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+.\" 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.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd December 21, 2009
+.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
+responds to a single
+.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
+.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.
+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!
+.Sh RETURN VALUES
+The ioctl 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
+.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 adds a software watchdog in the kernel, dropping to KDB
+or panic-ing when firing.
+.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 phk@FreeBSD.org .
+The software watchdog code and this manual page were written by
+.An Sean Kelly Aq smkelly@FreeBSD.org .
+Some contributions were made by
+.An Jeff Roberson Aq jeff@FreeBSD.org .
+.Sh BUGS
+The
+.Dv WD_PASSIVE
+option has not yet been implemented.