unkill

/*
 *  Create an input/output character device that will put in an
 *  uninterruptible sleep state the user process that opens it.
 *
 * Copyright 2014 Manlio Perillo. All rights reserved.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/fs.h>
#include <linux/delay.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Manlio Perillo");
MODULE_DESCRIPTION("A character device for uninterruptible sleep");

#define DEVICE_NAME "chardev"
#define DEVICE_FILE_NAME "unkill"
#define MAJOR_NUM 1975

// Default timeout in milliseconds.
// Can be overridden during build or installation.
#ifndef TIMEOUT
#define TIMEOUT 60 * 1000
#endif

static int timeout = TIMEOUT;

/*
 * Make timeout parameter visible in
 * /sys/module/unkill/parameters/timeout
 */
module_param(timeout, int, 0444);
MODULE_PARM_DESC(timeout, "Timeout in milliseconds");

static int device_open(struct inode *inode, struct file *file)
{
	printk(KERN_INFO "unkill: device_open will sleep for %d ms\n", timeout);

	/*
	 * Equivalent to:
	 * set_current_state(TASK_UNINTERRUPTIBLE);
	 * schedule_timeout();
	 */
	msleep(timeout);

	return -EBUSY;
}

struct file_operations Fops = {
	.open = device_open,
};

int init_module()
{
	int ret_val;

	ret_val = register_chrdev(MAJOR_NUM, DEVICE_NAME, &Fops);
	if (ret_val < 0) {
		printk(KERN_ALERT "register_chrdev() failed: %d\n", ret_val);

		return ret_val;
	}

	// Note that the device name is not important
	printk(KERN_INFO "unkill: mknod %s c %d 0\n", DEVICE_FILE_NAME, MAJOR_NUM);

	return 0;
}

void cleanup_module()
{
	(void) unregister_chrdev(MAJOR_NUM, DEVICE_NAME);
}