xfs: disable noattr2/attr2 mount options for CRC enabled filesystems

attr2 format is always enabled for v5 superblock filesystems, so the
mount options to enable or disable it need to be cause mount errors.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

Documentation/filesystems/xfs.txt

@@ -33,6 +33,9 @@ When mounting an XFS filesystem, the following options are accepted.
 	removing extended attributes) the on-disk superblock feature
 	bit field will be updated to reflect this format being in use.
 
+	CRC enabled filesystems always use the attr2 format, and so
+	will reject the noattr2 mount option if it is set.
+
   barrier
 	Enables the use of block layer write barriers for writes into
 	the journal and unwritten extent conversion.  This allows for

fs/xfs/xfs_super.c

@@ -1372,6 +1372,17 @@ xfs_finish_flags(
 		}
 	}
 
+	/*
+	 * V5 filesystems always use attr2 format for attributes.
+	 */
+	if (xfs_sb_version_hascrc(&mp->m_sb) &&
+	    (mp->m_flags & XFS_MOUNT_NOATTR2)) {
+		xfs_warn(mp,
+"Cannot mount a V5 filesystem as %s. %s is always enabled for V5 filesystems.",
+			MNTOPT_NOATTR2, MNTOPT_ATTR2);
+		return XFS_ERROR(EINVAL);
+	}
+
 	/*
 	 * mkfs'ed attr2 will turn on attr2 mount unless explicitly
 	 * told by noattr2 to turn it off