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

[John Garry <john.g.garry@oracle.com>]

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