man/man4/watchdog.4

.\" Copyright (c) 2004 Poul-Henning Kamp <phk@FreeBSD.org>
.\" Copyright (c) 2003, 2004 Sean M. Kelly <smkelly@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.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 set of operational
.Xr ioctl 2
calls:
.Bl -tag -width "WDIOC_CONTROL int  "
.It Dv WDIOCPATPAT
Pat the watchdog.
.It Dv WDIOC_CONTROL
Enable, disable, or reset the watchdog.
.El
.Pp
The
.Dv WDIOCPATPAT
.Xr ioctl 2
call takes a single argument which represents a timeout value specified as a
.Vt sbintime_t
of the timeout period for the watchdog.
.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 use the
.Dv WDIOC_CONTROL
.Xr ioctl 2
call with the
.Dv WD_CTRL_DISABLE
flag.
If disarming the watchdog(s) failed an error is returned.
The watchdog might
still be armed!
To reenable the watchdogs use the
.Dv WDIOC_CONTROL
.Xr ioctl 2
call with the
.Dv WD_CTRL_ENABLE
flag.
Another way to pat the watchdog is with the
.Dv WDIOC_CONTROL
.Xr ioctl 2
call passing the
.Dv WDIOC_CTRL_RESET
flag.
.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_GETPRETTIMEOUT sbintime_t"
.It Dv WDIOC_SETTIMEOUT Fa sbintime_t
set/reset the timer
.It Dv WDIOC_GETTIMEOUT Fa sbintime_t
get total timeout
.It Dv WDIOC_GETTIMELEFT Fa sbintime_t
get time left
.It Dv WDIOC_GETPRETIMEOUT Fa sbintime_t
get the pre-timeout
.It Dv WDIOC_SETPRETIMEOUT Fa sbintime_t
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.