sockets usage in kernel modules

cipicip · 12-21-2005, 10:47 AM

Hi guys!

I got a question for you related to the linux kernel modules. I was trying to build a module which would implement a server socket. For this I used an echo server example found on the net. Bellow is the code. And yes, you guessed right: it doesn’t compile. The server code compiles and works fine if compiled as a regular application.

Anyone has any idea why not? Can anyone help me?

Thanks

Code:

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/stdlib.h>
#include <linux/errno.h>
#include <linux/unistd.h>
#include <linux/string.h>
#include <linux/signal.h>
#include <linux/sys/wait.h>
#include <linux/sys/socket.h>
#include <linux/resolv.h>
#include <linux/arpa/inet.h>

void PANIC(char* msg);
#define PANIC(msg)  { printk(KERN_INFO msg); exit(-1); }

/*--------------------------------------------------------------------*/
/*--- Signal capture: SIGCHLD                                      ---*/
/*--------------------------------------------------------------------*/
void sig_handler(int sig)
{
    if ( sig == SIGCHLD )
    {   int retval;
        wait(&retval);
    }
}

/*--------------------------------------------------------------------*/
/*--- Child - echo servlet                                         ---*/
/*--------------------------------------------------------------------*/
void Child(void* arg)
{   char line[100];
    int bytes_read;
    int client = *(int *)arg;

    do
    {
        bytes_read = recv(client, line, sizeof(line), 0);
		if ( bytes_read < 0 )
			printk(KERN_INFO "Read socket");
        send(client, line, bytes_read, 0);
    }
    while (strncmp(line, "bye\r", 4) != 0  ||  bytes_read < 0 );
    close(client);
    exit(0);
}


static int __init mod_init(void) {

int sd;
struct sigaction act;
struct sockaddr_in addr;

    console_print("module loaded!\n");
    printk(KERN_INFO "module loaded!\n");

    bzero(&act, sizeof(act));
	act.sa_handler = sig_handler;
	act.sa_flags = SA_NOCLDSTOP;
    sigaction(SIGCHLD, &act, 0);
    if ( (sd = socket(PF_INET, SOCK_STREAM, 0)) < 0 )
        PANIC("Socket");
    addr.sin_family = AF_INET;
    addr.sin_port = htons(9999);
    addr.sin_addr.s_addr = INADDR_ANY;
    if ( bind(sd, (struct sockaddr*)&addr, sizeof(addr)) != 0 )
        PANIC("Bind");
    if ( listen(sd, 20) != 0 )
        PANIC("Listen");
    while (1)
    {   int client, addr_size = sizeof(addr);

        client = accept(sd, (struct sockaddr*)&addr, &addr_size);
		if ( client < 0 )
			printk(KERN_INFO "Accept");
		else
		{
	        printk(KERN_INFO "Connected: %s:%d\n", inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));
    	    if ( fork() )
        	    close(client);
	        else
    	    {
        	    close(sd);
            	Child(&client);
	            exit(0);
    	    }
		}
    }
    return 0;
}

static void __exit mod_exit(void) {
    console_print("module unloaded!\n");
}

module_init(mod_init);
module_exit(mod_exit);
MODULE_LICENSE("GPL");

cipicip · 12-22-2005, 03:11 AM

The Makefile content is this:

Code:

obj-m    := listen.o

KDIR    := /lib/modules/$(shell uname -r)/build
PWD    := /home/shared/module

default:
	$(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules

jtshaw · 12-22-2005, 08:54 AM

First off, a few of those includes are wrong or just don't exist.

Fixed include list:

Code:

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/unistd.h>
#include <linux/string.h>
#include <linux/signal.h>
#include <linux/wait.h>
#include <linux/socket.h>

Once you fix that you are going to have to re-write the parts that use sockaddr_in and such to use the correct kernel space structures (because things like struct sockaddr_in don't live in kernel space).

Also, when you compile this you have to make sure your CFLAGS are set to something like "-c -D__KERNEL__ -DMODULE".

cipicip · 12-22-2005, 09:10 AM

Thank you very much, Jtshaw.