给网桥添加端口——br_add_if（三）_siocbraddif

       上一节，我们了解如何，添加一个桥设备的大致步骤，现在我们看看如何在桥设备上添加一个端口。

       我们先来看一个命令
       brctrl addif br0 eth1

       这个命令的作用是在br0上添加一个eth1的接口，内核实现的相关函数是br_add_if.

       那么如何调用到这个接口呢？
       上节我们在将添加一个桥设备的时候，有一个参数br_netdev_ops，我们当时说这里面有很多的注册函数，
       调用add_del_if SIOCDEVPRIVATE，调用old_dev_ioctl函数，
       其实我们再看源码时就会发现，old_dev_ioctl函数后面其实也调用了add_del_if。add_del_if，
       最后在根据是添加还是删除接口的参数，进行相应的添加(SIOCBRADDIF),还是删除接口。
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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:
    case SIOCBRDELIF:
        return add_del_if(br, rq->ifr_ifindex, cmd == SIOCBRADDIF);

    }

    br_debug(br, "Bridge does not support ioctl 0x%x\n", cmd);
    return -EOPNOTSUPP;
}
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 该函数注册在，桥设备添加时候dev->netdev_ops = &br_netdev_ops; 
 在br_netdev_ops有一个函数指针.ndo_do_ioctl= br_dev_ioctl
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int br_add_if(struct net_bridge *br, struct net_device *dev)
{
    struct net_bridge_port *p;
    int err = 0;
    unsigned br_hr, dev_hr;
    bool changed_addr;

    /* Don't allow bridging non-ethernet like devices, or DSA-enabled
     * master network devices since the bridge layer rx_handler prevents
     * the DSA fake ethertype handler to be invoked, so we do not strip off
     * the DSA switch tag protocol header and the bridge layer just return
     * RX_HANDLER_CONSUMED, stopping RX processing for these frames.
     */

    if ((dev->flags & IFF_LOOPBACK) ||
        dev->type != ARPHRD_ETHER || dev->addr_len != ETH_ALEN ||
        !is_valid_ether_addr(dev->dev_addr) ||
        netdev_uses_dsa(dev))
        return -EINVAL;

    /* No bridging of bridges */
    if (dev->netdev_ops->ndo_start_xmit == br_dev_xmit)
        return -ELOOP;

    /* Device is already being bridged  */
    if (br_port_exists(dev))
        return -EBUSY;

    /* No bridging devices that dislike that (e.g. wireless) */
    if (dev->priv_flags & IFF_DONT_BRIDGE)
        return -EOPNOTSUPP;

    /*分配一个新网桥端口并对其初始化*/
    p = new_nbp(br, dev);
    if (IS_ERR(p))
        return PTR_ERR(p);

    /*调用设备通知链，告诉网络有这样一个设备*/
    call_netdevice_notifiers(NETDEV_JOIN, dev);

    /**向设备添加或删除所有多播帧的接收。*/
    err = dev_set_allmulti(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;
    /*把链路添加到sysfs*/
    err = br_sysfs_addif(p);
    if (err)
        goto err2;

    err = br_netpoll_enable(p);
    if (err)
        goto err3;

    /*注册设备接收帧函数*/
    err = netdev_rx_handler_register(dev, br_handle_frame, p);
    if (err)
        goto err4;

    /*给该端口指派默认优先权*/
    dev->priv_flags |= IFF_BRIDGE_PORT;

    /*向上级设备添加主链路*/
    err = netdev_master_upper_dev_link(dev, br->dev, NULL, NULL);
    if (err)
        goto err5;

    /*禁用网络设备上的大型接收卸载（LRO）。 
    必须在RTNL下调用。 
    如果接收到的数据包可能转发到另一个接口，
    则需要这样做。*/
    dev_disable_lro(dev);

    list_add_rcu(&p->list, &br->port_list);
    /*更新桥上的端口数,如果有更新，再进一步将其设为混杂模式*/
    nbp_update_port_count(br);
    /* 重新计算dev->features并发送通知（如果已更改）。 
    应该调用驱动程序或硬件依赖条件可能会改变影响功能。*/
    netdev_update_features(br->dev);

    br_hr = br->dev->needed_headroom;
    dev_hr = netdev_get_fwd_headroom(dev);
    if (br_hr < dev_hr)
        update_headroom(br, dev_hr);
    else
        netdev_set_rx_headroom(dev, br_hr);

    /*把dev的mac添加到转发数据库中*/
    if (br_fdb_insert(br, p, dev->dev_addr, 0))
        netdev_err(dev, "failed insert local address bridge forwarding table\n");

    /*初始化该桥端口的vlan*/
    err = nbp_vlan_init(p);
    if (err) {
        netdev_err(dev, "failed to initialize vlan filtering on this port\n");
        goto err6;
    }

    spin_lock_bh(&br->lock);
    /*更新网桥id*/
    changed_addr = br_stp_recalculate_bridge_id(br);
    /*设备是否启动，桥是否启动，设备上是否有载波信号(网桥没有载波状态，因为网桥是虚拟设备)*/
    if (netif_running(dev) && netif_oper_up(dev) &&
        (br->dev->flags & IFF_UP))
        /*启动网桥端口*/
        br_stp_enable_port(p);
    spin_unlock_bh(&br->lock);

    br_ifinfo_notify(RTM_NEWLINK, p);
    /*如果网桥的地址改变，则调用通知连相关的函数*/
    if (changed_addr)
        call_netdevice_notifiers(NETDEV_CHANGEADDR, br->dev);
    /*更新网桥mtu*/
    dev_set_mtu(br->dev, br_min_mtu(br));
    br_set_gso_limits(br);
    /*添加一个内核对象*/
    kobject_uevent(&p->kobj, KOBJ_ADD);

    return 0;

err6:
    list_del_rcu(&p->list);
    br_fdb_delete_by_port(br, p, 0, 1);
    nbp_update_port_count(br);
    netdev_upper_dev_unlink(dev, br->dev);

err5:
    dev->priv_flags &= ~IFF_BRIDGE_PORT;
    netdev_rx_handler_unregister(dev);
err4:
    br_netpoll_disable(p);
err3:
    sysfs_remove_link(br->ifobj, p->dev->name);
err2:
    kobject_put(&p->kobj);
    p = NULL; /* kobject_put frees */
err1:
    dev_set_allmulti(dev, -1);
put_back:
    dev_put(dev);
    kfree(p);
    return err;
}
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 在桥上添加接口的基本步骤，如上，删除桥端口，主要是把建立接口时所做的事情撤销，如添加接口出错时的一些处理。
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