/**************************************************************
 * Class::  CSC-415-01 Fall 2024
 * Name::  Uzair Hamed Mohammed
 * Student ID::  920142896
 * GitHub-Name::  gamersekofy
 * Project:: Assignment 6 - Device Driver
 *
 * File:: tempMonitor.c
 *
 * Description::  This is a complex kernel module that retrieves CPU temperature
 *data from /sys/class/thermal/thermal_zone*\/temp
 *
 **************************************************************/

#include <linux/device.h>
#include <linux/err.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/ioctl.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/random.h>
#include <linux/slab.h>
#include <linux/stat.h>
#include <linux/uaccess.h>

#define DEVICE_NAME "temp_monitor"
#define IOCTL_GET_TEMP _IOR('t', 1, int)

// The CPU temperature will be accessed from thermal_zone0/temp
#define TEMP_SENSOR_PATH "/sys/class/thermal/thermal_zone0/temp"
#define BUF_LEN 100

static int major_number;
static struct class *temp_monitor_class = NULL;
static struct device *temp_monitor_device = NULL;
static char temp_unit[BUF_LEN] = "C"; // Default unit is Celsius

/* A similar flag exists in the test/user application. If it's detected that
 * the user is in a virtual machine, a smulated temperature is returned */
static bool simulate_temp = false;

static int device_open(struct inode *inode, struct file *file) { return 0; }

static int device_release(struct inode *inode, struct file *file) { return 0; }

static ssize_t device_read(struct file *file, char __user *buffer, size_t len,
                           loff_t *offset) {
  int temp = 0;
  char temp_str[BUF_LEN];
  struct file *f;
  char *buf;
  loff_t pos = 0;
  bool is_simulated = false;

  // Check if the temperature file exists. If it doesn't, simulate the
  // temperature.
  f = filp_open(TEMP_SENSOR_PATH, O_RDONLY, 0);
  if (IS_ERR(f)) {
    printk(KERN_INFO "temp_monitor: Temperature file not found\n");
    is_simulated = true;
    get_random_bytes(&temp, sizeof(temp));
    // Simulate a temperature between 10 and 50 degrees
    temp = (temp % 40) + 10;
  } else {
    buf = kmalloc(16, GFP_KERNEL);
    if (!buf) {
      filp_close(f, NULL);
      return -ENOMEM;
    }

    // Read the temperature
    kernel_read(f, buf, 16, &pos);
    sscanf(buf, "%d", &temp);
    // Convert to degrees Celsius
    temp /= 1000;
    filp_close(f, NULL);
    kfree(buf);
  }

  // Convert to desired unit
  if (strcmp(temp_unit, "F") == 0) {
    temp = temp * 9 / 5 + 32;
    // Convert to Fahrenheit
  } else if (strcmp(temp_unit, "K") == 0) {
    temp += 273;
    // Convert to Kelvin
  }

  snprintf(temp_str, BUF_LEN, "%d %s%s\n", temp, temp_unit,
           is_simulated ? " (simulated temperature)" : "");

  // Copy the result to user-space
  if (copy_to_user(buffer, temp_str, strlen(temp_str) + 1)) {
    return -EFAULT;
  }

  return strlen(temp_str) + 1;
}

static ssize_t device_write(struct file *file, const char __user *buffer,
                            size_t len, loff_t *offset) {
  char msg[BUF_LEN];

  // Check if input too long
  if (len > BUF_LEN - 1) {
    return -EINVAL;
  }

  if (copy_from_user(msg, buffer, len)) {
    return -EFAULT;
  }
  msg[len] = '\0';

  if (strcmp(msg, "simulate") == 0) {
    simulate_temp = true;
  } else {
    simulate_temp = false;
    strncpy(temp_unit, msg, BUF_LEN - 1);
  }

  printk(KERN_INFO "temp_monitor: Write operation: %s\n", msg);

  return len;
}

static long device_ioctl(struct file *file, unsigned int cmd,
                         unsigned long arg) {
  switch (cmd) {
  case IOCTL_GET_TEMP: {
    int temp = 0;
    // Retrieve the temperature data
    if (copy_to_user((int *)arg, &temp, sizeof(temp))) {
      return -EACCES;
    }
    break;
  }
  default:
    return -EINVAL;
  }
  return 0;
}

static struct file_operations fops = {
    .open = device_open,
    .release = device_release,
    .read = device_read,
    .write = device_write,
    .unlocked_ioctl = device_ioctl,
};

static int __init temp_monitor_init(void) {
  major_number = register_chrdev(0, DEVICE_NAME, &fops);
  if (major_number < 0) {
    printk(KERN_ALERT "temp_monitor: Failed to register a major number\n");
    return major_number;
  }
  temp_monitor_class = class_create(THIS_MODULE->name); // Updated this line
  if (IS_ERR(temp_monitor_class)) {
    unregister_chrdev(major_number, DEVICE_NAME);
    printk(KERN_ALERT "temp_monitor: Failed to register device class\n");
    return PTR_ERR(temp_monitor_class);
  }
  temp_monitor_device = device_create(
      temp_monitor_class, NULL, MKDEV(major_number, 0), NULL, DEVICE_NAME);
  if (IS_ERR(temp_monitor_device)) {
    class_destroy(temp_monitor_class);
    unregister_chrdev(major_number, DEVICE_NAME);
    printk(KERN_ALERT "temp_monitor: Failed to create the device\n");
    return PTR_ERR(temp_monitor_device);
  }
  printk(KERN_INFO "temp_monitor: Device initialized with major number %d\n",
         major_number);
  return 0;
}

static void __exit temp_monitor_exit(void) {
  device_destroy(temp_monitor_class, MKDEV(major_number, 0));
  class_unregister(temp_monitor_class);
  class_destroy(temp_monitor_class);
  unregister_chrdev(major_number, DEVICE_NAME);
  printk(KERN_INFO "temp_monitor: Device removed\n");
}

module_init(temp_monitor_init);
module_exit(temp_monitor_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Uzair Hamed Mohammed");
MODULE_DESCRIPTION(
    "An Awesome and Super Complex CPU Temperature Monitoring Kernel Module");