[PATCH v6 03/13] iomap: rework IOMAP atomic flags

John Garry
2025-03-13T17:13:55Z

Flag IOMAP_ATOMIC_SW is not really required. The idea of having this flag
is that the FS ->iomap_begin callback could check if this flag is set to
decide whether to do a SW (FS-based) atomic write. But the FS can set
which ->iomap_begin callback it wants when deciding to do a FS-based
atomic write.

Furthermore, it was thought that IOMAP_ATOMIC_HW is not a proper name, as
the block driver can use SW-methods to emulate an atomic write. So change
back to IOMAP_ATOMIC.

The ->iomap_begin callback needs though to indicate to iomap core that
REQ_ATOMIC needs to be set, so add IOMAP_F_ATOMIC_BIO for that.

These changes were suggested by Christoph Hellwig and Dave Chinner.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
fs/ext4/inode.c | 5 ++++-
fs/iomap/direct-io.c | 8 +++-----
fs/iomap/trace.h | 2 +-
fs/xfs/xfs_iomap.c | 3 +++
include/linux/iomap.h | 12 +++++-------
5 files changed, 16 insertions(+), 14 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ba2f1e3db7c7..949d74d34926 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3290,6 +3290,9 @@ static void ext4_set_iomap(struct inode *inode, struct iomap *iomap,
if (map->m_flags & EXT4_MAP_NEW)
iomap->flags |= IOMAP_F_NEW;

+ if (flags & IOMAP_ATOMIC)
+ iomap->flags |= IOMAP_F_ATOMIC_BIO;
+
if (flags & IOMAP_DAX)
iomap->dax_dev = EXT4_SB(inode->i_sb)->s_daxdev;
else
@@ -3467,7 +3470,7 @@ static inline bool ext4_want_directio_fallback(unsigned flags, ssize_t written)
return false;

/* atomic writes are all-or-nothing */
- if (flags & IOMAP_ATOMIC_HW)
+ if (flags & IOMAP_ATOMIC)
return false;

/* can only try again if we wrote nothing */
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 9d72b99cb447..c28685fd3362 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -349,7 +349,7 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
if (dio->flags & IOMAP_DIO_WRITE) {
bio_opf |= REQ_OP_WRITE;

- if (iter->flags & IOMAP_ATOMIC_HW) {
+ if (iomap->flags & IOMAP_F_ATOMIC_BIO) {
/*
* Ensure that the mapping covers the full write length,
* otherwise we will submit multiple BIOs, which is
@@ -677,10 +677,8 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
iomi.flags |= IOMAP_OVERWRITE_ONLY;
}

- if (dio_flags & IOMAP_DIO_ATOMIC_SW)
- iomi.flags |= IOMAP_ATOMIC_SW;
- else if (iocb->ki_flags & IOCB_ATOMIC)
- iomi.flags |= IOMAP_ATOMIC_HW;
+ if (iocb->ki_flags & IOCB_ATOMIC)
+ iomi.flags |= IOMAP_ATOMIC;

/* for data sync or sync, we need sync completion processing */
if (iocb_is_dsync(iocb)) {
diff --git a/fs/iomap/trace.h b/fs/iomap/trace.h
index 69af89044ebd..9eab2c8ac3c5 100644
--- a/fs/iomap/trace.h
+++ b/fs/iomap/trace.h
@@ -99,7 +99,7 @@ DEFINE_RANGE_EVENT(iomap_dio_rw_queued);
{ IOMAP_FAULT, "FAULT" }, \
{ IOMAP_DIRECT, "DIRECT" }, \
{ IOMAP_NOWAIT, "NOWAIT" }, \
- { IOMAP_ATOMIC_HW, "ATOMIC_HW" }
+ { IOMAP_ATOMIC, "ATOMIC" }

#define IOMAP_F_FLAGS_STRINGS \
{ IOMAP_F_NEW, "NEW" }, \
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 30e257f683bb..9a22ecd794eb 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -831,6 +831,9 @@ xfs_direct_write_iomap_begin(
if (offset + length > i_size_read(inode))
iomap_flags |= IOMAP_F_DIRTY;

+ if (flags & IOMAP_ATOMIC)
+ iomap_flags |= IOMAP_F_ATOMIC_BIO;
+
/*
* COW writes may allocate delalloc space or convert unwritten COW
* extents, so we need to make sure to take the lock exclusively here.
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 9cd93530013c..51f4c13bd17a 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -60,6 +60,9 @@ struct vm_fault;
* IOMAP_F_ANON_WRITE indicates that (write) I/O does not have a target block
* assigned to it yet and the file system will do that in the bio submission
* handler, splitting the I/O as needed.
+ *
+ * IOMAP_F_ATOMIC_BIO indicates that (write) I/O needs to be issued as an
+ * atomic bio, i.e. set REQ_ATOMIC.
*/
#define IOMAP_F_NEW (1U << 0)
#define IOMAP_F_DIRTY (1U << 1)
@@ -73,6 +76,7 @@ struct vm_fault;
#define IOMAP_F_XATTR (1U << 5)
#define IOMAP_F_BOUNDARY (1U << 6)
#define IOMAP_F_ANON_WRITE (1U << 7)
+#define IOMAP_F_ATOMIC_BIO (1U << 8)

/*
* Flags set by the core iomap code during operations:
@@ -189,9 +193,8 @@ struct iomap_folio_ops {
#else
#define IOMAP_DAX 0
#endif /* CONFIG_FS_DAX */
-#define IOMAP_ATOMIC_HW (1 << 9) /* HW-based torn-write protection */
+#define IOMAP_ATOMIC (1 << 9) /* torn-write protection */
#define IOMAP_DONTCACHE (1 << 10)
-#define IOMAP_ATOMIC_SW (1 << 11)/* SW-based torn-write protection */

struct iomap_ops {
/*
@@ -503,11 +506,6 @@ struct iomap_dio_ops {
*/
#define IOMAP_DIO_PARTIAL (1 << 2)

-/*
- * Use software-based torn-write protection.
- */
-#define IOMAP_DIO_ATOMIC_SW (1 << 3)
-
ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
unsigned int dio_flags, void *private, size_t done_before);
--
2.31.1