[PATCH v3 5/5] xfs: Add alignment check for DAX mount

[Toshi Kani]

When a partition is not aligned by 4KB, mount -o dax succeeds,
but any read/write access to the filesystem fails, except for
metadata update.

Call bdev_supports_dax() to perform proper precondition checks
which includes this partition alignment check.

Signed-off-by: Toshi Kani <toshi.kani@xxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Boaz Harrosh <boaz@xxxxxxxxxxxxx>
---
 fs/xfs/xfs_super.c |   12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 187e14b..cc177da 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1558,14 +1558,12 @@ xfs_fs_fill_super(
 
 	if (mp->m_flags & XFS_MOUNT_DAX) {
 		xfs_warn(mp,
-	"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
-		if (sb->s_blocksize != PAGE_SIZE) {
-			xfs_alert(mp,
-		"Filesystem block size invalid for DAX Turning DAX off.");
-			mp->m_flags &= ~XFS_MOUNT_DAX;
-		} else if (!sb->s_bdev->bd_disk->fops->direct_access) {
+		"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
+
+		error = bdev_supports_dax(sb, sb->s_blocksize);
+		if (error) {
 			xfs_alert(mp,
-		"Block device does not support DAX Turning DAX off.");
+			"DAX unsupported by block device. Turning off DAX.");
 			mp->m_flags &= ~XFS_MOUNT_DAX;
 		}
 	}