it_ch
callout_init(&it->it_ch, CALLOUT_MPSAFE);
callout_setfunc(&it->it_ch, itimer_callout, it);
callout_halt(&it->it_ch, &itimer_mutex);
callout_destroy(&it->it_ch);
KASSERT(!callout_pending(&it->it_ch));
callout_schedule(&it->it_ch,
if (callout_halt(&it->it_ch, &itimer_mutex))
#define it_ch it_real.it_ch
callout_t it_ch;