diff --git a/include/linux/ceph/ceph_fs.h b/include/linux/ceph/ceph_fs.h
index 3b911ff889ddb4d59e6b4598c3c61940d24abb1f..bae833d0d05550dc03c5bb15fda1686e56b8379c 100644
--- a/include/linux/ceph/ceph_fs.h
+++ b/include/linux/ceph/ceph_fs.h
@@ -208,6 +208,8 @@ struct ceph_mon_subscribe_ack {
 	struct ceph_fsid fsid;
 } __attribute__ ((packed));
 
+#define CEPH_FS_CLUSTER_ID_NONE  -1
+
 /*
  * mdsmap flags
  */
diff --git a/include/linux/ceph/mon_client.h b/include/linux/ceph/mon_client.h
index 1d730993c3f8f7bd6ffa6680e34439048100be0d..e2a92df08b47d2f00d986c3547accf4eeb53cf6c 100644
--- a/include/linux/ceph/mon_client.h
+++ b/include/linux/ceph/mon_client.h
@@ -96,6 +96,7 @@ struct ceph_mon_client {
 		bool want;
 		u32 have; /* epoch */
 	} subs[3];
+	int fs_cluster_id; /* "mdsmap.<id>" sub */
 
 #ifdef CONFIG_DEBUG_FS
 	struct dentry *debugfs_file;
diff --git a/net/ceph/debugfs.c b/net/ceph/debugfs.c
index 6e434c75cd08c1617cb80b142afc5c950752dbdf..e77b04ca7802c046af213abd25650a11bcc6a6a3 100644
--- a/net/ceph/debugfs.c
+++ b/net/ceph/debugfs.c
@@ -128,6 +128,7 @@ static int monc_show(struct seq_file *s, void *p)
 					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;
diff --git a/net/ceph/mon_client.c b/net/ceph/mon_client.c
index 72a910bf7819d766030bd26d5a786cac14a33486..37c38a7fb5c586bf7698daaf71308b15bd973edb 100644
--- a/net/ceph/mon_client.c
+++ b/net/ceph/mon_client.c
@@ -260,20 +260,26 @@ static void __send_subscribe(struct ceph_mon_client *monc)
 	BUG_ON(num < 1); /* monmap sub is always there */
 	ceph_encode_32(&p, num);
 	for (i = 0; i < ARRAY_SIZE(monc->subs); i++) {
-		const char *s = ceph_sub_str[i];
+		char buf[32];
+		int len;
 
 		if (!monc->subs[i].want)
 			continue;
 
-		dout("%s %s start %llu flags 0x%x\n", __func__, s,
+		len = sprintf(buf, "%s", ceph_sub_str[i]);
+		if (i == CEPH_SUB_MDSMAP &&
+		    monc->fs_cluster_id != CEPH_FS_CLUSTER_ID_NONE)
+			len += sprintf(buf + len, ".%d", monc->fs_cluster_id);
+
+		dout("%s %s start %llu flags 0x%x\n", __func__, buf,
 		     le64_to_cpu(monc->subs[i].item.start),
 		     monc->subs[i].item.flags);
-		ceph_encode_string(&p, end, s, strlen(s));
+		ceph_encode_string(&p, end, buf, len);
 		memcpy(p, &monc->subs[i].item, sizeof(monc->subs[i].item));
 		p += sizeof(monc->subs[i].item);
 	}
 
-	BUG_ON(p != (end - 35 - (ARRAY_SIZE(monc->subs) - num) * 19));
+	BUG_ON(p > end);
 	msg->front.iov_len = p - msg->front.iov_base;
 	msg->hdr.front_len = cpu_to_le32(msg->front.iov_len);
 	ceph_msg_revoke(msg);
@@ -948,7 +954,7 @@ int ceph_monc_init(struct ceph_mon_client *monc, struct ceph_client *cl)
 	if (!monc->m_subscribe_ack)
 		goto out_auth;
 
-	monc->m_subscribe = ceph_msg_new(CEPH_MSG_MON_SUBSCRIBE, 96, GFP_NOFS,
+	monc->m_subscribe = ceph_msg_new(CEPH_MSG_MON_SUBSCRIBE, 128, GFP_NOFS,
 					 true);
 	if (!monc->m_subscribe)
 		goto out_subscribe_ack;
@@ -974,6 +980,8 @@ int ceph_monc_init(struct ceph_mon_client *monc, struct ceph_client *cl)
 	monc->generic_request_tree = RB_ROOT;
 	monc->last_tid = 0;
 
+	monc->fs_cluster_id = CEPH_FS_CLUSTER_ID_NONE;
+
 	return 0;
 
 out_auth_reply: