/* include/linux/netdevice.h */
struct packet_type {
__be16 type; /* This is really htons(ether_type). */
struct net_device *dev; /* NULL is wildcarded here */
int (*func) (struct sk_buff *,
struct net_device *,
struct packet_type *,
struct net_device *);
void *af_packet_priv;
struct list_head list;
            };

/* net/core/dev.c */
/**
* dev_add_pack - add packet handler
* @pt: packet type declaration
*
* Add a protocol handler to the networking stack. The passed &packet_type
* is linked into kernel lists and may not be freed until it has been
* removed from the kernel lists.
*
* This call does not sleep therefore it can not 
* guarantee all CPU's that are in middle of receiving packets
* will see the new packet type (until the next received packet).
*/
void dev_add_pack(struct packet_type *pt)
{
int hash;
spin_lock_bh(&ptype_lock);
// 如果类型是全部以太类型，则节点链接到ptype_all链
if (pt->type == htons(ETH_P_ALL)) {
netdev_nit++;
list_add_rcu(&pt->list, &ptype_all);
} else {
// 根据协议类型取个HASH，共15个HASH链表
hash = ntohs(pt->type) & 15;
// 将节点链接到HASH链表中，list_add_rcu是加了smp_wmb()保护的list_add链表操作
list_add_rcu(&pt->list, &ptype_base[hash]);
}
spin_unlock_bh(&ptype_lock);
            }