#ifndef _LINUX_ELEVATOR_H
  #define _LINUX_ELEVATOR_H

  #include <linux/percpu.h>

  #ifdef CONFIG_BLOCK

  typedef int (elevator_merge_fn) (struct request_queue *, struct request **,

  				 struct bio *);

  typedef void (elevator_merge_req_fn) (struct request_queue *, struct request *, struct request *);

  typedef void (elevator_merged_fn) (struct request_queue *, struct request *, int);

  typedef int (elevator_allow_merge_fn) (struct request_queue *, struct request *, struct bio *);

  typedef void (elevator_bio_merged_fn) (struct request_queue *,
  						struct request *, struct bio *);

  typedef int (elevator_dispatch_fn) (struct request_queue *, int);

  typedef void (elevator_add_req_fn) (struct request_queue *, struct request *);
  typedef int (elevator_queue_empty_fn) (struct request_queue *);
  typedef struct request *(elevator_request_list_fn) (struct request_queue *, struct request *);
  typedef void (elevator_completed_req_fn) (struct request_queue *, struct request *);
  typedef int (elevator_may_queue_fn) (struct request_queue *, int);

  typedef int (elevator_set_req_fn) (struct request_queue *, struct request *, gfp_t);

  typedef void (elevator_put_req_fn) (struct request *);

  typedef void (elevator_activate_req_fn) (struct request_queue *, struct request *);
  typedef void (elevator_deactivate_req_fn) (struct request_queue *, struct request *);

  typedef void *(elevator_init_fn) (struct request_queue *);

  typedef void (elevator_exit_fn) (struct elevator_queue *);

  
  struct elevator_ops
  {
  	elevator_merge_fn *elevator_merge_fn;
  	elevator_merged_fn *elevator_merged_fn;
  	elevator_merge_req_fn *elevator_merge_req_fn;

  	elevator_allow_merge_fn *elevator_allow_merge_fn;

  	elevator_bio_merged_fn *elevator_bio_merged_fn;

  	elevator_dispatch_fn *elevator_dispatch_fn;

  	elevator_add_req_fn *elevator_add_req_fn;

  	elevator_activate_req_fn *elevator_activate_req_fn;

  	elevator_deactivate_req_fn *elevator_deactivate_req_fn;
  
  	elevator_queue_empty_fn *elevator_queue_empty_fn;
  	elevator_completed_req_fn *elevator_completed_req_fn;
  
  	elevator_request_list_fn *elevator_former_req_fn;
  	elevator_request_list_fn *elevator_latter_req_fn;
  
  	elevator_set_req_fn *elevator_set_req_fn;
  	elevator_put_req_fn *elevator_put_req_fn;
  
  	elevator_may_queue_fn *elevator_may_queue_fn;
  
  	elevator_init_fn *elevator_init_fn;
  	elevator_exit_fn *elevator_exit_fn;

  	void (*trim)(struct io_context *);

  };
  
  #define ELV_NAME_MAX	(16)

  struct elv_fs_entry {
  	struct attribute attr;

  	ssize_t (*show)(struct elevator_queue *, char *);
  	ssize_t (*store)(struct elevator_queue *, const char *, size_t);

  };

  /*
   * identifies an elevator type, such as AS or deadline
   */
  struct elevator_type
  {
  	struct list_head list;
  	struct elevator_ops ops;

  	struct elv_fs_entry *elevator_attrs;

  	char elevator_name[ELV_NAME_MAX];
  	struct module *elevator_owner;
  };
  
  /*

   * each queue has an elevator_queue associated with it

   */
  struct elevator_queue
  {
  	struct elevator_ops *ops;
  	void *elevator_data;
  	struct kobject kobj;
  	struct elevator_type *elevator_type;

  	struct mutex sysfs_lock;

  	struct hlist_head *hash;

  };
  
  /*
   * block elevator interface
   */

  extern void elv_dispatch_sort(struct request_queue *, struct request *);
  extern void elv_dispatch_add_tail(struct request_queue *, struct request *);
  extern void elv_add_request(struct request_queue *, struct request *, int, int);
  extern void __elv_add_request(struct request_queue *, struct request *, int, int);
  extern void elv_insert(struct request_queue *, struct request *, int);
  extern int elv_merge(struct request_queue *, struct request **, struct bio *);
  extern void elv_merge_requests(struct request_queue *, struct request *,

  			       struct request *);

  extern void elv_merged_request(struct request_queue *, struct request *, int);

  extern void elv_bio_merged(struct request_queue *q, struct request *,
  				struct bio *);

  extern void elv_requeue_request(struct request_queue *, struct request *);
  extern int elv_queue_empty(struct request_queue *);

  extern struct request *elv_former_request(struct request_queue *, struct request *);
  extern struct request *elv_latter_request(struct request_queue *, struct request *);
  extern int elv_register_queue(struct request_queue *q);
  extern void elv_unregister_queue(struct request_queue *q);
  extern int elv_may_queue(struct request_queue *, int);

  extern void elv_abort_queue(struct request_queue *);

  extern void elv_completed_request(struct request_queue *, struct request *);
  extern int elv_set_request(struct request_queue *, struct request *, gfp_t);
  extern void elv_put_request(struct request_queue *, struct request *);

  extern void elv_drain_elevator(struct request_queue *);

  
  /*
   * io scheduler registration
   */

  extern void elv_register(struct elevator_type *);

  extern void elv_unregister(struct elevator_type *);
  
  /*
   * io scheduler sysfs switching
   */

  extern ssize_t elv_iosched_show(struct request_queue *, char *);
  extern ssize_t elv_iosched_store(struct request_queue *, const char *, size_t);

  extern int elevator_init(struct request_queue *, char *);

  extern void elevator_exit(struct elevator_queue *);

  extern int elevator_change(struct request_queue *, const char *);

  extern int elv_rq_merge_ok(struct request *, struct bio *);

  
  /*

   * Helper functions.
   */

  extern struct request *elv_rb_former_request(struct request_queue *, struct request *);
  extern struct request *elv_rb_latter_request(struct request_queue *, struct request *);

  
  /*
   * rb support functions.
   */
  extern struct request *elv_rb_add(struct rb_root *, struct request *);
  extern void elv_rb_del(struct rb_root *, struct request *);
  extern struct request *elv_rb_find(struct rb_root *, sector_t);
  
  /*

   * Return values from elevator merger
   */
  #define ELEVATOR_NO_MERGE	0
  #define ELEVATOR_FRONT_MERGE	1
  #define ELEVATOR_BACK_MERGE	2
  
  /*
   * Insertion selection
   */
  #define ELEVATOR_INSERT_FRONT	1
  #define ELEVATOR_INSERT_BACK	2
  #define ELEVATOR_INSERT_SORT	3

  #define ELEVATOR_INSERT_REQUEUE	4

  
  /*
   * return values from elevator_may_queue_fn
   */
  enum {
  	ELV_MQUEUE_MAY,
  	ELV_MQUEUE_NO,
  	ELV_MQUEUE_MUST,
  };

  #define rq_end_sector(rq)	(blk_rq_pos(rq) + blk_rq_sectors(rq))

  #define rb_entry_rq(node)	rb_entry((node), struct request, rb_node)

  /*

   * Hack to reuse the csd.list list_head as the fifo time holder while

   * the request is in the io scheduler. Saves an unsigned long in rq.
   */

  #define rq_fifo_time(rq)	((unsigned long) (rq)->csd.list.next)
  #define rq_set_fifo_time(rq,exp)	((rq)->csd.list.next = (void *) (exp))

  #define rq_entry_fifo(ptr)	list_entry((ptr), struct request, queuelist)
  #define rq_fifo_clear(rq)	do {		\
  	list_del_init(&(rq)->queuelist);	\

  	INIT_LIST_HEAD(&(rq)->csd.list);	\

  	} while (0)

  /*
   * io context count accounting
   */
  #define elv_ioc_count_mod(name, __val)				\
  	do {							\
  		preempt_disable();				\
  		__get_cpu_var(name) += (__val);			\
  		preempt_enable();				\
  	} while (0)
  
  #define elv_ioc_count_inc(name)	elv_ioc_count_mod(name, 1)
  #define elv_ioc_count_dec(name)	elv_ioc_count_mod(name, -1)
  
  #define elv_ioc_count_read(name)				\
  ({								\
  	unsigned long __val = 0;				\
  	int __cpu;						\
  	smp_wmb();						\
  	for_each_possible_cpu(__cpu)				\
  		__val += per_cpu(name, __cpu);			\
  	__val;							\
  })

  #endif /* CONFIG_BLOCK */

  #endif