watchdog: Add simple built-in watchdog daemon

This patch adds a simple but effective watchdog daemon with support for
handover to an external daemon, should one register using the API.

Disabled by default, enable by:

    configure --enable-watchdog

The watchdog forks to the background, opening /dev/watchdog setting a
three second timeout, and kicking every second.  At shutdown/reboot the
daemon will receive SIGPWR from Finit to exit and cause a WDT reboot.

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

Makefile.am

@@ -19,6 +19,9 @@ pkginclude_HEADERS = cond.h finit.h helpers.h inetd.h plugin.h svc.h
 if INETD
 finit_SOURCES     += inetd.c	inetd.h
 endif
+if WATCHDOGD
+finit_SOURCES     += watchdog.c	watchdog.h
+endif
 
 finit_CFLAGS       = -W -Wall -Wextra -std=gnu99 $(lite_CFLAGS) $(uev_CFLAGS)
 finit_LDADD        = $(lite_LIBS) $(uev_LIBS)

configure.ac

@@ -50,6 +50,9 @@ AC_ARG_ENABLE(rw-rootfs,
 AC_ARG_ENABLE(silent,
         AS_HELP_STRING([--enable-silent], [Completely silent operation, not even boot messages]))
 
+AC_ARG_ENABLE(watchdog,
+        AS_HELP_STRING([--enable-watchdog], [Enable built-in watchdog, uses /dev/watchdog]))
+
 AC_ARG_ENABLE(inetd,
         AS_HELP_STRING([--disable-inetd], [Disable built-in inetd super server, default enabled]))
 
@@ -134,6 +137,9 @@ AS_IF([test "x$enable_silent" = "xyes"], [
 	], [
 	AC_DEFINE(SILENT_MODE,  0, [Normal output, default])])
 
+AS_IF([test "x$enable_watchdog" = "xyes"], [
+        AC_DEFINE(BUILTIN_WATCHDOG,  1, [Enable built-in watchdog, kicks on /dev/watchdog])])
+
 ### Disable features ###########################################################################
 AS_IF([test "x$enable_inetd" != "xno"], enable_inetd="yes", [
 	AC_DEFINE(INETD_DISABLED,  1, [Disable built-in inetd])])
@@ -200,8 +206,9 @@ AS_IF([test "x$with_random_seed" != "xno"], [
 	AC_DEFINE_UNQUOTED(RANDOMSEED, "$lurvig", [Improve random at boot by seeding it with sth from before.])])
 
 # Control build with automake flags
-AM_CONDITIONAL(STATIC, [test "x$enable_static" = "xyes"])
+AM_CONDITIONAL(STATIC,    [test "x$enable_static" = "xyes"])
-AM_CONDITIONAL(INETD, [test "x$enable_inetd" = "xyes"])
+AM_CONDITIONAL(INETD,     [test "x$enable_inetd" = "xyes"])
+AM_CONDITIONAL(WATCHDOGD, [test "x$enable_watchdog" = "xyes"])
 
 # Generate all files
 AC_OUTPUT

finit.c

@@ -46,6 +46,7 @@
 #include "sm.h"
 #include "tty.h"
 #include "utmp-api.h"
+#include "watchdog.h"
 
 int   debug     = 0;
 int   quiet     = QUIET_MODE;	/* Delayed disable of silent mode. */
@@ -343,6 +344,11 @@ int main(int argc, char* argv[])
 	 */
 	conf_parse_config();
 
+	/*
+	 * Start built-in watchdog as soon as possible, if enabled
+	 */
+	watchdog(argv[0]);
+
 	/* Set hostname as soon as possible, for syslog et al. */
 	set_hostname(&hostname);
 

watchdog.c

@@ -0,0 +1,135 @@
+/* Built-in watchdog daemon
+ *
+ * Copyright (c) 2016  Joachim Nilsson <troglobit@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <paths.h>
+#include <sys/un.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <linux/watchdog.h>
+
+#include "finit.h"
+#include "helpers.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 exit;
+
+	rq.cmd      = INIT_CMD_WDOG_HELLO;
+	rq.magic    = INIT_MAGIC;
+	rq.runlevel = getpid();
+	len         = sizeof(rq);
+	if (write(sd, &rq, len) != len)
+		goto exit;
+
+	if (read(sd, &rq, len) != len)
+		goto exit;
+
+	result = 0;
+exit:
+	close(sd);
+	return result;
+}
+
+static void sighandler(int signo)
+{
+	if (signo == SIGTERM)
+		handover = 1;
+	running = 0;
+}
+
+static int init(char *progname, char *devnode, int timeout)
+{
+	int fd;
+
+	sprintf(progname, "@finit-watchdog");
+	signal(SIGTERM, sighandler);
+	signal(SIGPWR,  sighandler);
+
+	fd = open(devnode, O_WRONLY);
+	if (fd == -1)
+		return -1;
+
+	ioctl(fd, WDIOC_SETTIMEOUT, &timeout);
+
+	return fd;
+}
+
+static int loop(int fd)
+{
+	int done = 0;
+
+	while (running) {
+		do_sleep(1);
+		ioctl(fd, WDIOC_KEEPALIVE, &done);
+
+		if (!done && !notify())
+			done = 1;
+	}
+
+	if (handover)
+		return !write(fd, "V", 1);
+
+	return 0;
+}
+
+void watchdog(char *progname)
+{
+	if (fork() == 0) {
+		int fd, ret;
+
+		fd = init(progname, WDT_DEVNODE, WDT_TIMEOUT);
+		if (fd == -1) {
+			_pe("Failed connecting to watchdog %s", WDT_DEVNODE);
+			_exit(1);
+		}
+
+		ret = loop(fd);
+		close(fd);
+
+		_exit(ret);
+	}
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */

watchdog.h

@@ -0,0 +1,40 @@
+/* Built-in watchdog daemon
+ *
+ * Copyright (c) 2016  Joachim Nilsson <troglobit@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "config.h"		/* Generated by configure script */
+
+#define WDT_DEVNODE "/dev/watchdog"
+#define WDT_TIMEOUT 3
+
+#ifdef BUILTIN_WATCHDOG
+void    watchdog(char *progname);
+#else
+#define watchdog(progname)
+#endif /* BUILTIN_WATCHDOG */
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */