skb_header_pointer和skb_transport_header之间的区别? [英] Difference between skb_header_pointer and skb_transport_header?

问题描述

我正在尝试实现一个netfilter模块，在处理sk_buff时，我发现了两种可能的方法来检索TCP标头:

I'm trying to implement a netfilter module, while processing sk_buff I found two possible ways to retrieve TCP header:

struct iphdr *ip_header = (struct iphdr *)skb_network_header(skb);
struct tcphdr *tcp_header = (struct tcphdr *)skb_transport_header(skb);

还有

struct iphdr *ip_header = skb_header_pointer(skb, 0, sizeof(struct iphdr), &_iph)
struct tcphdr *tcp_header = skb_header_pointer(skb, ip_header->ihl * 4, sizeof(struct tcphdr), &_tcph);

我应该使用哪个?

推荐答案

您应使用 paged- skb

You should use ip_hdr() from /include/linux/ip.h and tcp_hdr() from /include/linux/tcp.h in case you know that there cannot be paged-skb here:

struct iphdr *ip_header = ip_hdr(skb);
if (ip_header->protocol == IPPROTO_TCP) {
    struct tcphdr *tcp_header = tcp_hdr(skb);
    //...

---

如果可能出现页面-skb，则应使用

skb_header_pointer().示例: IP ， TCP ， ICMP 等.
因此，如果标头位于页面数据中(全部或部分)，则skb_header_pointer()将正确处理它.
另外请记住检查skb_header_pointer()的返回值，它可以返回NULL.

---

skb_header_pointer() should be used in case the appearance of paged-skb is possible. Examples: IP, TCP, ICMP, etc.
So if the header is in paged data (fully or partially) - skb_header_pointer() will correctly handle it.
Also remember to check the return value of skb_header_pointer(), it can return NULL.

有用的链接: 1 ，2

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