Linux系统内核接收以太帧的处理程序
// 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
/* 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);
......
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
/* 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。
/* 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
