text: #ifndef _LINUX_BLKDEV_H
  #define _LINUX_BLKDEV_H
  
  #ifdef CONFIG_BLOCK
  
  #include <linux/sched.h>
  #include <linux/major.h>
  #include <linux/genhd.h>
  #include <linux/list.h>
  #include <linux/timer.h>
  #include <linux/workqueue.h>
  #include <linux/pagemap.h>
  #include <linux/backing-dev.h>
  #include <linux/wait.h>
  #include <linux/mempool.h>
  #include <linux/bio.h>
  #include <linux/module.h>
  #include <linux/stringify.h>
  #include <linux/bsg.h>
  
  #include <asm/scatterlist.h>
  
  struct scsi_ioctl_command;
  
  struct request_queue;
  typedef struct request_queue request_queue_t __deprecated;
  struct elevator_queue;
  typedef struct elevator_queue elevator_t;
  struct request_pm_state;
  struct blk_trace;
  struct request;
  struct sg_io_hdr;
  
  #define BLKDEV_MIN_RQ	4
  #define BLKDEV_MAX_RQ	128	/* Default maximum */
  
  /*
   * This is the per-process anticipatory I/O scheduler state.
   */
  struct as_io_context {
  	spinlock_t lock;
  
  	void (*dtor)(struct as_io_context *aic); /* destructor */
  	void (*exit)(struct as_io_context *aic); /* called on task exit */
  
  	unsigned long state;
  	atomic_t nr_queued; /* queued reads & sync writes */
  	atomic_t nr_dispatched; /* number of requests gone to the drivers */
  
  	/* IO History tracking */
  	/* Thinktime */
  	unsigned long last_end_request;
  	unsigned long ttime_total;
  	unsigned long ttime_samples;
  	unsigned long ttime_mean;
  	/* Layout pattern */
  	unsigned int seek_samples;
  	sector_t last_request_pos;
  	u64 seek_total;
  	sector_t seek_mean;
  };
  
  struct cfq_queue;
  struct cfq_io_context {
  	struct rb_node rb_node;
  	void *key;
  
  	struct cfq_queue *cfqq[2];
  
  	struct io_context *ioc;
  
  	unsigned long last_end_request;
  	sector_t last_request_pos;
  
  	unsigned long ttime_total;
  	unsigned long ttime_samples;
  	unsigned long ttime_mean;
  
  	unsigned int seek_samples;
  	u64 seek_total;
  	sector_t seek_mean;
  
  	struct list_head queue_list;
  
  	void (*dtor)(struct io_context *); /* destructor */
  	void (*exit)(struct io_context *); /* called on task exit */
  };
  
  /*
   * This is the per-process I/O subsystem state.  It is refcounted and
   * kmalloc'ed. Currently all fields are modified in process io context
   * (apart from the atomic refcount), so require no locking.
   */
  struct io_context {
  	atomic_t refcount;
  	struct task_struct *task;
  
  	unsigned int ioprio_changed;
  
  	/*
  	 * For request batching
  	 */
  	unsigned long last_waited; /* Time last woken after wait for request */
  	int nr_batch_requests;     /* Number of requests left in the batch */
  
  	struct as_io_context *aic;
  	struct rb_root cic_root;
  	void *ioc_data;
  };
  
  void put_io_context(struct io_context *ioc);
  void exit_io_context(void);
  struct io_context *get_io_context(gfp_t gfp_flags, int node);
  void copy_io_context(struct io_context **pdst, struct io_context **psrc);
  void swap_io_context(struct io_context **ioc1, struct io_context **ioc2);
  
  struct request;
  typedef void (rq_end_io_fn)(struct request *, int);
  
  struct request_list {
  	int count[2];
  	int starved[2];
  	int elvpriv;
  	mempool_t *rq_pool;
  	wait_queue_head_t wait[2];
  };
  
  /*
   * request command types
   */
  enum rq_cmd_type_bits {
  	REQ_TYPE_FS		= 1,	/* fs request */
  	REQ_TYPE_BLOCK_PC,		/* scsi command */
  	REQ_TYPE_SENSE,			/* sense request */
  	REQ_TYPE_PM_SUSPEND,		/* suspend request */
  	REQ_TYPE_PM_RESUME,		/* resume request */
  	REQ_TYPE_PM_SHUTDOWN,		/* shutdown request */
  	REQ_TYPE_FLUSH,			/* flush request */
  	REQ_TYPE_SPECIAL,		/* driver defined type */
  	REQ_TYPE_LINUX_BLOCK,		/* generic block layer message */
  	/*
  	 * for ATA/ATAPI devices. this really doesn't belong here, ide should
  	 * use REQ_TYPE_SPECIAL and use rq->cmd[0] with the range of driver
  	 * private REQ_LB opcodes to differentiate what type of request this is
  	 */
  	REQ_TYPE_ATA_CMD,
  	REQ_TYPE_ATA_TASK,
  	REQ_TYPE_ATA_TASKFILE,
  	REQ_TYPE_ATA_PC,
  };
  
  /*
   * For request of type REQ_TYPE_LINUX_BLOCK, rq->cmd[0] is the opcode being
   * sent down (similar to how REQ_TYPE_BLOCK_PC means that ->cmd[] holds a
   * SCSI cdb.
   *
   * 0x00 -> 0x3f are driver private, to be used for whatever purpose they need,
   * typically to differentiate REQ_TYPE_SPECIAL requests.
   *
   */
  enum {
  	/*
  	 * just examples for now
  	 */
  	REQ_LB_OP_EJECT	= 0x40,		/* eject request */
  	REQ_LB_OP_FLUSH = 0x41,		/* flush device */
  };
  
  /*
   * request type modified bits. first three bits match BIO_RW* bits, important
   */
  enum rq_flag_bits {
  	__REQ_RW,		/* not set, read. set, write */
  	__REQ_FAILFAST,		/* no low level driver retries */
  	__REQ_SORTED,		/* elevator knows about this request */
  	__REQ_SOFTBARRIER,	/* may not be passed by ioscheduler */
  	__REQ_HARDBARRIER,	/* may not be passed by drive either */
  	__REQ_FUA,		/* forced unit access */
  	__REQ_NOMERGE,		/* don't touch this for merging */
  	__REQ_STARTED,		/* drive already may have started this one */
  	__REQ_DONTPREP,		/* don't call prep for this one */
  	__REQ_QUEUED,		/* uses queueing */
  	__REQ_ELVPRIV,		/* elevator private data attached */
  	__REQ_FAILED,		/* set if the request failed */
  	__REQ_QUIET,		/* don't worry about errors */
  	__REQ_PREEMPT,		/* set for "ide_preempt" requests */
  	__REQ_ORDERED_COLOR,	/* is before or after barrier */
  	__REQ_RW_SYNC,		/* request is sync (O_DIRECT) */
  	__REQ_ALLOCED,		/* request came from our alloc pool */
  	__REQ_RW_META,		/* metadata io request */
  	__REQ_NR_BITS,		/* stops here */
  };
  
  #define REQ_RW		(1 << __REQ_RW)
  #define REQ_FAILFAST	(1 << __REQ_FAILFAST)
  #define REQ_SORTED	(1 << __REQ_SORTED)
  #define REQ_SOFTBARRIER	(1 << __REQ_SOFTBARRIER)
  #define REQ_HARDBARRIER	(1 << __REQ_HARDBARRIER)
  #define REQ_FUA		(1 << __REQ_FUA)
  #define REQ_NOMERGE	(1 << __REQ_NOMERGE)
  #define REQ_STARTED	(1 << __REQ_STARTED)
  #define REQ_DONTPREP	(1 << __REQ_DONTPREP)
  #define REQ_QUEUED	(1 << __REQ_QUEUED)
  #define REQ_ELVPRIV	(1 << __REQ_ELVPRIV)
  #define REQ_FAILED	(1 << __REQ_FAILED)
  #define REQ_QUIET	(1 << __REQ_QUIET)
  #define REQ_PREEMPT	(1 << __REQ_PREEMPT)
  #define REQ_ORDERED_COLOR	(1 << __REQ_ORDERED_COLOR)
  #define REQ_RW_SYNC	(1 << __REQ_RW_SYNC)
  #define REQ_ALLOCED	(1 << __REQ_ALLOCED)
  #define REQ_RW_META	(1 << __REQ_RW_META)
  
  #define BLK_MAX_CDB	16
  
  /*
   * try to put the fields that are referenced together in the same cacheline
   */
  struct request {
  	struct list_head queuelist;
  	struct list_head donelist;
  
  	struct request_queue *q;
  
  	unsigned int cmd_flags;
  	enum rq_cmd_type_bits cmd_type;
  
  	/* Maintain bio traversal state for part by part I/O submission.
  	 * hard_* are block layer internals, no driver should touch them!
  	 */
  
  	sector_t sector;		/* next sector to submit */
  	sector_t hard_sector;		/* next sector to complete */
  	unsigned long nr_sectors;	/* no. of sectors left to submit */
  	unsigned long hard_nr_sectors;	/* no. of sectors left to complete */
  	/* no. of sectors left to submit in the current segment */
  	unsigned int current_nr_sectors;
  
  	/* no. of sectors left to complete in the current segment */
  	unsigned int hard_cur_sectors;
  
  	struct bio *bio;
  	struct bio *biotail;
  
  	struct hlist_node hash;	/* merge hash */
  	/*
  	 * The rb_node is only used inside the io scheduler, requests
  	 * are pruned when moved to the dispatch queue. So let the
  	 * completion_data share space with the rb_node.
  	 */
  	union {
  		struct rb_node rb_node;	/* sort/lookup */
  		void *completion_data;
  	};
  
  	/*
  	 * two pointers are available for the IO schedulers, if they need
  	 * more they have to dynamically allocate it.
  	 */
  	void *elevator_private;
  	void *elevator_private2;
  
  	struct gendisk *rq_disk;
  	unsigned long start_time;
  
  	/* Number of scatter-gather DMA addr+len pairs after
  	 * physical address coalescing is performed.
  	 */
  	unsigned short nr_phys_segments;
  
  	/* Number of scatter-gather addr+len pairs after
  	 * physical and DMA remapping hardware coalescing is performed.
  	 * This is the number of scatter-gather entries the driver
  	 * will actually have to deal with after DMA mapping is done.
  	 */
  	unsigned short nr_hw_segments;
  
  	unsigned short ioprio;
  
  	void *special;
  	char *buffer;
  
  	int tag;
  	int errors;
  
  	int ref_count;
  
  	/*
  	 * when request is used as a packet command carrier
  	 */
  	unsigned int cmd_len;
  	unsigned char cmd[BLK_MAX_CDB];
  
  	unsigned int data_len;
  	unsigned int sense_len;
  	void *data;
  	void *sense;
  
  	unsigned int timeout;
  	int retries;
  
  	/*
  	 * completion callback.
  	 */
  	rq_end_io_fn *end_io;
  	void *end_io_data;
  
  	/* for bidi */
  	struct request *next_rq;
  };
  
  /*
   * State information carried for REQ_TYPE_PM_SUSPEND and REQ_TYPE_PM_RESUME
   * requests. Some step values could eventually be made generic.
   */
  struct request_pm_state
  {
  	/* PM state machine step value, currently driver specific */
  	int	pm_step;
  	/* requested PM state value (S1, S2, S3, S4, ...) */
  	u32	pm_state;
  	void*	data;		/* for driver use */
  };
  
  #include <linux/elevator.h>
  
  typedef void (request_fn_proc) (struct request_queue *q);
  typedef int (make_request_fn) (struct request_queue *q, struct bio *bio);
  typedef int (prep_rq_fn) (struct request_queue *, struct request *);
  typedef void (unplug_fn) (struct request_queue *);
  
  struct bio_vec;
  typedef int (merge_bvec_fn) (struct request_queue *, struct bio *, struct bio_vec *);
  typedef void (prepare_flush_fn) (struct request_queue *, struct request *);
  typedef void (softirq_done_fn)(struct request *);
  
  enum blk_queue_state {
  	Queue_down,
  	Queue_up,
  };
  
  struct blk_queue_tag {
  	struct request **tag_index;	/* map of busy tags */
  	unsigned long *tag_map;		/* bit map of free/busy tags */
  	int busy;			/* current depth */
  	int max_depth;			/* what we will send to device */
  	int real_max_depth;		/* what the array can hold */
  	atomic_t refcnt;		/* map can be shared */
  };
  
  struct request_queue
  {
  	/*
  	 * Together with queue_head for cacheline sharing
  	 */
  	struct list_head	queue_head;
  	struct request		*last_merge;
  	elevator_t		*elevator;
  
  	/*
  	 * the queue request freelist, one for reads and one for writes
  	 */
  	struct request_list	rq;
  
  	request_fn_proc		*request_fn;
  	make_request_fn		*make_request_fn;
  	prep_rq_fn		*prep_rq_fn;
  	unplug_fn		*unplug_fn;
  	merge_bvec_fn		*merge_bvec_fn;
  	prepare_flush_fn	*prepare_flush_fn;
  	softirq_done_fn		*softirq_done_fn;
  
  	/*
  	 * Dispatch queue sorting
  	 */
  	sector_t		end_sector;
  	struct request		*boundary_rq;
  
  	/*
  	 * Auto-unplugging state
  	 */
  	struct timer_list	unplug_timer;
  	int			unplug_thresh;	/* After this many requests */
  	unsigned long		unplug_delay;	/* After this many jiffies */
  	struct work_struct	unplug_work;
  
  	struct backing_dev_info	backing_dev_info;
  
  	/*
  	 * The queue owner gets to use this for whatever they like.
  	 * ll_rw_blk doesn't touch it.
  	 */
  	void			*queuedata;
  
  	/*
  	 * queue needs bounce pages for pages above this limit
  	 */
  	unsigned long		bounce_pfn;
  	gfp_t			bounce_gfp;
  
  	/*
  	 * various queue flags, see QUEUE_* below
  	 */
  	unsigned long		queue_flags;
  
  	/*
  	 * protects queue structures from reentrancy. ->__queue_lock should
  	 * _never_ be used directly, it is queue private. always use
  	 * ->queue_lock.
  	 */
  	spinlock_t		__queue_lock;
  	spinlock_t		*queue_lock;
  
  	/*
  	 * queue kobject
  	 */
  	struct kobject kobj;
  
  	/*
  	 * queue settings
  	 */
  	unsigned long		nr_requests;	/* Max # of requests */
  	unsigned int		nr_congestion_on;
  	unsigned int		nr_congestion_off;
  	unsigned int		nr_batching;
  
  	unsigned int		max_sectors;
  	unsigned int		max_hw_sectors;
  	unsigned short		max_phys_segments;
  	unsigned short		max_hw_segments;
  	unsigned short		hardsect_size;
  	unsigned int		max_segment_size;
  
  	unsigned long		seg_boundary_mask;
  	unsigned int		dma_alignment;
  
  	struct blk_queue_tag	*queue_tags;
  	struct list_head	tag_busy_list;
  
  	unsigned int		nr_sorted;
  	unsigned int		in_flight;
  
  	/*
  	 * sg stuff
  	 */
  	unsigned int		sg_timeout;
  	unsigned int		sg_reserved_size;
  	int			node;
  #ifdef CONFIG_BLK_DEV_IO_TRACE
  	struct blk_trace	*blk_trace;
  #endif
  	/*
  	 * reserved for flush operations
  	 */
  	unsigned int		ordered, next_ordered, ordseq;
  	int			orderr, ordcolor;
  	struct request		pre_flush_rq, bar_rq, post_flush_rq;
  	struct request		*orig_bar_rq;
  
  	struct mutex		sysfs_lock;
  
  #if defined(CONFIG_BLK_DEV_BSG)
  	struct bsg_class_device bsg_dev;
  #endif
  };
  
  #define QUEUE_FLAG_CLUSTER	0	/* cluster several segments into 1 */
  #define QUEUE_FLAG_QUEUED	1	/* uses generic tag queueing */
  #define QUEUE_FLAG_STOPPED	2	/* queue is stopped */
  #define	QUEUE_FLAG_READFULL	3	/* read queue has been filled */
  #define QUEUE_FLAG_WRITEFULL	4	/* write queue has been filled */
  #define QUEUE_FLAG_DEAD		5	/* queue being torn down */
  #define QUEUE_FLAG_REENTER	6	/* Re-entrancy avoidance */
  #define QUEUE_FLAG_PLUGGED	7	/* queue is plugged */
  #define QUEUE_FLAG_ELVSWITCH	8	/* don't use elevator, just do FIFO */
  #define QUEUE_FLAG_BIDI		9	/* queue supports bidi requests */
  
  enum {
  	/*
  	 * Hardbarrier is supported with one of the following methods.
  	 *
  	 * NONE		: hardbarrier unsupported
  	 * DRAIN	: ordering by draining is enough
  	 * DRAIN_FLUSH	: ordering by draining w/ pre and post flushes
  	 * DRAIN_FUA	: ordering by draining w/ pre flush and FUA write
  	 * TAG		: ordering by tag is enough
  	 * TAG_FLUSH	: ordering by tag w/ pre and post flushes
  	 * TAG_FUA	: ordering by tag w/ pre flush and FUA write
  	 */
  	QUEUE_ORDERED_NONE	= 0x00,
  	QUEUE_ORDERED_DRAIN	= 0x01,
  	QUEUE_ORDERED_TAG	= 0x02,
  
  	QUEUE_ORDERED_PREFLUSH	= 0x10,
  	QUEUE_ORDERED_POSTFLUSH	= 0x20,
  	QUEUE_ORDERED_FUA	= 0x40,
  
  	QUEUE_ORDERED_DRAIN_FLUSH = QUEUE_ORDERED_DRAIN |
  			QUEUE_ORDERED_PREFLUSH | QUEUE_ORDERED_POSTFLUSH,
  	QUEUE_ORDERED_DRAIN_FUA	= QUEUE_ORDERED_DRAIN |
  			QUEUE_ORDERED_PREFLUSH | QUEUE_ORDERED_FUA,
  	QUEUE_ORDERED_TAG_FLUSH	= QUEUE_ORDERED_TAG |
  			QUEUE_ORDERED_PREFLUSH | QUEUE_ORDERED_POSTFLUSH,
  	QUEUE_ORDERED_TAG_FUA	= QUEUE_ORDERED_TAG |
  			QUEUE_ORDERED_PREFLUSH | QUEUE_ORDERED_FUA,
  
  	/*
  	 * Ordered operation sequence
  	 */
  	QUEUE_ORDSEQ_STARTED	= 0x01,	/* flushing in progress */
  	QUEUE_ORDSEQ_DRAIN	= 0x02,	/* waiting for the queue to be drained */
  	QUEUE_ORDSEQ_PREFLUSH	= 0x04,	/* pre-flushing in progress */
  	QUEUE_ORDSEQ_BAR	= 0x08,	/* original barrier req in progress */
  	QUEUE_ORDSEQ_POSTFLUSH	= 0x10,	/* post-flushing in progress */
  	QUEUE_ORDSEQ_DONE	= 0x20,
  };
  
  #define blk_queue_plugged(q)	test_bit(QUEUE_FLAG_PLUGGED, &(q)->queue_flags)
  #define blk_queue_tagged(q)	test_bit(QUEUE_FLAG_QUEUED, &(q)->queue_flags)
  #define blk_queue_stopped(q)	test_bit(QUEUE_FLAG_STOPPED, &(q)->queue_flags)
  #define blk_queue_flushing(q)	((q)->ordseq)
  
  #define blk_fs_request(rq)	((rq)->cmd_type == REQ_TYPE_FS)
  #define blk_pc_request(rq)	((rq)->cmd_type == REQ_TYPE_BLOCK_PC)
  #define blk_special_request(rq)	((rq)->cmd_type == REQ_TYPE_SPECIAL)
  #define blk_sense_request(rq)	((rq)->cmd_type == REQ_TYPE_SENSE)
  
  #define blk_noretry_request(rq)	((rq)->cmd_flags & REQ_FAILFAST)
  #define blk_rq_started(rq)	((rq)->cmd_flags & REQ_STARTED)
  
  #define blk_account_rq(rq)	(blk_rq_started(rq) && blk_fs_request(rq))
  
  #define blk_pm_suspend_request(rq)	((rq)->cmd_type == REQ_TYPE_PM_SUSPEND)
  #define blk_pm_resume_request(rq)	((rq)->cmd_type == REQ_TYPE_PM_RESUME)
  #define blk_pm_request(rq)	\
  	(blk_pm_suspend_request(rq) || blk_pm_resume_request(rq))
  
  #define blk_sorted_rq(rq)	((rq)->cmd_flags & REQ_SORTED)
  #define blk_barrier_rq(rq)	((rq)->cmd_flags & REQ_HARDBARRIER)
  #define blk_fua_rq(rq)		((rq)->cmd_flags & REQ_FUA)
  #define blk_bidi_rq(rq)		((rq)->next_rq != NULL)
  #define blk_empty_barrier(rq)	(blk_barrier_rq(rq) && blk_fs_request(rq) && !(rq)->hard_nr_sectors)
  
  #define list_entry_rq(ptr)	list_entry((ptr), struct request, queuelist)
  
  #define rq_data_dir(rq)		((rq)->cmd_flags & 1)
  
  /*
   * We regard a request as sync, if it's a READ or a SYNC write.
   */
  #define rq_is_sync(rq)		(rq_data_dir((rq)) == READ || (rq)->cmd_flags & REQ_RW_SYNC)
  #define rq_is_meta(rq)		((rq)->cmd_flags & REQ_RW_META)
  
  static inline int blk_queue_full(struct request_queue *q, int rw)
  {
  	if (rw == READ)
  		return test_bit(QUEUE_FLAG_READFULL, &q->queue_flags);
  	return test_bit(QUEUE_FLAG_WRITEFULL, &q->queue_flags);
  }
  
  static inline void blk_set_queue_full(struct request_queue *q, int rw)
  {
  	if (rw == READ)
  		set_bit(QUEUE_FLAG_READFULL, &q->queue_flags);
  	else
  		set_bit(QUEUE_FLAG_WRITEFULL, &q->queue_flags);
  }
  
  static inline void blk_clear_queue_full(struct request_queue *q, int rw)
  {
  	if (rw == READ)
  		clear_bit(QUEUE_FLAG_READFULL, &q->queue_flags);
  	else
  		clear_bit(QUEUE_FLAG_WRITEFULL, &q->queue_flags);
  }
  
  
  /*
   * mergeable request must not have _NOMERGE or _BARRIER bit set, nor may
   * it already be started by driver.
   */
  #define RQ_NOMERGE_FLAGS	\
  	(REQ_NOMERGE | REQ_STARTED | REQ_HARDBARRIER | REQ_SOFTBARRIER)
  #define rq_mergeable(rq)	\
  	(!((rq)->cmd_flags & RQ_NOMERGE_FLAGS) && blk_fs_request((rq)))
  
  /*
   * q->prep_rq_fn return values
   */
  #define BLKPREP_OK		0	/* serve it */
  #define BLKPREP_KILL		1	/* fatal error, kill */
  #define BLKPREP_DEFER		2	/* leave on queue */
  
  extern unsigned long blk_max_low_pfn, blk_max_pfn;
  
  /*
   * standard bounce addresses:
   *
   * BLK_BOUNCE_HIGH	: bounce all highmem pages
   * BLK_BOUNCE_ANY	: don't bounce anything
   * BLK_BOUNCE_ISA	: bounce pages above ISA DMA boundary
   */
  #define BLK_BOUNCE_HIGH		((u64)blk_max_low_pfn << PAGE_SHIFT)
  #define BLK_BOUNCE_ANY		((u64)blk_max_pfn << PAGE_SHIFT)
  #define BLK_BOUNCE_ISA		(ISA_DMA_THRESHOLD)
  
  /*
   * default timeout for SG_IO if none specified
   */
  #define BLK_DEFAULT_SG_TIMEOUT	(60 * HZ)
  
  #ifdef CONFIG_BOUNCE
  extern int init_emergency_isa_pool(void);
  extern void blk_queue_bounce(struct request_queue *q, struct bio **bio);
  #else
  static inline int init_emergency_isa_pool(void)
  {
  	return 0;
  }
  static inline void blk_queue_bounce(struct request_queue *q, struct bio **bio)
  {
  }
  #endif /* CONFIG_MMU */
  
  struct req_iterator {
  	int i;
  	struct bio *bio;
  };
  
  /* This should not be used directly - use rq_for_each_segment */
  #define __rq_for_each_bio(_bio, rq)	\
  	if ((rq->bio))			\
  		for (_bio = (rq)->bio; _bio; _bio = _bio->bi_next)
  
  #define rq_for_each_segment(bvl, _rq, _iter)			\
  	__rq_for_each_bio(_iter.bio, _rq)			\
  		bio_for_each_segment(bvl, _iter.bio, _iter.i)
  
  #define rq_iter_last(rq, _iter)					\
  		(_iter.bio->bi_next == NULL && _iter.i == _iter.bio->bi_vcnt-1)
  
  extern int blk_register_queue(struct gendisk *disk);
  extern void blk_unregister_queue(struct gendisk *disk);
  extern void register_disk(struct gendisk *dev);
  extern void generic_make_request(struct bio *bio);
  extern void blk_put_request(struct request *);
  extern void __blk_put_request(struct request_queue *, struct request *);
  extern void blk_end_sync_rq(struct request *rq, int error);
  extern struct request *blk_get_request(struct request_queue *, int, gfp_t);
  extern void blk_insert_request(struct request_queue *, struct request *, int, void *);
  extern void blk_requeue_request(struct request_queue *, struct request *);
  extern void blk_plug_device(struct request_queue *);
  extern int blk_remove_plug(struct request_queue *);
  extern void blk_recount_segments(struct request_queue *, struct bio *);
  extern int scsi_cmd_ioctl(struct file *, struct request_queue *,
  			  struct gendisk *, unsigned int, void __user *);
  extern int sg_scsi_ioctl(struct file *, struct request_queue *,
  		struct gendisk *, struct scsi_ioctl_command __user *);
  
  /*
   * Temporary export, until SCSI gets fixed up.
   */
  extern int blk_rq_append_bio(struct request_queue *q, struct request *rq,
  			     struct bio *bio);
  
  /*
   * A queue has just exitted congestion.  Note this in the global counter of
   * congested queues, and wake up anyone who was waiting for requests to be
   * put back.
   */
  static inline void blk_clear_queue_congested(struct request_queue *q, int rw)
  {
  	clear_bdi_congested(&q->backing_dev_info, rw);
  }
  
  /*
   * A queue has just entered congestion.  Flag that in the queue's VM-visible
   * state flags and increment the global gounter of congested queues.
   */
  static inline void blk_set_queue_congested(struct request_queue *q, int rw)
  {
  	set_bdi_congested(&q->backing_dev_info, rw);
  }
  
  extern void blk_start_queue(struct request_queue *q);
  extern void blk_stop_queue(struct request_queue *q);
  extern void blk_sync_queue(struct request_queue *q);
  extern void __blk_stop_queue(struct request_queue *q);
  extern void blk_run_queue(struct request_queue *);
  extern void blk_start_queueing(struct request_queue *);
  extern int blk_rq_map_user(struct request_queue *, struct request *, void __user *, unsigned long);
  extern int blk_rq_unmap_user(struct bio *);
  extern int blk_rq_map_kern(struct request_queue *, struct request *, void *, unsigned int, gfp_t);
  extern int blk_rq_map_user_iov(struct request_queue *, struct request *,
  			       struct sg_iovec *, int, unsigned int);
  extern int blk_execute_rq(struct request_queue *, struct gendisk *,
  			  struct request *, int);
  extern void blk_execute_rq_nowait(struct request_queue *, struct gendisk *,
  				  struct request *, int, rq_end_io_fn *);
  extern int blk_verify_command(unsigned char *, int);
  extern void blk_unplug(struct request_queue *q);
  
  static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
  {
  	return bdev->bd_disk->queue;
  }
  
  static inline void blk_run_backing_dev(struct backing_dev_info *bdi,
  				       struct page *page)
  {
  	if (bdi && bdi->unplug_io_fn)
  		bdi->unplug_io_fn(bdi, page);
  }
  
  static inline void blk_run_address_space(struct address_space *mapping)
  {
  	if (mapping)
  		blk_run_backing_dev(mapping->backing_dev_info, NULL);
  }
  
  /*
   * end_request() and friends. Must be called with the request queue spinlock
   * acquired. All functions called within end_request() _must_be_ atomic.
   *
   * Several drivers define their own end_request and call
   * end_that_request_first() and end_that_request_last()
   * for parts of the original function. This prevents
   * code duplication in drivers.
   */
  extern int end_that_request_first(struct request *, int, int);
  extern int end_that_request_chunk(struct request *, int, int);
  extern void end_that_request_last(struct request *, int);
  extern void end_request(struct request *, int);
  extern void end_queued_request(struct request *, int);
  extern void end_dequeued_request(struct request *, int);
  extern void blk_complete_request(struct request *);
  
  /*
   * end_that_request_first/chunk() takes an uptodate argument. we account
   * any value <= as an io error. 0 means -EIO for compatability reasons,
   * any other < 0 value is the direct error type. An uptodate value of
   * 1 indicates successful io completion
   */
  #define end_io_error(uptodate)	(unlikely((uptodate) <= 0))
  
  static inline void blkdev_dequeue_request(struct request *req)
  {
  	elv_dequeue_request(req->q, req);
  }
  
  /*
   * Access functions for manipulating queue properties
   */
  extern struct request_queue *blk_init_queue_node(request_fn_proc *rfn,
  					spinlock_t *lock, int node_id);
  extern struct request_queue *blk_init_queue(request_fn_proc *, spinlock_t *);
  extern void blk_cleanup_queue(struct request_queue *);
  extern void blk_queue_make_request(struct request_queue *, make_request_fn *);
  extern void blk_queue_bounce_limit(struct request_queue *, u64);
  extern void blk_queue_max_sectors(struct request_queue *, unsigned int);
  extern void blk_queue_max_phys_segments(struct request_queue *, unsigned short);
  extern void blk_queue_max_hw_segments(struct request_queue *, unsigned short);
  extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
  extern void blk_queue_hardsect_size(struct request_queue *, unsigned short);
  extern void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b);
  extern void blk_queue_segment_boundary(struct request_queue *, unsigned long);
  extern void blk_queue_prep_rq(struct request_queue *, prep_rq_fn *pfn);
  extern void blk_queue_merge_bvec(struct request_queue *, merge_bvec_fn *);
  extern void blk_queue_dma_alignment(struct request_queue *, int);
  extern void blk_queue_softirq_done(struct request_queue *, softirq_done_fn *);
  extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
  extern int blk_queue_ordered(struct request_queue *, unsigned, prepare_flush_fn *);
  extern int blk_do_ordered(struct request_queue *, struct request **);
  extern unsigned blk_ordered_cur_seq(struct request_queue *);
  extern unsigned blk_ordered_req_seq(struct request *);
  extern void blk_ordered_complete_seq(struct request_queue *, unsigned, int);
  
  extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
  extern void blk_dump_rq_flags(struct request *, char *);
  extern void generic_unplug_device(struct request_queue *);
  extern void __generic_unplug_device(struct request_queue *);
  extern long nr_blockdev_pages(void);
  
  int blk_get_queue(struct request_queue *);
  struct request_queue *blk_alloc_queue(gfp_t);
  struct request_queue *blk_alloc_queue_node(gfp_t, int);
  extern void blk_put_queue(struct request_queue *);
  
  /*
   * tag stuff
   */
  #define blk_queue_tag_depth(q)		((q)->queue_tags->busy)
  #define blk_queue_tag_queue(q)		((q)->queue_tags->busy < (q)->queue_tags->max_depth)
  #define blk_rq_tagged(rq)		((rq)->cmd_flags & REQ_QUEUED)
  extern int blk_queue_start_tag(struct request_queue *, struct request *);
  extern struct request *blk_queue_find_tag(struct request_queue *, int);
  extern void blk_queue_end_tag(struct request_queue *, struct request *);
  extern int blk_queue_init_tags(struct request_queue *, int, struct blk_queue_tag *);
  extern void blk_queue_free_tags(struct request_queue *);
  extern int blk_queue_resize_tags(struct request_queue *, int);
  extern void blk_queue_invalidate_tags(struct request_queue *);
  extern struct blk_queue_tag *blk_init_tags(int);
  extern void blk_free_tags(struct blk_queue_tag *);
  
  static inline struct request *blk_map_queue_find_tag(struct blk_queue_tag *bqt,
  						int tag)
  {
  	if (unlikely(bqt == NULL || tag >= bqt->real_max_depth))
  		return NULL;
  	return bqt->tag_index[tag];
  }
  
  extern int blkdev_issue_flush(struct block_device *, sector_t *);
  
  #define MAX_PHYS_SEGMENTS 128
  #define MAX_HW_SEGMENTS 128
  #define SAFE_MAX_SECTORS 255
  #define BLK_DEF_MAX_SECTORS 1024
  
  #define MAX_SEGMENT_SIZE	65536
  
  #define blkdev_entry_to_request(entry) list_entry((entry), struct request, queuelist)
  
  static inline int queue_hardsect_size(struct request_queue *q)
  {
  	int retval = 512;
  
  	if (q && q->hardsect_size)
  		retval = q->hardsect_size;
  
  	return retval;
  }
  
  static inline int bdev_hardsect_size(struct block_device *bdev)
  {
  	return queue_hardsect_size(bdev_get_queue(bdev));
  }
  
  static inline int queue_dma_alignment(struct request_queue *q)
  {
  	int retval = 511;
  
  	if (q && q->dma_alignment)
  		retval = q->dma_alignment;
  
  	return retval;
  }
  
  /* assumes size > 256 */
  static inline unsigned int blksize_bits(unsigned int size)
  {
  	unsigned int bits = 8;
  	do {
  		bits++;
  		size >>= 1;
  	} while (size > 256);
  	return bits;
  }
  
  static inline unsigned int block_size(struct block_device *bdev)
  {
  	return bdev->bd_block_size;
  }
  
  typedef struct {struct page *v;} Sector;
  
  unsigned char *read_dev_sector(struct block_device *, sector_t, Sector *);
  
  static inline void put_dev_sector(Sector p)
  {
  	page_cache_release(p.v);
  }
  
  struct work_struct;
  int kblockd_schedule_work(struct work_struct *work);
  void kblockd_flush_work(struct work_struct *work);
  
  #define MODULE_ALIAS_BLOCKDEV(major,minor) \
  	MODULE_ALIAS("block-major-" __stringify(major) "-" __stringify(minor))
  #define MODULE_ALIAS_BLOCKDEV_MAJOR(major) \
  	MODULE_ALIAS("block-major-" __stringify(major) "-*")
  
  
  #else /* CONFIG_BLOCK */
  /*
   * stubs for when the block layer is configured out
   */
  #define buffer_heads_over_limit 0
  
  static inline long nr_blockdev_pages(void)
  {
  	return 0;
  }
  
  static inline void exit_io_context(void)
  {
  }
  
  #endif /* CONFIG_BLOCK */
  
  #endif
  