梦幻屋

#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;
}

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);