/*
 * Copyright (c) 2014-2020 François Tigeot <ftigeot@wolfpond.org>
 * All rights reserved.
 *
 * 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 unmodified, 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 THE AUTHOR 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.
 */
#ifndef _LINUX_COMPLETION_H_
#define _LINUX_COMPLETION_H_

#include <linux/wait.h>
#include <linux/errno.h>

#include <sys/kernel.h>

struct completion {
        unsigned int done;
        wait_queue_head_t wait;
};

static inline void
init_completion(struct completion *c)
{
        c->done = 0;
        init_waitqueue_head(&c->wait);
}

static inline void
reinit_completion(struct completion *c)
{
        c->done = 0;
}

#define INIT_COMPLETION(c)      (c.done = 0)

/*
 * Completion interlock and wakeup.  Be careful not to execute the wakeup
 * from inside the spinlock as this can deadlock if the IPIQ fifo is full.
 * (also note that wakeup() is asynchronous anyway, so no point doing that).
 */
static inline void
complete(struct completion *c)
{
        lockmgr(&c->wait.lock, LK_EXCLUSIVE);
        if (c->done != UINT_MAX)
                c->done++;
        lockmgr(&c->wait.lock, LK_RELEASE);
        wakeup_one(&c->wait);
}

static inline void
complete_all(struct completion *c)
{
        lockmgr(&c->wait.lock, LK_EXCLUSIVE);
        c->done = UINT_MAX;
        lockmgr(&c->wait.lock, LK_RELEASE);
        wakeup(&c->wait);
}

static inline long
__wait_for_completion_generic(struct completion *c,
                              unsigned long timeout, int flags)
{
        int start_jiffies, elapsed_jiffies, remaining_jiffies;
        bool timeout_expired = false, awakened = false;
        long ret = 1;

        start_jiffies = ticks;

        lockmgr(&c->wait.lock, LK_EXCLUSIVE);
        while (c->done == 0 && !timeout_expired) {
                ret = lksleep(&c->wait, &c->wait.lock, flags, "lwfcg", timeout);
                switch(ret) {
                case EWOULDBLOCK:
                        timeout_expired = true;
                        ret = 0;
                        break;
                case ERESTART:
                        ret = -ERESTARTSYS;
                        break;
                case 0:
                        awakened = true;
                        break;
                }
        }
        if (c->done && c->done != UINT_MAX)
                --c->done;
        lockmgr(&c->wait.lock, LK_RELEASE);

        if (awakened) {
                elapsed_jiffies = ticks - start_jiffies;
                remaining_jiffies = timeout - elapsed_jiffies;
                if (remaining_jiffies > 0)
                        ret = remaining_jiffies;
        }

        return ret;
}

int wait_for_completion_interruptible(struct completion *c);

static inline long
wait_for_completion_interruptible_timeout(struct completion *c,
                unsigned long timeout)
{
        return __wait_for_completion_generic(c, timeout, PCATCH);
}

static inline unsigned long
wait_for_completion_timeout(struct completion *c, unsigned long timeout)
{
        return __wait_for_completion_generic(c, timeout, 0);
}

void wait_for_completion(struct completion *c);

/*
 * try_wait_for_completion: try to decrement a completion without blocking
 *                          its thread
 * return: false if the completion thread would need to be blocked/queued
 *         true if a non-blocking decrement was successful
 */
static inline bool
try_wait_for_completion(struct completion *c)
{
        bool ret = false;

        /* we can't decrement c->done below 0 */
        if (READ_ONCE(c->done) == 0)
                return false;

        lockmgr(&c->wait.lock, LK_EXCLUSIVE);
        if (c->done > 0) {
                c->done--;
                ret = true;
        }
        lockmgr(&c->wait.lock, LK_RELEASE);

        return ret;
}

#endif  /* _LINUX_COMPLETION_H_ */