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分类: LINUX

2015-11-09 10:20:19

在内核,网桥是以模块的方式存在,注册源码路径:\net\brige\br.c

4.1 初始化
 

static int __init br_init(void)
{
    br_fdb_init();
//网桥数据库初始化,分配slab缓冲区



#ifdef CONFIG_BRIDGE_NETFILTER
    if (br_netfilter_init())
//netfilter钩子初始化

        return 1;
#endif
    brioctl_set(br_ioctl_deviceless_stub);
//设置ioctl钩子函数:br_ioctl_hook

    br_handle_frame_hook = br_handle_frame;
//设置报文处理钩子:br_ioctl_hook


    
//网桥数据库处理钩子

    br_fdb_get_hook = br_fdb_get;
    br_fdb_put_hook = br_fdb_put;

    
//在netdev_chain通知链表上注册

    register_netdevice_notifier(&br_device_notifier);

    return 0;
}

4.2 新建网桥

前面说到通过brctl addbr br0命令建立网桥,此处用户控件调用的brctl命令最终对应到内核中的br_ioctl_deviceless_stub处理函数:
 

int br_ioctl_deviceless_stub(unsigned int cmd, void __user *uarg)
{
    switch (cmd) {
    case SIOCGIFBR:
    case SIOCSIFBR:
        return old_deviceless(uarg);
        
    case SIOCBRADDBR:
//新建网桥

    case SIOCBRDELBR:
//删除网桥

    {
        char buf[IFNAMSIZ];

        if (!capable(CAP_NET_ADMIN))
            return -EPERM;
            
        
//copy_from_user:把用户空间的数据拷入内核空间

        if (copy_from_user(buf, uarg, IFNAMSIZ))
            return -EFAULT;

        buf[IFNAMSIZ-1] = 0;
        if (cmd == SIOCBRADDBR)
            return br_add_bridge(buf);

        return br_del_bridge(buf);
    }
    }
    return -EOPNOTSUPP;
}

在这里,我们传入的cmdSIOCBRADDBR.转入br_add_bridge(buf)中进行: 

int br_add_bridge(const char *name)
{
    struct net_device *dev;
    int ret;
    
    
//为虚拟桥新建一个net_device

    dev = new_bridge_dev(name);
    if (!dev)
        return -ENOMEM;

    rtnl_lock();
    
//由内核确定接口名字,例如eth0 eth1等

    if (strchr(dev->name, '%')) {
        ret = dev_alloc_name(dev, dev->name);
        if (ret < 0)
            goto err1;
    }
    
//向内核注册此网络设备

    ret = register_netdevice(dev);
    if (ret)
        goto err2;

    
/* network device kobject is not setup until
     * after rtnl_unlock does it's hotplug magic.
     * so hold reference to avoid race.
     */

    dev_hold(dev);
    rtnl_unlock();
    
    
//在sysfs中建立相关信息

    ret = br_sysfs_addbr(dev);
    dev_put(dev);

    if (ret)
        unregister_netdev(dev);
 out:
    return ret;

 err2:
    free_netdev(dev);
 err1:
    rtnl_unlock();
    goto out;
}

网桥是一个虚拟的设备,它的注册跟实际的物理网络设备注册是一样的。我们关心的是网桥对应的net_device结构是什么样的,继续跟踪进new_bridge_dev

static struct net_device *new_bridge_dev(const char *name)
{
    struct net_bridge *br;
    struct net_device *dev;

    
//分配net_device

    dev = alloc_netdev(sizeof(struct net_bridge), name,
             br_dev_setup);
    
    if (!dev)
        return NULL;
    
//网桥的私区结构为net_bridge

    br = netdev_priv(dev);
    
//私区结构中的dev字段指向设备本身

    br->dev = dev;

    spin_lock_init(&br->lock);
    
//队列初始化。在port_list中保存了这个桥上的端口列表

    INIT_LIST_HEAD(&br->port_list);
    spin_lock_init(&br->hash_lock);

    
//下面这部份代码跟stp协议相关,我们暂不关心

    br->bridge_id.prio[0] = 0x80;
    br->bridge_id.prio[1] = 0x00;
    memset(br->bridge_id.addr, 0, ETH_ALEN);

    br->stp_enabled = 0;
    br->designated_root = br->bridge_id;
    br->root_path_cost = 0;
    br->root_port = 0;
    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->topology_change = 0;
    br->topology_change_detected = 0;
    br->ageing_time = 300 * HZ;
    INIT_LIST_HEAD(&br->age_list);

    br_stp_timer_init(br);

    return dev;
}

br_dev_setup中还做了一些另外在函数指针初始化: 

void br_dev_setup(struct net_device *dev)
{
    
//将桥的MAC地址设为零

    memset(dev->dev_addr, 0, ETH_ALEN);
    
//初始化dev的部分函数指针,因为目前网桥设备主适用于以及网,

    
//以太网的部分功能对它也适用

    ether_setup(dev);
    
    
//设置设备的ioctl函数为br_dev_ioctl

    dev->do_ioctl = br_dev_ioctl;
    
//网桥与一般网卡不同,网桥统一统计它的数据包和字节数等信息

    dev->get_stats = br_dev_get_stats;
    
// 网桥接口的数据包发送函数,真实设备要向外发送数据时,是通过网卡向外发送数据

    
// 而该网桥设备要向外发送数据时,它的处理逻辑与网桥其它接口的基本一致。

    dev->hard_start_xmit = br_dev_xmit;
    dev->open = br_dev_open;
    dev->set_multicast_list = br_dev_set_multicast_list;
    dev->change_mtu = br_change_mtu;
    dev->destructor = free_netdev;
    SET_MODULE_OWNER(dev);
    dev->stop = br_dev_stop;
    dev->tx_queue_len = 0;
    dev->set_mac_address = NULL;
    dev->priv_flags = IFF_EBRIDGE;
}

仅仅创建网桥,还是不够的。实际应用中的网桥需要添加实际的端口(即物理接口),如例子中的eth1, eth2等。应用程序在使用ioctl来为网桥增加物理接口,对应内核函数br_dev_ioctl的代码和分析如下: 


int br_dev_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
{
    struct net_bridge *br = netdev_priv(dev);

    switch(cmd) {
    case SIOCDEVPRIVATE:
        return old_dev_ioctl(dev, rq, cmd);

    case SIOCBRADDIF:
//添加

    case SIOCBRDELIF:
//删除

        
//同一处理函数,默认为添加

        return add_del_if(br, rq->ifr_ifindex, cmd == SIOCBRADDIF);

    }

    pr_debug("Bridge does not support ioctl 0x%x\n", cmd);
    return -EOPNOTSUPP;
}

下面分析具体的添加删除函数add_del_if


static int add_del_if(struct net_bridge *br, int ifindex, int isadd)
{
    struct net_device *dev;
    int ret;

    if (!capable(CAP_NET_ADMIN))
        return -EPERM;

    dev = dev_get_by_index(ifindex);
    if (dev == NULL)
        return -EINVAL;
    
    if (isadd)
        ret = br_add_if(br, dev);
    else
        ret = br_del_if(br, dev);

    dev_put(dev);
    return ret;
}


对应的添加删除函数分别为:br_add_if, br_del_if

br_add_if

int br_add_if(struct net_bridge *br, struct net_device *dev)
{
    struct net_bridge_port *p;
    int err = 0;

    /*--Kernel仅支持以太网网桥--*/
    if (dev->flags & IFF_LOOPBACK || dev->type != ARPHRD_ETHER)
        return -EINVAL;

    
/*--把网桥接口当作物理接口加入到另一个网桥中,是不行的,
        逻辑和代码上都会出现 loop--*/

    if (dev->hard_start_xmit == br_dev_xmit)
        return -ELOOP;

    /*--该物理接口已经绑定到另一个网桥了--*/
    if (dev->br_port != NULL)
        return -EBUSY;

    /*--为该接口创建一个网桥端口数据,并初始化好该端口的相关数据--*/
    if (IS_ERR(p = new_nbp(br, dev, br_initial_port_cost(dev))))
        return PTR_ERR(p);
        
    
/*--将该接口的物理地址写入到 MAC-端口映射表中,
        该MAC是属于网桥内部端口的固定MAC地址,
        它在fdb中的记录是固定的,不会失效(agged)--*/

     if ((err = br_fdb_insert(br, p, dev->dev_addr)))
        destroy_nbp(p);
     /*--添加相应的系统文件信息--*/
    else if ((err = br_sysfs_addif(p)))
        del_nbp(p);
    else {
        
/*--打开该接口的混杂模式,网桥中的各个端口必须处于混杂模式,
            网桥才能正确工作--*/

        dev_set_promiscuity(dev, 1);
        
        /*--加到端口列表--*/
        list_add_rcu(&p->list, &br->port_list);

        /*--STP相关设置-*/
        spin_lock_bh(&br->lock);
        br_stp_recalculate_bridge_id(br);
        br_features_recompute(br);
        if ((br->dev->flags & IFF_UP)
         && (dev->flags & IFF_UP) && netif_carrier_ok(dev))
            br_stp_enable_port(p);
        spin_unlock_bh(&br->lock);
        
        /*--设置设备的mtu--*/
        dev_set_mtu(br->dev, br_min_mtu(br));
    }

    return err;
}


br_del_if

 

int br_del_if(struct net_bridge *br, struct net_device *dev)
{
    struct net_bridge_port *p = dev->br_port;
    
    if (!p || p->br != br)
        return -EINVAL;

    br_sysfs_removeif(p);
    del_nbp(p);

    spin_lock_bh(&br->lock);
    br_stp_recalculate_bridge_id(br);
    br_features_recompute(br);
    spin_unlock_bh(&br->lock);

    return 0;
}

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