client模式下对应接口加入桥接出错

client模式下，响应的接口wlan0 加入桥接时出现如下错误：

root@root:~# brctl addif br-lan wlan0
brctl: bridge br-lan: Operation not supported。

查看相应busybox代码（brctl.c），函数为 brctl_main，

strncpy_IFNAMSIZ(ifr.ifr_name, br);
  if (key == ARG_addif || key == ARG_delif) { /* addif or delif */
     brif = *argv;
     ifr.ifr_ifindex = if_nametoindex(brif);
    if (!ifr.ifr_ifindex) {
      bb_perror_msg_and_die("iface %s", brif);
    }
    ioctl_or_perror_and_die(fd,
         key == ARG_addif ? SIOCBRADDIF : SIOCBRDELIF,  &ifr, "bridge %s", br);
     goto done_next_argv;
  }

得到addif 和 delif 相应的ioctl命令码为   SIOCBRADDIF  和  SIOCBRDELIF。

内核中对应命令字的定义：
include/linux/sockios.h:#define SIOCBRADDIF     0x89a2         /* add interface to bridge，十进制为35234

查找内核中响应的代码, 此处内核版本为3.10.14。

* Perform the SIOCxIFxxx calls, inside rtnl_lock()
 */
static int dev_ifsioc(struct net *net, struct ifreq *ifr, unsigned int cmd)
{
 switch (cmd) {
  /*
  * Unknown or private ioctl
  */
   default:
  if ((cmd >= SIOCDEVPRIVATE &&
      cmd <= SIOCDEVPRIVATE + 15) ||
      cmd == SIOCBONDENSLAVE ||
      cmd == SIOCBONDRELEASE ||
      cmd == SIOCBONDSETHWADDR ||
      cmd == SIOCBONDSLAVEINFOQUERY ||
      cmd == SIOCBONDINFOQUERY ||
      cmd == SIOCBONDCHANGEACTIVE ||
      cmd == SIOCGMIIPHY ||
      cmd == SIOCGMIIREG ||
      cmd == SIOCSMIIREG ||
      cmd == SIOCBRADDIF ||      // 添加桥接接口
      cmd == SIOCBRDELIF ||      // 删除桥接接口
      cmd == SIOCSHWTSTAMP ||
      cmd == SIOCWANDEV) {
   　　　　　　err = -EOPNOTSUPP;
   　　　　　　if (ops->ndo_do_ioctl) {
   　　　　　　　　 if (netif_device_present(dev))
    　　　　　　　　　　 err = ops->ndo_do_ioctl(dev, ifr, cmd);  // 调用回调函数
   　　　　　　　　 else
    　　　　　　　　　　 err = -ENODEV;
   　　　　　　}
 　 } else
   　　err = -EINVAL;
 　}
}

对应的回调函数位于 /net/bridge/br_device.c中

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,    // 此处对应增加(addif)和删除(delif)的回调
#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,
};

查看回调函数如下：

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

　　// 旧式的处理方式
 　　case SIOCDEVPRIVATE:
  　　　　return old_dev_ioctl(dev, rq, cmd);

　　// 实现如下：
 　　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;
}

位于 /net/bridge/br_ioctl.c中
static int add_del_if(struct net_bridge *br, int ifindex, int isadd)
{
 struct net *net = dev_net(br->dev);
 struct net_device *dev;
 int ret;

if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
  return -EPERM;

dev = __dev_get_by_index(net, ifindex);
 if (dev == NULL)
  return -EINVAL;

if (isadd)
  ret = br_add_if(br, dev);   // 添加桥接接口
 else
  ret = br_del_if(br, dev);   // 删除桥接接口

return ret;
}

位于 /net/bridge/br_if.c中
int br_add_if(struct net_bridge *br, struct net_device *dev)
{
 struct net_bridge_port *p;
 int err = 0;
 bool changed_addr;

/* 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 */
 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)     //  wlan0加入桥接时在此处遇到问题，退出
    return -EOPNOTSUPP;

p = new_nbp(br, dev);
 if (IS_ERR(p))
  return PTR_ERR(p);

call_netdevice_notifiers(NETDEV_JOIN, dev);

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;

err = netdev_rx_handler_register(dev, br_handle_frame, p);
 if (err)
  goto err5;

dev->priv_flags |= IFF_BRIDGE_PORT;

dev_disable_lro(dev);

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);

br_ifinfo_notify(RTM_NEWLINK, p);

if (changed_addr)
  call_netdevice_notifiers(NETDEV_CHANGEADDR, br->dev);

dev_set_mtu(br->dev, br_min_mtu(br));

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;

err5:
 netdev_upper_dev_unlink(dev, br->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_promiscuity(dev, -1);
put_back:
 dev_put(dev);
 kfree(p);
 return err;
}

追溯出问题的地方，查找 IFF_DONT_BRIDGE 标志置位的地方，找到如下：

static int cfg80211_netdev_notifier_call(struct notifier_block *nb,
      unsigned long state, void *ndev)
{

.......
 switch (state) {
  case NETDEV_REGISTER:   // 注册设备
    if ((wdev->iftype == NL80211_IFTYPE_STATION ||
    　　wdev->iftype == NL80211_IFTYPE_P2P_CLIENT ||
    　　wdev->iftype == NL80211_IFTYPE_ADHOC) && !wdev->use_4addr)
   　　dev->priv_flags |= IFF_DONT_BRIDGE;   
  　　break;
 }

.........
}

从以上红色部分可以看出，当设备为client或者adhoc以及wds时，对应的无线接口是无法加入到桥接中去的。

在br_add_if 中判断标志位出错后，返回值为EOPNOTSUPP，定义如下：

#define EOPNOTSUPP  45 /* Op not supported on transport endpoint */

跟串口中配置出错时打印相符。