text: #ifndef BLK_INTERNAL_H
  #define BLK_INTERNAL_H
  
  #include <linux/idr.h>
  #include <linux/blk-mq.h>
  #include "blk-mq.h"
  
  /* Amount of time in which a process may batch requests */
  #define BLK_BATCH_TIME	(HZ/50UL)
  
  /* Number of requests a "batching" process may submit */
  #define BLK_BATCH_REQ	32
  
  /* Max future timer expiry for timeouts */
  #define BLK_MAX_TIMEOUT		(5 * HZ)
  
  struct blk_flush_queue {
  	unsigned int		flush_queue_delayed:1;
  	unsigned int		flush_pending_idx:1;
  	unsigned int		flush_running_idx:1;
  	unsigned long		flush_pending_since;
  	struct list_head	flush_queue[2];
  	struct list_head	flush_data_in_flight;
  	struct request		*flush_rq;
  
  	/*
  	 * flush_rq shares tag with this rq, both can't be active
  	 * at the same time
  	 */
  	struct request		*orig_rq;
  	spinlock_t		mq_flush_lock;
  };
  
  extern struct kmem_cache *blk_requestq_cachep;
  extern struct kmem_cache *request_cachep;
  extern struct kobj_type blk_queue_ktype;
  extern struct ida blk_queue_ida;
  
  static inline struct blk_flush_queue *blk_get_flush_queue(
  		struct request_queue *q, struct blk_mq_ctx *ctx)
  {
  	if (q->mq_ops)
  		return blk_mq_map_queue(q, ctx->cpu)->fq;
  	return q->fq;
  }
  
  static inline void __blk_get_queue(struct request_queue *q)
  {
  	kobject_get(&q->kobj);
  }
  
  struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
  		int node, int cmd_size);
  void blk_free_flush_queue(struct blk_flush_queue *q);
  
  int blk_init_rl(struct request_list *rl, struct request_queue *q,
  		gfp_t gfp_mask);
  void blk_exit_rl(struct request_list *rl);
  void init_request_from_bio(struct request *req, struct bio *bio);
  void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
  			struct bio *bio);
  void blk_queue_bypass_start(struct request_queue *q);
  void blk_queue_bypass_end(struct request_queue *q);
  void blk_dequeue_request(struct request *rq);
  void __blk_queue_free_tags(struct request_queue *q);
  bool __blk_end_bidi_request(struct request *rq, int error,
  			    unsigned int nr_bytes, unsigned int bidi_bytes);
  void blk_freeze_queue(struct request_queue *q);
  
  static inline void blk_queue_enter_live(struct request_queue *q)
  {
  	/*
  	 * Given that running in generic_make_request() context
  	 * guarantees that a live reference against q_usage_counter has
  	 * been established, further references under that same context
  	 * need not check that the queue has been frozen (marked dead).
  	 */
  	percpu_ref_get(&q->q_usage_counter);
  }
  
  #ifdef CONFIG_BLK_DEV_INTEGRITY
  void blk_flush_integrity(void);
  #else
  static inline void blk_flush_integrity(void)
  {
  }
  #endif
  
  void blk_timeout_work(struct work_struct *work);
  unsigned long blk_rq_timeout(unsigned long timeout);
  void blk_add_timer(struct request *req);
  void blk_delete_timer(struct request *);
  
  
  bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
  			     struct bio *bio);
  bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
  			    struct bio *bio);
  bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
  			    unsigned int *request_count,
  			    struct request **same_queue_rq);
  unsigned int blk_plug_queued_count(struct request_queue *q);
  
  void blk_account_io_start(struct request *req, bool new_io);
  void blk_account_io_completion(struct request *req, unsigned int bytes);
  void blk_account_io_done(struct request *req);
  
  /*
   * Internal atomic flags for request handling
   */
  enum rq_atomic_flags {
  	REQ_ATOM_COMPLETE = 0,
  	REQ_ATOM_STARTED,
  };
  
  /*
   * EH timer and IO completion will both attempt to 'grab' the request, make
   * sure that only one of them succeeds
   */
  static inline int blk_mark_rq_complete(struct request *rq)
  {
  	return test_and_set_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags);
  }
  
  static inline void blk_clear_rq_complete(struct request *rq)
  {
  	clear_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags);
  }
  
  /*
   * Internal elevator interface
   */
  #define ELV_ON_HASH(rq) ((rq)->cmd_flags & REQ_HASHED)
  
  void blk_insert_flush(struct request *rq);
  
  static inline struct request *__elv_next_request(struct request_queue *q)
  {
  	struct request *rq;
  	struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
  
  	while (1) {
  		if (!list_empty(&q->queue_head)) {
  			rq = list_entry_rq(q->queue_head.next);
  			return rq;
  		}
  
  		/*
  		 * Flush request is running and flush request isn't queueable
  		 * in the drive, we can hold the queue till flush request is
  		 * finished. Even we don't do this, driver can't dispatch next
  		 * requests and will requeue them. And this can improve
  		 * throughput too. For example, we have request flush1, write1,
  		 * flush 2. flush1 is dispatched, then queue is hold, write1
  		 * isn't inserted to queue. After flush1 is finished, flush2
  		 * will be dispatched. Since disk cache is already clean,
  		 * flush2 will be finished very soon, so looks like flush2 is
  		 * folded to flush1.
  		 * Since the queue is hold, a flag is set to indicate the queue
  		 * should be restarted later. Please see flush_end_io() for
  		 * details.
  		 */
  		if (fq->flush_pending_idx != fq->flush_running_idx &&
  				!queue_flush_queueable(q)) {
  			fq->flush_queue_delayed = 1;
  			return NULL;
  		}
  		if (unlikely(blk_queue_bypass(q)) ||
  		    !q->elevator->type->ops.elevator_dispatch_fn(q, 0))
  			return NULL;
  	}
  }
  
  static inline void elv_activate_rq(struct request_queue *q, struct request *rq)
  {
  	struct elevator_queue *e = q->elevator;
  
  	if (e->type->ops.elevator_activate_req_fn)
  		e->type->ops.elevator_activate_req_fn(q, rq);
  }
  
  static inline void elv_deactivate_rq(struct request_queue *q, struct request *rq)
  {
  	struct elevator_queue *e = q->elevator;
  
  	if (e->type->ops.elevator_deactivate_req_fn)
  		e->type->ops.elevator_deactivate_req_fn(q, rq);
  }
  
  #ifdef CONFIG_FAIL_IO_TIMEOUT
  int blk_should_fake_timeout(struct request_queue *);
  ssize_t part_timeout_show(struct device *, struct device_attribute *, char *);
  ssize_t part_timeout_store(struct device *, struct device_attribute *,
  				const char *, size_t);
  #else
  static inline int blk_should_fake_timeout(struct request_queue *q)
  {
  	return 0;
  }
  #endif
  
  int ll_back_merge_fn(struct request_queue *q, struct request *req,
  		     struct bio *bio);
  int ll_front_merge_fn(struct request_queue *q, struct request *req, 
  		      struct bio *bio);
  int attempt_back_merge(struct request_queue *q, struct request *rq);
  int attempt_front_merge(struct request_queue *q, struct request *rq);
  int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
  				struct request *next);
  void blk_recalc_rq_segments(struct request *rq);
  void blk_rq_set_mixed_merge(struct request *rq);
  bool blk_rq_merge_ok(struct request *rq, struct bio *bio);
  int blk_try_merge(struct request *rq, struct bio *bio);
  
  void blk_queue_congestion_threshold(struct request_queue *q);
  
  int blk_dev_init(void);
  
  
  /*
   * Return the threshold (number of used requests) at which the queue is
   * considered to be congested.  It include a little hysteresis to keep the
   * context switch rate down.
   */
  static inline int queue_congestion_on_threshold(struct request_queue *q)
  {
  	return q->nr_congestion_on;
  }
  
  /*
   * The threshold at which a queue is considered to be uncongested
   */
  static inline int queue_congestion_off_threshold(struct request_queue *q)
  {
  	return q->nr_congestion_off;
  }
  
  extern int blk_update_nr_requests(struct request_queue *, unsigned int);
  
  /*
   * Contribute to IO statistics IFF:
   *
   *	a) it's attached to a gendisk, and
   *	b) the queue had IO stats enabled when this request was started, and
   *	c) it's a file system request
   */
  static inline int blk_do_io_stat(struct request *rq)
  {
  	return rq->rq_disk &&
  	       (rq->cmd_flags & REQ_IO_STAT) &&
  		(rq->cmd_type == REQ_TYPE_FS);
  }
  
  /*
   * Internal io_context interface
   */
  void get_io_context(struct io_context *ioc);
  struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q);
  struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
  			     gfp_t gfp_mask);
  void ioc_clear_queue(struct request_queue *q);
  
  int create_task_io_context(struct task_struct *task, gfp_t gfp_mask, int node);
  
  /**
   * create_io_context - try to create task->io_context
   * @gfp_mask: allocation mask
   * @node: allocation node
   *
   * If %current->io_context is %NULL, allocate a new io_context and install
   * it.  Returns the current %current->io_context which may be %NULL if
   * allocation failed.
   *
   * Note that this function can't be called with IRQ disabled because
   * task_lock which protects %current->io_context is IRQ-unsafe.
   */
  static inline struct io_context *create_io_context(gfp_t gfp_mask, int node)
  {
  	WARN_ON_ONCE(irqs_disabled());
  	if (unlikely(!current->io_context))
  		create_task_io_context(current, gfp_mask, node);
  	return current->io_context;
  }
  
  /*
   * Internal throttling interface
   */
  #ifdef CONFIG_BLK_DEV_THROTTLING
  extern void blk_throtl_drain(struct request_queue *q);
  extern int blk_throtl_init(struct request_queue *q);
  extern void blk_throtl_exit(struct request_queue *q);
  #else /* CONFIG_BLK_DEV_THROTTLING */
  static inline void blk_throtl_drain(struct request_queue *q) { }
  static inline int blk_throtl_init(struct request_queue *q) { return 0; }
  static inline void blk_throtl_exit(struct request_queue *q) { }
  #endif /* CONFIG_BLK_DEV_THROTTLING */
  
  #endif /* BLK_INTERNAL_H */
  