libceph: support for subscribing to "mdsmap.<id>" maps

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
diff --git a/net/ceph/debugfs.c b/net/ceph/debugfs.c
index 6e434c7..e77b04c 100644
--- a/net/ceph/debugfs.c
+++ b/net/ceph/debugfs.c
@@ -128,6 +128,7 @@
 					CEPH_SUBSCRIBE_ONETIME ?  "" : "+"));
 		seq_putc(s, '\n');
 	}
+	seq_printf(s, "fs_cluster_id %d\n", monc->fs_cluster_id);
 
 	for (rp = rb_first(&monc->generic_request_tree); rp; rp = rb_next(rp)) {
 		__u16 op;