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Old 02-05-2013, 07:34 AM   #1
Registered: Sep 2006
Location: Italy
Distribution: Suse 10.1
Posts: 78

Rep: Reputation: 15
character device driver not created

I wrote a very simple character device driver. It compiles correctly and
insmod can insert it.
The problem is that I can't see my driver listed in /dev after insmomd has executed.
I also tried to execute mknod chardev c 250 0 after insmod, but the problem persists (250 is the major number yielded by register_chrdev.
I have Linux 10.04, kernel 2.6.32-21-generic
Any suggestion?
Thank you in advance

The code follows

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <asm/uaccess.h>

void cleanup_module(void); 
int init_module(void);
static int device_open(struct inode *, struct file*);
static int device_release(struct inode *, struct file*);
static ssize_t device_read(struct file*, char __user*, size_t, loff_t*);
static ssize_t device_write(struct file*,const char __user*, size_t, loff_t*); 

#define SUCCESS 0
#define DEVICE_NAME "chardev"
#define BUF_LEN 80
static int Major;
static int Device_Open = 0; 
static char msg[BUF_LEN];
static char* msg_ptr;

static struct file_operations fops = {
	.read = device_read,
	.write = device_write,
	.open = device_open,
	.release = device_release


//static int __init chardev_init(void){
int init_module(void){
	Major =  register_chrdev(0, DEVICE_NAME, &fops);
		printk(KERN_ALERT "Registering char device failed with %d\n",Major);
		return Major;
	printk(KERN_INFO "Major number: %d\n",Major);
	printk(KERN_INFO "'mknod /dev/%s c %d 0'.\n",DEVICE_NAME,Major);
	return SUCCESS; 
int device_open(struct inode* inode, struct file* file){
	static int count = 0; //Why counter is here? Why not global? 
		return -EBUSY; 
	sprintf(msg, "I already told you hello %d times", count++) ; 
	msg_ptr = msg;
	return SUCCESS; 
static ssize_t device_read(struct file* filp, char __user* buffer, size_t length,
 loff_t* offset){
	int bytes_read = 0; 

	if(*msg_ptr == 0)
		return 0; 
	while(*msg_ptr && length ){
		put_user(*(msg_ptr++),buffer++); //Why they are both pointer?
	return bytes_read; 
static ssize_t device_write(struct file* filp,const char __user* buffer, size_t len, loff_t* off) {
	printk(KERN_ALERT "Sorry, this operation isn't supported \n");
	return -EINVAL; 
static int device_release(struct inode* inode, struct file* file){
	return 0; 
//static void __exit chardev_exit(void){
void cleanup_module(void){
//	int ret = 
//	if(ret < 0)
		printk(KERN_ALERT "Unregistering chrdev \n");

obj-m += chardev.o
	make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) modules
	make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) clean


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