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$FreeBSD: releng/11.0/share/man/man4/watchdog.4 267938 2014-06-26 21:46:14Z bapt $
.Dd December 21, 2009 .Dt WATCHDOG 4 .Os .Sh NAME .Nm watchdog .Nd "hardware and software watchdog" .Sh SYNOPSIS n sys/watchdog.h .Sh DESCRIPTION The .Nm facility is used for controlling hardware and software watchdogs.
p The device
a /dev/fido responds to a single .Xr ioctl 2 call, .Dv 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.
p .Dv WD_ACTIVE indicates that the .Nm will be kept from timing out from userland, for instance by the .Xr watchdogd 8 daemon. .Dv WD_PASSIVE indicates that the .Nm will be kept from timing out from the kernel.
p The .Xr ioctl 2 call will return success if just one of the available .Xr 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 .Xr watchdog 9 implementations support the timeout length, all watchdogs are disabled and must be explicitly re-enabled.
p To disable the watchdogs pass .Dv WD_TO_NEVER . If disarming the watchdog(s) failed an error is returned. The watchdog might still be armed! .Sh RETURN VALUES The ioctl returns zero on success and non-zero on failure. l -tag -width Er t Bq Er EOPNOTSUPP No watchdog present in the kernel or none of the watchdogs supports the requested timeout value (timeout value other than 0). t Bq Er EOPNOTSUPP Watchdog could not be disabled (timeout value of 0). t Bq Er EINVAL Invalid flag combination passed. .El .Sh EXAMPLES d -literal -offset indent #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); .Ed
p Enables a watchdog to recover from a potentially freezing piece of code.
p .Dl "options SW_WATCHDOG"
p in your kernel config adds a software watchdog in the kernel, dropping to KDB or panic-ing when firing. .Sh SEE ALSO .Xr watchdogd 8 , .Xr watchdog 9 .Sh HISTORY The .Nm code first appeared in .Fx 5.1 . .Sh AUTHORS .An -nosplit The .Nm facility was written by .An Poul-Henning Kamp Aq Mt phk@FreeBSD.org . The software watchdog code and this manual page were written by .An Sean Kelly Aq Mt smkelly@FreeBSD.org . Some contributions were made by .An Jeff Roberson Aq Mt jeff@FreeBSD.org . .Sh BUGS The .Dv WD_PASSIVE option has not yet been implemented.