lib: msg: make short-circuit connections guaranteed

lib/mgmt_msg.c

@@ -634,7 +634,7 @@ static void msg_client_sched_connect(struct msg_client *client,
 				&client->conn_retry_tmr);
 }
 
-static bool msg_client_connect_short_circuit(struct msg_client *client)
+static int msg_client_connect_short_circuit(struct msg_client *client)
 {
 	struct msg_conn *server_conn;
 	struct msg_server *server;
@@ -648,18 +648,17 @@ static bool msg_client_connect_short_circuit(struct msg_client *client)
 			break;
 	if (!server) {
 		MGMT_MSG_DBG(dbgtag,
-			     "no short-circuit connection available for %s",
+			     "no short-circuit server available yet for %s",
 			     client->sopath);
-
-		return false;
+		return -1;
 	}
 
 	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockets)) {
 		MGMT_MSG_ERR(
 			&client->conn.mstate,
 			"socketpair failed trying to short-circuit connection on %s: %s",
 			client->sopath, safe_strerror(errno));
-		return false;
+		return -1;
 	}
 
 	/* client side */
@@ -687,7 +686,7 @@ static bool msg_client_connect_short_circuit(struct msg_client *client)
 		client->sopath, client->conn.mstate.idtag, client->conn.fd,
 		server_conn->mstate.idtag, server_conn->fd);
 
-	return true;
+	return 0;
 }
 
 
@@ -697,11 +696,12 @@ static void msg_client_connect(struct msg_client *client)
 	struct msg_conn *conn = &client->conn;
 	const char *dbgtag = conn->debug ? conn->mstate.idtag : NULL;
 
-	if (!client->short_circuit_ok ||
-	    !msg_client_connect_short_circuit(client))
+	if (!client->short_circuit_ok)
 		conn->fd =
 			mgmt_msg_connect(client->sopath, MSG_CONN_SEND_BUF_SIZE,
 					 MSG_CONN_RECV_BUF_SIZE, dbgtag);
+	else if (msg_client_connect_short_circuit(client))
+		conn->fd = -1;
 
 	if (conn->fd == -1)
 		/* retry the connection */
@@ -741,7 +741,6 @@ void msg_client_init(struct msg_client *client, struct event_loop *tm,
 	mgmt_msg_init(&conn->mstate, max_read_buf, max_write_buf, max_msg_sz,
 		      idtag);
 
-	/* XXX maybe just have client kick this off */
 	/* Start trying to connect to server */
 	msg_client_sched_connect(client, 0);
 }

lib/mgmt_msg.h

@@ -136,6 +136,10 @@ struct msg_client {
 extern void msg_client_cleanup(struct msg_client *client);
 
 /*
+ * If `short_circuit_ok` is true, then the client-server connection will use a
+ * socketpair() rather than a unix-domain socket. This must be passed true if
+ * you wish to send messages short-circuit later.
+ *
  * `notify_disconnect` is not called when the user `msg_client_cleanup` is
  * called for a client which is currently connected. The socket is closed
  * but there is no notification.

mgmtd/mgmt.c

@@ -52,17 +52,26 @@ void mgmt_init(void)
 	/* Initialize the MGMTD Frontend Adapter Module */
 	mgmt_fe_adapter_init(mm->master);
 
-	/* Initialize the CLI frontend client */
+	/*
+	 * Initialize the CLI frontend client -- this queues an event for the
+	 * client to short-circuit connect to the server (ourselves).
+	 */
 	vty_init_mgmt_fe();
 
-	/* MGMTD VTY commands installation. */
+	/*
+	 * MGMTD VTY commands installation -- the frr lib code will queue an
+	 * event to read the config files which needs to happen after the
+	 * connect from above is made.
+	 */
 	mgmt_vty_init();
 
 	/*
 	 * Initialize the MGMTD Backend Adapter Module
 	 *
-	 * We do this after the FE stuff so that we always read our config file
-	 * prior to any BE connection.
+	 * We do this after the FE stuff so that we have read our config file
+	 * prior to any BE connection. Setting up the server will queue a
+	 * "socket read" event to accept BE connections. So the code is counting
+	 * on the above 2 events to run prior to any `accept` event from here.
 	 */
 	mgmt_be_adapter_init(mm->master);
 }

mgmtd/mgmt_vty.c

@@ -452,7 +452,14 @@ DEFPY(debug_mgmt, debug_mgmt_cmd,
 
 static void mgmt_config_read_in(struct event *event)
 {
-	mgmt_vty_read_configs();
+	if (vty_mgmt_fe_enabled())
+		mgmt_vty_read_configs();
+	else {
+		zlog_warn("%s: no connection to front-end server, retry in 1s",
+			  __func__);
+		event_add_timer(mm->master, mgmt_config_read_in, NULL, 1,
+				&mgmt_daemon_info->read_in);
+	}
 }
 
 void mgmt_vty_init(void)