copy_xx_user.c

内核空间地址向用户空间地址的映射实例

 
 /* 马上练习 copy_to_user/copy_from_user()的用法，毕竟put_user()/get_user()的效率有点低， 而且老加上while（）循环，不好看
  */
  
  
//#define KERNEL_DEBUG
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <asm/uaccess.h>	/* for put_user */
#include <linux/init.h>


#define KERNEL_DEBUG
#include "mod_head.h"

/*
*  Prototypes - this would normally go in a .h file
*/
static __init int chardev_init(void);
static __exit void chardev_exit(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 *, size_t, loff_t *);

static ssize_t device_write(struct file *, const char *, size_t, loff_t *);



#define SUCCESS 0
#define DEVICE_NAME "chardev_bob_test"	/* Dev name as it appears in /proc/devices   */
#define BUF_LEN 6		/* Max length of the message from the device */

/*
* Global variables are declared as static, so are global within the file.
*/

static int Major;		/* Major number assigned to our device driver */
static char msg[BUF_LEN] = {'\0'};	/* The msg the device will give when asked */
static char *msg_Ptr;

static volatile unsigned long chardev_users = 0UL;  //防止互斥， 这里用更严格的test_and_set_bit() 函数

static int device_open(struct inode *inode, struct file *file)
{
	//	if (Device_Open)
	//		return -EBUSY;
	//	Device_Open++;
	//	上面的办法太不可靠了。用原子操作或者bit操作才是最可靠的。
	if(test_and_set_bit(0,&chardev_users))
		return -EBUSY;

	msg_Ptr = msg;
	try_module_get(THIS_MODULE); 

	return SUCCESS;
}


static int device_release(struct inode *inode, struct file *file)
{
	if( !test_and_clear_bit(0,&chardev_users)) {  //如果value还为1，就错了
		dbg("It looks that the bit operation is wrong \n");
		return -1;
	}
		
	module_put(THIS_MODULE);

	return 0;
}


static ssize_t device_read(struct file *filp,	/* see include/linux/fs.h   */
			char *buffer,	/* buffer to fill with data */
			size_t length,	/* length of the buffer     */
			loff_t * offset)	/* loff_t  ==   long long */
{
	//	Number of bytes actually written to the buffer
	int bytes_read = 0;
	
	if (*msg_Ptr == 0)
		return 0;

//	while (length && *msg_Ptr) {
//
//		//	   kernel  ----> user
//		put_user(*(msg_Ptr++), buffer++);
//
//		length--;
//		bytes_read++;
//	}
	
	/* copy_to_user() 的用法很简单 */
	dbg("msg_Ptr length=%d\n",strlen(msg_Ptr));
	if(copy_to_user(buffer,msg_Ptr,
			min(strlen(msg_Ptr),length)))
	{
		dbg("copy_to_user() error \n");
		return -EFAULT;
	}
	bytes_read = min(strlen(msg_Ptr),length);
	
	return bytes_read;
	
}


static ssize_t
device_write(struct file *filp, 
		const char *buffer, 
		size_t len, 
		loff_t * off)
{
	int bytes_write = 0;
	int max_bytes = sizeof(msg) -1;

	memset(msg,'\0',sizeof(msg));

//	while( *buffer && bytes_write < len && bytes_write < max_bytes )
//	{			
//		//	   kernel <---user
//		get_user(*(msg_Ptr++),buffer++);//msg_Ptr[i] is same
//		bytes_write++;
//	}
	copy_from_user(msg_Ptr,buffer,
			min( min(strlen(buffer),len), sizeof(msg)-1));
	bytes_write = min( min(strlen(buffer),len), sizeof(msg)-1 );
	
	dbg("write %d bytes \n",bytes_write);

	return bytes_write;

}


static struct file_operations fops = {
	.owner	= THIS_MODULE,
	.read 	= device_read,
	.write 	= device_write,
	.open 	= device_open,
//	.ioctl  = device_ioctl,	//bob add to get pid of some process
	.release= device_release
	//others are NULL;
};


/*
* Functions
*/
static __init int chardev_init(void)
{
	Major = register_chrdev(0, DEVICE_NAME, &fops);

	if (Major < 0) {
		dbg("Registering the character device failed with %d\n", Major);
		return Major;
	}

	dbg("I was assigned major number %d.  To talk to\n", Major);
	dbg("the driver, create a dev file with\n");
	dbg("'mknod /dev/hello c %d 0'.\n", Major);
	dbg("Try various minor numbers.  Try to cat and echo to\n");
	dbg("the device file.\n");
	dbg("Remove the device file and module when done.\n");

	return 0;
}

static __exit void chardev_exit(void)
{
	int ret = unregister_chrdev(Major, DEVICE_NAME);
	if (ret < 0)
		dbg("Error in unregister_chrdev: %d\n", ret);
}



module_init(chardev_init);
module_exit(chardev_exit);