Linux内核如何接收不同类型以太帧

共有 2 条评论

1. Informix 于 2006-11-15 09:43:19发表:

   　　由于IP协议部分不能作为内核模块，所以是没有卸载函数的，没必要调用dev_remove_pack()函数。
   
   　　4.2 8021q vlan
   
   

   引用:

   /* net/8021q/vlan.c */
   static struct packet_type vlan_packet_type = {
   .type = __constant_htons(ETH_P_8021Q),
   .func = vlan_skb_recv, /* VLAN receive method */
   };
   ......
   static int __init vlan_proto_init(void)
   {
   ......
   dev_add_pack(&vlan_packet_type);
   ......
   
   static void __exit vlan_cleanup_module(void)
   {
   ......
   dev_remove_pack(&vlan_packet_type);
   ......

   
   
   　　由于VLAN可为模块方式存在，所以在模块清除函数中要调用dev_remove_pack()。
   
   　　5. 网络接收
   
   　　网卡驱动收到数据包构造出skb后，通过接口函数netif_receive_skb()传递到上层进行协议处理分配。
   
   

   引用:

   /* net/core/dev.c */
   int netif_receive_skb(struct sk_buff *skb)
   {
   ......
   // 先查处理所有以太类型的链表各节点
   list_for_each_entry_rcu(ptype, &ptype_all, list) {
   if (!ptype->dev || ptype->dev == skb->dev) {
   if (pt_prev)
   ret = deliver_skb(skb, pt_prev, orig_dev);
   pt_prev = ptype;
   }
   }
   ......
   // 再查指定协议的HASH链表
   list_for_each_entry_rcu(ptype, &ptype_base[ntohs(type)&15], list) {
   if (ptype->type == type &&
   (!ptype->dev || ptype->dev == skb->dev)) {
   if (pt_prev)
   ret = deliver_skb(skb, pt_prev, orig_dev);
   pt_prev = ptype;
   }
   }
   ......
   
   // 该函数就是调用个协议的接收函数处理该skb包，进入第三层网络层处理
   static __inline__ int deliver_skb(struct sk_buff *skb,
   struct packet_type *pt_prev,
   struct net_device *orig_dev)
   {
   atomic_inc(&skb->users);
   return pt_prev->func(skb, skb->dev, pt_prev, orig_dev);
   }

   
   
   　　6. 结论
   
   　　通过链表挂接方式，Linux内核可以很容易的添加各种协议的接收处理函数。
   
   　　数据流程:
   
   　　网卡驱动--->netif_rx()--->netif_receive_skb()->deliver_skb()->packet_type.func

2. Informix 于 2006-11-15 09:42:24发表:

   　　3.2 删除节点
   
   

   引用:

   /**
   * __dev_remove_pack - remove packet handler
   * @pt: packet type declaration
   *
   * Remove a protocol handler that was previously added to the kernel
   * protocol handlers by dev_add_pack(). The passed &packet_type is removed
   * from the kernel lists and can be freed or reused once this function
   * returns.
   *
   * The packet type might still be in use by receivers
   * and must not be freed until after all the CPU's have gone
   * through a quiescent state.
   */
   void __dev_remove_pack(struct packet_type *pt)
   {
   struct list_head *head;
   struct packet_type *pt1;
   spin_lock_bh(&ptype_lock);
   // 根据协议类型找是在ptype_all表还是某一HASH链表中
   if (pt->type == htons(ETH_P_ALL)) {
   netdev_nit--;
   head = &ptype_all;
   } else
   head = &ptype_base[ntohs(pt->type) & 15];
   // 直接用地址比对进行查找，而不是类型，因为同一个类型也可能有多个节点
   list_for_each_entry(pt1, head, list) {
   if (pt == pt1) {
   list_del_rcu(&pt->list);
   goto out;
   }
   }
   printk(KERN_WARNING "dev_remove_pack: %p not found.\n", pt);
   out:
   spin_unlock_bh(&ptype_lock);
   }
   /**
   * dev_remove_pack - remove packet handler
   * @pt: packet type declaration
   *
   * Remove a protocol handler that was previously added to the kernel
   * protocol handlers by dev_add_pack(). The passed &packet_type is removed
   * from the kernel lists and can be freed or reused once this function
   * returns.
   *
   * This call sleeps to guarantee that no CPU is looking at the packet
   * type after return.
   */
   // 只是__dev_remove_pack()的包裹函数
   void dev_remove_pack(struct packet_type *pt)
   {
   __dev_remove_pack(pt);
   
   synchronize_net();
   }

   
   
   　　4. 实例
   
   　　4.1 IP
   
   

   引用:

   /* net/ipv4/af_inet.c */
   static struct packet_type ip_packet_type = {
   .type = __constant_htons(ETH_P_IP),
   .func = ip_rcv, // IP接收数据的入口点
   };
   static int __init inet_init(void)
   {
   ......
   dev_add_pack(&ip_packet_type);
   ......