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

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Developer");
MODULE_DESCRIPTION("A Hello World Module with debugfs functionality");
MODULE_VERSION("1.0");

static struct dentry *dir_ret = NULL;
static struct dentry *file_ret = NULL;

// Triggered when a userspace process reads the debugfs file
static ssize_t hello_write(struct file *fp, const char __user *user_buffer, size_t count, loff_t *position)
{
	char buf[60] = "UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU";
	int rc;

	pr_info("pos=%lld count=%lu\n", *position, count);

	rc = simple_write_to_buffer(buf, sizeof(buf), position, user_buffer, count);
	if (rc < 0)
		return rc;
	buf[rc] = '\0';

	pr_info("rc=%d buf %s\n", rc, buf);

	return count;
}

// Map the custom read logic to file operations structure
static const struct file_operations hello_fops = {
	.owner = THIS_MODULE,
	.write = hello_write,
};

// Module Initialization
static int __init hello_init(void)
{
	pr_info("hello_debugfs: Module loaded successfully\n");

	// 1. Create top-level parent directory in debugfs root
	dir_ret = debugfs_create_dir("hello_dir", NULL);
	if (IS_ERR(dir_ret)) {
		pr_err("hello_debugfs: Failed to create parent directory\n");
		return PTR_ERR(dir_ret);
	}

	// 2. Create target communication file inside the parent directory (Read-only for all: 0444)
	file_ret = debugfs_create_file("hello_file", 0444, dir_ret, NULL, &hello_fops);
	if (IS_ERR(file_ret)) {
		pr_err("hello_debugfs: Failed to create communication file\n");
		debugfs_remove_recursive(dir_ret);
		return PTR_ERR(file_ret);
	}

	return 0;
}

// Module Cleanup
static void __exit hello_exit(void)
{
	// Recursively destroys the created files and directory nodes
	debugfs_remove_recursive(dir_ret);
	pr_info("hello_debugfs: Module unloaded successfully\n");
}

module_init(hello_init);
module_exit(hello_exit);