前分析过linux kernel 2.6.32的bridge转发逻辑&＃xff0c;下面分析一下linux kernel 3.10的bridge转发逻辑。这样正是CentOS 5和CentOS 7对应的内核。3.10 kernel中bridge逻辑的最大改变就是增加了vlan处理逻辑以及brdige入口函数的设置。
1. netdev_rx_handler_register
在分析之前首先要介绍一个重要函数&＃xff1a;netdev_rx_handler_register&＃xff0c;这个函数是2.6内核所没有的。
netdev_rx_handler_register
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/*
* 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&＃xff0c;然后在__netif_receive_skb函数中根据接收skb的设备接口&＃xff0c;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&＃xff0c;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&＃xff0c;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
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staTIc struct vport *netdev_create(const struct vport_parms *parms)
{
struct vport *vport;
/....../
err &＃61; 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&＃xff0c;这也是整个openvswitch的入口函数&＃xff0c;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&＃xff0c;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&＃xff0c;这个函数算是进入协议栈的入口。
neTIf_receive_skb
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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&＃xff0c;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 &＃61; &voidflow;
int cpu &＃61; get_rps_cpu(skb->dev, skb, &rflow);
if (cpu >&＃61; 0) {
ret &＃61; enqueue_to_backlog(skb, cpu, &rflow->last_qtail);
rcu_read_unlock();
return ret;
}
}
#endif
ret &＃61; __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&＃xff0c;然后调用__netif_receive_skb。
__netif_receive_skb并没有其他多余的处理逻辑&＃xff0c;主要调用 __netif_receive_skb_core&＃xff0c;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
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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 &＃61; false;
int ret &＃61; NET_RX_DROP;
__be16 type;
/*......*/
orig_dev &＃61; skb->dev;
skb_reset_network_header(skb);
pt_prev &＃61; NULL;
skb->skb_iif &＃61; skb->dev->ifindex;
/*ptype_all协议处理&＃xff0c;tcpdump抓包就在这里*/
list_for_each_entry_rcu(ptype, &ptype_all, list) {
if (!ptype->dev || ptype->dev &＃61;&＃61; skb->dev) {
if (pt_prev)
ret &＃61; deliver_skb(skb, pt_prev, orig_dev);
pt_prev &＃61; ptype;
}
}
/*调用接收设备的rx_handler*/
rx_handler &＃61; rcu_dereference(skb->dev->rx_handler);
if (rx_handler) {
if (pt_prev) {
ret &＃61; deliver_skb(skb, pt_prev, orig_dev);
pt_prev &＃61; NULL;
}
switch (rx_handler(&skb)) {
case RX_HANDLER_CONSUMED:
ret &＃61; NET_RX_SUCCESS;
goto out;
case RX_HANDLER_ANOTHER:
goto another_round;
case RX_HANDLER_EXACT:
deliver_exact &＃61; true;
case RX_HANDLER_PASS:
break;
default:
BUG();
}
}
/*根据 skb->protocol传递给上层协议*/
type &＃61; skb->protocol;
list_for_each_entry_rcu(ptype,&ptype_base[ntohs(type) & PTYPE_HASH_MASK], list) {
if (ptype->type &＃61;&＃61; type && (ptype->dev &＃61;&＃61; null_or_dev || ptype->dev &＃61;&＃61; skb->dev ||ptype->dev &＃61;&＃61; orig_dev)) {
if (pt_prev)
ret &＃61; deliver_skb(skb, pt_prev, orig_dev);
pt_prev &＃61; ptype;
}
}
if (pt_prev) {
if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
goto drop;
else
ret &＃61; pt_prev->func(skb, skb->dev, pt_prev, orig_dev);
} else {
drop:
atomic_long_inc(&skb->dev->rx_dropped);
kfree_skb(skb);
ret &＃61; 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)&＃xff0c;的这个接口设备的rx_handler被设置为br_handle_frame函数&＃xff0c;这是在br_add_if函数中设置的&＃xff0c;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
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int br_add_if(struct net_bridge *br, struct net_device *dev)
{
/*......*/
err &＃61; netdev_rx_handler_register(dev, br_handle_frame, p);
/*......*/
}
br_handle_frame
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rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
{
struct net_bridge_port *p;
struct sk_buff *skb &＃61; *pskb;
const unsigned char *dest &＃61; eth_hdr(skb)->h_dest;
br_should_route_hook_t *rhook;
if (unlikely(skb->pkt_type &＃61;&＃61; PACKET_LOOPBACK))
return RX_HANDLER_PASS;
if (!is_valid_ether_addr(eth_hdr(skb)->h_source))
goto drop;
skb &＃61; skb_share_check(skb, GFP_ATOMIC);
if (!skb)
return RX_HANDLER_CONSUMED;
/*获取dev对应的bridge port*/
p &＃61; 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 &＃61;&＃61; 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 < goto forward; } /* LOCAL_IN hook点&＃xff0c;注意经过这个hook点并不代表发送到主机协议栈(只有特殊目的mac 01-80-C2才会走到这里)*/ if (NF_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_IN, skb, skb->dev, NULL, br_handle_local_finish)) { return RX_HANDLER_CONSUMED; /* consumed by filter */ } else { *pskb &＃61; skb; return RX_HANDLER_PASS; /* continue processing */ } } /*转发逻辑*/ forward: switch (p->state) { case BR_STATE_FORWARDING: rhook &＃61; rcu_dereference(br_should_route_hook); if (rhook) { if ((*rhook)(skb)) { *pskb &＃61; skb; return RX_HANDLER_PASS; } dest &＃61; eth_hdr(skb)->h_dest; } /* fall through */ case BR_STATE_LEARNING: /*skb的目的mac和bridge的mac一样&＃xff0c;则将skb发往本机协议栈*/ if (ether_addr_equal(p->br->dev->dev_addr, dest)) skb->pkt_type &＃61; 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 1 2 3 4 5 6 7 8 9 10 static int br_handle_local_finish(struct sk_buff *skb) { struct net_bridge_port *p &＃61; br_port_get_rcu(skb->dev); u16 vid &＃61; 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&＃xff0c;注意vlan id也是参数&＃xff0c;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 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 int br_handle_frame_finish(struct sk_buff *skb) { const unsigned char *dest &＃61; eth_hdr(skb)->h_dest; struct net_bridge_port *p &＃61; 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 &＃61; 0; if (!p || p->state &＃61;&＃61; BR_STATE_DISABLED) goto drop; /*这个判断主要是vlan的相关检查&＃xff0c;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 &＃61; 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 &＃61;&＃61; BR_STATE_LEARNING) goto drop; BR_INPUT_SKB_CB(skb)->brdev &＃61; br->dev; /* The packet skb2 goes to the local host (NULL to skip). */ skb2 &＃61; NULL; /*如果网桥被设置为混杂模式*/ if (br->dev->flags & IFF_PROMISC) skb2 &＃61; skb; dst &＃61; NULL; /*如果skb的目的mac是广播*/ if (is_broadcast_ether_addr(dest)) skb2 &＃61; skb; else if (is_multicast_ether_addr(dest)) { /*多播*/ mdst &＃61; 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 &＃61; skb; br_multicast_forward(mdst, skb, skb2); skb &＃61; NULL; if (!skb2) goto out; } else skb2 &＃61; skb; br->dev->stats.multicast&＃43;&＃43;; } else if ((dst &＃61; __br_fdb_get(br, dest, vid)) && dst->is_local) {/*目的地址是本机mac&＃xff0c;则发往本机协议栈*/ skb2 &＃61; skb; /* Do not forward the packet since it&＃39;s local. */ skb &＃61; NULL; } if (skb) { if (dst) { dst->used &＃61; 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; } {C} 我们先看发往本机协议栈的函数br_pass_frame_up。 br_pass_frame_up 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 static int br_pass_frame_up(struct sk_buff *skb) { struct net_device *indev, *brdev &＃61; BR_INPUT_SKB_CB(skb)->brdev; struct net_bridge *br &＃61; 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 &＃61; br_handle_vlan(br, br_get_vlan_info(br), skb); if (!skb) return NET_RX_DROP; indev &＃61; skb->dev; skb->dev &＃61; brdev; //重点&＃xff0c;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); } {C} 再次进入netif_receive_skb&＃xff0c;由于skb-dev被设置成了bridge&＃xff0c;而bridge设备的rx_handler函数是没有被设置的&＃xff0c;所以就不会再次进入bridge逻辑&＃xff0c;而直接进入了主机上层协议栈。 下面看转发逻辑&＃xff0c;转发逻辑主要在br_forward函数中&＃xff0c;而br_forward主要调用__br_forward函数。 __br_forward 1 2 3 4 5 6 7 8 9 10 11 12 13 14 static void __br_forward(const struct net_bridge_port *to, struct sk_buff *skb) { struct net_device *indev; //vlan处理 skb &＃61; br_handle_vlan(to->br, nbp_get_vlan_info(to), skb); if (!skb) return; indev &＃61; skb->dev; skb->dev &＃61; to->dev; //skb->dev设置为出口设备dev skb_forward_csum(skb); //经过NF_BR_FORWARD hook点&＃xff0c;调用br_forward_finish NF_HOOK(NFPROTO_BRIDGE, NF_BR_FORWARD, skb, indev, skb->dev, br_forward_finish); } {C} br_forward_finish 1 2 3 4 5 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); } {C} br_dev_queue_push_xmit 1 2 3 4 5 6 7 8 9 10 11 12 int br_dev_queue_push_xmit(struct sk_buff *skb) { /* ip_fragment doesn&＃39;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&＃xff1a; 注意&＃xff0c;和2.6kernel一样&＃xff0c;bridge的OUTPUT hook点在bridge dev的发送函数中&＃xff0c;这里不再分析列出。
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