字符设备框架：管理同主设备号、不同次设备号设备

以下代码针对迅为开发板RK3568，开发板系统是ubuntu20.04，

正文

以下是我写的字符设备框架，实现了管理同主设备号、不同次设备号的功能。

代码：

private_data_test.c

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

/* 一个驱动兼容不同设备实验 */

/*
  定义一个设备结构体，专门存放设备号、设备类、设备类中的设备。显得很规整。
*/
struct device_test
{
    dev_t dev_num;          /* 设备号 */
    int major;              /* 定义 int 类型的主设备号 major */
    int minor;              /* 定义 int 类型的次设备号 minor */
    struct cdev cdev_test;  /* 设备暂起名cdev_test */
    struct class * class ;  /* 类 */
    struct device * device; /* 设备 */
    char kbuffer[64];      /* 缓存区 buf */
};

/* dev1和dev2的主设备号相同，次设备号不同。 */
static struct device_test dev1;
static struct device_test dev2;

static int cdev_test_ops_open (struct inode * inode, struct file * file)
{
    dev1.minor = 0; //设置 dev1 的次设备号为 0
    dev2.minor = 1; //设置 dev2 的次设备号为 1
/*
    container_of 函数
    函数原型: container_of(ptr, type, member)
    函数功能: 通过结构体变量中某个成员的首地址获取到整个结构体变量的首地址。
    函数参数: 第一个参数ptr是结构体变量中某个成员的地址。
            第二个参数type是结构体的类型。
            第三个参数member是该结构体变量的具体名字。
*/
    file->private_data = container_of(inode->i_cdev,struct device_test, cdev_test);//现在程序自动判断是dev1还是dev2
    printk(KERN_ERR "This is cdev_test_ops_open in Kernel\r\n");
    return 0;
};

static ssize_t cdev_test_ops_read (struct file * file, char __user * buf, size_t size, loff_t * off)
{
    struct device_test * test_dev = (struct device_test *)file->private_data;
    int ret = 0;
    ret = copy_to_user(buf, test_dev->kbuffer, strlen(test_dev->kbuffer)); //拷贝结束且健康，返回0
    if(ret != 0) //返回值≠0，就是拷贝到用户态失败。
    {
        printk(KERN_ERR "copy_to_user, failed\r\n");
        return -1;
    }
    printk(KERN_ERR "copy_to_user, successed\r\n");
    printk(KERN_ERR "Kernel Message:This is cdev_test_ops_read\r\n");
    return 0;
};

static ssize_t cdev_test_ops_write (struct file *file , const char __user * buf, size_t size, loff_t * off)
{
    int ret = 0;
    struct device_test * test_dev = (struct device_test *)file->private_data;
    if(test_dev->minor == 0)
    {
        printk(KERN_ERR "This is dev1\r\n");
        ret = copy_from_user(test_dev->kbuffer, buf, size); //拷贝结束且健康，返回0
        if(ret != 0)
        {
            printk(KERN_ERR "copy_from_user, failed\r\n");
            return -1;
        }
        printk(KERN_ERR "copy_from_user, successed\r\n");
        printk(KERN_ERR "test_dev->kbuffer is %s\r\n", test_dev->kbuffer);
    }
    else if(test_dev->minor == 1)
    {
        printk(KERN_ERR "This is dev2\r\n");
        ret = copy_from_user(test_dev->kbuffer, buf, size); //拷贝结束且健康，返回0
        if(ret != 0)
        {
            printk(KERN_ERR "copy_from_user, failed\r\n");
            return -1;
        }
        printk(KERN_ERR "copy_from_user, successed\r\n");
        printk(KERN_ERR "test_dev->kbuffer is %s\r\n", test_dev->kbuffer);
    }
    printk(KERN_ERR "This is cdev_test_ops_write in Kernel\r\n");
    return 0;
};

static int cdev_test_ops_release (struct inode * inode, struct file * file)
{
    printk(KERN_ERR "This is cdev_test_ops_release in Kernel\r\n");
    return 0;
};

static struct file_operations cdev_test_ops = {
    .owner = THIS_MODULE,
    .open = cdev_test_ops_open, //open字段指向 cdev_test_ops_open
    .read = cdev_test_ops_read,
    .write = cdev_test_ops_write,
    .release = cdev_test_ops_release
};

/***************************** 接下来是入口函数 ********************************/

static int __init module_cdev_init(void)
{
    int ret = 0;    //ret value，返回值

    printk(KERN_ERR "Enter Module Init\r\n");

    ret = alloc_chrdev_region(&dev1.dev_num, 0, 2, "dynamically alloc dev1 number");
    if(ret < 0)
    {
        printk(KERN_ERR "apply_cdev1_num, failed\r\n");
    }
    printk(KERN_ERR "apply_cdev1_num, successed\r\n");

    dev1.major = MAJOR(dev1.dev_num);
    dev1.minor = MINOR(dev1.dev_num);
    printk(KERN_ERR "dev1:major is %d,minor is %d\r\n", dev1.major, dev1.minor);

    /* dev1的一套东西 */
    dev1.cdev_test.owner = THIS_MODULE; //将owner字段指向本模块，可以避免在模块的操作正在被使用时卸载该模块
    cdev_init(&dev1.cdev_test, &cdev_test_ops);
    ret = cdev_add(&dev1.cdev_test, dev1.dev_num, 1);
    if(ret < 0)
    {
        printk(KERN_ERR "cdev_add1, failed\r\n");
    }
    printk(KERN_ERR "cdev_add1, successed\r\n");

    dev1.class = class_create(THIS_MODULE, "test1_class");
    dev1.device = device_create(dev1.class, NULL, dev1.dev_num, NULL, "test1_dev"); 

    /* dev2的一套东西 */
    ret = alloc_chrdev_region(&dev2.dev_num, 0, 2, "dynamically alloc dev2 number");
    if(ret < 0)
    {
        printk(KERN_ERR "apply_cdev2_num, failed\r\n");
    }
    dev2.major = MAJOR(dev1.dev_num);
    dev2.minor = MINOR(dev1.dev_num + 1);
    printk(KERN_ERR "dev2:major is %d,minor is %d\r\n", dev2.major, dev2.minor);

    dev2.cdev_test.owner = THIS_MODULE;
    cdev_init(&dev2.cdev_test, &cdev_test_ops);
    ret = cdev_add(&dev2.cdev_test, MKDEV(dev2.major,dev2.minor), 1);
    if(ret < 0)
    {
        printk(KERN_ERR "cdev2_add, failed\r\n");
    }
    printk(KERN_ERR "cdev2_add, successed\r\n");
    dev2.class = class_create(THIS_MODULE, "test2_class"); 
    dev2.device = device_create(dev2.class, NULL, MKDEV(dev2.major,dev2.minor), NULL, "test2_dev");

    return 0;
}

static void __exit  module_cdev_exit(void)
{
    cdev_del(&dev1.cdev_test); //删除添加的字符设备 cdev_test
    cdev_del(&dev2.cdev_test); //删除添加的字符设备 cdev_test

    device_destroy(dev1.class, dev1.dev_num); //删除创建的设备
    device_destroy(dev2.class, MKDEV(dev2.major,dev2.minor)); //删除创建的设备

    class_destroy(dev1.class); //删除创建的类
    class_destroy(dev2.class); //删除创建的类

    unregister_chrdev_region(dev1.dev_num, 1); // 释放字符驱动设备号
    unregister_chrdev_region(dev1.dev_num+1, 1); // 释放字符驱动设备号

    printk(KERN_ERR "module_cdev_exit, bye bye\r\n");
}

module_init(module_cdev_init); //注册入口函数
module_exit(module_cdev_exit); //注册出口函数

MODULE_LICENSE("GPL");
MODULE_AUTHOR("my_topeet_drv");
MODULE_VERSION("v1.0.0");

app.c

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

int main(int arc, char *argv[])
{
    int fd1, fd2;
    char buf1[64] = "/dev/test1, hello dev1 from app layer in user space\n";
    char buf2[64] = "/dev/test2, hello dev2 from app layer in user space\n";

    /*设备节点1*/
    fd1 = open("/dev/test1_dev", O_RDWR, 0666);
    if(fd1 < 0)
    {
        perror("open /dev/test1_dev error\n");
        return fd1;
    }
    write(fd1, buf1, sizeof(buf1));
    close(fd1);

    /*设备节点2*/
    fd2 = open("/dev/test2_dev", O_RDWR, 0666);
    if(fd2 < 0)
    {
        perror("open /dev/test2_dev error\n");
        return fd2;
    }
    write(fd2, buf2, sizeof(buf2));
    close(fd2);
    
    return 0;
}

结果

root@topeet:/home/topeet/myko$ make insmod
insmod private_data_test.ko
[   83.775025] Enter Module Init
[   83.775094] apply_cdev1_num, successed
[   83.775103] dev1:major is 236,minor isroot@topeet:/home/topeet/myko$  0
[   83.775115] cdev_add1, successed
[   83.775735] dev2:major is 236,minor is 1
[   83.775765] cdev2_add, successed
./a.out
[   88.615091] This is cdev_test_ops_open in Kernel
[   88.615177] This isroot@topeet:/home/topeet/myko$ dev1
[   88.615188] copy_from_user, successed
[   88.615197] test_dev->kbuffer is /dev/test1, hello dev1 from app layer in user space
[   88.615197]
[   88.615205] This is cdev_test_ops_write in Kernel
[   88.615219] This is cdev_test_ops_release in Kernel
[   88.615245] This is cdev_test_ops_open in Kernel
[   88.615254] This is dev2
[   88.615260] copy_from_user, successed
[   88.615265] test_dev->kbuffer is /dev/test2, hello dev2 from app layer in user space
[   88.615265]
[   88.615271] This is cdev_test_ops_write in Kernel
[   88.615278] This is cdev_test_ops_release in Kernel

遇到的坑：

1、设备2的设备号，也要使用动态分配语句 alloc_chrdev_region 来做；

2、设备节点名字必须不一样（设备节点名在语句 device_create 里修改）；

3、动态分配语句 alloc_chrdev_region 里的第四个参数，在两次获取设备号的语句中，建议写为不一样的为好。