[PATCH 04/19] btrfs: disable fallocate in HMZONED mode

[Naohiro Aota]

fallocate() is implemented by reserving actual extent instead of
reservations. This can result in exposing the sequential write constraint
of host-managed zoned block devices to the application, which would break
the POSIX semantic for the fallocated file.  To avoid this, report
fallocate() as not supported when in HMZONED mode for now.

In the future, we may be able to implement "in-memory" fallocate() in
HMZONED mode by utilizing space_info->bytes_may_use or so.

Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
---
 fs/btrfs/file.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 89f5be2bfb43..e664b5363697 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -3027,6 +3027,10 @@ static long btrfs_fallocate(struct file *file, int mode,
 	alloc_end = round_up(offset + len, blocksize);
 	cur_offset = alloc_start;
 
+	/* Do not allow fallocate in HMZONED mode */
+	if (btrfs_fs_incompat(btrfs_sb(inode->i_sb), HMZONED))
+		return -EOPNOTSUPP;
+
 	/* Make sure we aren't being give some crap mode */
 	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
 		     FALLOC_FL_ZERO_RANGE))
-- 
2.21.0