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#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)
{
//获得自选锁
spin_lock(&spin);
//临界资源访问
if (globalvar_count)
{
spin_unlock(&spin);
return - EBUSY;
}
globalvar_count++;
//释放自选锁
spin_unlock(&spin);
return 0;
}
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