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<P class=post>發信人: AngelFalls (TRY IT), 信區: SysInternals<BR>標 題:
[轉載] Linux的TCP/IP協議棧閱讀筆記(8)<BR>發信站: 武漢白云黃鶴站 (Wed Oct 4 01:37:35
2000), 轉信<BR><BR>【 以下文字轉載自 Security 討論區 】<BR>【 原文由 AngelFalls 所發表
】<BR>我們已經知道了,如果使用socket(AF_SOCKET, ..)產生一個PACKET
SOCKET的話,<BR>dev_add_pack加入的函數是packet_rcv,下面是這個在net/packet/af_packet.c里<BR>面的函數:<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>//我們在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>在這個函數里面有個地方我很疑惑,那就是pkt_type屬性,不知道這個屬性是什么<BR>地方確定的,從網卡驅動->netif_rx->net_bh中間都沒有,而且甚至在net_bh函數<BR>中間就有if(skb->pkt_type==...)這樣的語句,說明在驅動中間就設置了,但是沒<BR>有找到,我faint了.這個屬性以后還會大量使用,還是很重要的.<BR><BR>這里還有幾個函數要說明:<BR>skb_pull在include/linux/skbuff.h中間:<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>不過是把頭部的數據空出來,相應調整數據頭部data的地址和長度.<BR><BR>同樣skb_push在include/linux/skbuff.h中間:<BR>extern
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