zebra: only perform shutdown signal processing once

Avoid running the shutdown/sigint handler code more than once. With
the async dataplane, once shutdown has been initiated, the completion
of all async updates triggers final shutdown of the zebra main
pthread. During that time, avoid taking and processing a second
signal, such as SIGINT or SIGTERM.

Signed-off-by: Mark Stapp <mjs@voltanet.io>

zebra/main.c

@@ -142,6 +142,12 @@ static void sigint(void)
 	struct zebra_vrf *zvrf;
 	struct listnode *ln, *nn;
 	struct zserv *client;
+	static bool sigint_done;
+
+	if (sigint_done)
+		return;
+
+	sigint_done = true;
 
 	zlog_notice("Terminating on signal");
 
@@ -174,11 +180,17 @@ static void sigint(void)
 
 	list_delete(&zebrad.client_list);
 
-	/* Indicate that all new dplane work has been enqueued */
+	/* Indicate that all new dplane work has been enqueued. When that
+	 * work is complete, the dataplane will enqueue an event
+	 * with the 'finalize' function.
+	 */
 	zebra_dplane_finish();
 }
 
-/* TODO */
+/*
+ * Final shutdown step for the zebra main thread. This is run after all
+ * async update processing has completed.
+ */
 int zebra_finalize(struct thread *dummy)
 {
 	zlog_info("Zebra final shutdown");