[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.k...@hpe.com>
Cc: Dave Chinner <da...@fromorbit.com>
Cc: Dan Williams <dan.j.willi...@intel.com>
Cc: Ross Zwisler <ross.zwis...@linux.intel.com>
Cc: Christoph Hellwig <h...@infradead.org>
Cc: Boaz Harrosh <b...@plexistor.com>
---
 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;
                }
        }