lib: add sigevent_check api

Add an api that blocks application-handled signals (SIGINT,
SIGTERM, e.g.) then tests whether any signals have been received.
This helps to manage a race between signal reception and the poll
call in the main event loop.

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

lib/sigevent.c

@@ -63,6 +63,33 @@ static void quagga_signal_handler(int signo)
 	sigmaster.caught = 1;
 }
 
+/*
+ * Check whether any signals have been received and are pending. This is done
+ * with the application's key signals blocked. The complete set of signals
+ * is returned in 'setp', so the caller can restore them when appropriate.
+ * If there are pending signals, returns 'true', 'false' otherwise.
+ */
+bool frr_sigevent_check(sigset_t *setp)
+{
+	sigset_t blocked;
+	int i;
+	bool ret;
+
+	sigemptyset(setp);
+	sigemptyset(&blocked);
+
+	/* Set up mask of application's signals */
+	for (i = 0; i < sigmaster.sigc; i++)
+		sigaddset(&blocked, sigmaster.signals[i].signal);
+
+	pthread_sigmask(SIG_BLOCK, &blocked, setp);
+
+	/* Now that the application's signals are blocked, test. */
+	ret = (sigmaster.caught != 0);
+
+	return ret;
+}
+
 /* check if signals have been caught and run appropriate handlers */
 int quagga_sigevent_process(void)
 {

lib/sigevent.h

@@ -48,6 +48,15 @@ struct quagga_signal_t {
 extern void signal_init(struct thread_master *m, int sigc,
 			struct quagga_signal_t *signals);
 
+
+/*
+ * Check whether any signals have been received and are pending. This is done
+ * with the application's key signals blocked. The complete set of signals
+ * is returned in 'setp', so the caller can restore them when appropriate.
+ * If there are pending signals, returns 'true', 'false' otherwise.
+ */
+bool frr_sigevent_check(sigset_t *setp);
+
 /* check whether there are signals to handle, process any found */
 extern int quagga_sigevent_process(void);