GFS2: let spectator mount do read only recovery

Previously, a spectator mount would not even attempt to do
journal recovery for a failed node.  This meant that if all
mounted nodes were spectators, everyone would be stuck after
a node failed, all waiting for recovery to be performed.
This is unnecessary since the failed node had a clean journal.

Instead, allow a spectator mount to do a partial "read only"
recovery, which means it will check if the failed journal is
clean, and if so, report a successful recovery.  If the failed
journal is not clean, it reports that journal recovery failed.
This makes it work the same as a read only mount on a read only
block device.

Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index b9422bc8..e5701c7 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -498,6 +498,7 @@
 	SDF_NORECOVERY		= 4,
 	SDF_DEMOTE		= 5,
 	SDF_NOJOURNALID		= 6,
+	SDF_RORECOVERY		= 7, /* read only recovery */
 };
 
 #define GFS2_FSNAME_LEN		256