Segmentation fault in linux driver - c

Question

I'm trying to write a linux driver. The kernel version is 2.4.18 and the distribution is Red Hat linux 8.0.
The code of my driver is:
#define LINUX
#include <linux/kernel.h> /* We're doing kernel work */
#include <linux/module.h> /* Specifically, a module */
#include <linux/fs.h>
#include <asm-i386/semaphore.h>
#include "rng.h"
#include <linux/random.h>
#include <linux/slab.h>
#define DEVICE_NAME "rng"
#define BUF_LEN 80
static int major;
int init_module();
void cleanup_module();
static int device_open(struct inode *, struct file *);
static int device_release(struct inode *, struct file *);
struct file_operations my_fops = {
open: device_open,
release: device_release,
};
/* Init and Cleanup */
int init_module() {
SET_MODULE_OWNER(&my_fops);
major = register_chrdev(0, DEVICE_NAME, &my_fops);
return 0;
}
void cleanup_module() {
int ret = unregister_chrdev(major, DEVICE_NAME);
if (ret < 0)
printk("Error in unregister_chrdev: %d\n", ret);
}
static int device_open(struct inode *inode, struct file *file) {
file->f_op=&my_fops;
return 1;
}
static int device_release(struct inode *inode, struct file *file) {
return 0;
}
And the code I'm using in order to test my driver is:
#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
int openTest() {
int game1 = open("/dev/game1", O_RDONLY); // SEGMENTATION FAULT
int retValue=1;
close(game1);
return retValue;
}
int main() {
int res;
if (openTest() < 1) {
fprintf(stderr, "open didnt work\n");
return -1;
}
fprintf(stderr, "everything works :)\n");
return 0;
}
In the code above, I'm getting a segmentation fault when I'm trying to open the device. Can somebody explain to me why I'm getting this segmentation fault? I really don't understand.
Thanks a lot!

Answer 1

In Linux kernel land, it is convention to return a 0 (zero) when there are no errors. Your device_open() routine is hardcoded to return a 1 (one), which may be causing your segfault.
This Linux Device Drivers book may be helpful to you. The linked edition is written for kernel 2.0.x - 2.4.x, so the information should be appropriate for the dusty and ancient kernel you are using.

Answer 2

This line seems to be wrong file->f_op=&my_fops;
Basically when writing a linux driver operations are setup at build time itself.