代碼如下

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/device.h>  


int demo_major = 250;
int demo_minor = 0;
int demo_count = 1;

struct cdev cdev;

static struct class *demo_class;
 
static struct device *demo_device;

int  demo_open(struct inode *inodep, struct file * filep) // 打開設備
{
    printk("%s,%d\n", __func__, __LINE__);
    return 0;
}

int demo_release(struct inode * inodep, struct file * filep)  // 關閉設備
{
    printk("%s,%d\n", __func__, __LINE__);
    return 0;
}

struct file_operations  fops =
{
    .owner 
 
= THIS_MODULE,
    .open = demo_open,
    .release = demo_release,
};

static int __init demo_init(void)
{
    int ret = 0;
    dev_t  devno;
    
    printk("%s,%d\n", __func__, __LINE__);

    //使用下列宏則可以通過主設備號和次設備號生成 dev_t
    devno = MKDEV(demo_major, demo_minor);

    printk("devno:%d\n", devno);
    printk(
 
"demo_major:%d\n", demo_major);

    /**在調用 cdev_add()函數向系統註冊字符設備之前，
      *應首先調用 register_chrdev_region()或alloc_chrdev_region()函數向系統申請設備號
      **/
    if (demo_major)
    {
　　　　 //使用cat /proc/devices | grep demo 來查詢
        ret = register_chrdev_region(devno, 1, "demo");
    }
    else 
    {
        ret = alloc_chrdev_region(&devno, demo_minor, 1, "demo");
    }

    if(ret)
    {
        printk("Failed to register_chrdev_region.\n");
        return ret;
    } 
    
    //cdev_init()函數用於初始化 cdev 的成員，並建立 cdev 和 file_operations 之間的連接
    cdev_init(&cdev, &fops);
    cdev.owner = THIS_MODULE;

    //系統添加一個 cdev，完成字符設備的註冊。
    ret = cdev_add(&cdev, devno, demo_count);
    if(ret)
    {
        printk(KERN_NOTICE " Failed to cdev_add [Error] %d adding demo%d", ret, demo_minor);
        
        goto failure_cdev_add;
        
    }
    
    /*自動創建設備節點文件*/
    
    //1.註冊設備類  /sys/class/demo的文件夾 
　　//使用 ls /sys/class/demo
    demo_class = class_create(THIS_MODULE, "demo");
    if( IS_ERR(demo_class))
    {
        printk("class_create failed!\n");
        ret = PTR_ERR("demo_class");
        goto failure_class_create;
    }
    
    
    //2.註冊設備  /sys/class/demo/demo0      /dev/demo0
    demo_device = device_create(demo_class, NULL, MKDEV(demo_major, demo_minor), NULL, "demo%d", demo_minor);
    if(IS_ERR(demo_device)){
        printk("device_create failed!\n");
        ret = PTR_ERR("demo_device");
        goto failure_device_create;
    }
    return 0;

failure_device_create:
    class_destroy(demo_class);
failure_class_create:
    cdev_del(&cdev);
failure_cdev_add:
    unregister_chrdev_region(devno, demo_count);
failure_register_chrdev:
    return ret;
}

static void __exit demo_exit(void)
{
    printk("%s,%d\n", __func__, __LINE__);
    
    /*逆序消除*/
    //從內核中刪除設備
    device_destroy(demo_class,MKDEV(demo_major, demo_minor));
    //從內核中刪除設備類
    class_destroy(demo_class);
    //刪除一個 cdev，完成字符設備的註銷。
    cdev_del(&cdev);
    //在調用cdev_del()函數從系統註銷字符設備之後，unregister_chrdev_region()應該被調用以釋放原先申請的設備號
    unregister_chrdev_region( MKDEV(demo_major, demo_minor), demo_count );
}

module_init(demo_init);
module_exit(demo_exit);

MODULE_AUTHOR(" libra13179 ");
MODULE_LICENSE("GPL v2");

KVERS = $(shell uname -r)

# Kernel modules
obj-m += demo.o

# Specify flags for the module compilation.
#EXTRA_CFLAGS=-g -O0

build: kernel_modules

kernel_modules:
    make -C /lib/modules/$(KVERS)/build M=$(CURDIR) modules
#    @echo $(KVERS)

clean:
    make -C /lib/modules/$(KVERS)/build M=$(CURDIR) clean

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <stdio.h>





int main(int argc, const char *argv[])

{

    int fd;

    int val = 1;

    fd = open("/dev/demo0", O_RDWR);

    if (fd < 0)

    {

        printf("can‘t open!\n");

        return -1;

    }

    else

    {

        printf("open success.\n");

    }

 

 

    getchar();

 

 

    close(fd);



    return 0;

}

linux驅動開發（三） 字符設備驅動框架(自動創建設備節點)