linux-kernel - Re: [PATCH] ip.7: Add not supported by SOCK

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Date: Wed, 6 Mar 2024 11:50:54 +0100
From: Alejandro Colomar <alx@...nel.org>
To: Oliver Crumrine <ozlinuxc@...il.com>
Cc: linux-man@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ip.7: Add not supported by SOCK_STREAM to socket options

Hi Oliver,

On Tue, Mar 05, 2024 at 02:31:48PM -0500, Oliver Crumrine wrote:
> #include<stdio.h>	//printf
> #include<string.h> //memset
> #include<stdlib.h> //exit(0);
> #include<arpa/inet.h>
> #include<sys/socket.h>
> #include<unistd.h>
> 
> #define BUFLEN 1500	//Max length of buffer

You could use BUFSIZ, which is in <stdio.h>.  It also removes magic
numbers like 1500 (why not 1000?).

> #define PORT 8888	//The port on which to listen for incoming data
> 
> 
> //Hi Alex,
> //These are the two lines that allow you to switch between the three socket options outlined in my patch
> //The socket options tell the kernel to add a control message (cmsg), allowing the program
> //to recieve the data it is requesting. The three options are: IP_RECVTOS for the type of service byte,
> //IP_RECVORIGDSTADDR for the orignial dst address, and IP_PKTINFO for some random packet info.
> #define SOCKOPT IP_RECVORIGDSTADDR
> //This field is synonymous with the above one. Valid options are: IP_TOS, IP_ORIGDSTADDR, and IP_PKTINFO
> #define RECIVEOPTION IP_ORIGDSTADDR
> 
> void die(char *s)
> {
> 	perror(s);
> 	exit(1);
> }
> 
> int main(void)
> {
> 	struct sockaddr_in si_me, si_other;
> 	
> 	int s, i, slen = sizeof(si_other) , recv_len;

Unused variables 'i' and 'slen' (in both programs).

> 	char buf[BUFLEN];

Unused variable 'buf' (in both programs).

> 	
> 	if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)

This is more readable (and safer) in two lines:

	s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
	if (s == -1)

> 	{
> 		die("socket");

You could use
		err(1, "socket");

which is in <err.h>.

> 	}
> 	
> 	memset((char *) &si_me, 0, sizeof(si_me));
> 	
> 	si_me.sin_family = AF_INET;
> 	si_me.sin_port = htons(PORT);
> 	si_me.sin_addr.s_addr = htonl(INADDR_ANY);
> 	
> 	if( bind(s , (struct sockaddr*)&si_me, sizeof(si_me) ) == -1)

The use of spaces is quite inconsistent.

> 	{
> 		die("bind");
> 	}
> 	int yes = 1;
> 	if(setsockopt(s, IPPROTO_IP, SOCKOPT, &yes, sizeof(yes)) != 0){

!= 0 is inconsistent with other == -1 checks.

Also placement of braces.

Have a lovely day!
Alex

> 		die("setsockopt");
> 	}
> 	while(1)
> 	{
> 		struct msghdr mhdr;
> 		struct iovec iov[1];
> 		struct cmsghdr *cmhdr;
> 		char control[1000];
> 		char databuf[1500];
> 		unsigned char tos = 0;
> 		
> 		mhdr.msg_name = &si_me;
> 		mhdr.msg_namelen = sizeof(si_me);
> 		mhdr.msg_iov = iov;
> 		mhdr.msg_iovlen = 1;
> 		mhdr.msg_control = &control;
> 		mhdr.msg_controllen = sizeof(control);
> 		iov[0].iov_base = databuf;
> 		iov[0].iov_len = sizeof(databuf);
> 		memset(databuf, 0, sizeof(databuf));	
> 		fflush(stdout);
> 		
> 		//this is blocking
> 		if ((recv_len = recvmsg(s, &mhdr, 0)) == -1)
> 		{
> 			die("recvfrom()");
> 		}
> 		cmhdr = CMSG_FIRSTHDR(&mhdr);
> 		while (cmhdr) {
> 			printf("cmsg recieved\n");
>     		    if (cmhdr->cmsg_level == IPPROTO_IP && cmhdr->cmsg_type == RECIVEOPTION) {
>     		        //read the byte recieved
> 			    tos = ((unsigned char *)CMSG_DATA(cmhdr))[0];
>     		    }
>     		    cmhdr = CMSG_NXTHDR(&mhdr, cmhdr);
>     		}
> 		//print out the data recieved as a hex byte
>     		printf("data read: %sbyte = %02X\n", databuf, tos); 	
> 		
> 	}
> 
> 	close(s);
> 	return 0;
> }

> #include<stdio.h>	//printf
> #include<string.h> //memset
> #include<stdlib.h> //exit(0);
> #include<arpa/inet.h>
> #include<sys/socket.h>
> #include<unistd.h>
> 
> #define BUFLEN 1500	//Max length of buffer
> #define PORT 8888	//The port on which to listen for incoming data
> 
> //Hi Alex,
> //These are the two lines that allow you to switch between the three socket options outlined in my patch
> //The socket options tell the kernel to add a control message (cmsg), allowing the program
> //to recieve the data it is requesting. The three options are: IP_RECVTOS for the type of service byte,
> //IP_RECVORIGDSTADDR for the orignial dst address, and IP_PKTINFO for some random packet info.
> #define SOCKOPT IP_RECVORIGDSTADDR
> //This field is synonymous with the above one. Valid options are: IP_TOS, IP_ORIGDSTADDR, and IP_PKTINFO
> #define RECIVEOPTION IP_ORIGDSTADDR
> 
> void die(char *s)
> {
> 	perror(s);
> 	exit(1);
> }
> 
> int main(void)
> {
> 	struct sockaddr_in si_me, si_other;
> 	
> 	int s, i, slen = sizeof(si_other) , recv_len;
> 	char buf[BUFLEN];
> 	
> 	if ((s=socket(AF_INET, SOCK_STREAM, 0)) == -1)
> 	{
> 		die("socket");
> 	}
> 	
> 	memset((char *) &si_me, 0, sizeof(si_me));
> 	
> 	si_me.sin_family = AF_INET;
> 	si_me.sin_port = htons(PORT);
> 	si_me.sin_addr.s_addr = htonl(INADDR_ANY);
> 	
> 	if( bind(s , (struct sockaddr*)&si_me, sizeof(si_me) ) == -1)
> 	{
> 		die("bind");
> 	}
> 	listen(s, 10);
> 	while(1)
> 	{
> 		int connectedfd = accept(s, (struct sockaddr*)NULL, NULL);
> 		int yes = 1;                                                     	
> 		if(setsockopt(connectedfd, IPPROTO_IP, SOCKOPT, &yes, sizeof(yes)) != 0){
> 			die("setsockopt");
> 		}
> 
> 		
> 		
> 		struct msghdr mhdr;
> 		struct iovec iov[1];
> 		struct cmsghdr *cmhdr;
> 		char control[1000];
> 		char databuf[1500];
> 		unsigned char tos = 0;
> 		
> 		mhdr.msg_name = &si_me;
> 		mhdr.msg_namelen = sizeof(si_me);
> 		mhdr.msg_iov = iov;
> 		mhdr.msg_iovlen = 1;
> 		mhdr.msg_control = &control;
> 		mhdr.msg_controllen = sizeof(control);
> 		iov[0].iov_base = databuf;
> 		iov[0].iov_len = sizeof(databuf);
> 		memset(databuf, 0, sizeof(databuf));	
> 		fflush(stdout);
> 		
> 		//this is blocking
> 		if ((recv_len = recvmsg(connectedfd, &mhdr, 0)) == -1)
> 		{
> 			die("recvfrom()");
> 		}
> 		cmhdr = CMSG_FIRSTHDR(&mhdr);
> 		while (cmhdr) {
> 			printf("cmsg recieved \n");
>     		    if (cmhdr->cmsg_level == IPPROTO_IP && cmhdr->cmsg_type == RECIVEOPTION) {
>     		        //read the byte recieved
> 			    tos = ((unsigned char *)CMSG_DATA(cmhdr))[0];
>     		    }
>     		    cmhdr = CMSG_NXTHDR(&mhdr, cmhdr);
>     		}
> 		//print out the data recieved as a hex byte
>     		printf("data read: %sbyte = %02X\n", databuf, tos); 	
> 		close(connectedfd);	
> 	}
> 
> 	close(s);
> 	return 0;
> }


-- 
<https://www.alejandro-colomar.es/>
Looking for a remote C programming job at the moment.

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