一、添加頭文件

二、構造fileoperation結構體

    static struct fileoperations second_drv_fops = {
    
    　　.owner = THIS_MODULE;
    
    　　.open  = second_drv_open;
    
    　　.write = ;second_drv_write
    
    }

三、填充file_operations中的成員函數
static int second_drv_open(struct inode *inode,struct file *file)
{
    



    
 
return 0;
}

ssize_t second_drv_read(struct file *file,char __user *buf,size_t size,loff_t *ppos)
{


    return 0;
}


還有初始化函數

static int second_drv_init(void)
{
    major = register_chrdev(0,"second_drv",&second_drv_fops);
    return 0;
}

static int second_drv_exit(void)
{
    unregister_chrdev(major,
 
"second_drv");
    return 0;
}


module_init(second_drv_init);
module_exit(second_drv_exit);


要使用udev(mdev機制)根據信息來創造設備節點
    先創建一個class，再創建一個設備。
定義兩個結構體：
static struct class *seconddrv_class;
static struct class_device *seconddrv_class_dev;

static int second_drv_init(void)
{
//創建一個類，在類下面創建一個設備。
//mdev是udev的簡化版本
 

    major = register_chrdev(0,"second_drv",&second_drv_fops);
    seconddrv_class = class_create(THIS_MODULE,"seconddrv");
    seconddrv_class_dev = class_device_create(seconddrv_class,NULL,MKDEV(major,0),NULL,"buttons");
    return 0;
}

static void second_drv_exit(void)
{
    unregister_chrdev(major,"first_drv");

    class_device_unregister(seconddrv_class_dev);
    class_destroy(seconddrv_class);
}

字符驅動之按鍵（一：無腦輪詢法）