v3 service: SIGCHLD handler

Hi!

Now we're ignoring SIGCHLD from forked children.
This patch provides SIGCHLD handler, that will wait for child and write some
information about it's exit status to logfile.
Signed-off-by: Ruslan Kuprieiev <kupruser@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

cr-service.c

@@ -253,6 +253,69 @@ err:
 	return -1;
 }
 
+static void reap_worker(int signo)
+{
+	int saved_errno;
+	int status;
+	pid_t pid;
+
+	saved_errno = errno;
+
+	/*
+	 * As we block SIGCHLD, lets wait for every child that has
+	 * already changed state.
+	 */
+	while (1) {
+		pid = waitpid(-1, &status, WNOHANG);
+
+		if (pid <= 0) {
+			errno = saved_errno;
+			return;
+		}
+
+		if (WIFEXITED(status))
+			pr_info("Worker(pid %d) exited with %d\n",
+				pid, WEXITSTATUS(status));
+		else if (WIFSIGNALED(status))
+			pr_info("Worker(pid %d) was killed by %d\n",
+				pid, WTERMSIG(status));
+	}
+}
+
+static int setup_sigchld_handler()
+{
+	struct sigaction action;
+
+	sigemptyset(&action.sa_mask);
+	sigaddset(&action.sa_mask, SIGCHLD);
+	action.sa_handler	= reap_worker;
+	action.sa_flags		= SA_RESTART;
+
+	if (sigaction(SIGCHLD, &action, NULL)) {
+		pr_perror("Can't setup SIGCHLD handler");
+		return -1;
+	}
+
+	return 0;
+}
+
+static int restore_sigchld_handler()
+{
+	struct sigaction action;
+
+	sigemptyset(&action.sa_mask);
+	sigaddset(&action.sa_mask, SIGCHLD);
+	action.sa_handler	= SIG_DFL;
+	action.sa_flags		= SA_RESTART;
+
+	if (sigaction(SIGCHLD, &action, NULL)) {
+		pr_perror("Can't restore SIGCHLD handler");
+		return -1;
+	}
+
+	return 0;
+}
+
 int cr_service(bool daemon_mode)
 {
 	int server_fd = -1;
@@ -318,8 +381,8 @@ int cr_service(bool daemon_mode)
 		}
 	}
 
-	/* FIXME Do not ignore children's return values */
-	signal(SIGCHLD, SIG_IGN);
+	if (setup_sigchld_handler())
+		goto err;
 
 	while (1) {
 		int sk;
@@ -337,6 +400,9 @@ int cr_service(bool daemon_mode)
 		if (child_pid == 0) {
 			int ret;
 
+			if (restore_sigchld_handler())
+				exit(1);
+
 			close(server_fd);
 			ret = cr_service_work(sk);
 			close(sk);