Function ng_pptpgre_xmit

freebsd/netgraph/ng_pptpgre.c:585–696

* Transmit an outgoing frame, or just an ack if m is NULL. */

 * Transmit an outgoing frame, or just an ack if m is NULL.
 */
static int
ng_pptpgre_xmit(hpriv_p hpriv, item_p item)
{
	const priv_p priv = NG_NODE_PRIVATE(hpriv->node);
	u_char buf[sizeof(struct greheader) + 2 * sizeof(u_int32_t)];
	struct greheader *const gre = (struct greheader *)buf;
	int grelen, error;
	struct mbuf *m;

	mtx_assert(&hpriv->mtx, MA_OWNED);

	if (item) {
		NGI_GET_M(item, m);
	} else {
		m = NULL;
	}
	/* Check if there's data */
	if (m != NULL) {
		/* Check if windowing is enabled */
		if (hpriv->conf.enableWindowing) {
			/* Is our transmit window full? */
			if ((u_int32_t)PPTP_SEQ_DIFF(hpriv->xmitSeq,
			    hpriv->recvAck) >= hpriv->xmitWin) {
				priv->stats.xmitDrops++;
				ERROUT(ENOBUFS);
			}
		}

		/* Sanity check frame length */
		if (m->m_pkthdr.len > PPTP_MAX_PAYLOAD) {
			priv->stats.xmitTooBig++;
			ERROUT(EMSGSIZE);
		}
	} else {
		priv->stats.xmitLoneAcks++;
	}

	/* Build GRE header */
	be32enc(gre, PPTP_INIT_VALUE);
	be16enc(&gre->length, (m != NULL) ? m->m_pkthdr.len : 0);
	be16enc(&gre->cid, hpriv->conf.peerCid);

	/* Include sequence number if packet contains any data */
	if (m != NULL) {
		gre->hasSeq = 1;
		if (hpriv->conf.enableWindowing) {
			hpriv->timeSent[hpriv->xmitSeq - hpriv->recvAck]
			    = ng_pptpgre_time();
		}
		hpriv->xmitSeq++;
		be32enc(&gre->data[0], hpriv->xmitSeq);
	}

	/* Include acknowledgement (and stop send ack timer) if needed */
	if (hpriv->conf.enableAlwaysAck || hpriv->xmitAck != hpriv->recvSeq) {
		gre->hasAck = 1;
		be32enc(&gre->data[gre->hasSeq], hpriv->recvSeq);
		hpriv->xmitAck = hpriv->recvSeq;