globalvar_bak2.c

Some simple source code to show specific function like mouse and graphic.

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

#include <asm/semaphore.h> 

MODULE_LICENSE("GPL");

#define MAJOR_NUM 254

static ssize_t globalvar_read(struct file *, char *, size_t, loff_t*);
static ssize_t globalvar_write(struct file *, const char *, size_t, loff_t*);
static int globalvar_open(struct inode *inode, struct file *filp);
static int globalvar_release(struct inode *inode, struct file *filp);

struct file_operations globalvar_fops =
{
read: globalvar_read,
write: globalvar_write,
open: globalvar_open,
release:globalvar_release,
};

static int global_var = 0;
static int globalvar_count = 0;
static struct semaphore sem;
static spinlock_t spin = SPIN_LOCK_UNLOCKED;

static int __init globalvar_init(void)
{
int ret;
ret = register_chrdev(MAJOR_NUM, "globalvar", &globalvar_fops);
if (ret)
{
printk("globalvar register failure");
}
else
{
printk("globalvar register success");
init_MUTEX(&sem);
}
return ret;
}

static void __exit globalvar_exit(void)
{
int ret;


ret = unregister_chrdev(MAJOR_NUM, "globalvar");
if (ret)
{
printk("globalvar unregister failure");
}
else
{
printk("globalvar unregister success");
}
}

static int globalvar_open(struct inode *inode,struct file *filp)
{
	spin_lock(&spin);
	if(globalvar_count)
	{
		spin_unlock(&spin);
		return -EBUSY;
	}
	globalvar_count++;
	spin_unlock(&spin);
	return 0;
}
static int globalvar_release(struct inode *inode,struct file *filp)
{
	globalvar_count--;
	return 0;
}
static ssize_t globalvar_read(struct file *filp, char *buf, size_t len, loff_t *off)
{
	if (down_interruptible(&sem))
	{
		return - ERESTARTSYS;
	}
	
	if (copy_to_user(buf, &global_var, sizeof(int)))
	{
		up(&sem);
		return - EFAULT;
	} 
	
	up(&sem);
	return sizeof(int);
}

static ssize_t globalvar_write(struct file *filp, const char *buf, size_t len, loff_t *off)
{
if (down_interruptible(&sem))
{
	return - ERESTARTSYS;
}
if (copy_from_user(&global_var, buf, sizeof(int)))
{
up(&sem);
return - EFAULT;
} 
up(&sem);
return sizeof(int);
}

module_init(globalvar_init);
module_exit(globalvar_exit);