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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.
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
BUGS
The WD_PASSIVE option has not yet been implemented.
FreeBSD 14.0-RELEASE-p6 January 2, 2018 FreeBSD 14.0-RELEASE-p6