Linux系统内核接收以太帧的处理程序 （1）

/* 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);
}

/**
* __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();
}

/* 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);
......