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>

fs/gfs2/incore.h

@@ -498,6 +498,7 @@ enum {
 	SDF_NORECOVERY		= 4,
 	SDF_DEMOTE		= 5,
 	SDF_NOJOURNALID		= 6,
+	SDF_RORECOVERY		= 7, /* read only recovery */
 };
 
 #define GFS2_FSNAME_LEN		256

fs/gfs2/ops_fstype.c

@@ -1078,7 +1078,7 @@ static int fill_super(struct super_block *sb, struct gfs2_args *args, int silent
 
 	if (sdp->sd_args.ar_spectator) {
                 sb->s_flags |= MS_RDONLY;
-		set_bit(SDF_NORECOVERY, &sdp->sd_flags);
+		set_bit(SDF_RORECOVERY, &sdp->sd_flags);
 	}
 	if (sdp->sd_args.ar_posix_acl)
 		sb->s_flags |= MS_POSIXACL;

fs/gfs2/recovery.c

@@ -516,7 +516,9 @@ void gfs2_recover_func(struct work_struct *work)
 		if (error)
 			goto fail_gunlock_ji;
 
-		if (test_bit(SDF_JOURNAL_CHECKED, &sdp->sd_flags)) {
+		if (test_bit(SDF_RORECOVERY, &sdp->sd_flags)) {
+			ro = 1;
+		} else if (test_bit(SDF_JOURNAL_CHECKED, &sdp->sd_flags)) {
 			if (!test_bit(SDF_JOURNAL_LIVE, &sdp->sd_flags))
 				ro = 1;
 		} else {