// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/debugfs.h>

#define VALUE "tomoron"

extern struct dentry *module_dir;
ssize_t id_read(struct file *f, char __user *buf, size_t len, loff_t *off);
ssize_t id_write(struct file *f, const char __user *buf, size_t len, loff_t *off);
int init_id(void);


static const struct file_operations fops = {
	.owner = THIS_MODULE,
	.read = id_read,
	.write = id_write,
};

ssize_t id_read(struct file *f, char __user *buf, size_t len, loff_t *off)
{
	char msg[] = VALUE;

	pr_info("someone read from the file\n");
	return simple_read_from_buffer(buf, len, off, msg, sizeof(msg) - 1);
}


ssize_t id_write(struct file *f, const char __user *buf, size_t len, loff_t *off)
{
	char kbuf[64];

	if (len > sizeof(kbuf) - 1)
		return -EINVAL;
	if (copy_from_user(kbuf, buf, len))
		return -EINVAL;

	kbuf[len] = '\0';

	if (strcmp(kbuf, VALUE) == 0) {
		pr_info("someone wrote the right string\n");
		return len;
	}
	pr_info("someone wrote the wrong string\n");
	return -EINVAL;
}

int init_id(void)
{
	struct dentry *ret;

	ret = debugfs_create_file("id", 0666, module_dir, NULL, &fops);
	if (IS_ERR(ret))
		return PTR_ERR(ret);
	return 0;
}