Hello,
Thanks for your answer, my question is why when I read from the buffer data is already in host byte order and not in network byte order.
Thanks 
Pietro Paolini.


From: Mandeep Sandhu [mailto:mandeepsandhu.chd at gmail.com] 
Sent: sabato 13 ottobre 2012 05:30
To: Pietro Paolini
Cc: kernelnewbies at kernelnewbies.org
Subject: Re: Network Byte order not reached reading from a sock RAW


On Oct 12, 2012 9:36 PM, "Pietro Paolini" [off-list ref] wrote:

Hello,

I am struggling with the byte order question on a x86_32 arch, I am doing some modifications on a program which actually works fine on a MIPS arch.

I do a reading from a RAW socket in this way:

? ? ? ? /* Configure socket */
? ? ? ? if ((fd = socket(AF_INET, SOCK_RAW, IPPROTO_IGMP)) < 0) {
? ? ? ? ? ? ? ? perror("Error on socket creation, exit");
? ? ? ? ? ? ? ? exit(1);
? ? ? ? }
? ? ? ? ? ....
? ? ? ? if (setsockopt(fd, IPPROTO_IP, IP_PKTINFO, (void *)&va, sizeof(va))) {
? ? ? ? ? ? ? ? perror("Error on setsockopt, exit");
? ? ? ? ? ? ? ? exit(1);
? ? ? ? }
? ? ? ? va = 0;
? ? ? ? ....
? ? ? ? ....
? ? ? ? struct msghdr mhdr;
? ? ? ? struct __in_pktinfo *pktinfo = NULL;
? ? ? ? ...
? ? ? ? ...
? ? ? ? nrd = recvmsg(env->mrouter_fd, &mhdr, 0);
? ? ? ? ...
? ? ? ? ip = (struct iphdr *)iov.iov_base;

When I print the saddr (or daddr) of the received ip packet it is printed as host byte order instead of what I am expecting, the network byte order. I can just use the htonl() family functions for solve the problem but I would like understand if it is the normal behavior or if there is an issues on my code, or if the device driver of my NIC can influence the question.

I think you should use ntoh*() functions when accessing data rx'ed from the n/w. Network byte order is big endian and your host is little endian, so you'll have convert it to the right order before accessing. You should use hton*() functions when tx'ing data. CMIIW.
HTH,
-mandeep

Many thanks,
Pietro.


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