#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>
#include <linux/wait.h>

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

DECLARE_WAIT_QUEUE_HEAD(myqueue);

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

ssize_t sleep_read(struct file *filp, char __user *buf, size_t len,
		loff_t *offset)
{
	printk(KERN_ALERT "sleep_read: putting process %d (%s) to sleep...\n",
			current->pid, current->comm);
	count = 0;
	if (wait_event_interruptible(myqueue, count))
		return -ERESTARTSYS;
	return 0;
}

ssize_t sleep_write(struct file *filp, const char __user *buf, size_t len,
		loff_t *offset)
{
	printk(KERN_ALERT "sleep_write: process %d (%s) brings salvation :D\n",
			current->pid, current->comm);
	count = 1;
	wake_up_interruptible(&myqueue);
	return -EPERM;
}

struct file_operations fops = {
	.owner = THIS_MODULE,
	.open = sleep_open,
	.read = sleep_read,
	.write = sleep_write,
};

static int __init sleep_init(void)
{
	int err;

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

	if ((err = alloc_chrdev_region(&mydev, 0, 1, devname)))
		printk(KERN_ALERT "sleep_init: error %d in alloc_chrdev_region\n", err);
	else
		printk(KERN_ALERT "sleep_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 "sleep_init: error %d in cdev_add\n", err);

	return 0;
}

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

module_init(sleep_init);
module_exit(sleep_exit);

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