[LINUX] Simple character device driver creation memo (cdev)

Premise

--Use cdev function instead of register_chrdev --This seems to be recommended for Linux kernel 2.6 or later --Others are the same as Previous article

Note

code

simple_device_driver3.c


#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <asm/uaccess.h> // copy_from_user
#include <linux/cdev.h> // cdev★
#define NODE_NAME "kuredev"
#define SUCCESS 0

MODULE_LICENSE("Dual BSD/GPL");

static int major_num = 0;
static unsigned char k_buf[1024];
static int data_size;
static int read_count = 0;
static int minor_num = 1;//★
static struct cdev kure_cdev;//★

static int kure_open(struct inode *inode, struct file *file){
        printk("kure_open\n");
        return SUCCESS;
}

static int kure_release(struct inode *inode, struct file *file){
        printk("kure_release\n");
        return SUCCESS;
}

static ssize_t kure_read(struct file *file, char __user *buf, size_t count, loff_t *f_pos){
        printk("kure_read, count: %d, data_size: %d\n", count, data_size);
        if(read_count){
                return 0;
        }
        int len;
        if(count > data_size){
                len = data_size;
        }else{
                len = count;
        }
        printk("len: %d\n", len);
        copy_to_user(buf, k_buf, len);
        read_count++;
        return len;
}

static ssize_t kure_write(struct file *file, char __user *buf, size_t count,loff_t *f_pos){
        printk("kure_write, count = %d\n", count);
        copy_from_user(k_buf, buf, count);
        data_size = count;
        return count;
}

struct file_operations kure_fops = {
        .owner = THIS_MODULE,
        .read = kure_read,
        .write = kure_write,
        .open = kure_open,
        .release = kure_release
};

static int kure_init(void){
//      major_num = register_chrdev(major_num, NODE_NAME, &kure_fops);
        dev_t dev = MKDEV(major_num, 0);//★
        alloc_chrdev_region(&dev, 0, minor_num, NODE_NAME);//★
        major_num = MAJOR(dev);//★
        cdev_init(&kure_cdev, &kure_fops);//★
        kure_cdev.owner = THIS_MODULE;//★
        cdev_add(&kure_cdev, MKDEV(major_num, 0), minor_num);//★

        printk("kure_init\n");
        return SUCCESS;
}

static void kure_exit(void){
//      unregister_chrdev(major_num, NODE_NAME);
        dev_t dev = MKDEV(major_num, 0);//★
        cdev_del(&kure_cdev);//★
        unregister_chrdev_region(dev, minor_num);//★

        printk("kure_exit\n");
}

module_init(kure_init);
module_exit(kure_exit);

Execution result

With Last time

reference

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