【内核】：定时器的使用

 总的来说，timer的用法还是很简单的。主要需要定义一个timer_list变量timer、先初始化timer
　
　　init_timer（&timer）；
　
　　then 对timer的相关参数赋值：
　
　　timer.function = fun；
　
　　timer.expires = jiffies + TIMER_DELAY；
　
　　add_timer（&timer）；
　
　　在定时器时间到的时候，会执行fun，如果继续定时，可以通过
　
　　在fun中执行
　
　　mod_timer（&timer， jiffies + TIMER_DELAY）；
　
　　在不需要的时候通过调用
　
　　del_timer（&timer）；
　
　　删除定时器。
　
　　简单吧。这样一个简单的定时器就完成了。
　
　　呵呵。
　
　　附程序：
　
　　 #include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <linux/timer.h>
#include <asm/atomic.h>

#define SECOND_MAJOR 0

static int second_major = SECOND_MAJOR;

struct second_dev
{
struct cdev cdev;
atomic_t counter;
struct timer_list s_timer;
};

struct second_dev *second_devp;

static void second_timer_handle(unsigned long arg)
{
mod_timer(&second_devp->s_timer, jiffies + HZ);
atomic_inc(&second_devp->counter);

printk(KERN_ERR "current jiffies is %ld\n",jiffies);
}

int second_open(struct inode *inode, struct file *filp)
{
init_timer(&second_devp->s_timer);
second_devp->s_timer.function = &second_timer_handle;
second_devp->s_timer.expires = jiffies + HZ;

add_timer(&second_devp->s_timer);
atomic_set(&second_devp->counter, 0);
return 0; 
}

int second_release(struct inode *inode, struct file *filp)
{
del_timer(&second_devp->s_timer);

return 0;
}
static ssize_t second_read(struct file *filp, char __user *buf, size_t count, 
loff_t *ppos)
{
int counter;

counter = atomic_read(&second_devp->counter);
if (put_user(counter, (int *)buf))
{
return -EFAULT;
}else
{
return sizeof(unsigned int);
}

}

static const struct file_operations second_fops =
{
.owner = THIS_MODULE,
.open = second_open,
.release = second_release,
.read = second_read,
};
static void second_setup_cdev(struct second_dev *dev, int index)
{
int err, devno = MKDEV(second_major, index);
cdev_init(&dev->cdev, &second_fops);
dev->cdev.owner = THIS_MODULE;
dev->cdev.ops = &second_fops;
err = cdev_add(&dev->cdev, devno, 1);
if (err)
{
printk(KERN_NOTICE "Error %d add second%d", err, index);
}
}
int second_init(void)
{
int ret;
dev_t devno = MKDEV(second_major, 0);

if (second_major)
{
ret = register_chrdev_region(devno, 1, "second");
}else
{
ret = alloc_chrdev_region(&devno, 0, 1, "second");
second_major = MAJOR(devno);
}
if (ret < 0)
{
return ret;
}

second_devp = kmalloc(sizeof(struct second_dev), GFP_KERNEL);
if (!second_devp)
{
ret = -ENOMEM;
goto fail_malloc;
}

memset(second_devp, 0, sizeof(struct second_dev));

second_setup_cdev(second_devp, 0);

return 0;

fail_malloc:
unregister_chrdev_region(devno, 1);
}

void second_exit(void)
{
cdev_del(&second_devp->cdev);
kfree(second_devp);
unregister_chrdev_region(MKDEV(second_major, 0), 1);
}

MODULE_AUTHOR("Song Baohua");
MODULE_LICENSE("Dual BSD/GPL");

module_param(second_major, int, S_IRUGO);

module_init(second_init);
module_exit(second_exit);

附上用户端的测试程序：
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

int main(void)
{
int fd, i;
int data;
fd = open("/dev/second",O_RDONLY);
if (fd < 0)
{
printf("open /dev/second error\n");
}
for(i = 0; i < 20; i++)
{
read(fd, &data, sizeof(data));
printf("read /dev/second is %d\n",data);
sleep(1);
}
close(fd);
}