Refactor, simplify registration of built-in watchdog daemon

This patch not only greatly simplifies the registration of the built-in
watchdog daemon, it also fixes a nasty race condition with an external
watchdog daemon.  The INIT_CMD_WDOG_HELLO could reach finit in reversed
order, leading to the built-in daemon shutting down, but finit killing
the just registered external daemon.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/finit.c

@@ -390,7 +390,7 @@ int main(int argc, char* argv[])
 	/*
 	 * Start built-in watchdog as soon as possible, if enabled
 	 */
-	watchdog(argv[0]);
+	wdogpid = watchdog(argv[0]);
 
 	/* Set hostname as soon as possible, for syslog et al. */
 	set_hostname(&hostname);

src/watchdog.c

@@ -21,54 +21,17 @@
  * THE SOFTWARE.
  */
 
-#include <paths.h>
 #include <signal.h>
-#include <sys/un.h>
 #include <sys/ioctl.h>
-#include <sys/socket.h>
 #include <linux/watchdog.h>
 
 #include "finit.h"
-#include "helpers.h"
-#include "util.h"
+#include "log.h"
 #include "watchdog.h"
 
 int running  = 1;
 int handover = 0;
 
-static int notify(void)
-{
-	int sd, result = 255;
-	ssize_t len;
-	struct sockaddr_un sun = {
-		.sun_family = AF_UNIX,
-		.sun_path   = INIT_SOCKET,
-	};
-	struct init_request rq;
-
-	sd = socket(AF_UNIX, SOCK_STREAM, 0);
-	if (-1 == sd)
-		return -1;
-
-	if (connect(sd, (struct sockaddr*)&sun, sizeof(sun)) == -1)
-		goto bye;
-
-	rq.cmd      = INIT_CMD_WDOG_HELLO;
-	rq.magic    = INIT_MAGIC;
-	rq.runlevel = getpid();
-	len         = sizeof(rq);
-	if (write(sd, &rq, len) != len)
-		goto bye;
-
-	if (read(sd, &rq, len) != len)
-		goto bye;
-
-	result = 0;
-bye:
-	close(sd);
-	return result;
-}
-
 static void sighandler(int signo)
 {
 	if (signo == SIGTERM)
@@ -95,27 +58,27 @@ static int init(char *progname, char *devnode, int timeout)
 
 static int loop(int fd)
 {
-	int done = 0;
+	int dummy = 0;
 
 	while (running) {
 		do_sleep(1);
-		ioctl(fd, WDIOC_KEEPALIVE, &done);
-
-		if (!done && !notify())
-			done = 1;
+		ioctl(fd, WDIOC_KEEPALIVE, &dummy);
 	}
 
 	if (handover) {
-		ioctl(fd, WDIOC_KEEPALIVE, &done);
+		ioctl(fd, WDIOC_KEEPALIVE, &dummy);
 		return !write(fd, "V", 1);
 	}
 
 	return 0;
 }
 
-void watchdog(char *progname)
+int watchdog(char *progname)
 {
-	if (fork() == 0) {
+	int pid;
+
+	pid = fork();
+	if (pid == 0) {
 		int fd, ret;
 
 		fd = init(progname, WDT_DEVNODE, WDT_TIMEOUT);
@@ -129,6 +92,8 @@ void watchdog(char *progname)
 
 		_exit(ret);
 	}
+
+	return pid;
 }
 
 /**

src/watchdog.h

@@ -27,9 +27,9 @@
 #define WDT_TIMEOUT 3
 
 #ifdef BUILTIN_WATCHDOG
-void    watchdog(char *progname);
+int     watchdog(char *progname);
 #else
-#define watchdog(progname)
+#define watchdog(progname) 0
 #endif /* BUILTIN_WATCHDOG */
 
 /**