timer定时器

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/cdev.h>
#include <linux/timer.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/wait.h>
#include <asm/uaccess.h>

#define DEVICE_NAME "chardev"

static ssize_t chardev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos);

static struct file_operations chardev_fops = {
        .read = chardev_read,
};

static struct cdev *cdevp = NULL;
static dev_t devno;
static wait_queue_head_t queue;
static int flag = 0;
static struct timer_list timer;

static void timer_callback(unsigned long arg)
{
        flag = 1;
        wake_up_interruptible(&queue);
}

static ssize_t chardev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
        char res[] = "hello";

        init_timer(&timer);
        timer.expires = jiffies + HZ * 3;
        timer.data = 0;
        timer.function = timer_callback;

        add_timer(&timer);
        wait_event_interruptible(queue, flag != 0);
        flag = 0;
        del_timer(&timer);
        copy_to_user(buf, res, strlen(res));

        return strlen(res);
}

static int __init chardev_init(void)
{
        int ret;

        ret = alloc_chrdev_region(&devno, 0, 1, DEVICE_NAME);
        if (ret < 0)
                goto out;

        cdevp = cdev_alloc();
        if (!cdevp)
                goto alloc_err;

        init_waitqueue_head(&queue);
        cdev_init(cdevp, &chardev_fops);
        ret = cdev_add(cdevp, devno, 1);
        if (!ret)
                goto out;

        cdev_del(cdevp);
alloc_err:
        unregister_chrdev_region(devno, 1);
out:
        return ret;
}

static void __exit chardev_exit(void)
{
        cdev_del(cdevp);

        unregister_chrdev_region(devno, 1);
}

MODULE_LICENSE("GPL");

module_init(chardev_init);
module_exit(chardev_exit);