[PATCH v4 17/22] fs: Add FS_XFLAG_ATOMICWRITES flag

[John Garry]

Add a flag indicating that a regular file is enabled for atomic writes.

This is a file attribute that mirrors an ondisk inode flag.  Actual support
for untorn file writes (for now) depends on both the iflag and the
underlying storage devices, which we can only really check at statx and
pwritev2() time.  This is the same story as FS_XFLAG_DAX, which signals to
the fs that we should try to enable the fsdax IO path on the file (instead
of the regular page cache), but applications have to query STAT_ATTR_DAX
to find out if they really got that IO path.

Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
 include/uapi/linux/fs.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 6a6bcb53594a..0eae5383a0b4 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -160,6 +160,7 @@ struct fsxattr {
 #define FS_XFLAG_COWEXTSIZE	0x00010000	/* CoW extent size allocator hint */
 /* data extent mappings for regular files must be aligned to extent size hint */
 #define FS_XFLAG_FORCEALIGN	0x00020000
+#define FS_XFLAG_ATOMICWRITES	0x00040000	/* atomic writes enabled */
 #define FS_XFLAG_HASATTR	0x80000000	/* no DIFLAG for this	*/
 
 /* the read-only stuff doesn't really belong here, but any other place is
-- 
2.31.1