POLL_HUP
case POLL_HUP:
pipeselwakeup(pipe, pipe, POLL_HUP);
pipeselwakeup(ppipe, ppipe, POLL_HUP);
case POLL_HUP:
sowakeup(so, &so->so_rcv, POLL_HUP);
a = POLL_HUP;
fownsignal(tp->tun_pgid, SIGIO, POLL_HUP, 0, NULL);