mds: use a random nonce in Messenger

The MDS is a client to the OSDs, and responds
to blacklists by respawning itself.  Usually
respawns of a daemonized process result in a PID
change, but it's not guaranteed, and it's definitely
not the case when someone runs in foreground (e.g.
teuthology).

Using a random nonce makes sure we won't match
against an existing blacklist entry from a failed
instance of an MDS daemon with the same name as us.

Related to: http://tracker.ceph.com/issues/17236
Signed-off-by: John Spray <john.spray@redhat.com>

src/ceph_mds.cc

@@ -136,9 +136,12 @@ int main(int argc, const char **argv)
       "MDS names may not start with a numeric digit." << dendl;
   }
 
+  uint64_t nonce = 0;
+  get_random_bytes((char*)&nonce, sizeof(nonce));
+
   Messenger *msgr = Messenger::create(g_ceph_context, g_conf->ms_type,
 				      entity_name_t::MDS(-1), "mds",
-				      getpid(), 0, Messenger::HAS_MANY_CONNECTIONS);
+				      nonce, 0, Messenger::HAS_MANY_CONNECTIONS);
   if (!msgr)
     exit(1);
   msgr->set_cluster_protocol(CEPH_MDS_PROTOCOL);