ARP输入 之 arp_rcv

概述

arp_rcv是ARP包的入口函数，ARP模块在二层注册了类型为ETH_P_ARP的数据包回调函数arp_rcv，当收到ARP包时，二层进行分发，调用arp_rcv；

arp_rcv对ARP输入包的合法性进行检查，然后经过netfilter的ARP_IN钩子点，之后调用arp_process处理输出包；

源码分析

 /*
  *    Called once on startup.
  */

 static struct packet_type arp_packet_type __read_mostly = {
     .type =    cpu_to_be16(ETH_P_ARP),
     .func =    arp_rcv,
 };

 /*
  *    Receive an arp request from the device layer.
  */

 static int arp_rcv(struct sk_buff *skb, struct net_device *dev,
            struct packet_type *pt, struct net_device *orig_dev)
 {
     const struct arphdr *arp;

     /* do not tweak dropwatch on an ARP we will ignore */
     /* 不支持ARP，非本机包，回环包，不处理 */
     if (dev->flags & IFF_NOARP ||
         skb->pkt_type == PACKET_OTHERHOST ||
         skb->pkt_type == PACKET_LOOPBACK)
         goto consumeskb;

     /* skb如果是共享的，则克隆一个 */
     skb = skb_share_check(skb, GFP_ATOMIC);
     if (!skb)
         goto out_of_mem;

     /* ARP header, plus 2 device addresses, plus 2 IP addresses.  */
     /* 检查arp包完整性 */
     if (!pskb_may_pull(skb, arp_hdr_len(dev)))
         goto freeskb;

     /* 获取arp头 */
     arp = arp_hdr(skb);

     /* 地址长度和协议长度检查 */
     if (arp->ar_hln != dev->addr_len || arp->ar_pln != )
         goto freeskb;

     /* 清空neighCB */
     memset(NEIGH_CB(skb), , sizeof(struct neighbour_cb));

     /* 经过NF的ARP_IN钩子点，然后调用arp_process */
     return NF_HOOK(NFPROTO_ARP, NF_ARP_IN,
                dev_net(dev), NULL, skb, dev, NULL,
                arp_process);

 consumeskb:
     consume_skb(skb);
     return NET_RX_SUCCESS;
 freeskb:
     kfree_skb(skb);
 out_of_mem:
     return NET_RX_DROP;
 }