驱动：
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/errno.h> #include <linux/cdev.h>//cdev
#include <linux/device.h>//udev
#include <linux/sched.h>//schedule
#include <linux/uaccess.h>//copy_to_user
#include <linux/slab.h>//kmalloc() #define DEVICE_NAME "second_drv"
static int second_major=;/*主设备号*/
struct class *second_class; /*second设备结构体*/
static struct second_dev
{
struct cdev cdev;/*cdev 结构体*/
atomic_t counter;/*一共经历了多少时间；定义原子变量*/
struct timer_list s_timer;/*定义一个定时器*/
};
struct second_dev *second_devp;/*定义设备结构体指针*/ /*定时器处理函数*/
static void second_timer_handler(unsigned long arg)
{
mod_timer(&second_devp->s_timer,jiffies+HZ);/*再次调度定时器*/
atomic_inc(&second_devp->counter);/*counter 加1*/
printk(KERN_NOTICE"current jiffies is %d!!\n",jiffies);
} static int second_open(struct inode *inode, struct file *filp)
{
//printk("in the second_open!!\n");
filp->private_data=second_devp;/*将设备结构体指针赋值给文件私有数据指针*/ /*初始化定时器*/
init_timer(&second_devp->s_timer);
second_devp->s_timer.function=&second_timer_handler;
second_devp->s_timer.expires=jiffies+HZ;
add_timer(&second_devp->s_timer);/*添加定时器*/ atomic_set(&second_devp->counter,);/*计数清零*/ return ;
} static int second_release(struct inode *inode,struct file *filp)
{
del_timer(&second_devp->s_timer);/*删除定时器*/
return ;
} static ssize_t second_read(struct file *filp,char __user *buf,ssize_t count,loff_t *ppos)
{
//printk("in the second_read!!\n");
int counter;
counter=atomic_read(&second_devp->counter);/*获取count值*/ if(copy_to_user(buf,&counter,count))
return -EFAULT;
else
return sizeof(unsigned int);
} static ssize_t second_write(struct file *filp,const char __user *buf,ssize_t count,loff_t *ppos)
{
return ;
} /*文件操作结构体*/
static const struct file_operations second_fops={
.owner = THIS_MODULE,
.open =second_open,
.release =second_release,
.read =second_read,
.write =second_write,
}; /*初始化并注册cdev*/
static void second_setup_cdev(struct second_dev *dev,int index)
{
int err;
dev_t devno=MKDEV(second_major,index);
cdev_init(&dev->cdev,&second_fops);/*初始化cdev成员*/
dev->cdev.owner=THIS_MODULE;
err=cdev_add(&dev->cdev,devno,);/*向系统注册字符设备*/
if(err)
printk(KERN_NOTICE"error=%d",err);
} /*设备驱动模块加载函数*/
static int __init second_init(void)
{
/*申请设备号*/
int ret;
dev_t devno=MKDEV(second_major,);/*获得设备号*/
if(second_major)
ret=register_chrdev_region(devno,,DEVICE_NAME);
else
{
/*动态申请设备号*/
ret=alloc_chrdev_region(&devno,,,DEVICE_NAME);
second_major=MAJOR(devno);
}
if(ret)
{
printk("request chrdev failed!!\n");
return ret;
} /*动态申请设备结构体内存*/
second_devp=kmalloc(sizeof(struct second_dev),GFP_KERNEL);
if(!second_devp)
{
ret= -ENOMEM;
goto fail_kmalloc;
}
memset(second_devp,,sizeof(struct second_dev));/*申请到的内存空间清零*/ /*注册字符设备*/
second_setup_cdev(second_devp,); /*用udev机制自动创建设备文件结点*/
second_class=class_create(THIS_MODULE,"second_class");/*在sys/class下添加second_class这个类*/
if (IS_ERR(second_class))
{
printk(KERN_ERR "class_create() failed for second_class\n");
goto fail_class_create;
}
device_create(second_class,NULL,devno,NULL,DEVICE_NAME);/*创建设备/dev/$DEVICE_NAME*/ printk("init second_drv success!!,major=%d!!\n",second_major);
return ;
fail_class_create:
cdev_del(&second_devp->cdev);/*注销cdev*/
kfree(second_devp);/*释放设备结构体内存*/
fail_kmalloc:
unregister_chrdev_region(devno,);/*释放设备号*/ return ret;
} /*设备驱动模块卸载函数*/
static void __exit second_exit(void)
{
device_destroy(second_class,MKDEV(second_major,));/*注销设备*/
class_destroy(second_class);/*注销类*/
cdev_del(&second_devp->cdev);/*注销cdev*/
kfree(second_devp);/*释放设备结构体内存*/
unregister_chrdev_region(MKDEV(second_major,),);/*释放设备号*/
} MODULE_AUTHOR("mhb@SEU");
MODULE_LICENSE("GPL"); module_init(second_init);
module_exit(second_exit);
测试代码：
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <fcntl.h> main(int argc,char *argv[])
{
int fd;
int counter=;
int counter_old=; if ((fd=open("/dev/second_drv",O_RDONLY )) < )
{
printf("Open Device failed.\r\n");
exit();
}
else
while()
{
//printf("in the while(1)!\n");
read(fd,&counter,sizeof(unsigned int));
if(counter!=counter_old)
{
printf("seconds after open /dev/second_drv :%d\n",counter);
counter_old=counter;
}
} }