WATCHDOG(4)						   BSD Kernel Interfaces Manual 					       WATCHDOG(4)

NAME

     watchdog -- hardware and software watchdog

SYNOPSIS

     #include <sys/watchdog.h>

DESCRIPTION

     The watchdog 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 watchdog will be kept from timing out from userland, for instance by the watchdogd(8) daemon.  WD_PASSIVE indi-
     cates that the watchdog 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.

     [EOPNOTSUPP]	No watchdog present in the kernel or none of the watchdogs supports the requested timeout value (timeout value other than
			0).

     [EOPNOTSUPP]	Watchdog could not be disabled (timeout value of 0).

     [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.

SEE ALSO

     watchdogd(8), watchdog(9)

HISTORY

     The watchdog code first appeared in FreeBSD 5.1.

AUTHORS

     The watchdog facility was written by Poul-Henning Kamp <phk@FreeBSD.org>.	The software watchdog code and this manual page were written by
     Sean Kelly <smkelly@FreeBSD.org>.	Some contributions were made by Jeff Roberson <jeff@FreeBSD.org>.

BUGS

     The WD_PASSIVE option has not yet been implemented.

BSD
								 December 21, 2009							       BSD