watchdog: stop watchdog first on startup

Some watchdog implementations may do things other than issue
a reboot on a watchdog timeout.  In this case, there's the
possibility of restarting this program from the state of
the watchdog device not being properly stopped (done by writing
a 'V' and closing the device).  Since it wasn't stopped, the
driver may not be able to restart the watchdog when this program
reopens it and starts pinging it.

To fix this, the code will always first issue the stop when it
starts up.

function                                             old     new   delta
shutdown_on_signal                                     -      32     +32
watchdog_main                                        268     298     +30
shutdown_watchdog                                      -      25     +25
watchdog_shutdown                                     41       -     -41
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 1/0 up/down: 87/-41)             Total: 46 bytes

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 25 insertions, 7 deletions

diff --git a/miscutils/watchdog.c b/miscutils/watchdog.c
index 07ae64e..95e2f1a 100644
--- a/miscutils/watchdog.c
+++ b/miscutils/watchdog.c
@@ -42,17 +42,36 @@
 #define OPT_STIMER      (1 << 1)
 #define OPT_HTIMER      (1 << 2)
 
-static void watchdog_shutdown(int sig UNUSED_PARAM)
+static void shutdown_watchdog(void)
 {
 	static const char V = 'V';
+	write(3, &V, 1);  /* Magic, see watchdog-api.txt in kernel */
+	close(3);
+}
 
+static void shutdown_on_signal(int sig UNUSED_PARAM)
+{
 	remove_pidfile(CONFIG_PID_FILE_PATH "/watchdog.pid");
-	write(3, &V, 1);  /* Magic, see watchdog-api.txt in kernel */
-	if (ENABLE_FEATURE_CLEAN_UP)
-		close(3);
+	shutdown_watchdog();
 	_exit(EXIT_SUCCESS);
 }
 
+static void watchdog_open(const char* device)
+{
+	/* Use known fd # - avoid needing global 'int fd' */
+	xmove_fd(xopen(device, O_WRONLY), 3);
+
+	/* If the watchdog driver can do something other than cause a reboot
+	 * on a timeout, then it's possible this program may be starting from
+	 * a state when the watchdog hadn't been previously stopped with
+	 * the magic write followed by a close.  In this case the driver may
+	 * not start properly, so always do the proper stop first just in case.
+	 */
+	shutdown_watchdog();
+
+	xmove_fd(xopen(device, O_WRONLY), 3);
+}
+
 int watchdog_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int watchdog_main(int argc, char **argv)
 {
@@ -86,10 +105,9 @@ int watchdog_main(int argc, char **argv)
 	if (opts & OPT_STIMER)
 		stimer_duration = xatou_sfx(st_arg, suffixes);
 
-	bb_signals(BB_FATAL_SIGS, watchdog_shutdown);
+	bb_signals(BB_FATAL_SIGS, shutdown_on_signal);
 
-	/* Use known fd # - avoid needing global 'int fd' */
-	xmove_fd(xopen(argv[argc - 1], O_WRONLY), 3);
+	watchdog_open(argv[argc - 1]);
 
 	/* WDIOC_SETTIMEOUT takes seconds, not milliseconds */
 	htimer_duration = htimer_duration / 1000;