watchdog: add support for starting/stopping kernel watchdog

Extend the ubus watchdog cmd with the parameter magicclose; when set and
in case the stopped parameter is enabled the kernel watchdog will be stopped
by first sending the magic character 'V' followed by a close of the watchdog
fd. In case stopped is set to disabled the watchdog fd will be created again.

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>
Acked-by: John Crispin <john@phrozen.org>

system.c

@@ -288,6 +288,7 @@ static int system_reboot(struct ubus_context *ctx, struct ubus_object *obj,
 enum {
 	WDT_FREQUENCY,
 	WDT_TIMEOUT,
+	WDT_MAGICCLOSE,
 	WDT_STOP,
 	__WDT_MAX
 };
@@ -295,6 +296,7 @@ enum {
 static const struct blobmsg_policy watchdog_policy[__WDT_MAX] = {
 	[WDT_FREQUENCY] = { .name = "frequency", .type = BLOBMSG_TYPE_INT32 },
 	[WDT_TIMEOUT] = { .name = "timeout", .type = BLOBMSG_TYPE_INT32 },
+	[WDT_MAGICCLOSE] = { .name = "magicclose", .type = BLOBMSG_TYPE_BOOL },
 	[WDT_STOP] = { .name = "stop", .type = BLOBMSG_TYPE_BOOL },
 };
 
@@ -329,6 +331,9 @@ static int watchdog_set(struct ubus_context *ctx, struct ubus_object *obj,
 		 watchdog_timeout(timeout);
 	}
 
+	if (tb[WDT_MAGICCLOSE])
+		watchdog_set_magicclose(blobmsg_get_bool(tb[WDT_MAGICCLOSE]));
+
 	if (tb[WDT_STOP])
 		watchdog_set_stopped(blobmsg_get_bool(tb[WDT_STOP]));
 
@@ -343,6 +348,7 @@ static int watchdog_set(struct ubus_context *ctx, struct ubus_object *obj,
 	blobmsg_add_string(&b, "status", status);
 	blobmsg_add_u32(&b, "timeout", watchdog_timeout(0));
 	blobmsg_add_u32(&b, "frequency", watchdog_frequency(0));
+	blobmsg_add_u8(&b, "magicclose", watchdog_get_magicclose());
 	ubus_send_reply(ctx, req, b.head);
 
 	return 0;

watchdog.c

@@ -31,6 +31,7 @@
 static struct uloop_timeout wdt_timeout;
 static int wdt_fd = -1;
 static int wdt_frequency = 5;
+static bool wdt_magicclose = false;
 
 void watchdog_ping(void)
 {
@@ -45,12 +46,66 @@ static void watchdog_timeout_cb(struct uloop_timeout *t)
 	uloop_timeout_set(t, wdt_frequency * 1000);
 }
 
+static int watchdog_open(bool cloexec)
+{
+	char *env = getenv("WDTFD");
+
+	if (wdt_fd >= 0)
+		return wdt_fd;
+
+	if (env) {
+		DEBUG(2, "Watchdog handover: fd=%s\n", env);
+		wdt_fd = atoi(env);
+		unsetenv("WDTFD");
+	} else {
+		wdt_fd = open(WDT_PATH, O_WRONLY);
+	}
+
+	if (wdt_fd < 0)
+		return wdt_fd;
+
+	if (cloexec)
+		fcntl(wdt_fd, F_SETFD, fcntl(wdt_fd, F_GETFD) | FD_CLOEXEC);
+
+	return wdt_fd;
+}
+
+static void watchdog_close(void)
+{
+	if (wdt_fd < 0)
+		return;
+
+	if (write(wdt_fd, "V", 1) < 0)
+		ERROR("WDT failed to write release: %s\n", strerror(errno));
+
+	if (close(wdt_fd) == -1)
+		ERROR("WDT failed to close watchdog: %s\n", strerror(errno));
+
+	wdt_fd = -1;
+}
+
+void watchdog_set_magicclose(bool val)
+{
+	wdt_magicclose = val;
+}
+
+bool watchdog_get_magicclose(void)
+{
+	return wdt_magicclose;
+}
+
 void watchdog_set_stopped(bool val)
 {
-	if (val)
+	if (val) {
 		uloop_timeout_cancel(&wdt_timeout);
-	else
+
+		if (wdt_magicclose)
+			watchdog_close();
+	}
+	else {
+		watchdog_open(true);
 		watchdog_timeout_cb(&wdt_timeout);
+	}
 }
 
 bool watchdog_get_stopped(void)
@@ -98,26 +153,11 @@ char* watchdog_fd(void)
 
 void watchdog_init(int preinit)
 {
-	char *env = getenv("WDTFD");
-
-	if (wdt_fd >= 0)
-		return;
-
 	wdt_timeout.cb = watchdog_timeout_cb;
-	if (env) {
-		DEBUG(2, "Watchdog handover: fd=%s\n", env);
-		wdt_fd = atoi(env);
-		unsetenv("WDTFD");
-	} else {
-		wdt_fd = open("/dev/watchdog", O_WRONLY);
-	}
 
-	if (wdt_fd < 0)
+	if (watchdog_open(!preinit) < 0)
 		return;
 
-	if (!preinit)
-		fcntl(wdt_fd, F_SETFD, fcntl(wdt_fd, F_GETFD) | FD_CLOEXEC);
-
 	LOG("- watchdog -\n");
 	watchdog_timeout(30);
 	watchdog_timeout_cb(&wdt_timeout);

watchdog.h

@@ -20,6 +20,8 @@ void watchdog_init(int preinit);
 char* watchdog_fd(void);
 int watchdog_timeout(int timeout);
 int watchdog_frequency(int frequency);
+void watchdog_set_magicclose(bool val);
+bool watchdog_get_magicclose(void);
 void watchdog_set_stopped(bool val);
 bool watchdog_get_stopped(void);
 void watchdog_no_cloexec(void);
@@ -44,6 +46,14 @@ static inline int watchdog_frequency(int frequency)
 	return 0;
 }
 
+static inline void watchdog_set_magicclose(bool val)
+{
+}
+
+static inline void watchdog_get_magicclose(bool val)
+{
+}
+
 static inline void watchdog_set_stopped(bool val)
 {
 }