驱动源码

在驱动中直接创建字符设备节点/dev/mychardev

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

#define DEVICE_NAME "mychardev"
#define CLASS_NAME "mychardev_class"
#define BUF_SIZE 1024

static char device_buf[BUF_SIZE];
static int device_open = 0;
static dev_t dev_num;
static struct class *chardev_class;
static struct device *chardev_device;
static struct cdev chardev_cdev;

static int mychardev_open(struct inode *inode, struct file *file)
{
    if (device_open)
        return -EBUSY;

    device_open++;
    return 0;
}

static int mychardev_release(struct inode *inode, struct file *file)
{
    device_open--;
    return 0;
}

static ssize_t mychardev_read(struct file *file, char __user *buf, size_t count, loff_t *offset)
{
    if (copy_to_user(buf, device_buf, count) != 0)
        return -EFAULT;

    return count;
}

static ssize_t mychardev_write(struct file *file, const char __user *buf, size_t count, loff_t *offset)
{
    if (copy_from_user(device_buf, buf, count) != 0)
        return -EFAULT;

    return count;
}

static struct file_operations mychardev_fops = {
    .owner = THIS_MODULE,
    .open = mychardev_open,
    .release = mychardev_release,
    .read = mychardev_read,
    .write = mychardev_write,
};

static int __init mychardev_init(void)
{
    //动态申请字符设备号，参数为：返回的设备号，次设备号从几开始，个数，设备名称
    if (alloc_chrdev_region(&dev_num, 0, 1, DEVICE_NAME) < 0) {
        printk(KERN_ERR "Failed to allocate device number\n");
        return -1;
    }
    //初始化字符设备，主要就是关联fops和cdev结构体
    cdev_init(&chardev_cdev, &mychardev_fops);
    //向系统添加字符设备，参数：要添加的字符设备对象的指针，设备号，个数
    if (cdev_add(&chardev_cdev, dev_num, 1) < 0) {
        printk(KERN_ERR "Failed to add char device\n");
        unregister_chrdev_region(dev_num, 1);
        return -1;
    }
    //创建设备类，参数为指定拥有该设备类的内核模块，通常使用THIS_MODULE；设备类的名称
    chardev_class = class_create(THIS_MODULE, CLASS_NAME);
    if (IS_ERR(chardev_class)) {
        printk(KERN_ERR "Failed to create device class\n");
        cdev_del(&chardev_cdev);
        unregister_chrdev_region(dev_num, 1);
        return PTR_ERR(chardev_class);
    }
    //创建设备节点,参数为：设备所属的设备类；指定父设备的指针，通常为NUL；指定设备的设备号；指定与设备相关的驱动数据，通常为NULL；设备名称
    chardev_device = device_create(chardev_class, NULL, dev_num, NULL, DEVICE_NAME);
    if (IS_ERR(chardev_device)) {
        printk(KERN_ERR "Failed to create device\n");
        class_destroy(chardev_class);
        cdev_del(&chardev_cdev);
        unregister_chrdev_region(dev_num, 1);
        return PTR_ERR(chardev_device);
    }

    printk(KERN_INFO "mychardev module loaded\n");
    return 0;
}

static void __exit mychardev_exit(void)
{
    //销毁设备
    device_destroy(chardev_class, dev_num);
    //注销类
    class_unregister(chardev_class);
    //销毁类
    class_destroy(chardev_class);
    //删除设备
    cdev_del(&chardev_cdev);
    //注销设备号
    unregister_chrdev_region(dev_num, 1);
    printk(KERN_INFO "mychardev module unloaded\n");
}

module_init(mychardev_init);
module_exit(mychardev_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("A simple character device driver example");

Makefile文件：

obj-m += chardev.o

all:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

测试程序：

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>

#define DEVICE_PATH "/dev/mychardev"
#define BUF_LEN 1024

int main() {
    int fd;
    char read_buf[BUF_LEN];
    char write_buf[BUF_LEN] = "Hello from user space!\n";

    // Open device file
    fd = open(DEVICE_PATH, O_RDWR);
    if (fd < 0) {
        perror("Failed to open the device");
        return -1;
    }

    // Write to device
    printf("Writing to device: %s\n", write_buf);
    write(fd, write_buf, strlen(write_buf));

    // Read from device
    printf("Reading from device...\n");
    read(fd, read_buf, BUF_LEN);
    printf("Data read from device: %s\n", read_buf);

    // Close device file
    close(fd);

    return 0;
}