struct ip 和struct iphdr && struct icmp 和 struct icmphdr-白红宇

struct ip 和struct iphdr && struct icmp 和 struct icmphdr

阅读量：5735 次

发布时间：2019-06-18

本文共 3483 字，大约阅读时间需要 11 分钟。

1 struct ip { 2 #if BYTE_ORDER == LITTLE_ENDIAN  3     u_char  ip_hl:4,        /* header length */ 4         ip_v:4;         /* version */ 5 #endif 6 #if BYTE_ORDER == BIG_ENDIAN  7     u_char  ip_v:4,         /* version */ 8         ip_hl:4;        /* header length */ 9 #endif10     u_char  ip_tos;         /* type of service */11     short   ip_len;         /* total length */12     u_short ip_id;          /* identification */13     short   ip_off;         /* fragment offset field */14 #define IP_DF 0x4000            /* dont fragment flag */15 #define IP_MF 0x2000            /* more fragments flag */16     u_char  ip_ttl;         /* time to live */17     u_char  ip_p;           /* protocol */18     u_short ip_sum;         /* checksum */19     struct  in_addr ip_src,ip_dst;  /* source and dest address */20 };

1 struct iphdr { 2     #if defined(__LITTLE_ENDIAN_BITFIELD) 3         __u8    ihl:4, 4                 version:4; 5     #elif defined (__BIG_ENDIAN_BITFIELD) 6         __u8    version:4, 7                 ihl:4; 8     #else 9         #error  "Please fix 
     
      "10     #endif11          __u8   tos;12          __u16  tot_len;13          __u16  id;14          __u16  frag_off;15          __u8   ttl;16          __u8   protocol;17          __u16  check;18          __u32  saddr;19          __u32  daddr;20          /*The options start here. */21 };

struct ip 和struct iphdr

struct ip and struct iphdr are two different definitions of the same underlying structure, brought in from different places.

struct ip is defined in <netinet/ip.h>, which is a reasonably standard header on UNIX systems.

struct iphdr is defined in <linux/ip.h>. This header (and structure) are Linux-specific, and will not be present in other operating systems.

If you're not sure which one to use, use struct ip; code which uses this structure is more likely to be portable to non-Linux systems.

struct icmp and struct icmphdr are a messier situation:

<netinet/icmp.h> defines both struct icmp and struct icmphdr.

<linux/icmp.h> also defines struct icmphdr, with a similar structure (but, as usual, different field names) as the definition from <netinet/icmp.h>.

First: Don't include <linux/icmp.h> unless you have a very good reason. You cannot include both headers -- they will conflict -- and most software will expect the netinet definition.

Second: struct icmphdr is, as the name implies, the header. struct icmp defines the contents of a structured ICMP message, like a destination unreachable message.

（2）<netinet/*.h> 和 <linux/*.h>

The linux/*.h headers were really meant for internal kernel use and if Linux were being created today, these files would not even exist under /usr/include. But early on, a lot of the userspace libc (libc4 and libc5 at the time) relied on Linux headers to define types, constants, structures, etc. for use in userspace, so netinet/in.h contained just #include <linux/in.h> or similar, and the lovely tradition got started. Today the only headers in the linux tree that should be used for userspace apps are some things related to supporting specific hardware at a low level, like the Linux console, framebuffer, video4linux, etc.

In short, you should use netinet/in.h (the standard header specified by POSIX) and pretend you never saw linux/in.h. :-)

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作者：zhongyoubing

来源：CSDN

原文：https://blog.csdn.net/zhongyoubing/article/details/77434719

转载于:https://www.cnblogs.com/ming-michelle/p/10147908.html

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