Function iflib_parse_header

freebsd/net/iflib.c:3126–3296

#define IS_TX_OFFLOAD6(pi) ((pi)->ipi_csum_flags & (CSUM_IP6_TCP | CSUM_IP6_TSO))

static int
iflib_parse_header(iflib_txq_t txq, if_pkt_info_t pi, struct mbuf **mp)
{
	if_shared_ctx_t sctx = txq->ift_ctx->ifc_sctx;
	struct ether_vlan_header *eh;
	struct mbuf *m;

	m = *mp;
	if ((sctx->isc_flags & IFLIB_NEED_SCRATCH) &&
	    M_WRITABLE(m) == 0) {
		if ((m = m_dup(m, M_NOWAIT)) == NULL) {
			return (ENOMEM);
		} else {
			m_freem(*mp);
			DBG_COUNTER_INC(tx_frees);
			*mp = m;
		}
	}

	/*
	 * Determine where frame payload starts.
	 * Jump over vlan headers if already present,
	 * helpful for QinQ too.
	 */
	if (__predict_false(m->m_len < sizeof(*eh))) {
		txq->ift_pullups++;
		if (__predict_false((m = m_pullup(m, sizeof(*eh))) == NULL))
			return (ENOMEM);
	}
	eh = mtod(m, struct ether_vlan_header *);
	if (eh->evl_encap_proto == htons(ETHERTYPE_VLAN)) {
		pi->ipi_etype = ntohs(eh->evl_proto);
		pi->ipi_ehdrlen = ETHER_HDR_LEN + ETHER_VLAN_ENCAP_LEN;
	} else {
		pi->ipi_etype = ntohs(eh->evl_encap_proto);
		pi->ipi_ehdrlen = ETHER_HDR_LEN;
	}

	switch (pi->ipi_etype) {
#ifdef INET
	case ETHERTYPE_IP:
	{
		struct mbuf *n;
		struct ip *ip = NULL;
		struct tcphdr *th = NULL;
		int minthlen;

		minthlen = min(m->m_pkthdr.len, pi->ipi_ehdrlen + sizeof(*ip) + sizeof(*th));
		if (__predict_false(m->m_len < minthlen)) {
			/*
			 * if this code bloat is causing too much of a hit
			 * move it to a separate function and mark it noinline
			 */
			if (m->m_len == pi->ipi_ehdrlen) {
				n = m->m_next;
				MPASS(n);
				if (n->m_len >= sizeof(*ip))  {
					ip = (struct ip *)n->m_data;