GFS2: Add some useful messages

The following patch adds a message to indicate when barriers have been
disabled due to a block device which doesn't support them. You could
already tell this via the mount options in /proc/mounts, but all the
other filesystems also log a message at the same time.

Also, the same mechanisms are used to indicate when the lock
demote interface has been used (only ever used for debugging)
which is a request from our support team.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 7a93e9f..4d1aad3 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1334,7 +1334,8 @@
 	}
 	if (test_bit(SDF_NOBARRIERS, &sdp->sd_flags))
 		seq_printf(s, ",nobarrier");
-
+	if (test_bit(SDF_DEMOTE, &sdp->sd_flags))
+		seq_printf(s, ",demote_interface_used");
 	return 0;
 }