__inet_insert_ifa/__inet_del_ifa

两个函数分别完成ip地址的添加和删除工作，具体见下面源码分析；

 /*
     添加ip地址
     主地址添加到最后一个满足范围的主地址后面
     从地址添加到整个列表后面
     若列表中存在与插入地址在同一子网的地址，则
     要求ip地址不同且范围相同，并且插入地址认为是从地址
 */
 static int __inet_insert_ifa(struct in_ifaddr *ifa, struct nlmsghdr *nlh,
                  u32 portid)
 {
     struct in_device *in_dev = ifa->ifa_dev;
     struct in_ifaddr *ifa1, **ifap, **last_primary;

     ASSERT_RTNL();

     /* 地址不存在 */
     if (!ifa->ifa_local) {
         inet_free_ifa(ifa);
         return ;
     }

     /* 清除从地址标记 */
     ifa->ifa_flags &= ~IFA_F_SECONDARY;

     /* 记录最后一个满足范围的主地址位置，用于插入 */
     last_primary = &in_dev->ifa_list;

     /* 遍历地址列表 */
     for (ifap = &in_dev->ifa_list; (ifa1 = *ifap) != NULL;
          ifap = &ifa1->ifa_next) {
          /* 不是从地址&& 范围值小于当前地址 */
         if (!(ifa1->ifa_flags & IFA_F_SECONDARY) &&
             ifa->ifa_scope <= ifa1->ifa_scope)
             /* 记录主地址的next指针 */
             last_primary = &ifa1->ifa_next;

         /* 同一子网 */
         if (ifa1->ifa_mask == ifa->ifa_mask &&
             inet_ifa_match(ifa1->ifa_address, ifa)) {
             /* 地址相同 */
             if (ifa1->ifa_local == ifa->ifa_local) {
                 /* 地址已存在 */
                 inet_free_ifa(ifa);
                 return -EEXIST;
             }

             /* 范围不同 */
             if (ifa1->ifa_scope != ifa->ifa_scope) {
                 /* 非法地址 */
                 inet_free_ifa(ifa);
                 return -EINVAL;
             }

             /* 同子网范围相同的不同ip地址为从地址 */
             ifa->ifa_flags |= IFA_F_SECONDARY;
         }
     }

     /* 下面添加地址规则 */
     /* 主地址放在最后一个满足范围的主地址的后面 */
     /* 从地址放在最后一个(从)地址的后面 */

     /* 地址为主地址 */
     if (!(ifa->ifa_flags & IFA_F_SECONDARY)) {
         prandom_seed((__force u32) ifa->ifa_local);
         /*  ifap指向最后一个主地址的next指针 */
         ifap = last_primary;
     }

     /* ifa的next赋值为ifap保存的值，也就是待插入位置的下一个节点地址 */
     ifa->ifa_next = *ifap;

     /* 而前面保存下一个节点的next指针指向新的ifa */
     *ifap = ifa;

     /* 插入hash表 */
     inet_hash_insert(dev_net(in_dev->dev), ifa);

     /* 重新开启检查生命周期任务 */
     cancel_delayed_work(&check_lifetime_work);
     queue_delayed_work(system_power_efficient_wq, &check_lifetime_work, );

     /* Send message first, then call notifier.
        Notifier will trigger FIB update, so that
        listeners of netlink will know about new ifaddr */

     /* 发送添加新地址消息 */
     rtmsg_ifa(RTM_NEWADDR, ifa, nlh, portid);

     /* 通知设备启动 */
     blocking_notifier_call_chain(&inetaddr_chain, NETDEV_UP, ifa);

     return ;
 }

 /* 删除ip地址，如果从地址允许提升为主地址，则提升 */
 static void __inet_del_ifa(struct in_device *in_dev, struct in_ifaddr **ifap,
              int destroy, struct nlmsghdr *nlh, u32 portid)
 {
     struct in_ifaddr *promote = NULL;
     struct in_ifaddr *ifa, *ifa1 = *ifap;
     struct in_ifaddr *last_prim = in_dev->ifa_list;
     struct in_ifaddr *prev_prom = NULL;

     /* 从地址是否允许提升为主地址 */
     int do_promote = IN_DEV_PROMOTE_SECONDARIES(in_dev);

     ASSERT_RTNL();

     /* ip控制块正在被销毁 */
     if (in_dev->dead)
         goto no_promotions;

     /* 1. Deleting primary ifaddr forces deletion all secondaries
      * unless alias promotion is set
      **/

     /* 如果是主地址 */
     if (!(ifa1->ifa_flags & IFA_F_SECONDARY)) {
         struct in_ifaddr **ifap1 = &ifa1->ifa_next;

         /* 遍历链表 */
         while ((ifa = *ifap1) != NULL) {

             /* 最后一个满足范围的主地址 */
             if (!(ifa->ifa_flags & IFA_F_SECONDARY) &&
                 ifa1->ifa_scope <= ifa->ifa_scope)
                 last_prim = ifa;

             /* 主地址|| 子网掩码不同 || 网络前缀不同 */
             if (!(ifa->ifa_flags & IFA_F_SECONDARY) ||
                 ifa1->ifa_mask != ifa->ifa_mask ||
                 !inet_ifa_match(ifa1->ifa_address, ifa)) {
                 ifap1 = &ifa->ifa_next;
                 prev_prom = ifa;
                 continue;
             }

             /* 找到在同一子网的从地址 */

             /* 不允许提升ip地址 */
             if (!do_promote) {
                 /* 删除地址 */
                 inet_hash_remove(ifa);
                 *ifap1 = ifa->ifa_next;

                 /* 发送删除地址消息 */
                 rtmsg_ifa(RTM_DELADDR, ifa, nlh, portid);
                 /* 通知设备关闭 */
                 blocking_notifier_call_chain(&inetaddr_chain,
                         NETDEV_DOWN, ifa);
                 inet_free_ifa(ifa);
             } else {
                 /* 需要提升的从地址为找到的地址 */
                 promote = ifa;
                 break;
             }
         }
     }

     /* On promotion all secondaries from subnet are changing
      * the primary IP, we must remove all their routes silently
      * and later to add them back with new prefsrc. Do this
      * while all addresses are on the device list.
      */
     /* 因为允许提升从地址，需要 删除从地址的路由 */
     for (ifa = promote; ifa; ifa = ifa->ifa_next) {
         if (ifa1->ifa_mask == ifa->ifa_mask &&
             inet_ifa_match(ifa1->ifa_address, ifa))
             fib_del_ifaddr(ifa, ifa1);
     }

 no_promotions:
     /* 2. Unlink it */

     /* 删除地址 */
     *ifap = ifa1->ifa_next;
     inet_hash_remove(ifa1);

     /* 3. Announce address deletion */

     /* Send message first, then call notifier.
        At first sight, FIB update triggered by notifier
        will refer to already deleted ifaddr, that could confuse
        netlink listeners. It is not true: look, gated sees
        that route deleted and if it still thinks that ifaddr
        is valid, it will try to restore deleted routes... Grr.
        So that, this order is correct.
      */
     /* 发送删除地址消息 */
     rtmsg_ifa(RTM_DELADDR, ifa1, nlh, portid);
     /* 通知设备关闭 */
     blocking_notifier_call_chain(&inetaddr_chain, NETDEV_DOWN, ifa1);

     /* 允许提升从ip为主ip */
     if (promote) {
         struct in_ifaddr *next_sec = promote->ifa_next;

         /* 插入该从地址到主地址位置 */
         if (prev_prom) {
             prev_prom->ifa_next = promote->ifa_next;
             promote->ifa_next = last_prim->ifa_next;
             last_prim->ifa_next = promote;
         }

         /* 修改该ip为主地址 */
         promote->ifa_flags &= ~IFA_F_SECONDARY;

         /* 发送新地址消息 */
         rtmsg_ifa(RTM_NEWADDR, promote, nlh, portid);
         /* 通知设备启动 */
         blocking_notifier_call_chain(&inetaddr_chain,
                 NETDEV_UP, promote);

         /* 重新添加路由表 */
         for (ifa = next_sec; ifa; ifa = ifa->ifa_next) {
             if (ifa1->ifa_mask != ifa->ifa_mask ||
                 !inet_ifa_match(ifa1->ifa_address, ifa))
                     continue;
             fib_add_ifaddr(ifa);
         }

     }

     /* 需要释放则释放内存 */
     if (destroy)
         inet_free_ifa(ifa1);
 }