commit 2a09d8d2da4b1acc8b761e235d2301ab225e40a7
Author: Mikolaj Golub <trociny@freebsd.org>
Date:   Sat Feb 11 10:42:51 2012 +0200

    Add -r option to restart the program if it has been terminated.
    
    Suggested by:	Andrey Zonov <andrey zonov org>
    Discussed with:	pjd
    MFC after:	2 weeks

diff --git a/usr.sbin/daemon/daemon.8 b/usr.sbin/daemon/daemon.8
index ce29ebe..858086c 100644
--- a/usr.sbin/daemon/daemon.8
+++ b/usr.sbin/daemon/daemon.8
@@ -71,16 +71,28 @@ owner is the user who runs the
 regardless of whether the
 .Fl u
 option is used or not.
-If the monitoring
+.It Fl r
+Supervise and restart the program if it has been terminated.
+.It Fl u Ar user
+Login name of the user to execute the program under.
+Requires adequate superuser privileges.
+.El
+.Pp
+If the
+.Fl p
+or
+.Fl r
+option is specified the program is executed in a spawned child process.
+The
+.Nm
+waits until it terminates to keep the pid file locked and removes it
+after the process exits or restarts the program.
+In this case if the monitoring
 .Nm
 receives software termination signal (SIGTERM) it forwards it to the
 spawned process.
 Normally it will cause the child to exit followed by the termination
 of the supervising process after removing the pidfile.
-.It Fl u Ar user
-Login name of the user to execute the program under.
-Requires adequate superuser privileges.
-.El
 .Sh EXIT STATUS
 The
 .Nm
diff --git a/usr.sbin/daemon/daemon.c b/usr.sbin/daemon/daemon.c
index 4df7641..8ec294e 100644
--- a/usr.sbin/daemon/daemon.c
+++ b/usr.sbin/daemon/daemon.c
@@ -46,7 +46,7 @@ __FBSDID("$FreeBSD$");
 
 static void dummy_sighandler(int);
 static void restrict_process(const char *);
-static void wait_child(pid_t pid, sigset_t *mask);
+static int  wait_child(pid_t pid, sigset_t *mask);
 static void usage(void);
 
 int
@@ -54,13 +54,14 @@ main(int argc, char *argv[])
 {
 	struct pidfh *pfh = NULL;
 	sigset_t mask, oldmask;
-	int ch, nochdir, noclose;
+	int ch, nochdir, noclose, restart;
 	const char *pidfile, *user;
 	pid_t otherpid, pid;
 
 	nochdir = noclose = 1;
+	restart = 0;
 	pidfile = user = NULL;
-	while ((ch = getopt(argc, argv, "-cfp:u:")) != -1) {
+	while ((ch = getopt(argc, argv, "-cfp:ru:")) != -1) {
 		switch (ch) {
 		case 'c':
 			nochdir = 0;
@@ -71,6 +72,9 @@ main(int argc, char *argv[])
 		case 'p':
 			pidfile = optarg;
 			break;
+		case 'r':
+			restart = 1;
+			break;
 		case 'u':
 			user = optarg;
 			break;
@@ -104,15 +108,16 @@ main(int argc, char *argv[])
 		err(1, NULL);
 
 	/*
-	 * If the pidfile option is specified the daemon executes the
-	 * command in a forked process and wait on child exit to
-	 * remove the pidfile. Normally we don't want the monitoring
-	 * daemon to be terminated leaving the running process and the
-	 * stale pidfile, so we catch SIGTERM and pass it to the
-	 * children expecting to get SIGCHLD eventually.
+	 * If the pidfile or restart option is specified the daemon
+	 * executes the command in a forked process and wait on child
+	 * exit to remove the pidfile or restart the command. Normally
+	 * we don't want the monitoring daemon to be terminated
+	 * leaving the running process and the stale pidfile, so we
+	 * catch SIGTERM and forward it to the children expecting to
+	 * get SIGCHLD eventually.
 	 */
 	pid = -1;
-	if (pidfile) {
+	if (pidfile != NULL || restart) {
 		/*
 		 * Restore default action for SIGTERM in case the
 		 * parent process decided to ignore it.
@@ -133,6 +138,7 @@ main(int argc, char *argv[])
 		sigaddset(&mask, SIGCHLD);
 		if (sigprocmask(SIG_SETMASK, &mask, &oldmask) == -1)
 			err(1, "sigprocmask");
+restart:
 		/*
 		 * Spawn a child to exec the command, so in the parent
 		 * we could wait for it to exit and remove pidfile.
@@ -164,7 +170,10 @@ main(int argc, char *argv[])
 		err(1, "%s", argv[0]);
 	}
 	setproctitle("%s[%d]", argv[0], pid);
-	wait_child(pid, &mask);
+	if (wait_child(pid, &mask) == 0 && restart) {
+		sleep(1);
+		goto restart;
+	}
 	pidfile_remove(pfh);
 	exit(0); /* Exit status does not matter. */
 }
@@ -188,28 +197,30 @@ restrict_process(const char *user)
 		errx(1, "failed to set user environment");
 }
 
-static void
+static int
 wait_child(pid_t pid, sigset_t *mask)
 {
-	int signo;
+	int terminate, signo;
 
+	terminate = 0;
 	for (;;) {
 		if (sigwait(mask, &signo) == -1) {
 			warn("sigwaitinfo");
-			return;
+			return (-1);
 		}
 		switch (signo) {
 		case SIGCHLD:
-			return;
+			return (terminate);
 		case SIGTERM:
+			terminate = 1;
 			if (kill(pid, signo) == -1) {
 				warn("kill");
-				return;
+				return (-1);
 			}
 			continue;
 		default:
 			warnx("sigwaitinfo: invalid signal: %d", signo);
-			return;
+			return (-1);
 		}
 	}
 }