[PATCH v3 13/59] netfs: Add support for DIO buffering

David Howells
2023-12-07T21:23:07Z

Add a bvec array pointer and an iterator to netfs_io_request for either
holding a copy of a DIO iterator or a list of all the bits of buffer
pointed to by a DIO iterator.

There are two problems: Firstly, if an iovec-class iov_iter is passed to
->read_iter() or ->write_iter(), this cannot be passed directly to
kernel_sendmsg() or kernel_recvmsg() as that may cause locking recursion if
a fault is generated, so we need to keep track of the pages involved
separately.

Secondly, if the I/O is asynchronous, we must copy the iov_iter describing
the buffer before returning to the caller as it may be immediately
deallocated.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
---
fs/netfs/objects.c | 10 ++++++++++
include/linux/netfs.h | 4 ++++
2 files changed, 14 insertions(+)

diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index 1bd20bdad983..4df5e5eeada6 100644
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -76,6 +76,7 @@ static void netfs_free_request(struct work_struct *work)
{
struct netfs_io_request *rreq =
container_of(work, struct netfs_io_request, work);
+ unsigned int i;

trace_netfs_rreq(rreq, netfs_rreq_trace_free);
netfs_proc_del_rreq(rreq);
@@ -84,6 +85,15 @@ static void netfs_free_request(struct work_struct *work)
rreq->netfs_ops->free_request(rreq);
if (rreq->cache_resources.ops)
rreq->cache_resources.ops->end_operation(&rreq->cache_resources);
+ if (rreq->direct_bv) {
+ for (i = 0; i < rreq->direct_bv_count; i++) {
+ if (rreq->direct_bv[i].bv_page) {
+ if (rreq->direct_bv_unpin)
+ unpin_user_page(rreq->direct_bv[i].bv_page);
+ }
+ }
+ kvfree(rreq->direct_bv);
+ }
kfree_rcu(rreq, rcu);
netfs_stat_d(&netfs_n_rh_rreq);
}
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 3da962e977f5..bbb33ccbf719 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -190,6 +190,9 @@ struct netfs_io_request {
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 */
+ struct bio_vec *direct_bv /* DIO buffer list (when handling iovec-iter) */
+ __counted_by(direct_bv_count);
+ unsigned int direct_bv_count; /* Number of elements in direct_bv[] */
unsigned int debug_id;
atomic_t nr_outstanding; /* Number of ops in progress */
atomic_t nr_copy_ops; /* Number of copy-to-cache ops in progress */
@@ -197,6 +200,7 @@ struct netfs_io_request {
size_t len; /* Length of the 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 */
loff_t i_size; /* Size of the file */
loff_t start; /* Start position */
pgoff_t no_unlock_folio; /* Don't unlock this folio after read */