/*      $NetBSD: sysmon_taskq.c,v 1.23 2021/12/31 14:29:14 riastradh Exp $      */

/*
 * Copyright (c) 2001, 2003 Wasabi Systems, Inc.
 * All rights reserved.
 *
 * Written by Jason R. Thorpe for Wasabi Systems, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed for the NetBSD Project by
 *      Wasabi Systems, Inc.
 * 4. The name of Wasabi Systems, Inc. may not be used to endorse
 *    or promote products derived from this software without specific prior
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY WASABI SYSTEMS, INC. ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL WASABI SYSTEMS, INC
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * General purpose task queue for sysmon back-ends.  This can be
 * used to run callbacks that require thread context.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: sysmon_taskq.c,v 1.23 2021/12/31 14:29:14 riastradh Exp $");

#include <sys/param.h>
#include <sys/malloc.h>
#include <sys/queue.h>
#include <sys/proc.h>
#include <sys/kthread.h>
#include <sys/systm.h>
#include <sys/module.h>
#include <sys/once.h>

#include <dev/sysmon/sysmon_taskq.h>

struct sysmon_task {
        TAILQ_ENTRY(sysmon_task) st_list;
        void (*st_func)(void *);
        void *st_arg;
        u_int st_pri;
};

static TAILQ_HEAD(, sysmon_task) sysmon_task_queue =
    TAILQ_HEAD_INITIALIZER(sysmon_task_queue);

static kmutex_t sysmon_task_queue_mtx;
static kmutex_t sysmon_task_queue_init_mtx;
static kcondvar_t sysmon_task_queue_cv;

static int sysmon_task_queue_initialized;
static int sysmon_task_queue_cleanup_sem;
static struct lwp *sysmon_task_queue_lwp;
static void sysmon_task_queue_thread(void *);

MODULE(MODULE_CLASS_MISC, sysmon_taskq, NULL);

/*
 * XXX  Normally, all initialization would be handled as part of
 *      the module(9) framework.  However, there are a number of
 *      users of the sysmon_taskq facility that are not modular,
 *      and these can directly call sysmon_task_queue_init()
 *      directly.  To accommodate these non-standard users, we
 *      make sure that sysmon_task_queue_init() handles multiple
 *      invocations.  And we also ensure that, if any non-module
 *      user exists, we don't allow the module to be unloaded.
 *      (We can't use module_hold() for this, since the module(9)
 *      framework itself isn't necessarily initialized yet.)
 */

/*
 * tq_preinit:
 *
 *      Early one-time initialization of task-queue
 */

ONCE_DECL(once_tq);

static int
tq_preinit(void)
{

        mutex_init(&sysmon_task_queue_mtx, MUTEX_DEFAULT, IPL_VM);
        mutex_init(&sysmon_task_queue_init_mtx, MUTEX_DEFAULT, IPL_NONE);
        cv_init(&sysmon_task_queue_cv, "smtaskq");
        sysmon_task_queue_initialized = 0;

        return 0;
}

/*
 * sysmon_task_queue_init:
 *
 *      Initialize the sysmon task queue.
 */
void
sysmon_task_queue_init(void)
{
        int error;

        (void)RUN_ONCE(&once_tq, tq_preinit);

        mutex_enter(&sysmon_task_queue_init_mtx);
        if (sysmon_task_queue_initialized++) {
                mutex_exit(&sysmon_task_queue_init_mtx);
                return;
        }

        mutex_exit(&sysmon_task_queue_init_mtx);

        error = kthread_create(PRI_NONE, KTHREAD_MPSAFE, NULL,
            sysmon_task_queue_thread, NULL, &sysmon_task_queue_lwp, "sysmon");
        if (error) {
                printf("Unable to create sysmon task queue thread, "
                    "error = %d\n", error);
                panic("sysmon_task_queue_init");
        }
}

/*
 * sysmon_task_queue_fini:
 *
 *      Tear town the sysmon task queue.
 */
int
sysmon_task_queue_fini(void)
{

        if (sysmon_task_queue_initialized > 1)
                return EBUSY;

        mutex_enter(&sysmon_task_queue_mtx);

        sysmon_task_queue_cleanup_sem = 1;
        cv_signal(&sysmon_task_queue_cv);

        while (sysmon_task_queue_cleanup_sem != 0)
                cv_wait(&sysmon_task_queue_cv,
                        &sysmon_task_queue_mtx);

        mutex_exit(&sysmon_task_queue_mtx);

        return 0;
}

/*
 * sysmon_task_queue_thread:
 *
 *      The sysmon task queue execution thread.  We execute callbacks that
 *      have been queued for us.
 */
static void
sysmon_task_queue_thread(void *arg)
{
        struct sysmon_task *st;

        /*
         * Run through all the tasks before we check for the exit
         * condition; it's probably more important to actually run
         * all the tasks before we exit.
         */
        mutex_enter(&sysmon_task_queue_mtx);
        for (;;) {
                st = TAILQ_FIRST(&sysmon_task_queue);
                if (st != NULL) {
                        TAILQ_REMOVE(&sysmon_task_queue, st, st_list);
                        mutex_exit(&sysmon_task_queue_mtx);
                        (*st->st_func)(st->st_arg);
                        free(st, M_TEMP);
                        mutex_enter(&sysmon_task_queue_mtx);
                } else {
                        /* Check for the exit condition. */
                        if (sysmon_task_queue_cleanup_sem != 0)
                                break;
                        cv_wait(&sysmon_task_queue_cv, &sysmon_task_queue_mtx);
                }
        }
        /* Time to die. */
        sysmon_task_queue_cleanup_sem = 0;
        cv_broadcast(&sysmon_task_queue_cv);
        mutex_exit(&sysmon_task_queue_mtx);
        kthread_exit(0);
}

static void
sysmon_task_queue_sched_task(struct sysmon_task *st)
{
        struct sysmon_task *lst;

        mutex_enter(&sysmon_task_queue_mtx);
        TAILQ_FOREACH(lst, &sysmon_task_queue, st_list) {
                if (st->st_pri > lst->st_pri) {
                        TAILQ_INSERT_BEFORE(lst, st, st_list);
                        break;
                }
        }

        if (lst == NULL)
                TAILQ_INSERT_TAIL(&sysmon_task_queue, st, st_list);

        cv_broadcast(&sysmon_task_queue_cv);
        mutex_exit(&sysmon_task_queue_mtx);
}

/*
 * sysmon_task_queue_sched:
 *
 *      Schedule a task for deferred execution.
 */
int
sysmon_task_queue_sched(u_int pri, void (*func)(void *), void *arg)
{
        struct sysmon_task *st;

        (void)RUN_ONCE(&once_tq, tq_preinit);

        if (sysmon_task_queue_lwp == NULL)
                aprint_debug("WARNING: Callback scheduled before sysmon "
                    "task queue thread present\n");

        if (func == NULL)
                return EINVAL;

        st = malloc(sizeof(*st), M_TEMP, M_NOWAIT);
        if (st == NULL)
                return ENOMEM;

        st->st_func = func;
        st->st_arg = arg;
        st->st_pri = pri;

        sysmon_task_queue_sched_task(st);

        return 0;
}

struct tqbarrier {
        kmutex_t        lock;
        kcondvar_t      cv;
        bool            done;
};

static void
tqbarrier_task(void *cookie)
{
        struct tqbarrier *bar = cookie;

        mutex_enter(&bar->lock);
        bar->done = true;
        cv_broadcast(&bar->cv);
        mutex_exit(&bar->lock);
}

/*
 * sysmon_task_queue_barrier:
 *
 *      Wait for the completion of all tasks at priority pri or lower
 *      currently queued at the time of the call.
 */
void
sysmon_task_queue_barrier(u_int pri)
{
        struct sysmon_task *st;
        struct tqbarrier bar;

        (void)RUN_ONCE(&once_tq, tq_preinit);

        KASSERT(sysmon_task_queue_lwp);
        KASSERT(curlwp != sysmon_task_queue_lwp);

        mutex_init(&bar.lock, MUTEX_DEFAULT, IPL_NONE);
        cv_init(&bar.cv, "sysmontq");
        bar.done = false;

        st = malloc(sizeof(*st), M_TEMP, M_WAITOK);
        st->st_func = &tqbarrier_task;
        st->st_arg = &bar;
        st->st_pri = pri;

        sysmon_task_queue_sched_task(st);

        mutex_enter(&bar.lock);
        while (!bar.done)
                cv_wait(&bar.cv, &bar.lock);
        mutex_exit(&bar.lock);

        cv_destroy(&bar.cv);
        mutex_destroy(&bar.lock);
}

static int
sysmon_taskq_modcmd(modcmd_t cmd, void *arg)
{
        int ret;

        switch (cmd) {
        case MODULE_CMD_INIT:
                sysmon_task_queue_init();
                ret = 0;
                break;
        case MODULE_CMD_FINI:
                ret = sysmon_task_queue_fini();
                break;
        case MODULE_CMD_STAT:
        default:
                ret = ENOTTY;
        }

        return ret;
}