[PATCH v3 3/3] xfs: reject max_atomic_write mount option for no reflink

[John Garry]

If the FS has no reflink, then atomic writes greater than 1x block are not
supported. As such, for no reflink it is pointless to accept setting
max_atomic_write when it cannot be supported, so reject max_atomic_write
mount option in this case.

It could be still possible to accept max_atomic_write option of size 1x
block if HW atomics are supported, so check for this specifically.

Fixes: 4528b9052731 ("xfs: allow sysadmins to specify a maximum atomic write limit at mount time")
Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
 fs/xfs/xfs_mount.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 0b690bc119d7..1ec70f4e57b4 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -784,6 +784,25 @@ xfs_set_max_atomic_write_opt(
 		return -EINVAL;
 	}
 
+	if (xfs_has_reflink(mp))
+		goto set_limit;
+
+	if (new_max_fsbs == 1) {
+		if (mp->m_ddev_targp->bt_awu_max ||
+		    (mp->m_rtdev_targp && mp->m_rtdev_targp->bt_awu_max)) {
+		} else {
+			xfs_warn(mp,
+ "cannot support atomic writes of size %lluk with no reflink or HW support",
+				new_max_bytes >> 10);
+			return -EINVAL;
+		}
+	} else {
+		xfs_warn(mp,
+ "cannot support atomic writes of size %lluk with no reflink support",
+				new_max_bytes >> 10);
+		return -EINVAL;
+	}
+
 set_limit:
 	error = xfs_calc_atomic_write_reservation(mp, new_max_fsbs);
 	if (error) {
-- 
2.43.5