// SPDX-License-Identifier: GPL-2.0

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

static int major;

static int my_open(struct inode *inode, struct file *filp)
{
	pr_info("hello_cdev - Major: %d, Minor %d\n", imajor(inode), iminor(inode));
	
	pr_info("hello_cdev - filp->f_pos: %lld\n", filp->f_pos);
	pr_info("hello_cdev - filp->f_mode: 0x%x\n", filp->f_mode);
	pr_info("hello_cdev - filp->f_flags: 0x%x\n", filp->f_flags);

	return 0;
}

static int my_release(struct inode *inode, struct file *filp)
{
	pr_info("hello_cdev - File is closed\n");

	return 0;
}

static struct file_operations fops = {
	.open = my_open,
	.release = my_release
};

/**
 * @brief This function is called when the module is loaded into the kernel
 */
static int __init my_init(void)
{
	/**
	 * First argument 0 auto allocates major device number
	 * returns device number
	 * Enter a number eg 64 to allocate all minor num 0 - 255
	 * 0 returned if successfull
	 */

	major = register_chrdev(0, "hello_cdev", &fops);
	if (major < 0)
	{
		pr_err("hello_cdev - Error registering chrdev\n");
		return major;
	}
	pr_info("hello_cdev - Major device number: %d\n", major);
	return 0;
}

/**
 * @brief This function is called when the module is removed from the kernel
 */
static void __exit my_exit(void)
{
	pr_info("Goodbye, Kernel\n");
	unregister_chrdev(major, "hello_cdev");
}

module_init(my_init);
module_exit(my_exit);

/* Meta Information */
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("David D'Ulisse");
MODULE_DESCRIPTION("A simple character device driver");