xfs: don't allow DAX on reflink filesystems

Now that reflink is no longer experimental, reject attempts to mount
with DAX until that whole mess gets sorted out.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Bill O'Donnell <billodo@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/xfs_super.c

@@ -1666,9 +1666,12 @@ xfs_fs_fill_super(
 			"DAX unsupported by block device. Turning off DAX.");
 			mp->m_flags &= ~XFS_MOUNT_DAX;
 		}
-		if (xfs_sb_version_hasreflink(&mp->m_sb))
+		if (xfs_sb_version_hasreflink(&mp->m_sb)) {
 			xfs_alert(mp,
 		"DAX and reflink cannot be used together!");
+			error = -EINVAL;
+			goto out_filestream_unmount;
+		}
 	}
 
 	if (mp->m_flags & XFS_MOUNT_DISCARD) {