TS_ISPTSTTY
if ((tp->t_state & TS_ISPTSTTY) && (*mp->b_rptr & FLUSHBAND))
if ((tp->t_state & TS_ISPTSTTY) &&
(msgdsize(mp) || !(tp->t_state & TS_ISPTSTTY))) {
(tp->t_state & TS_ISPTSTTY))
tp->t_state |= TS_ISPTSTTY;