globalvar_bak1.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> 
 
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*);

struct file_operations globalvar_fops =
{
read: globalvar_read,
write: globalvar_write,
};

static int global_var = 0;

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");
}
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 ssize_t globalvar_read(struct file *filp, char *buf, size_t len, loff_t *off)
{
if (copy_to_user(buf, &global_var, sizeof(int)))
{
	return - EFAULT;
} 

return sizeof(int);
}


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

module_init(globalvar_init);
module_exit(globalvar_exit);