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/*
* watchdog
*
* Copyright 2017 Raptor Engineering, LLC
* Copyright 2014-present Facebook. All Rights Reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#include "watchdog.h"
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <syslog.h>
#include <unistd.h>
#include <time.h>
#include <sys/ioctl.h>
#include <linux/watchdog.h>
// #define DEBUG_WATCHDOG 1
#define WATCHDOG_START_KEY "x"
#define WATCHDOG_STOP_KEY "X"
/* The "magic close" character (as defined in Linux watchdog specs). */
#define WATCHDOG_PERSISTENT_KEY "V"
#define WATCHDOG_NON_PERSISTENT_KEY "a"
#ifdef DEBUG_WATCHDOG
static time_t watchdog_last_kick = 0;
#endif
static int watchdog_dev = -1;
/* This is needed to prevent rapid consecutive stop/start watchdog calls from
* generating multiple threads. */
static int watchdog_started = 0;
static const char* watchdog_kick_key = WATCHDOG_PERSISTENT_KEY;
static pthread_t watchdog_tid;
static pthread_mutex_t watchdog_lock = PTHREAD_MUTEX_INITIALIZER;
/* Forward declarations. */
static void* watchdog_thread(void* args);
static int kick_watchdog_unsafe();
/*
* When started, this background thread will constantly reset the watchdog
* at every 5 second interval.
*/
static void* watchdog_thread(void* args) {
pthread_detach(pthread_self());
/* Make sure another instance of the thread hasn't already been started. */
pthread_mutex_lock(&watchdog_lock);
if (watchdog_started) {
goto done;
} else {
watchdog_started = 1;
}
pthread_mutex_unlock(&watchdog_lock);
/* Actual loop for refreshing the watchdog timer. */
while (1) {
pthread_mutex_lock(&watchdog_lock);
if (watchdog_dev != -1) {
kick_watchdog_unsafe();
} else {
break;
}
pthread_mutex_unlock(&watchdog_lock);
sleep(5);
}
/* Broke out of loop because watchdog was stopped. */
watchdog_started = 0;
done:
pthread_mutex_unlock(&watchdog_lock);
return NULL;
}
/*
* Starts the watchdog timer. timer counts down and restarts the ARM chip
* upon timeout. use kick_watchdog() to restart the timer.
*
* Returns: 1 on success; 0 otherwise.
*/
int start_watchdog(const int auto_mode) {
int status;
pthread_mutex_lock(&watchdog_lock);
/* Don't start the watchdog again if it has already been started. */
if (watchdog_dev != -1) {
while ((status = write(watchdog_dev, WATCHDOG_START_KEY, 1)) == 0
&& errno == EINTR);
pthread_mutex_unlock(&watchdog_lock);
syslog(LOG_WARNING, "system watchdog already started.\n");
return 0;
}
while (((watchdog_dev = open("/dev/watchdog", O_RDWR)) == -1) &&
errno == EINTR);
/* Fail if watchdog device is invalid or if the user asked for auto
* mode and the thread failed to spawn. */
if ((watchdog_dev == -1) ||
(auto_mode == 1 && watchdog_started == 0 &&
pthread_create(&watchdog_tid, NULL, watchdog_thread, NULL) != 0)) {
goto fail;
}
while ((status = write(watchdog_dev, WATCHDOG_START_KEY, 1)) == 0
&& errno == EINTR);
pthread_mutex_unlock(&watchdog_lock);
#ifdef DEBUG_WATCHDOG
watchdog_last_kick = time(NULL);
#endif
syslog(LOG_INFO, "system watchdog started.\n");
return 1;
fail:
if (watchdog_dev != -1) {
close(watchdog_dev);
watchdog_dev = -1;
}
pthread_mutex_unlock(&watchdog_lock);
syslog(LOG_WARNING, "system watchdog failed to start!\n");
return 0;
}
/*
* Toggles between watchdog persistent modes. In persistent mode, the watchdog
* timer will continue to tick even after process shutdown. Under non-
* persistent mode, the watchdog timer will automatically be disabled when the
* process shuts down.
*/
void set_persistent_watchdog(enum watchdog_persistent_en persistent) {
switch (persistent) {
case WATCHDOG_SET_PERSISTENT:
watchdog_kick_key = WATCHDOG_PERSISTENT_KEY;
break;
default:
watchdog_kick_key = WATCHDOG_NON_PERSISTENT_KEY;
break;
}
kick_watchdog();
}
/*
* Restarts the countdown timer on the watchdog, delaying restart by another
* timeout period (default: 11 seconds as configured in the device driver).
*
* This function assumes the watchdog lock has already been acquired and is
* only used internally within the watchdog code.
*
* Returns 1 on success; 0 or -1 indicates failure (check errno).
*/
static int kick_watchdog_unsafe() {
int status = 0;
#ifdef DEBUG_WATCHDOG
int timeout = -1;
if (ioctl(watchdog_dev, WDIOC_GETTIMEOUT, &timeout) < 0) {
syslog(LOG_DEBUG, "Watchdog: WDIOC_GETTIMEOUT ioctl failed with errno %d\n", errno);
}
else {
syslog(LOG_DEBUG, "Watchdog: timeout set to %d seconds (last kick was %d seconds ago)\n", timeout, time(NULL) - watchdog_last_kick);
}
watchdog_last_kick = time(NULL);
#endif
if (watchdog_dev != -1) {
while ((status = write(watchdog_dev, watchdog_kick_key, 1)) == 0
&& errno == EINTR);
}
return status;
}
/*
* Acquires the watchdog lock and resets the watchdog atomically. For use by
* library users.
*/
int kick_watchdog() {
int result;
pthread_mutex_lock(&watchdog_lock);
result = kick_watchdog_unsafe();
pthread_mutex_unlock(&watchdog_lock);
return result;
}
/* Shuts down the watchdog gracefully and disables the watchdog timer so that
* restarts no longer happen.
*/
void stop_watchdog() {
int status;
pthread_mutex_lock(&watchdog_lock);
if (watchdog_dev != -1) {
while ((status = write(watchdog_dev, WATCHDOG_STOP_KEY, 1)) == 0
&& errno == EINTR);
close(watchdog_dev);
watchdog_dev = -1;
syslog(LOG_INFO, "system watchdog stopped.\n");
}
pthread_mutex_unlock(&watchdog_lock);
}
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