completions.c

/*
 * completions.c
 */
#include <linux/completion.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/kthread.h>
#include <linux/module.h>

static struct {
    struct completion crank_comp;
    struct completion flywheel_comp;
} machine;

static int machine_crank_thread(void *arg)
{
    pr_info("Turn the crank\n");

    complete_all(&machine.crank_comp);
    complete_and_exit(&machine.crank_comp, 0);
}

static int machine_flywheel_spinup_thread(void *arg)
{
    wait_for_completion(&machine.crank_comp);

    pr_info("Flywheel spins up\n");

    complete_all(&machine.flywheel_comp);
    complete_and_exit(&machine.flywheel_comp, 0);
}

static int completions_init(void)
{
    struct task_struct *crank_thread;
    struct task_struct *flywheel_thread;

    pr_info("completions example\n");

    init_completion(&machine.crank_comp);
    init_completion(&machine.flywheel_comp);

    crank_thread = kthread_create(machine_crank_thread, NULL, "KThread Crank");
    if (IS_ERR(crank_thread))
        goto ERROR_THREAD_1;

    flywheel_thread = kthread_create(machine_flywheel_spinup_thread, NULL,
                                     "KThread Flywheel");
    if (IS_ERR(flywheel_thread))
        goto ERROR_THREAD_2;

    wake_up_process(flywheel_thread);
    wake_up_process(crank_thread);

    return 0;

ERROR_THREAD_2:
    kthread_stop(crank_thread);
ERROR_THREAD_1:

    return -1;
}

static void completions_exit(void)
{
    wait_for_completion(&machine.crank_comp);
    wait_for_completion(&machine.flywheel_comp);

    pr_info("completions exit\n");
}

module_init(completions_init);
module_exit(completions_exit);

MODULE_DESCRIPTION("Completions example");
MODULE_LICENSE("GPL");