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.Dd February 28, 2004
.Dt WATCHDOG 9
.Os
.Sh NAME
.Nm watchdog
.Nd "software and hardware watchdog facility"
.Sh SYNOPSIS
.In sys/watchdog.h
.Ft void
.Fn watchdog_fn "void *private" "u_int cmd" "int *error"
.Fn EVENTHANDLER_REGISTER watchdog_list watchdog_fn private 0
.Fn EVENTHANDLER_DEREGISTER watchdog_list eventhandler_tag
.Sh DESCRIPTION
To implement a watchdog in software or hardware, only a single
function needs to be written and registered on the global
.Va watchdog_list .
.Pp
The function must examine the
.Fa cmd
argument and act on it as
follows:
.Pp
If
.Fa cmd
is zero, the watchdog must be disabled and the
.Fa error
argument left untouched.
If the watchdog cannot be disabled, the
.Fa error
argument must be set to
.Dv EOPNOTSUPP .
.Pp
Else the watchdog should be reset and configured to a timeout of
.Pq 1 << Pq Fa cmd No & Dv WD_INTERVAL
nanoseconds or larger and the
.Fa error
argument be set to zero to signal arming of a watchdog.
.Pp
If the watchdog cannot be configured to the proposed timeout, it
must be disabled and the
.Fa error
argument left as is (to avoid hiding the arming of another watchdog).
.Pp
There is no specification of what the watchdog should do when it
times out, but a hardware reset or similar
.Dq "drastic but certain"
behaviour is recommended.
.Sh SEE ALSO
.Xr watchdog 4
.Sh AUTHORS
.An -nosplit
The
.Nm
facility and this manual page was written
.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org .