PDUF_BUSY
pdu->pdu_flags &= ~PDUF_BUSY;
pdu->pdu_flags &= ~(PDUF_INQUEUE | PDUF_BUSY);
pdu->pdu_flags |= PDUF_BUSY;
if (pdu == NULL || (pdu->pdu_flags & PDUF_BUSY)) {
pdu->pdu_flags |= PDUF_BUSY;