ceph: connect to export targets if mds is laggy

If an MDS we are talking to may have failed, we need to open sessions to
its potential export targets to ensure that any in-progress migration that
may have involved some of our caps is properly handled.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/mds_client.c

@@ -2470,6 +2470,21 @@ static void check_new_map(struct ceph_mds_client *mdsc,
 			wake_up_session_caps(s, 1);
 		}
 	}
+
+	for (i = 0; i < newmap->m_max_mds && i < mdsc->max_sessions; i++) {
+		s = mdsc->sessions[i];
+		if (!s)
+			continue;
+		if (!ceph_mdsmap_is_laggy(newmap, i))
+			continue;
+		if (s->s_state == CEPH_MDS_SESSION_OPEN ||
+		    s->s_state == CEPH_MDS_SESSION_HUNG ||
+		    s->s_state == CEPH_MDS_SESSION_CLOSING) {
+			dout(" connecting to export targets of laggy mds%d\n",
+			     i);
+			__open_export_target_sessions(mdsc, s);
+		}
+	}
 }