[系统运维]linux网络协议栈br_handle_frame_finish

/* note: already called with rcu_read_lock */
int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
{
	const unsigned char *dest = eth_hdr(skb)->h_dest;
	struct net_bridge_port *p = br_port_get_rcu(skb->dev);
	struct net_bridge *br;
	struct net_bridge_fdb_entry *dst;
	struct net_bridge_mdb_entry *mdst;
	struct sk_buff *skb2;
	bool unicast = true;
	u16 vid = 0;

	if (!p || p->state == BR_STATE_DISABLED)
		goto drop;
    
    //检查报文是否允许进入bridge
	if (!br_allowed_ingress(p->br, nbp_vlan_group_rcu(p), skb, &vid))
		goto out;

	/* insert into forwarding database after filtering to avoid spoofing */
	br = p->br;
    //更新fdb表
	if (p->flags & BR_LEARNING)
		br_fdb_update(br, p, eth_hdr(skb)->h_source, vid, false);

	if (!is_broadcast_ether_addr(dest) && is_multicast_ether_addr(dest) &&
	    br_multicast_rcv(br, p, skb, vid))
		goto drop;

	if (p->state == BR_STATE_LEARNING)
		goto drop;

	BR_INPUT_SKB_CB(skb)->brdev = br->dev;
    
    //决定报文的出方向:1.forward 2.local host 3.flood
	/* The packet skb2 goes to the local host (NULL to skip). */
	skb2 = NULL;

	if (br->dev->flags & IFF_PROMISC)
		skb2 = skb;

	dst = NULL;

	if (IS_ENABLED(CONFIG_INET) && skb->protocol == htons(ETH_P_ARP))
		br_do_proxy_arp(skb, br, vid, p);

	if (is_broadcast_ether_addr(dest)) {
		skb2 = skb;
		unicast = false;
	} else if (is_multicast_ether_addr(dest)) {
		mdst = br_mdb_get(br, skb, vid);
		if ((mdst || BR_INPUT_SKB_CB_MROUTERS_ONLY(skb)) &&
		    br_multicast_querier_exists(br, eth_hdr(skb))) {
			if ((mdst && mdst->mglist) ||
			    br_multicast_is_router(br))
				skb2 = skb;
			br_multicast_forward(mdst, skb, skb2);
			skb = NULL;
			if (!skb2)
				goto out;
		} else
			skb2 = skb;

		unicast = false;
		br->dev->stats.multicast++;
	} else if ((dst = __br_fdb_get(br, dest, vid)) &&
			dst->is_local) {
		skb2 = skb;
		/* Do not forward the packet since it's local. */
		skb = NULL;
	}

	if (skb) {
		if (dst) {
			dst->used = jiffies;
			br_forward(dst->dst, skb, skb2);
		} else
			br_flood_forward(br, skb, skb2, unicast);
	}

	if (skb2)
		return br_pass_frame_up(skb2);

out:
	return 0;
drop:
	kfree_skb(skb);
	goto out;
}

主要流程：

? ? ? ? 1.检查报文是否允许进入bridge：主要是对vlan的处理?

? ? ? ? 2.更新fdb表

? ? ? ? 3.根据目的MAC决定报文的出方向:

? ? ? ? ? ? ? ? 3.1.forward

????????????????3.2.local host ：最后会重新调用netif_receive_skb，但此时skb->dev已经替换为网桥设备，网桥上没有注册rx_handler，因此不会再次进入桥处理，然后会调用ptype协议链上对应的协议处理函数进入上层处理

? ? ? ? ? ? ? ? 3.3.flood

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