freebsd-skq/share/man/man4/watchdog.4

.\" Copyright (c) 2004 Poul-Henning Kamp <phk@FreeBSD.org>
.\" Copyright (c) 2003, 2004 Sean M. Kelly <smkelly@FreeBSD.org>
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.Dd December 21, 2009
.Dt WATCHDOG 4
.Os
.Sh NAME
.Nm watchdog
.Nd "hardware and software watchdog"
.Sh SYNOPSIS
.In sys/watchdog.h
.Sh DESCRIPTION
The
.Nm
facility is used for controlling hardware and software watchdogs.
.Pp
.Pa /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.
.Pp
.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.
.Pp
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.
.Pp
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.
.Bl -tag -width Er
.It Bq Er EOPNOTSUPP
No watchdog present in the kernel or
none of the watchdogs supports the requested timeout value
(timeout value other than 0).
.It Bq Er EOPNOTSUPP
Watchdog could not be disabled (timeout value of 0).
.It Bq Er EINVAL
Invalid flag combination passed.
.El
.Sh EXAMPLES
.Bd -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
.Pp
Enables a watchdog to recover from a potentially freezing piece of code.
.Pp
.Dl "options SW_WATCHDOG"
.Pp
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 phk@FreeBSD.org .
The software watchdog code and this manual page were written by
.An Sean Kelly Aq smkelly@FreeBSD.org .
Some contributions were made by
.An Jeff Roberson Aq jeff@FreeBSD.org .
.Sh BUGS
The
.Dv WD_PASSIVE
option has not yet been implemented.