TF_SACK_PERMITTED
tp->t_flags |= TF_SACK_PERMITTED;
if ((tp->t_flags & (TF_SACK_PERMITTED | TF_NOOPT)) ==
TF_SACK_PERMITTED &&
tp->t_flags & TF_SACK_PERMITTED) {
tp->t_flags |= TF_SACK_PERMITTED;
#define TCP_DO_SACK(tp) ((tp)->t_flags & TF_SACK_PERMITTED)
TF_SACK_PERMITTED) ?