#include <linux/miscdevice.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>

#define STUDENT_LOGIN "cchauvet"

MODULE_LICENSE("GPL");

static ssize_t misc_write(struct file *file, const char __user *buf,
               size_t len, loff_t *ppos)
{
	char data[10];
	size_t len_red = 10 > len ? len : 10;

	if (copy_from_user(data, buf, len_red))
		return -EFAULT;
	
	if (strcmp(data, STUDENT_LOGIN))
		return -EINVAL;

	return len_red;
}
 
static ssize_t misc_read(struct file *file, char __user *buf,
                    size_t count, loff_t *f_pos)
{
	char data[] = STUDENT_LOGIN;
	size_t len = strlen(data);

	if(*f_pos > 0)
		return 0;

	if (copy_to_user(buf, data, len))
		return -EFAULT;

	*f_pos += len;
	return len;
}

const struct file_operations fops = {
    .write          = misc_write,
    .read           = misc_read,
};

static struct miscdevice misc_device = {
    .name = "fortytwo",
    .minor = MISC_DYNAMIC_MINOR,
    .fops = &fops,
};

static int __init module_start(void)
{
    int error = misc_register(&misc_device);

    if (error) {
        pr_err("misc_register failed!!!\n");
        return error;
    }
 
    pr_info("misc_register init done!!!\n");
    return 0;
}

static void __exit module_end(void)
{
    misc_deregister(&misc_device);
    pr_info("misc_register exit done!!!\n");
}
 
module_init(module_start)
module_exit(module_end)