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 January 2, 2018
.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
The device
.Pa /dev/fido
supports several optional
.Xr ioctl 2
calls for configuration, and
responds to a single operational
.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
.Dv WDIOCPATPAT
.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.
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
.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!
.Pp
The optional configuration
.Xr ioctl 2
commands are listed here, along with the type of the parameter used.
Examples of their use can be found in
.Xr watchdogd 8 .
.Bl -tag -width "WDIOC_SETSOFTTIMEOUTACT int  "
.It Dv WDIOC_SETTIMEOUT Fa int
set/reset the timer
.It Dv WDIOC_GETTIMEOUT Fa int
get total timeout
.It Dv WDIOC_GETTIMELEFT Fa int
get time left
.It Dv WDIOC_GETPRETIMEOUT Fa int
get the pre-timeout
.It Dv WDIOC_SETPRETIMEOUT Fa int
set the pre-timeout
.It Dv WDIOC_SETPRETIMEOUTACT Fa int
Set the action when a pre-timeout occurs (see
.Li WD_SOFT_*
below).
.It Dv WDIOC_SETSOFT Fa 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.
.It Dv WDIOC_SETSOFTTIMEOUTACT Fa int
Set the action when a soft timeout occurs.
.El
.Pp
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.
.Bl -tag -width  WD_SOFT_PRINT
.It Dv WD_SOFT_PANIC
panic
.It Dv WD_SOFT_DDB
enter debugger
.It Dv WD_SOFT_LOG
log(9)
.It Dv WD_SOFT_PRINT
printf(9)
.El
.Sh RETURN VALUES
The
.Dv WDIOCPATPAT
.Xr ioctl 2
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
.Pp
The configuration
.Xr ioctl 2
operations return zero on success and non-zero on failure.
.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 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.
.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.