拓扑

vlan_dev --> br-lan --> IP层 (br本身也会有一个fdb条目)

网桥创建/添加节点

模块初始化

static int __init br_init(void)
{int err;/*注册STP协议*/err = stp_proto_register(&br_stp_proto);/*分配fdb的slab: "bridge_fdb_cache", 变量br_fdb_cache*/err = br_fdb_init();/*命名空间退出时删除掉bridge*/err = register_pernet_subsys(&br_net_ops);/*初始化br_netfilter*/err = br_netfilter_init();/*注册netdev通知链，监听网络接口变化时间*/err = register_netdevice_notifier(&br_device_notifier);err = br_netlink_init();/*注册IOCTL函数*/brioctl_set(br_ioctl_deviceless_stub);#if IS_ENABLED(CONFIG_ATM_LANE)br_fdb_test_addr_hook = br_fdb_test_addr;
#endifreturn 0;
....../*异常处理*/
}

数据结构

net_bridge

struct net_bridge
{spinlock_t         lock;/*port链表*/struct list_head     port_list;/*cpu port的net_dev*/struct net_device     *dev;struct br_cpu_netstats __percpu *stats;spinlock_t          hash_lock;/*fdb hash表*/struct hlist_head        hash[BR_HASH_SIZE];
#ifdef CONFIG_BRIDGE_NETFILTERstruct rtable             fake_rtable;bool                nf_call_iptables;bool               nf_call_ip6tables;bool              nf_call_arptables;
#endifu16               group_fwd_mask;/* STP */bridge_id           designated_root;bridge_id           bridge_id;u32               root_path_cost;unsigned long            max_age;unsigned long           hello_time;unsigned long            forward_delay;unsigned long         bridge_max_age;unsigned long            ageing_time;unsigned long           bridge_hello_time;unsigned long         bridge_forward_delay;u8             group_addr[ETH_ALEN];u16                root_port;enum {BR_NO_STP,      /* no spanning tree */BR_KERNEL_STP,        /* old STP in kernel */BR_USER_STP,     /* new RSTP in userspace */} stp_enabled;/*拓扑变化事件*/unsigned char            topology_change;unsigned char           topology_change_detected;#ifdef CONFIG_BRIDGE_IGMP_SNOOPINGunsigned char            multicast_router;u8             multicast_disabled:1;u8             multicast_querier:1;u32             hash_elasticity;u32             hash_max;u32                multicast_last_member_count;u32             multicast_startup_queries_sent;u32              multicast_startup_query_count;unsigned long         multicast_last_member_interval;unsigned long            multicast_membership_interval;unsigned long         multicast_querier_interval;unsigned long            multicast_query_interval;unsigned long          multicast_query_response_interval;unsigned long         multicast_startup_query_interval;spinlock_t         multicast_lock;struct net_bridge_mdb_htable __rcu *mdb;struct hlist_head        router_list;struct timer_list       multicast_router_timer;struct timer_list        multicast_querier_timer;struct timer_list       multicast_query_timer;
#endif/*STP相关定时器*/struct timer_list     hello_timer;struct timer_list       tcn_timer;struct timer_list     topology_change_timer;/*fdb条目回收定时器*/struct timer_list       gc_timer;struct kobject         *ifobj;
#ifdef CONFIG_BRIDGE_VLAN_FILTERINGu8               vlan_enabled;struct net_port_vlans __rcu    *vlan_info;
#endif
};

net_bridge_port

struct net_bridge_port
{/*关联的网桥*/struct net_bridge     *br;struct net_device       *dev;struct list_head       list;/* STP */u8                priority;/*状态: 转发or学习*/u8               state;u16               port_no;unsigned char           topology_change_ack;unsigned char           config_pending;/*端口号*/port_id               port_id;port_id             designated_port;bridge_id           designated_root;bridge_id           designated_bridge;u32               path_cost;u32               designated_cost;unsigned long           designated_age;struct timer_list        forward_delay_timer;struct timer_list       hold_timer;struct timer_list        message_age_timer;struct kobject            kobj;struct rcu_head            rcu;unsigned long           flags;
#define BR_HAIRPIN_MODE     0x00000001
#define BR_BPDU_GUARD           0x00000002
#define BR_ROOT_BLOCK       0x00000004
#define BR_MULTICAST_FAST_LEAVE 0x00000008
#define BR_ADMIN_COST       0x00000010#ifdef CONFIG_BRIDGE_IGMP_SNOOPINGu32             multicast_startup_queries_sent;unsigned char            multicast_router;struct timer_list      multicast_router_timer;struct timer_list        multicast_query_timer;struct hlist_head     mglist;struct hlist_node        rlist;
#endif#ifdef CONFIG_SYSFSchar               sysfs_name[IFNAMSIZ];
#endif#ifdef CONFIG_NET_POLL_CONTROLLERstruct netpoll           *np;
#endif
#ifdef CONFIG_BRIDGE_VLAN_FILTERING/*vlan信息*/struct net_port_vlans __rcu    *vlan_info;
#endif
};

创建网桥

创建网桥是在 sock_ioctl中

static long sock_ioctl(struct file *file, unsigned cmd, unsigned long arg)
{case SIOCGIFBR:case SIOCSIFBR:case SIOCBRADDBR:case SIOCBRDELBR:err = -ENOPKG;if (!br_ioctl_hook)request_module("bridge");mutex_lock(&br_ioctl_mutex);if (br_ioctl_hook)err = br_ioctl_hook(net, cmd, argp);mutex_unlock(&br_ioctl_mutex);
}

br_ioctl_hook的钩子在br_init复制，指向br_ioctl_deviceless_stub函数。

int br_ioctl_deviceless_stub(struct net *net, unsigned int cmd, void __user *uarg)
{switch (cmd) {case SIOCGIFBR:case SIOCSIFBR:return old_deviceless(net, uarg);case SIOCBRADDBR:case SIOCBRDELBR:{char buf[IFNAMSIZ];if (!ns_capable(net->user_ns, CAP_NET_ADMIN))return -EPERM;if (copy_from_user(buf, uarg, IFNAMSIZ))return -EFAULT;buf[IFNAMSIZ-1] = 0;if (cmd == SIOCBRADDBR)return br_add_bridge(net, buf);return br_del_bridge(net, buf);}}return -EOPNOTSUPP;
}

创建网桥设备：br_add_bridge函数<br_if.c>

删除网桥设备：br_del_bridge函数

创建网桥：

int br_add_bridge(struct net *net, const char *name)
{struct net_device *dev;int res;/*分配net_device, 同时使用br_dev_setup初始化*/dev = alloc_netdev(sizeof(struct net_bridge), name,br_dev_setup);/*linkops有何用？*/dev_net_set(dev, net);dev->rtnl_link_ops = &br_link_ops;/*注册*/res = register_netdev(dev);}

很简单: 注册一个net_device而已，唯一的区别在net_device的赋值上，赋值函数br_dev_setup<br_device.c>。

void br_dev_setup(struct net_device *dev)
{/*net_device的私有数据存储net_bridge* 继承关系*/struct net_bridge *br = netdev_priv(dev);/*随机生成一个mac*/eth_hw_addr_random(dev);/*设置以太网dev的参数*/ether_setup(dev);/*重点: 操作集发包函数和ioctl*/dev->netdev_ops = &br_netdev_ops;dev->destructor = br_dev_free;/*ethtools工具的ops*/SET_ETHTOOL_OPS(dev, &br_ethtool_ops);/*设置device_type为bridge*/SET_NETDEV_DEVTYPE(dev, &br_type);/*rx队列的长度设置为0？*/dev->tx_queue_len = 0;/*接口标识： IFF_EBRIDGE 网桥设备*/dev->priv_flags = IFF_EBRIDGE;dev->features = NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_HIGHDMA |NETIF_F_GSO_MASK | NETIF_F_HW_CSUM | NETIF_F_LLTX |NETIF_F_NETNS_LOCAL | NETIF_F_HW_VLAN_CTAG_TX;dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_HIGHDMA |NETIF_F_GSO_MASK | NETIF_F_HW_CSUM |NETIF_F_HW_VLAN_CTAG_TX;br->dev = dev;spin_lock_init(&br->lock);INIT_LIST_HEAD(&br->port_list);spin_lock_init(&br->hash_lock);br->bridge_id.prio[0] = 0x80;br->bridge_id.prio[1] = 0x00;memcpy(br->group_addr, eth_reserved_addr_base, ETH_ALEN);/*默认是不开STP的*/br->stp_enabled = BR_NO_STP;br->group_fwd_mask = BR_GROUPFWD_DEFAULT;/*STP相关参数*/br->designated_root = br->bridge_id;br->bridge_max_age = br->max_age = 20 * HZ;br->bridge_hello_time = br->hello_time = 2 * HZ;br->bridge_forward_delay = br->forward_delay = 15 * HZ;br->ageing_time = 300 * HZ;/*设置虚拟的路由fake_rtable*/br_netfilter_rtable_init(br);/*STP定时器*/br_stp_timer_init(br);/*空函数*/br_multicast_init(br);
}

bridge结构保存在net_device的私有数据中，继承关系；
随机生成一个mac；
设置以太网dev的参数
设置net_dev操作集netdev_ops为br_netdev_ops，主要关注发包函数和ioctl
接口标识： IFF_EBRIDGE
设置STP定时器以及参数，默认是不开STP的；
设置虚拟路由；？

net_device的操作集：br_netdev_ops

static const struct net_device_ops br_netdev_ops = {.ndo_open        = br_dev_open,.ndo_stop        = br_dev_stop,.ndo_init        = br_dev_init,.ndo_start_xmit      = br_dev_xmit,.ndo_get_stats64     = br_get_stats64,.ndo_set_mac_address  = br_set_mac_address,.ndo_set_rx_mode  = br_dev_set_multicast_list,.ndo_change_mtu        = br_change_mtu,.ndo_do_ioctl      = br_dev_ioctl,
#ifdef CONFIG_NET_POLL_CONTROLLER.ndo_netpoll_setup  = br_netpoll_setup,.ndo_netpoll_cleanup    = br_netpoll_cleanup,.ndo_poll_controller  = br_poll_controller,
#endif.ndo_add_slave         = br_add_slave,.ndo_del_slave      = br_del_slave,.ndo_fix_features        = br_fix_features,.ndo_fdb_add        = br_fdb_add,.ndo_fdb_del      = br_fdb_delete,.ndo_fdb_dump      = br_fdb_dump,.ndo_bridge_getlink  = br_getlink,.ndo_bridge_setlink   = br_setlink,.ndo_bridge_dellink   = br_dellink,
};

发包函数： ndo_start_xmit = br_dev_xmit；

ioctl: ndo_do_ioctl = br_dev_ioctl;

还有FDB的添加删除操作：ndo_fdb_add等。

添加接口

添加接口是在net_dev_ops中的ioctl函数br_dev_ioctl中。

int br_dev_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
{struct net_bridge *br = netdev_priv(dev);switch(cmd) {case SIOCDEVPRIVATE:/*旧的IOCTL接口：add/devif* 获取bridge/port信息* 设置STP参数* 设置FDB老化时间*/return old_dev_ioctl(dev, rq, cmd);case SIOCBRADDIF:case SIOCBRDELIF:return add_del_if(br, rq->ifr_ifindex, cmd == SIOCBRADDIF);}
}

最终的给网桥添加接口的函数br_add_if

int br_add_if(struct net_bridge *br, struct net_device *dev)
{struct net_bridge_port *p;int err = 0;bool changed_addr;/*非以太网设备不支持添加*//* Don't allow bridging non-ethernet like devices */if ((dev->flags & IFF_LOOPBACK) ||dev->type != ARPHRD_ETHER || dev->addr_len != ETH_ALEN ||!is_valid_ether_addr(dev->dev_addr))return -EINVAL;/* No bridging of bridges *//*不支持bridge下挂bridge*/if (dev->netdev_ops->ndo_start_xmit == br_dev_xmit)return -ELOOP;/* Device is already being bridged */if (br_port_exists(dev))return -EBUSY;/*接口不支持网桥*//* No bridging devices that dislike that (e.g. wireless) */if (dev->priv_flags & IFF_DONT_BRIDGE)return -EOPNOTSUPP;p = new_nbp(br, dev);if (IS_ERR(p))return PTR_ERR(p);/*调用NETDEC_JOIN通知链*/call_netdevice_notifiers(NETDEV_JOIN, dev);/*设置混杂模式，不然会丢弃目的mac不是自己的包*/err = dev_set_promiscuity(dev, 1);if (err)goto put_back;err = kobject_init_and_add(&p->kobj, &brport_ktype, &(dev->dev.kobj),SYSFS_BRIDGE_PORT_ATTR);if (err)goto err1;err = br_sysfs_addif(p);if (err)goto err2;if (br_netpoll_info(br) && ((err = br_netpoll_enable(p, GFP_KERNEL))))goto err3;err = netdev_master_upper_dev_link(dev, br->dev);if (err)goto err4;/*设置设备的接收函数为网桥的接收函数br_handle_frame*/err = netdev_rx_handler_register(dev, br_handle_frame, p);if (err)goto err5;/*设置dev标记为bridge的一个port*/dev->priv_flags |= IFF_BRIDGE_PORT;/*禁止设备的lro*/dev_disable_lro(dev);/*加入网桥的port_list*/list_add_rcu(&p->list, &br->port_list);netdev_update_features(br->dev);spin_lock_bh(&br->lock);changed_addr = br_stp_recalculate_bridge_id(br);if (netif_running(dev) && netif_oper_up(dev) &&(br->dev->flags & IFF_UP))br_stp_enable_port(p);spin_unlock_bh(&br->lock);/*发送netlink通知newlink*/br_ifinfo_notify(RTM_NEWLINK, p);if (changed_addr)call_netdevice_notifiers(NETDEV_CHANGEADDR, br->dev);/*设置接口的mtu为网桥中最小的mtu， 重点*/dev_set_mtu(br->dev, br_min_mtu(br));/*创建一条该接口的fdb，命中直接走协议栈，不转发*/if (br_fdb_insert(br, p, dev->dev_addr, 0))netdev_err(dev, "failed insert local address bridge forwarding table\n");kobject_uevent(&p->kobj, KOBJ_ADD);return 0;}

首先过滤条件：

非以太网设备不能加入bridge
网桥设备不能加入bridge，准确来说是发送函数是br_dev_xmit的设备不能再加入网桥。
待加入的设备设置了不支持网桥的priv_flag：IFF_DONT_BRIDGE

然后步骤:

分配一个网桥端口结构：net_bridge_port
发送netdev通知链事件NETDEV_JOIN
标记带加入设备为网桥的一个port: IFF_BRIDGE_PORT
将net_bridge_port加入br的port_list链表
设置待加入设备的接收函数为网桥接收函数br_handle_frame
设置待加入设备mtu为网桥中最小的mtu
禁止待加入设备的lro功能
linux4.x的内核，还会根据加入设备的headroom扩展br的headroom
STP相关后面章节讨论

br_netfilter

datapath

发送

br的tx函数为net_device_ops的ndo_start_xmit成员：br_dev_xmit

netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
{struct net_bridge *br = netdev_priv(dev);const unsigned char *dest = skb->data;struct net_bridge_fdb_entry *dst;struct net_bridge_mdb_entry *mdst;struct br_cpu_netstats *brstats = this_cpu_ptr(br->stats);u16 vid = 0;rcu_read_lock();
#ifdef CONFIG_BRIDGE_NETFILTERif (skb->nf_bridge && (skb->nf_bridge->mask & BRNF_BRIDGED_DNAT)) {br_nf_pre_routing_finish_bridge_slow(skb);rcu_read_unlock();return NETDEV_TX_OK;}
#endifu64_stats_update_begin(&brstats->syncp);brstats->tx_packets++;brstats->tx_bytes += skb->len;u64_stats_update_end(&brstats->syncp);/*查看skb是否有vid， 且和br的vid是否一致*/if (!br_allowed_ingress(br, br_get_vlan_info(br), skb, &vid))goto out;BR_INPUT_SKB_CB(skb)->brdev = dev;skb_reset_mac_header(skb);skb_pull(skb, ETH_HLEN);if (is_broadcast_ether_addr(dest))br_flood_deliver(br, skb);else if (is_multicast_ether_addr(dest)) {if (unlikely(netpoll_tx_running(dev))) {br_flood_deliver(br, skb);goto out;}if (br_multicast_rcv(br, NULL, skb)) {kfree_skb(skb);goto out;}mdst = br_mdb_get(br, skb, vid);if (mdst || BR_INPUT_SKB_CB_MROUTERS_ONLY(skb))br_multicast_deliver(mdst, skb);elsebr_flood_deliver(br, skb);} else if ((dst = __br_fdb_get(br, dest, vid)) != NULL)/*直接发往对应端口*/br_deliver(dst->dst, skb);else/*没找到fdb，则洪范*/br_flood_deliver(br, skb);out:rcu_read_unlock();return NETDEV_TX_OK;
}

先检查skb的vid和br的cpuport的vid是否一致，不一致则不能发送；br本身也是可以有vid的。

单播: 找到fdb调用 br_deliver发往对应端口

没找到fdb则调用br_flood_deliver洪范

__br_deliver函数:

static void __br_deliver(const struct net_bridge_port *to, struct sk_buff *skb)
{skb = br_handle_vlan(to->br, nbp_get_vlan_info(to), skb);if (!skb)return;skb->dev = to->dev;if (unlikely(netpoll_tx_running(to->br->dev))) {if (packet_length(skb) > skb->dev->mtu && !skb_is_gso(skb))kfree_skb(skb);else {skb_push(skb, ETH_HLEN);br_netpoll_send_skb(to, skb);}return;}NF_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_OUT, skb, NULL, skb->dev,br_forward_finish);
}

检查是否支持netpool
最终调用br_forward_finish将报文发出

接收

数据报文的接收函数: 每个port dev对应的的rx_handler: br_handle_frame<br_imput.c>

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;/*如果有shareinfo则clone skb*/skb = skb_share_check(skb, GFP_ATOMIC);if (!skb)return RX_HANDLER_CONSUMED;p = br_port_get_rcu(skb->dev);/*预留地址01-80-C2开头的*/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* 端口聚合的目的地址也是特殊地址？* (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*//*最后一个字节*/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;/*MAC的流量控制pause帧，pouse帧的目的MAC为预留地址* 01-80-C2-00-00-01*/case 0x01:    /* IEEE MAC (Pause) */goto drop;default:/* Allow selective forwarding for most other protocols */if (p->br->group_fwd_mask & (1u << dest[5]))goto forward;}/* Deliver packet to local host only */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 = skb;return RX_HANDLER_PASS; /* continue processing */}}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:/*目的地是br的MAC，是发往本机的*/if (ether_addr_equal(p->br->dev->dev_addr, dest))skb->pkt_type = PACKET_HOST;/*转发*/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;
}

如果skb有shareinfo则clone skb， shareinfo一般用作gso和paged data；
根据dev查找网桥的port
如果目的MAC是预留地址如pause帧则丢弃，pause帧的目的地址是01-80-C2-00-00-01
如果目的MAC是br的MAC则是发往本地的，置skb的pkt_type为PACKET_HOST；
转发并调用br_netfilter；

tips：该接收函数只用于接收mac帧，即数据帧，不接受stp协议报文，stp协议报文是llc协议，并不是mac协议。

br_handle_frame_finish函数

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;/*检查报文vid和端口的pvid是否一致*/if (!br_allowed_ingress(p->br, nbp_get_vlan_info(p), skb, &vid))goto drop;/* insert into forwarding database after filtering to avoid spoofing */br = p->br;/*根据源mac和vid更新fdb，添加fdb条目*/br_fdb_update(br, p, eth_hdr(skb)->h_source, vid);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;if (br->dev->flags & IFF_PROMISC)skb2 = skb;dst = NULL;if (is_broadcast_ether_addr(dest))skb2 = skb;else if (is_multicast_ether_addr(dest)) {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;} elseskb2 = skb;br->dev->stats.multicast++;/*根据vlan和目的mac查找fdb* is_local表示是否是发往本地的*/} 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/*没找到端口，则洪范*/br_flood_forward(br, skb, skb2);}/*发往本地*/if (skb2)return br_pass_frame_up(skb2);out:return 0;
drop:kfree_skb(skb);goto out;
}

检查报文vid和端口的pvid是否一致，不一致则丢弃报文；
根据源mac和vid更新/添加fdb条目;
多播和单播处理，单播查找fdb
如果是发往本地的调用br_pass_frame_up；转发调用br_forward；
如果没有找到fdb，则洪范，即转发也发到本机，洪范转发br_flood_forward。

转发函数 ==> 最终调用 br_dev_queue_push_xmit发包。

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);/*删除虚拟的路由，直接调用设备的发包函数*/br_drop_fake_rtable(skb);dev_queue_xmit(skb);}return 0;
}

fdb

数据结构

net_bridge_fdb_entry

struct net_bridge_fdb_entry
{struct hlist_node      hlist;struct net_bridge_port        *dst;       /*网桥端口*/struct rcu_head         rcu;unsigned long           updated; /*上次更新的jiffes*/unsigned long           used;   /*上次使用jiffes*/mac_addr          addr;       /*mac地址用于匹配*/unsigned char          is_local;       /*是否是发往本地的*/unsigned char           is_static;      /*静态，不老化，永久*/__u16                vlan_id;    /*vlan_id用于*/
};

组织方式

内存 slab：br+fdb+cache

组织: 哈希表br->hash； net_bridge的hash成员。哈希桶的槽位256。

条目上限:无上限；

学习

透明网桥,接收报文时自动学习.

br_handle_frame_finish中调用br_fdb_update学习fdb条目。

老化

gc_timer：资源回收定时器。

在

br_dev_setup

->br_stp_timer_init设置,处理函数为br_fdb_cleanup

setup_timer(&br->gc_timer, br_fdb_cleanup, (unsigned long) br);

br_fdb_cleanup函数中：

比较条目的上次的更新时间是否足够久去老化，条目老化的时间，通过hold_time(br)函数获取。

void br_fdb_cleanup(unsigned long _data)
{struct net_bridge *br = (struct net_bridge *)_data;unsigned long delay = hold_time(br);unsigned long next_timer = jiffies + br->ageing_time;int i;spin_lock(&br->hash_lock);for (i = 0; i < BR_HASH_SIZE; i++) {struct net_bridge_fdb_entry *f;struct hlist_node *n;hlist_for_each_entry_safe(f, n, &br->hash[i], hlist) {unsigned long this_timer;if (f->is_static)continue;this_timer = f->updated + delay;if (time_before_eq(this_timer, jiffies))fdb_delete(br, f);else if (time_before(this_timer, next_timer))next_timer = this_timer;}}spin_unlock(&br->hash_lock);mod_timer(&br->gc_timer, round_jiffies_up(next_timer));
}

老化时间：如果拓扑变化了，则为forward_delay：即15s；

否则老化时间：300s；此时间在br_dev_setup函数中设置。

static inline unsigned long hold_time(const struct net_bridge *br)
{return br->topology_change ? br->forward_delay : br->ageing_time;
}
#define BR_DEFAULT_AGEING_TIME (300*HZ)

多播的datapath

mdb

STP

使用LLC协议而不是MAC的链路协议

BPDU包

LLC协议

netlink接口

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拓扑

网桥创建/添加节点

模块初始化

数据结构

创建网桥

添加接口

br_netfilter

datapath

发送

接收

fdb

数据结构

组织方式

学习

老化

多播的datapath

STP

LLC协议

netlink接口

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