/*

   * Copyright (C) 1991, 1992 Linus Torvalds
   * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
   * Elevator latency, (C) 2000  Andrea Arcangeli <andrea@suse.de> SuSE
   * Queue request tables / lock, selectable elevator, Jens Axboe <axboe@suse.de>

   * kernel-doc documentation started by NeilBrown <neilb@cse.unsw.edu.au>
   *	-  July2000

   * bio rewrite, highmem i/o, etc, Jens Axboe <axboe@suse.de> - may 2001
   */
  
  /*
   * This handles all read/write requests to block devices
   */

  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/backing-dev.h>
  #include <linux/bio.h>
  #include <linux/blkdev.h>

  #include <linux/blk-mq.h>

  #include <linux/highmem.h>
  #include <linux/mm.h>
  #include <linux/kernel_stat.h>
  #include <linux/string.h>
  #include <linux/init.h>

  #include <linux/completion.h>
  #include <linux/slab.h>
  #include <linux/swap.h>
  #include <linux/writeback.h>

  #include <linux/task_io_accounting_ops.h>

  #include <linux/fault-inject.h>

  #include <linux/list_sort.h>

  #include <linux/delay.h>

  #include <linux/ratelimit.h>

  #include <linux/pm_runtime.h>

  
  #define CREATE_TRACE_POINTS
  #include <trace/events/block.h>

  #include "blk.h"

  #include "blk-cgroup.h"

  #include "blk-mq.h"

  EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);

  EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);

  EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_complete);

  EXPORT_TRACEPOINT_SYMBOL_GPL(block_unplug);

  DEFINE_IDA(blk_queue_ida);

  /*
   * For the allocated request tables
   */

  struct kmem_cache *request_cachep = NULL;

  
  /*
   * For queue allocation
   */

  struct kmem_cache *blk_requestq_cachep;

  
  /*

   * Controlling structure to kblockd
   */

  static struct workqueue_struct *kblockd_workqueue;

  void blk_queue_congestion_threshold(struct request_queue *q)

  {
  	int nr;
  
  	nr = q->nr_requests - (q->nr_requests / 8) + 1;
  	if (nr > q->nr_requests)
  		nr = q->nr_requests;
  	q->nr_congestion_on = nr;
  
  	nr = q->nr_requests - (q->nr_requests / 8) - (q->nr_requests / 16) - 1;
  	if (nr < 1)
  		nr = 1;
  	q->nr_congestion_off = nr;
  }

  /**
   * blk_get_backing_dev_info - get the address of a queue's backing_dev_info
   * @bdev:	device
   *
   * Locates the passed device's request queue and returns the address of its
   * backing_dev_info
   *
   * Will return NULL if the request queue cannot be located.
   */
  struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
  {
  	struct backing_dev_info *ret = NULL;

  	struct request_queue *q = bdev_get_queue(bdev);

  
  	if (q)
  		ret = &q->backing_dev_info;
  	return ret;
  }

  EXPORT_SYMBOL(blk_get_backing_dev_info);

  void blk_rq_init(struct request_queue *q, struct request *rq)

  {

  	memset(rq, 0, sizeof(*rq));

  	INIT_LIST_HEAD(&rq->queuelist);

  	INIT_LIST_HEAD(&rq->timeout_list);

  	rq->cpu = -1;

  	rq->q = q;

  	rq->__sector = (sector_t) -1;

  	INIT_HLIST_NODE(&rq->hash);
  	RB_CLEAR_NODE(&rq->rb_node);

  	rq->cmd = rq->__cmd;

  	rq->cmd_len = BLK_MAX_CDB;

  	rq->tag = -1;

  	rq->start_time = jiffies;

  	set_start_time_ns(rq);

  	rq->part = NULL;

  }

  EXPORT_SYMBOL(blk_rq_init);

  static void req_bio_endio(struct request *rq, struct bio *bio,
  			  unsigned int nbytes, int error)

  {

  	if (error)
  		clear_bit(BIO_UPTODATE, &bio->bi_flags);
  	else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
  		error = -EIO;

  	if (unlikely(rq->cmd_flags & REQ_QUIET))
  		set_bit(BIO_QUIET, &bio->bi_flags);

  	bio_advance(bio, nbytes);

  	/* don't actually finish bio if it's part of flush sequence */

  	if (bio->bi_iter.bi_size == 0 && !(rq->cmd_flags & REQ_FLUSH_SEQ))

  		bio_endio(bio, error);

  }

  void blk_dump_rq_flags(struct request *rq, char *msg)
  {
  	int bit;

  	printk(KERN_INFO "%s: dev %s: type=%x, flags=%llx
  ", msg,

  		rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->cmd_type,

  		(unsigned long long) rq->cmd_flags);

  	printk(KERN_INFO "  sector %llu, nr/cnr %u/%u
  ",
  	       (unsigned long long)blk_rq_pos(rq),
  	       blk_rq_sectors(rq), blk_rq_cur_sectors(rq));

  	printk(KERN_INFO "  bio %p, biotail %p, buffer %p, len %u
  ",

  	       rq->bio, rq->biotail, rq->buffer, blk_rq_bytes(rq));

  	if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {

  		printk(KERN_INFO "  cdb: ");

  		for (bit = 0; bit < BLK_MAX_CDB; bit++)

  			printk("%02x ", rq->cmd[bit]);
  		printk("
  ");
  	}
  }

  EXPORT_SYMBOL(blk_dump_rq_flags);

  static void blk_delay_work(struct work_struct *work)

  {

  	struct request_queue *q;

  	q = container_of(work, struct request_queue, delay_work.work);
  	spin_lock_irq(q->queue_lock);

  	__blk_run_queue(q);

  	spin_unlock_irq(q->queue_lock);

  }

  
  /**

   * blk_delay_queue - restart queueing after defined interval
   * @q:		The &struct request_queue in question
   * @msecs:	Delay in msecs

   *
   * Description:

   *   Sometimes queueing needs to be postponed for a little while, to allow
   *   resources to come back. This function will make sure that queueing is

   *   restarted around the specified time. Queue lock must be held.

   */
  void blk_delay_queue(struct request_queue *q, unsigned long msecs)

  {

  	if (likely(!blk_queue_dead(q)))
  		queue_delayed_work(kblockd_workqueue, &q->delay_work,
  				   msecs_to_jiffies(msecs));

  }

  EXPORT_SYMBOL(blk_delay_queue);

  /**
   * blk_start_queue - restart a previously stopped queue

   * @q:    The &struct request_queue in question

   *
   * Description:
   *   blk_start_queue() will clear the stop flag on the queue, and call
   *   the request_fn for the queue if it was in a stopped state when
   *   entered. Also see blk_stop_queue(). Queue lock must be held.
   **/

  void blk_start_queue(struct request_queue *q)

  {

  	WARN_ON(!irqs_disabled());

  	queue_flag_clear(QUEUE_FLAG_STOPPED, q);

  	__blk_run_queue(q);

  }

  EXPORT_SYMBOL(blk_start_queue);
  
  /**
   * blk_stop_queue - stop a queue

   * @q:    The &struct request_queue in question

   *
   * Description:
   *   The Linux block layer assumes that a block driver will consume all
   *   entries on the request queue when the request_fn strategy is called.
   *   Often this will not happen, because of hardware limitations (queue
   *   depth settings). If a device driver gets a 'queue full' response,
   *   or if it simply chooses not to queue more I/O at one point, it can
   *   call this function to prevent the request_fn from being called until
   *   the driver has signalled it's ready to go again. This happens by calling
   *   blk_start_queue() to restart queue operations. Queue lock must be held.
   **/

  void blk_stop_queue(struct request_queue *q)

  {

  	cancel_delayed_work(&q->delay_work);

  	queue_flag_set(QUEUE_FLAG_STOPPED, q);

  }
  EXPORT_SYMBOL(blk_stop_queue);
  
  /**
   * blk_sync_queue - cancel any pending callbacks on a queue
   * @q: the queue
   *
   * Description:
   *     The block layer may perform asynchronous callback activity
   *     on a queue, such as calling the unplug function after a timeout.
   *     A block device may call blk_sync_queue to ensure that any
   *     such activity is cancelled, thus allowing it to release resources

   *     that the callbacks might use. The caller must already have made sure

   *     that its ->make_request_fn will not re-add plugging prior to calling
   *     this function.
   *

   *     This function does not cancel any asynchronous activity arising
   *     out of elevator or throttling code. That would require elevaotor_exit()

   *     and blkcg_exit_queue() to be called with queue lock initialized.

   *

   */
  void blk_sync_queue(struct request_queue *q)
  {

  	del_timer_sync(&q->timeout);

  
  	if (q->mq_ops) {
  		struct blk_mq_hw_ctx *hctx;
  		int i;
  
  		queue_for_each_hw_ctx(q, hctx, i)
  			cancel_delayed_work_sync(&hctx->delayed_work);
  	} else {
  		cancel_delayed_work_sync(&q->delay_work);
  	}

  }
  EXPORT_SYMBOL(blk_sync_queue);
  
  /**

   * __blk_run_queue_uncond - run a queue whether or not it has been stopped
   * @q:	The queue to run
   *
   * Description:
   *    Invoke request handling on a queue if there are any pending requests.
   *    May be used to restart request handling after a request has completed.
   *    This variant runs the queue whether or not the queue has been
   *    stopped. Must be called with the queue lock held and interrupts
   *    disabled. See also @blk_run_queue.
   */
  inline void __blk_run_queue_uncond(struct request_queue *q)
  {
  	if (unlikely(blk_queue_dead(q)))
  		return;

  	/*
  	 * Some request_fn implementations, e.g. scsi_request_fn(), unlock
  	 * the queue lock internally. As a result multiple threads may be
  	 * running such a request function concurrently. Keep track of the
  	 * number of active request_fn invocations such that blk_drain_queue()
  	 * can wait until all these request_fn calls have finished.
  	 */
  	q->request_fn_active++;

  	q->request_fn(q);

  	q->request_fn_active--;

  }
  
  /**

   * __blk_run_queue - run a single device queue

   * @q:	The queue to run

   *
   * Description:
   *    See @blk_run_queue. This variant must be called with the queue lock

   *    held and interrupts disabled.

   */

  void __blk_run_queue(struct request_queue *q)

  {

  	if (unlikely(blk_queue_stopped(q)))
  		return;

  	__blk_run_queue_uncond(q);

  }
  EXPORT_SYMBOL(__blk_run_queue);

  /**

   * blk_run_queue_async - run a single device queue in workqueue context
   * @q:	The queue to run
   *
   * Description:
   *    Tells kblockd to perform the equivalent of @blk_run_queue on behalf

   *    of us. The caller must hold the queue lock.

   */
  void blk_run_queue_async(struct request_queue *q)
  {

  	if (likely(!blk_queue_stopped(q) && !blk_queue_dead(q)))

  		mod_delayed_work(kblockd_workqueue, &q->delay_work, 0);

  }

  EXPORT_SYMBOL(blk_run_queue_async);

  
  /**

   * blk_run_queue - run a single device queue
   * @q: The queue to run

   *
   * Description:
   *    Invoke request handling on this queue, if it has pending work to do.

   *    May be used to restart queueing when a request has completed.

   */
  void blk_run_queue(struct request_queue *q)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(q->queue_lock, flags);

  	__blk_run_queue(q);

  	spin_unlock_irqrestore(q->queue_lock, flags);
  }
  EXPORT_SYMBOL(blk_run_queue);

  void blk_put_queue(struct request_queue *q)

  {
  	kobject_put(&q->kobj);
  }

  EXPORT_SYMBOL(blk_put_queue);

  /**

   * __blk_drain_queue - drain requests from request_queue

   * @q: queue to drain

   * @drain_all: whether to drain all requests or only the ones w/ ELVPRIV

   *

   * Drain requests from @q.  If @drain_all is set, all requests are drained.
   * If not, only ELVPRIV requests are drained.  The caller is responsible
   * for ensuring that no new requests which need to be drained are queued.

   */

  static void __blk_drain_queue(struct request_queue *q, bool drain_all)
  	__releases(q->queue_lock)
  	__acquires(q->queue_lock)

  {

  	int i;

  	lockdep_assert_held(q->queue_lock);

  	while (true) {

  		bool drain = false;

  		/*
  		 * The caller might be trying to drain @q before its
  		 * elevator is initialized.
  		 */
  		if (q->elevator)
  			elv_drain_elevator(q);

  		blkcg_drain_queue(q);

  		/*
  		 * This function might be called on a queue which failed

  		 * driver init after queue creation or is not yet fully
  		 * active yet.  Some drivers (e.g. fd and loop) get unhappy
  		 * in such cases.  Kick queue iff dispatch queue has
  		 * something on it and @q has request_fn set.

  		 */

  		if (!list_empty(&q->queue_head) && q->request_fn)

  			__blk_run_queue(q);

  		drain |= q->nr_rqs_elvpriv;

  		drain |= q->request_fn_active;

  
  		/*
  		 * Unfortunately, requests are queued at and tracked from
  		 * multiple places and there's no single counter which can
  		 * be drained.  Check all the queues and counters.
  		 */
  		if (drain_all) {
  			drain |= !list_empty(&q->queue_head);
  			for (i = 0; i < 2; i++) {

  				drain |= q->nr_rqs[i];

  				drain |= q->in_flight[i];
  				drain |= !list_empty(&q->flush_queue[i]);
  			}
  		}

  		if (!drain)

  			break;

  
  		spin_unlock_irq(q->queue_lock);

  		msleep(10);

  
  		spin_lock_irq(q->queue_lock);

  	}

  
  	/*
  	 * With queue marked dead, any woken up waiter will fail the
  	 * allocation path, so the wakeup chaining is lost and we're
  	 * left with hung waiters. We need to wake up those waiters.
  	 */
  	if (q->request_fn) {

  		struct request_list *rl;

  		blk_queue_for_each_rl(rl, q)
  			for (i = 0; i < ARRAY_SIZE(rl->wait); i++)
  				wake_up_all(&rl->wait[i]);

  	}

  }

  /**

   * blk_queue_bypass_start - enter queue bypass mode
   * @q: queue of interest
   *
   * In bypass mode, only the dispatch FIFO queue of @q is used.  This
   * function makes @q enter bypass mode and drains all requests which were

   * throttled or issued before.  On return, it's guaranteed that no request

   * is being throttled or has ELVPRIV set and blk_queue_bypass() %true
   * inside queue or RCU read lock.

   */
  void blk_queue_bypass_start(struct request_queue *q)
  {

  	bool drain;

  	spin_lock_irq(q->queue_lock);

  	drain = !q->bypass_depth++;

  	queue_flag_set(QUEUE_FLAG_BYPASS, q);
  	spin_unlock_irq(q->queue_lock);

  	if (drain) {

  		spin_lock_irq(q->queue_lock);
  		__blk_drain_queue(q, false);
  		spin_unlock_irq(q->queue_lock);

  		/* ensure blk_queue_bypass() is %true inside RCU read lock */
  		synchronize_rcu();
  	}

  }
  EXPORT_SYMBOL_GPL(blk_queue_bypass_start);
  
  /**
   * blk_queue_bypass_end - leave queue bypass mode
   * @q: queue of interest
   *
   * Leave bypass mode and restore the normal queueing behavior.
   */
  void blk_queue_bypass_end(struct request_queue *q)
  {
  	spin_lock_irq(q->queue_lock);
  	if (!--q->bypass_depth)
  		queue_flag_clear(QUEUE_FLAG_BYPASS, q);
  	WARN_ON_ONCE(q->bypass_depth < 0);
  	spin_unlock_irq(q->queue_lock);
  }
  EXPORT_SYMBOL_GPL(blk_queue_bypass_end);
  
  /**

   * blk_cleanup_queue - shutdown a request queue
   * @q: request queue to shutdown
   *

   * Mark @q DYING, drain all pending requests, mark @q DEAD, destroy and
   * put it.  All future requests will be failed immediately with -ENODEV.

   */

  void blk_cleanup_queue(struct request_queue *q)

  {

  	spinlock_t *lock = q->queue_lock;

  	/* mark @q DYING, no new request or merges will be allowed afterwards */

  	mutex_lock(&q->sysfs_lock);

  	queue_flag_set_unlocked(QUEUE_FLAG_DYING, q);

  	spin_lock_irq(lock);

  	/*

  	 * A dying queue is permanently in bypass mode till released.  Note

  	 * that, unlike blk_queue_bypass_start(), we aren't performing
  	 * synchronize_rcu() after entering bypass mode to avoid the delay
  	 * as some drivers create and destroy a lot of queues while
  	 * probing.  This is still safe because blk_release_queue() will be
  	 * called only after the queue refcnt drops to zero and nothing,
  	 * RCU or not, would be traversing the queue by then.
  	 */

  	q->bypass_depth++;
  	queue_flag_set(QUEUE_FLAG_BYPASS, q);

  	queue_flag_set(QUEUE_FLAG_NOMERGES, q);
  	queue_flag_set(QUEUE_FLAG_NOXMERGES, q);

  	queue_flag_set(QUEUE_FLAG_DYING, q);

  	spin_unlock_irq(lock);
  	mutex_unlock(&q->sysfs_lock);

  	/*
  	 * Drain all requests queued before DYING marking. Set DEAD flag to
  	 * prevent that q->request_fn() gets invoked after draining finished.
  	 */

  	if (q->mq_ops) {
  		blk_mq_drain_queue(q);
  		spin_lock_irq(lock);
  	} else {
  		spin_lock_irq(lock);
  		__blk_drain_queue(q, true);
  	}

  	queue_flag_set(QUEUE_FLAG_DEAD, q);

  	spin_unlock_irq(lock);

  
  	/* @q won't process any more request, flush async actions */
  	del_timer_sync(&q->backing_dev_info.laptop_mode_wb_timer);
  	blk_sync_queue(q);

  	spin_lock_irq(lock);
  	if (q->queue_lock != &q->__queue_lock)
  		q->queue_lock = &q->__queue_lock;
  	spin_unlock_irq(lock);

  	/* @q is and will stay empty, shutdown and put */

  	blk_put_queue(q);
  }

  EXPORT_SYMBOL(blk_cleanup_queue);

  int blk_init_rl(struct request_list *rl, struct request_queue *q,
  		gfp_t gfp_mask)

  {

  	if (unlikely(rl->rq_pool))
  		return 0;

  	rl->q = q;

  	rl->count[BLK_RW_SYNC] = rl->count[BLK_RW_ASYNC] = 0;
  	rl->starved[BLK_RW_SYNC] = rl->starved[BLK_RW_ASYNC] = 0;

  	init_waitqueue_head(&rl->wait[BLK_RW_SYNC]);
  	init_waitqueue_head(&rl->wait[BLK_RW_ASYNC]);

  	rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,

  					  mempool_free_slab, request_cachep,

  					  gfp_mask, q->node);

  	if (!rl->rq_pool)
  		return -ENOMEM;
  
  	return 0;
  }

  void blk_exit_rl(struct request_list *rl)
  {
  	if (rl->rq_pool)
  		mempool_destroy(rl->rq_pool);
  }

  struct request_queue *blk_alloc_queue(gfp_t gfp_mask)

  {

  	return blk_alloc_queue_node(gfp_mask, NUMA_NO_NODE);

  }
  EXPORT_SYMBOL(blk_alloc_queue);

  struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)

  {

  	struct request_queue *q;

  	int err;

  	q = kmem_cache_alloc_node(blk_requestq_cachep,

  				gfp_mask | __GFP_ZERO, node_id);

  	if (!q)
  		return NULL;

  	if (percpu_counter_init(&q->mq_usage_counter, 0))
  		goto fail_q;

  	q->id = ida_simple_get(&blk_queue_ida, 0, 0, gfp_mask);

  	if (q->id < 0)

  		goto fail_c;

  	q->backing_dev_info.ra_pages =
  			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
  	q->backing_dev_info.state = 0;
  	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;

  	q->backing_dev_info.name = "block";

  	q->node = node_id;

  	err = bdi_init(&q->backing_dev_info);

  	if (err)
  		goto fail_id;

  	setup_timer(&q->backing_dev_info.laptop_mode_wb_timer,
  		    laptop_mode_timer_fn, (unsigned long) q);

  	setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q);

  	INIT_LIST_HEAD(&q->queue_head);

  	INIT_LIST_HEAD(&q->timeout_list);

  	INIT_LIST_HEAD(&q->icq_list);

  #ifdef CONFIG_BLK_CGROUP

  	INIT_LIST_HEAD(&q->blkg_list);

  #endif

  	INIT_LIST_HEAD(&q->flush_queue[0]);
  	INIT_LIST_HEAD(&q->flush_queue[1]);
  	INIT_LIST_HEAD(&q->flush_data_in_flight);

  	INIT_DELAYED_WORK(&q->delay_work, blk_delay_work);

  	kobject_init(&q->kobj, &blk_queue_ktype);

  	mutex_init(&q->sysfs_lock);

  	spin_lock_init(&q->__queue_lock);

  	/*
  	 * By default initialize queue_lock to internal lock and driver can
  	 * override it later if need be.
  	 */
  	q->queue_lock = &q->__queue_lock;

  	/*
  	 * A queue starts its life with bypass turned on to avoid
  	 * unnecessary bypass on/off overhead and nasty surprises during

  	 * init.  The initial bypass will be finished when the queue is
  	 * registered by blk_register_queue().

  	 */
  	q->bypass_depth = 1;
  	__set_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);

  	init_waitqueue_head(&q->mq_freeze_wq);

  	if (blkcg_init_queue(q))

  		goto fail_bdi;

  	return q;

  fail_bdi:
  	bdi_destroy(&q->backing_dev_info);

  fail_id:
  	ida_simple_remove(&blk_queue_ida, q->id);

  fail_c:
  	percpu_counter_destroy(&q->mq_usage_counter);

  fail_q:
  	kmem_cache_free(blk_requestq_cachep, q);
  	return NULL;

  }

  EXPORT_SYMBOL(blk_alloc_queue_node);

  
  /**
   * blk_init_queue  - prepare a request queue for use with a block device
   * @rfn:  The function to be called to process requests that have been
   *        placed on the queue.
   * @lock: Request queue spin lock
   *
   * Description:
   *    If a block device wishes to use the standard request handling procedures,
   *    which sorts requests and coalesces adjacent requests, then it must
   *    call blk_init_queue().  The function @rfn will be called when there
   *    are requests on the queue that need to be processed.  If the device
   *    supports plugging, then @rfn may not be called immediately when requests
   *    are available on the queue, but may be called at some time later instead.
   *    Plugged queues are generally unplugged when a buffer belonging to one
   *    of the requests on the queue is needed, or due to memory pressure.
   *
   *    @rfn is not required, or even expected, to remove all requests off the
   *    queue, but only as many as it can handle at a time.  If it does leave
   *    requests on the queue, it is responsible for arranging that the requests
   *    get dealt with eventually.
   *
   *    The queue spin lock must be held while manipulating the requests on the

   *    request queue; this lock will be taken also from interrupt context, so irq
   *    disabling is needed for it.

   *

   *    Function returns a pointer to the initialized request queue, or %NULL if

   *    it didn't succeed.
   *
   * Note:
   *    blk_init_queue() must be paired with a blk_cleanup_queue() call
   *    when the block device is deactivated (such as at module unload).
   **/

  struct request_queue *blk_init_queue(request_fn_proc *rfn, spinlock_t *lock)

  {

  	return blk_init_queue_node(rfn, lock, NUMA_NO_NODE);

  }
  EXPORT_SYMBOL(blk_init_queue);

  struct request_queue *

  blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
  {

  	struct request_queue *uninit_q, *q;

  	uninit_q = blk_alloc_queue_node(GFP_KERNEL, node_id);
  	if (!uninit_q)
  		return NULL;

  	uninit_q->flush_rq = kzalloc(sizeof(struct request), GFP_KERNEL);
  	if (!uninit_q->flush_rq)
  		goto out_cleanup_queue;

  	q = blk_init_allocated_queue(uninit_q, rfn, lock);

  	if (!q)

  		goto out_free_flush_rq;

  	return q;

  
  out_free_flush_rq:
  	kfree(uninit_q->flush_rq);
  out_cleanup_queue:
  	blk_cleanup_queue(uninit_q);
  	return NULL;

  }
  EXPORT_SYMBOL(blk_init_queue_node);
  
  struct request_queue *
  blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
  			 spinlock_t *lock)
  {

  	if (!q)
  		return NULL;

  	if (blk_init_rl(&q->root_rl, q, GFP_KERNEL))

  		return NULL;

  
  	q->request_fn		= rfn;

  	q->prep_rq_fn		= NULL;

  	q->unprep_rq_fn		= NULL;

  	q->queue_flags		|= QUEUE_FLAG_DEFAULT;

  
  	/* Override internal queue lock with supplied lock pointer */
  	if (lock)
  		q->queue_lock		= lock;

  	/*
  	 * This also sets hw/phys segments, boundary and size
  	 */

  	blk_queue_make_request(q, blk_queue_bio);

  	q->sg_reserved_size = INT_MAX;

  	/* Protect q->elevator from elevator_change */
  	mutex_lock(&q->sysfs_lock);

  	/* init elevator */

  	if (elevator_init(q, NULL)) {
  		mutex_unlock(&q->sysfs_lock);

  		return NULL;

  	}
  
  	mutex_unlock(&q->sysfs_lock);

  	return q;

  }

  EXPORT_SYMBOL(blk_init_allocated_queue);

  bool blk_get_queue(struct request_queue *q)

  {

  	if (likely(!blk_queue_dying(q))) {

  		__blk_get_queue(q);
  		return true;

  	}

  	return false;

  }

  EXPORT_SYMBOL(blk_get_queue);

  static inline void blk_free_request(struct request_list *rl, struct request *rq)

  {

  	if (rq->cmd_flags & REQ_ELVPRIV) {

  		elv_put_request(rl->q, rq);

  		if (rq->elv.icq)

  			put_io_context(rq->elv.icq->ioc);

  	}

  	mempool_free(rq, rl->rq_pool);

  }

  /*
   * ioc_batching returns true if the ioc is a valid batching request and
   * should be given priority access to a request.
   */

  static inline int ioc_batching(struct request_queue *q, struct io_context *ioc)

  {
  	if (!ioc)
  		return 0;
  
  	/*
  	 * Make sure the process is able to allocate at least 1 request
  	 * even if the batch times out, otherwise we could theoretically
  	 * lose wakeups.
  	 */
  	return ioc->nr_batch_requests == q->nr_batching ||
  		(ioc->nr_batch_requests > 0
  		&& time_before(jiffies, ioc->last_waited + BLK_BATCH_TIME));
  }
  
  /*
   * ioc_set_batching sets ioc to be a new "batcher" if it is not one. This
   * will cause the process to be a "batcher" on all queues in the system. This
   * is the behaviour we want though - once it gets a wakeup it should be given
   * a nice run.
   */

  static void ioc_set_batching(struct request_queue *q, struct io_context *ioc)

  {
  	if (!ioc || ioc_batching(q, ioc))
  		return;
  
  	ioc->nr_batch_requests = q->nr_batching;
  	ioc->last_waited = jiffies;
  }

  static void __freed_request(struct request_list *rl, int sync)

  {

  	struct request_queue *q = rl->q;

  	/*
  	 * bdi isn't aware of blkcg yet.  As all async IOs end up root
  	 * blkcg anyway, just use root blkcg state.
  	 */
  	if (rl == &q->root_rl &&
  	    rl->count[sync] < queue_congestion_off_threshold(q))

  		blk_clear_queue_congested(q, sync);

  	if (rl->count[sync] + 1 <= q->nr_requests) {
  		if (waitqueue_active(&rl->wait[sync]))
  			wake_up(&rl->wait[sync]);

  		blk_clear_rl_full(rl, sync);

  	}
  }
  
  /*
   * A request has just been released.  Account for it, update the full and
   * congestion status, wake up any waiters.   Called under q->queue_lock.
   */

  static void freed_request(struct request_list *rl, unsigned int flags)

  {

  	struct request_queue *q = rl->q;

  	int sync = rw_is_sync(flags);

  	q->nr_rqs[sync]--;

  	rl->count[sync]--;

  	if (flags & REQ_ELVPRIV)

  		q->nr_rqs_elvpriv--;

  	__freed_request(rl, sync);

  	if (unlikely(rl->starved[sync ^ 1]))

  		__freed_request(rl, sync ^ 1);

  }

  /*

   * Determine if elevator data should be initialized when allocating the
   * request associated with @bio.
   */
  static bool blk_rq_should_init_elevator(struct bio *bio)
  {
  	if (!bio)
  		return true;
  
  	/*
  	 * Flush requests do not use the elevator so skip initialization.
  	 * This allows a request to share the flush and elevator data.
  	 */
  	if (bio->bi_rw & (REQ_FLUSH | REQ_FUA))
  		return false;
  
  	return true;
  }

  /**

   * rq_ioc - determine io_context for request allocation
   * @bio: request being allocated is for this bio (can be %NULL)
   *
   * Determine io_context to use for request allocation for @bio.  May return
   * %NULL if %current->io_context doesn't exist.
   */
  static struct io_context *rq_ioc(struct bio *bio)
  {
  #ifdef CONFIG_BLK_CGROUP
  	if (bio && bio->bi_ioc)
  		return bio->bi_ioc;
  #endif
  	return current->io_context;
  }
  
  /**

   * __get_request - get a free request

   * @rl: request list to allocate from

   * @rw_flags: RW and SYNC flags
   * @bio: bio to allocate request for (can be %NULL)
   * @gfp_mask: allocation mask
   *
   * Get a free request from @q.  This function may fail under memory
   * pressure or if @q is dead.
   *
   * Must be callled with @q->queue_lock held and,
   * Returns %NULL on failure, with @q->queue_lock held.
   * Returns !%NULL on success, with @q->queue_lock *not held*.

   */

  static struct request *__get_request(struct request_list *rl, int rw_flags,

  				     struct bio *bio, gfp_t gfp_mask)

  {

  	struct request_queue *q = rl->q;

  	struct request *rq;

  	struct elevator_type *et = q->elevator->type;
  	struct io_context *ioc = rq_ioc(bio);

  	struct io_cq *icq = NULL;

  	const bool is_sync = rw_is_sync(rw_flags) != 0;

  	int may_queue;

  	if (unlikely(blk_queue_dying(q)))

  		return NULL;

  	may_queue = elv_may_queue(q, rw_flags);

  	if (may_queue == ELV_MQUEUE_NO)
  		goto rq_starved;

  	if (rl->count[is_sync]+1 >= queue_congestion_on_threshold(q)) {
  		if (rl->count[is_sync]+1 >= q->nr_requests) {

  			/*

  			 * The queue will fill after this allocation, so set
  			 * it as full, and mark this process as "batching".
  			 * This process will be allowed to complete a batch of
  			 * requests, others will be blocked.
  			 */

  			if (!blk_rl_full(rl, is_sync)) {

  				ioc_set_batching(q, ioc);

  				blk_set_rl_full(rl, is_sync);

  			} else {
  				if (may_queue != ELV_MQUEUE_MUST
  						&& !ioc_batching(q, ioc)) {
  					/*
  					 * The queue is full and the allocating
  					 * process is not a "batcher", and not
  					 * exempted by the IO scheduler
  					 */

  					return NULL;

  				}
  			}

  		}

  		/*
  		 * bdi isn't aware of blkcg yet.  As all async IOs end up
  		 * root blkcg anyway, just use root blkcg state.
  		 */
  		if (rl == &q->root_rl)
  			blk_set_queue_congested(q, is_sync);

  	}

  	/*
  	 * Only allow batching queuers to allocate up to 50% over the defined
  	 * limit of requests, otherwise we could have thousands of requests
  	 * allocated with any setting of ->nr_requests
  	 */

  	if (rl->count[is_sync] >= (3 * q->nr_requests / 2))

  		return NULL;

  	q->nr_rqs[is_sync]++;

  	rl->count[is_sync]++;
  	rl->starved[is_sync] = 0;

  	/*
  	 * Decide whether the new request will be managed by elevator.  If
  	 * so, mark @rw_flags and increment elvpriv.  Non-zero elvpriv will
  	 * prevent the current elevator from being destroyed until the new
  	 * request is freed.  This guarantees icq's won't be destroyed and
  	 * makes creating new ones safe.
  	 *
  	 * Also, lookup icq while holding queue_lock.  If it doesn't exist,
  	 * it will be created after releasing queue_lock.
  	 */

  	if (blk_rq_should_init_elevator(bio) && !blk_queue_bypass(q)) {

  		rw_flags |= REQ_ELVPRIV;

  		q->nr_rqs_elvpriv++;

  		if (et->icq_cache && ioc)
  			icq = ioc_lookup_icq(ioc, q);

  	}

  	if (blk_queue_io_stat(q))
  		rw_flags |= REQ_IO_STAT;

  	spin_unlock_irq(q->queue_lock);

  	/* allocate and init request */

  	rq = mempool_alloc(rl->rq_pool, gfp_mask);

  	if (!rq)

  		goto fail_alloc;

  	blk_rq_init(q, rq);

  	blk_rq_set_rl(rq, rl);

  	rq->cmd_flags = rw_flags | REQ_ALLOCED;

  	/* init elvpriv */

  	if (rw_flags & REQ_ELVPRIV) {

  		if (unlikely(et->icq_cache && !icq)) {

  			if (ioc)
  				icq = ioc_create_icq(ioc, q, gfp_mask);

  			if (!icq)
  				goto fail_elvpriv;

  		}

  
  		rq->elv.icq = icq;
  		if (unlikely(elv_set_request(q, rq, bio, gfp_mask)))
  			goto fail_elvpriv;
  
  		/* @rq->elv.icq holds io_context until @rq is freed */

  		if (icq)
  			get_io_context(icq->ioc);
  	}

  out:

  	/*
  	 * ioc may be NULL here, and ioc_batching will be false. That's
  	 * OK, if the queue is under the request limit then requests need
  	 * not count toward the nr_batch_requests limit. There will always
  	 * be some limit enforced by BLK_BATCH_TIME.
  	 */

  	if (ioc_batching(q, ioc))
  		ioc->nr_batch_requests--;

  	trace_block_getrq(q, bio, rw_flags & 1);

  	return rq;

  fail_elvpriv:
  	/*
  	 * elvpriv init failed.  ioc, icq and elvpriv aren't mempool backed
  	 * and may fail indefinitely under memory pressure and thus
  	 * shouldn't stall IO.  Treat this request as !elvpriv.  This will
  	 * disturb iosched and blkcg but weird is bettern than dead.
  	 */
  	printk_ratelimited(KERN_WARNING "%s: request aux data allocation failed, iosched may be disturbed
  ",
  			   dev_name(q->backing_dev_info.dev));
  
  	rq->cmd_flags &= ~REQ_ELVPRIV;
  	rq->elv.icq = NULL;
  
  	spin_lock_irq(q->queue_lock);

  	q->nr_rqs_elvpriv--;

  	spin_unlock_irq(q->queue_lock);
  	goto out;

  fail_alloc:
  	/*
  	 * Allocation failed presumably due to memory. Undo anything we
  	 * might have messed up.
  	 *
  	 * Allocating task should really be put onto the front of the wait
  	 * queue, but this is pretty rare.
  	 */
  	spin_lock_irq(q->queue_lock);

  	freed_request(rl, rw_flags);

  
  	/*
  	 * in the very unlikely event that allocation failed and no
  	 * requests for this direction was pending, mark us starved so that
  	 * freeing of a request in the other direction will notice
  	 * us. another possible fix would be to split the rq mempool into
  	 * READ and WRITE
  	 */
  rq_starved:
  	if (unlikely(rl->count[is_sync] == 0))
  		rl->starved[is_sync] = 1;
  	return NULL;

  }

  /**

   * get_request - get a free request

   * @q: request_queue to allocate request from
   * @rw_flags: RW and SYNC flags
   * @bio: bio to allocate request for (can be %NULL)

   * @gfp_mask: allocation mask

   *

   * Get a free request from @q.  If %__GFP_WAIT is set in @gfp_mask, this
   * function keeps retrying under memory pressure and fails iff @q is dead.

   *

   * Must be callled with @q->queue_lock held and,
   * Returns %NULL on failure, with @q->queue_lock held.
   * Returns !%NULL on success, with @q->queue_lock *not held*.

   */

  static struct request *get_request(struct request_queue *q, int rw_flags,
  				   struct bio *bio, gfp_t gfp_mask)

  {

  	const bool is_sync = rw_is_sync(rw_flags) != 0;

  	DEFINE_WAIT(wait);

  	struct request_list *rl;

  	struct request *rq;

  
  	rl = blk_get_rl(q, bio);	/* transferred to @rq on success */

  retry:

  	rq = __get_request(rl, rw_flags, bio, gfp_mask);

  	if (rq)
  		return rq;

  	if (!(gfp_mask & __GFP_WAIT) || unlikely(blk_queue_dying(q))) {

  		blk_put_rl(rl);

  		return NULL;

  	}

  	/* wait on @rl and retry */
  	prepare_to_wait_exclusive(&rl->wait[is_sync], &wait,
  				  TASK_UNINTERRUPTIBLE);

  	trace_block_sleeprq(q, bio, rw_flags & 1);

  	spin_unlock_irq(q->queue_lock);
  	io_schedule();

  	/*
  	 * After sleeping, we become a "batching" process and will be able
  	 * to allocate at least one request, and up to a big batch of them
  	 * for a small period time.  See ioc_batching, ioc_set_batching
  	 */

  	ioc_set_batching(q, current->io_context);

  	spin_lock_irq(q->queue_lock);
  	finish_wait(&rl->wait[is_sync], &wait);

  	goto retry;

  }

  static struct request *blk_old_get_request(struct request_queue *q, int rw,
  		gfp_t gfp_mask)

  {
  	struct request *rq;
  
  	BUG_ON(rw != READ && rw != WRITE);

  	/* create ioc upfront */
  	create_io_context(gfp_mask, q->node);

  	spin_lock_irq(q->queue_lock);

  	rq = get_request(q, rw, NULL, gfp_mask);

  	if (!rq)
  		spin_unlock_irq(q->queue_lock);

  	/* q->queue_lock is unlocked at this point */

  
  	return rq;
  }

  
  struct request *blk_get_request(struct request_queue *q, int rw, gfp_t gfp_mask)
  {
  	if (q->mq_ops)

  		return blk_mq_alloc_request(q, rw, gfp_mask);

  	else
  		return blk_old_get_request(q, rw, gfp_mask);
  }

  EXPORT_SYMBOL(blk_get_request);
  
  /**

   * blk_make_request - given a bio, allocate a corresponding struct request.

   * @q: target request queue

   * @bio:  The bio describing the memory mappings that will be submitted for IO.
   *        It may be a chained-bio properly constructed by block/bio layer.

   * @gfp_mask: gfp flags to be used for memory allocation

   *

   * blk_make_request is the parallel of generic_make_request for BLOCK_PC
   * type commands. Where the struct request needs to be farther initialized by
   * the caller. It is passed a &struct bio, which describes the memory info of
   * the I/O transfer.

   *

   * The caller of blk_make_request must make sure that bi_io_vec
   * are set to describe the memory buffers. That bio_data_dir() will return
   * the needed direction of the request. (And all bio's in the passed bio-chain
   * are properly set accordingly)
   *
   * If called under none-sleepable conditions, mapped bio buffers must not
   * need bouncing, by calling the appropriate masked or flagged allocator,
   * suitable for the target device. Otherwise the call to blk_queue_bounce will
   * BUG.

   *
   * WARNING: When allocating/cloning a bio-chain, careful consideration should be
   * given to how you allocate bios. In particular, you cannot use __GFP_WAIT for
   * anything but the first bio in the chain. Otherwise you risk waiting for IO
   * completion of a bio that hasn't been submitted yet, thus resulting in a
   * deadlock. Alternatively bios should be allocated using bio_kmalloc() instead
   * of bio_alloc(), as that avoids the mempool deadlock.
   * If possible a big IO should be split into smaller parts when allocation
   * fails. Partial allocation should not be an error, or you risk a live-lock.

   */

  struct request *blk_make_request(struct request_queue *q, struct bio *bio,
  				 gfp_t gfp_mask)

  {

  	struct request *rq = blk_get_request(q, bio_data_dir(bio), gfp_mask);
  
  	if (unlikely(!rq))
  		return ERR_PTR(-ENOMEM);
  
  	for_each_bio(bio) {
  		struct bio *bounce_bio = bio;
  		int ret;
  
  		blk_queue_bounce(q, &bounce_bio);
  		ret = blk_rq_append_bio(q, rq, bounce_bio);
  		if (unlikely(ret)) {
  			blk_put_request(rq);
  			return ERR_PTR(ret);
  		}
  	}
  
  	return rq;

  }

  EXPORT_SYMBOL(blk_make_request);

  
  /**

   * blk_requeue_request - put a request back on queue
   * @q:		request queue where request should be inserted
   * @rq:		request to be inserted
   *
   * Description:
   *    Drivers often keep queueing requests until the hardware cannot accept
   *    more, when that condition happens we need to put the request back
   *    on the queue. Must be called with queue lock held.
   */

  void blk_requeue_request(struct request_queue *q, struct request *rq)

  {

  	blk_delete_timer(rq);
  	blk_clear_rq_complete(rq);

  	trace_block_rq_requeue(q, rq);

  	if (blk_rq_tagged(rq))
  		blk_queue_end_tag(q, rq);

  	BUG_ON(blk_queued_rq(rq));

  	elv_requeue_request(q, rq);
  }

  EXPORT_SYMBOL(blk_requeue_request);

  static void add_acct_request(struct request_queue *q, struct request *rq,
  			     int where)
  {

  	blk_account_io_start(rq, true);

  	__elv_add_request(q, rq, where);

  }

  static void part_round_stats_single(int cpu, struct hd_struct *part,
  				    unsigned long now)
  {
  	if (now == part->stamp)
  		return;

  	if (part_in_flight(part)) {

  		__part_stat_add(cpu, part, time_in_queue,

  				part_in_flight(part) * (now - part->stamp));

  		__part_stat_add(cpu, part, io_ticks, (now - part->stamp));
  	}
  	part->stamp = now;
  }
  
  /**

   * part_round_stats() - Round off the performance stats on a struct disk_stats.
   * @cpu: cpu number for stats access
   * @part: target partition

   *
   * The average IO queue length and utilisation statistics are maintained
   * by observing the current state of the queue length and the amount of
   * time it has been in this state for.
   *
   * Normally, that accounting is done on IO completion, but that can result
   * in more than a second's worth of IO being accounted for within any one
   * second, leading to >100% utilisation.  To deal with that, we call this
   * function to do a round-off before returning the results when reading
   * /proc/diskstats.  This accounts immediately for all queue usage up to
   * the current jiffies and restarts the counters again.
   */

  void part_round_stats(int cpu, struct hd_struct *part)

  {
  	unsigned long now = jiffies;

  	if (part->partno)
  		part_round_stats_single(cpu, &part_to_disk(part)->part0, now);
  	part_round_stats_single(cpu, part, now);

  }

  EXPORT_SYMBOL_GPL(part_round_stats);

  #ifdef CONFIG_PM_RUNTIME
  static void blk_pm_put_request(struct request *rq)
  {
  	if (rq->q->dev && !(rq->cmd_flags & REQ_PM) && !--rq->q->nr_pending)
  		pm_runtime_mark_last_busy(rq->q->dev);
  }
  #else
  static inline void blk_pm_put_request(struct request *rq) {}
  #endif

  /*
   * queue lock must be held
   */

  void __blk_put_request(struct request_queue *q, struct request *req)

  {

  	if (unlikely(!q))
  		return;

  	if (q->mq_ops) {
  		blk_mq_free_request(req);
  		return;
  	}

  	blk_pm_put_request(req);

  	elv_completed_request(q, req);

  	/* this is a bio leak */
  	WARN_ON(req->bio != NULL);

  	/*
  	 * Request may not have originated from ll_rw_blk. if not,
  	 * it didn't come out of our reserved rq pools
  	 */

  	if (req->cmd_flags & REQ_ALLOCED) {

  		unsigned int flags = req->cmd_flags;

  		struct request_list *rl = blk_rq_rl(req);

  		BUG_ON(!list_empty(&req->queuelist));

  		BUG_ON(!hlist_unhashed(&req->hash));

  		blk_free_request(rl, req);
  		freed_request(rl, flags);
  		blk_put_rl(rl);

  	}
  }

  EXPORT_SYMBOL_GPL(__blk_put_request);

  void blk_put_request(struct request *req)
  {

  	struct request_queue *q = req->q;

  	if (q->mq_ops)
  		blk_mq_free_request(req);
  	else {
  		unsigned long flags;
  
  		spin_lock_irqsave(q->queue_lock, flags);
  		__blk_put_request(q, req);
  		spin_unlock_irqrestore(q->queue_lock, flags);
  	}

  }

  EXPORT_SYMBOL(blk_put_request);

  /**
   * blk_add_request_payload - add a payload to a request
   * @rq: request to update
   * @page: page backing the payload
   * @len: length of the payload.
   *
   * This allows to later add a payload to an already submitted request by
   * a block driver.  The driver needs to take care of freeing the payload
   * itself.
   *
   * Note that this is a quite horrible hack and nothing but handling of
   * discard requests should ever use it.
   */
  void blk_add_request_payload(struct request *rq, struct page *page,
  		unsigned int len)
  {
  	struct bio *bio = rq->bio;
  
  	bio->bi_io_vec->bv_page = page;
  	bio->bi_io_vec->bv_offset = 0;
  	bio->bi_io_vec->bv_len = len;

  	bio->bi_iter.bi_size = len;

  	bio->bi_vcnt = 1;
  	bio->bi_phys_segments = 1;
  
  	rq->__data_len = rq->resid_len = len;
  	rq->nr_phys_segments = 1;
  	rq->buffer = bio_data(bio);
  }
  EXPORT_SYMBOL_GPL(blk_add_request_payload);

  bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
  			    struct bio *bio)

  {
  	const int ff = bio->bi_rw & REQ_FAILFAST_MASK;

  	if (!ll_back_merge_fn(q, req, bio))
  		return false;

  	trace_block_bio_backmerge(q, req, bio);

  
  	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
  		blk_rq_set_mixed_merge(req);
  
  	req->biotail->bi_next = bio;
  	req->biotail = bio;

  	req->__data_len += bio->bi_iter.bi_size;

  	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));

  	blk_account_io_start(req, false);

  	return true;
  }

  bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
  			     struct bio *bio)

  {
  	const int ff = bio->bi_rw & REQ_FAILFAST_MASK;

  	if (!ll_front_merge_fn(q, req, bio))
  		return false;

  	trace_block_bio_frontmerge(q, req, bio);

  
  	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
  		blk_rq_set_mixed_merge(req);

  	bio->bi_next = req->bio;
  	req->bio = bio;
  
  	/*
  	 * may not be valid. if the low level driver said
  	 * it didn't need a bounce buffer then it better
  	 * not touch req->buffer either...
  	 */
  	req->buffer = bio_data(bio);

  	req->__sector = bio->bi_iter.bi_sector;
  	req->__data_len += bio->bi_iter.bi_size;

  	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));

  	blk_account_io_start(req, false);

  	return true;
  }

  /**

   * blk_attempt_plug_merge - try to merge with %current's plugged list

   * @q: request_queue new bio is being queued at
   * @bio: new bio being queued
   * @request_count: out parameter for number of traversed plugged requests
   *
   * Determine whether @bio being queued on @q can be merged with a request
   * on %current's plugged list.  Returns %true if merge was successful,
   * otherwise %false.
   *

   * Plugging coalesces IOs from the same issuer for the same purpose without
   * going through @q->queue_lock.  As such it's more of an issuing mechanism
   * than scheduling, and the request, while may have elvpriv data, is not
   * added on the elevator at this point.  In addition, we don't have
   * reliable access to the elevator outside queue lock.  Only check basic
   * merging parameters without querying the elevator.

   */

  bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
  			    unsigned int *request_count)

  {
  	struct blk_plug *plug;
  	struct request *rq;
  	bool ret = false;

  	struct list_head *plug_list;

  	if (blk_queue_nomerges(q))
  		goto out;

  	plug = current->plug;

  	if (!plug)
  		goto out;

  	*request_count = 0;

  	if (q->mq_ops)
  		plug_list = &plug->mq_list;
  	else
  		plug_list = &plug->list;
  
  	list_for_each_entry_reverse(rq, plug_list, queuelist) {

  		int el_ret;

  		if (rq->q == q)
  			(*request_count)++;

  		if (rq->q != q || !blk_rq_merge_ok(rq, bio))

  			continue;

  		el_ret = blk_try_merge(rq, bio);

  		if (el_ret == ELEVATOR_BACK_MERGE) {
  			ret = bio_attempt_back_merge(q, rq, bio);
  			if (ret)
  				break;
  		} else if (el_ret == ELEVATOR_FRONT_MERGE) {
  			ret = bio_attempt_front_merge(q, rq, bio);
  			if (ret)
  				break;
  		}
  	}
  out:
  	return ret;
  }

  void init_request_from_bio(struct request *req, struct bio *bio)

  {

  	req->cmd_type = REQ_TYPE_FS;

  	req->cmd_flags |= bio->bi_rw & REQ_COMMON_MASK;
  	if (bio->bi_rw & REQ_RAHEAD)

  		req->cmd_flags |= REQ_FAILFAST_MASK;

  	req->errors = 0;

  	req->__sector = bio->bi_iter.bi_sector;

  	req->ioprio = bio_prio(bio);