CLOCK_PROF
((clockid) == CLOCK_VIRTUAL || (clockid) == CLOCK_PROF)
CTASSERT(ITIMER_PROF == CLOCK_PROF);
KASSERT(itn->it_clockid == CLOCK_PROF);
KASSERT(itn->it_clockid == CLOCK_PROF);
case CLOCK_PROF:
case CLOCK_PROF:
check_resolution("CLOCK_PROF", CLOCK_PROF);
(fd = timerfd_create(CLOCK_PROF, 0)) == -1);