WATCHDOG(4)            FreeBSD 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 supports several optional ioctl(2) calls for
     configuration, and responds to a single operational ioctl 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 WDIOCPATPAT 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.  By
     default, this will be a hardware watchdog if one is present, but if no
     hardware watchdog is able to process the request, a default software
     watchdog is enabled.  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!

     The optional configuration ioctl commands are listed here, along with the
     type of the parameter used.  Examples of their use can be found in
     watchdogd(8).

     WDIOC_SETTIMEOUT int           set/reset the timer

     WDIOC_GETTIMEOUT int           get total timeout

     WDIOC_GETTIMELEFT int          get time left

     WDIOC_GETPRETIMEOUT int        get the pre-timeout

     WDIOC_SETPRETIMEOUT int        set the pre-timeout

     WDIOC_SETPRETIMEOUTACT int     Set the action when a pre-timeout occurs
                                    (see WD_SOFT_* below).

     WDIOC_SETSOFT int              Use an internal software watchdog instead
                                    of hardware.  There is also an external
                                    software watchdog, which is used by
                                    default if no hardware watchdog was
                                    attached.

     WDIOC_SETSOFTTIMEOUTACT int    Set the action whan a soft timeout occurs.

     The actions that may be specified for the pre-timeout or the internal
     software watchdog are listed here.  Multiple actions can be specified by
     ORing values together.

     WD_SOFT_PANIC  panic

     WD_SOFT_DDB    enter debugger

     WD_SOFT_LOG    log(9)

     WD_SOFT_PRINT  printf(9)

RETURN VALUES
     The WDIOCPATPAT 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.

     The configuration ioctl operations return zero on success and non-zero on
     failure.

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 forces a software watchdog in the kernel to be
     configured even if a hardware watchdog is configured, dropping to KDB or
     panicking when firing, depending on the KDB and KDB_UNATTENDED kernel
     configuration options.

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.

FreeBSD 13.1-RELEASE-p6         January 2, 2018        FreeBSD 13.1-RELEASE-p6