📒 笔记文档

自动创建设备节点，不需要使用mknod去创建/dev下的设备节点

流程

• 编译和挂载

  make
  

  insmod 005_udev_mdev.ko
  

• 查看

  ls /sys/class/005_udev_mdev #struct class *class_test 的 class_create(THIS_MODULE, name)中的name对应
  

  lsmod #命令
  Module                  Size  Used by
  005_udev_mdev          16384  0
  

  cat /proc/devices # 命令
  Character devices:
  	237 005_udev_mdev
  

  ls /dev/005_udev_mdev #device_create(class_test, NULL, dev_no, NULL, name)中的name对应
  

• 卸载

  会卸载**/proc/devices**，/dev，/sys/class下有的东西

  rmmod 005_udev_mdev.ko
  

代码：005_udev_mdev.c

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

dev_t dev_no; // 设备号
struct cdev cdev_test; // 字符设备结构体

struct class *class_test; // 类
struct device *device_test; // 设备

static int test_open(struct inode *inode,struct file *file)
{
    printk("open\n");
    return 0;
}
static ssize_t test_read(struct file *file,char __user *buf, size_t size,loff_t *off){
    printk("read\n");
    return 0;
}
static ssize_t test_write(struct file *file,const char __user *buf, size_t size,loff_t *off){
    printk("write\n");
    *off += size;
    return size;
}
static int test_release(struct inode *inode,struct file *file)
{
    printk("release\n");
    return 0;
}
struct file_operations fops = {
    .owner = THIS_MODULE,
    .open = test_open,
    .read = test_read,
    .write = test_write,
    .release = test_release,
};

//设备名称
static char* name = "005_udev_mdev";

MODULE_LICENSE("GPL");
MODULE_AUTHOR("wyl");
MODULE_DESCRIPTION("005_udev_mdev");
static int modulecdev_init(void)
{ 
    int ret;
    ret = alloc_chrdev_region(&dev_no, 0, 1, name);
    if (ret<0) {
        printk("alloc_chrdev_region failed\n");
        return ret;
    }
    printk("major:%d, minor:%d\n", MAJOR(dev_no), MINOR(dev_no));
    cdev_init(&cdev_test, &fops);
    cdev_add(&cdev_test, dev_no, 1);

    class_test = class_create(THIS_MODULE, name); //创建类
    device_test = device_create(class_test, NULL, dev_no, NULL, name);
    return 0;
}
static void modulecdev_exit(void)
{
    // 1. 先销毁设备节点
    device_destroy(class_test, dev_no);
    
    // 2. 销毁类 (原代码缺失此步，必须添加)
    class_destroy(class_test);
    
    // 3. 删除字符设备
    cdev_del(&cdev_test);
    
    // 4. 最后注销设备号
    unregister_chrdev_region(dev_no, 1);
    
    printk("modulecdev exit\n");
}

module_init(modulecdev_init);
module_exit(modulecdev_exit);

代码：app.c

#include <stdio.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>

int main() {
  int fd = open("/dev/005_udev_mdev", O_RDWR);
  if (fd < 0) {
    printf("open error\n");
    return -1;
  }
  printf("open success\n");
  close(fd);
  return 0;
}