實現/dev/zero字符設備驅動

在類UNIX 操作系統中, /dev/zero 是一個特殊的文件，當你讀它的時候，它會提供無限的空字符(NULL, ASCII NUL, 0x00)，即獲取的是一串二進制0。其中的一個典型用法是用它提供的字符流來覆蓋信息，另一個常見用法是產生一個特定大小的空白文件。具體驅動實現如下

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/uaccess.h>
#ifdef CONFIG_MODVERSIONS
#define MODVERSIONS
#include <linux/version.h>
#endif
#define DEVICE_NUM 0
static int dev_num = 0;
static int openNum = 0;

static int mydev_zero_open(struct inode *inode, struct file *filp);
static int mydev_zero_release(struct inode *inode, struct file* filp);
static ssize_t mydev_zero_read(struct file *file, char __user *buf, size_t count, loff_t *f_pos);
static ssize_t mydev_zero_write(struct file *file, const char __user *buf, size_t count, loff_t *f_pos);

static const struct file_operations mydev_file_operations = {
	.owner = THIS_MODULE,
	.read = mydev_zero_read,
	.write = mydev_zero_write,
	.open = mydev_zero_open,
	.release = mydev_zero_release, 
};

static int mydev_zero_open(struct inode *inode, struct file *filp)
{	

	printk("\nMajor device number is %d, and the minor device number is %d\n", MAJOR(inode->i_rdev), MINOR(inode->i_rdev));
	if (openNum == 0) {
		++ openNum;
		return 0;
	}else {
		printk(KERN_ALERT "Another process open the char device.\n");
		return -1;
	}
}

static ssize_t mydev_zero_read(struct file *file, char __user *buf, size_t count, loff_t *f_pos)
{
	int i=0;
	while(i<count){
		buf[i++] = 0;
	}
	return count;
}

static ssize_t mydev_zero_write(struct file *file, const char __user *buf, size_t count, loff_t *f_pos)
{
	printk("write success\n");
	return 1;
}

static int mydev_zero_release(struct inode *inode, struct file* filp)
{
	-- openNum;
	printk("The device is released!\n");
	return 0;
}

static int __init mydev_zero_init(void)
{
	int temp;
	printk(KERN_ALERT "Begin to init Char Device!\n");
	temp = register_chrdev(DEVICE_NUM, "mydev_zero", &mydev_file_operations);
	if (temp < 0) {
		printk(KERN_WARNING "mydev_zero: register failure\n");
		return -1;
	}else {
		printk("mydev_zero: register success!\n");
		dev_num = temp;
		return 0;
	}
}

static void __exit mydev_zero_exit(void)
{
	printk(KERN_ALERT "Unloading...\n");
	unregister_chrdev(dev_num, "mydev_zero");
	printk("unregister success!\n");
}

MODULE_AUTHOR("Fang Xieyun");
MODULE_LICENSE("GPL");

module_init(mydev_zero_init);
module_exit(mydev_zero_exit);