#include "linux/fs.h"
#include "linux/types.h"
#include <linux/gpio/consumer.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>

/*
 * Last compiled with Linux 6.14.5-300.fc42.x86_64
 */

/* Meta Info */
MODULE_DESCRIPTION("Chardev kernel module.");
MODULE_VERSION("0.0.1");
MODULE_AUTHOR("Imbus");
MODULE_LICENSE("GPL");

// Since were dynamically assigned a major device number, we will store it here
static int major;
static char text[64];

// Regular forward decls
static ssize_t my_read(struct file *f, char __user *u, size_t l, loff_t *o);
static ssize_t my_write(struct file *, const char __user *, size_t, loff_t *);
static int my_open(struct inode *, struct file *);
static int my_release(struct inode *, struct file *);

// See: https://elixir.bootlin.com/linux/v6.14.5/source/include/linux/fs.h#L2131
static struct file_operations fops = {
    .read = my_read, .write = my_write, .open = my_open, .release = my_release};

static ssize_t my_write(struct file *filp, const char __user *user_buf,
                        size_t len, loff_t *off) {
  printk(KERN_INFO "hello_cdev - Write is called by %s...\n", current->comm);

  int not_copied, delta,
      to_copy = (len + *off) < sizeof(text) ? len : (sizeof(text) - *off);

  if (*off >= sizeof(text))
    return 0;

  not_copied = copy_from_user(text, user_buf, to_copy);
  delta = to_copy - not_copied;

  if (not_copied)
    pr_warn("hello_cdev - Could only copy %d bytes\n", delta);

  *off = delta;

  return delta;
}

static ssize_t my_read(struct file *filp, char __user *user_buf, size_t len,
                       loff_t *off) {
  printk(KERN_INFO "hello_cdev - Read is called\n");

  int not_copied, delta,
      to_copy = (len + *off) < sizeof(text) ? len : (sizeof(text) - *off);

  if (*off >= sizeof(text))
    return 0;

  not_copied = copy_to_user(user_buf, text, to_copy);
  delta = to_copy - not_copied;

  if (not_copied)
    pr_warn("hello_cdev - Could only copy %d bytes\n", delta);

  *off = delta;

  return delta;
}

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 - Closed \n");
  return 0;
}

/**
 * @brief Called on load
 */
static int __init demo_mod_init(void) {
  major = register_chrdev(0, "hello_cdev", &fops);

  if (major < 0) {
    printk(KERN_INFO "hello_cdev - Error registering chrdev\n");
    return major;
  }

  printk(KERN_INFO "hello_cdev - Major nbr %d loaded successfully...", major);
  return 0;
}

/**
 * @brief Called on unload
 */
static void __exit demo_mod_exit(void) {
  unregister_chrdev(major, "hello_cdev");
  printk(KERN_INFO "hello_cdev - unloaded successfully...");
}

module_init(demo_mod_init);
module_exit(demo_mod_exit);