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     watchdog - software and hardware watchdog facility


     #include <sys/watchdog.h>

     watchdog_fn(void *private, u_int cmd, int *error);

     EVENTHANDLER_REGISTER(watchdog_list, watchdog_fn, private, 0);

     EVENTHANDLER_DEREGISTER(watchdog_list, eventhandler_tag);


     To implement a watchdog in software or hardware, only a single function
     needs to be written and registered on the global watchdog_list.

     The function must examine the cmd argument and act on it as follows:

     If cmd is zero, the watchdog must be disabled and the error argument left
     untouched.  If the watchdog cannot be disabled, the error argument must
     be set to EOPNOTSUPP.

     Else the watchdog should be reset and configured to a timeout of (1 <<
     (cmd & WD_INTERVAL)) nanoseconds or larger and the error argument be set
     to zero to signal arming of a watchdog.

     If the watchdog cannot be configured to the proposed timeout, it must be
     disabled and the error argument left as is (to avoid hiding the arming of
     another watchdog).

     There is no specification of what the watchdog should do when it times
     out, but a hardware reset or similar “drastic but certain” behaviour is




     The watchdog facility and this manual page was written Poul-Henning Kamp