LinuxQuestions.org
Register a domain and help support LQ
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - Software > Linux - Kernel
User Name
Password
Linux - Kernel This forum is for all discussion relating to the Linux kernel.

Notices

Reply
 
Search this Thread
Old 02-05-2013, 07:34 AM   #1
puntino
Member
 
Registered: Sep 2006
Location: Italy
Distribution: Suse 10.1
Posts: 71

Rep: Reputation: 15
character device driver not created


Hello,
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
chardev.c

Code:
#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);
	if(Major<0){
		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? 
	if(Device_Open==0) 
		return -EBUSY; 
	sprintf(msg, "I already told you hello %d times", count++) ; 
	msg_ptr = msg;
	try_module_get(THIS_MODULE);
	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?
		length--; 
		bytes_read++;
	} 
	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){
	Device_Open--;
	module_put(THIS_MODULE);
	return 0; 
}
//static void __exit chardev_exit(void){
void cleanup_module(void){
//	int ret = 
	unregister_chrdev(Major,DEVICE_NAME);
//	if(ret < 0)
		printk(KERN_ALERT "Unregistering chrdev \n");

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


Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Changing character device file permission which is created by driver AnkurTank Programming 1 10-28-2012 07:20 PM
i2c character device file not created in linux 2.6.24 on at91sam9263ek john_schimandle Linux - Kernel 5 05-27-2010 11:03 AM
Character Device driver: How to load it automatically ? shendeswanand Linux - Software 0 02-09-2006 09:59 PM
Character device driver calsoft_pg Linux - Software 0 01-03-2006 12:17 PM


All times are GMT -5. The time now is 05:05 PM.

Main Menu
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
identi.ca: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration