TDF_BOUNDARY
(td->td_flags & TDF_BOUNDARY) == 0) {
(td2->td_flags & TDF_BOUNDARY) == 0) {
KASSERT((td2->td_flags & TDF_BOUNDARY) != 0,
td->td_flags |= TDF_BOUNDARY;
if (boundary && (td->td_flags & TDF_BOUNDARY) != 0) {
td->td_flags &= ~TDF_BOUNDARY;
((td->td_flags & TDF_BOUNDARY) != 0 && TD_IS_SUSPENDED(td)),