SW_WATCHDOG (4)
Leading comments
Copyright (c) 2004 Poul-Henning Kamp <phk@FreeBSD.org> Copyright (c) 2003, 2004 Sean M. Kelly <smkelly@FreeBSD.org> All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this ...
NAME
watchdog - hardware and software watchdogSYNOPSIS
In sys/watchdog.hDESCRIPTION
The facility is used for controlling hardware and software watchdogs.The device /dev/fido responds to a single ioctl(2) call, WDIOCPATPAT It takes a single argument which represents a timeout value specified as a power of two nanoseconds, or-ed with a flag selecting active or passive control of the watchdog.
WD_ACTIVE indicates that the will be kept from timing out from userland, for instance by the watchdogd(8) daemon. WD_PASSIVE indicates that the will be kept from timing out from the kernel.
The ioctl(2) call will return success if just one of the available watchdog(9) implementations supports setting the timeout to the specified timeout. This means that at least one watchdog is armed. If the call fails, for instance if none of watchdog(9) implementations support the timeout length, all watchdogs are disabled and must be explicitly re-enabled.
To disable the watchdogs pass WD_TO_NEVER If disarming the watchdog(s) failed an error is returned. The watchdog might still be armed!
RETURN VALUES
The ioctl returns zero on success and non-zero on failure.- Bq Er EOPNOTSUPP
- No watchdog present in the kernel or none of the watchdogs supports the requested timeout value (timeout value other than 0).
- Bq Er EOPNOTSUPP
- Watchdog could not be disabled (timeout value of 0).
- Bq Er EINVAL
- Invalid flag combination passed.
EXAMPLES
#include <paths.h>
#include <sys/watchdog.h>
#define WDPATH "/dev/" _PATH_WATCHDOG
int wdfd = -1;
static void
wd_init(void)
{
wdfd = open(WDPATH, O_RDWR);
if (wdfd == -1)
err(1, WDPATH);
}
static void
wd_reset(u_int timeout)
{
if (ioctl(wdfd, WDIOCPATPAT, &timeout) == -1)
err(1, "WDIOCPATPAT");
}
/* in main() */
wd_init();
wd_reset(WD_ACTIVE|WD_TO_8SEC);
/* potential freeze point */
wd_reset(WD_TO_NEVER);
Enables a watchdog to recover from a potentially freezing piece of code.
"options SW_WATCHDOG"
in your kernel config adds a software watchdog in the kernel, dropping to KDB or panic-ing when firing.