FIFOHIWATW
if ((fn_dflag & (FIFOHIWATW | FIFOISOPEN)) ==
(FIFOHIWATW | FIFOISOPEN)) {
fn_dest->fn_flag = fn_dflag & ~(FIFOWANTW | FIFOHIWATW | FIFOPOLLW);
fnp->fn_flag |= FIFOHIWATW;
if (fn_dest->fn_flag & (FIFOWANTW | FIFOHIWATW) &&
fnp->fn_flag |= FIFOHIWATW;