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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 recommended.




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