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

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  [PATCH v3 5/5] xfs: Add alignment check for DAX mount Toshi Kani <toshi.kani@hpe.com> - 2016-05-06 02:40 +0200
    Re: [PATCH v3 5/5] xfs: Add alignment check for DAX mount Christoph Hellwig <hch@infradead.org> - 2016-05-08 11:00 +0200

#1395527 — [PATCH v3 5/5] xfs: Add alignment check for DAX mount

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@hpe.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Boaz Harrosh <boaz@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;
 		}
 	}

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#1396398

Looks fine for now.  In the long run we'll need to check it for the
RT subvolume as well, or prohibit DAX if there is an active RT
subvolume.

Reviewed-by: Christoph Hellwig <hch@lst.de>

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