/*
   * Functions related to tagged command queuing
   */
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/bio.h>
  #include <linux/blkdev.h>
  #include <linux/slab.h>
  
  #include "blk.h"
  
  /**
   * blk_queue_find_tag - find a request by its tag and queue
   * @q:	 The request queue for the device
   * @tag: The tag of the request
   *
   * Notes:
   *    Should be used when a device returns a tag and you want to match
   *    it with a request.
   *
   *    no locks need be held.
   **/
  struct request *blk_queue_find_tag(struct request_queue *q, int tag)
  {
  	return blk_map_queue_find_tag(q->queue_tags, tag);
  }
  EXPORT_SYMBOL(blk_queue_find_tag);
  
  /**
   * blk_free_tags - release a given set of tag maintenance info
   * @bqt:	the tag map to free
   *
   * Drop the reference count on @bqt and frees it when the last reference
   * is dropped.
   */
  void blk_free_tags(struct blk_queue_tag *bqt)
  {
  	if (atomic_dec_and_test(&bqt->refcnt)) {
  		BUG_ON(find_first_bit(bqt->tag_map, bqt->max_depth) <
  							bqt->max_depth);
  
  		kfree(bqt->tag_index);
  		bqt->tag_index = NULL;
  
  		kfree(bqt->tag_map);
  		bqt->tag_map = NULL;
  
  		kfree(bqt);
  	}
  }
  EXPORT_SYMBOL(blk_free_tags);
  
  /**
   * __blk_queue_free_tags - release tag maintenance info
   * @q:  the request queue for the device
   *
   *  Notes:
   *    blk_cleanup_queue() will take care of calling this function, if tagging
   *    has been used. So there's no need to call this directly.
   **/
  void __blk_queue_free_tags(struct request_queue *q)
  {
  	struct blk_queue_tag *bqt = q->queue_tags;
  
  	if (!bqt)
  		return;
  
  	blk_free_tags(bqt);
  
  	q->queue_tags = NULL;
  	queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
  }
  
  /**
   * blk_queue_free_tags - release tag maintenance info
   * @q:  the request queue for the device
   *
   *  Notes:
   *	This is used to disable tagged queuing to a device, yet leave
   *	queue in function.
   **/
  void blk_queue_free_tags(struct request_queue *q)
  {
  	queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
  }
  EXPORT_SYMBOL(blk_queue_free_tags);
  
  static int
  init_tag_map(struct request_queue *q, struct blk_queue_tag *tags, int depth)
  {
  	struct request **tag_index;
  	unsigned long *tag_map;
  	int nr_ulongs;
  
  	if (q && depth > q->nr_requests * 2) {
  		depth = q->nr_requests * 2;
  		printk(KERN_ERR "%s: adjusted depth to %d
  ",
  		       __func__, depth);
  	}
  
  	tag_index = kzalloc(depth * sizeof(struct request *), GFP_ATOMIC);
  	if (!tag_index)
  		goto fail;
  
  	nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
  	tag_map = kzalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
  	if (!tag_map)
  		goto fail;
  
  	tags->real_max_depth = depth;
  	tags->max_depth = depth;
  	tags->tag_index = tag_index;
  	tags->tag_map = tag_map;
  
  	return 0;
  fail:
  	kfree(tag_index);
  	return -ENOMEM;
  }
  
  static struct blk_queue_tag *__blk_queue_init_tags(struct request_queue *q,
  						int depth, int alloc_policy)
  {
  	struct blk_queue_tag *tags;
  
  	tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
  	if (!tags)
  		goto fail;
  
  	if (init_tag_map(q, tags, depth))
  		goto fail;
  
  	atomic_set(&tags->refcnt, 1);
  	tags->alloc_policy = alloc_policy;
  	tags->next_tag = 0;
  	return tags;
  fail:
  	kfree(tags);
  	return NULL;
  }
  
  /**
   * blk_init_tags - initialize the tag info for an external tag map
   * @depth:	the maximum queue depth supported
   * @alloc_policy: tag allocation policy
   **/
  struct blk_queue_tag *blk_init_tags(int depth, int alloc_policy)
  {
  	return __blk_queue_init_tags(NULL, depth, alloc_policy);
  }
  EXPORT_SYMBOL(blk_init_tags);
  
  /**
   * blk_queue_init_tags - initialize the queue tag info
   * @q:  the request queue for the device
   * @depth:  the maximum queue depth supported
   * @tags: the tag to use
   * @alloc_policy: tag allocation policy
   *
   * Queue lock must be held here if the function is called to resize an
   * existing map.
   **/
  int blk_queue_init_tags(struct request_queue *q, int depth,
  			struct blk_queue_tag *tags, int alloc_policy)
  {
  	int rc;
  
  	BUG_ON(tags && q->queue_tags && tags != q->queue_tags);
  
  	if (!tags && !q->queue_tags) {
  		tags = __blk_queue_init_tags(q, depth, alloc_policy);
  
  		if (!tags)
  			return -ENOMEM;
  
  	} else if (q->queue_tags) {
  		rc = blk_queue_resize_tags(q, depth);
  		if (rc)
  			return rc;
  		queue_flag_set(QUEUE_FLAG_QUEUED, q);
  		return 0;
  	} else
  		atomic_inc(&tags->refcnt);
  
  	/*
  	 * assign it, all done
  	 */
  	q->queue_tags = tags;
  	queue_flag_set_unlocked(QUEUE_FLAG_QUEUED, q);
  	INIT_LIST_HEAD(&q->tag_busy_list);
  	return 0;
  }
  EXPORT_SYMBOL(blk_queue_init_tags);
  
  /**
   * blk_queue_resize_tags - change the queueing depth
   * @q:  the request queue for the device
   * @new_depth: the new max command queueing depth
   *
   *  Notes:
   *    Must be called with the queue lock held.
   **/
  int blk_queue_resize_tags(struct request_queue *q, int new_depth)
  {
  	struct blk_queue_tag *bqt = q->queue_tags;
  	struct request **tag_index;
  	unsigned long *tag_map;
  	int max_depth, nr_ulongs;
  
  	if (!bqt)
  		return -ENXIO;
  
  	/*
  	 * if we already have large enough real_max_depth.  just
  	 * adjust max_depth.  *NOTE* as requests with tag value
  	 * between new_depth and real_max_depth can be in-flight, tag
  	 * map can not be shrunk blindly here.
  	 */
  	if (new_depth <= bqt->real_max_depth) {
  		bqt->max_depth = new_depth;
  		return 0;
  	}
  
  	/*
  	 * Currently cannot replace a shared tag map with a new
  	 * one, so error out if this is the case
  	 */
  	if (atomic_read(&bqt->refcnt) != 1)
  		return -EBUSY;
  
  	/*
  	 * save the old state info, so we can copy it back
  	 */
  	tag_index = bqt->tag_index;
  	tag_map = bqt->tag_map;
  	max_depth = bqt->real_max_depth;
  
  	if (init_tag_map(q, bqt, new_depth))
  		return -ENOMEM;
  
  	memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
  	nr_ulongs = ALIGN(max_depth, BITS_PER_LONG) / BITS_PER_LONG;
  	memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));
  
  	kfree(tag_index);
  	kfree(tag_map);
  	return 0;
  }
  EXPORT_SYMBOL(blk_queue_resize_tags);
  
  /**
   * blk_queue_end_tag - end tag operations for a request
   * @q:  the request queue for the device
   * @rq: the request that has completed
   *
   *  Description:
   *    Typically called when end_that_request_first() returns %0, meaning
   *    all transfers have been done for a request. It's important to call
   *    this function before end_that_request_last(), as that will put the
   *    request back on the free list thus corrupting the internal tag list.
   *
   *  Notes:
   *   queue lock must be held.
   **/
  void blk_queue_end_tag(struct request_queue *q, struct request *rq)
  {
  	struct blk_queue_tag *bqt = q->queue_tags;
  	unsigned tag = rq->tag; /* negative tags invalid */
  
  	BUG_ON(tag >= bqt->real_max_depth);
  
  	list_del_init(&rq->queuelist);
  	rq->cmd_flags &= ~REQ_QUEUED;
  	rq->tag = -1;
  
  	if (unlikely(bqt->tag_index[tag] == NULL))
  		printk(KERN_ERR "%s: tag %d is missing
  ",
  		       __func__, tag);
  
  	bqt->tag_index[tag] = NULL;
  
  	if (unlikely(!test_bit(tag, bqt->tag_map))) {
  		printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)
  ",
  		       __func__, tag);
  		return;
  	}
  	/*
  	 * The tag_map bit acts as a lock for tag_index[bit], so we need
  	 * unlock memory barrier semantics.
  	 */
  	clear_bit_unlock(tag, bqt->tag_map);
  }
  EXPORT_SYMBOL(blk_queue_end_tag);
  
  /**
   * blk_queue_start_tag - find a free tag and assign it
   * @q:  the request queue for the device
   * @rq:  the block request that needs tagging
   *
   *  Description:
   *    This can either be used as a stand-alone helper, or possibly be
   *    assigned as the queue &prep_rq_fn (in which case &struct request
   *    automagically gets a tag assigned). Note that this function
   *    assumes that any type of request can be queued! if this is not
   *    true for your device, you must check the request type before
   *    calling this function.  The request will also be removed from
   *    the request queue, so it's the drivers responsibility to readd
   *    it if it should need to be restarted for some reason.
   *
   *  Notes:
   *   queue lock must be held.
   **/
  int blk_queue_start_tag(struct request_queue *q, struct request *rq)
  {
  	struct blk_queue_tag *bqt = q->queue_tags;
  	unsigned max_depth;
  	int tag;
  
  	if (unlikely((rq->cmd_flags & REQ_QUEUED))) {
  		printk(KERN_ERR
  		       "%s: request %p for device [%s] already tagged %d",
  		       __func__, rq,
  		       rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->tag);
  		BUG();
  	}
  
  	/*
  	 * Protect against shared tag maps, as we may not have exclusive
  	 * access to the tag map.
  	 *
  	 * We reserve a few tags just for sync IO, since we don't want
  	 * to starve sync IO on behalf of flooding async IO.
  	 */
  	max_depth = bqt->max_depth;
  	if (!rq_is_sync(rq) && max_depth > 1) {
  		switch (max_depth) {
  		case 2:
  			max_depth = 1;
  			break;
  		case 3:
  			max_depth = 2;
  			break;
  		default:
  			max_depth -= 2;
  		}
  		if (q->in_flight[BLK_RW_ASYNC] > max_depth)
  			return 1;
  	}
  
  	do {
  		if (bqt->alloc_policy == BLK_TAG_ALLOC_FIFO) {
  			tag = find_first_zero_bit(bqt->tag_map, max_depth);
  			if (tag >= max_depth)
  				return 1;
  		} else {
  			int start = bqt->next_tag;
  			int size = min_t(int, bqt->max_depth, max_depth + start);
  			tag = find_next_zero_bit(bqt->tag_map, size, start);
  			if (tag >= size && start + size > bqt->max_depth) {
  				size = start + size - bqt->max_depth;
  				tag = find_first_zero_bit(bqt->tag_map, size);
  			}
  			if (tag >= size)
  				return 1;
  		}
  
  	} while (test_and_set_bit_lock(tag, bqt->tag_map));
  	/*
  	 * We need lock ordering semantics given by test_and_set_bit_lock.
  	 * See blk_queue_end_tag for details.
  	 */
  
  	bqt->next_tag = (tag + 1) % bqt->max_depth;
  	rq->cmd_flags |= REQ_QUEUED;
  	rq->tag = tag;
  	bqt->tag_index[tag] = rq;
  	blk_start_request(rq);
  	list_add(&rq->queuelist, &q->tag_busy_list);
  	return 0;
  }
  EXPORT_SYMBOL(blk_queue_start_tag);
  
  /**
   * blk_queue_invalidate_tags - invalidate all pending tags
   * @q:  the request queue for the device
   *
   *  Description:
   *   Hardware conditions may dictate a need to stop all pending requests.
   *   In this case, we will safely clear the block side of the tag queue and
   *   readd all requests to the request queue in the right order.
   *
   *  Notes:
   *   queue lock must be held.
   **/
  void blk_queue_invalidate_tags(struct request_queue *q)
  {
  	struct list_head *tmp, *n;
  
  	list_for_each_safe(tmp, n, &q->tag_busy_list)
  		blk_requeue_request(q, list_entry_rq(tmp));
  }
  EXPORT_SYMBOL(blk_queue_invalidate_tags);