#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/hrtimer.h>

#define THREAD_PRIORITY (80)
#define THREAD_SCHEDULER SCHED_FIFO
#define MODULE_NAME "test-module"
#define KLOG_PREFIX MODULE_NAME ": "

struct task_struct *thread;
static ktime_t thread_next;
static ktime_t now;

/*
 * Threaded Runloop
 */
static int runloop(void *unused)
{

	struct sched_param param = { .sched_priority = THREAD_PRIORITY };

	/* Set realtime priorty */
	sched_setscheduler(thread, THREAD_SCHEDULER, &param);

	/* Allow SIGTERM signal */
	allow_signal(SIGTERM);

	/* Calculate first shot */
	now = ktime_get();
	thread_next = ktime_add_us(now, 500);

	do {
		set_current_state(TASK_UNINTERRUPTIBLE);
		schedule_hrtimeout(&thread_next, HRTIMER_MODE_ABS);

		thread_next = ktime_add_us(thread_next, 500);
	} while (!kthread_should_stop());

	printk(KERN_INFO KLOG_PREFIX "Thread exited\n");
	return 0;
}

int __init init_test_module(void)
{
	/* Create kernel thread */
	thread = kthread_run((void *)&runloop, NULL, MODULE_NAME);
        if (IS_ERR(thread)) 
        {
		printk(KERN_INFO KLOG_PREFIX ": unable to start kernel thread\n");
                return -ENOMEM;
        }

	return 0;
}

void __exit cleanup_test_module(void)
{
        if(thread != NULL)
                kthread_stop(thread);
        thread = NULL;
}

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Stefan Agner <stefan@anger.ch");
MODULE_DESCRIPTION("kthread test module");

module_init(init_test_module);
module_exit(cleanup_test_module);