iomap: rework IOMAP atomic flags

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>
Link: https://lore.kernel.org/r/20250320120250.4087011-4-john.g.garry@oracle.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>

4 files changed, 13 insertions, 7 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ba2f1e3db7c7..d04d8a7f12e7 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3290,6 +3290,10 @@ static void ext4_set_iomap(struct inode *inode, struct iomap *iomap,
 	if (map->m_flags & EXT4_MAP_NEW)
 		iomap->flags |= IOMAP_F_NEW;
 
+	/* HW-offload atomics are always used */
+	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 +3471,7 @@ 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 b9f59ca43c15..6ac7a1534f7c 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 it won't be submitted as a single
@@ -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 5dd0922fe2d1..ee40dc509413 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -828,6 +828,10 @@ xfs_direct_write_iomap_begin(
 	if (offset + length > i_size_read(inode))
 		iomap_flags |= IOMAP_F_DIRTY;
 
+	/* HW-offload atomics are always used in this path */
+	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.