my_watchdog
static void my_watchdog(void *);
callout_reset(&sc->my_watchdog, hz, my_watchdog, sc);
callout_reset(&sc->my_watchdog, hz, my_watchdog, sc);
callout_stop(&sc->my_watchdog);
callout_init_mtx(&sc->my_watchdog, &sc->my_mtx, 0);
callout_drain(&sc->my_watchdog);
struct callout my_watchdog;