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linux内核网络协议栈
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1. netdev_rx_handler_register
在分析之前首先要介绍一个重要函数：netdev_rx_handler_register，这个函数是2.6内核所没有的。 netdev_rx_handler_register /* * dev: 要注册接收函数的dev * rx_handler: 要注册的接收函数 * rx_handler_data: 指向rx_handler_data使用的数据 */ int netdev_rx_handler_register(struct net_device *dev, rx_handler_func_t *rx_handler, void *rx_handler_data) { ASSERT_RTNL(); if (dev->rx_handler) return -EBUSY; /* Note: rx_handler_data must be set before rx_handler */ rcu_assign_pointer(dev->rx_handler_data, rx_handler_data); rcu_assign_pointer(dev->rx_handler, rx_handler); return 0; }这个函数可以给设备（net_device）注册接收函数，然后在__netif_receive_skb函数中根据接收skb的设备接口，再调用这个被注册的接收函数。比如为网桥下的接口注册br_handle_frame函数，为bonding接口注册bond_handle_frame函数。这相对于老式的网桥处理更灵活，有了这个机制也可以在模块中自行注册处理函数。比如3.10中的openvswitch（OpenvSwitch在3.10已经合入了内核）创建netdev vport的函数netdev_create。 netdev_create static struct vport *netdev_create(const struct vport_parms *parms) { struct vport *vport; /....../ err = netdev_rx_handler_register(netdev_vport->dev, netdev_frame_hook,vport); /....../ }这个函数在创建netdev vport时将设备的接收函数设置为netdev_frame_hook函数，这也是整个openvswitch的入口函数，如果查看OpenvSwitch的源码可以看到当安装于2.6内核时这里是替换掉bridge的br_handle_frame_hook函数，从而由bridge逻辑进入OpenvSwitch逻辑。 2. Bridge转发逻辑分析还是先从netif_receive_skb函数分析，这个函数算是进入协议栈的入口。 netif_receive_skb int netif_receive_skb(struct sk_buff *skb) { int ret; if (skb_defer_rx_timestamp(skb)) return NET_RX_SUCCESS; rcu_read_lock(); /*RPS逻辑处理，现在内核中使用了RPS机制, 将报文分散到各个cpu的接收队列中进行负载均衡处理*/ #ifdef CONFIG_RPS if (static_key_false(&rps_needed)) { struct rps_dev_flow voidflow, *rflow = &voidflow; int cpu = get_rps_cpu(skb->dev, skb, &rflow); if (cpu >= 0) { ret = enqueue_to_backlog(skb, cpu, &rflow->last_qtail); rcu_read_unlock(); return ret; } } #endif ret = __netif_receive_skb(skb); rcu_read_unlock(); return ret; }netif_receive_skb只是对数据包进行了RPS的处理，然后调用__netif_receive_skb。 __netif_receive_skb并没有其他多余的处理逻辑，主要调用 __netif_receive_skb_core，这个函数才真正相当于2.6内核的netif_receive_skb。以下代码省略了和bridge无关的逻辑。 __netif_receive_skb_core static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc) { struct packet_type *ptype, *pt_prev; rx_handler_func_t *rx_handler; struct net_device *orig_dev; struct net_device *null_or_dev; bool deliver_exact = false; int ret = NET_RX_DROP; __be16 type; /*......*/ orig_dev = skb->dev; skb_reset_network_header(skb); pt_prev = NULL; skb->skb_iif = skb->dev->ifindex; /*ptype_all协议处理，tcpdump抓包就在这里*/ list_for_each_entry_rcu(ptype, &ptype_all, list) { if (!ptype->dev || ptype->dev == skb->dev) { if (pt_prev) ret = deliver_skb(skb, pt_prev, orig_dev); pt_prev = ptype; } } /*调用接收设备的rx_handler*/ rx_handler = rcu_dereference(skb->dev->rx_handler); if (rx_handler) { if (pt_prev) { ret = deliver_skb(skb, pt_prev, orig_dev); pt_prev = NULL; } switch (rx_handler(&skb)) { case RX_HANDLER_CONSUMED: ret = NET_RX_SUCCESS; goto out; case RX_HANDLER_ANOTHER: goto another_round; case RX_HANDLER_EXACT: deliver_exact = true; case RX_HANDLER_PASS: break; default: BUG(); } } /*根据 skb->protocol传递给上层协议*/ type = skb->protocol; list_for_each_entry_rcu(ptype,&ptype_base[ntohs(type) & PTYPE_HASH_MASK], list) { if (ptype->type == type && (ptype->dev == null_or_dev || ptype->dev == skb->dev ||ptype->dev == orig_dev)) { if (pt_prev) ret = deliver_skb(skb, pt_prev, orig_dev); pt_prev = ptype; } } if (pt_prev) { if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC))) goto drop; else ret = pt_prev->func(skb, skb->dev, pt_prev, orig_dev); } else { drop: atomic_long_inc(&skb->dev->rx_dropped); kfree_skb(skb); ret = NET_RX_DROP; } out: return ret; }如果一个dev被添加到一个bridge（做为bridge的一个接口），的这个接口设备的rx_handler被设置为br_handle_frame函数，这是在br_add_if函数中设置的，而br_add_if (net/bridge/br_if.c)是在向网桥设备上添加接口时设置的。进入br_handle_frame也就进入了bridge的逻辑代码。 br_add_if int br_add_if(struct net_bridge *br, struct net_device *dev) { /*......*/ err = netdev_rx_handler_register(dev, br_handle_frame, p); /*......*/ } br_handle_frame rx_handler_result_t br_handle_frame(struct sk_buff **pskb) { struct net_bridge_port *p; struct sk_buff *skb = *pskb; const unsigned char *dest = eth_hdr(skb)->h_dest; br_should_route_hook_t *rhook; if (unlikely(skb->pkt_type == PACKET_LOOPBACK)) return RX_HANDLER_PASS; if (!is_valid_ether_addr(eth_hdr(skb)->h_source)) goto drop; skb = skb_share_check(skb, GFP_ATOMIC); if (!skb) return RX_HANDLER_CONSUMED; /*获取dev对应的bridge port*/ p = br_port_get_rcu(skb->dev); /*特殊目的mac地址的处理*/ if (unlikely(is_link_local_ether_addr(dest))) { /* * See IEEE 802.1D Table 7-10 Reserved addresses * * Assignment Value * Bridge Group Address 01-80-C2-00-00-00 * (MAC Control) 802.3 01-80-C2-00-00-01 * (Link Aggregation) 802.3 01-80-C2-00-00-02 * 802.1X PAE address 01-80-C2-00-00-03 * * 802.1AB LLDP 01-80-C2-00-00-0E * * Others reserved for future standardization */ switch (dest[5]) { case 0x00: /* Bridge Group Address */ /* If STP is turned off,then must forward to keep loop detection */ if (p->br->stp_enabled == BR_NO_STP) goto forward; break; case 0x01: /* IEEE MAC (Pause) */ goto drop; default: /* Allow selective forwarding for most other protocols */ if (p->br->group_fwd_mask & (1u *pskb = skb; return RX_HANDLER_PASS; /* continue processing */ } } /*转发逻辑*/ forward: switch (p->state) { case BR_STATE_FORWARDING: rhook = rcu_dereference(br_should_route_hook); if (rhook) { if ((*rhook)(skb)) { *pskb = skb; return RX_HANDLER_PASS; } dest = eth_hdr(skb)->h_dest; } /* fall through */ case BR_STATE_LEARNING: /*skb的目的mac和bridge的mac一样，则将skb发往本机协议栈*/ if (ether_addr_equal(p->br->dev->dev_addr, dest)) skb->pkt_type = PACKET_HOST; /*NF_BR_PRE_ROUTING hook点*/ NF_HOOK(NFPROTO_BRIDGE, NF_BR_PRE_ROUTING, skb, skb->dev, NULL,br_handle_frame_finish); break; default: drop: kfree_skb(skb); } return RX_HANDLER_CONSUMED; }经过NF_BR_LOCAL_IN hook点会执行br_handle_local_finish函数。 br_handle_local_finish 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，所以就不会再次进入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_forward_finish(struct sk_buff *skb) { //经过NF_BR_POST_ROUTING hook点,调用br_dev_queue_push_xmit return NF_HOOK(NFPROTO_BRIDGE, NF_BR_POST_ROUTING, skb, NULL, skb->dev, br_dev_queue_push_xmit); } br_dev_queue_push_xmit 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就会调用相应设备驱动的发送函数。也就出了bridge逻辑。所以整个3.10kernel的bridge转发逻辑如下图所示： 原文链接：http://www.embeddedlinux.org.cn/emb-linux/kernel-driver/201611/10-5842.html |
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。【本文地址】
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