/*

 * Copyright (c) 2020 Red Hat, Inc.

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 * 

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 * 

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

 * 02110-1301, USA. 

 *

 * $Id: //eng/vdo-releases/aluminum/src/c++/vdo/kernel/deadlockQueue.h#1 $

 */

#ifndef DEADLOCK_QUEUE_H

#define DEADLOCK_QUEUE_H

#include <linux/kernel.h>

#include "bio.h"

/**

 * A holding space for incoming bios if we're not able to block until VIOs

 * become available to process them.

 **/

typedef struct deadlockQueue {

  /* Protection for the other fields. */

  spinlock_t      lock;

  /* List of bios we had to accept but don't have VIOs for. */

  struct bio_list list;

  /*

   * Arrival time to use for statistics tracking for the above bios, since we

   * haven't the space to store individual arrival times for each.

   */

  Jiffies         arrivalTime;

} DeadlockQueue;

/**

 * Initialize the DeadlockQueue structure.

 *

 * @param queue  The structure to initialize

 **/

void initializeDeadlockQueue(DeadlockQueue *queue);

/**

 * Add an incoming bio to the list of saved-up bios we're not ready to start

 * processing yet.

 *

 * This excess buffering on top of what the caller implements is generally a

 * bad idea, and should be used only when necessary, such as to avoid a

 * possible deadlock situation.

 *

 * @param queue        The incoming-bio queue structure

 * @param bio          The new incoming bio to save

 * @param arrivalTime  The arrival time of this new bio

 **/

void addToDeadlockQueue(DeadlockQueue *queue, BIO *bio, Jiffies arrivalTime);

/**

 * Pull an incoming bio off the queue.

 *

 * The arrival time returned may be incorrect if multiple bios were saved, as

 * there is no per-bio storage used, only one saved arrival time for the whole

 * queue.

 *

 * @param [in]  queue        The incoming-bio queue

 * @param [out] arrivalTime  The arrival time to use for this bio

 *

 * @return  a BIO pointer, or NULL if none were queued

 **/

static inline BIO *pollDeadlockQueue(DeadlockQueue *queue,

                                     Jiffies       *arrivalTime)

{

  spin_lock(&queue->lock);

  BIO *bio = bio_list_pop(&queue->list);

  if (unlikely(bio != NULL)) {

    *arrivalTime = queue->arrivalTime;

  }

  spin_unlock(&queue->lock);

  return bio;

}

#endif // DEADLOCK_QUEUE_H