📄 [转载] linux的tcp-ip协议栈阅读笔记(8) - china linux forum.htm
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<P class=post>发信人: AngelFalls (TRY IT), 信区: SysInternals<BR>标 题:
[转载] Linux的TCP/IP协议栈阅读笔记(8)<BR>发信站: 武汉白云黄鹤站 (Wed Oct 4 01:37:35
2000), 转信<BR><BR>【 以下文字转载自 Security 讨论区 】<BR>【 原文由 AngelFalls 所发表
】<BR>我们已经知道了,如果使用socket(AF_SOCKET, ..)产生一个PACKET
SOCKET的话,<BR>dev_add_pack加入的函数是packet_rcv,下面是这个在net/packet/af_packet.c里<BR>面的函数:<BR>static
int packet_rcv(struct sk_buff *skb, struct device *dev, <BR>struct
packet_type *pt)<BR>{<BR>struct sock *sk;<BR>struct sockaddr_ll *sll
= (struct sockaddr_ll*)skb->cb;<BR><BR>sk = (struct sock *)
pt->data;<BR>//我们在packet_create中令data = sk了,remember?<BR><BR>if
(skb->pkt_type == PACKET_LOOPBACK) {<BR>kfree_skb(skb);<BR>return
0;<BR>}<BR><BR>skb->dev = dev;<BR><BR>sll->sll_family =
AF_PACKET;<BR>sll->sll_hatype =
dev->type;<BR>sll->sll_protocol =
skb->protocol;<BR>sll->sll_pkttype =
skb->pkt_type;<BR>sll->sll_ifindex =
dev->ifindex;<BR>sll->sll_halen = 0;<BR><BR>if
(dev->hard_header_parse)<BR>sll->sll_halen =
dev->hard_header_parse(skb, sll->sll_addr);<BR><BR>if
(dev->hard_header)<BR>if (sk->type !=
SOCK_DGRAM)<BR>skb_push(skb, skb->data -
skb->mac.raw);<BR>else if (skb->pkt_type ==
PACKET_OUTGOING)<BR>skb_pull(skb, skb->nh.raw -
skb->data);<BR><BR>if
(sock_queue_rcv_skb(sk,skb)<0)<BR>{<BR>kfree_skb(skb);<BR>return
0;<BR>}<BR>return(0);<BR>}<BR>在这个函数里面有个地方我很疑惑,那就是pkt_type属性,不知道这个属性是什么<BR>地方确定的,从网卡驱动->netif_rx->net_bh中间都没有,而且甚至在net_bh函数<BR>中间就有if(skb->pkt_type==...)这样的语句,说明在驱动中间就设置了,但是没<BR>有找到,我faint了.这个属性以后还会大量使用,还是很重要的.<BR><BR>这里还有几个函数要说明:<BR>skb_pull在include/linux/skbuff.h中间:<BR>extern
__inline__ char *__skb_pull(struct sk_buff *skb, <BR>unsigned int
len)<BR>{<BR>skb->len-=len;<BR>return
skb->data+=len;<BR>}<BR><BR>extern __inline__ unsigned char *
skb_pull(struct sk_buff *skb, <BR>unsigned int len)<BR>{ <BR>if (len
> skb->len)<BR>return NULL;<BR>return
__skb_pull(skb,len);<BR>}<BR>不过是把头部的数据空出来,相应调整数据头部data的地址和长度.<BR><BR>同样skb_push在include/linux/skbuff.h中间:<BR>extern
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