#include <asm/uaccess.h>
#include <linux/cdev.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kdev_t.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/errno.h>

static char devname[] = "pidevice";
static char modname[] = "pidevice.ko";
static dev_t mydev = 0;
static struct cdev cdev;

static int count = 1;

int pidev_open(struct inode *i, struct file *filp)
{
	count = 1;
	printk(KERN_ALERT "pidev_open: device (%d-%d) opened\n",
			imajor(i), iminor(i));
	printk(KERN_ALERT "pidev_open: mode %c%c\n", filp->f_mode & FMODE_READ ? 'R' : '-',
			filp->f_mode & FMODE_WRITE ? 'W' : '-');
	return 0;
}

ssize_t pidev_read(struct file *filp, char __user *buf,
		size_t len, loff_t *off)
{
	if (count--) {
		if (copy_to_user(buf, modname, 12))
			printk(KERN_ALERT "pidev_read: error reading from (__user) %p\n", buf);
		return 12;
	} else {
		return 0;
	}
}

ssize_t pidev_write(struct file *filp, const char __user *buf,
		size_t len, loff_t *off)
{
	char localbuf[40];
	if (copy_from_user(localbuf, buf, 40))
		printk(KERN_ALERT "pidev_write: error writing in (__user) %p\n", buf);
	localbuf[len] = '\0';

	printk(KERN_ALERT "pidev_write: received: %s", localbuf);
	return -EPERM;
}

long pidev_ioctl(struct file *filp, unsigned msg, unsigned long param)
{
	printk(KERN_ALERT "pidev_ioctl: received msg %d / param %ld\n", msg, param);
	return 0;
}

struct file_operations fops = {
	.owner = THIS_MODULE,
	.open = pidev_open,
	.read = pidev_read,
	.write = pidev_write,
	.unlocked_ioctl = pidev_ioctl,
};

static int __init pidev_init(void)
{
	int err;

	printk(KERN_ALERT "pidev_init: %s loaded by %s (%d)\n",
			modname, current->comm, current->pid);

	if ((err = alloc_chrdev_region(&mydev, 0, 1, devname)))
		printk(KERN_ALERT "pidev_init: error %d in alloc_chrdev_region\n", err);
	else
		printk(KERN_ALERT "pidev_init: %s successfully registered with"
				"%d %d numbers\n", devname, MAJOR(mydev), MINOR(mydev));

	cdev_init(&cdev, &fops);
	cdev.owner = THIS_MODULE;
	if ((err = cdev_add(&cdev, mydev, 1)))
		printk(KERN_ALERT "pidev_init: error %d in cdev_add\n", err);

	return 0;
}

static void __exit pidev_exit(void)
{
	unregister_chrdev_region(mydev, 1);
	cdev_del(&cdev);
	printk(KERN_ALERT "pidev_exit: %s unloaded\n", modname);
}

module_init(pidev_init);
module_exit(pidev_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Guillermo Ramos");