Function vlan_transmit

freebsd/net/if_vlan.c:1169–1235

* The if_transmit method for vlan(4) interface. */

 * The if_transmit method for vlan(4) interface.
 */
static int
vlan_transmit(struct ifnet *ifp, struct mbuf *m)
{
	struct ifvlan *ifv;
	struct ifnet *p;
	int error, len, mcast;

	NET_EPOCH_ASSERT();

	ifv = ifp->if_softc;
	if (TRUNK(ifv) == NULL) {
		if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
		m_freem(m);
		return (ENETDOWN);
	}
	p = PARENT(ifv);
	len = m->m_pkthdr.len;
	mcast = (m->m_flags & (M_MCAST | M_BCAST)) ? 1 : 0;

	BPF_MTAP(ifp, m);

#if defined(KERN_TLS) || defined(RATELIMIT)
	if (m->m_pkthdr.csum_flags & CSUM_SND_TAG) {
		struct vlan_snd_tag *vst;
		struct m_snd_tag *mst;

		MPASS(m->m_pkthdr.snd_tag->ifp == ifp);
		mst = m->m_pkthdr.snd_tag;
		vst = mst_to_vst(mst);
		if (vst->tag->ifp != p) {
			if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
			m_freem(m);
			return (EAGAIN);
		}

		m->m_pkthdr.snd_tag = m_snd_tag_ref(vst->tag);
		m_snd_tag_rele(mst);
	}
#endif

	/*
	 * Do not run parent's if_transmit() if the parent is not up,
	 * or parent's driver will cause a system crash.
	 */
	if (!UP_AND_RUNNING(p)) {
		if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
		m_freem(m);
		return (ENETDOWN);
	}

	if (!ether_8021q_frame(&m, ifp, p, &ifv->ifv_qtag)) {
		if_inc_counter(ifp, IFCOUNTER_OERRORS, 1);
		return (0);
	}

	/*
	 * Send it, precisely as ether_output() would have.
	 */