Linux 3.10 kernel bridge转发逻辑

　　经过NF_BR_LOCAL_IN hook点会执行br_handle_local_finish函数。
　　static int br_handle_local_finish(struct sk_buff *skb)
　　{
　　struct net_bridge_port *p = br_port_get_rcu(skb->dev);
　　u16 vid = 0;
　　/*获取skb的vlan id(3.10的bridge支持vlan)*/
　　br_vlan_get_tag(skb， &vid);
　　/*更新bridge的mac表，注意vlan id也是参数，说明每个vlan有一个独立的mac表*/
　　br_fdb_update(p->br， p， eth_hdr(skb)->h_source， vid);
　　return 0; /* process further */
　　}
　　经过NF_BR_PRE_ROUTING hook点会执行br_handle_frame_finish函数。
　　br_handle_frame_finish
int br_handle_frame_finish(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;
u16 vid = 0;
if (!p || p->state == BR_STATE_DISABLED)
goto drop;
/*这个判断主要是vlan的相关检查，如是否和接收接口配置的vlan相同*/
if (!br_allowed_ingress(p->br， nbp_get_vlan_info(p)， skb， &vid))
goto out;
/* insert into forwarding database after filtering to avoid spoofing */
br = p->br;
/*更新转发数据库*/
br_fdb_update(br， p， eth_hdr(skb)->h_source， vid);
/*多播mac的处理*/
if (!is_broadcast_ether_addr(dest) && is_multicast_ether_addr(dest) &&
br_multicast_rcv(br， p， skb))
goto drop;
if (p->state == BR_STATE_LEARNING)
goto drop;
BR_INPUT_SKB_CB(skb)->brdev = br->dev;
/* The packet skb2 goes to the local host (NULL to skip). */
skb2 = NULL;
/*如果网桥被设置为混杂模式*/
if (br->dev->flags & IFF_PROMISC)
skb2 = skb;
dst = NULL;
/*如果skb的目的mac是广播*/
if (is_broadcast_ether_addr(dest))
skb2 = skb;
else if (is_multicast_ether_addr(dest)) { /*多播*/
mdst = br_mdb_get(br， skb， vid);
if (mdst || BR_INPUT_SKB_CB_MROUTERS_ONLY(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;
br->dev->stats.multicast++;
} else if ((dst = __br_fdb_get(br， dest， vid)) && dst->is_local) {/*目的地址是本机mac，则发往本机协议栈*/
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); //转发给目的接口
} else
br_flood_forward(br， skb， skb2); //找不到目的接口则广播
}
if (skb2)
return br_pass_frame_up(skb2); //发往本机协议栈
out:
return 0;
drop:
kfree_skb(skb);
goto out;
}
　　我们先看发往本机协议栈的函数br_pass_frame_up。
　　br_pass_frame_up
static int br_pass_frame_up(struct sk_buff *skb)
{
struct net_device *indev， *brdev = BR_INPUT_SKB_CB(skb)->brdev;
struct net_bridge *br = netdev_priv(brdev);
//更新统计计数(略)
/* Bridge is just like any other port. Make sure the
* packet is allowed except in promisc modue when someone
* may be running packet capture.
*/
if (!(brdev->flags & IFF_PROMISC) && !br_allowed_egress(br， br_get_vlan_info(br)， skb)) {
kfree_skb(skb); //如果不是混杂模式且vlan处理不合要求则丢弃
return NET_RX_DROP;
}
//vlan处理逻辑
skb = br_handle_vlan(br， br_get_vlan_info(br)， skb);
if (!skb)
return NET_RX_DROP;
indev = skb->dev;
skb->dev = brdev; //重点，这里修改了skb->dev为bridge
//经过NF_BR_LOCAL_IN再次进入协议栈
return NF_HOOK(NFPROTO_BRIDGE， NF_BR_LOCAL_IN， skb， indev， NULL，
netif_receive_skb);
}
　　再次进入netif_receive_skb，由于skb-dev被设置成了bridge，而bridge设备的rx_handler函数是没有被设置的，所以不会再次进入bridge逻辑，而直接进入了主机上层协议栈。
　　下面看转发逻辑，转发逻辑主要在br_forward函数中，而br_forward主要调用__br_forward函数。
　　__br_forward
static void __br_forward(const struct net_bridge_port *to， struct sk_buff *skb)
{
struct net_device *indev;
//vlan处理
skb = br_handle_vlan(to->br， nbp_get_vlan_info(to)， skb);
if (!skb)
return;
indev = skb->dev;
skb->dev = to->dev; //skb->dev设置为出口设备dev
skb_forward_csum(skb);
//经过NF_BR_FORWARD hook点，调用br_forward_finish
NF_HOOK(NFPROTO_BRIDGE， NF_BR_FORWARD， skb， indev， skb->dev，
br_forward_finish);
}
　　br_forward_finish
int br_dev_queue_push_xmit(struct sk_buff *skb)
{
/* ip_fragment doesn't copy the MAC header */
if (nf_bridge_maybe_copy_header(skb) || (packet_length(skb) > skb->dev->mtu && !skb_is_gso(skb))) {
kfree_skb(skb);
} else {
skb_push(skb， ETH_HLEN);
br_drop_fake_rtable(skb);
dev_queue_xmit(skb); //发送到链路层
}
return 0;
}
　　Skb进入dev_queue_xmit会调用相应设备驱动的发送函数。也出了bridge逻辑。所以整个3.10kernel的bridge转发逻辑如下图所示：

　　注意，和2.6kernel一样，bridge的OUTPUT hook点在bridge dev的发送函数中，这里不再分析列出。