linux中秒字符设备驱动(宋宝华设备驱动开发详解第10章）
from: http://blog.sina.com.cn/s/blog_95268f5001015mqb.html
1. secondchar.c:
#include
#include
#include
#include //建立自动设备节点要包含的头文件
#include
#include
#include
#include
#include
#include
//#include
#include
#include
#define SECOND_MAJOR 248
#define SECOND_MINOR 100
static struct class *firstdrv_class;//自动建立设备节点时要用到一个类
static int second_major = SECOND_MAJOR;//定义主设备号为248
static int second_minor = SECOND_MINOR;//定义次设备号为100
//设备结构体
struct second_dev
{
struct cdev cdev;
atomic_t counter;//定义一个原子变量
struct timer_list s_timer;//定义定时器结构体里面包含定时处理函数，定时到期时间等
};
struct second_dev *second_devp;//设备结构体指针
//定时器处理函数
static void second_timer_handle(unsigned long arg)
{
mod_timer(&second_devp->s_timer,jiffies + HZ);//重新加载定时器的到期时间在原来基础上加多1s
atomic_inc(&second_devp->counter);//原子变量值加1
printk(KERN_NOTICE "current jiffies is %ld\n",jiffies);//打印，我们定时处理函数实现功能就是打印
}
int second_open(struct inode *inode,struct file *filp)//打开函数
{
init_timer(&second_devp->s_timer);//初始化定时器
second_devp->s_timer.function = &second_timer_handle;//指定定时处理函数
second_devp->s_timer.expires = jiffies + HZ;//指定定时到期时间，在原来上1s后调用定时处理函数
add_timer(&second_devp->s_timer);//将定时器加到内核动态定时器链表中，注册定时器
atomic_set(&second_devp->counter,0);//初始化原子变量的值为0
return 0;
}
//关闭文件
int second_release(struct inode *inode,struct file *filp)
{
del_timer(&second_devp->s_timer);//删除定时器
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);//获得原子变量的值
if(put_user(counter,(int *)buf))//put_user()实现内核->用户
return -EFAULT;
else
return sizeof(unsigned int);//返回字节
}
static const struct file_operations second_fops = {
.owner = THIS_MODULE,
.open = second_open,
.release = second_release,
.read = second_read,
};
//用于cdev初始化函数
static void second_setup_cdev(struct second_dev *dev,int index)
{
int err,devno = MKDEV(second_major,index);//合并主次设备号
cdev_init(&dev->cdev,&second_fops);//初始化设备（cdev），建立cdev和file_operations 连接
dev->cdev.owner = THIS_MODULE;
err = cdev_add(&dev->cdev,devno,1);//注册设备到内核
if(err)
printk(KERN_NOTICE "Error %d adding LED%d",err,index);
}
int second_init(void)
{
int ret;
dev_t devno = MKDEV(second_major,second_minor);//合并主次设备号为dev_t格式
if(second_major)
ret = register_chrdev_region(devno,1,"second");//申请设备号
else
{
ret = alloc_chrdev_region(&devno, 0, 1, "second");//动态申请设备号
second_major = MAJOR(devno);//获得主设备号
second_minor = MINOR(devno);
}
if(ret < 0)
return ret;
firstdrv_class = class_create(THIS_MODULE, "second_major");//建立firstdrv这个类
device_create(firstdrv_class,NULL,devno,NULL,"second");//自动创建设备节点/dev/second
second_devp = kmalloc(sizeof(struct second_dev),GFP_KERNEL);//动态申请设备结构体内存
if(!second_devp)
{
ret = -ENOMEM;
goto fail_malloc;
}
memset(second_devp,0,sizeof(struct second_dev));//清除设备结构体内存
second_setup_cdev(second_devp,second_minor);//初始化cdev
return 0;
fail_malloc:
unregister_chrdev_region(devno, 1);
return ret;
}
void second_exit(void)
{
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,second_minor),1);//释放设备号
device_destroy(firstdrv_class,MKDEV(second_major,second_minor));
class_destroy(firstdrv_class);//释放这个类，干掉它
}
MODULE_LICENSE("Dual BSD/GPL");
module_init(second_init);
module_exit(second_exit);
2. test.c:
#include
#include
#include
#include
int main()
{
int fd;
int counter = 0;
int old_counter = 0;
fd = open("/dev/second",O_RDONLY);//打开设备
if(fd != -1)
{
while(1)
{
read(fd,&counter,sizeof(unsigned int));//从fd指向描述符中读取sizeof(unsigned int）字节到counter
if(counter != old_counter) //是否等于old_counter
{
printf("seconds after open /dev/second : %d\n",counter);
old_counter = counter;//这样的话就同步了
}
}
}
else
{
printf("Device open failure\n");
}
} 3. 测试：
insmod secondchar.ko;
sudo ./test 输出如下：
注意：上面insmod secondchar.ko后会自动创建设备节点：/dev/second
等价于:mknod /dev/second c 248 100
自动创建设备节点：
从linux内核2.6的某个版本之后，devfs不复存在，udev成为devfs的替代。相比devfs，udev有很多优势，