Linux-4.20.8内核桥收包源码解析（六）----------决策函数br_handle_frame

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作者：lwyang?
内核版本：Linux-4.20.8

br_handle_frame_finish函数主要是决策将不同类别的数据包做不同的分发路径，它会决定数据包是转发还是交给上层协议栈去处理，所以我给这个函数取名为决策函数，也是即将离开NF_BR_PRE_ROUTING链时做的处理

int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
{//获取网桥端口 dev->rx_handler_datastruct net_bridge_port *p = br_port_get_rcu(skb->dev);enum br_pkt_type pkt_type = BR_PKT_UNICAST;struct net_bridge_fdb_entry *dst = NULL;struct net_bridge_mdb_entry *mdst;bool local_rcv, mcast_hit = false;const unsigned char *dest;struct net_bridge *br;u16 vid = 0;//如果网桥端口不存在或者网桥端口状态为BR_STATE_DISABLED，则丢弃if (!p || p->state == BR_STATE_DISABLED)goto drop;//判断是否允许进入桥内，如果没有开启vlan则所有的数据包都可以进入， //如果开启了vlan则根据vlan相应的规则,从桥上进行数据包转发if (!br_allowed_ingress(p->br, nbp_vlan_group_rcu(p), skb, &vid))goto out;//BR_INPUT_SKB_CB(skb)->offload_fwd_mark = p->offload_fwd_marknbp_switchdev_frame_mark(p, skb);/* insert into forwarding database after filtering to avoid spoofing *///获取网桥，下面会将网桥的device放入skb的私有数据中br = p->br;//如果网桥端口标志有BR_LEARNING，则更新fdb表//一般新建网桥端口p->flags = BR_LEARNING | BR_FLOOD | BR_MCAST_FLOOD | BR_BCAST_FLOODif (p->flags & BR_LEARNING)br_fdb_update(br, p, eth_hdr(skb)->h_source, vid, false);//发往本地数据包标记，!!的作用是转换为bool值local_rcv = !!(br->dev->flags & IFF_PROMISC);dest = eth_hdr(skb)->h_dest;if (is_multicast_ether_addr(dest)) {/* by definition the broadcast is also a multicast address *///若目的mac地址为广播包 （FF:FF:FF:FF:FF:FF），会发往本地一份if (is_broadcast_ether_addr(dest)) {pkt_type = BR_PKT_BROADCAST;local_rcv = true;} else {//若为组播包pkt_type = BR_PKT_MULTICAST;//igmp snooping留给网桥子系统的外部接口函数，当网桥接收了igmp数据包后就会调用该函数进行后续处理if (br_multicast_rcv(br, p, skb, vid))goto drop;}}//如果网桥端口状态此时还是BR_STATE_LEARNING，则丢弃if (p->state == BR_STATE_LEARNING)goto drop;//将网桥所属的net_device放入skb的私有数据中（struct br_input_skb_cb）BR_INPUT_SKB_CB(skb)->brdev = br->dev;BR_INPUT_SKB_CB(skb)->src_port_isolated = !!(p->flags & BR_ISOLATED);//进行与arp协议相关的处理 ？TODOif (IS_ENABLED(CONFIG_INET) &&(skb->protocol == htons(ETH_P_ARP) ||skb->protocol == htons(ETH_P_RARP))) {br_do_proxy_suppress_arp(skb, br, vid, p);} else if (IS_ENABLED(CONFIG_IPV6) &&skb->protocol == htons(ETH_P_IPV6) &&br_opt_get(br, BROPT_NEIGH_SUPPRESS_ENABLED) &&pskb_may_pull(skb, sizeof(struct ipv6hdr) +sizeof(struct nd_msg)) &&ipv6_hdr(skb)->nexthdr == IPPROTO_ICMPV6) {struct nd_msg *msg, _msg;msg = br_is_nd_neigh_msg(skb, &_msg);if (msg)br_do_suppress_nd(skb, br, vid, p, msg);}switch (pkt_type) {//若为组播包case BR_PKT_MULTICAST://获取组播转发项，设置local_rcv为true，组播包也要发往本地一份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->host_joined) ||br_multicast_is_router(br)) {local_rcv = true;br->dev->stats.multicast++;}//可以获取到数据包对应的组播转发信息mcast_hit = true;} else {local_rcv = true;br->dev->stats.multicast++;}break;//既不是广播包，也不是组播包，则是单播包case BR_PKT_UNICAST://根据目的mac地址查找fdb表，看是否有对应的表项dst = br_fdb_find_rcu(br, dest, vid);default:break;}//如果找到目的mac对应转发表项if (dst) {unsigned long now = jiffies;//dst->is_local为真，送入上层处理if (dst->is_local)return br_pass_frame_up(skb);if (now != dst->used)dst->used = now;//根据fdb转发表项进行转发，若这里local_rcv 为1,（即端口处于混杂模式IFF_PROMISC），则会克隆一份再转发//传入的第一个参数dst->dst 即为要转发的目的端口br_forward(dst->dst, skb, local_rcv, false);} else {  //如果没有找到目的mac对应转发表项//进行广播或者组播洪泛if (!mcast_hit)br_flood(br, skb, pkt_type, local_rcv, false);elsebr_multicast_flood(mdst, skb, local_rcv, false);}//local_rcv标记为1，送入上层处理if (local_rcv)return br_pass_frame_up(skb);out:return 0;
drop:kfree_skb(skb);goto out;
}