bionic (4) SW_WATCHDOG.4freebsd.gz

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 indicates 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.