)
 {
 	struct afs_vnode *vnode = AFS_FS_I(folio->mapping->host);

[PATCH 18/24] netfs: Speed up buffered reading

[David Howells]

Improve the efficiency of buffered reads in a number of ways:

 (1) Overhaul the algorithm in general so that it's a lot more compact and
     split the read submission code between buffered and unbuffered
     versions.  The unbuffered version can be vastly simplified.

 (2) Read-result collection is handed off to a work queue rather than being
     done in the I/O thread.  Multiple subrequests can be processes
     simultaneously.

 (3) When a subrequest is collected, any folios it fully spans are
     collected and "spare" data on either side is donated to either the
     previous or the next subrequest in the sequence.

Notes:

 (*) Readahead expansion is massively slows down fio, presumably because it
     causes a load of extra allocations, both folio and xarray, up front
     before RPC requests can be transmitted.

 (*) RDMA with cifs does appear to work, both with SIW and RXE.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/9p/vfs_addr.c             |   5 +-
 fs/afs/file.c                |  20 +-
 fs/afs/fsclient.c            |   9 +-
 fs/afs/yfsclient.c           |   9 +-
 fs/ceph/addr.c               |  72 ++--
 fs/netfs/Makefile            |   3 +-
 fs/netfs/buffered_read.c     | 677 ++++++++++++++++++++++++-----------
 fs/netfs/direct_read.c       | 147 +++++++-
 fs/netfs/internal.h          |  19 +-
 fs/netfs/iterator.c          |  50 +++
 fs/netfs/main.c              |   3 +-
 fs/netfs/objects.c           |   8 +-
 fs/netfs/read_collect.c      | 540 ++++++++++++++++++++++++++++
 fs/netfs/read_retry.c        | 256 +++++++++++++
 fs/netfs/write_issue.c       |   4 -
 fs/nfs/fscache.c             |  19 +-
 fs/nfs/fscache.h             |   7 +-
 fs/smb/client/cifssmb.c      |   6 +-
 fs/smb/client/file.c         |  57 +--
 fs/smb/client/smb2pdu.c      |  10 +-
 include/linux/netfs.h        |  24 +-
 include/trace/events/netfs.h |  99 ++++-
 22 files changed, 1707 insertions(+), 337 deletions(-)
 create mode 100644 fs/netfs/read_collect.c
 create mode 100644 fs/netfs/read_retry.c

diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index a97ceb105cd8..ee2f24647303 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -77,7 +77,10 @@ static void v9fs_issue_read(struct netfs_io_subrequest *subreq)
 	 * cache won't be on server and is zeroes */
 	__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
 
-	netfs_subreq_terminated(subreq, err ?: total, false);
+	if (!err)
+		subreq->transferred += total;
+
+	netfs_read_subreq_terminated(subreq, err, false);
 }
 
 /**
diff --git a/fs/afs/file.c b/fs/afs/file.c
index addb106dba4c..492d857a3fa0 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -16,6 +16,7 @@
 #include <linux/mm.h>
 #include <linux/swap.h>
 #include <linux/netfs.h>
+#include <trace/events/netfs.h>
 #include "internal.h"
 
 static int afs_file_mmap(struct file *file, struct vm_area_struct *vma);
@@ -242,8 +243,10 @@ static void afs_fetch_data_notify(struct afs_operation *op)
 
 	req->error = error;
 	if (subreq) {
-		__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
-		netfs_subreq_terminated(subreq, error ?: req->actual_len, false);
+		subreq->rreq->i_size = req->file_size;
+		if (req->pos + req->actual_len >= req->file_size)
+			__set_bit(NETFS_SREQ_HIT_EOF, &subreq->flags);
+		netfs_read_subreq_terminated(subreq, error, false);
 		req->subreq = NULL;
 	} else if (req->done) {
 		req->done(req);
@@ -261,6 +264,12 @@ static void afs_fetch_data_success(struct afs_operation *op)
 	afs_fetch_data_notify(op);
 }
 
+static void afs_fetch_data_aborted(struct afs_operation *op)
+{
+	afs_check_for_remote_deletion(op);
+	afs_fetch_data_notify(op);
+}
+
 static void afs_fetch_data_put(struct afs_operation *op)
 {
 	op->fetch.req->error = afs_op_error(op);
@@ -271,7 +280,7 @@ static const struct afs_operation_ops afs_fetch_data_operation = {
 	.issue_afs_rpc	= afs_fs_fetch_data,
 	.issue_yfs_rpc	= yfs_fs_fetch_data,
 	.success	= afs_fetch_data_success,
-	.aborted	= afs_check_for_remote_deletion,
+	.aborted	= afs_fetch_data_aborted,
 	.failed		= afs_fetch_data_notify,
 	.put		= afs_fetch_data_put,
 };
@@ -293,7 +302,7 @@ int afs_fetch_data(struct afs_vnode *vnode, struct afs_read *req)
 	op = afs_alloc_operation(req->key, vnode->volume);
 	if (IS_ERR(op)) {
 		if (req->subreq)
-			netfs_subreq_terminated(req->subreq, PTR_ERR(op), false);
+			netfs_read_subreq_terminated(req->subreq, PTR_ERR(op), false);
 		return PTR_ERR(op);
 	}
 
@@ -312,7 +321,7 @@ static void afs_read_worker(struct work_struct *work)
 
 	fsreq = afs_alloc_read(GFP_NOFS);
 	if (!fsreq)
-		return netfs_subreq_terminated(subreq, -ENOMEM, false);
+		return netfs_read_subreq_terminated(subreq, -ENOMEM, false);
 
 	fsreq->subreq	= subreq;
 	fsreq->pos	= subreq->start + subreq->transferred;
@@ -321,6 +330,7 @@ static void afs_read_worker(struct work_struct *work)
 	fsreq->vnode	= vnode;
 	fsreq->iter	= &subreq->io_iter;
 
+	trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
 	afs_fetch_data(fsreq->vnode, fsreq);
 	afs_put_read(fsreq);
 }
diff --git a/fs/afs/fsclient.c b/fs/afs/fsclient.c
index 79cd30775b7a..098fa034a1cc 100644
--- a/fs/afs/fsclient.c
+++ b/fs/afs/fsclient.c
@@ -304,6 +304,7 @@ static int afs_deliver_fs_fetch_data(struct afs_call *call)
 	struct afs_vnode_param *vp = &op->file[0];
 	struct afs_read *req = op->fetch.req;
 	const __be32 *bp;
+	size_t count_before;
 	int ret;
 
 	_enter("{%u,%zu,%zu/%llu}",
@@ -345,10 +346,14 @@ static int afs_deliver_fs_fetch_data(struct afs_call *call)
 
 		/* extract the returned data */
 	case 2:
-		_debug("extract data %zu/%llu",
-		       iov_iter_count(call->iter), req->actual_len);
+		count_before = call->iov_len;
+		_debug("extract data %zu/%llu", count_before, req->actual_len);
 
 		ret = afs_extract_data(call, true);
+		if (req->subreq) {
+			req->subreq->transferred += count_before - call->iov_len;
+			netfs_read_subreq_progress(req->subreq, false);
+		}
 		if (ret < 0)
 			return ret;
 
diff --git a/fs/afs/yfsclient.c b/fs/afs/yfsclient.c
index f521e66d3bf6..024227aba4cd 100644
--- a/fs/afs/yfsclient.c
+++ b/fs/afs/yfsclient.c
@@ -355,6 +355,7 @@ static int yfs_deliver_fs_fetch_data64(struct afs_call *call)
 	struct afs_vnode_param *vp = &op->file[0];
 	struct afs_read *req = op->fetch.req;
 	const __be32 *bp;
+	size_t count_before;
 	int ret;
 
 	_enter("{%u,%zu, %zu/%llu}",
@@ -391,10 +392,14 @@ static int yfs_deliver_fs_fetch_data64(struct afs_call *call)
 
 		/* extract the returned data */
 	case 2:
-		_debug("extract data %zu/%llu",
-		       iov_iter_count(call->iter), req->actual_len);
+		count_before = call->iov_len;
+		_debug("extract data %zu/%llu", count_before, req->actual_len);
 
 		ret = afs_extract_data(call, true);
+		if (req->subreq) {
+			req->subreq->transferred += count_before - call->iov_len;
+			netfs_read_subreq_progress(req->subreq, false);
+		}
 		if (ret < 0)
 			return ret;
 
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 8c16bc5250ef..997843269304 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -205,21 +205,6 @@ static void ceph_netfs_expand_readahead(struct netfs_io_request *rreq)
 	}
 }
 
-static bool ceph_netfs_clamp_length(struct netfs_io_subrequest *subreq)
-{
-	struct inode *inode = subreq->rreq->inode;
-	struct ceph_fs_client *fsc = ceph_inode_to_fs_client(inode);
-	struct ceph_inode_info *ci = ceph_inode(inode);
-	u64 objno, objoff;
-	u32 xlen;
-
-	/* Truncate the extent at the end of the current block */
-	ceph_calc_file_object_mapping(&ci->i_layout, subreq->start, subreq->len,
-				      &objno, &objoff, &xlen);
-	subreq->len = min(xlen, fsc->mount_options->rsize);
-	return true;
-}
-
 static void finish_netfs_read(struct ceph_osd_request *req)
 {
 	struct inode *inode = req->r_inode;
@@ -263,7 +248,11 @@ static void finish_netfs_read(struct ceph_osd_request *req)
 				     calc_pages_for(osd_data->alignment,
 					osd_data->length), false);
 	}
-	netfs_subreq_terminated(subreq, err, false);
+	if (err > 0) {
+		subreq->transferred = err;
+		err = 0;
+	}
+	netfs_read_subreq_terminated(subreq, err, false);
 	iput(req->r_inode);
 	ceph_dec_osd_stopping_blocker(fsc->mdsc);
 }
@@ -277,7 +266,6 @@ static bool ceph_netfs_issue_op_inline(struct netfs_io_subrequest *subreq)
 	struct ceph_mds_request *req;
 	struct ceph_mds_client *mdsc = ceph_sb_to_mdsc(inode->i_sb);
 	struct ceph_inode_info *ci = ceph_inode(inode);
-	struct iov_iter iter;
 	ssize_t err = 0;
 	size_t len;
 	int mode;
@@ -312,17 +300,36 @@ static bool ceph_netfs_issue_op_inline(struct netfs_io_subrequest *subreq)
 	}
 
 	len = min_t(size_t, iinfo->inline_len - subreq->start, subreq->len);
-	iov_iter_xarray(&iter, ITER_DEST, &rreq->mapping->i_pages, subreq->start, len);
-	err = copy_to_iter(iinfo->inline_data + subreq->start, len, &iter);
-	if (err == 0)
+	err = copy_to_iter(iinfo->inline_data + subreq->start, len, &subreq->io_iter);
+	if (err == 0) {
 		err = -EFAULT;
+	} else {
+		subreq->transferred += err;
+		err = 0;
+	}
 
 	ceph_mdsc_put_request(req);
 out:
-	netfs_subreq_terminated(subreq, err, false);
+	netfs_read_subreq_terminated(subreq, err, false);
 	return true;
 }
 
+static int ceph_netfs_prepare_read(struct netfs_io_subrequest *subreq)
+{
+	struct netfs_io_request *rreq = subreq->rreq;
+	struct inode *inode = rreq->inode;
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	struct ceph_fs_client *fsc = ceph_inode_to_fs_client(inode);
+	u64 objno, objoff;
+	u32 xlen;
+
+	/* Truncate the extent at the end of the current block */
+	ceph_calc_file_object_mapping(&ci->i_layout, subreq->start, subreq->len,
+				      &objno, &objoff, &xlen);
+	rreq->io_streams[0].sreq_max_len = umin(xlen, fsc->mount_options->rsize);
+	return 0;
+}
+
 static void ceph_netfs_issue_read(struct netfs_io_subrequest *subreq)
 {
 	struct netfs_io_request *rreq = subreq->rreq;
@@ -332,9 +339,8 @@ static void ceph_netfs_issue_read(struct netfs_io_subrequest *subreq)
 	struct ceph_client *cl = fsc->client;
 	struct ceph_osd_request *req = NULL;
 	struct ceph_vino vino = ceph_vino(inode);
-	struct iov_iter iter;
-	int err = 0;
-	u64 len = subreq->len;
+	int err;
+	u64 len;
 	bool sparse = IS_ENCRYPTED(inode) || ceph_test_mount_opt(fsc, SPARSEREAD);
 	u64 off = subreq->start;
 	int extent_cnt;
@@ -347,6 +353,12 @@ static void ceph_netfs_issue_read(struct netfs_io_subrequest *subreq)
 	if (ceph_has_inline_data(ci) && ceph_netfs_issue_op_inline(subreq))
 		return;
 
+	// TODO: This rounding here is slightly dodgy.  It *should* work, for
+	// now, as the cache only deals in blocks that are a multiple of
+	// PAGE_SIZE and fscrypt blocks are at most PAGE_SIZE.  What needs to
+	// happen is for the fscrypt driving to be moved into netfslib and the
+	// data in the cache also to be stored encrypted.
+	len = subreq->len;
 	ceph_fscrypt_adjust_off_and_len(inode, &off, &len);
 
 	req = ceph_osdc_new_request(&fsc->client->osdc, &ci->i_layout, vino,
@@ -369,8 +381,6 @@ static void ceph_netfs_issue_read(struct netfs_io_subrequest *subreq)
 	doutc(cl, "%llx.%llx pos=%llu orig_len=%zu len=%llu\n",
 	      ceph_vinop(inode), subreq->start, subreq->len, len);
 
-	iov_iter_xarray(&iter, ITER_DEST, &rreq->mapping->i_pages, subreq->start, len);
-
 	/*
 	 * FIXME: For now, use CEPH_OSD_DATA_TYPE_PAGES instead of _ITER for
 	 * encrypted inodes. We'd need infrastructure that handles an iov_iter
@@ -382,7 +392,7 @@ static void ceph_netfs_issue_read(struct netfs_io_subrequest *subreq)
 		struct page **pages;
 		size_t page_off;
 
-		err = iov_iter_get_pages_alloc2(&iter, &pages, len, &page_off);
+		err = iov_iter_get_pages_alloc2(&subreq->io_iter, &pages, len, &page_off);
 		if (err < 0) {
 			doutc(cl, "%llx.%llx failed to allocate pages, %d\n",
 			      ceph_vinop(inode), err);
@@ -397,7 +407,7 @@ static void ceph_netfs_issue_read(struct netfs_io_subrequest *subreq)
 		osd_req_op_extent_osd_data_pages(req, 0, pages, len, 0, false,
 						 false);
 	} else {
-		osd_req_op_extent_osd_iter(req, 0, &iter);
+		osd_req_op_extent_osd_iter(req, 0, &subreq->io_iter);
 	}
 	if (!ceph_inc_osd_stopping_blocker(fsc->mdsc)) {
 		err = -EIO;
@@ -412,13 +422,14 @@ static void ceph_netfs_issue_read(struct netfs_io_subrequest *subreq)
 out:
 	ceph_osdc_put_request(req);
 	if (err)
-		netfs_subreq_terminated(subreq, err, false);
+		netfs_read_subreq_terminated(subreq, err, false);
 	doutc(cl, "%llx.%llx result %d\n", ceph_vinop(inode), err);
 }
 
 static int ceph_init_request(struct netfs_io_request *rreq, struct file *file)
 {
 	struct inode *inode = rreq->inode;
+	struct ceph_fs_client *fsc = ceph_inode_to_fs_client(inode);
 	struct ceph_client *cl = ceph_inode_to_client(inode);
 	int got = 0, want = CEPH_CAP_FILE_CACHE;
 	struct ceph_netfs_request_data *priv;
@@ -467,6 +478,7 @@ static int ceph_init_request(struct netfs_io_request *rreq, struct file *file)
 
 	priv->caps = got;
 	rreq->netfs_priv = priv;
+	rreq->io_streams[0].sreq_max_len = fsc->mount_options->rsize;
 
 out:
 	if (ret < 0)
@@ -491,9 +503,9 @@ static void ceph_netfs_free_request(struct netfs_io_request *rreq)
 const struct netfs_request_ops ceph_netfs_ops = {
 	.init_request		= ceph_init_request,
 	.free_request		= ceph_netfs_free_request,
+	.prepare_read		= ceph_netfs_prepare_read,
 	.issue_read		= ceph_netfs_issue_read,
 	.expand_readahead	= ceph_netfs_expand_readahead,
-	.clamp_length		= ceph_netfs_clamp_length,
 	.check_write_begin	= ceph_netfs_check_write_begin,
 };
 
diff --git a/fs/netfs/Makefile b/fs/netfs/Makefile
index 8e6781e0b10b..cadeb28b8e47 100644
--- a/fs/netfs/Makefile
+++ b/fs/netfs/Makefile
@@ -5,12 +5,13 @@ netfs-y := \
 	buffered_write.o \
 	direct_read.o \
 	direct_write.o \
-	io.o \
 	iterator.o \
 	locking.o \
 	main.o \
 	misc.o \
 	objects.o \
+	read_collect.o \
+	read_retry.o \
 	write_collect.o \
 	write_issue.o
 
diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index a688d4c75d99..97d33614553e 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -9,126 +9,6 @@
 #include <linux/task_io_accounting_ops.h>
 #include "internal.h"
 
-/*
- * Unlock the folios in a read operation.  We need to set PG_writeback on any
- * folios we're going to write back before we unlock them.
- *
- * Note that if the deprecated NETFS_RREQ_USE_PGPRIV2 is set then we use
- * PG_private_2 and do a direct write to the cache from here instead.
- */
-void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
-{
-	struct netfs_io_subrequest *subreq;
-	struct netfs_folio *finfo;
-	struct folio *folio;
-	pgoff_t start_page = rreq->start / PAGE_SIZE;
-	pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
-	size_t account = 0;
-	bool subreq_failed = false;
-
-	XA_STATE(xas, &rreq->mapping->i_pages, start_page);
-
-	if (test_bit(NETFS_RREQ_FAILED, &rreq->flags)) {
-		__clear_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags);
-		list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
-			__clear_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags);
-		}
-	}
-
-	/* Walk through the pagecache and the I/O request lists simultaneously.
-	 * We may have a mixture of cached and uncached sections and we only
-	 * really want to write out the uncached sections.  This is slightly
-	 * complicated by the possibility that we might have huge pages with a
-	 * mixture inside.
-	 */
-	subreq = list_first_entry(&rreq->subrequests,
-				  struct netfs_io_subrequest, rreq_link);
-	subreq_failed = (subreq->error < 0);
-
-	trace_netfs_rreq(rreq, netfs_rreq_trace_unlock);
-
-	rcu_read_lock();
-	xas_for_each(&xas, folio, last_page) {
-		loff_t pg_end;
-		bool pg_failed = false;
-		bool wback_to_cache = false;
-		bool folio_started = false;
-
-		if (xas_retry(&xas, folio))
-			continue;
-
-		pg_end = folio_pos(folio) + folio_size(folio) - 1;
-
-		for (;;) {
-			loff_t sreq_end;
-
-			if (!subreq) {
-				pg_failed = true;
-				break;
-			}
-			if (test_bit(NETFS_RREQ_USE_PGPRIV2, &rreq->flags)) {
-				if (!folio_started && test_bit(NETFS_SREQ_COPY_TO_CACHE,
-							       &subreq->flags)) {
-					trace_netfs_folio(folio, netfs_folio_trace_copy_to_cache);
-					folio_start_private_2(folio);
-					folio_started = true;
-				}
-			} else {
-				wback_to_cache |=
-					test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags);
-			}
-			pg_failed |= subreq_failed;
-			sreq_end = subreq->start + subreq->len - 1;
-			if (pg_end < sreq_end)
-				break;
-
-			account += subreq->transferred;
-			if (!list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
-				subreq = list_next_entry(subreq, rreq_link);
-				subreq_failed = (subreq->error < 0);
-			} else {
-				subreq = NULL;
-				subreq_failed = false;
-			}
-
-			if (pg_end == sreq_end)
-				break;
-		}
-
-		if (!pg_failed) {
-			flush_dcache_folio(folio);
-			finfo = netfs_folio_info(folio);
-			if (finfo) {
-				trace_netfs_folio(folio, netfs_folio_trace_filled_gaps);
-				if (finfo->netfs_group)
-					folio_change_private(folio, finfo->netfs_group);
-				else
-					folio_detach_private(folio);
-				kfree(finfo);
-			}
-			folio_mark_uptodate(folio);
-			if (wback_to_cache && !WARN_ON_ONCE(folio_get_private(folio) != NULL)) {
-				trace_netfs_folio(folio, netfs_folio_trace_copy_to_cache);
-				folio_attach_private(folio, NETFS_FOLIO_COPY_TO_CACHE);
-				filemap_dirty_folio(folio->mapping, folio);
-			}
-		}
-
-		if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
-			if (folio->index == rreq->no_unlock_folio &&
-			    test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags))
-				_debug("no unlock");
-			else
-				folio_unlock(folio);
-		}
-	}
-	rcu_read_unlock();
-
-	task_io_account_read(account);
-	if (rreq->netfs_ops->done)
-		rreq->netfs_ops->done(rreq);
-}
-
 static void netfs_cache_expand_readahead(struct netfs_io_request *rreq,
 					 unsigned long long *_start,
 					 unsigned long long *_len,
@@ -183,6 +63,323 @@ static int netfs_begin_cache_read(struct netfs_io_request *rreq, struct netfs_in
 	return fscache_begin_read_operation(&rreq->cache_resources, netfs_i_cookie(ctx));
 }
 
+/*
+ * Decant the list of folios to read into a rolling buffer.
+ */
+static size_t netfs_load_buffer_from_ra(struct netfs_io_request *rreq,
+					struct folio_queue *folioq)
+{
+	unsigned int order, nr;
+	size_t size = 0;
+
+	nr = __readahead_batch(rreq->ractl, (struct page **)folioq->vec.folios,
+			       ARRAY_SIZE(folioq->vec.folios));
+	folioq->vec.nr = nr;
+	for (int i = 0; i < nr; i++) {
+		struct folio *folio = folioq_folio(folioq, i);
+
+		trace_netfs_folio(folio, netfs_folio_trace_read);
+		order = folio_order(folio);
+		folioq->orders[i] = order;
+		size += PAGE_SIZE << order;
+	}
+
+	for (int i = nr; i < folioq_nr_slots(folioq); i++)
+		folioq_clear(folioq, i);
+
+	return size;
+}
+
+/*
+ * netfs_prepare_read_iterator - Prepare the subreq iterator for I/O
+ * @subreq: The subrequest to be set up
+ *
+ * Prepare the I/O iterator representing the read buffer on a subrequest for
+ * the filesystem to use for I/O (it can be passed directly to a socket).  This
+ * is intended to be called from the ->issue_read() method once the filesystem
+ * has trimmed the request to the size it wants.
+ *
+ * Returns the limited size if successful and -ENOMEM if insufficient memory
+ * available.
+ *
+ * [!] NOTE: This must be run in the same thread as ->issue_read() was called
+ * in as we access the readahead_control struct.
+ */
+static ssize_t netfs_prepare_read_iterator(struct netfs_io_subrequest *subreq)
+{
+	struct netfs_io_request *rreq = subreq->rreq;
+	size_t rsize;
+
+	rsize = umin(subreq->len, rreq->io_streams[0].sreq_max_len);
+
+	if (rreq->ractl) {
+		/* If we don't have sufficient folios in the rolling buffer,
+		 * extract a folioq's worth from the readahead region at a time
+		 * into the buffer.  Note that this acquires a ref on each page
+		 * that we will need to release later - but we don't want to do
+		 * that until after we've started the I/O.
+		 */
+		while (rreq->submitted < subreq->start + rsize) {
+			struct folio_queue *tail = rreq->buffer_tail, *new;
+			size_t added;
+
+			new = kmalloc(sizeof(*new), GFP_NOFS);
+			if (!new)
+				return -ENOMEM;
+			netfs_stat(&netfs_n_folioq);
+			folioq_init(new);
+			new->prev = tail;
+			tail->next = new;
+			rreq->buffer_tail = new;
+			added = netfs_load_buffer_from_ra(rreq, new);
+			rreq->iter.count += added;
+			rreq->submitted += added;
+		}
+	}
+
+	subreq->len = rsize;
+	if (unlikely(rreq->io_streams[0].sreq_max_segs)) {
+		size_t limit = netfs_limit_iter(&rreq->iter, 0, rsize,
+						rreq->io_streams[0].sreq_max_segs);
+
+		if (limit < rsize) {
+			subreq->len = limit;
+			trace_netfs_sreq(subreq, netfs_sreq_trace_limited);
+		}
+	}
+
+	subreq->io_iter	= rreq->iter;
+
+	if (iov_iter_is_folioq(&subreq->io_iter)) {
+		subreq->curr_folioq = (struct folio_queue *)subreq->io_iter.folioq;
+		subreq->curr_folioq_slot = subreq->io_iter.folioq_slot;
+		subreq->curr_folio_order = subreq->curr_folioq->orders[subreq->curr_folioq_slot];
+	}
+
+	iov_iter_truncate(&subreq->io_iter, subreq->len);
+	iov_iter_advance(&rreq->iter, subreq->len);
+	return subreq->len;
+}
+
+static enum netfs_io_source netfs_cache_prepare_read(struct netfs_io_request *rreq,
+						     struct netfs_io_subrequest *subreq,
+						     loff_t i_size)
+{
+	struct netfs_cache_resources *cres = &rreq->cache_resources;
+
+	if (!cres->ops)
+		return NETFS_DOWNLOAD_FROM_SERVER;
+	return cres->ops->prepare_read(subreq, i_size);
+}
+
+static void netfs_cache_read_terminated(void *priv, ssize_t transferred_or_error,
+					bool was_async)
+{
+	struct netfs_io_subrequest *subreq = priv;
+
+	if (transferred_or_error < 0) {
+		netfs_read_subreq_terminated(subreq, transferred_or_error, was_async);
+		return;
+	}
+
+	if (transferred_or_error > 0)
+		subreq->transferred += transferred_or_error;
+	netfs_read_subreq_terminated(subreq, 0, was_async);
+}
+
+/*
+ * Issue a read against the cache.
+ * - Eats the caller's ref on subreq.
+ */
+static void netfs_read_cache_to_pagecache(struct netfs_io_request *rreq,
+					  struct netfs_io_subrequest *subreq)
+{
+	struct netfs_cache_resources *cres = &rreq->cache_resources;
+
+	netfs_stat(&netfs_n_rh_read);
+	cres->ops->read(cres, subreq->start, &subreq->io_iter, NETFS_READ_HOLE_IGNORE,
+			netfs_cache_read_terminated, subreq);
+}
+
+/*
+ * Perform a read to the pagecache from a series of sources of different types,
+ * slicing up the region to be read according to available cache blocks and
+ * network rsize.
+ */
+static void netfs_read_to_pagecache(struct netfs_io_request *rreq)
+{
+	struct netfs_inode *ictx = netfs_inode(rreq->inode);
+	unsigned long long start = rreq->start;
+	ssize_t size = rreq->len;
+	int ret = 0;
+
+	atomic_inc(&rreq->nr_outstanding);
+
+	do {
+		struct netfs_io_subrequest *subreq;
+		enum netfs_io_source source = NETFS_DOWNLOAD_FROM_SERVER;
+		ssize_t slice;
+
+		subreq = netfs_alloc_subrequest(rreq);
+		if (!subreq) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		subreq->start	= start;
+		subreq->len	= size;
+
+		atomic_inc(&rreq->nr_outstanding);
+		spin_lock_bh(&rreq->lock);
+		list_add_tail(&subreq->rreq_link, &rreq->subrequests);
+		subreq->prev_donated = rreq->prev_donated;
+		rreq->prev_donated = 0;
+		trace_netfs_sreq(subreq, netfs_sreq_trace_added);
+		spin_unlock_bh(&rreq->lock);
+
+		source = netfs_cache_prepare_read(rreq, subreq, rreq->i_size);
+		subreq->source = source;
+		if (source == NETFS_DOWNLOAD_FROM_SERVER) {
+			unsigned long long zp = umin(ictx->zero_point, rreq->i_size);
+			size_t len = subreq->len;
+
+			if (subreq->start >= zp) {
+				subreq->source = source = NETFS_FILL_WITH_ZEROES;
+				goto fill_with_zeroes;
+			}
+
+			if (len > zp - subreq->start)
+				len = zp - subreq->start;
+			if (len == 0) {
+				pr_err("ZERO-LEN READ: R=%08x[%x] l=%zx/%zx s=%llx z=%llx i=%llx",
+				       rreq->debug_id, subreq->debug_index,
+				       subreq->len, size,
+				       subreq->start, ictx->zero_point, rreq->i_size);
+				break;
+			}
+			subreq->len = len;
+
+			netfs_stat(&netfs_n_rh_download);
+			if (rreq->netfs_ops->prepare_read) {
+				ret = rreq->netfs_ops->prepare_read(subreq);
+				if (ret < 0) {
+					atomic_dec(&rreq->nr_outstanding);
+					netfs_put_subrequest(subreq, false,
+							     netfs_sreq_trace_put_cancel);
+					break;
+				}
+				trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
+			}
+
+			slice = netfs_prepare_read_iterator(subreq);
+			if (slice < 0) {
+				atomic_dec(&rreq->nr_outstanding);
+				netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_cancel);
+				ret = slice;
+				break;
+			}
+
+			rreq->netfs_ops->issue_read(subreq);
+			goto done;
+		}
+
+	fill_with_zeroes:
+		if (source == NETFS_FILL_WITH_ZEROES) {
+			subreq->source = NETFS_FILL_WITH_ZEROES;
+			trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
+			netfs_stat(&netfs_n_rh_zero);
+			slice = netfs_prepare_read_iterator(subreq);
+			__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
+			netfs_read_subreq_terminated(subreq, 0, false);
+			goto done;
+		}
+
+		if (source == NETFS_READ_FROM_CACHE) {
+			trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
+			slice = netfs_prepare_read_iterator(subreq);
+			netfs_read_cache_to_pagecache(rreq, subreq);
+			goto done;
+		}
+
+		if (source == NETFS_INVALID_READ)
+			break;
+
+	done:
+		size -= slice;
+		start += slice;
+		cond_resched();
+	} while (size > 0);
+
+	if (atomic_dec_and_test(&rreq->nr_outstanding))
+		netfs_rreq_terminated(rreq, false);
+
+	/* Defer error return as we may need to wait for outstanding I/O. */
+	cmpxchg(&rreq->error, 0, ret);
+}
+
+/*
+ * Wait for the read operation to complete, successfully or otherwise.
+ */
+static int netfs_wait_for_read(struct netfs_io_request *rreq)
+{
+	int ret;
+
+	trace_netfs_rreq(rreq, netfs_rreq_trace_wait_ip);
+	wait_on_bit(&rreq->flags, NETFS_RREQ_IN_PROGRESS, TASK_UNINTERRUPTIBLE);
+	ret = rreq->error;
+	if (ret == 0 && rreq->submitted < rreq->len) {
+		trace_netfs_failure(rreq, NULL, ret, netfs_fail_short_read);
+		ret = -EIO;
+	}
+
+	return ret;
+}
+
+/*
+ * Set up the initial folioq of buffer folios in the rolling buffer and set the
+ * iterator to refer to it.
+ */
+static int netfs_prime_buffer(struct netfs_io_request *rreq)
+{
+	struct folio_queue *folioq;
+	size_t added;
+
+	folioq = kmalloc(sizeof(*folioq), GFP_KERNEL);
+	if (!folioq)
+		return -ENOMEM;
+	netfs_stat(&netfs_n_folioq);
+	folioq_init(folioq);
+	rreq->buffer = folioq;
+	rreq->buffer_tail = folioq;
+	rreq->submitted = rreq->start;
+	iov_iter_folio_queue(&rreq->iter, ITER_DEST, folioq, 0, 0, 0);
+
+	added = netfs_load_buffer_from_ra(rreq, folioq);
+	rreq->iter.count += added;
+	rreq->submitted += added;
+	return 0;
+}
+
+/*
+ * Drop the ref on each folio that we inherited from the VM readahead code.  We
+ * still have the folio locks to pin the page until we complete the I/O.
+ */
+static void netfs_put_ra_refs(struct folio_queue *folioq)
+{
+	while (folioq) {
+#if 0
+		for (unsigned int slot = 0; slot < folioq_count(folioq); slot++) {
+			if (!folioq_folio(folioq, slot))
+				continue;
+			trace_netfs_folio(folioq_folio(folioq, slot),
+					  netfs_folio_trace_read_put);
+		}
+#endif
+		folio_batch_release(&folioq->vec);
+		folioq = folioq->next;
+	}
+}
+
 /**
  * netfs_readahead - Helper to manage a read request
  * @ractl: The description of the readahead request
@@ -201,22 +398,17 @@ static int netfs_begin_cache_read(struct netfs_io_request *rreq, struct netfs_in
 void netfs_readahead(struct readahead_control *ractl)
 {
 	struct netfs_io_request *rreq;
-	struct netfs_inode *ctx = netfs_inode(ractl->mapping->host);
+	struct netfs_inode *ictx = netfs_inode(ractl->mapping->host);
+	unsigned long long start = readahead_pos(ractl);
+	size_t size = readahead_length(ractl);
 	int ret;
 
-	_enter("%lx,%x", readahead_index(ractl), readahead_count(ractl));
-
-	if (readahead_count(ractl) == 0)
-		return;
-
-	rreq = netfs_alloc_request(ractl->mapping, ractl->file,
-				   readahead_pos(ractl),
-				   readahead_length(ractl),
+	rreq = netfs_alloc_request(ractl->mapping, ractl->file, start, size,
 				   NETFS_READAHEAD);
 	if (IS_ERR(rreq))
 		return;
 
-	ret = netfs_begin_cache_read(rreq, ctx);
+	ret = netfs_begin_cache_read(rreq, ictx);
 	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
 		goto cleanup_free;
 
@@ -226,18 +418,15 @@ void netfs_readahead(struct readahead_control *ractl)
 
 	netfs_rreq_expand(rreq, ractl);
 
-	/* Set up the output buffer */
-	iov_iter_xarray(&rreq->iter, ITER_DEST, &ractl->mapping->i_pages,
-			rreq->start, rreq->len);
+	rreq->ractl = ractl;
+	if (netfs_prime_buffer(rreq) < 0)
+		goto cleanup_free;
+	netfs_read_to_pagecache(rreq);
 
-	/* Drop the refs on the folios here rather than in the cache or
-	 * filesystem.  The locks will be dropped in netfs_rreq_unlock().
-	 */
-	while (readahead_folio(ractl))
-		;
+	/* Release the folio refs whilst we're waiting for the I/O. */
+	netfs_put_ra_refs(rreq->buffer);
 
-	netfs_begin_read(rreq, false);
-	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
+	netfs_put_request(rreq, true, netfs_rreq_trace_put_return);
 	return;
 
 cleanup_free:
@@ -246,6 +435,117 @@ void netfs_readahead(struct readahead_control *ractl)
 }
 EXPORT_SYMBOL(netfs_readahead);
 
+/*
+ * Create a rolling buffer with a single occupying folio.
+ */
+static int netfs_create_singular_buffer(struct netfs_io_request *rreq, struct folio *folio)
+{
+	struct folio_queue *folioq;
+
+	folioq = kmalloc(sizeof(*folioq), GFP_KERNEL);
+	if (!folioq)
+		return -ENOMEM;
+
+	netfs_stat(&netfs_n_folioq);
+	folioq_init(folioq);
+	folioq_append(folioq, folio);
+	BUG_ON(folioq_folio(folioq, 0) != folio);
+	BUG_ON(folioq_folio_order(folioq, 0) != folio_order(folio));
+	rreq->buffer = folioq;
+	rreq->buffer_tail = folioq;
+	rreq->submitted = rreq->start + rreq->len;
+	iov_iter_folio_queue(&rreq->iter, ITER_DEST, folioq, 0, 0, rreq->len);
+	rreq->ractl = (struct readahead_control *)1UL;
+	return 0;
+}
+
+/*
+ * Read into gaps in a folio partially filled by a streaming write.
+ */
+static int netfs_read_gaps(struct file *file, struct folio *folio)
+{
+	struct netfs_io_request *rreq;
+	struct address_space *mapping = folio->mapping;
+	struct netfs_folio *finfo = netfs_folio_info(folio);
+	struct netfs_inode *ctx = netfs_inode(mapping->host);
+	struct folio *sink = NULL;
+	struct bio_vec *bvec;
+	unsigned int from = finfo->dirty_offset;
+	unsigned int to = from + finfo->dirty_len;
+	unsigned int off = 0, i = 0;
+	size_t flen = folio_size(folio);
+	size_t nr_bvec = flen / PAGE_SIZE + 2;
+	size_t part;
+	int ret;
+
+	_enter("%lx", folio->index);
+
+	rreq = netfs_alloc_request(mapping, file, folio_pos(folio), flen, NETFS_READ_GAPS);
+	if (IS_ERR(rreq)) {
+		ret = PTR_ERR(rreq);
+		goto alloc_error;
+	}
+
+	ret = netfs_begin_cache_read(rreq, ctx);
+	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+		goto discard;
+
+	netfs_stat(&netfs_n_rh_read_folio);
+	trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_read_gaps);
+
+	/* Fiddle the buffer so that a gap at the beginning and/or a gap at the
+	 * end get copied to, but the middle is discarded.
+	 */
+	ret = -ENOMEM;
+	bvec = kmalloc_array(nr_bvec, sizeof(*bvec), GFP_KERNEL);
+	if (!bvec)
+		goto discard;
+
+	sink = folio_alloc(GFP_KERNEL, 0);
+	if (!sink) {
+		kfree(bvec);
+		goto discard;
+	}
+
+	trace_netfs_folio(folio, netfs_folio_trace_read_gaps);
+
+	rreq->direct_bv = bvec;
+	rreq->direct_bv_count = nr_bvec;
+	if (from > 0) {
+		bvec_set_folio(&bvec[i++], folio, from, 0);
+		off = from;
+	}
+	while (off < to) {
+		part = min_t(size_t, to - off, PAGE_SIZE);
+		bvec_set_folio(&bvec[i++], sink, part, 0);
+		off += part;
+	}
+	if (to < flen)
+		bvec_set_folio(&bvec[i++], folio, flen - to, to);
+	iov_iter_bvec(&rreq->iter, ITER_DEST, bvec, i, rreq->len);
+	rreq->submitted = rreq->start + flen;
+
+	netfs_read_to_pagecache(rreq);
+
+	if (sink)
+		folio_put(sink);
+
+	ret = netfs_wait_for_read(rreq);
+	if (ret == 0) {
+		flush_dcache_folio(folio);
+		folio_mark_uptodate(folio);
+	}
+	folio_unlock(folio);
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
+	return ret < 0 ? ret : 0;
+
+discard:
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
+alloc_error:
+	folio_unlock(folio);
+	return ret;
+}
+
 /**
  * netfs_read_folio - Helper to manage a read_folio request
  * @file: The file to read from
@@ -265,9 +565,13 @@ int netfs_read_folio(struct file *file, struct folio *folio)
 	struct address_space *mapping = folio->mapping;
 	struct netfs_io_request *rreq;
 	struct netfs_inode *ctx = netfs_inode(mapping->host);
-	struct folio *sink = NULL;
 	int ret;
 
+	if (folio_test_dirty(folio)) {
+		trace_netfs_folio(folio, netfs_folio_trace_read_gaps);
+		return netfs_read_gaps(file, folio);
+	}
+
 	_enter("%lx", folio->index);
 
 	rreq = netfs_alloc_request(mapping, file,
@@ -286,54 +590,12 @@ int netfs_read_folio(struct file *file, struct folio *folio)
 	trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
 
 	/* Set up the output buffer */
-	if (folio_test_dirty(folio)) {
-		/* Handle someone trying to read from an unflushed streaming
-		 * write.  We fiddle the buffer so that a gap at the beginning
-		 * and/or a gap at the end get copied to, but the middle is
-		 * discarded.
-		 */
-		struct netfs_folio *finfo = netfs_folio_info(folio);
-		struct bio_vec *bvec;
-		unsigned int from = finfo->dirty_offset;
-		unsigned int to = from + finfo->dirty_len;
-		unsigned int off = 0, i = 0;
-		size_t flen = folio_size(folio);
-		size_t nr_bvec = flen / PAGE_SIZE + 2;
-		size_t part;
-
-		ret = -ENOMEM;
-		bvec = kmalloc_array(nr_bvec, sizeof(*bvec), GFP_KERNEL);
-		if (!bvec)
-			goto discard;
-
-		sink = folio_alloc(GFP_KERNEL, 0);
-		if (!sink)
-			goto discard;
-
-		trace_netfs_folio(folio, netfs_folio_trace_read_gaps);
-
-		rreq->direct_bv = bvec;
-		rreq->direct_bv_count = nr_bvec;
-		if (from > 0) {
-			bvec_set_folio(&bvec[i++], folio, from, 0);
-			off = from;
-		}
-		while (off < to) {
-			part = min_t(size_t, to - off, PAGE_SIZE);
-			bvec_set_folio(&bvec[i++], sink, part, 0);
-			off += part;
-		}
-		if (to < flen)
-			bvec_set_folio(&bvec[i++], folio, flen - to, to);
-		iov_iter_bvec(&rreq->iter, ITER_DEST, bvec, i, rreq->len);
-	} else {
-		iov_iter_xarray(&rreq->iter, ITER_DEST, &mapping->i_pages,
-				rreq->start, rreq->len);
-	}
+	ret = netfs_create_singular_buffer(rreq, folio);
+	if (ret < 0)
+		goto discard;
 
-	ret = netfs_begin_read(rreq, true);
-	if (sink)
-		folio_put(sink);
+	netfs_read_to_pagecache(rreq);
+	ret = netfs_wait_for_read(rreq);
 	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
 	return ret < 0 ? ret : 0;
 
@@ -395,7 +657,7 @@ static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
 }
 
 /**
- * netfs_write_begin - Helper to prepare for writing
+ * netfs_write_begin - Helper to prepare for writing [DEPRECATED]
  * @ctx: The netfs context
  * @file: The file to read from
  * @mapping: The mapping to read from
@@ -406,13 +668,10 @@ static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
  *
  * Pre-read data for a write-begin request by drawing data from the cache if
  * possible, or the netfs if not.  Space beyond the EOF is zero-filled.
- * Multiple I/O requests from different sources will get munged together.  If
- * necessary, the readahead window can be expanded in either direction to a
- * more convenient alighment for RPC efficiency or to make storage in the cache
- * feasible.
+ * Multiple I/O requests from different sources will get munged together.
  *
  * The calling netfs must provide a table of operations, only one of which,
- * issue_op, is mandatory.
+ * issue_read, is mandatory.
  *
  * The check_write_begin() operation can be provided to check for and flush
  * conflicting writes once the folio is grabbed and locked.  It is passed a
@@ -437,8 +696,6 @@ int netfs_write_begin(struct netfs_inode *ctx,
 	pgoff_t index = pos >> PAGE_SHIFT;
 	int ret;
 
-	DEFINE_READAHEAD(ractl, file, NULL, mapping, index);
-
 retry:
 	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
 				    mapping_gfp_mask(mapping));
@@ -486,22 +743,13 @@ int netfs_write_begin(struct netfs_inode *ctx,
 	netfs_stat(&netfs_n_rh_write_begin);
 	trace_netfs_read(rreq, pos, len, netfs_read_trace_write_begin);
 
-	/* Expand the request to meet caching requirements and download
-	 * preferences.
-	 */
-	ractl._nr_pages = folio_nr_pages(folio);
-	netfs_rreq_expand(rreq, &ractl);
-
 	/* Set up the output buffer */
-	iov_iter_xarray(&rreq->iter, ITER_DEST, &mapping->i_pages,
-			rreq->start, rreq->len);
-
-	/* We hold the folio locks, so we can drop the references */
-	folio_get(folio);
-	while (readahead_folio(&ractl))
-		;
+	ret = netfs_create_singular_buffer(rreq, folio);
+	if (ret < 0)
+		goto error_put;
 
-	ret = netfs_begin_read(rreq, true);
+	netfs_read_to_pagecache(rreq);
+	ret = netfs_wait_for_read(rreq);
 	if (ret < 0)
 		goto error;
 	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
@@ -557,10 +805,13 @@ int netfs_prefetch_for_write(struct file *file, struct folio *folio,
 	trace_netfs_read(rreq, start, flen, netfs_read_trace_prefetch_for_write);
 
 	/* Set up the output buffer */
-	iov_iter_xarray(&rreq->iter, ITER_DEST, &mapping->i_pages,
-			rreq->start, rreq->len);
+	ret = netfs_create_singular_buffer(rreq, folio);
+	if (ret < 0)
+		goto error_put;
 
-	ret = netfs_begin_read(rreq, true);
+	folioq_mark2(rreq->buffer, 0);
+	netfs_read_to_pagecache(rreq);
+	ret = netfs_wait_for_read(rreq);
 	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
 	return ret;
 
diff --git a/fs/netfs/direct_read.c b/fs/netfs/direct_read.c
index 10a1e4da6bda..b1a66a6e6bc2 100644
--- a/fs/netfs/direct_read.c
+++ b/fs/netfs/direct_read.c
@@ -16,6 +16,143 @@
 #include <linux/netfs.h>
 #include "internal.h"
 
+static void netfs_prepare_dio_read_iterator(struct netfs_io_subrequest *subreq)
+{
+	struct netfs_io_request *rreq = subreq->rreq;
+	size_t rsize;
+
+	rsize = umin(subreq->len, rreq->io_streams[0].sreq_max_len);
+	subreq->len = rsize;
+
+	if (unlikely(rreq->io_streams[0].sreq_max_segs)) {
+		size_t limit = netfs_limit_iter(&rreq->iter, 0, rsize,
+						rreq->io_streams[0].sreq_max_segs);
+
+		if (limit < rsize) {
+			subreq->len = limit;
+			trace_netfs_sreq(subreq, netfs_sreq_trace_limited);
+		}
+	}
+
+	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
+
+	subreq->io_iter	= rreq->iter;
+	iov_iter_truncate(&subreq->io_iter, subreq->len);
+	iov_iter_advance(&rreq->iter, subreq->len);
+}
+
+/*
+ * Perform a read to a buffer from the server, slicing up the region to be read
+ * according to the network rsize.
+ */
+static int netfs_dispatch_unbuffered_reads(struct netfs_io_request *rreq)
+{
+	unsigned long long start = rreq->start;
+	ssize_t size = rreq->len;
+	int ret = 0;
+
+	atomic_set(&rreq->nr_outstanding, 1);
+
+	do {
+		struct netfs_io_subrequest *subreq;
+		ssize_t slice;
+
+		subreq = netfs_alloc_subrequest(rreq);
+		if (!subreq) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		subreq->source	= NETFS_DOWNLOAD_FROM_SERVER;
+		subreq->start	= start;
+		subreq->len	= size;
+
+		atomic_inc(&rreq->nr_outstanding);
+		spin_lock_bh(&rreq->lock);
+		list_add_tail(&subreq->rreq_link, &rreq->subrequests);
+		subreq->prev_donated = rreq->prev_donated;
+		rreq->prev_donated = 0;
+		trace_netfs_sreq(subreq, netfs_sreq_trace_added);
+		spin_unlock_bh(&rreq->lock);
+
+		netfs_stat(&netfs_n_rh_download);
+		if (rreq->netfs_ops->prepare_read) {
+			ret = rreq->netfs_ops->prepare_read(subreq);
+			if (ret < 0) {
+				atomic_dec(&rreq->nr_outstanding);
+				netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_cancel);
+				break;
+			}
+		}
+
+		netfs_prepare_dio_read_iterator(subreq);
+		slice = subreq->len;
+		rreq->netfs_ops->issue_read(subreq);
+
+		size -= slice;
+		start += slice;
+		rreq->submitted += slice;
+
+		if (test_bit(NETFS_RREQ_BLOCKED, &rreq->flags) &&
+		    test_bit(NETFS_RREQ_NONBLOCK, &rreq->flags))
+			break;
+		cond_resched();
+	} while (size > 0);
+
+	if (atomic_dec_and_test(&rreq->nr_outstanding))
+		netfs_rreq_terminated(rreq, false);
+	return ret;
+}
+
+/*
+ * Perform a read to an application buffer, bypassing the pagecache and the
+ * local disk cache.
+ */
+static int netfs_unbuffered_read(struct netfs_io_request *rreq, bool sync)
+{
+	int ret;
+
+	_enter("R=%x %llx-%llx",
+	       rreq->debug_id, rreq->start, rreq->start + rreq->len - 1);
+
+	if (rreq->len == 0) {
+		pr_err("Zero-sized read [R=%x]\n", rreq->debug_id);
+		return -EIO;
+	}
+
+	// TODO: Use bounce buffer if requested
+
+	inode_dio_begin(rreq->inode);
+
+	ret = netfs_dispatch_unbuffered_reads(rreq);
+
+	if (!rreq->submitted) {
+		netfs_put_request(rreq, false, netfs_rreq_trace_put_no_submit);
+		inode_dio_end(rreq->inode);
+		ret = 0;
+		goto out;
+	}
+
+	if (sync) {
+		trace_netfs_rreq(rreq, netfs_rreq_trace_wait_ip);
+		wait_on_bit(&rreq->flags, NETFS_RREQ_IN_PROGRESS,
+			    TASK_UNINTERRUPTIBLE);
+
+		ret = rreq->error;
+		if (ret == 0 && rreq->submitted < rreq->len &&
+		    rreq->origin != NETFS_DIO_READ) {
+			trace_netfs_failure(rreq, NULL, ret, netfs_fail_short_read);
+			ret = -EIO;
+		}
+	} else {
+		ret = -EIOCBQUEUED;
+	}
+
+out:
+	_leave(" = %d", ret);
+	return ret;
+}
+
 /**
  * netfs_unbuffered_read_iter_locked - Perform an unbuffered or direct I/O read
  * @iocb: The I/O control descriptor describing the read
@@ -31,7 +168,7 @@ ssize_t netfs_unbuffered_read_iter_locked(struct kiocb *iocb, struct iov_iter *i
 	struct netfs_io_request *rreq;
 	ssize_t ret;
 	size_t orig_count = iov_iter_count(iter);
-	bool async = !is_sync_kiocb(iocb);
+	bool sync = is_sync_kiocb(iocb);
 
 	_enter("");
 
@@ -78,13 +215,13 @@ ssize_t netfs_unbuffered_read_iter_locked(struct kiocb *iocb, struct iov_iter *i
 
 	// TODO: Set up bounce buffer if needed
 
-	if (async)
+	if (!sync)
 		rreq->iocb = iocb;
 
-	ret = netfs_begin_read(rreq, is_sync_kiocb(iocb));
+	ret = netfs_unbuffered_read(rreq, sync);
 	if (ret < 0)
 		goto out; /* May be -EIOCBQUEUED */
-	if (!async) {
+	if (sync) {
 		// TODO: Copy from bounce buffer
 		iocb->ki_pos += rreq->transferred;
 		ret = rreq->transferred;
@@ -94,8 +231,6 @@ ssize_t netfs_unbuffered_read_iter_locked(struct kiocb *iocb, struct iov_iter *i
 	netfs_put_request(rreq, false, netfs_rreq_trace_put_return);
 	if (ret > 0)
 		orig_count -= ret;
-	if (ret != -EIOCBQUEUED)
-		iov_iter_revert(iter, orig_count - iov_iter_count(iter));
 	return ret;
 }
 EXPORT_SYMBOL(netfs_unbuffered_read_iter_locked);
diff --git a/fs/netfs/internal.h b/fs/netfs/internal.h
index 21a3c7d13585..a4ee0cebf014 100644
--- a/fs/netfs/internal.h
+++ b/fs/netfs/internal.h
@@ -23,16 +23,9 @@
 /*
  * buffered_read.c
  */
-void netfs_rreq_unlock_folios(struct netfs_io_request *rreq);
 int netfs_prefetch_for_write(struct file *file, struct folio *folio,
 			     size_t offset, size_t len);
 
-/*
- * io.c
- */
-void netfs_rreq_work(struct work_struct *work);
-int netfs_begin_read(struct netfs_io_request *rreq, bool sync);
-
 /*
  * main.c
  */
@@ -90,6 +83,18 @@ static inline void netfs_see_request(struct netfs_io_request *rreq,
 	trace_netfs_rreq_ref(rreq->debug_id, refcount_read(&rreq->ref), what);
 }
 
+/*
+ * read_collect.c
+ */
+void netfs_read_termination_worker(struct work_struct *work);
+void netfs_rreq_terminated(struct netfs_io_request *rreq, bool was_async);
+
+/*
+ * read_retry.c
+ */
+void netfs_retry_reads(struct netfs_io_request *rreq);
+void netfs_unlock_abandoned_read_pages(struct netfs_io_request *rreq);
+
 /*
  * stats.c
  */
diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c
index b781bbbf1d8d..72a435e5fc6d 100644
--- a/fs/netfs/iterator.c
+++ b/fs/netfs/iterator.c
@@ -188,9 +188,59 @@ static size_t netfs_limit_xarray(const struct iov_iter *iter, size_t start_offse
 	return min(span, max_size);
 }
 
+/*
+ * Select the span of a folio queue iterator we're going to use.  Limit it by
+ * both maximum size and maximum number of segments.  Returns the size of the
+ * span in bytes.
+ */
+static size_t netfs_limit_folioq(const struct iov_iter *iter, size_t start_offset,
+				 size_t max_size, size_t max_segs)
+{
+	const struct folio_queue *folioq = iter->folioq;
+	unsigned int nsegs = 0;
+	unsigned int slot = iter->folioq_slot;
+	size_t span = 0, n = iter->count;
+
+	if (WARN_ON(!iov_iter_is_folioq(iter)) ||
+	    WARN_ON(start_offset > n) ||
+	    n == 0)
+		return 0;
+	max_size = umin(max_size, n - start_offset);
+
+	if (slot >= folioq_nr_slots(folioq)) {
+		folioq = folioq->next;
+		slot = 0;
+	}
+
+	start_offset += iter->iov_offset;
+	do {
+		size_t flen = folioq_folio_size(folioq, slot);
+
+		if (start_offset < flen) {
+			span += flen - start_offset;
+			nsegs++;
+			start_offset = 0;
+		} else {
+			start_offset -= flen;
+		}
+		if (span >= max_size || nsegs >= max_segs)
+			break;
+
+		slot++;
+		if (slot >= folioq_nr_slots(folioq)) {
+			folioq = folioq->next;
+			slot = 0;
+		}
+	} while (folioq);
+
+	return umin(span, max_size);
+}
+
 size_t netfs_limit_iter(const struct iov_iter *iter, size_t start_offset,
 			size_t max_size, size_t max_segs)
 {
+	if (iov_iter_is_folioq(iter))
+		return netfs_limit_folioq(iter, start_offset, max_size, max_segs);
 	if (iov_iter_is_bvec(iter))
 		return netfs_limit_bvec(iter, start_offset, max_size, max_segs);
 	if (iov_iter_is_xarray(iter))
diff --git a/fs/netfs/main.c b/fs/netfs/main.c
index 1ee712bb3610..ca416235bdf7 100644
--- a/fs/netfs/main.c
+++ b/fs/netfs/main.c
@@ -36,6 +36,7 @@ DEFINE_SPINLOCK(netfs_proc_lock);
 static const char *netfs_origins[nr__netfs_io_origin] = {
 	[NETFS_READAHEAD]		= "RA",
 	[NETFS_READPAGE]		= "RP",
+	[NETFS_READ_GAPS]		= "RG",
 	[NETFS_READ_FOR_WRITE]		= "RW",
 	[NETFS_DIO_READ]		= "DR",
 	[NETFS_WRITEBACK]		= "WB",
@@ -61,7 +62,7 @@ static int netfs_requests_seq_show(struct seq_file *m, void *v)
 
 	rreq = list_entry(v, struct netfs_io_request, proc_link);
 	seq_printf(m,
-		   "%08x %s %3d %2lx %4d %3d @%04llx %llx/%llx",
+		   "%08x %s %3d %2lx %4ld %3d @%04llx %llx/%llx",
 		   rreq->debug_id,
 		   netfs_origins[rreq->origin],
 		   refcount_read(&rreq->ref),
diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index 9d2563d4dab8..da8314c48483 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -40,7 +40,6 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 	memset(rreq, 0, kmem_cache_size(cache));
 	rreq->start	= start;
 	rreq->len	= len;
-	rreq->upper_len	= len;
 	rreq->origin	= origin;
 	rreq->netfs_ops	= ctx->ops;
 	rreq->mapping	= mapping;
@@ -48,6 +47,8 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 	rreq->i_size	= i_size_read(inode);
 	rreq->debug_id	= atomic_inc_return(&debug_ids);
 	rreq->wsize	= INT_MAX;
+	rreq->io_streams[0].sreq_max_len = ULONG_MAX;
+	rreq->io_streams[0].sreq_max_segs = 0;
 	spin_lock_init(&rreq->lock);
 	INIT_LIST_HEAD(&rreq->io_streams[0].subrequests);
 	INIT_LIST_HEAD(&rreq->io_streams[1].subrequests);
@@ -56,9 +57,10 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
 
 	if (origin == NETFS_READAHEAD ||
 	    origin == NETFS_READPAGE ||
+	    origin == NETFS_READ_GAPS ||
 	    origin == NETFS_READ_FOR_WRITE ||
 	    origin == NETFS_DIO_READ)
-		INIT_WORK(&rreq->work, netfs_rreq_work);
+		INIT_WORK(&rreq->work, netfs_read_termination_worker);
 	else
 		INIT_WORK(&rreq->work, netfs_write_collection_worker);
 
@@ -173,7 +175,7 @@ void netfs_put_request(struct netfs_io_request *rreq, bool was_async,
 			if (was_async) {
 				rreq->work.func = netfs_free_request;
 				if (!queue_work(system_unbound_wq, &rreq->work))
-					BUG();
+					WARN_ON(1);
 			} else {
 				netfs_free_request(&rreq->work);
 			}
diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
new file mode 100644
index 000000000000..f9907907106c
--- /dev/null
+++ b/fs/netfs/read_collect.c
@@ -0,0 +1,540 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Network filesystem read subrequest result collection, assessment and
+ * retrying.
+ *
+ * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/slab.h>
+#include <linux/task_io_accounting_ops.h>
+#include "internal.h"
+
+/*
+ * Clear the unread part of an I/O request.
+ */
+static void netfs_clear_unread(struct netfs_io_subrequest *subreq)
+{
+	netfs_reset_iter(subreq);
+	WARN_ON_ONCE(subreq->len - subreq->transferred != iov_iter_count(&subreq->io_iter));
+	iov_iter_zero(iov_iter_count(&subreq->io_iter), &subreq->io_iter);
+	if (subreq->start + subreq->transferred >= subreq->rreq->i_size)
+		__set_bit(NETFS_SREQ_HIT_EOF, &subreq->flags);
+}
+
+/*
+ * Flush, mark and unlock a folio that's now completely read.  If we want to
+ * cache the folio, we set the group to NETFS_FOLIO_COPY_TO_CACHE, mark it
+ * dirty and let writeback handle it.
+ */
+static void netfs_unlock_read_folio(struct netfs_io_subrequest *subreq,
+				    struct netfs_io_request *rreq,
+				    struct folio *folio)
+{
+	struct netfs_folio *finfo;
+
+	flush_dcache_folio(folio);
+	folio_mark_uptodate(folio);
+
+	if (!test_bit(NETFS_RREQ_USE_PGPRIV2, &rreq->flags)) {
+		finfo = netfs_folio_info(folio);
+		if (finfo) {
+			trace_netfs_folio(folio, netfs_folio_trace_filled_gaps);
+			if (finfo->netfs_group)
+				folio_change_private(folio, finfo->netfs_group);
+			else
+				folio_detach_private(folio);
+			kfree(finfo);
+		}
+
+		if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags)) {
+			if (!WARN_ON_ONCE(folio_get_private(folio) != NULL)) {
+				trace_netfs_folio(folio, netfs_folio_trace_copy_to_cache);
+				folio_attach_private(folio, NETFS_FOLIO_COPY_TO_CACHE);
+				folio_mark_dirty(folio);
+			}
+		} else {
+			trace_netfs_folio(folio, netfs_folio_trace_read_done);
+		}
+	} else {
+		// TODO: Use of PG_private_2 is deprecated.
+		if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags)) {
+			trace_netfs_folio(folio, netfs_folio_trace_copy_to_cache);
+			folio_start_private_2(folio);
+		}
+	}
+
+	if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
+		if (folio->index == rreq->no_unlock_folio &&
+		    test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags))
+			_debug("no unlock");
+		else
+			folio_unlock(folio);
+	}
+}
+
+/*
+ * Unlock any folios that are now completely read.  Returns true if the
+ * subrequest is removed from the list.
+ */
+static bool netfs_consume_read_data(struct netfs_io_subrequest *subreq, bool was_async)
+{
+	struct netfs_io_subrequest *prev, *next;
+	struct netfs_io_request *rreq = subreq->rreq;
+	struct folio_queue *folioq = subreq->curr_folioq;
+	size_t avail, prev_donated, next_donated, fsize, part, excess;
+	loff_t fpos, start;
+	loff_t fend;
+	int slot = subreq->curr_folioq_slot;
+
+	if (WARN(subreq->transferred > subreq->len,
+		 "Subreq overread: R%x[%x] %zu > %zu",
+		 rreq->debug_id, subreq->debug_index,
+		 subreq->transferred, subreq->len))
+		subreq->transferred = subreq->len;
+
+next_folio:
+	fsize = PAGE_SIZE << subreq->curr_folio_order;
+	fpos = round_down(subreq->start + subreq->consumed, fsize);
+	fend = fpos + fsize;
+
+	if (WARN_ON_ONCE(!folioq) ||
+	    WARN_ON_ONCE(!folioq_folio(folioq, slot)) ||
+	    WARN_ON_ONCE(folioq_folio(folioq, slot)->index != fpos / PAGE_SIZE)) {
+		pr_err("R=%08x[%x] s=%llx-%llx ctl=%zx/%zx/%zx sl=%u\n",
+		       rreq->debug_id, subreq->debug_index,
+		       subreq->start, subreq->start + subreq->transferred - 1,
+		       subreq->consumed, subreq->transferred, subreq->len,
+		       slot);
+		if (folioq) {
+			struct folio *folio = folioq_folio(folioq, slot);
+
+			pr_err("folioq: %02x%02x%02x%02x\n",
+			       folioq->orders[0], folioq->orders[1],
+			       folioq->orders[2], folioq->orders[3]);
+			if (folio)
+				pr_err("folio: %llx-%llx ix=%llx o=%u qo=%u\n",
+				       fpos, fend - 1, folio_pos(folio), folio_order(folio),
+				       folioq_folio_order(folioq, slot));
+		}
+	}
+
+donation_changed:
+	/* Try to consume the current folio if we've hit or passed the end of
+	 * it.  There's a possibility that this subreq doesn't start at the
+	 * beginning of the folio, in which case we need to donate to/from the
+	 * preceding subreq.
+	 *
+	 * We also need to include any potential donation back from the
+	 * following subreq.
+	 */
+	prev_donated = READ_ONCE(subreq->prev_donated);
+	next_donated =  READ_ONCE(subreq->next_donated);
+	if (prev_donated || next_donated) {
+		spin_lock_bh(&rreq->lock);
+		prev_donated = subreq->prev_donated;
+		next_donated =  subreq->next_donated;
+		subreq->start -= prev_donated;
+		subreq->len += prev_donated;
+		subreq->transferred += prev_donated;
+		prev_donated = subreq->prev_donated = 0;
+		if (subreq->transferred == subreq->len) {
+			subreq->len += next_donated;
+			subreq->transferred += next_donated;
+			next_donated = subreq->next_donated = 0;
+		}
+		trace_netfs_sreq(subreq, netfs_sreq_trace_add_donations);
+		spin_unlock_bh(&rreq->lock);
+	}
+
+	avail = subreq->transferred;
+	if (avail == subreq->len)
+		avail += next_donated;
+	start = subreq->start;
+	if (subreq->consumed == 0) {
+		start -= prev_donated;
+		avail += prev_donated;
+	} else {
+		start += subreq->consumed;
+		avail -= subreq->consumed;
+	}
+	part = umin(avail, fsize);
+
+	trace_netfs_progress(subreq, start, avail, part);
+
+	if (start + avail >= fend) {
+		if (fpos == start) {
+			/* Flush, unlock and mark for caching any folio we've just read. */
+			subreq->consumed = fend - subreq->start;
+			netfs_unlock_read_folio(subreq, rreq, folioq_folio(folioq, slot));
+			folioq_mark2(folioq, slot);
+			if (subreq->consumed >= subreq->len)
+				goto remove_subreq;
+		} else if (fpos < start) {
+			excess = fend - subreq->start;
+
+			spin_lock_bh(&rreq->lock);
+			/* If we complete first on a folio split with the
+			 * preceding subreq, donate to that subreq - otherwise
+			 * we get the responsibility.
+			 */
+			if (subreq->prev_donated != prev_donated) {
+				spin_unlock_bh(&rreq->lock);
+				goto donation_changed;
+			}
+
+			if (list_is_first(&subreq->rreq_link, &rreq->subrequests)) {
+				spin_unlock_bh(&rreq->lock);
+				pr_err("Can't donate prior to front\n");
+				goto bad;
+			}
+
+			prev = list_prev_entry(subreq, rreq_link);
+			WRITE_ONCE(prev->next_donated, prev->next_donated + excess);
+			subreq->start += excess;
+			subreq->len -= excess;
+			subreq->transferred -= excess;
+			trace_netfs_donate(rreq, subreq, prev, excess,
+					   netfs_trace_donate_tail_to_prev);
+			trace_netfs_sreq(subreq, netfs_sreq_trace_donate_to_prev);
+
+			if (subreq->consumed >= subreq->len)
+				goto remove_subreq_locked;
+			spin_unlock_bh(&rreq->lock);
+		} else {
+			pr_err("fpos > start\n");
+			goto bad;
+		}
+
+		/* Advance the rolling buffer to the next folio. */
+		slot++;
+		if (slot >= folioq_nr_slots(folioq)) {
+			slot = 0;
+			folioq = folioq->next;
+			subreq->curr_folioq = folioq;
+		}
+		subreq->curr_folioq_slot = slot;
+		if (folioq && folioq_folio(folioq, slot))
+			subreq->curr_folio_order = folioq->orders[slot];
+		if (!was_async)
+			cond_resched();
+		goto next_folio;
+	}
+
+	/* Deal with partial progress. */
+	if (subreq->transferred < subreq->len)
+		return false;
+
+	/* Donate the remaining downloaded data to one of the neighbouring
+	 * subrequests.  Note that we may race with them doing the same thing.
+	 */
+	spin_lock_bh(&rreq->lock);
+
+	if (subreq->prev_donated != prev_donated ||
+	    subreq->next_donated != next_donated) {
+		spin_unlock_bh(&rreq->lock);
+		cond_resched();
+		goto donation_changed;
+	}
+
+	/* Deal with the trickiest case: that this subreq is in the middle of a
+	 * folio, not touching either edge, but finishes first.  In such a
+	 * case, we donate to the previous subreq, if there is one, so that the
+	 * donation is only handled when that completes - and remove this
+	 * subreq from the list.
+	 *
+	 * If the previous subreq finished first, we will have acquired their
+	 * donation and should be able to unlock folios and/or donate nextwards.
+	 */
+	if (!subreq->consumed &&
+	    !prev_donated &&
+	    !list_is_first(&subreq->rreq_link, &rreq->subrequests)) {
+		prev = list_prev_entry(subreq, rreq_link);
+		WRITE_ONCE(prev->next_donated, prev->next_donated + subreq->len);
+		subreq->start += subreq->len;
+		subreq->len = 0;
+		subreq->transferred = 0;
+		trace_netfs_donate(rreq, subreq, prev, subreq->len,
+				   netfs_trace_donate_to_prev);
+		trace_netfs_sreq(subreq, netfs_sreq_trace_donate_to_prev);
+		goto remove_subreq_locked;
+	}
+
+	/* If we can't donate down the chain, donate up the chain instead. */
+	excess = subreq->len - subreq->consumed + next_donated;
+
+	if (!subreq->consumed)
+		excess += prev_donated;
+
+	if (list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
+		rreq->prev_donated = excess;
+		trace_netfs_donate(rreq, subreq, NULL, excess,
+				   netfs_trace_donate_to_deferred_next);
+	} else {
+		next = list_next_entry(subreq, rreq_link);
+		WRITE_ONCE(next->prev_donated, excess);
+		trace_netfs_donate(rreq, subreq, next, excess,
+				   netfs_trace_donate_to_next);
+	}
+	trace_netfs_sreq(subreq, netfs_sreq_trace_donate_to_next);
+	subreq->len = subreq->consumed;
+	subreq->transferred = subreq->consumed;
+	goto remove_subreq_locked;
+
+remove_subreq:
+	spin_lock_bh(&rreq->lock);
+remove_subreq_locked:
+	subreq->consumed = subreq->len;
+	list_del(&subreq->rreq_link);
+	spin_unlock_bh(&rreq->lock);
+	netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_consumed);
+	return true;
+
+bad:
+	/* Errr... prev and next both donated to us, but insufficient to finish
+	 * the folio.
+	 */
+	printk("R=%08x[%x] s=%llx-%llx %zx/%zx/%zx\n",
+	       rreq->debug_id, subreq->debug_index,
+	       subreq->start, subreq->start + subreq->transferred - 1,
+	       subreq->consumed, subreq->transferred, subreq->len);
+	printk("folio: %llx-%llx\n", fpos, fend - 1);
+	printk("donated: prev=%zx next=%zx\n", prev_donated, next_donated);
+	printk("s=%llx av=%zx part=%zx\n", start, avail, part);
+	BUG();
+}
+
+/*
+ * Do page flushing and suchlike after DIO.
+ */
+static void netfs_rreq_assess_dio(struct netfs_io_request *rreq)
+{
+	struct netfs_io_subrequest *subreq;
+	unsigned int i;
+
+	/* Collect unbuffered reads and direct reads, adding up the transfer
+	 * sizes until we find the first short or failed subrequest.
+	 */
+	list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
+		rreq->transferred += subreq->transferred;
+
+		if (subreq->transferred < subreq->len ||
+		    test_bit(NETFS_SREQ_FAILED, &subreq->flags)) {
+			rreq->error = subreq->error;
+			break;
+		}
+	}
+
+	if (rreq->origin == NETFS_DIO_READ) {
+		for (i = 0; i < rreq->direct_bv_count; i++) {
+			flush_dcache_page(rreq->direct_bv[i].bv_page);
+			// TODO: cifs marks pages in the destination buffer
+			// dirty under some circumstances after a read.  Do we
+			// need to do that too?
+			set_page_dirty(rreq->direct_bv[i].bv_page);
+		}
+	}
+
+	if (rreq->iocb) {
+		rreq->iocb->ki_pos += rreq->transferred;
+		if (rreq->iocb->ki_complete)
+			rreq->iocb->ki_complete(
+				rreq->iocb, rreq->error ? rreq->error : rreq->transferred);
+	}
+	if (rreq->netfs_ops->done)
+		rreq->netfs_ops->done(rreq);
+	if (rreq->origin == NETFS_DIO_READ)
+		inode_dio_end(rreq->inode);
+}
+
+/*
+ * Assess the state of a read request and decide what to do next.
+ *
+ * Note that we could be in an ordinary kernel thread, on a workqueue or in
+ * softirq context at this point.  We inherit a ref from the caller.
+ */
+static void netfs_rreq_assess(struct netfs_io_request *rreq)
+{
+	trace_netfs_rreq(rreq, netfs_rreq_trace_assess);
+
+	//netfs_rreq_is_still_valid(rreq);
+
+	if (test_and_clear_bit(NETFS_RREQ_NEED_RETRY, &rreq->flags)) {
+		netfs_retry_reads(rreq);
+		return;
+	}
+
+	if (rreq->origin == NETFS_DIO_READ ||
+	    rreq->origin == NETFS_READ_GAPS)
+		netfs_rreq_assess_dio(rreq);
+	task_io_account_read(rreq->transferred);
+
+	trace_netfs_rreq(rreq, netfs_rreq_trace_wake_ip);
+	clear_bit_unlock(NETFS_RREQ_IN_PROGRESS, &rreq->flags);
+	wake_up_bit(&rreq->flags, NETFS_RREQ_IN_PROGRESS);
+
+	trace_netfs_rreq(rreq, netfs_rreq_trace_done);
+	netfs_clear_subrequests(rreq, false);
+	netfs_unlock_abandoned_read_pages(rreq);
+}
+
+void netfs_read_termination_worker(struct work_struct *work)
+{
+	struct netfs_io_request *rreq =
+		container_of(work, struct netfs_io_request, work);
+	netfs_see_request(rreq, netfs_rreq_trace_see_work);
+	netfs_rreq_assess(rreq);
+	netfs_put_request(rreq, false, netfs_rreq_trace_put_work_complete);
+}
+
+/*
+ * Handle the completion of all outstanding I/O operations on a read request.
+ * We inherit a ref from the caller.
+ */
+void netfs_rreq_terminated(struct netfs_io_request *rreq, bool was_async)
+{
+	if (!was_async)
+		return netfs_rreq_assess(rreq);
+	if (!work_pending(&rreq->work)) {
+		netfs_get_request(rreq, netfs_rreq_trace_get_work);
+		if (!queue_work(system_unbound_wq, &rreq->work))
+			netfs_put_request(rreq, was_async, netfs_rreq_trace_put_work_nq);
+	}
+}
+
+/**
+ * netfs_read_subreq_progress - Note progress of a read operation.
+ * @subreq: The read request that has terminated.
+ * @was_async: True if we're in an asynchronous context.
+ *
+ * This tells the read side of netfs lib that a contributory I/O operation has
+ * made some progress and that it may be possible to unlock some folios.
+ *
+ * Before calling, the filesystem should update subreq->transferred to track
+ * the amount of data copied into the output buffer.
+ *
+ * If @was_async is true, the caller might be running in softirq or interrupt
+ * context and we can't sleep.
+ */
+void netfs_read_subreq_progress(struct netfs_io_subrequest *subreq,
+				bool was_async)
+{
+	struct netfs_io_request *rreq = subreq->rreq;
+
+	trace_netfs_sreq(subreq, netfs_sreq_trace_progress);
+
+	if (subreq->transferred > subreq->consumed &&
+	    (rreq->origin == NETFS_READAHEAD ||
+	     rreq->origin == NETFS_READPAGE ||
+	     rreq->origin == NETFS_READ_FOR_WRITE)) {
+		netfs_consume_read_data(subreq, was_async);
+		__clear_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags);
+	}
+}
+EXPORT_SYMBOL(netfs_read_subreq_progress);
+
+/**
+ * netfs_read_subreq_terminated - Note the termination of an I/O operation.
+ * @subreq: The I/O request that has terminated.
+ * @error: Error code indicating type of completion.
+ * @was_async: The termination was asynchronous
+ *
+ * This tells the read helper that a contributory I/O operation has terminated,
+ * one way or another, and that it should integrate the results.
+ *
+ * The caller indicates the outcome of the operation through @error, supplying
+ * 0 to indicate a successful or retryable transfer (if NETFS_SREQ_NEED_RETRY
+ * is set) or a negative error code.  The helper will look after reissuing I/O
+ * operations as appropriate and writing downloaded data to the cache.
+ *
+ * Before calling, the filesystem should update subreq->transferred to track
+ * the amount of data copied into the output buffer.
+ *
+ * If @was_async is true, the caller might be running in softirq or interrupt
+ * context and we can't sleep.
+ */
+void netfs_read_subreq_terminated(struct netfs_io_subrequest *subreq,
+				  int error, bool was_async)
+{
+	struct netfs_io_request *rreq = subreq->rreq;
+
+	switch (subreq->source) {
+	case NETFS_READ_FROM_CACHE:
+		netfs_stat(&netfs_n_rh_read_done);
+		break;
+	case NETFS_DOWNLOAD_FROM_SERVER:
+		netfs_stat(&netfs_n_rh_download_done);
+		break;
+	default:
+		break;
+	}
+
+	if (rreq->origin != NETFS_DIO_READ) {
+		/* Collect buffered reads.
+		 *
+		 * If the read completed validly short, then we can clear the
+		 * tail before going on to unlock the folios.
+		 */
+		if (error == 0 && subreq->transferred < subreq->len &&
+		    (test_bit(NETFS_SREQ_HIT_EOF, &subreq->flags) ||
+		     test_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags))) {
+			netfs_clear_unread(subreq);
+			subreq->transferred = subreq->len;
+			trace_netfs_sreq(subreq, netfs_sreq_trace_clear);
+		}
+		if (subreq->transferred > subreq->consumed &&
+		    (rreq->origin == NETFS_READAHEAD ||
+		     rreq->origin == NETFS_READPAGE ||
+		     rreq->origin == NETFS_READ_FOR_WRITE)) {
+			netfs_consume_read_data(subreq, was_async);
+			__clear_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags);
+		}
+		rreq->transferred += subreq->transferred;
+	}
+
+	/* Deal with retry requests, short reads and errors.  If we retry
+	 * but don't make progress, we abandon the attempt.
+	 */
+	if (!error && subreq->transferred < subreq->len) {
+		if (test_bit(NETFS_SREQ_HIT_EOF, &subreq->flags)) {
+			trace_netfs_sreq(subreq, netfs_sreq_trace_hit_eof);
+		} else {
+			trace_netfs_sreq(subreq, netfs_sreq_trace_short);
+			if (subreq->transferred > subreq->consumed) {
+				__set_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
+				__clear_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags);
+				set_bit(NETFS_RREQ_NEED_RETRY, &rreq->flags);
+			} else if (!__test_and_set_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags)) {
+				__set_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
+				set_bit(NETFS_RREQ_NEED_RETRY, &rreq->flags);
+			} else {
+				__set_bit(NETFS_SREQ_FAILED, &subreq->flags);
+				error = -ENODATA;
+			}
+		}
+	}
+
+	subreq->error = error;
+	trace_netfs_sreq(subreq, netfs_sreq_trace_terminated);
+
+	if (unlikely(error < 0)) {
+		trace_netfs_failure(rreq, subreq, error, netfs_fail_read);
+		if (subreq->source == NETFS_READ_FROM_CACHE) {
+			netfs_stat(&netfs_n_rh_read_failed);
+		} else {
+			netfs_stat(&netfs_n_rh_download_failed);
+			set_bit(NETFS_RREQ_FAILED, &rreq->flags);
+			rreq->error = subreq->error;
+		}
+	}
+
+	if (atomic_dec_and_test(&rreq->nr_outstanding))
+		netfs_rreq_terminated(rreq, was_async);
+
+	netfs_put_subrequest(subreq, was_async, netfs_sreq_trace_put_terminated);
+}
+EXPORT_SYMBOL(netfs_read_subreq_terminated);
diff --git a/fs/netfs/read_retry.c b/fs/netfs/read_retry.c
new file mode 100644
index 000000000000..0350592ea804
--- /dev/null
+++ b/fs/netfs/read_retry.c
@@ -0,0 +1,256 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Network filesystem read subrequest retrying.
+ *
+ * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include "internal.h"
+
+static void netfs_reissue_read(struct netfs_io_request *rreq,
+			       struct netfs_io_subrequest *subreq)
+{
+	struct iov_iter *io_iter = &subreq->io_iter;
+
+	if (iov_iter_is_folioq(io_iter)) {
+		subreq->curr_folioq = (struct folio_queue *)io_iter->folioq;
+		subreq->curr_folioq_slot = io_iter->folioq_slot;
+		subreq->curr_folio_order = subreq->curr_folioq->orders[subreq->curr_folioq_slot];
+	}
+
+	atomic_inc(&rreq->nr_outstanding);
+	__set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags);
+	netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
+	subreq->rreq->netfs_ops->issue_read(subreq);
+}
+
+/*
+ * Go through the list of failed/short reads, retrying all retryable ones.  We
+ * need to switch failed cache reads to network downloads.
+ */
+static void netfs_retry_read_subrequests(struct netfs_io_request *rreq)
+{
+	struct netfs_io_subrequest *subreq;
+	struct netfs_io_stream *stream0 = &rreq->io_streams[0];
+	LIST_HEAD(sublist);
+	LIST_HEAD(queue);
+
+	_enter("R=%x", rreq->debug_id);
+
+	if (list_empty(&rreq->subrequests))
+		return;
+
+	if (rreq->netfs_ops->retry_request)
+		rreq->netfs_ops->retry_request(rreq, NULL);
+
+	/* If there's no renegotiation to do, just resend each retryable subreq
+	 * up to the first permanently failed one.
+	 */
+	if (!rreq->netfs_ops->prepare_read &&
+	    !test_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags)) {
+		struct netfs_io_subrequest *subreq;
+
+		list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
+			if (test_bit(NETFS_SREQ_FAILED, &subreq->flags))
+				break;
+			if (__test_and_clear_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags)) {
+				netfs_reset_iter(subreq);
+				netfs_reissue_read(rreq, subreq);
+			}
+		}
+		return;
+	}
+
+	/* Okay, we need to renegotiate all the download requests and flip any
+	 * failed cache reads over to being download requests and negotiate
+	 * those also.  All fully successful subreqs have been removed from the
+	 * list and any spare data from those has been donated.
+	 *
+	 * What we do is decant the list and rebuild it one subreq at a time so
+	 * that we don't end up with donations jumping over a gap we're busy
+	 * populating with smaller subrequests.  In the event that the subreq
+	 * we just launched finishes before we insert the next subreq, it'll
+	 * fill in rreq->prev_donated instead.
+
+	 * Note: Alternatively, we could split the tail subrequest right before
+	 * we reissue it and fix up the donations under lock.
+	 */
+	list_splice_init(&rreq->subrequests, &queue);
+
+	do {
+		struct netfs_io_subrequest *from;
+		struct iov_iter source;
+		unsigned long long start, len;
+		size_t part, deferred_next_donated = 0;
+		bool boundary = false;
+
+		/* Go through the subreqs and find the next span of contiguous
+		 * buffer that we then rejig (cifs, for example, needs the
+		 * rsize renegotiating) and reissue.
+		 */
+		from = list_first_entry(&queue, struct netfs_io_subrequest, rreq_link);
+		list_move_tail(&from->rreq_link, &sublist);
+		start = from->start + from->transferred;
+		len   = from->len   - from->transferred;
+
+		_debug("from R=%08x[%x] s=%llx ctl=%zx/%zx/%zx",
+		       rreq->debug_id, from->debug_index,
+		       from->start, from->consumed, from->transferred, from->len);
+
+		if (test_bit(NETFS_SREQ_FAILED, &from->flags) ||
+		    !test_bit(NETFS_SREQ_NEED_RETRY, &from->flags))
+			goto abandon;
+
+		deferred_next_donated = from->next_donated;
+		while ((subreq = list_first_entry_or_null(
+				&queue, struct netfs_io_subrequest, rreq_link))) {
+			if (subreq->start != start + len ||
+			    subreq->transferred > 0 ||
+			    !test_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags))
+				break;
+			list_move_tail(&subreq->rreq_link, &sublist);
+			len += subreq->len;
+			deferred_next_donated = subreq->next_donated;
+			if (test_bit(NETFS_SREQ_BOUNDARY, &subreq->flags))
+				break;
+		}
+
+		_debug(" - range: %llx-%llx %llx", start, start + len - 1, len);
+
+		/* Determine the set of buffers we're going to use.  Each
+		 * subreq gets a subset of a single overall contiguous buffer.
+		 */
+		netfs_reset_iter(from);
+		source = from->io_iter;
+		source.count = len;
+
+		/* Work through the sublist. */
+		while ((subreq = list_first_entry_or_null(
+				&sublist, struct netfs_io_subrequest, rreq_link))) {
+			list_del(&subreq->rreq_link);
+
+			subreq->source	= NETFS_DOWNLOAD_FROM_SERVER;
+			subreq->start	= start - subreq->transferred;
+			subreq->len	= len   + subreq->transferred;
+			stream0->sreq_max_len = subreq->len;
+
+			__clear_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
+			__set_bit(NETFS_SREQ_RETRYING, &subreq->flags);
+
+			spin_lock_bh(&rreq->lock);
+			list_add_tail(&subreq->rreq_link, &rreq->subrequests);
+			subreq->prev_donated += rreq->prev_donated;
+			rreq->prev_donated = 0;
+			trace_netfs_sreq(subreq, netfs_sreq_trace_retry);
+			spin_unlock_bh(&rreq->lock);
+
+			BUG_ON(!len);
+
+			/* Renegotiate max_len (rsize) */
+			if (rreq->netfs_ops->prepare_read(subreq) < 0) {
+				trace_netfs_sreq(subreq, netfs_sreq_trace_reprep_failed);
+				__set_bit(NETFS_SREQ_FAILED, &subreq->flags);
+			}
+
+			part = umin(len, stream0->sreq_max_len);
+			if (unlikely(rreq->io_streams[0].sreq_max_segs))
+				part = netfs_limit_iter(&source, 0, part, stream0->sreq_max_segs);
+			subreq->len = subreq->transferred + part;
+			subreq->io_iter = source;
+			iov_iter_truncate(&subreq->io_iter, part);
+			iov_iter_advance(&source, part);
+			len -= part;
+			start += part;
+			if (!len) {
+				if (boundary)
+					__set_bit(NETFS_SREQ_BOUNDARY, &subreq->flags);
+				subreq->next_donated = deferred_next_donated;
+			} else {
+				__clear_bit(NETFS_SREQ_BOUNDARY, &subreq->flags);
+				subreq->next_donated = 0;
+			}
+
+			netfs_reissue_read(rreq, subreq);
+			if (!len)
+				break;
+
+			/* If we ran out of subrequests, allocate another. */
+			if (list_empty(&sublist)) {
+				subreq = netfs_alloc_subrequest(rreq);
+				if (!subreq)
+					goto abandon;
+				subreq->source = NETFS_DOWNLOAD_FROM_SERVER;
+				subreq->start = start;
+
+				/* We get two refs, but need just one. */
+				netfs_put_subrequest(subreq, false, netfs_sreq_trace_new);
+				trace_netfs_sreq(subreq, netfs_sreq_trace_split);
+				list_add_tail(&subreq->rreq_link, &sublist);
+			}
+		}
+
+		/* If we managed to use fewer subreqs, we can discard the
+		 * excess.
+		 */
+		while ((subreq = list_first_entry_or_null(
+				&sublist, struct netfs_io_subrequest, rreq_link))) {
+			trace_netfs_sreq(subreq, netfs_sreq_trace_discard);
+			list_del(&subreq->rreq_link);
+			netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_done);
+		}
+
+	} while (!list_empty(&queue));
+
+	return;
+
+	/* If we hit ENOMEM, fail all remaining subrequests */
+abandon:
+	list_splice_init(&sublist, &queue);
+	list_for_each_entry(subreq, &queue, rreq_link) {
+		if (!subreq->error)
+			subreq->error = -ENOMEM;
+		__clear_bit(NETFS_SREQ_FAILED, &subreq->flags);
+		__clear_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags);
+		__clear_bit(NETFS_SREQ_RETRYING, &subreq->flags);
+	}
+	spin_lock_bh(&rreq->lock);
+	list_splice_tail_init(&queue, &rreq->subrequests);
+	spin_unlock_bh(&rreq->lock);
+}
+
+/*
+ * Retry reads.
+ */
+void netfs_retry_reads(struct netfs_io_request *rreq)
+{
+	trace_netfs_rreq(rreq, netfs_rreq_trace_resubmit);
+
+	atomic_inc(&rreq->nr_outstanding);
+
+	netfs_retry_read_subrequests(rreq);
+
+	if (atomic_dec_and_test(&rreq->nr_outstanding))
+		netfs_rreq_terminated(rreq, false);
+}
+
+/*
+ * Unlock any the pages that haven't been unlocked yet due to abandoned
+ * subrequests.
+ */
+void netfs_unlock_abandoned_read_pages(struct netfs_io_request *rreq)
+{
+	struct folio_queue *p;
+
+	for (p = rreq->buffer; p; p = p->next) {
+		for (int slot = 0; slot < folioq_count(p); slot++) {
+			struct folio *folio = folioq_folio(p, slot);
+
+			if (folio && !folioq_is_marked2(p, slot)) {
+				trace_netfs_folio(folio, netfs_folio_trace_abandon);
+				folio_unlock(folio);
+			}
+		}
+	}
+}
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 10ff2bd290cb..43cec03c6514 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -159,10 +159,6 @@ static void netfs_prepare_write(struct netfs_io_request *wreq,
 
 	_enter("R=%x[%x]", wreq->debug_id, subreq->debug_index);
 
-	trace_netfs_sreq_ref(wreq->debug_id, subreq->debug_index,
-			     refcount_read(&subreq->ref),
-			     netfs_sreq_trace_new);
-
 	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
 
 	stream->sreq_max_len	= UINT_MAX;
diff --git a/fs/nfs/fscache.c b/fs/nfs/fscache.c
index 7202ce84d0eb..cc93cfb16f9d 100644
--- a/fs/nfs/fscache.c
+++ b/fs/nfs/fscache.c
@@ -265,6 +265,7 @@ static int nfs_netfs_init_request(struct netfs_io_request *rreq, struct file *fi
 {
 	rreq->netfs_priv = get_nfs_open_context(nfs_file_open_context(file));
 	rreq->debug_id = atomic_inc_return(&nfs_netfs_debug_id);
+	rreq->io_streams[0].sreq_max_len = NFS_SB(rreq->inode->i_sb)->rsize;
 
 	return 0;
 }
@@ -286,14 +287,6 @@ static struct nfs_netfs_io_data *nfs_netfs_alloc(struct netfs_io_subrequest *sre
 	return netfs;
 }
 
-static bool nfs_netfs_clamp_length(struct netfs_io_subrequest *sreq)
-{
-	size_t	rsize = NFS_SB(sreq->rreq->inode->i_sb)->rsize;
-
-	sreq->len = min(sreq->len, rsize);
-	return true;
-}
-
 static void nfs_netfs_issue_read(struct netfs_io_subrequest *sreq)
 {
 	struct nfs_netfs_io_data	*netfs;
@@ -302,17 +295,18 @@ static void nfs_netfs_issue_read(struct netfs_io_subrequest *sreq)
 	struct nfs_open_context *ctx = sreq->rreq->netfs_priv;
 	struct page *page;
 	unsigned long idx;
+	pgoff_t start, last;
 	int err;
-	pgoff_t start = (sreq->start + sreq->transferred) >> PAGE_SHIFT;
-	pgoff_t last = ((sreq->start + sreq->len -
-			 sreq->transferred - 1) >> PAGE_SHIFT);
+
+	start = (sreq->start + sreq->transferred) >> PAGE_SHIFT;
+	last = ((sreq->start + sreq->len - sreq->transferred - 1) >> PAGE_SHIFT);
 
 	nfs_pageio_init_read(&pgio, inode, false,
 			     &nfs_async_read_completion_ops);
 
 	netfs = nfs_netfs_alloc(sreq);
 	if (!netfs)
-		return netfs_subreq_terminated(sreq, -ENOMEM, false);
+		return netfs_read_subreq_terminated(sreq, -ENOMEM, false);
 
 	pgio.pg_netfs = netfs; /* used in completion */
 
@@ -377,5 +371,4 @@ const struct netfs_request_ops nfs_netfs_ops = {
 	.init_request		= nfs_netfs_init_request,
 	.free_request		= nfs_netfs_free_request,
 	.issue_read		= nfs_netfs_issue_read,
-	.clamp_length		= nfs_netfs_clamp_length
 };
diff --git a/fs/nfs/fscache.h b/fs/nfs/fscache.h
index fbed0027996f..5edebcff8ddf 100644
--- a/fs/nfs/fscache.h
+++ b/fs/nfs/fscache.h
@@ -60,8 +60,6 @@ static inline void nfs_netfs_get(struct nfs_netfs_io_data *netfs)
 
 static inline void nfs_netfs_put(struct nfs_netfs_io_data *netfs)
 {
-	ssize_t final_len;
-
 	/* Only the last RPC completion should call netfs_subreq_terminated() */
 	if (!refcount_dec_and_test(&netfs->refcount))
 		return;
@@ -74,8 +72,9 @@ static inline void nfs_netfs_put(struct nfs_netfs_io_data *netfs)
 	 * Correct the final length here to be no larger than the netfs subrequest
 	 * length, and thus avoid netfs's "Subreq overread" warning message.
 	 */
-	final_len = min_t(s64, netfs->sreq->len, atomic64_read(&netfs->transferred));
-	netfs_subreq_terminated(netfs->sreq, netfs->error ?: final_len, false);
+	netfs->sreq->transferred = min_t(s64, netfs->sreq->len,
+					 atomic64_read(&netfs->transferred));
+	netfs_read_subreq_terminated(netfs->sreq, netfs->error, false);
 	kfree(netfs);
 }
 static inline void nfs_netfs_inode_init(struct nfs_inode *nfsi)
diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
index 595c4b673707..d5e1bbefd5e8 100644
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -1309,10 +1309,8 @@ cifs_readv_callback(struct mid_q_entry *mid)
 	if (rdata->result == 0 || rdata->result == -EAGAIN)
 		iov_iter_advance(&rdata->subreq.io_iter, rdata->got_bytes);
 	rdata->credits.value = 0;
-	netfs_subreq_terminated(&rdata->subreq,
-				(rdata->result == 0 || rdata->result == -EAGAIN) ?
-				rdata->got_bytes : rdata->result,
-				false);
+	rdata->subreq.transferred += rdata->got_bytes;
+	netfs_read_subreq_terminated(&rdata->subreq, rdata->result, false);
 	release_mid(mid);
 	add_credits(server, &credits, 0);
 }
diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
index c1d8c5d2ac71..569c17b41b8e 100644
--- a/fs/smb/client/file.c
+++ b/fs/smb/client/file.c
@@ -140,25 +140,22 @@ static void cifs_netfs_invalidate_cache(struct netfs_io_request *wreq)
 }
 
 /*
- * Split the read up according to how many credits we can get for each piece.
- * It's okay to sleep here if we need to wait for more credit to become
- * available.
- *
- * We also choose the server and allocate an operation ID to be cleaned up
- * later.
+ * Negotiate the size of a read operation on behalf of the netfs library.
  */
-static bool cifs_clamp_length(struct netfs_io_subrequest *subreq)
+static int cifs_prepare_read(struct netfs_io_subrequest *subreq)
 {
 	struct netfs_io_request *rreq = subreq->rreq;
-	struct netfs_io_stream *stream = &rreq->io_streams[subreq->stream_nr];
 	struct cifs_io_subrequest *rdata = container_of(subreq, struct cifs_io_subrequest, subreq);
 	struct cifs_io_request *req = container_of(subreq->rreq, struct cifs_io_request, rreq);
 	struct TCP_Server_Info *server = req->server;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(rreq->inode->i_sb);
-	int rc;
+	size_t size;
+	int rc = 0;
 
-	rdata->xid = get_xid();
-	rdata->have_xid = true;
+	if (!rdata->have_xid) {
+		rdata->xid = get_xid();
+		rdata->have_xid = true;
+	}
 	rdata->server = server;
 
 	if (cifs_sb->ctx->rsize == 0)
@@ -166,13 +163,12 @@ static bool cifs_clamp_length(struct netfs_io_subrequest *subreq)
 			server->ops->negotiate_rsize(tlink_tcon(req->cfile->tlink),
 						     cifs_sb->ctx);
 
-
 	rc = server->ops->wait_mtu_credits(server, cifs_sb->ctx->rsize,
-					   &stream->sreq_max_len, &rdata->credits);
-	if (rc) {
-		subreq->error = rc;
-		return false;
-	}
+					   &size, &rdata->credits);
+	if (rc)
+		return rc;
+
+	rreq->io_streams[0].sreq_max_len = size;
 
 	rdata->credits.in_flight_check = 1;
 	rdata->credits.rreq_debug_id = rreq->debug_id;
@@ -184,13 +180,11 @@ static bool cifs_clamp_length(struct netfs_io_subrequest *subreq)
 			      server->credits, server->in_flight, 0,
 			      cifs_trace_rw_credits_read_submit);
 
-	subreq->len = umin(subreq->len, stream->sreq_max_len);
-
 #ifdef CONFIG_CIFS_SMB_DIRECT
 	if (server->smbd_conn)
-		stream->sreq_max_segs = server->smbd_conn->max_frmr_depth;
+		rreq->io_streams[0].sreq_max_segs = server->smbd_conn->max_frmr_depth;
 #endif
-	return true;
+	return 0;
 }
 
 /*
@@ -199,31 +193,40 @@ static bool cifs_clamp_length(struct netfs_io_subrequest *subreq)
  * to only read a portion of that, but as long as we read something, the netfs
  * helper will call us again so that we can issue another read.
  */
-static void cifs_req_issue_read(struct netfs_io_subrequest *subreq)
+static void cifs_issue_read(struct netfs_io_subrequest *subreq)
 {
 	struct netfs_io_request *rreq = subreq->rreq;
 	struct cifs_io_subrequest *rdata = container_of(subreq, struct cifs_io_subrequest, subreq);
 	struct cifs_io_request *req = container_of(subreq->rreq, struct cifs_io_request, rreq);
+	struct TCP_Server_Info *server = req->server;
 	int rc = 0;
 
 	cifs_dbg(FYI, "%s: op=%08x[%x] mapping=%p len=%zu/%zu\n",
 		 __func__, rreq->debug_id, subreq->debug_index, rreq->mapping,
 		 subreq->transferred, subreq->len);
 
+	rc = adjust_credits(server, rdata, cifs_trace_rw_credits_issue_read_adjust);
+	if (rc)
+		goto failed;
+
 	if (req->cfile->invalidHandle) {
 		do {
 			rc = cifs_reopen_file(req->cfile, true);
 		} while (rc == -EAGAIN);
 		if (rc)
-			goto out;
+			goto failed;
 	}
 
 	__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
 
+	trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
 	rc = rdata->server->ops->async_readv(rdata);
-out:
 	if (rc)
-		netfs_subreq_terminated(subreq, rc, false);
+		goto failed;
+	return;
+
+failed:
+	netfs_read_subreq_terminated(subreq, rc, false);
 }
 
 /*
@@ -330,8 +333,8 @@ const struct netfs_request_ops cifs_req_ops = {
 	.init_request		= cifs_init_request,
 	.free_request		= cifs_free_request,
 	.free_subrequest	= cifs_free_subrequest,
-	.clamp_length		= cifs_clamp_length,
-	.issue_read		= cifs_req_issue_read,
+	.prepare_read		= cifs_prepare_read,
+	.issue_read		= cifs_issue_read,
 	.done			= cifs_rreq_done,
 	.begin_writeback	= cifs_begin_writeback,
 	.prepare_write		= cifs_prepare_write,
diff --git a/fs/smb/client/smb2pdu.c b/fs/smb/client/smb2pdu.c
index 9a06b5594669..dbc9e69ad223 100644
--- a/fs/smb/client/smb2pdu.c
+++ b/fs/smb/client/smb2pdu.c
@@ -4495,9 +4495,7 @@ static void smb2_readv_worker(struct work_struct *work)
 	struct cifs_io_subrequest *rdata =
 		container_of(work, struct cifs_io_subrequest, subreq.work);
 
-	netfs_subreq_terminated(&rdata->subreq,
-				(rdata->result == 0 || rdata->result == -EAGAIN) ?
-				rdata->got_bytes : rdata->result, true);
+	netfs_read_subreq_terminated(&rdata->subreq, rdata->result, false);
 }
 
 static void
@@ -4551,6 +4549,7 @@ smb2_readv_callback(struct mid_q_entry *mid)
 		break;
 	case MID_REQUEST_SUBMITTED:
 	case MID_RETRY_NEEDED:
+		__set_bit(NETFS_SREQ_NEED_RETRY, &rdata->subreq.flags);
 		rdata->result = -EAGAIN;
 		if (server->sign && rdata->got_bytes)
 			/* reset bytes number since we can not check a sign */
@@ -4604,6 +4603,10 @@ smb2_readv_callback(struct mid_q_entry *mid)
 			      server->credits, server->in_flight,
 			      0, cifs_trace_rw_credits_read_response_clear);
 	rdata->credits.value = 0;
+	rdata->subreq.transferred += rdata->got_bytes;
+	if (rdata->subreq.start + rdata->subreq.transferred >= rdata->subreq.rreq->i_size)
+		__set_bit(NETFS_SREQ_HIT_EOF, &rdata->subreq.flags);
+	trace_netfs_sreq(&rdata->subreq, netfs_sreq_trace_io_progress);
 	INIT_WORK(&rdata->subreq.work, smb2_readv_worker);
 	queue_work(cifsiod_wq, &rdata->subreq.work);
 	release_mid(mid);
@@ -4867,6 +4870,7 @@ smb2_writev_callback(struct mid_q_entry *mid)
 			      server->credits, server->in_flight,
 			      0, cifs_trace_rw_credits_write_response_clear);
 	wdata->credits.value = 0;
+	trace_netfs_sreq(&wdata->subreq, netfs_sreq_trace_io_progress);
 	cifs_write_subrequest_terminated(wdata, result ?: written, true);
 	release_mid(mid);
 	trace_smb3_rw_credits(rreq_debug_id, subreq_debug_index, 0,
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index c47753a24623..be1686f0fe34 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -180,20 +180,26 @@ struct netfs_io_subrequest {
 	unsigned long long	start;		/* Where to start the I/O */
 	size_t			len;		/* Size of the I/O */
 	size_t			transferred;	/* Amount of data transferred */
+	size_t			consumed;	/* Amount of read data consumed */
+	size_t			prev_donated;	/* Amount of data donated from previous subreq */
+	size_t			next_donated;	/* Amount of data donated from next subreq */
 	refcount_t		ref;
 	short			error;		/* 0 or error that occurred */
 	unsigned short		debug_index;	/* Index in list (for debugging output) */
 	unsigned int		nr_segs;	/* Number of segs in io_iter */
 	enum netfs_io_source	source;		/* Where to read from/write to */
 	unsigned char		stream_nr;	/* I/O stream this belongs to */
+	unsigned char		curr_folioq_slot; /* Folio currently being read */
+	unsigned char		curr_folio_order; /* Order of folio */
+	struct folio_queue	*curr_folioq;	/* Queue segment in which current folio resides */
 	unsigned long		flags;
 #define NETFS_SREQ_COPY_TO_CACHE	0	/* Set if should copy the data to the cache */
 #define NETFS_SREQ_CLEAR_TAIL		1	/* Set if the rest of the read should be cleared */
-#define NETFS_SREQ_SHORT_IO		2	/* Set if the I/O was short */
 #define NETFS_SREQ_SEEK_DATA_READ	3	/* Set if ->read() should SEEK_DATA first */
 #define NETFS_SREQ_NO_PROGRESS		4	/* Set if we didn't manage to read any data */
 #define NETFS_SREQ_ONDEMAND		5	/* Set if it's from on-demand read mode */
 #define NETFS_SREQ_BOUNDARY		6	/* Set if ends on hard boundary (eg. ceph object) */
+#define NETFS_SREQ_HIT_EOF		7	/* Set if short due to EOF */
 #define NETFS_SREQ_IN_PROGRESS		8	/* Unlocked when the subrequest completes */
 #define NETFS_SREQ_NEED_RETRY		9	/* Set if the filesystem requests a retry */
 #define NETFS_SREQ_RETRYING		10	/* Set if we're retrying */
@@ -203,6 +209,7 @@ struct netfs_io_subrequest {
 enum netfs_io_origin {
 	NETFS_READAHEAD,		/* This read was triggered by readahead */
 	NETFS_READPAGE,			/* This read is a synchronous read */
+	NETFS_READ_GAPS,		/* This read is a synchronous read to fill gaps */
 	NETFS_READ_FOR_WRITE,		/* This read is to prepare a write */
 	NETFS_DIO_READ,			/* This is a direct I/O read */
 	NETFS_WRITEBACK,		/* This write was triggered by writepages */
@@ -225,6 +232,7 @@ struct netfs_io_request {
 	struct address_space	*mapping;	/* The mapping being accessed */
 	struct kiocb		*iocb;		/* AIO completion vector */
 	struct netfs_cache_resources cache_resources;
+	struct readahead_control *ractl;	/* Readahead descriptor */
 	struct list_head	proc_link;	/* Link in netfs_iorequests */
 	struct list_head	subrequests;	/* Contributory I/O operations */
 	struct netfs_io_stream	io_streams[2];	/* Streams of parallel I/O operations */
@@ -245,12 +253,10 @@ struct netfs_io_request {
 	unsigned int		nr_group_rel;	/* Number of refs to release on ->group */
 	spinlock_t		lock;		/* Lock for queuing subreqs */
 	atomic_t		nr_outstanding;	/* Number of ops in progress */
-	atomic_t		nr_copy_ops;	/* Number of copy-to-cache ops in progress */
-	size_t			upper_len;	/* Length can be extended to here */
 	unsigned long long	submitted;	/* Amount submitted for I/O so far */
 	unsigned long long	len;		/* Length of the request */
 	size_t			transferred;	/* Amount to be indicated as transferred */
-	short			error;		/* 0 or error that occurred */
+	long			error;		/* 0 or error that occurred */
 	enum netfs_io_origin	origin;		/* Origin of the request */
 	bool			direct_bv_unpin; /* T if direct_bv[] must be unpinned */
 	u8			buffer_head_slot; /* First slot in ->buffer */
@@ -261,9 +267,9 @@ struct netfs_io_request {
 	unsigned long long	collected_to;	/* Point we've collected to */
 	unsigned long long	cleaned_to;	/* Position we've cleaned folios to */
 	pgoff_t			no_unlock_folio; /* Don't unlock this folio after read */
+	size_t			prev_donated;	/* Fallback for subreq->prev_donated */
 	refcount_t		ref;
 	unsigned long		flags;
-#define NETFS_RREQ_INCOMPLETE_IO	0	/* Some ioreqs terminated short or with error */
 #define NETFS_RREQ_COPY_TO_CACHE	1	/* Need to write to the cache */
 #define NETFS_RREQ_NO_UNLOCK_FOLIO	2	/* Don't unlock no_unlock_folio on completion */
 #define NETFS_RREQ_DONT_UNLOCK_FOLIOS	3	/* Don't unlock the folios on completion */
@@ -276,6 +282,7 @@ struct netfs_io_request {
 #define NETFS_RREQ_PAUSE		11	/* Pause subrequest generation */
 #define NETFS_RREQ_USE_IO_ITER		12	/* Use ->io_iter rather than ->i_pages */
 #define NETFS_RREQ_ALL_QUEUED		13	/* All subreqs are now queued */
+#define NETFS_RREQ_NEED_RETRY		14	/* Need to try retrying */
 #define NETFS_RREQ_USE_PGPRIV2		31	/* [DEPRECATED] Use PG_private_2 to mark
 						 * write to cache on read */
 	const struct netfs_request_ops *netfs_ops;
@@ -294,7 +301,7 @@ struct netfs_request_ops {
 
 	/* Read request handling */
 	void (*expand_readahead)(struct netfs_io_request *rreq);
-	bool (*clamp_length)(struct netfs_io_subrequest *subreq);
+	int (*prepare_read)(struct netfs_io_subrequest *subreq);
 	void (*issue_read)(struct netfs_io_subrequest *subreq);
 	bool (*is_still_valid)(struct netfs_io_request *rreq);
 	int (*check_write_begin)(struct file *file, loff_t pos, unsigned len,
@@ -424,7 +431,10 @@ bool netfs_release_folio(struct folio *folio, gfp_t gfp);
 vm_fault_t netfs_page_mkwrite(struct vm_fault *vmf, struct netfs_group *netfs_group);
 
 /* (Sub)request management API. */
-void netfs_subreq_terminated(struct netfs_io_subrequest *, ssize_t, bool);
+void netfs_read_subreq_progress(struct netfs_io_subrequest *subreq,
+				bool was_async);
+void netfs_read_subreq_terminated(struct netfs_io_subrequest *subreq,
+				  int error, bool was_async);
 void netfs_get_subrequest(struct netfs_io_subrequest *subreq,
 			  enum netfs_sreq_ref_trace what);
 void netfs_put_subrequest(struct netfs_io_subrequest *subreq,
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index 065fa168f964..4ac3b5d56ebd 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -20,6 +20,7 @@
 	EM(netfs_read_trace_expanded,		"EXPANDED ")	\
 	EM(netfs_read_trace_readahead,		"READAHEAD")	\
 	EM(netfs_read_trace_readpage,		"READPAGE ")	\
+	EM(netfs_read_trace_read_gaps,		"READ-GAPS")	\
 	EM(netfs_read_trace_prefetch_for_write,	"PREFETCHW")	\
 	E_(netfs_read_trace_write_begin,	"WRITEBEGN")
 
@@ -33,6 +34,7 @@
 #define netfs_rreq_origins					\
 	EM(NETFS_READAHEAD,			"RA")		\
 	EM(NETFS_READPAGE,			"RP")		\
+	EM(NETFS_READ_GAPS,			"RG")		\
 	EM(NETFS_READ_FOR_WRITE,		"RW")		\
 	EM(NETFS_DIO_READ,			"DR")		\
 	EM(NETFS_WRITEBACK,			"WB")		\
@@ -68,15 +70,25 @@
 	E_(NETFS_INVALID_WRITE,			"INVL")
 
 #define netfs_sreq_traces					\
+	EM(netfs_sreq_trace_add_donations,	"+DON ")	\
+	EM(netfs_sreq_trace_added,		"ADD  ")	\
+	EM(netfs_sreq_trace_clear,		"CLEAR")	\
 	EM(netfs_sreq_trace_discard,		"DSCRD")	\
+	EM(netfs_sreq_trace_donate_to_prev,	"DON-P")	\
+	EM(netfs_sreq_trace_donate_to_next,	"DON-N")	\
 	EM(netfs_sreq_trace_download_instead,	"RDOWN")	\
 	EM(netfs_sreq_trace_fail,		"FAIL ")	\
 	EM(netfs_sreq_trace_free,		"FREE ")	\
+	EM(netfs_sreq_trace_hit_eof,		"EOF  ")	\
+	EM(netfs_sreq_trace_io_progress,	"IO   ")	\
 	EM(netfs_sreq_trace_limited,		"LIMIT")	\
 	EM(netfs_sreq_trace_prepare,		"PREP ")	\
 	EM(netfs_sreq_trace_prep_failed,	"PRPFL")	\
-	EM(netfs_sreq_trace_resubmit_short,	"SHORT")	\
+	EM(netfs_sreq_trace_progress,		"PRGRS")	\
+	EM(netfs_sreq_trace_reprep_failed,	"REPFL")	\
 	EM(netfs_sreq_trace_retry,		"RETRY")	\
+	EM(netfs_sreq_trace_short,		"SHORT")	\
+	EM(netfs_sreq_trace_split,		"SPLIT")	\
 	EM(netfs_sreq_trace_submit,		"SUBMT")	\
 	EM(netfs_sreq_trace_terminated,		"TERM ")	\
 	EM(netfs_sreq_trace_write,		"WRITE")	\
@@ -117,7 +129,7 @@
 	EM(netfs_sreq_trace_new,		"NEW        ")	\
 	EM(netfs_sreq_trace_put_cancel,		"PUT CANCEL ")	\
 	EM(netfs_sreq_trace_put_clear,		"PUT CLEAR  ")	\
-	EM(netfs_sreq_trace_put_discard,	"PUT DISCARD")	\
+	EM(netfs_sreq_trace_put_consumed,	"PUT CONSUME")	\
 	EM(netfs_sreq_trace_put_done,		"PUT DONE   ")	\
 	EM(netfs_sreq_trace_put_failed,		"PUT FAILED ")	\
 	EM(netfs_sreq_trace_put_merged,		"PUT MERGED ")	\
@@ -137,6 +149,7 @@
 	EM(netfs_flush_content,			"flush")	\
 	EM(netfs_streaming_filled_page,		"mod-streamw-f") \
 	EM(netfs_streaming_cont_filled_page,	"mod-streamw-f+") \
+	EM(netfs_folio_trace_abandon,		"abandon")	\
 	EM(netfs_folio_trace_cancel_copy,	"cancel-copy")	\
 	EM(netfs_folio_trace_clear,		"clear")	\
 	EM(netfs_folio_trace_clear_cc,		"clear-cc")	\
@@ -152,7 +165,10 @@
 	EM(netfs_folio_trace_mkwrite_plus,	"mkwrite+")	\
 	EM(netfs_folio_trace_not_under_wback,	"!wback")	\
 	EM(netfs_folio_trace_put,		"put")		\
+	EM(netfs_folio_trace_read,		"read")		\
+	EM(netfs_folio_trace_read_done,		"read-done")	\
 	EM(netfs_folio_trace_read_gaps,		"read-gaps")	\
+	EM(netfs_folio_trace_read_put,		"read-put")	\
 	EM(netfs_folio_trace_redirtied,		"redirtied")	\
 	EM(netfs_folio_trace_store,		"store")	\
 	EM(netfs_folio_trace_store_copy,	"store-copy")	\
@@ -165,6 +181,12 @@
 	EM(netfs_contig_trace_jump,		"-->JUMP-->")	\
 	E_(netfs_contig_trace_unlock,		"Unlock")
 
+#define netfs_donate_traces					\
+	EM(netfs_trace_donate_tail_to_prev,	"tail-to-prev")	\
+	EM(netfs_trace_donate_to_prev,		"to-prev")	\
+	EM(netfs_trace_donate_to_next,		"to-next")	\
+	E_(netfs_trace_donate_to_deferred_next,	"defer-next")
+
 #ifndef __NETFS_DECLARE_TRACE_ENUMS_ONCE_ONLY
 #define __NETFS_DECLARE_TRACE_ENUMS_ONCE_ONLY
 
@@ -182,6 +204,7 @@ enum netfs_rreq_ref_trace { netfs_rreq_ref_traces } __mode(byte);
 enum netfs_sreq_ref_trace { netfs_sreq_ref_traces } __mode(byte);
 enum netfs_folio_trace { netfs_folio_traces } __mode(byte);
 enum netfs_collect_contig_trace { netfs_collect_contig_traces } __mode(byte);
+enum netfs_donate_trace { netfs_donate_traces } __mode(byte);
 
 #endif
 
@@ -204,6 +227,7 @@ netfs_rreq_ref_traces;
 netfs_sreq_ref_traces;
 netfs_folio_traces;
 netfs_collect_contig_traces;
+netfs_donate_traces;
 
 /*
  * Now redefine the EM() and E_() macros to map the enums to the strings that
@@ -224,6 +248,7 @@ TRACE_EVENT(netfs_read,
 	    TP_STRUCT__entry(
 		    __field(unsigned int,		rreq		)
 		    __field(unsigned int,		cookie		)
+		    __field(loff_t,			i_size		)
 		    __field(loff_t,			start		)
 		    __field(size_t,			len		)
 		    __field(enum netfs_read_trace,	what		)
@@ -233,18 +258,19 @@ TRACE_EVENT(netfs_read,
 	    TP_fast_assign(
 		    __entry->rreq	= rreq->debug_id;
 		    __entry->cookie	= rreq->cache_resources.debug_id;
+		    __entry->i_size	= rreq->i_size;
 		    __entry->start	= start;
 		    __entry->len	= len;
 		    __entry->what	= what;
 		    __entry->netfs_inode = rreq->inode->i_ino;
 			   ),
 
-	    TP_printk("R=%08x %s c=%08x ni=%x s=%llx %zx",
+	    TP_printk("R=%08x %s c=%08x ni=%x s=%llx l=%zx sz=%llx",
 		      __entry->rreq,
 		      __print_symbolic(__entry->what, netfs_read_traces),
 		      __entry->cookie,
 		      __entry->netfs_inode,
-		      __entry->start, __entry->len)
+		      __entry->start, __entry->len, __entry->i_size)
 	    );
 
 TRACE_EVENT(netfs_rreq,
@@ -649,6 +675,71 @@ TRACE_EVENT(netfs_collect_stream,
 		      __entry->collected_to, __entry->front)
 	    );
 
+TRACE_EVENT(netfs_progress,
+	    TP_PROTO(const struct netfs_io_subrequest *subreq,
+		     unsigned long long start, size_t avail, size_t part),
+
+	    TP_ARGS(subreq, start, avail, part),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,		rreq)
+		    __field(unsigned int,		subreq)
+		    __field(unsigned int,		consumed)
+		    __field(unsigned int,		transferred)
+		    __field(unsigned long long,		f_start)
+		    __field(unsigned int,		f_avail)
+		    __field(unsigned int,		f_part)
+		    __field(unsigned char,		slot)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->rreq	= subreq->rreq->debug_id;
+		    __entry->subreq	= subreq->debug_index;
+		    __entry->consumed	= subreq->consumed;
+		    __entry->transferred = subreq->transferred;
+		    __entry->f_start	= start;
+		    __entry->f_avail	= avail;
+		    __entry->f_part	= part;
+		    __entry->slot	= subreq->curr_folioq_slot;
+			   ),
+
+	    TP_printk("R=%08x[%02x] s=%llx ct=%x/%x pa=%x/%x sl=%x",
+		      __entry->rreq, __entry->subreq, __entry->f_start,
+		      __entry->consumed, __entry->transferred,
+		      __entry->f_part, __entry->f_avail,  __entry->slot)
+	    );
+
+TRACE_EVENT(netfs_donate,
+	    TP_PROTO(const struct netfs_io_request *rreq,
+		     const struct netfs_io_subrequest *from,
+		     const struct netfs_io_subrequest *to,
+		     size_t amount,
+		     enum netfs_donate_trace trace),
+
+	    TP_ARGS(rreq, from, to, amount, trace),
+
+	    TP_STRUCT__entry(
+		    __field(unsigned int,		rreq)
+		    __field(unsigned int,		from)
+		    __field(unsigned int,		to)
+		    __field(unsigned int,		amount)
+		    __field(enum netfs_donate_trace,	trace)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->rreq	= rreq->debug_id;
+		    __entry->from	= from->debug_index;
+		    __entry->to		= to ? to->debug_index : -1;
+		    __entry->amount	= amount;
+		    __entry->trace	= trace;
+			   ),
+
+	    TP_printk("R=%08x[%02x] -> [%02x] %s am=%x",
+		      __entry->rreq, __entry->from, __entry->to,
+		      __print_symbolic(__entry->trace, netfs_donate_traces),
+		      __entry->amount)
+	    );
+
 #undef EM
 #undef E_
 #endif /* _TRACE_NETFS_H */

[PATCH 19/24] netfs: Remove fs/netfs/io.c

[David Howells]

Remove fs/netfs/io.c as it is no longer used.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/io.c | 645 --------------------------------------------------
 1 file changed, 645 deletions(-)
 delete mode 100644 fs/netfs/io.c

diff --git a/fs/netfs/io.c b/fs/netfs/io.c
deleted file mode 100644
index 874bbf2386a4..000000000000
--- a/fs/netfs/io.c
+++ /dev/null
@@ -1,645 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/* Network filesystem high-level read support.
- *
- * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
- * Written by David Howells (dhowells@redhat.com)
- */
-
-#include <linux/module.h>
-#include <linux/export.h>
-#include <linux/fs.h>
-#include <linux/mm.h>
-#include <linux/pagemap.h>
-#include <linux/slab.h>
-#include <linux/uio.h>
-#include <linux/sched/mm.h>
-#include <linux/task_io_accounting_ops.h>
-#include "internal.h"
-
-/*
- * Clear the unread part of an I/O request.
- */
-static void netfs_clear_unread(struct netfs_io_subrequest *subreq)
-{
-	iov_iter_zero(iov_iter_count(&subreq->io_iter), &subreq->io_iter);
-}
-
-static void netfs_cache_read_terminated(void *priv, ssize_t transferred_or_error,
-					bool was_async)
-{
-	struct netfs_io_subrequest *subreq = priv;
-
-	netfs_subreq_terminated(subreq, transferred_or_error, was_async);
-}
-
-/*
- * Issue a read against the cache.
- * - Eats the caller's ref on subreq.
- */
-static void netfs_read_from_cache(struct netfs_io_request *rreq,
-				  struct netfs_io_subrequest *subreq,
-				  enum netfs_read_from_hole read_hole)
-{
-	struct netfs_cache_resources *cres = &rreq->cache_resources;
-
-	netfs_stat(&netfs_n_rh_read);
-	cres->ops->read(cres, subreq->start, &subreq->io_iter, read_hole,
-			netfs_cache_read_terminated, subreq);
-}
-
-/*
- * Fill a subrequest region with zeroes.
- */
-static void netfs_fill_with_zeroes(struct netfs_io_request *rreq,
-				   struct netfs_io_subrequest *subreq)
-{
-	netfs_stat(&netfs_n_rh_zero);
-	__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
-	netfs_subreq_terminated(subreq, 0, false);
-}
-
-/*
- * Ask the netfs to issue a read request to the server for us.
- *
- * The netfs is expected to read from subreq->pos + subreq->transferred to
- * subreq->pos + subreq->len - 1.  It may not backtrack and write data into the
- * buffer prior to the transferred point as it might clobber dirty data
- * obtained from the cache.
- *
- * Alternatively, the netfs is allowed to indicate one of two things:
- *
- * - NETFS_SREQ_SHORT_READ: A short read - it will get called again to try and
- *   make progress.
- *
- * - NETFS_SREQ_CLEAR_TAIL: A short read - the rest of the buffer will be
- *   cleared.
- */
-static void netfs_read_from_server(struct netfs_io_request *rreq,
-				   struct netfs_io_subrequest *subreq)
-{
-	netfs_stat(&netfs_n_rh_download);
-
-	if (rreq->origin != NETFS_DIO_READ &&
-	    iov_iter_count(&subreq->io_iter) != subreq->len - subreq->transferred)
-		pr_warn("R=%08x[%u] ITER PRE-MISMATCH %zx != %zx-%zx %lx\n",
-			rreq->debug_id, subreq->debug_index,
-			iov_iter_count(&subreq->io_iter), subreq->len,
-			subreq->transferred, subreq->flags);
-	rreq->netfs_ops->issue_read(subreq);
-}
-
-/*
- * Release those waiting.
- */
-static void netfs_rreq_completed(struct netfs_io_request *rreq, bool was_async)
-{
-	trace_netfs_rreq(rreq, netfs_rreq_trace_done);
-	netfs_clear_subrequests(rreq, was_async);
-	netfs_put_request(rreq, was_async, netfs_rreq_trace_put_complete);
-}
-
-/*
- * Handle a short read.
- */
-static void netfs_rreq_short_read(struct netfs_io_request *rreq,
-				  struct netfs_io_subrequest *subreq)
-{
-	__clear_bit(NETFS_SREQ_SHORT_IO, &subreq->flags);
-	__set_bit(NETFS_SREQ_SEEK_DATA_READ, &subreq->flags);
-
-	netfs_stat(&netfs_n_rh_short_read);
-	trace_netfs_sreq(subreq, netfs_sreq_trace_resubmit_short);
-
-	netfs_get_subrequest(subreq, netfs_sreq_trace_get_short_read);
-	atomic_inc(&rreq->nr_outstanding);
-	if (subreq->source == NETFS_READ_FROM_CACHE)
-		netfs_read_from_cache(rreq, subreq, NETFS_READ_HOLE_CLEAR);
-	else
-		netfs_read_from_server(rreq, subreq);
-}
-
-/*
- * Reset the subrequest iterator prior to resubmission.
- */
-static void netfs_reset_subreq_iter(struct netfs_io_request *rreq,
-				    struct netfs_io_subrequest *subreq)
-{
-	size_t remaining = subreq->len - subreq->transferred;
-	size_t count = iov_iter_count(&subreq->io_iter);
-
-	if (count == remaining)
-		return;
-
-	_debug("R=%08x[%u] ITER RESUB-MISMATCH %zx != %zx-%zx-%llx %x\n",
-	       rreq->debug_id, subreq->debug_index,
-	       iov_iter_count(&subreq->io_iter), subreq->transferred,
-	       subreq->len, rreq->i_size,
-	       subreq->io_iter.iter_type);
-
-	if (count < remaining)
-		iov_iter_revert(&subreq->io_iter, remaining - count);
-	else
-		iov_iter_advance(&subreq->io_iter, count - remaining);
-}
-
-/*
- * Resubmit any short or failed operations.  Returns true if we got the rreq
- * ref back.
- */
-static bool netfs_rreq_perform_resubmissions(struct netfs_io_request *rreq)
-{
-	struct netfs_io_subrequest *subreq;
-
-	WARN_ON(in_interrupt());
-
-	trace_netfs_rreq(rreq, netfs_rreq_trace_resubmit);
-
-	/* We don't want terminating submissions trying to wake us up whilst
-	 * we're still going through the list.
-	 */
-	atomic_inc(&rreq->nr_outstanding);
-
-	__clear_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags);
-	list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
-		if (subreq->error) {
-			if (subreq->source != NETFS_READ_FROM_CACHE)
-				break;
-			subreq->source = NETFS_DOWNLOAD_FROM_SERVER;
-			subreq->error = 0;
-			netfs_stat(&netfs_n_rh_download_instead);
-			trace_netfs_sreq(subreq, netfs_sreq_trace_download_instead);
-			netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit);
-			atomic_inc(&rreq->nr_outstanding);
-			netfs_reset_subreq_iter(rreq, subreq);
-			netfs_read_from_server(rreq, subreq);
-		} else if (test_bit(NETFS_SREQ_SHORT_IO, &subreq->flags)) {
-			netfs_rreq_short_read(rreq, subreq);
-		}
-	}
-
-	/* If we decrement nr_outstanding to 0, the usage ref belongs to us. */
-	if (atomic_dec_and_test(&rreq->nr_outstanding))
-		return true;
-
-	wake_up_var(&rreq->nr_outstanding);
-	return false;
-}
-
-/*
- * Check to see if the data read is still valid.
- */
-static void netfs_rreq_is_still_valid(struct netfs_io_request *rreq)
-{
-	struct netfs_io_subrequest *subreq;
-
-	if (!rreq->netfs_ops->is_still_valid ||
-	    rreq->netfs_ops->is_still_valid(rreq))
-		return;
-
-	list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
-		if (subreq->source == NETFS_READ_FROM_CACHE) {
-			subreq->error = -ESTALE;
-			__set_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags);
-		}
-	}
-}
-
-/*
- * Determine how much we can admit to having read from a DIO read.
- */
-static void netfs_rreq_assess_dio(struct netfs_io_request *rreq)
-{
-	struct netfs_io_subrequest *subreq;
-	unsigned int i;
-	size_t transferred = 0;
-
-	for (i = 0; i < rreq->direct_bv_count; i++) {
-		flush_dcache_page(rreq->direct_bv[i].bv_page);
-		// TODO: cifs marks pages in the destination buffer
-		// dirty under some circumstances after a read.  Do we
-		// need to do that too?
-		set_page_dirty(rreq->direct_bv[i].bv_page);
-	}
-
-	list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
-		if (subreq->error || subreq->transferred == 0)
-			break;
-		transferred += subreq->transferred;
-		if (subreq->transferred < subreq->len)
-			break;
-	}
-
-	for (i = 0; i < rreq->direct_bv_count; i++)
-		flush_dcache_page(rreq->direct_bv[i].bv_page);
-
-	rreq->transferred = transferred;
-	task_io_account_read(transferred);
-
-	if (rreq->iocb) {
-		rreq->iocb->ki_pos += transferred;
-		if (rreq->iocb->ki_complete)
-			rreq->iocb->ki_complete(
-				rreq->iocb, rreq->error ? rreq->error : transferred);
-	}
-	if (rreq->netfs_ops->done)
-		rreq->netfs_ops->done(rreq);
-	inode_dio_end(rreq->inode);
-}
-
-/*
- * Assess the state of a read request and decide what to do next.
- *
- * Note that we could be in an ordinary kernel thread, on a workqueue or in
- * softirq context at this point.  We inherit a ref from the caller.
- */
-static void netfs_rreq_assess(struct netfs_io_request *rreq, bool was_async)
-{
-	trace_netfs_rreq(rreq, netfs_rreq_trace_assess);
-
-again:
-	netfs_rreq_is_still_valid(rreq);
-
-	if (!test_bit(NETFS_RREQ_FAILED, &rreq->flags) &&
-	    test_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags)) {
-		if (netfs_rreq_perform_resubmissions(rreq))
-			goto again;
-		return;
-	}
-
-	if (rreq->origin != NETFS_DIO_READ)
-		netfs_rreq_unlock_folios(rreq);
-	else
-		netfs_rreq_assess_dio(rreq);
-
-	trace_netfs_rreq(rreq, netfs_rreq_trace_wake_ip);
-	clear_bit_unlock(NETFS_RREQ_IN_PROGRESS, &rreq->flags);
-	wake_up_bit(&rreq->flags, NETFS_RREQ_IN_PROGRESS);
-
-	netfs_rreq_completed(rreq, was_async);
-}
-
-void netfs_rreq_work(struct work_struct *work)
-{
-	struct netfs_io_request *rreq =
-		container_of(work, struct netfs_io_request, work);
-	netfs_rreq_assess(rreq, false);
-}
-
-/*
- * Handle the completion of all outstanding I/O operations on a read request.
- * We inherit a ref from the caller.
- */
-static void netfs_rreq_terminated(struct netfs_io_request *rreq,
-				  bool was_async)
-{
-	if (test_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags) &&
-	    was_async) {
-		if (!queue_work(system_unbound_wq, &rreq->work))
-			BUG();
-	} else {
-		netfs_rreq_assess(rreq, was_async);
-	}
-}
-
-/**
- * netfs_subreq_terminated - Note the termination of an I/O operation.
- * @subreq: The I/O request that has terminated.
- * @transferred_or_error: The amount of data transferred or an error code.
- * @was_async: The termination was asynchronous
- *
- * This tells the read helper that a contributory I/O operation has terminated,
- * one way or another, and that it should integrate the results.
- *
- * The caller indicates in @transferred_or_error the outcome of the operation,
- * supplying a positive value to indicate the number of bytes transferred, 0 to
- * indicate a failure to transfer anything that should be retried or a negative
- * error code.  The helper will look after reissuing I/O operations as
- * appropriate and writing downloaded data to the cache.
- *
- * If @was_async is true, the caller might be running in softirq or interrupt
- * context and we can't sleep.
- */
-void netfs_subreq_terminated(struct netfs_io_subrequest *subreq,
-			     ssize_t transferred_or_error,
-			     bool was_async)
-{
-	struct netfs_io_request *rreq = subreq->rreq;
-	int u;
-
-	_enter("R=%x[%x]{%llx,%lx},%zd",
-	       rreq->debug_id, subreq->debug_index,
-	       subreq->start, subreq->flags, transferred_or_error);
-
-	switch (subreq->source) {
-	case NETFS_READ_FROM_CACHE:
-		netfs_stat(&netfs_n_rh_read_done);
-		break;
-	case NETFS_DOWNLOAD_FROM_SERVER:
-		netfs_stat(&netfs_n_rh_download_done);
-		break;
-	default:
-		break;
-	}
-
-	if (IS_ERR_VALUE(transferred_or_error)) {
-		subreq->error = transferred_or_error;
-		trace_netfs_failure(rreq, subreq, transferred_or_error,
-				    netfs_fail_read);
-		goto failed;
-	}
-
-	if (WARN(transferred_or_error > subreq->len - subreq->transferred,
-		 "Subreq overread: R%x[%x] %zd > %zu - %zu",
-		 rreq->debug_id, subreq->debug_index,
-		 transferred_or_error, subreq->len, subreq->transferred))
-		transferred_or_error = subreq->len - subreq->transferred;
-
-	subreq->error = 0;
-	subreq->transferred += transferred_or_error;
-	if (subreq->transferred < subreq->len)
-		goto incomplete;
-
-complete:
-	__clear_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags);
-	if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags))
-		set_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags);
-
-out:
-	trace_netfs_sreq(subreq, netfs_sreq_trace_terminated);
-
-	/* If we decrement nr_outstanding to 0, the ref belongs to us. */
-	u = atomic_dec_return(&rreq->nr_outstanding);
-	if (u == 0)
-		netfs_rreq_terminated(rreq, was_async);
-	else if (u == 1)
-		wake_up_var(&rreq->nr_outstanding);
-
-	netfs_put_subrequest(subreq, was_async, netfs_sreq_trace_put_terminated);
-	return;
-
-incomplete:
-	if (test_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags)) {
-		netfs_clear_unread(subreq);
-		subreq->transferred = subreq->len;
-		goto complete;
-	}
-
-	if (transferred_or_error == 0) {
-		if (__test_and_set_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags)) {
-			subreq->error = -ENODATA;
-			goto failed;
-		}
-	} else {
-		__clear_bit(NETFS_SREQ_NO_PROGRESS, &subreq->flags);
-	}
-
-	__set_bit(NETFS_SREQ_SHORT_IO, &subreq->flags);
-	set_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags);
-	goto out;
-
-failed:
-	if (subreq->source == NETFS_READ_FROM_CACHE) {
-		netfs_stat(&netfs_n_rh_read_failed);
-		set_bit(NETFS_RREQ_INCOMPLETE_IO, &rreq->flags);
-	} else {
-		netfs_stat(&netfs_n_rh_download_failed);
-		set_bit(NETFS_RREQ_FAILED, &rreq->flags);
-		rreq->error = subreq->error;
-	}
-	goto out;
-}
-EXPORT_SYMBOL(netfs_subreq_terminated);
-
-static enum netfs_io_source netfs_cache_prepare_read(struct netfs_io_subrequest *subreq,
-						       loff_t i_size)
-{
-	struct netfs_io_request *rreq = subreq->rreq;
-	struct netfs_cache_resources *cres = &rreq->cache_resources;
-
-	if (cres->ops)
-		return cres->ops->prepare_read(subreq, i_size);
-	if (subreq->start >= rreq->i_size)
-		return NETFS_FILL_WITH_ZEROES;
-	return NETFS_DOWNLOAD_FROM_SERVER;
-}
-
-/*
- * Work out what sort of subrequest the next one will be.
- */
-static enum netfs_io_source
-netfs_rreq_prepare_read(struct netfs_io_request *rreq,
-			struct netfs_io_subrequest *subreq,
-			struct iov_iter *io_iter)
-{
-	enum netfs_io_source source = NETFS_DOWNLOAD_FROM_SERVER;
-	struct netfs_inode *ictx = netfs_inode(rreq->inode);
-	size_t lsize;
-
-	_enter("%llx-%llx,%llx", subreq->start, subreq->start + subreq->len, rreq->i_size);
-
-	if (rreq->origin != NETFS_DIO_READ) {
-		source = netfs_cache_prepare_read(subreq, rreq->i_size);
-		if (source == NETFS_INVALID_READ)
-			goto out;
-	}
-
-	if (source == NETFS_DOWNLOAD_FROM_SERVER) {
-		/* Call out to the netfs to let it shrink the request to fit
-		 * its own I/O sizes and boundaries.  If it shinks it here, it
-		 * will be called again to make simultaneous calls; if it wants
-		 * to make serial calls, it can indicate a short read and then
-		 * we will call it again.
-		 */
-		if (rreq->origin != NETFS_DIO_READ) {
-			if (subreq->start >= ictx->zero_point) {
-				source = NETFS_FILL_WITH_ZEROES;
-				goto set;
-			}
-			if (subreq->len > ictx->zero_point - subreq->start)
-				subreq->len = ictx->zero_point - subreq->start;
-		}
-		if (subreq->len > rreq->i_size - subreq->start)
-			subreq->len = rreq->i_size - subreq->start;
-		if (rreq->rsize && subreq->len > rreq->rsize)
-			subreq->len = rreq->rsize;
-
-		if (rreq->netfs_ops->clamp_length &&
-		    !rreq->netfs_ops->clamp_length(subreq)) {
-			source = NETFS_INVALID_READ;
-			goto out;
-		}
-
-		if (rreq->io_streams[0].sreq_max_segs) {
-			lsize = netfs_limit_iter(io_iter, 0, subreq->len,
-						 rreq->io_streams[0].sreq_max_segs);
-			if (subreq->len > lsize) {
-				subreq->len = lsize;
-				trace_netfs_sreq(subreq, netfs_sreq_trace_limited);
-			}
-		}
-	}
-
-set:
-	if (subreq->len > rreq->len)
-		pr_warn("R=%08x[%u] SREQ>RREQ %zx > %llx\n",
-			rreq->debug_id, subreq->debug_index,
-			subreq->len, rreq->len);
-
-	if (WARN_ON(subreq->len == 0)) {
-		source = NETFS_INVALID_READ;
-		goto out;
-	}
-
-	subreq->source = source;
-	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
-
-	subreq->io_iter = *io_iter;
-	iov_iter_truncate(&subreq->io_iter, subreq->len);
-	iov_iter_advance(io_iter, subreq->len);
-out:
-	subreq->source = source;
-	trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
-	return source;
-}
-
-/*
- * Slice off a piece of a read request and submit an I/O request for it.
- */
-static bool netfs_rreq_submit_slice(struct netfs_io_request *rreq,
-				    struct iov_iter *io_iter)
-{
-	struct netfs_io_subrequest *subreq;
-	enum netfs_io_source source;
-
-	subreq = netfs_alloc_subrequest(rreq);
-	if (!subreq)
-		return false;
-
-	subreq->start		= rreq->start + rreq->submitted;
-	subreq->len		= io_iter->count;
-
-	_debug("slice %llx,%zx,%llx", subreq->start, subreq->len, rreq->submitted);
-	list_add_tail(&subreq->rreq_link, &rreq->subrequests);
-
-	/* Call out to the cache to find out what it can do with the remaining
-	 * subset.  It tells us in subreq->flags what it decided should be done
-	 * and adjusts subreq->len down if the subset crosses a cache boundary.
-	 *
-	 * Then when we hand the subset, it can choose to take a subset of that
-	 * (the starts must coincide), in which case, we go around the loop
-	 * again and ask it to download the next piece.
-	 */
-	source = netfs_rreq_prepare_read(rreq, subreq, io_iter);
-	if (source == NETFS_INVALID_READ)
-		goto subreq_failed;
-
-	atomic_inc(&rreq->nr_outstanding);
-
-	rreq->submitted += subreq->len;
-
-	trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
-	switch (source) {
-	case NETFS_FILL_WITH_ZEROES:
-		netfs_fill_with_zeroes(rreq, subreq);
-		break;
-	case NETFS_DOWNLOAD_FROM_SERVER:
-		netfs_read_from_server(rreq, subreq);
-		break;
-	case NETFS_READ_FROM_CACHE:
-		netfs_read_from_cache(rreq, subreq, NETFS_READ_HOLE_IGNORE);
-		break;
-	default:
-		BUG();
-	}
-
-	return true;
-
-subreq_failed:
-	rreq->error = subreq->error;
-	netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_failed);
-	return false;
-}
-
-/*
- * Begin the process of reading in a chunk of data, where that data may be
- * stitched together from multiple sources, including multiple servers and the
- * local cache.
- */
-int netfs_begin_read(struct netfs_io_request *rreq, bool sync)
-{
-	struct iov_iter io_iter;
-	int ret;
-
-	_enter("R=%x %llx-%llx",
-	       rreq->debug_id, rreq->start, rreq->start + rreq->len - 1);
-
-	if (rreq->len == 0) {
-		pr_err("Zero-sized read [R=%x]\n", rreq->debug_id);
-		return -EIO;
-	}
-
-	if (rreq->origin == NETFS_DIO_READ)
-		inode_dio_begin(rreq->inode);
-
-	// TODO: Use bounce buffer if requested
-	rreq->io_iter = rreq->iter;
-
-	/* Chop the read into slices according to what the cache and the netfs
-	 * want and submit each one.
-	 */
-	netfs_get_request(rreq, netfs_rreq_trace_get_for_outstanding);
-	atomic_set(&rreq->nr_outstanding, 1);
-	io_iter = rreq->io_iter;
-	do {
-		_debug("submit %llx + %llx >= %llx",
-		       rreq->start, rreq->submitted, rreq->i_size);
-		if (rreq->origin == NETFS_DIO_READ &&
-		    rreq->start + rreq->submitted >= rreq->i_size)
-			break;
-		if (!netfs_rreq_submit_slice(rreq, &io_iter))
-			break;
-		if (test_bit(NETFS_RREQ_BLOCKED, &rreq->flags) &&
-		    test_bit(NETFS_RREQ_NONBLOCK, &rreq->flags))
-			break;
-
-	} while (rreq->submitted < rreq->len);
-
-	if (!rreq->submitted) {
-		netfs_put_request(rreq, false, netfs_rreq_trace_put_no_submit);
-		if (rreq->origin == NETFS_DIO_READ)
-			inode_dio_end(rreq->inode);
-		ret = 0;
-		goto out;
-	}
-
-	if (sync) {
-		/* Keep nr_outstanding incremented so that the ref always
-		 * belongs to us, and the service code isn't punted off to a
-		 * random thread pool to process.  Note that this might start
-		 * further work, such as writing to the cache.
-		 */
-		wait_var_event(&rreq->nr_outstanding,
-			       atomic_read(&rreq->nr_outstanding) == 1);
-		if (atomic_dec_and_test(&rreq->nr_outstanding))
-			netfs_rreq_assess(rreq, false);
-
-		trace_netfs_rreq(rreq, netfs_rreq_trace_wait_ip);
-		wait_on_bit(&rreq->flags, NETFS_RREQ_IN_PROGRESS,
-			    TASK_UNINTERRUPTIBLE);
-
-		ret = rreq->error;
-		if (ret == 0 && rreq->submitted < rreq->len &&
-		    rreq->origin != NETFS_DIO_READ) {
-			trace_netfs_failure(rreq, NULL, ret, netfs_fail_short_read);
-			ret = -EIO;
-		}
-	} else {
-		/* If we decrement nr_outstanding to 0, the ref belongs to us. */
-		if (atomic_dec_and_test(&rreq->nr_outstanding))
-			netfs_rreq_assess(rreq, false);
-		ret = -EIOCBQUEUED;
-	}
-
-out:
-	return ret;
-}

[PATCH 20/24] cachefiles, netfs: Fix write to partial block at EOF

[David Howells]

Because it uses DIO writes, cachefiles is unable to make a write to the
backing file if that write is not aligned to and sized according to the
backing file's DIO block alignment.  This makes it tricky to handle a write
to the cache where the EOF on the network file is not correctly aligned.

To get around this, netfslib attempts to tell the driver it is calling how
much more data there is available beyond the EOF that it can use to pad the
write (netfslib preclears the part of the folio above the EOF).  However,
it tries to tell the cache what the maximum length is, but doesn't
calculate this correctly; and, in any case, cachefiles actually ignores the
value and just skips the block.

Fix this by:

 (1) Change the value passed to indicate the amount of extra data that can
     be added to the operation (now ->submit_extendable_to).  This is much
     simpler to calculate as it's just the end of the folio minus the top
     of the data within the folio - rather than having to account for data
     spread over multiple folios.

 (2) Make cachefiles add some of this data if the subrequest it is given
     ends at the network file's i_size if the extra data is sufficient to
     pad out to a whole block.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/cachefiles/io.c     | 14 ++++++++++++++
 fs/netfs/write_issue.c |  5 ++---
 include/linux/netfs.h  |  2 +-
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index 5b82ba7785cd..6a821a959b59 100644
--- a/fs/cachefiles/io.c
+++ b/fs/cachefiles/io.c
@@ -648,6 +648,7 @@ static void cachefiles_issue_write(struct netfs_io_subrequest *subreq)
 	struct netfs_cache_resources *cres = &wreq->cache_resources;
 	struct cachefiles_object *object = cachefiles_cres_object(cres);
 	struct cachefiles_cache *cache = object->volume->cache;
+	struct netfs_io_stream *stream = &wreq->io_streams[subreq->stream_nr];
 	const struct cred *saved_cred;
 	size_t off, pre, post, len = subreq->len;
 	loff_t start = subreq->start;
@@ -661,6 +662,7 @@ static void cachefiles_issue_write(struct netfs_io_subrequest *subreq)
 	if (off) {
 		pre = CACHEFILES_DIO_BLOCK_SIZE - off;
 		if (pre >= len) {
+			fscache_count_dio_misfit();
 			netfs_write_subrequest_terminated(subreq, len, false);
 			return;
 		}
@@ -671,10 +673,22 @@ static void cachefiles_issue_write(struct netfs_io_subrequest *subreq)
 	}
 
 	/* We also need to end on the cache granularity boundary */
+	if (start + len == wreq->i_size) {
+		size_t part = len % CACHEFILES_DIO_BLOCK_SIZE;
+		size_t need = CACHEFILES_DIO_BLOCK_SIZE - part;
+
+		if (part && stream->submit_extendable_to >= need) {
+			len += need;
+			subreq->len += need;
+			subreq->io_iter.count += need;
+		}
+	}
+
 	post = len & (CACHEFILES_DIO_BLOCK_SIZE - 1);
 	if (post) {
 		len -= post;
 		if (len == 0) {
+			fscache_count_dio_misfit();
 			netfs_write_subrequest_terminated(subreq, post, false);
 			return;
 		}
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 43cec03c6514..87a5aeb77073 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -280,6 +280,7 @@ static int netfs_advance_write(struct netfs_io_request *wreq,
 	_debug("part %zx/%zx %zx/%zx", subreq->len, stream->sreq_max_len, part, len);
 	subreq->len += part;
 	subreq->nr_segs++;
+	stream->submit_extendable_to -= part;
 
 	if (subreq->len >= stream->sreq_max_len ||
 	    subreq->nr_segs >= stream->sreq_max_segs ||
@@ -421,7 +422,6 @@ static int netfs_write_folio(struct netfs_io_request *wreq,
 	 */
 	for (int s = 0; s < NR_IO_STREAMS; s++) {
 		stream = &wreq->io_streams[s];
-		stream->submit_max_len = fsize;
 		stream->submit_off = foff;
 		stream->submit_len = flen;
 		if ((stream->source == NETFS_WRITE_TO_CACHE && streamw) ||
@@ -429,7 +429,6 @@ static int netfs_write_folio(struct netfs_io_request *wreq,
 		     fgroup == NETFS_FOLIO_COPY_TO_CACHE)) {
 			stream->submit_off = UINT_MAX;
 			stream->submit_len = 0;
-			stream->submit_max_len = 0;
 		}
 	}
 
@@ -459,10 +458,10 @@ static int netfs_write_folio(struct netfs_io_request *wreq,
 		wreq->io_iter.iov_offset = stream->submit_off;
 
 		atomic64_set(&wreq->issued_to, fpos + stream->submit_off);
+		stream->submit_extendable_to = fsize - stream->submit_off;
 		part = netfs_advance_write(wreq, stream, fpos + stream->submit_off,
 					   stream->submit_len, to_eof);
 		stream->submit_off += part;
-		stream->submit_max_len -= part;
 		if (part > stream->submit_len)
 			stream->submit_len = 0;
 		else
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index be1686f0fe34..d34ef6beed62 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -137,7 +137,7 @@ struct netfs_io_stream {
 	unsigned int		sreq_max_segs;	/* 0 or max number of segments in an iterator */
 	unsigned int		submit_off;	/* Folio offset we're submitting from */
 	unsigned int		submit_len;	/* Amount of data left to submit */
-	unsigned int		submit_max_len;	/* Amount I/O can be rounded up to */
+	unsigned int		submit_extendable_to; /* Amount I/O can be rounded up to */
 	void (*prepare_write)(struct netfs_io_subrequest *subreq);
 	void (*issue_write)(struct netfs_io_subrequest *subreq);
 	/* Collection tracking */

[PATCH 21/24] netfs: Cancel dirty folios that have no storage destination

[David Howells]

Kafs wants to be able to cache the contents of directories (and symlinks),
but whilst these are downloaded from the server with the FS.FetchData RPC
op and similar, the same as for regular files, they can't be updated by
FS.StoreData, but rather have special operations (FS.MakeDir, etc.).

Now, rather than redownloading a directory's content after each change made
to that directory, kafs modifies the local blob.  This blob can be saved
out to the cache, and since it's using netfslib, kafs just marks the folios
dirty and lets ->writepages() on the directory take care of it, as for an
regular file.

This is fine as long as there's a cache as although the upload stream is
disabled, there's a cache stream to drive the procedure.  But if the cache
goes away in the meantime, suddenly there's no way do any writes and the
code gets confused, complains "R=%x: No submit" to dmesg and leaves the
dirty folio hanging.

Fix this by just cancelling the store of the folio if neither stream is
active.  (If there's no cache at the time of dirtying, we should just not
mark the folio dirty).

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/write_issue.c       | 6 +++++-
 include/trace/events/netfs.h | 1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 87a5aeb77073..0cd12c86ea91 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -397,13 +397,17 @@ static int netfs_write_folio(struct netfs_io_request *wreq,
 	folio_unlock(folio);
 
 	if (fgroup == NETFS_FOLIO_COPY_TO_CACHE) {
-		if (!fscache_resources_valid(&wreq->cache_resources)) {
+		if (!cache->avail) {
 			trace_netfs_folio(folio, netfs_folio_trace_cancel_copy);
 			netfs_issue_write(wreq, upload);
 			netfs_folio_written_back(folio);
 			return 0;
 		}
 		trace_netfs_folio(folio, netfs_folio_trace_store_copy);
+	} else if (!upload->avail && !cache->avail) {
+		trace_netfs_folio(folio, netfs_folio_trace_cancel_store);
+		netfs_folio_written_back(folio);
+		return 0;
 	} else if (!upload->construct) {
 		trace_netfs_folio(folio, netfs_folio_trace_store);
 	} else {
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
index 4ac3b5d56ebd..1ece47af0b2f 100644
--- a/include/trace/events/netfs.h
+++ b/include/trace/events/netfs.h
@@ -151,6 +151,7 @@
 	EM(netfs_streaming_cont_filled_page,	"mod-streamw-f+") \
 	EM(netfs_folio_trace_abandon,		"abandon")	\
 	EM(netfs_folio_trace_cancel_copy,	"cancel-copy")	\
+	EM(netfs_folio_trace_cancel_store,	"cancel-store")	\
 	EM(netfs_folio_trace_clear,		"clear")	\
 	EM(netfs_folio_trace_clear_cc,		"clear-cc")	\
 	EM(netfs_folio_trace_clear_g,		"clear-g")	\

[PATCH 22/24] cifs: Use iterate_and_advance*() routines directly for hashing

[David Howells]

Replace the bespoke cifs iterators of ITER_BVEC and ITER_KVEC to do hashing
with iterate_and_advance_kernel() - a variant on iterate_and_advance() that
only supports kernel-internal ITER_* types and not UBUF/IOVEC types.

The bespoke ITER_XARRAY is left because we don't really want to be calling
crypto_shash_update() under the RCU read lock for large amounts of data;
besides, ITER_XARRAY is going to be phased out.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Tom Talpey <tom@talpey.com>
cc: Enzo Matsumiya <ematsumiya@suse.de>
cc: linux-cifs@vger.kernel.org
---
 fs/smb/client/cifsencrypt.c | 109 ++++++++----------------------------
 include/linux/iov_iter.h    |  47 ++++++++++++++++
 2 files changed, 70 insertions(+), 86 deletions(-)

diff --git a/fs/smb/client/cifsencrypt.c b/fs/smb/client/cifsencrypt.c
index 6322f0f68a17..991a1ab047e7 100644
--- a/fs/smb/client/cifsencrypt.c
+++ b/fs/smb/client/cifsencrypt.c
@@ -21,82 +21,10 @@
 #include <linux/random.h>
 #include <linux/highmem.h>
 #include <linux/fips.h>
+#include <linux/iov_iter.h>
 #include "../common/arc4.h"
 #include <crypto/aead.h>
 
-/*
- * Hash data from a BVEC-type iterator.
- */
-static int cifs_shash_bvec(const struct iov_iter *iter, ssize_t maxsize,
-			   struct shash_desc *shash)
-{
-	const struct bio_vec *bv = iter->bvec;
-	unsigned long start = iter->iov_offset;
-	unsigned int i;
-	void *p;
-	int ret;
-
-	for (i = 0; i < iter->nr_segs; i++) {
-		size_t off, len;
-
-		len = bv[i].bv_len;
-		if (start >= len) {
-			start -= len;
-			continue;
-		}
-
-		len = min_t(size_t, maxsize, len - start);
-		off = bv[i].bv_offset + start;
-
-		p = kmap_local_page(bv[i].bv_page);
-		ret = crypto_shash_update(shash, p + off, len);
-		kunmap_local(p);
-		if (ret < 0)
-			return ret;
-
-		maxsize -= len;
-		if (maxsize <= 0)
-			break;
-		start = 0;
-	}
-
-	return 0;
-}
-
-/*
- * Hash data from a KVEC-type iterator.
- */
-static int cifs_shash_kvec(const struct iov_iter *iter, ssize_t maxsize,
-			   struct shash_desc *shash)
-{
-	const struct kvec *kv = iter->kvec;
-	unsigned long start = iter->iov_offset;
-	unsigned int i;
-	int ret;
-
-	for (i = 0; i < iter->nr_segs; i++) {
-		size_t len;
-
-		len = kv[i].iov_len;
-		if (start >= len) {
-			start -= len;
-			continue;
-		}
-
-		len = min_t(size_t, maxsize, len - start);
-		ret = crypto_shash_update(shash, kv[i].iov_base + start, len);
-		if (ret < 0)
-			return ret;
-		maxsize -= len;
-
-		if (maxsize <= 0)
-			break;
-		start = 0;
-	}
-
-	return 0;
-}
-
 /*
  * Hash data from an XARRAY-type iterator.
  */
@@ -145,27 +73,36 @@ static ssize_t cifs_shash_xarray(const struct iov_iter *iter, ssize_t maxsize,
 	return 0;
 }
 
+static size_t cifs_shash_step(void *iter_base, size_t progress, size_t len,
+			      void *priv, void *priv2)
+{
+	struct shash_desc *shash = priv;
+	int ret, *pret = priv2;
+
+	ret = crypto_shash_update(shash, iter_base, len);
+	if (ret < 0) {
+		*pret = ret;
+		return len;
+	}
+	return 0;
+}
+
 /*
  * Pass the data from an iterator into a hash.
  */
 static int cifs_shash_iter(const struct iov_iter *iter, size_t maxsize,
 			   struct shash_desc *shash)
 {
-	if (maxsize == 0)
-		return 0;
+	struct iov_iter tmp_iter = *iter;
+	int err = -EIO;
 
-	switch (iov_iter_type(iter)) {
-	case ITER_BVEC:
-		return cifs_shash_bvec(iter, maxsize, shash);
-	case ITER_KVEC:
-		return cifs_shash_kvec(iter, maxsize, shash);
-	case ITER_XARRAY:
+	if (iov_iter_type(iter) == ITER_XARRAY)
 		return cifs_shash_xarray(iter, maxsize, shash);
-	default:
-		pr_err("cifs_shash_iter(%u) unsupported\n", iov_iter_type(iter));
-		WARN_ON_ONCE(1);
-		return -EIO;
-	}
+
+	if (iterate_and_advance_kernel(&tmp_iter, maxsize, shash, &err,
+				       cifs_shash_step) != maxsize)
+		return err;
+	return 0;
 }
 
 int __cifs_calc_signature(struct smb_rqst *rqst,
diff --git a/include/linux/iov_iter.h b/include/linux/iov_iter.h
index a223370a59a7..c4aa58032faf 100644
--- a/include/linux/iov_iter.h
+++ b/include/linux/iov_iter.h
@@ -328,4 +328,51 @@ size_t iterate_and_advance(struct iov_iter *iter, size_t len, void *priv,
 	return iterate_and_advance2(iter, len, priv, NULL, ustep, step);
 }
 
+/**
+ * iterate_and_advance_kernel - Iterate over a kernel-internal iterator
+ * @iter: The iterator to iterate over.
+ * @len: The amount to iterate over.
+ * @priv: Data for the step functions.
+ * @priv2: More data for the step functions.
+ * @step: Function for other iterators; given kernel addresses.
+ *
+ * Iterate over the next part of an iterator, up to the specified length.  The
+ * buffer is presented in segments, which for kernel iteration are broken up by
+ * physical pages and mapped, with the mapped address being presented.
+ *
+ * [!] Note This will only handle BVEC, KVEC, FOLIOQ, XARRAY and DISCARD-type
+ * iterators; it will not handle UBUF or IOVEC-type iterators.
+ *
+ * A step functions, @step, must be provided, one for handling mapped kernel
+ * addresses and the other is given user addresses which have the potential to
+ * fault since no pinning is performed.
+ *
+ * The step functions are passed the address and length of the segment, @priv,
+ * @priv2 and the amount of data so far iterated over (which can, for example,
+ * be added to @priv to point to the right part of a second buffer).  The step
+ * functions should return the amount of the segment they didn't process (ie. 0
+ * indicates complete processsing).
+ *
+ * This function returns the amount of data processed (ie. 0 means nothing was
+ * processed and the value of @len means processes to completion).
+ */
+static __always_inline
+size_t iterate_and_advance_kernel(struct iov_iter *iter, size_t len, void *priv,
+				  void *priv2, iov_step_f step)
+{
+	if (unlikely(iter->count < len))
+		len = iter->count;
+	if (unlikely(!len))
+		return 0;
+	if (iov_iter_is_bvec(iter))
+		return iterate_bvec(iter, len, priv, priv2, step);
+	if (iov_iter_is_kvec(iter))
+		return iterate_kvec(iter, len, priv, priv2, step);
+	if (iov_iter_is_folioq(iter))
+		return iterate_folioq(iter, len, priv, priv2, step);
+	if (iov_iter_is_xarray(iter))
+		return iterate_xarray(iter, len, priv, priv2, step);
+	return iterate_discard(iter, len, priv, priv2, step);
+}
+
 #endif /* _LINUX_IOV_ITER_H */

[PATCH 23/24] cifs: Switch crypto buffer to use a folio_queue rather than an xarray

[David Howells]

Switch cifs from using an xarray to hold the transport crypto buffer to
using a folio_queue and use ITER_FOLIOQ rather than ITER_XARRAY.

This is part of the process of phasing out ITER_XARRAY.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Tom Talpey <tom@talpey.com>
cc: Enzo Matsumiya <ematsumiya@suse.de>
cc: linux-cifs@vger.kernel.org
---
 fs/smb/client/cifsglob.h |   2 +-
 fs/smb/client/smb2ops.c  | 218 +++++++++++++++++++++------------------
 include/linux/uio.h      |   6 ++
 3 files changed, 127 insertions(+), 99 deletions(-)

diff --git a/fs/smb/client/cifsglob.h b/fs/smb/client/cifsglob.h
index 85e6495dc440..c6bf5f7b2144 100644
--- a/fs/smb/client/cifsglob.h
+++ b/fs/smb/client/cifsglob.h
@@ -256,7 +256,7 @@ struct smb_rqst {
 	unsigned int	rq_nvec;	/* number of kvecs in array */
 	size_t		rq_iter_size;	/* Amount of data in ->rq_iter */
 	struct iov_iter	rq_iter;	/* Data iterator */
-	struct xarray	rq_buffer;	/* Page buffer for encryption */
+	struct folio_queue *rq_buffer;	/* Buffer for encryption */
 };
 
 struct mid_q_entry;
diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index 322cabc69c6f..cb9a18e31b03 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -13,6 +13,7 @@
 #include <linux/sort.h>
 #include <crypto/aead.h>
 #include <linux/fiemap.h>
+#include <linux/folio_queue.h>
 #include <uapi/linux/magic.h>
 #include "cifsfs.h"
 #include "cifsglob.h"
@@ -4356,30 +4357,86 @@ crypt_message(struct TCP_Server_Info *server, int num_rqst,
 }
 
 /*
- * Clear a read buffer, discarding the folios which have XA_MARK_0 set.
+ * Clear a read buffer, discarding the folios which have the 1st mark set.
  */
-static void cifs_clear_xarray_buffer(struct xarray *buffer)
+static void cifs_clear_folioq_buffer(struct folio_queue *buffer)
 {
+	struct folio_queue *folioq;
+
+	while ((folioq = buffer)) {
+		for (int s = 0; s < folioq_count(folioq); s++)
+			if (folioq_is_marked(folioq, s))
+				folio_put(folioq_folio(folioq, s));
+		buffer = folioq->next;
+		kfree(folioq);
+	}
+}
+
+/*
+ * Allocate buffer space into a folio queue.
+ */
+static struct folio_queue *cifs_alloc_folioq_buffer(ssize_t size)
+{
+	struct folio_queue *buffer = NULL, *tail = NULL, *p;
 	struct folio *folio;
+	unsigned int slot;
+
+	do {
+		if (!tail || folioq_full(tail)) {
+			p = kmalloc(sizeof(*p), GFP_NOFS);
+			if (!p)
+				goto nomem;
+			folioq_init(p);
+			if (tail) {
+				tail->next = p;
+				p->prev = tail;
+			} else {
+				buffer = p;
+			}
+			tail = p;
+		}
+
+		folio = folio_alloc(GFP_KERNEL|__GFP_HIGHMEM, 0);
+		if (!folio)
+			goto nomem;
+
+		slot = folioq_append_mark(tail, folio);
+		size -= folioq_folio_size(tail, slot);
+	} while (size > 0);
+
+	return buffer;
+
+nomem:
+	cifs_clear_folioq_buffer(buffer);
+	return NULL;
+}
+
+/*
+ * Copy data from an iterator to the folios in a folio queue buffer.
+ */
+static bool cifs_copy_iter_to_folioq(struct iov_iter *iter, size_t size,
+				     struct folio_queue *buffer)
+{
+	for (; buffer; buffer = buffer->next) {
+		for (int s = 0; s < folioq_count(buffer); s++) {
+			struct folio *folio = folioq_folio(buffer, s);
+			size_t part = folioq_folio_size(buffer, s);
 
-	XA_STATE(xas, buffer, 0);
+			part = umin(part, size);
 
-	rcu_read_lock();
-	xas_for_each_marked(&xas, folio, ULONG_MAX, XA_MARK_0) {
-		folio_put(folio);
+			if (copy_folio_from_iter(folio, 0, part, iter) != part)
+				return false;
+			size -= part;
+		}
 	}
-	rcu_read_unlock();
-	xa_destroy(buffer);
+	return true;
 }
 
 void
 smb3_free_compound_rqst(int num_rqst, struct smb_rqst *rqst)
 {
-	int i;
-
-	for (i = 0; i < num_rqst; i++)
-		if (!xa_empty(&rqst[i].rq_buffer))
-			cifs_clear_xarray_buffer(&rqst[i].rq_buffer);
+	for (int i = 0; i < num_rqst; i++)
+		cifs_clear_folioq_buffer(rqst[i].rq_buffer);
 }
 
 /*
@@ -4400,53 +4457,33 @@ smb3_init_transform_rq(struct TCP_Server_Info *server, int num_rqst,
 		       struct smb_rqst *new_rq, struct smb_rqst *old_rq)
 {
 	struct smb2_transform_hdr *tr_hdr = new_rq[0].rq_iov[0].iov_base;
-	struct page *page;
 	unsigned int orig_len = 0;
-	int i, j;
 	int rc = -ENOMEM;
 
-	for (i = 1; i < num_rqst; i++) {
+	for (int i = 1; i < num_rqst; i++) {
 		struct smb_rqst *old = &old_rq[i - 1];
 		struct smb_rqst *new = &new_rq[i];
-		struct xarray *buffer = &new->rq_buffer;
-		size_t size = iov_iter_count(&old->rq_iter), seg, copied = 0;
+		struct folio_queue *buffer;
+		size_t size = iov_iter_count(&old->rq_iter);
 
 		orig_len += smb_rqst_len(server, old);
 		new->rq_iov = old->rq_iov;
 		new->rq_nvec = old->rq_nvec;
 
-		xa_init(buffer);
-
 		if (size > 0) {
-			unsigned int npages = DIV_ROUND_UP(size, PAGE_SIZE);
-
-			for (j = 0; j < npages; j++) {
-				void *o;
-
-				rc = -ENOMEM;
-				page = alloc_page(GFP_KERNEL|__GFP_HIGHMEM);
-				if (!page)
-					goto err_free;
-				page->index = j;
-				o = xa_store(buffer, j, page, GFP_KERNEL);
-				if (xa_is_err(o)) {
-					rc = xa_err(o);
-					put_page(page);
-					goto err_free;
-				}
+			buffer = cifs_alloc_folioq_buffer(size);
+			if (!buffer)
+				goto err_free;
 
-				xa_set_mark(buffer, j, XA_MARK_0);
+			new->rq_buffer = buffer;
+			iov_iter_folio_queue(&new->rq_iter, ITER_SOURCE,
+					     buffer, 0, 0, size);
+			new->rq_iter_size = size;
 
-				seg = min_t(size_t, size - copied, PAGE_SIZE);
-				if (copy_page_from_iter(page, 0, seg, &old->rq_iter) != seg) {
-					rc = -EFAULT;
-					goto err_free;
-				}
-				copied += seg;
+			if (!cifs_copy_iter_to_folioq(&old->rq_iter, size, buffer)) {
+				rc = -EIO;
+				goto err_free;
 			}
-			iov_iter_xarray(&new->rq_iter, ITER_SOURCE,
-					buffer, 0, size);
-			new->rq_iter_size = size;
 		}
 	}
 
@@ -4511,22 +4548,23 @@ decrypt_raw_data(struct TCP_Server_Info *server, char *buf,
 }
 
 static int
-cifs_copy_pages_to_iter(struct xarray *pages, unsigned int data_size,
-			unsigned int skip, struct iov_iter *iter)
+cifs_copy_folioq_to_iter(struct folio_queue *folioq, size_t data_size,
+			 size_t skip, struct iov_iter *iter)
 {
-	struct page *page;
-	unsigned long index;
-
-	xa_for_each(pages, index, page) {
-		size_t n, len = min_t(unsigned int, PAGE_SIZE - skip, data_size);
-
-		n = copy_page_to_iter(page, skip, len, iter);
-		if (n != len) {
-			cifs_dbg(VFS, "%s: something went wrong\n", __func__);
-			return -EIO;
+	for (; folioq; folioq = folioq->next) {
+		for (int s = 0; s < folioq_count(folioq); s++) {
+			struct folio *folio = folioq_folio(folioq, s);
+			size_t fsize = folio_size(folio);
+			size_t n, len = umin(fsize - skip, data_size);
+
+			n = copy_folio_to_iter(folio, skip, len, iter);
+			if (n != len) {
+				cifs_dbg(VFS, "%s: something went wrong\n", __func__);
+				return -EIO;
+			}
+			data_size -= n;
+			skip = 0;
 		}
-		data_size -= n;
-		skip = 0;
 	}
 
 	return 0;
@@ -4534,8 +4572,8 @@ cifs_copy_pages_to_iter(struct xarray *pages, unsigned int data_size,
 
 static int
 handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
-		 char *buf, unsigned int buf_len, struct xarray *pages,
-		 unsigned int pages_len, bool is_offloaded)
+		 char *buf, unsigned int buf_len, struct folio_queue *buffer,
+		 unsigned int buffer_len, bool is_offloaded)
 {
 	unsigned int data_offset;
 	unsigned int data_len;
@@ -4632,7 +4670,7 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 			return 0;
 		}
 
-		if (data_len > pages_len - pad_len) {
+		if (data_len > buffer_len - pad_len) {
 			/* data_len is corrupt -- discard frame */
 			rdata->result = -EIO;
 			if (is_offloaded)
@@ -4643,8 +4681,8 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 		}
 
 		/* Copy the data to the output I/O iterator. */
-		rdata->result = cifs_copy_pages_to_iter(pages, pages_len,
-							cur_off, &rdata->subreq.io_iter);
+		rdata->result = cifs_copy_folioq_to_iter(buffer, buffer_len,
+							 cur_off, &rdata->subreq.io_iter);
 		if (rdata->result != 0) {
 			if (is_offloaded)
 				mid->mid_state = MID_RESPONSE_MALFORMED;
@@ -4652,12 +4690,11 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 				dequeue_mid(mid, rdata->result);
 			return 0;
 		}
-		rdata->got_bytes = pages_len;
+		rdata->got_bytes = buffer_len;
 
 	} else if (buf_len >= data_offset + data_len) {
 		/* read response payload is in buf */
-		WARN_ONCE(pages && !xa_empty(pages),
-			  "read data can be either in buf or in pages");
+		WARN_ONCE(buffer, "read data can be either in buf or in buffer");
 		length = copy_to_iter(buf + data_offset, data_len, &rdata->subreq.io_iter);
 		if (length < 0)
 			return length;
@@ -4683,7 +4720,7 @@ handle_read_data(struct TCP_Server_Info *server, struct mid_q_entry *mid,
 struct smb2_decrypt_work {
 	struct work_struct decrypt;
 	struct TCP_Server_Info *server;
-	struct xarray buffer;
+	struct folio_queue *buffer;
 	char *buf;
 	unsigned int len;
 };
@@ -4697,7 +4734,7 @@ static void smb2_decrypt_offload(struct work_struct *work)
 	struct mid_q_entry *mid;
 	struct iov_iter iter;
 
-	iov_iter_xarray(&iter, ITER_DEST, &dw->buffer, 0, dw->len);
+	iov_iter_folio_queue(&iter, ITER_DEST, dw->buffer, 0, 0, dw->len);
 	rc = decrypt_raw_data(dw->server, dw->buf, dw->server->vals->read_rsp_size,
 			      &iter, true);
 	if (rc) {
@@ -4713,7 +4750,7 @@ static void smb2_decrypt_offload(struct work_struct *work)
 		mid->decrypted = true;
 		rc = handle_read_data(dw->server, mid, dw->buf,
 				      dw->server->vals->read_rsp_size,
-				      &dw->buffer, dw->len,
+				      dw->buffer, dw->len,
 				      true);
 		if (rc >= 0) {
 #ifdef CONFIG_CIFS_STATS2
@@ -4746,7 +4783,7 @@ static void smb2_decrypt_offload(struct work_struct *work)
 	}
 
 free_pages:
-	cifs_clear_xarray_buffer(&dw->buffer);
+	cifs_clear_folioq_buffer(dw->buffer);
 	cifs_small_buf_release(dw->buf);
 	kfree(dw);
 }
@@ -4756,20 +4793,17 @@ static int
 receive_encrypted_read(struct TCP_Server_Info *server, struct mid_q_entry **mid,
 		       int *num_mids)
 {
-	struct page *page;
 	char *buf = server->smallbuf;
 	struct smb2_transform_hdr *tr_hdr = (struct smb2_transform_hdr *)buf;
 	struct iov_iter iter;
-	unsigned int len, npages;
+	unsigned int len;
 	unsigned int buflen = server->pdu_size;
 	int rc;
-	int i = 0;
 	struct smb2_decrypt_work *dw;
 
 	dw = kzalloc(sizeof(struct smb2_decrypt_work), GFP_KERNEL);
 	if (!dw)
 		return -ENOMEM;
-	xa_init(&dw->buffer);
 	INIT_WORK(&dw->decrypt, smb2_decrypt_offload);
 	dw->server = server;
 
@@ -4785,26 +4819,14 @@ receive_encrypted_read(struct TCP_Server_Info *server, struct mid_q_entry **mid,
 	len = le32_to_cpu(tr_hdr->OriginalMessageSize) -
 		server->vals->read_rsp_size;
 	dw->len = len;
-	npages = DIV_ROUND_UP(len, PAGE_SIZE);
+	len = round_up(dw->len, PAGE_SIZE);
 
 	rc = -ENOMEM;
-	for (; i < npages; i++) {
-		void *old;
-
-		page = alloc_page(GFP_KERNEL|__GFP_HIGHMEM);
-		if (!page)
-			goto discard_data;
-		page->index = i;
-		old = xa_store(&dw->buffer, i, page, GFP_KERNEL);
-		if (xa_is_err(old)) {
-			rc = xa_err(old);
-			put_page(page);
-			goto discard_data;
-		}
-		xa_set_mark(&dw->buffer, i, XA_MARK_0);
-	}
+	dw->buffer = cifs_alloc_folioq_buffer(len);
+	if (!dw->buffer)
+		goto discard_data;
 
-	iov_iter_xarray(&iter, ITER_DEST, &dw->buffer, 0, npages * PAGE_SIZE);
+	iov_iter_folio_queue(&iter, ITER_DEST, dw->buffer, 0, 0, len);
 
 	/* Read the data into the buffer and clear excess bufferage. */
 	rc = cifs_read_iter_from_socket(server, &iter, dw->len);
@@ -4812,9 +4834,9 @@ receive_encrypted_read(struct TCP_Server_Info *server, struct mid_q_entry **mid,
 		goto discard_data;
 
 	server->total_read += rc;
-	if (rc < npages * PAGE_SIZE)
-		iov_iter_zero(npages * PAGE_SIZE - rc, &iter);
-	iov_iter_revert(&iter, npages * PAGE_SIZE);
+	if (rc < len)
+		iov_iter_zero(len - rc, &iter);
+	iov_iter_revert(&iter, len);
 	iov_iter_truncate(&iter, dw->len);
 
 	rc = cifs_discard_remaining_data(server);
@@ -4849,7 +4871,7 @@ receive_encrypted_read(struct TCP_Server_Info *server, struct mid_q_entry **mid,
 		(*mid)->decrypted = true;
 		rc = handle_read_data(server, *mid, buf,
 				      server->vals->read_rsp_size,
-				      &dw->buffer, dw->len, false);
+				      dw->buffer, dw->len, false);
 		if (rc >= 0) {
 			if (server->ops->is_network_name_deleted) {
 				server->ops->is_network_name_deleted(buf,
@@ -4859,7 +4881,7 @@ receive_encrypted_read(struct TCP_Server_Info *server, struct mid_q_entry **mid,
 	}
 
 free_pages:
-	cifs_clear_xarray_buffer(&dw->buffer);
+	cifs_clear_folioq_buffer(dw->buffer);
 free_dw:
 	kfree(dw);
 	return rc;
diff --git a/include/linux/uio.h b/include/linux/uio.h
index 845d110acadc..853f9de5aa05 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -189,6 +189,12 @@ static inline size_t copy_folio_to_iter(struct folio *folio, size_t offset,
 	return copy_page_to_iter(&folio->page, offset, bytes, i);
 }
 
+static inline size_t copy_folio_from_iter(struct folio *folio, size_t offset,
+					  size_t bytes, struct iov_iter *i)
+{
+	return copy_page_from_iter(&folio->page, offset, bytes, i);
+}
+
 static inline size_t copy_folio_from_iter_atomic(struct folio *folio,
 		size_t offset, size_t bytes, struct iov_iter *i)
 {

[PATCH 24/24] cifs: Don't support ITER_XARRAY

[David Howells]

There's now no need to support ITER_XARRAY in cifs as netfslib hands down
ITER_FOLIOQ instead - and that's simpler to use with iterate_and_advance()
as it doesn't hold the RCU read lock over the step function.

This is part of the process of phasing out ITER_XARRAY.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Tom Talpey <tom@talpey.com>
cc: Enzo Matsumiya <ematsumiya@suse.de>
cc: linux-cifs@vger.kernel.org
---
 fs/smb/client/cifsencrypt.c | 51 -------------------------------------
 fs/smb/client/smbdirect.c   | 49 -----------------------------------
 2 files changed, 100 deletions(-)

diff --git a/fs/smb/client/cifsencrypt.c b/fs/smb/client/cifsencrypt.c
index 991a1ab047e7..7481b21a0489 100644
--- a/fs/smb/client/cifsencrypt.c
+++ b/fs/smb/client/cifsencrypt.c
@@ -25,54 +25,6 @@
 #include "../common/arc4.h"
 #include <crypto/aead.h>
 
-/*
- * Hash data from an XARRAY-type iterator.
- */
-static ssize_t cifs_shash_xarray(const struct iov_iter *iter, ssize_t maxsize,
-				 struct shash_desc *shash)
-{
-	struct folio *folios[16], *folio;
-	unsigned int nr, i, j, npages;
-	loff_t start = iter->xarray_start + iter->iov_offset;
-	pgoff_t last, index = start / PAGE_SIZE;
-	ssize_t ret = 0;
-	size_t len, offset, foffset;
-	void *p;
-
-	if (maxsize == 0)
-		return 0;
-
-	last = (start + maxsize - 1) / PAGE_SIZE;
-	do {
-		nr = xa_extract(iter->xarray, (void **)folios, index, last,
-				ARRAY_SIZE(folios), XA_PRESENT);
-		if (nr == 0)
-			return -EIO;
-
-		for (i = 0; i < nr; i++) {
-			folio = folios[i];
-			npages = folio_nr_pages(folio);
-			foffset = start - folio_pos(folio);
-			offset = foffset % PAGE_SIZE;
-			for (j = foffset / PAGE_SIZE; j < npages; j++) {
-				len = min_t(size_t, maxsize, PAGE_SIZE - offset);
-				p = kmap_local_page(folio_page(folio, j));
-				ret = crypto_shash_update(shash, p, len);
-				kunmap_local(p);
-				if (ret < 0)
-					return ret;
-				maxsize -= len;
-				if (maxsize <= 0)
-					return 0;
-				start += len;
-				offset = 0;
-				index++;
-			}
-		}
-	} while (nr == ARRAY_SIZE(folios));
-	return 0;
-}
-
 static size_t cifs_shash_step(void *iter_base, size_t progress, size_t len,
 			      void *priv, void *priv2)
 {
@@ -96,9 +48,6 @@ static int cifs_shash_iter(const struct iov_iter *iter, size_t maxsize,
 	struct iov_iter tmp_iter = *iter;
 	int err = -EIO;
 
-	if (iov_iter_type(iter) == ITER_XARRAY)
-		return cifs_shash_xarray(iter, maxsize, shash);
-
 	if (iterate_and_advance_kernel(&tmp_iter, maxsize, shash, &err,
 				       cifs_shash_step) != maxsize)
 		return err;
diff --git a/fs/smb/client/smbdirect.c b/fs/smb/client/smbdirect.c
index 52acead63d9d..ee63c570d505 100644
--- a/fs/smb/client/smbdirect.c
+++ b/fs/smb/client/smbdirect.c
@@ -2584,52 +2584,6 @@ static ssize_t smb_extract_folioq_to_rdma(struct iov_iter *iter,
 	return ret;
 }
 
-/*
- * Extract folio fragments from an XARRAY-class iterator and add them to an
- * RDMA list.  The folios are not pinned.
- */
-static ssize_t smb_extract_xarray_to_rdma(struct iov_iter *iter,
-					  struct smb_extract_to_rdma *rdma,
-					  ssize_t maxsize)
-{
-	struct xarray *xa = iter->xarray;
-	struct folio *folio;
-	loff_t start = iter->xarray_start + iter->iov_offset;
-	pgoff_t index = start / PAGE_SIZE;
-	ssize_t ret = 0;
-	size_t off, len;
-	XA_STATE(xas, xa, index);
-
-	rcu_read_lock();
-
-	xas_for_each(&xas, folio, ULONG_MAX) {
-		if (xas_retry(&xas, folio))
-			continue;
-		if (WARN_ON(xa_is_value(folio)))
-			break;
-		if (WARN_ON(folio_test_hugetlb(folio)))
-			break;
-
-		off = offset_in_folio(folio, start);
-		len = min_t(size_t, maxsize, folio_size(folio) - off);
-
-		if (!smb_set_sge(rdma, folio_page(folio, 0), off, len)) {
-			rcu_read_unlock();
-			return -EIO;
-		}
-
-		maxsize -= len;
-		ret += len;
-		if (rdma->nr_sge >= rdma->max_sge || maxsize <= 0)
-			break;
-	}
-
-	rcu_read_unlock();
-	if (ret > 0)
-		iov_iter_advance(iter, ret);
-	return ret;
-}
-
 /*
  * Extract page fragments from up to the given amount of the source iterator
  * and build up an RDMA list that refers to all of those bits.  The RDMA list
@@ -2657,9 +2611,6 @@ static ssize_t smb_extract_iter_to_rdma(struct iov_iter *iter, size_t len,
 	case ITER_FOLIOQ:
 		ret = smb_extract_folioq_to_rdma(iter, rdma, len);
 		break;
-	case ITER_XARRAY:
-		ret = smb_extract_xarray_to_rdma(iter, rdma, len);
-		break;
 	default:
 		WARN_ON_ONCE(1);
 		return -EIO;

Re: (subset) [PATCH 00/24] netfs: Read/write improvements

[Christian Brauner]

On Mon, 29 Jul 2024 17:19:29 +0100, David Howells wrote:
> This set of patches includes one fscache fix and one cachefiles fix
> 
>  (1) Fix a cookie access race in fscache.
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[01/24] fs/netfs/fscache_cookie: add missing "n_accesses" check
        https://git.kernel.org/vfs/vfs/c/965a561e4026

Re: (subset) [PATCH 00/24] netfs: Read/write improvements

[Christian Brauner]

On Mon, 29 Jul 2024 17:19:29 +0100, David Howells wrote:
> This set of patches includes one fscache fix and one cachefiles fix
> 
>  (1) Fix a cookie access race in fscache.
> 
>  (2) Fix the setxattr/removexattr syscalls to pull their arguments into
>      kernel space before taking the sb_writers lock to avoid a deadlock
>      against mm->mmap_lock.
> 
> [...]

Applied to the vfs.netfs branch of the vfs/vfs.git tree.
Patches in the vfs.netfs branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.netfs

[03/24] - [24/24]

Re: [PATCH 18/24] netfs: Speed up buffered reading

[Simon Horman]

On Mon, Jul 29, 2024 at 05:19:47PM +0100, David Howells wrote:

...

> diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c

...

> +/*
> + * Perform a read to the pagecache from a series of sources of different types,
> + * slicing up the region to be read according to available cache blocks and
> + * network rsize.
> + */
> +static void netfs_read_to_pagecache(struct netfs_io_request *rreq)
> +{
> +	struct netfs_inode *ictx = netfs_inode(rreq->inode);
> +	unsigned long long start = rreq->start;
> +	ssize_t size = rreq->len;
> +	int ret = 0;
> +
> +	atomic_inc(&rreq->nr_outstanding);
> +
> +	do {
> +		struct netfs_io_subrequest *subreq;
> +		enum netfs_io_source source = NETFS_DOWNLOAD_FROM_SERVER;
> +		ssize_t slice;
> +
> +		subreq = netfs_alloc_subrequest(rreq);
> +		if (!subreq) {
> +			ret = -ENOMEM;
> +			break;
> +		}
> +
> +		subreq->start	= start;
> +		subreq->len	= size;
> +
> +		atomic_inc(&rreq->nr_outstanding);
> +		spin_lock_bh(&rreq->lock);
> +		list_add_tail(&subreq->rreq_link, &rreq->subrequests);
> +		subreq->prev_donated = rreq->prev_donated;
> +		rreq->prev_donated = 0;
> +		trace_netfs_sreq(subreq, netfs_sreq_trace_added);
> +		spin_unlock_bh(&rreq->lock);
> +
> +		source = netfs_cache_prepare_read(rreq, subreq, rreq->i_size);
> +		subreq->source = source;
> +		if (source == NETFS_DOWNLOAD_FROM_SERVER) {
> +			unsigned long long zp = umin(ictx->zero_point, rreq->i_size);
> +			size_t len = subreq->len;
> +
> +			if (subreq->start >= zp) {
> +				subreq->source = source = NETFS_FILL_WITH_ZEROES;
> +				goto fill_with_zeroes;
> +			}
> +
> +			if (len > zp - subreq->start)
> +				len = zp - subreq->start;
> +			if (len == 0) {
> +				pr_err("ZERO-LEN READ: R=%08x[%x] l=%zx/%zx s=%llx z=%llx i=%llx",
> +				       rreq->debug_id, subreq->debug_index,
> +				       subreq->len, size,
> +				       subreq->start, ictx->zero_point, rreq->i_size);
> +				break;
> +			}
> +			subreq->len = len;
> +
> +			netfs_stat(&netfs_n_rh_download);
> +			if (rreq->netfs_ops->prepare_read) {
> +				ret = rreq->netfs_ops->prepare_read(subreq);
> +				if (ret < 0) {
> +					atomic_dec(&rreq->nr_outstanding);
> +					netfs_put_subrequest(subreq, false,
> +							     netfs_sreq_trace_put_cancel);
> +					break;
> +				}
> +				trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
> +			}
> +
> +			slice = netfs_prepare_read_iterator(subreq);
> +			if (slice < 0) {
> +				atomic_dec(&rreq->nr_outstanding);
> +				netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_cancel);
> +				ret = slice;
> +				break;
> +			}
> +
> +			rreq->netfs_ops->issue_read(subreq);
> +			goto done;
> +		}
> +
> +	fill_with_zeroes:
> +		if (source == NETFS_FILL_WITH_ZEROES) {
> +			subreq->source = NETFS_FILL_WITH_ZEROES;
> +			trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
> +			netfs_stat(&netfs_n_rh_zero);
> +			slice = netfs_prepare_read_iterator(subreq);
> +			__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
> +			netfs_read_subreq_terminated(subreq, 0, false);
> +			goto done;
> +		}
> +
> +		if (source == NETFS_READ_FROM_CACHE) {
> +			trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
> +			slice = netfs_prepare_read_iterator(subreq);
> +			netfs_read_cache_to_pagecache(rreq, subreq);
> +			goto done;
> +		}
> +
> +		if (source == NETFS_INVALID_READ)
> +			break;

Hi David,

I feel a sense of deja vu here. So apologies if this was already
discussed in the past.

If the code ever reaches this line, then slice will be used
uninitialised below.

Flagged by W=1 allmodconfig builds on x86_64 with Clang 18.1.8.

> +
> +	done:
> +		size -= slice;
> +		start += slice;
> +		cond_resched();
> +	} while (size > 0);
> +
> +	if (atomic_dec_and_test(&rreq->nr_outstanding))
> +		netfs_rreq_terminated(rreq, false);
> +
> +	/* Defer error return as we may need to wait for outstanding I/O. */
> +	cmpxchg(&rreq->error, 0, ret);
> +}

...

> +/*
> + * Unlock any folios that are now completely read.  Returns true if the
> + * subrequest is removed from the list.
> + */
> +static bool netfs_consume_read_data(struct netfs_io_subrequest *subreq, bool was_async)
> +{
> +	struct netfs_io_subrequest *prev, *next;
> +	struct netfs_io_request *rreq = subreq->rreq;
> +	struct folio_queue *folioq = subreq->curr_folioq;
> +	size_t avail, prev_donated, next_donated, fsize, part, excess;
> +	loff_t fpos, start;
> +	loff_t fend;
> +	int slot = subreq->curr_folioq_slot;
> +
> +	if (WARN(subreq->transferred > subreq->len,
> +		 "Subreq overread: R%x[%x] %zu > %zu",
> +		 rreq->debug_id, subreq->debug_index,
> +		 subreq->transferred, subreq->len))
> +		subreq->transferred = subreq->len;
> +
> +next_folio:
> +	fsize = PAGE_SIZE << subreq->curr_folio_order;
> +	fpos = round_down(subreq->start + subreq->consumed, fsize);
> +	fend = fpos + fsize;
> +
> +	if (WARN_ON_ONCE(!folioq) ||
> +	    WARN_ON_ONCE(!folioq_folio(folioq, slot)) ||
> +	    WARN_ON_ONCE(folioq_folio(folioq, slot)->index != fpos / PAGE_SIZE)) {
> +		pr_err("R=%08x[%x] s=%llx-%llx ctl=%zx/%zx/%zx sl=%u\n",
> +		       rreq->debug_id, subreq->debug_index,
> +		       subreq->start, subreq->start + subreq->transferred - 1,
> +		       subreq->consumed, subreq->transferred, subreq->len,
> +		       slot);
> +		if (folioq) {
> +			struct folio *folio = folioq_folio(folioq, slot);
> +
> +			pr_err("folioq: %02x%02x%02x%02x\n",
> +			       folioq->orders[0], folioq->orders[1],
> +			       folioq->orders[2], folioq->orders[3]);
> +			if (folio)
> +				pr_err("folio: %llx-%llx ix=%llx o=%u qo=%u\n",
> +				       fpos, fend - 1, folio_pos(folio), folio_order(folio),
> +				       folioq_folio_order(folioq, slot));
> +		}
> +	}
> +
> +donation_changed:
> +	/* Try to consume the current folio if we've hit or passed the end of
> +	 * it.  There's a possibility that this subreq doesn't start at the
> +	 * beginning of the folio, in which case we need to donate to/from the
> +	 * preceding subreq.
> +	 *
> +	 * We also need to include any potential donation back from the
> +	 * following subreq.
> +	 */
> +	prev_donated = READ_ONCE(subreq->prev_donated);
> +	next_donated =  READ_ONCE(subreq->next_donated);
> +	if (prev_donated || next_donated) {
> +		spin_lock_bh(&rreq->lock);
> +		prev_donated = subreq->prev_donated;
> +		next_donated =  subreq->next_donated;
> +		subreq->start -= prev_donated;
> +		subreq->len += prev_donated;
> +		subreq->transferred += prev_donated;
> +		prev_donated = subreq->prev_donated = 0;
> +		if (subreq->transferred == subreq->len) {
> +			subreq->len += next_donated;
> +			subreq->transferred += next_donated;
> +			next_donated = subreq->next_donated = 0;
> +		}
> +		trace_netfs_sreq(subreq, netfs_sreq_trace_add_donations);
> +		spin_unlock_bh(&rreq->lock);
> +	}
> +
> +	avail = subreq->transferred;
> +	if (avail == subreq->len)
> +		avail += next_donated;
> +	start = subreq->start;
> +	if (subreq->consumed == 0) {
> +		start -= prev_donated;
> +		avail += prev_donated;
> +	} else {
> +		start += subreq->consumed;
> +		avail -= subreq->consumed;
> +	}
> +	part = umin(avail, fsize);
> +
> +	trace_netfs_progress(subreq, start, avail, part);
> +
> +	if (start + avail >= fend) {
> +		if (fpos == start) {
> +			/* Flush, unlock and mark for caching any folio we've just read. */
> +			subreq->consumed = fend - subreq->start;
> +			netfs_unlock_read_folio(subreq, rreq, folioq_folio(folioq, slot));

Earlier and later in this function it was assumed that folioq may be NULL.
But here it appears to be used dereferenced unconditionally
by folioq_folio().

Flagged by Smatch.

> +			folioq_mark2(folioq, slot);
> +			if (subreq->consumed >= subreq->len)
> +				goto remove_subreq;
> +		} else if (fpos < start) {
> +			excess = fend - subreq->start;
> +
> +			spin_lock_bh(&rreq->lock);
> +			/* If we complete first on a folio split with the
> +			 * preceding subreq, donate to that subreq - otherwise
> +			 * we get the responsibility.
> +			 */
> +			if (subreq->prev_donated != prev_donated) {
> +				spin_unlock_bh(&rreq->lock);
> +				goto donation_changed;
> +			}
> +
> +			if (list_is_first(&subreq->rreq_link, &rreq->subrequests)) {
> +				spin_unlock_bh(&rreq->lock);
> +				pr_err("Can't donate prior to front\n");
> +				goto bad;
> +			}
> +
> +			prev = list_prev_entry(subreq, rreq_link);
> +			WRITE_ONCE(prev->next_donated, prev->next_donated + excess);
> +			subreq->start += excess;
> +			subreq->len -= excess;
> +			subreq->transferred -= excess;
> +			trace_netfs_donate(rreq, subreq, prev, excess,
> +					   netfs_trace_donate_tail_to_prev);
> +			trace_netfs_sreq(subreq, netfs_sreq_trace_donate_to_prev);
> +
> +			if (subreq->consumed >= subreq->len)
> +				goto remove_subreq_locked;
> +			spin_unlock_bh(&rreq->lock);
> +		} else {
> +			pr_err("fpos > start\n");
> +			goto bad;
> +		}
> +
> +		/* Advance the rolling buffer to the next folio. */
> +		slot++;
> +		if (slot >= folioq_nr_slots(folioq)) {
> +			slot = 0;
> +			folioq = folioq->next;
> +			subreq->curr_folioq = folioq;
> +		}
> +		subreq->curr_folioq_slot = slot;
> +		if (folioq && folioq_folio(folioq, slot))
> +			subreq->curr_folio_order = folioq->orders[slot];
> +		if (!was_async)
> +			cond_resched();
> +		goto next_folio;
> +	}
> +
> +	/* Deal with partial progress. */
> +	if (subreq->transferred < subreq->len)
> +		return false;
> +
> +	/* Donate the remaining downloaded data to one of the neighbouring
> +	 * subrequests.  Note that we may race with them doing the same thing.
> +	 */
> +	spin_lock_bh(&rreq->lock);
> +
> +	if (subreq->prev_donated != prev_donated ||
> +	    subreq->next_donated != next_donated) {
> +		spin_unlock_bh(&rreq->lock);
> +		cond_resched();
> +		goto donation_changed;
> +	}
> +
> +	/* Deal with the trickiest case: that this subreq is in the middle of a
> +	 * folio, not touching either edge, but finishes first.  In such a
> +	 * case, we donate to the previous subreq, if there is one, so that the
> +	 * donation is only handled when that completes - and remove this
> +	 * subreq from the list.
> +	 *
> +	 * If the previous subreq finished first, we will have acquired their
> +	 * donation and should be able to unlock folios and/or donate nextwards.
> +	 */
> +	if (!subreq->consumed &&
> +	    !prev_donated &&
> +	    !list_is_first(&subreq->rreq_link, &rreq->subrequests)) {
> +		prev = list_prev_entry(subreq, rreq_link);
> +		WRITE_ONCE(prev->next_donated, prev->next_donated + subreq->len);
> +		subreq->start += subreq->len;
> +		subreq->len = 0;
> +		subreq->transferred = 0;
> +		trace_netfs_donate(rreq, subreq, prev, subreq->len,
> +				   netfs_trace_donate_to_prev);
> +		trace_netfs_sreq(subreq, netfs_sreq_trace_donate_to_prev);
> +		goto remove_subreq_locked;
> +	}
> +
> +	/* If we can't donate down the chain, donate up the chain instead. */
> +	excess = subreq->len - subreq->consumed + next_donated;
> +
> +	if (!subreq->consumed)
> +		excess += prev_donated;
> +
> +	if (list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
> +		rreq->prev_donated = excess;
> +		trace_netfs_donate(rreq, subreq, NULL, excess,
> +				   netfs_trace_donate_to_deferred_next);
> +	} else {
> +		next = list_next_entry(subreq, rreq_link);
> +		WRITE_ONCE(next->prev_donated, excess);
> +		trace_netfs_donate(rreq, subreq, next, excess,
> +				   netfs_trace_donate_to_next);
> +	}
> +	trace_netfs_sreq(subreq, netfs_sreq_trace_donate_to_next);
> +	subreq->len = subreq->consumed;
> +	subreq->transferred = subreq->consumed;
> +	goto remove_subreq_locked;
> +
> +remove_subreq:
> +	spin_lock_bh(&rreq->lock);
> +remove_subreq_locked:
> +	subreq->consumed = subreq->len;
> +	list_del(&subreq->rreq_link);
> +	spin_unlock_bh(&rreq->lock);
> +	netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_consumed);
> +	return true;
> +
> +bad:
> +	/* Errr... prev and next both donated to us, but insufficient to finish
> +	 * the folio.
> +	 */
> +	printk("R=%08x[%x] s=%llx-%llx %zx/%zx/%zx\n",
> +	       rreq->debug_id, subreq->debug_index,
> +	       subreq->start, subreq->start + subreq->transferred - 1,
> +	       subreq->consumed, subreq->transferred, subreq->len);
> +	printk("folio: %llx-%llx\n", fpos, fend - 1);
> +	printk("donated: prev=%zx next=%zx\n", prev_donated, next_donated);
> +	printk("s=%llx av=%zx part=%zx\n", start, avail, part);
> +	BUG();
> +}

...

Re: [PATCH 18/24] netfs: Speed up buffered reading

[Nathan Chancellor]

On Wed, Jul 31, 2024 at 08:07:42PM +0100, Simon Horman wrote:
> On Mon, Jul 29, 2024 at 05:19:47PM +0100, David Howells wrote:
> 
> ...
> 
> > diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
> 
> ...
> 
> > +/*
> > + * Perform a read to the pagecache from a series of sources of different types,
> > + * slicing up the region to be read according to available cache blocks and
> > + * network rsize.
> > + */
> > +static void netfs_read_to_pagecache(struct netfs_io_request *rreq)
> > +{
> > +	struct netfs_inode *ictx = netfs_inode(rreq->inode);
> > +	unsigned long long start = rreq->start;
> > +	ssize_t size = rreq->len;
> > +	int ret = 0;
> > +
> > +	atomic_inc(&rreq->nr_outstanding);
> > +
> > +	do {
> > +		struct netfs_io_subrequest *subreq;
> > +		enum netfs_io_source source = NETFS_DOWNLOAD_FROM_SERVER;
> > +		ssize_t slice;
> > +
> > +		subreq = netfs_alloc_subrequest(rreq);
> > +		if (!subreq) {
> > +			ret = -ENOMEM;
> > +			break;
> > +		}
> > +
> > +		subreq->start	= start;
> > +		subreq->len	= size;
> > +
> > +		atomic_inc(&rreq->nr_outstanding);
> > +		spin_lock_bh(&rreq->lock);
> > +		list_add_tail(&subreq->rreq_link, &rreq->subrequests);
> > +		subreq->prev_donated = rreq->prev_donated;
> > +		rreq->prev_donated = 0;
> > +		trace_netfs_sreq(subreq, netfs_sreq_trace_added);
> > +		spin_unlock_bh(&rreq->lock);
> > +
> > +		source = netfs_cache_prepare_read(rreq, subreq, rreq->i_size);
> > +		subreq->source = source;
> > +		if (source == NETFS_DOWNLOAD_FROM_SERVER) {
> > +			unsigned long long zp = umin(ictx->zero_point, rreq->i_size);
> > +			size_t len = subreq->len;
> > +
> > +			if (subreq->start >= zp) {
> > +				subreq->source = source = NETFS_FILL_WITH_ZEROES;
> > +				goto fill_with_zeroes;
> > +			}
> > +
> > +			if (len > zp - subreq->start)
> > +				len = zp - subreq->start;
> > +			if (len == 0) {
> > +				pr_err("ZERO-LEN READ: R=%08x[%x] l=%zx/%zx s=%llx z=%llx i=%llx",
> > +				       rreq->debug_id, subreq->debug_index,
> > +				       subreq->len, size,
> > +				       subreq->start, ictx->zero_point, rreq->i_size);
> > +				break;
> > +			}
> > +			subreq->len = len;
> > +
> > +			netfs_stat(&netfs_n_rh_download);
> > +			if (rreq->netfs_ops->prepare_read) {
> > +				ret = rreq->netfs_ops->prepare_read(subreq);
> > +				if (ret < 0) {
> > +					atomic_dec(&rreq->nr_outstanding);
> > +					netfs_put_subrequest(subreq, false,
> > +							     netfs_sreq_trace_put_cancel);
> > +					break;
> > +				}
> > +				trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
> > +			}
> > +
> > +			slice = netfs_prepare_read_iterator(subreq);
> > +			if (slice < 0) {
> > +				atomic_dec(&rreq->nr_outstanding);
> > +				netfs_put_subrequest(subreq, false, netfs_sreq_trace_put_cancel);
> > +				ret = slice;
> > +				break;
> > +			}
> > +
> > +			rreq->netfs_ops->issue_read(subreq);
> > +			goto done;
> > +		}
> > +
> > +	fill_with_zeroes:
> > +		if (source == NETFS_FILL_WITH_ZEROES) {
> > +			subreq->source = NETFS_FILL_WITH_ZEROES;
> > +			trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
> > +			netfs_stat(&netfs_n_rh_zero);
> > +			slice = netfs_prepare_read_iterator(subreq);
> > +			__set_bit(NETFS_SREQ_CLEAR_TAIL, &subreq->flags);
> > +			netfs_read_subreq_terminated(subreq, 0, false);
> > +			goto done;
> > +		}
> > +
> > +		if (source == NETFS_READ_FROM_CACHE) {
> > +			trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
> > +			slice = netfs_prepare_read_iterator(subreq);
> > +			netfs_read_cache_to_pagecache(rreq, subreq);
> > +			goto done;
> > +		}
> > +
> > +		if (source == NETFS_INVALID_READ)
> > +			break;
> 
> Hi David,
> 
> I feel a sense of deja vu here. So apologies if this was already
> discussed in the past.
> 
> If the code ever reaches this line, then slice will be used
> uninitialised below.
> 
> Flagged by W=1 allmodconfig builds on x86_64 with Clang 18.1.8.

which now breaks the build in next-20240801:

  fs/netfs/buffered_read.c:304:7: error: variable 'slice' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
    304 |                 if (source == NETFS_INVALID_READ)
        |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
  fs/netfs/buffered_read.c:308:11: note: uninitialized use occurs here
    308 |                 size -= slice;
        |                         ^~~~~
  fs/netfs/buffered_read.c:304:3: note: remove the 'if' if its condition is always true
    304 |                 if (source == NETFS_INVALID_READ)
        |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    305 |                         break;
  fs/netfs/buffered_read.c:221:16: note: initialize the variable 'slice' to silence this warning
    221 |                 ssize_t slice;
        |                              ^
        |                               = 0
  1 error generated.

If source has to be one of these values, perhaps switching to a switch
statement and having a default with a WARN_ON() or something would
convey that to the compiler?

Cheers,
Nathan

Re: [PATCH 18/24] netfs: Speed up buffered reading

[David Howells]

Simon Horman <horms@kernel.org> wrote:

> If the code ever reaches this line, then slice will be used
> uninitialised below.

It can't actually happen (or, at least, it shouldn't).  There are only three
ways of obtaining data: downloading from the server
(NETFS_DOWNLOAD_FROM_SERVER), reading from the cache (NETFS_READ_FROM_CACHE)
and just clearing space (NETFS_FILL_WITH_ZEROES); each of those has its own
if-statement that will set 'slice' or will switch the source to a different
type that will set 'slice'.

The problem is that the compiler doesn't know this.

The check for NETFS_INVALID_READ is there just in case.  Possibly:

		if (source == NETFS_INVALID_READ)
			break;

could be replaced with a WARN_ON_ONCE() and an unconditional break.

David

Re: [PATCH 18/24] netfs: Speed up buffered reading

[Simon Horman]

On Fri, Aug 02, 2024 at 03:18:02PM +0100, David Howells wrote:
> Simon Horman <horms@kernel.org> wrote:
> 
> > If the code ever reaches this line, then slice will be used
> > uninitialised below.
> 
> It can't actually happen (or, at least, it shouldn't).  There are only three
> ways of obtaining data: downloading from the server
> (NETFS_DOWNLOAD_FROM_SERVER), reading from the cache (NETFS_READ_FROM_CACHE)
> and just clearing space (NETFS_FILL_WITH_ZEROES); each of those has its own
> if-statement that will set 'slice' or will switch the source to a different
> type that will set 'slice'.
> 
> The problem is that the compiler doesn't know this.
> 
> The check for NETFS_INVALID_READ is there just in case.  Possibly:
> 
> 		if (source == NETFS_INVALID_READ)
> 			break;
> 
> could be replaced with a WARN_ON_ONCE() and an unconditional break.

Thanks, I think that should make the compiler happy without
significantly altering the flow or readability of the code.