[PATCH v2 3/3] 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_direct_access to check the alignment when -o dax is
specified.

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 |   23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 187e14b..b7ee323 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1557,15 +1557,30 @@ xfs_fs_fill_super(
 		sb->s_flags |= MS_I_VERSION;
 
 	if (mp->m_flags & XFS_MOUNT_DAX) {
+		struct blk_dax_ctl dax = {
+			.sector = 0,
+			.size = PAGE_SIZE,
+		};
 		xfs_warn(mp,
-	"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
+		"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) {
-			xfs_alert(mp,
-		"Block device does not support DAX Turning DAX off.");
+		} else if ((error = bdev_direct_access(sb->s_bdev, &dax)) < 0) {
+			switch (error) {
+			case -EOPNOTSUPP:
+				xfs_alert(mp,
+			"Block device does not support DAX Turning DAX off.");
+				break;
+			case -EINVAL:
+				xfs_alert(mp,
+			"Partition alignment invalid for DAX Turning DAX off.");
+				break;
+			default:
+				xfs_alert(mp,
+			"DAX access failed (%d) DAX Turning DAX off.", error);
+			}
 			mp->m_flags &= ~XFS_MOUNT_DAX;
 		}
 	}