freg.c sample DON'T EDIT.

freg-register_chrdev.c

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

/* 主设备号 */
#define MAJOR_NUM 250 

static ssize_t freg_read(struct file* filp, char __user *buf, size_t count, loff_t* f_pos);
static ssize_t freg_write(struct file* filp, const char __user *buf, size_t count, loff_t* f_pos);

/* "freg"设备的全局变量 */
static int freg_var = 0; 


static ssize_t freg_read(struct file *filp, char *buf, size_t len, loff_t *off)
{
	/* 将freg_var从内核空间复制到用户空间 */  
	if (copy_to_user(buf, &freg_var, sizeof(int))) { 
		return - EFAULT;
	} 
	printk("freg_read enter ,the data is %d\n",freg_var);
	return sizeof(int);
}

static ssize_t freg_write (struct file *filp, const char *buf, size_t len, loff_t *off)
{
	/* 将用户空间的数据复制到内核空间的freg_var */
	if (copy_from_user(&freg_var, buf, sizeof(int))) {
		return -EFAULT;
	} 
	printk("freg_write enter ,the data is %d\n",freg_var);
	return sizeof(int);
}

/* 初始化字符设备驱动的file_operations结构体 */
struct file_operations freg_fops = {
		.owner = THIS_MODULE,
		.write = freg_write,
		.read  = freg_read,
};

static int __init freg_init(void)
{
	int ret;
	
	printk(KERN_ALERT"Initializing freg device.\n");
	
	/* 注册设备驱动 */
	ret = register_chrdev(MAJOR_NUM, "freg", &freg_fops); 
	if (ret) {
		printk("freg register failure");
	}
	else{
		printk("freg register success");
	}
	return ret;
}

static void __exit freg_exit(void)
{
	printk(KERN_ALERT"Destroy freg device.\n");
	unregister_chrdev(MAJOR_NUM, "freg");
}

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Fake Register Driver");

module_init(freg_init);
module_exit(freg_exit);