/*

   * Tag allocation using scalable bitmaps. Uses active queue tracking to support
   * fairer distribution of tags between multiple submitters when a shared tag map
   * is used.

   *
   * Copyright (C) 2013-2014 Jens Axboe
   */

  #include <linux/kernel.h>
  #include <linux/module.h>

  
  #include <linux/blk-mq.h>
  #include "blk.h"
  #include "blk-mq.h"
  #include "blk-mq-tag.h"

  bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
  {

  	if (!tags)
  		return true;

  	return sbitmap_any_bit_clear(&tags->bitmap_tags.sb);

  }
  
  /*
   * If a previously inactive queue goes active, bump the active user count.

   * We need to do this before try to allocate driver tag, then even if fail
   * to get tag when first time, the other shared-tag users could reserve
   * budget for it.

   */
  bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
  {
  	if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
  	    !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
  		atomic_inc(&hctx->tags->active_queues);
  
  	return true;
  }
  
  /*

   * Wakeup all potentially sleeping on tags

   */

  void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)

  {

  	sbitmap_queue_wake_all(&tags->bitmap_tags);
  	if (include_reserve)
  		sbitmap_queue_wake_all(&tags->breserved_tags);

  }
  
  /*

   * If a previously busy queue goes inactive, potential waiters could now
   * be allowed to queue. Wake them up and check.
   */
  void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
  {
  	struct blk_mq_tags *tags = hctx->tags;
  
  	if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
  		return;
  
  	atomic_dec(&tags->active_queues);

  	blk_mq_tag_wakeup_all(tags, false);

  }
  
  /*

   * For shared tag users, we track the number of currently active users
   * and attempt to provide a fair share of the tag depth for each of them.
   */
  static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,

  				  struct sbitmap_queue *bt)

  {
  	unsigned int depth, users;
  
  	if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_SHARED))
  		return true;
  	if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
  		return true;
  
  	/*
  	 * Don't try dividing an ant
  	 */

  	if (bt->sb.depth == 1)

  		return true;
  
  	users = atomic_read(&hctx->tags->active_queues);
  	if (!users)
  		return true;
  
  	/*
  	 * Allow at least some tags
  	 */

  	depth = max((bt->sb.depth + users - 1) / users, 4U);

  	return atomic_read(&hctx->nr_active) < depth;
  }

  static int __blk_mq_get_tag(struct blk_mq_alloc_data *data,
  			    struct sbitmap_queue *bt)

  {

  	if (!(data->flags & BLK_MQ_REQ_INTERNAL) &&
  	    !hctx_may_queue(data->hctx, bt))

  		return -1;

  	if (data->shallow_depth)
  		return __sbitmap_queue_get_shallow(bt, data->shallow_depth);
  	else
  		return __sbitmap_queue_get(bt);

  }

  unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)

  {

  	struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
  	struct sbitmap_queue *bt;

  	struct sbq_wait_state *ws;

  	DEFINE_WAIT(wait);

  	unsigned int tag_offset;

  	bool drop_ctx;

  	int tag;

  	if (data->flags & BLK_MQ_REQ_RESERVED) {
  		if (unlikely(!tags->nr_reserved_tags)) {
  			WARN_ON_ONCE(1);
  			return BLK_MQ_TAG_FAIL;
  		}
  		bt = &tags->breserved_tags;
  		tag_offset = 0;
  	} else {
  		bt = &tags->bitmap_tags;
  		tag_offset = tags->nr_reserved_tags;
  	}

  	tag = __blk_mq_get_tag(data, bt);

  	if (tag != -1)

  		goto found_tag;

  	if (data->flags & BLK_MQ_REQ_NOWAIT)

  		return BLK_MQ_TAG_FAIL;

  	ws = bt_wait_ptr(bt, data->hctx);

  	drop_ctx = data->ctx == NULL;

  	do {

  		struct sbitmap_queue *bt_prev;

  		/*
  		 * We're out of tags on this hardware queue, kick any
  		 * pending IO submits before going to sleep waiting for

  		 * some to complete.

  		 */

  		blk_mq_run_hw_queue(data->hctx, false);

  		/*
  		 * Retry tag allocation after running the hardware queue,
  		 * as running the queue may also have found completions.
  		 */

  		tag = __blk_mq_get_tag(data, bt);

  		if (tag != -1)
  			break;

  		prepare_to_wait_exclusive(&ws->wait, &wait,
  						TASK_UNINTERRUPTIBLE);
  
  		tag = __blk_mq_get_tag(data, bt);
  		if (tag != -1)
  			break;

  		if (data->ctx)
  			blk_mq_put_ctx(data->ctx);

  		bt_prev = bt;

  		io_schedule();

  
  		data->ctx = blk_mq_get_ctx(data->q);

  		data->hctx = blk_mq_map_queue(data->q, data->ctx->cpu);

  		tags = blk_mq_tags_from_data(data);
  		if (data->flags & BLK_MQ_REQ_RESERVED)
  			bt = &tags->breserved_tags;
  		else
  			bt = &tags->bitmap_tags;

  		finish_wait(&ws->wait, &wait);

  
  		/*
  		 * If destination hw queue is changed, fake wake up on
  		 * previous queue for compensating the wake up miss, so
  		 * other allocations on previous queue won't be starved.
  		 */
  		if (bt != bt_prev)
  			sbitmap_queue_wake_up(bt_prev);

  		ws = bt_wait_ptr(bt, data->hctx);

  	} while (1);

  	if (drop_ctx && data->ctx)
  		blk_mq_put_ctx(data->ctx);

  	finish_wait(&ws->wait, &wait);

  found_tag:
  	return tag + tag_offset;

  }

  void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, struct blk_mq_tags *tags,
  		    struct blk_mq_ctx *ctx, unsigned int tag)

  {

  	if (!blk_mq_tag_is_reserved(tags, tag)) {

  		const int real_tag = tag - tags->nr_reserved_tags;

  		BUG_ON(real_tag >= tags->nr_tags);

  		sbitmap_queue_clear(&tags->bitmap_tags, real_tag, ctx->cpu);

  	} else {
  		BUG_ON(tag >= tags->nr_reserved_tags);

  		sbitmap_queue_clear(&tags->breserved_tags, tag, ctx->cpu);

  	}

  }

  struct bt_iter_data {
  	struct blk_mq_hw_ctx *hctx;
  	busy_iter_fn *fn;
  	void *data;
  	bool reserved;
  };
  
  static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)

  {

  	struct bt_iter_data *iter_data = data;
  	struct blk_mq_hw_ctx *hctx = iter_data->hctx;
  	struct blk_mq_tags *tags = hctx->tags;
  	bool reserved = iter_data->reserved;

  	struct request *rq;

  	if (!reserved)
  		bitnr += tags->nr_reserved_tags;
  	rq = tags->rqs[bitnr];

  	/*
  	 * We can hit rq == NULL here, because the tagging functions
  	 * test and set the bit before assining ->rqs[].
  	 */
  	if (rq && rq->q == hctx->queue)

  		iter_data->fn(hctx, rq, iter_data->data, reserved);
  	return true;
  }

  static void bt_for_each(struct blk_mq_hw_ctx *hctx, struct sbitmap_queue *bt,
  			busy_iter_fn *fn, void *data, bool reserved)
  {
  	struct bt_iter_data iter_data = {
  		.hctx = hctx,
  		.fn = fn,
  		.data = data,
  		.reserved = reserved,
  	};
  
  	sbitmap_for_each_set(&bt->sb, bt_iter, &iter_data);

  }

  struct bt_tags_iter_data {
  	struct blk_mq_tags *tags;
  	busy_tag_iter_fn *fn;
  	void *data;
  	bool reserved;
  };
  
  static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)

  {

  	struct bt_tags_iter_data *iter_data = data;
  	struct blk_mq_tags *tags = iter_data->tags;
  	bool reserved = iter_data->reserved;

  	struct request *rq;

  	if (!reserved)
  		bitnr += tags->nr_reserved_tags;

  
  	/*
  	 * We can hit rq == NULL here, because the tagging functions
  	 * test and set the bit before assining ->rqs[].
  	 */

  	rq = tags->rqs[bitnr];

  	if (rq && blk_mq_request_started(rq))

  		iter_data->fn(rq, iter_data->data, reserved);

  	return true;
  }
  
  static void bt_tags_for_each(struct blk_mq_tags *tags, struct sbitmap_queue *bt,
  			     busy_tag_iter_fn *fn, void *data, bool reserved)
  {
  	struct bt_tags_iter_data iter_data = {
  		.tags = tags,
  		.fn = fn,
  		.data = data,
  		.reserved = reserved,
  	};
  
  	if (tags->rqs)
  		sbitmap_for_each_set(&bt->sb, bt_tags_iter, &iter_data);

  }

  static void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags,
  		busy_tag_iter_fn *fn, void *priv)

  {
  	if (tags->nr_reserved_tags)

  		bt_tags_for_each(tags, &tags->breserved_tags, fn, priv, true);
  	bt_tags_for_each(tags, &tags->bitmap_tags, fn, priv, false);

  }

  void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
  		busy_tag_iter_fn *fn, void *priv)
  {
  	int i;
  
  	for (i = 0; i < tagset->nr_hw_queues; i++) {
  		if (tagset->tags && tagset->tags[i])
  			blk_mq_all_tag_busy_iter(tagset->tags[i], fn, priv);
  	}
  }
  EXPORT_SYMBOL(blk_mq_tagset_busy_iter);

  void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,

  		void *priv)

  {

  	struct blk_mq_hw_ctx *hctx;
  	int i;

  	/*
  	 * __blk_mq_update_nr_hw_queues will update the nr_hw_queues and

  	 * queue_hw_ctx after freeze the queue, so we use q_usage_counter
  	 * to avoid race with it.

  	 */

  	if (!percpu_ref_tryget(&q->q_usage_counter))

  		return;

  
  	queue_for_each_hw_ctx(q, hctx, i) {
  		struct blk_mq_tags *tags = hctx->tags;
  
  		/*
  		 * If not software queues are currently mapped to this
  		 * hardware queue, there's nothing to check
  		 */
  		if (!blk_mq_hw_queue_mapped(hctx))
  			continue;
  
  		if (tags->nr_reserved_tags)

  			bt_for_each(hctx, &tags->breserved_tags, fn, priv, true);
  		bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false);

  	}

  	blk_queue_exit(q);

  }

  static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,
  		    bool round_robin, int node)

  {

  	return sbitmap_queue_init_node(bt, depth, -1, round_robin, GFP_KERNEL,
  				       node);

  }
  
  static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,

  						   int node, int alloc_policy)

  {
  	unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;

  	bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;

  	if (bt_alloc(&tags->bitmap_tags, depth, round_robin, node))

  		goto free_tags;

  	if (bt_alloc(&tags->breserved_tags, tags->nr_reserved_tags, round_robin,
  		     node))

  		goto free_bitmap_tags;

  
  	return tags;

  free_bitmap_tags:
  	sbitmap_queue_free(&tags->bitmap_tags);
  free_tags:

  	kfree(tags);
  	return NULL;
  }

  struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,

  				     unsigned int reserved_tags,
  				     int node, int alloc_policy)

  {

  	struct blk_mq_tags *tags;

  
  	if (total_tags > BLK_MQ_TAG_MAX) {
  		pr_err("blk-mq: tag depth too large
  ");
  		return NULL;
  	}
  
  	tags = kzalloc_node(sizeof(*tags), GFP_KERNEL, node);
  	if (!tags)
  		return NULL;

  	tags->nr_tags = total_tags;
  	tags->nr_reserved_tags = reserved_tags;

  	return blk_mq_init_bitmap_tags(tags, node, alloc_policy);

  }
  
  void blk_mq_free_tags(struct blk_mq_tags *tags)
  {

  	sbitmap_queue_free(&tags->bitmap_tags);
  	sbitmap_queue_free(&tags->breserved_tags);

  	kfree(tags);
  }

  int blk_mq_tag_update_depth(struct blk_mq_hw_ctx *hctx,
  			    struct blk_mq_tags **tagsptr, unsigned int tdepth,
  			    bool can_grow)

  {

  	struct blk_mq_tags *tags = *tagsptr;
  
  	if (tdepth <= tags->nr_reserved_tags)

  		return -EINVAL;
  
  	/*

  	 * If we are allowed to grow beyond the original size, allocate
  	 * a new set of tags before freeing the old one.

  	 */

  	if (tdepth > tags->nr_tags) {
  		struct blk_mq_tag_set *set = hctx->queue->tag_set;
  		struct blk_mq_tags *new;
  		bool ret;
  
  		if (!can_grow)
  			return -EINVAL;
  
  		/*
  		 * We need some sort of upper limit, set it high enough that
  		 * no valid use cases should require more.
  		 */
  		if (tdepth > 16 * BLKDEV_MAX_RQ)
  			return -EINVAL;

  		new = blk_mq_alloc_rq_map(set, hctx->queue_num, tdepth,
  				tags->nr_reserved_tags);

  		if (!new)
  			return -ENOMEM;
  		ret = blk_mq_alloc_rqs(set, new, hctx->queue_num, tdepth);
  		if (ret) {
  			blk_mq_free_rq_map(new);
  			return -ENOMEM;
  		}
  
  		blk_mq_free_rqs(set, *tagsptr, hctx->queue_num);
  		blk_mq_free_rq_map(*tagsptr);
  		*tagsptr = new;
  	} else {
  		/*
  		 * Don't need (or can't) update reserved tags here, they
  		 * remain static and should never need resizing.
  		 */

  		sbitmap_queue_resize(&tags->bitmap_tags,
  				tdepth - tags->nr_reserved_tags);

  	}

  	return 0;
  }

  /**
   * blk_mq_unique_tag() - return a tag that is unique queue-wide
   * @rq: request for which to compute a unique tag
   *
   * The tag field in struct request is unique per hardware queue but not over
   * all hardware queues. Hence this function that returns a tag with the
   * hardware context index in the upper bits and the per hardware queue tag in
   * the lower bits.
   *
   * Note: When called for a request that is queued on a non-multiqueue request
   * queue, the hardware context index is set to zero.
   */
  u32 blk_mq_unique_tag(struct request *rq)
  {
  	struct request_queue *q = rq->q;
  	struct blk_mq_hw_ctx *hctx;
  	int hwq = 0;
  
  	if (q->mq_ops) {

  		hctx = blk_mq_map_queue(q, rq->mq_ctx->cpu);

  		hwq = hctx->queue_num;
  	}
  
  	return (hwq << BLK_MQ_UNIQUE_TAG_BITS) |
  		(rq->tag & BLK_MQ_UNIQUE_TAG_MASK);
  }
  EXPORT_SYMBOL(blk_mq_unique_tag);