SS_SENTLASTREADSIG
if ((events & POLLRDHUP) && (state & SS_SENTLASTREADSIG))
mask = SS_SENTLASTREADSIG | SS_SENTLASTWRITESIG;
SS_HAVEOOBDATA|SS_HADOOBDATA|SS_SENTLASTREADSIG|SS_SENTLASTWRITESIG)
if (!(so->so_state & SS_SENTLASTREADSIG)) {
so->so_state |= SS_SENTLASTREADSIG;