TDB_BOUNDARY
old_boundary = ~TDB_BOUNDARY | (td->td_dbgflags & TDB_BOUNDARY);
td->td_dbgflags |= TDB_BOUNDARY;
td->td_dbgflags &= ~(TDB_SCE | TDB_BOUNDARY);
MPASS((td->td_dbgflags & TDB_BOUNDARY) == 0);
td->td_dbgflags |= TDB_BOUNDARY;
TDB_BOUNDARY);
MPASS((td->td_dbgflags & TDB_BOUNDARY) == 0);
if ((td2->td_dbgflags & TDB_BOUNDARY) == 0) {