device driver 3

root@KMU-UBUNTU:/work/dev_simple# mknod /dev/simple c 249 0

root@KMU-UBUNTU:/work/dev_simple# ls -l /dev/simple 

crw-r--r-- 1 root root 249, 0 May 23 19:07 /dev/simple

#include <linux/kernel.h>

#include <linux/module.h>

#include <linux/init.h>

#include <linux/fs.h>

#include <asm/uaccess.h>

int simple_open(struct inode* pinode,struct file* pfile){

    printk(KERN_INFO "Open Simple\n");

    return 0;

}

int simple_release(struct inode* pinode, struct file* pfile){

    printk(KERN_INFO "Release Simple");

    return 0;

}

ssize_t simple_read(struct file* pfile, char* ubuf, size_t length,

        loff_t* offset) {

    int result;

    char message[20] = "Kim Jeong Been";

    result = copy_to_user(ubuf, message, length);

    if(result <0) {

        printk(KERN_ERR " READ ERR \n");

        return result;

    }

    return result;

}

ssize_t simple_write(struct file* pfile,const char* ubuf, size_t length,

                loff_t* offset){

    char message[20];

    int result;

    result = copy_from_user(message, ubuf, length);

    if(result <0) {

        printk(KERN_ERR " Write ERR \n");

        return result;

    }

    printk(KERN_INFO " from user : %s\n ", message);

    return 0;

}

struct file_operations simple_fops = {

    read : simple_read,

    write : simple_write,

    open : simple_open,

    release : simple_release,

};

int simple_init(void){

    int result;

    result = register_chrdev(249, "simple_driver",&simple_fops);

    if(result < 0) {

        printk(KERN_ERR "Registration Error\n");

        return result;

    }

    printk(KERN_INFO "Hello Simple\n");

    return 0;

}

void simple_exit(void){

    printk(KERN_INFO "Bye Simple\n");

    unregister_chrdev(249, "simple_driver");

}

module_init(simple_init);

module_exit(simple_exit);

MODULE_LICENSE("GPL");

#include <stdio.h>

#include <fcntl.h>

#include <unistd.h>

#include <stdlib.h>

#include <string.h>

int main(void){

    int fd;

    char buffer[20];

    char number[20] = "5112648";

    fd = open("/dev/simple", O_RDWR);

    if(fd < 0) {

        perror("open");

        exit(1);

    }

    write(fd, number, strlen(number)+1);

    read(fd,buffer,20);

    printf("from kernel : %s\n", buffer);

    close(fd);

    return 0;

}