Function ng_l2tp_xmit_ctrl

freebsd/netgraph/ng_l2tp.c:1505–1583

* Transmit a control stream packet, payload optional. * The transmit sequence number is not incremented. */

 * The transmit sequence number is not incremented.
 */
static int
ng_l2tp_xmit_ctrl(priv_p priv, struct mbuf *m, u_int16_t ns)
{
	struct l2tp_seq *const seq = &priv->seq;
	uint8_t *p;
	u_int16_t session_id = 0;
	int error;

	mtx_lock(&seq->mtx);

	/* Stop ack timer: we're sending an ack with this packet.
	   Doing this before to keep state predictable after error. */
	if (callout_active(&seq->xack_timer))
		ng_uncallout(&seq->xack_timer, priv->node);

	seq->xack = seq->nr;

	mtx_unlock(&seq->mtx);

	/* If no mbuf passed, send an empty packet (ZLB) */
	if (m == NULL) {
		/* Create a new mbuf for ZLB packet */
		MGETHDR(m, M_NOWAIT, MT_DATA);
		if (m == NULL) {
			priv->stats.memoryFailures++;
			return (ENOBUFS);
		}
		m->m_len = m->m_pkthdr.len = 12;
		m->m_pkthdr.rcvif = NULL;
		priv->stats.xmitZLBs++;
	} else {
		/* Strip off session ID */
		if (m->m_len < 2 && (m = m_pullup(m, 2)) == NULL) {
			priv->stats.memoryFailures++;
			return (ENOBUFS);
		}
		session_id = (mtod(m, u_int8_t *)[0] << 8) + mtod(m, u_int8_t *)[1];

		/* Make room for L2TP header */
		M_PREPEND(m, 10, M_NOWAIT);	/* - 2 + 12 = 10 */
		if (m == NULL) {
			priv->stats.memoryFailures++;
			return (ENOBUFS);
		}

		/*
		 * The below requires 12 contiguous bytes for the L2TP header
		 * to be written into.
		 */
		m = m_pullup(m, 12);
		if (m == NULL) {
			priv->stats.memoryFailures++;
			return (ENOBUFS);
		}
	}

	/* Fill in L2TP header */
	p = mtod(m, u_int8_t *);