watchdog —
hardware and software watchdog
#include
<sys/watchdog.h>
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.
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.
WD_SOFT_PANIC- panic
WD_SOFT_DDB- enter debugger
WD_SOFT_LOG- log(9)
WD_SOFT_PRINT- printf(9)
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.
#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.
watchdogd(8),
watchdog(9)
The
watchdog code first appeared in
FreeBSD 5.1.
The
watchdog facility was written by
Poul-Henning Kamp
<
[email protected]>.
The software watchdog code and this manual page were written by
Sean Kelly
<
[email protected]>.
Some contributions were made by
Jeff
Roberson
<
[email protected]>.
The
WD_PASSIVE option has not yet been
implemented.