kernel:linux-2.6.18
Packet_type数据结构包含协议类型、指向网络设备的指针、指向协议的接收数据处理例程的指针等。
结构体:
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struct packet_type {
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__be16 type; /* This is really htons(ether_type). */
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struct net_device *dev; /* NULL is wildcarded here */
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int (*func) (struct sk_buff *,
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struct net_device *,
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struct packet_type *,
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struct net_device *);
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struct sk_buff *(*gso_segment)(struct sk_buff *skb,
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int features);
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int (*gso_send_check)(struct sk_buff *skb);
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void *af_packet_priv;
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struct list_head list;
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};
定义:
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static struct list_head ptype_base[16]; /* 16 way hashed list */
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static struct list_head ptype_all; /* Taps */
ptype_all为一个双向链表。Ptype_base是一个哈希表,其哈希函数以协议标识符为参数,内核通常利用该哈希表判断应当接受传入的网络数据报的协议。
初始化:
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INIT_LIST_HEAD(&ptype_all);
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for (i = 0; i < 16; i++)
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INIT_LIST_HEAD(&ptype_base[i]);
在Linux进行网络层的初始化时,每个协议要在ptype_all链表或ptype_base哈希表中以packet_type数据结构通过dev_add_pack函数进行注册和dev_remove_pack进行删除。
操作:
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void dev_add_pack(struct packet_type *pt)
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{
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int hash;
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spin_lock_bh(&ptype_lock);
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//如果是ETH_P_ALL将其加到ptype_all链表中
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if (pt->type == htons(ETH_P_ALL)) {
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netdev_nit++;
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list_add_rcu(&pt->list, &ptype_all);
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} else {
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hash = ntohs(pt->type) & 15;
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list_add_rcu(&pt->list, &ptype_base[hash]);
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}
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spin_unlock_bh(&ptype_lock);
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}
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void __dev_remove_pack(struct packet_type *pt)
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{
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struct list_head *head;
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struct packet_type *pt1;
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spin_lock_bh(&ptype_lock);
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if (pt->type == htons(ETH_P_ALL)) {
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netdev_nit--;
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head = &ptype_all;
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} else
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head = &ptype_base[ntohs(pt->type) & 15];
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list_for_each_entry(pt1, head, list) {
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if (pt == pt1) {
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list_del_rcu(&pt->list);
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goto out;
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}
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}
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printk(KERN_WARNING "dev_remove_pack: %p not found.\n", pt);
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out:
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spin_unlock_bh(&ptype_lock);
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}
ARP协议进行注册流程:
ARP协议结构体:
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static struct packet_type arp_packet_type = {
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.type = __constant_htons(ETH_P_ARP),
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.func = arp_rcv,
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};
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arp_init()初始化,把arp_packet_type加入到ptype_base。
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void __init arp_init(void)
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{
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neigh_table_init(&arp_tbl);
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dev_add_pack(&arp_packet_type);
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arp_proc_init();
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register_netdevice_notifier(&arp_netdev_notifier);
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}
当协议类型为ETH_P_ARP的数据都会交由arp_rcv处理.在netif_receive_skb函数中,有ptype_all和ptype_base的调用.
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list_for_each_entry_rcu(ptype, &ptype_all, list) {
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if (!ptype->dev || ptype->dev == skb->dev) {
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if (pt_prev)
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ret = deliver_skb(skb, pt_prev, orig_dev);
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pt_prev = ptype;
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}
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}
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list_for_each_entry_rcu(ptype, &ptype_base[ntohs(type)&15], list) {
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if (ptype->type == type &&
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(!ptype->dev || ptype->dev == skb->dev)) {
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if (pt_prev)
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ret = deliver_skb(skb, pt_prev, orig_dev);
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pt_prev = ptype;
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}
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}
deliver_skb函数实现packet_type结构体中func函数指针调用:
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static __inline__ int deliver_skb(struct sk_buff *skb,
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struct packet_type *pt_prev,
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struct net_device *orig_dev)
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{
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atomic_inc(&skb->users);
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//如果type==ETH_P_ARP,就会调用arp_rcv函数(pt_prev->func指向arp_rcv函数)。
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return pt_prev->func(skb, skb->dev, pt_prev, orig_dev);
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}
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