mds: gracefully exit if newer gid replaces us by name

If 'mds enforce unique name' is set, and another MDS with the same name
kicks us out of the MDSMap, gracefully exit instead of respawning and
fighting over our position.

Signed-off-by: Sage Weil <sage@inktank.com>

src/mds/MDS.cc

@@ -903,6 +903,20 @@ void MDS::handle_mds_map(MMDSMap *m)
       if (want_state == MDSMap::STATE_BOOT) {
         dout(10) << "not in map yet" << dendl;
       } else {
+	// did i get kicked by someone else?
+	if (g_conf->mds_enforce_unique_name) {
+	  if (uint64_t existing = mdsmap->find_mds_gid_by_name(name)) {
+	    MDSMap::mds_info_t& i = mdsmap->get_info_gid(existing);
+	    if (i.global_id > monc->get_global_id()) {
+	      dout(1) << "handle_mds_map i (" << addr
+		      << ") dne in the mdsmap, new instance has larger gid " << i.global_id
+		      << ", suicide" << dendl;
+	      suicide();
+	      goto out;
+	    }
+	  }
+	}
+
         dout(1) << "handle_mds_map i (" << addr
             << ") dne in the mdsmap, respawning myself" << dendl;
         respawn();