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