text: #ifndef _LINUX_BLKDEV_H
  #define _LINUX_BLKDEV_H
  
  #include <linux/sched.h>
  
  #ifdef CONFIG_BLOCK
  
  #include <linux/major.h>
  #include <linux/genhd.h>
  #include <linux/list.h>
  #include <linux/llist.h>
  #include <linux/timer.h>
  #include <linux/workqueue.h>
  #include <linux/pagemap.h>
  #include <linux/backing-dev-defs.h>
  #include <linux/wait.h>
  #include <linux/mempool.h>
  #include <linux/bio.h>
  #include <linux/stringify.h>
  #include <linux/gfp.h>
  #include <linux/bsg.h>
  #include <linux/smp.h>
  #include <linux/rcupdate.h>
  #include <linux/percpu-refcount.h>
  #include <linux/scatterlist.h>
  
  struct module;
  struct scsi_ioctl_command;
  
  struct request_queue;
  struct elevator_queue;
  struct blk_trace;
  struct request;
  struct sg_io_hdr;
  struct bsg_job;
  struct blkcg_gq;
  struct blk_flush_queue;
  struct pr_ops;
  
  #define BLKDEV_MIN_RQ	4
  #define BLKDEV_MAX_RQ	128	/* Default maximum */
  
  /*
   * Maximum number of blkcg policies allowed to be registered concurrently.
   * Defined here to simplify include dependency.
   */
  #define BLKCG_MAX_POLS		2
  
  struct request;
  typedef void (rq_end_io_fn)(struct request *, int);
  
  #define BLK_RL_SYNCFULL		(1U << 0)
  #define BLK_RL_ASYNCFULL	(1U << 1)
  
  struct request_list {
  	struct request_queue	*q;	/* the queue this rl belongs to */
  #ifdef CONFIG_BLK_CGROUP
  	struct blkcg_gq		*blkg;	/* blkg this request pool belongs to */
  #endif
  	/*
  	 * count[], starved[], and wait[] are indexed by
  	 * BLK_RW_SYNC/BLK_RW_ASYNC
  	 */
  	int			count[2];
  	int			starved[2];
  	mempool_t		*rq_pool;
  	wait_queue_head_t	wait[2];
  	unsigned int		flags;
  };
  
  /*
   * request command types
   */
  enum rq_cmd_type_bits {
  	REQ_TYPE_FS		= 1,	/* fs request */
  	REQ_TYPE_BLOCK_PC,		/* scsi command */
  	REQ_TYPE_DRV_PRIV,		/* driver defined types from here */
  };
  
  #define BLK_MAX_CDB	16
  
  /*
   * Try to put the fields that are referenced together in the same cacheline.
   *
   * If you modify this structure, make sure to update blk_rq_init() and
   * especially blk_mq_rq_ctx_init() to take care of the added fields.
   */
  struct request {
  	struct list_head queuelist;
  	union {
  		struct call_single_data csd;
  		struct work_struct work;
  		unsigned long fifo_time;
  	};
  
  	struct request_queue *q;
  	struct blk_mq_ctx *mq_ctx;
  
  	u64 cmd_flags;
  	unsigned cmd_type;
  	unsigned long atomic_flags;
  
  	int cpu;
  
  	/* the following two fields are internal, NEVER access directly */
  	unsigned int __data_len;	/* total data len */
  	sector_t __sector;		/* sector cursor */
  
  	struct bio *bio;
  	struct bio *biotail;
  
  	/*
  	 * The hash is used inside the scheduler, and killed once the
  	 * request reaches the dispatch list. The ipi_list is only used
  	 * to queue the request for softirq completion, which is long
  	 * after the request has been unhashed (and even removed from
  	 * the dispatch list).
  	 */
  	union {
  		struct hlist_node hash;	/* merge hash */
  		struct list_head ipi_list;
  	};
  
  	/*
  	 * 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;
  	};
  
  	/*
  	 * Three pointers are available for the IO schedulers, if they need
  	 * more they have to dynamically allocate it.  Flush requests are
  	 * never put on the IO scheduler. So let the flush fields share
  	 * space with the elevator data.
  	 */
  	union {
  		struct {
  			struct io_cq		*icq;
  			void			*priv[2];
  		} elv;
  
  		struct {
  			unsigned int		seq;
  			struct list_head	list;
  			rq_end_io_fn		*saved_end_io;
  		} flush;
  	};
  
  	struct gendisk *rq_disk;
  	struct hd_struct *part;
  	unsigned long start_time;
  #ifdef CONFIG_BLK_CGROUP
  	struct request_list *rl;		/* rl this rq is alloced from */
  	unsigned long long start_time_ns;
  	unsigned long long io_start_time_ns;    /* when passed to hardware */
  #endif
  	/* Number of scatter-gather DMA addr+len pairs after
  	 * physical address coalescing is performed.
  	 */
  	unsigned short nr_phys_segments;
  #if defined(CONFIG_BLK_DEV_INTEGRITY)
  	unsigned short nr_integrity_segments;
  #endif
  
  	unsigned short ioprio;
  
  	void *special;		/* opaque pointer available for LLD use */
  
  	int tag;
  	int errors;
  
  	/*
  	 * when request is used as a packet command carrier
  	 */
  	unsigned char __cmd[BLK_MAX_CDB];
  	unsigned char *cmd;
  	unsigned short cmd_len;
  
  	unsigned int extra_len;	/* length of alignment and padding */
  	unsigned int sense_len;
  	unsigned int resid_len;	/* residual count */
  	void *sense;
  
  	unsigned long deadline;
  	struct list_head timeout_list;
  	unsigned int timeout;
  	int retries;
  
  	/*
  	 * completion callback.
  	 */
  	rq_end_io_fn *end_io;
  	void *end_io_data;
  
  	/* for bidi */
  	struct request *next_rq;
  };
  
  static inline unsigned short req_get_ioprio(struct request *req)
  {
  	return req->ioprio;
  }
  
  #include <linux/elevator.h>
  
  struct blk_queue_ctx;
  
  typedef void (request_fn_proc) (struct request_queue *q);
  typedef blk_qc_t (make_request_fn) (struct request_queue *q, struct bio *bio);
  typedef int (prep_rq_fn) (struct request_queue *, struct request *);
  typedef void (unprep_rq_fn) (struct request_queue *, struct request *);
  
  struct bio_vec;
  typedef void (softirq_done_fn)(struct request *);
  typedef int (dma_drain_needed_fn)(struct request *);
  typedef int (lld_busy_fn) (struct request_queue *q);
  typedef int (bsg_job_fn) (struct bsg_job *);
  
  enum blk_eh_timer_return {
  	BLK_EH_NOT_HANDLED,
  	BLK_EH_HANDLED,
  	BLK_EH_RESET_TIMER,
  };
  
  typedef enum blk_eh_timer_return (rq_timed_out_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 */
  	int alloc_policy;		/* tag allocation policy */
  	int next_tag;			/* next tag */
  };
  #define BLK_TAG_ALLOC_FIFO 0 /* allocate starting from 0 */
  #define BLK_TAG_ALLOC_RR 1 /* allocate starting from last allocated tag */
  
  #define BLK_SCSI_MAX_CMDS	(256)
  #define BLK_SCSI_CMD_PER_LONG	(BLK_SCSI_MAX_CMDS / (sizeof(long) * 8))
  
  struct queue_limits {
  	unsigned long		bounce_pfn;
  	unsigned long		seg_boundary_mask;
  	unsigned long		virt_boundary_mask;
  
  	unsigned int		max_hw_sectors;
  	unsigned int		max_dev_sectors;
  	unsigned int		chunk_sectors;
  	unsigned int		max_sectors;
  	unsigned int		max_segment_size;
  	unsigned int		physical_block_size;
  	unsigned int		alignment_offset;
  	unsigned int		io_min;
  	unsigned int		io_opt;
  	unsigned int		max_discard_sectors;
  	unsigned int		max_hw_discard_sectors;
  	unsigned int		max_write_same_sectors;
  	unsigned int		discard_granularity;
  	unsigned int		discard_alignment;
  
  	unsigned short		logical_block_size;
  	unsigned short		max_segments;
  	unsigned short		max_integrity_segments;
  
  	unsigned char		misaligned;
  	unsigned char		discard_misaligned;
  	unsigned char		cluster;
  	unsigned char		discard_zeroes_data;
  	unsigned char		raid_partial_stripes_expensive;
  };
  
  struct request_queue {
  	/*
  	 * Together with queue_head for cacheline sharing
  	 */
  	struct list_head	queue_head;
  	struct request		*last_merge;
  	struct elevator_queue	*elevator;
  	int			nr_rqs[2];	/* # allocated [a]sync rqs */
  	int			nr_rqs_elvpriv;	/* # allocated rqs w/ elvpriv */
  
  	/*
  	 * If blkcg is not used, @q->root_rl serves all requests.  If blkcg
  	 * is used, root blkg allocates from @q->root_rl and all other
  	 * blkgs from their own blkg->rl.  Which one to use should be
  	 * determined using bio_request_list().
  	 */
  	struct request_list	root_rl;
  
  	request_fn_proc		*request_fn;
  	make_request_fn		*make_request_fn;
  	prep_rq_fn		*prep_rq_fn;
  	unprep_rq_fn		*unprep_rq_fn;
  	softirq_done_fn		*softirq_done_fn;
  	rq_timed_out_fn		*rq_timed_out_fn;
  	dma_drain_needed_fn	*dma_drain_needed;
  	lld_busy_fn		*lld_busy_fn;
  
  	struct blk_mq_ops	*mq_ops;
  
  	unsigned int		*mq_map;
  
  	/* sw queues */
  	struct blk_mq_ctx __percpu	*queue_ctx;
  	unsigned int		nr_queues;
  
  	/* hw dispatch queues */
  	struct blk_mq_hw_ctx	**queue_hw_ctx;
  	unsigned int		nr_hw_queues;
  
  	/*
  	 * Dispatch queue sorting
  	 */
  	sector_t		end_sector;
  	struct request		*boundary_rq;
  
  	/*
  	 * Delayed queue handling
  	 */
  	struct delayed_work	delay_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;
  
  	/*
  	 * various queue flags, see QUEUE_* below
  	 */
  	unsigned long		queue_flags;
  
  	/*
  	 * ida allocated id for this queue.  Used to index queues from
  	 * ioctx.
  	 */
  	int			id;
  
  	/*
  	 * queue needs bounce pages for pages above this limit
  	 */
  	gfp_t			bounce_gfp;
  
  	/*
  	 * 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;
  
  	/*
  	 * mq queue kobject
  	 */
  	struct kobject mq_kobj;
  
  #ifdef  CONFIG_BLK_DEV_INTEGRITY
  	struct blk_integrity integrity;
  #endif	/* CONFIG_BLK_DEV_INTEGRITY */
  
  #ifdef CONFIG_PM
  	struct device		*dev;
  	int			rpm_status;
  	unsigned int		nr_pending;
  #endif
  
  	/*
  	 * 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		dma_drain_size;
  	void			*dma_drain_buffer;
  	unsigned int		dma_pad_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[2];
  	/*
  	 * Number of active block driver functions for which blk_drain_queue()
  	 * must wait. Must be incremented around functions that unlock the
  	 * queue_lock internally, e.g. scsi_request_fn().
  	 */
  	unsigned int		request_fn_active;
  
  	unsigned int		rq_timeout;
  	struct timer_list	timeout;
  	struct list_head	timeout_list;
  
  	struct list_head	icq_list;
  #ifdef CONFIG_BLK_CGROUP
  	DECLARE_BITMAP		(blkcg_pols, BLKCG_MAX_POLS);
  	struct blkcg_gq		*root_blkg;
  	struct list_head	blkg_list;
  #endif
  
  	struct queue_limits	limits;
  
  	/*
  	 * 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
  	/*
  	 * for flush operations
  	 */
  	unsigned int		flush_flags;
  	unsigned int		flush_not_queueable:1;
  	struct blk_flush_queue	*fq;
  
  	struct list_head	requeue_list;
  	spinlock_t		requeue_lock;
  	struct work_struct	requeue_work;
  
  	struct mutex		sysfs_lock;
  
  	int			bypass_depth;
  	atomic_t		mq_freeze_depth;
  
  #if defined(CONFIG_BLK_DEV_BSG)
  	bsg_job_fn		*bsg_job_fn;
  	int			bsg_job_size;
  	struct bsg_class_device bsg_dev;
  #endif
  
  #ifdef CONFIG_BLK_DEV_THROTTLING
  	/* Throttle data */
  	struct throtl_data *td;
  #endif
  	struct rcu_head		rcu_head;
  	struct swait_queue_head	mq_freeze_wq;
  	struct percpu_ref	q_usage_counter;
  	struct list_head	all_q_node;
  
  	struct blk_mq_tag_set	*tag_set;
  	struct list_head	tag_set_list;
  	struct bio_set		*bio_split;
  
  	bool			mq_sysfs_init_done;
  };
  
  #define QUEUE_FLAG_QUEUED	1	/* uses generic tag queueing */
  #define QUEUE_FLAG_STOPPED	2	/* queue is stopped */
  #define	QUEUE_FLAG_SYNCFULL	3	/* read queue has been filled */
  #define QUEUE_FLAG_ASYNCFULL	4	/* write queue has been filled */
  #define QUEUE_FLAG_DYING	5	/* queue being torn down */
  #define QUEUE_FLAG_BYPASS	6	/* act as dumb FIFO queue */
  #define QUEUE_FLAG_BIDI		7	/* queue supports bidi requests */
  #define QUEUE_FLAG_NOMERGES     8	/* disable merge attempts */
  #define QUEUE_FLAG_SAME_COMP	9	/* complete on same CPU-group */
  #define QUEUE_FLAG_FAIL_IO     10	/* fake timeout */
  #define QUEUE_FLAG_STACKABLE   11	/* supports request stacking */
  #define QUEUE_FLAG_NONROT      12	/* non-rotational device (SSD) */
  #define QUEUE_FLAG_VIRT        QUEUE_FLAG_NONROT /* paravirt device */
  #define QUEUE_FLAG_IO_STAT     13	/* do IO stats */
  #define QUEUE_FLAG_DISCARD     14	/* supports DISCARD */
  #define QUEUE_FLAG_NOXMERGES   15	/* No extended merges */
  #define QUEUE_FLAG_ADD_RANDOM  16	/* Contributes to random pool */
  #define QUEUE_FLAG_SECDISCARD  17	/* supports SECDISCARD */
  #define QUEUE_FLAG_SAME_FORCE  18	/* force complete on same CPU */
  #define QUEUE_FLAG_DEAD        19	/* queue tear-down finished */
  #define QUEUE_FLAG_INIT_DONE   20	/* queue is initialized */
  #define QUEUE_FLAG_NO_SG_MERGE 21	/* don't attempt to merge SG segments*/
  #define QUEUE_FLAG_POLL	       22	/* IO polling enabled if set */
  
  #define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
  				 (1 << QUEUE_FLAG_STACKABLE)	|	\
  				 (1 << QUEUE_FLAG_SAME_COMP)	|	\
  				 (1 << QUEUE_FLAG_ADD_RANDOM))
  
  #define QUEUE_FLAG_MQ_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
  				 (1 << QUEUE_FLAG_STACKABLE)	|	\
  				 (1 << QUEUE_FLAG_SAME_COMP))
  
  static inline void queue_lockdep_assert_held(struct request_queue *q)
  {
  	if (q->queue_lock)
  		lockdep_assert_held(q->queue_lock);
  }
  
  static inline void queue_flag_set_unlocked(unsigned int flag,
  					   struct request_queue *q)
  {
  	__set_bit(flag, &q->queue_flags);
  }
  
  static inline int queue_flag_test_and_clear(unsigned int flag,
  					    struct request_queue *q)
  {
  	queue_lockdep_assert_held(q);
  
  	if (test_bit(flag, &q->queue_flags)) {
  		__clear_bit(flag, &q->queue_flags);
  		return 1;
  	}
  
  	return 0;
  }
  
  static inline int queue_flag_test_and_set(unsigned int flag,
  					  struct request_queue *q)
  {
  	queue_lockdep_assert_held(q);
  
  	if (!test_bit(flag, &q->queue_flags)) {
  		__set_bit(flag, &q->queue_flags);
  		return 0;
  	}
  
  	return 1;
  }
  
  static inline void queue_flag_set(unsigned int flag, struct request_queue *q)
  {
  	queue_lockdep_assert_held(q);
  	__set_bit(flag, &q->queue_flags);
  }
  
  static inline void queue_flag_clear_unlocked(unsigned int flag,
  					     struct request_queue *q)
  {
  	__clear_bit(flag, &q->queue_flags);
  }
  
  static inline int queue_in_flight(struct request_queue *q)
  {
  	return q->in_flight[0] + q->in_flight[1];
  }
  
  static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
  {
  	queue_lockdep_assert_held(q);
  	__clear_bit(flag, &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_dying(q)	test_bit(QUEUE_FLAG_DYING, &(q)->queue_flags)
  #define blk_queue_dead(q)	test_bit(QUEUE_FLAG_DEAD, &(q)->queue_flags)
  #define blk_queue_bypass(q)	test_bit(QUEUE_FLAG_BYPASS, &(q)->queue_flags)
  #define blk_queue_init_done(q)	test_bit(QUEUE_FLAG_INIT_DONE, &(q)->queue_flags)
  #define blk_queue_nomerges(q)	test_bit(QUEUE_FLAG_NOMERGES, &(q)->queue_flags)
  #define blk_queue_noxmerges(q)	\
  	test_bit(QUEUE_FLAG_NOXMERGES, &(q)->queue_flags)
  #define blk_queue_nonrot(q)	test_bit(QUEUE_FLAG_NONROT, &(q)->queue_flags)
  #define blk_queue_io_stat(q)	test_bit(QUEUE_FLAG_IO_STAT, &(q)->queue_flags)
  #define blk_queue_add_random(q)	test_bit(QUEUE_FLAG_ADD_RANDOM, &(q)->queue_flags)
  #define blk_queue_stackable(q)	\
  	test_bit(QUEUE_FLAG_STACKABLE, &(q)->queue_flags)
  #define blk_queue_discard(q)	test_bit(QUEUE_FLAG_DISCARD, &(q)->queue_flags)
  #define blk_queue_secdiscard(q)	(blk_queue_discard(q) && \
  	test_bit(QUEUE_FLAG_SECDISCARD, &(q)->queue_flags))
  
  #define blk_noretry_request(rq) \
  	((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \
  			     REQ_FAILFAST_DRIVER))
  
  #define blk_account_rq(rq) \
  	(((rq)->cmd_flags & REQ_STARTED) && \
  	 ((rq)->cmd_type == REQ_TYPE_FS))
  
  #define blk_rq_cpu_valid(rq)	((rq)->cpu != -1)
  #define blk_bidi_rq(rq)		((rq)->next_rq != NULL)
  /* rq->queuelist of dequeued request must be list_empty() */
  #define blk_queued_rq(rq)	(!list_empty(&(rq)->queuelist))
  
  #define list_entry_rq(ptr)	list_entry((ptr), struct request, queuelist)
  
  #define rq_data_dir(rq)		((int)((rq)->cmd_flags & 1))
  
  /*
   * Driver can handle struct request, if it either has an old style
   * request_fn defined, or is blk-mq based.
   */
  static inline bool queue_is_rq_based(struct request_queue *q)
  {
  	return q->request_fn || q->mq_ops;
  }
  
  static inline unsigned int blk_queue_cluster(struct request_queue *q)
  {
  	return q->limits.cluster;
  }
  
  /*
   * We regard a request as sync, if either a read or a sync write
   */
  static inline bool rw_is_sync(unsigned int rw_flags)
  {
  	return !(rw_flags & REQ_WRITE) || (rw_flags & REQ_SYNC);
  }
  
  static inline bool rq_is_sync(struct request *rq)
  {
  	return rw_is_sync(rq->cmd_flags);
  }
  
  static inline bool blk_rl_full(struct request_list *rl, bool sync)
  {
  	unsigned int flag = sync ? BLK_RL_SYNCFULL : BLK_RL_ASYNCFULL;
  
  	return rl->flags & flag;
  }
  
  static inline void blk_set_rl_full(struct request_list *rl, bool sync)
  {
  	unsigned int flag = sync ? BLK_RL_SYNCFULL : BLK_RL_ASYNCFULL;
  
  	rl->flags |= flag;
  }
  
  static inline void blk_clear_rl_full(struct request_list *rl, bool sync)
  {
  	unsigned int flag = sync ? BLK_RL_SYNCFULL : BLK_RL_ASYNCFULL;
  
  	rl->flags &= ~flag;
  }
  
  static inline bool rq_mergeable(struct request *rq)
  {
  	if (rq->cmd_type != REQ_TYPE_FS)
  		return false;
  
  	if (rq->cmd_flags & REQ_NOMERGE_FLAGS)
  		return false;
  
  	return true;
  }
  
  static inline bool blk_check_merge_flags(unsigned int flags1,
  					 unsigned int flags2)
  {
  	if ((flags1 & REQ_DISCARD) != (flags2 & REQ_DISCARD))
  		return false;
  
  	if ((flags1 & REQ_SECURE) != (flags2 & REQ_SECURE))
  		return false;
  
  	if ((flags1 & REQ_WRITE_SAME) != (flags2 & REQ_WRITE_SAME))
  		return false;
  
  	return true;
  }
  
  static inline bool blk_write_same_mergeable(struct bio *a, struct bio *b)
  {
  	if (bio_data(a) == bio_data(b))
  		return true;
  
  	return false;
  }
  
  /*
   * 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
   */
  
  #if BITS_PER_LONG == 32
  #define BLK_BOUNCE_HIGH		((u64)blk_max_low_pfn << PAGE_SHIFT)
  #else
  #define BLK_BOUNCE_HIGH		-1ULL
  #endif
  #define BLK_BOUNCE_ANY		(-1ULL)
  #define BLK_BOUNCE_ISA		(DMA_BIT_MASK(24))
  
  /*
   * default timeout for SG_IO if none specified
   */
  #define BLK_DEFAULT_SG_TIMEOUT	(60 * HZ)
  #define BLK_MIN_SG_TIMEOUT	(7 * 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 rq_map_data {
  	struct page **pages;
  	int page_order;
  	int nr_entries;
  	unsigned long offset;
  	int null_mapped;
  	int from_user;
  };
  
  struct req_iterator {
  	struct bvec_iter iter;
  	struct bio *bio;
  };
  
  /* This should not be used directly - use rq_for_each_segment */
  #define for_each_bio(_bio)		\
  	for (; _bio; _bio = _bio->bi_next)
  #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.iter)
  
  #define rq_iter_last(bvec, _iter)				\
  		(_iter.bio->bi_next == NULL &&			\
  		 bio_iter_last(bvec, _iter.iter))
  
  #ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
  # error	"You should define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE for your platform"
  #endif
  #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
  extern void rq_flush_dcache_pages(struct request *rq);
  #else
  static inline void rq_flush_dcache_pages(struct request *rq)
  {
  }
  #endif
  
  extern int blk_register_queue(struct gendisk *disk);
  extern void blk_unregister_queue(struct gendisk *disk);
  extern blk_qc_t generic_make_request(struct bio *bio);
  extern void blk_rq_init(struct request_queue *q, struct request *rq);
  extern void blk_put_request(struct request *);
  extern void __blk_put_request(struct request_queue *, struct request *);
  extern struct request *blk_get_request(struct request_queue *, int, gfp_t);
  extern struct request *blk_make_request(struct request_queue *, struct bio *,
  					gfp_t);
  extern void blk_rq_set_block_pc(struct request *);
  extern void blk_requeue_request(struct request_queue *, struct request *);
  extern void blk_add_request_payload(struct request *rq, struct page *page,
  		unsigned int len);
  extern int blk_lld_busy(struct request_queue *q);
  extern int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
  			     struct bio_set *bs, gfp_t gfp_mask,
  			     int (*bio_ctr)(struct bio *, struct bio *, void *),
  			     void *data);
  extern void blk_rq_unprep_clone(struct request *rq);
  extern int blk_insert_cloned_request(struct request_queue *q,
  				     struct request *rq);
  extern void blk_delay_queue(struct request_queue *, unsigned long);
  extern void blk_queue_split(struct request_queue *, struct bio **,
  			    struct bio_set *);
  extern void blk_recount_segments(struct request_queue *, struct bio *);
  extern int scsi_verify_blk_ioctl(struct block_device *, unsigned int);
  extern int scsi_cmd_blk_ioctl(struct block_device *, fmode_t,
  			      unsigned int, void __user *);
  extern int scsi_cmd_ioctl(struct request_queue *, struct gendisk *, fmode_t,
  			  unsigned int, void __user *);
  extern int sg_scsi_ioctl(struct request_queue *, struct gendisk *, fmode_t,
  			 struct scsi_ioctl_command __user *);
  
  extern int blk_queue_enter(struct request_queue *q, gfp_t gfp);
  extern void blk_queue_exit(struct request_queue *q);
  extern void blk_start_queue(struct request_queue *q);
  extern void blk_start_queue_async(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 *q);
  extern void __blk_run_queue_uncond(struct request_queue *q);
  extern void blk_run_queue(struct request_queue *);
  extern void blk_run_queue_async(struct request_queue *q);
  extern int blk_rq_map_user(struct request_queue *, struct request *,
  			   struct rq_map_data *, void __user *, unsigned long,
  			   gfp_t);
  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 rq_map_data *, const struct iov_iter *,
  			       gfp_t);
  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 *);
  
  bool blk_poll(struct request_queue *q, blk_qc_t cookie);
  
  static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
  {
  	return bdev->bd_disk->queue;	/* this is never NULL */
  }
  
  /*
   * blk_rq_pos()			: the current sector
   * blk_rq_bytes()		: bytes left in the entire request
   * blk_rq_cur_bytes()		: bytes left in the current segment
   * blk_rq_err_bytes()		: bytes left till the next error boundary
   * blk_rq_sectors()		: sectors left in the entire request
   * blk_rq_cur_sectors()		: sectors left in the current segment
   */
  static inline sector_t blk_rq_pos(const struct request *rq)
  {
  	return rq->__sector;
  }
  
  static inline unsigned int blk_rq_bytes(const struct request *rq)
  {
  	return rq->__data_len;
  }
  
  static inline int blk_rq_cur_bytes(const struct request *rq)
  {
  	return rq->bio ? bio_cur_bytes(rq->bio) : 0;
  }
  
  extern unsigned int blk_rq_err_bytes(const struct request *rq);
  
  static inline unsigned int blk_rq_sectors(const struct request *rq)
  {
  	return blk_rq_bytes(rq) >> 9;
  }
  
  static inline unsigned int blk_rq_cur_sectors(const struct request *rq)
  {
  	return blk_rq_cur_bytes(rq) >> 9;
  }
  
  static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q,
  						     unsigned int cmd_flags)
  {
  	if (unlikely(cmd_flags & REQ_DISCARD))
  		return min(q->limits.max_discard_sectors, UINT_MAX >> 9);
  
  	if (unlikely(cmd_flags & REQ_WRITE_SAME))
  		return q->limits.max_write_same_sectors;
  
  	return q->limits.max_sectors;
  }
  
  /*
   * Return maximum size of a request at given offset. Only valid for
   * file system requests.
   */
  static inline unsigned int blk_max_size_offset(struct request_queue *q,
  					       sector_t offset)
  {
  	if (!q->limits.chunk_sectors)
  		return q->limits.max_sectors;
  
  	return q->limits.chunk_sectors -
  			(offset & (q->limits.chunk_sectors - 1));
  }
  
  static inline unsigned int blk_rq_get_max_sectors(struct request *rq)
  {
  	struct request_queue *q = rq->q;
  
  	if (unlikely(rq->cmd_type != REQ_TYPE_FS))
  		return q->limits.max_hw_sectors;
  
  	if (!q->limits.chunk_sectors || (rq->cmd_flags & REQ_DISCARD))
  		return blk_queue_get_max_sectors(q, rq->cmd_flags);
  
  	return min(blk_max_size_offset(q, blk_rq_pos(rq)),
  			blk_queue_get_max_sectors(q, rq->cmd_flags));
  }
  
  static inline unsigned int blk_rq_count_bios(struct request *rq)
  {
  	unsigned int nr_bios = 0;
  	struct bio *bio;
  
  	__rq_for_each_bio(bio, rq)
  		nr_bios++;
  
  	return nr_bios;
  }
  
  /*
   * Request issue related functions.
   */
  extern struct request *blk_peek_request(struct request_queue *q);
  extern void blk_start_request(struct request *rq);
  extern struct request *blk_fetch_request(struct request_queue *q);
  
  /*
   * Request completion related functions.
   *
   * blk_update_request() completes given number of bytes and updates
   * the request without completing it.
   *
   * blk_end_request() and friends.  __blk_end_request() must be called
   * with the request queue spinlock acquired.
   *
   * Several drivers define their own end_request and call
   * blk_end_request() for parts of the original function.
   * This prevents code duplication in drivers.
   */
  extern bool blk_update_request(struct request *rq, int error,
  			       unsigned int nr_bytes);
  extern void blk_finish_request(struct request *rq, int error);
  extern bool blk_end_request(struct request *rq, int error,
  			    unsigned int nr_bytes);
  extern void blk_end_request_all(struct request *rq, int error);
  extern bool blk_end_request_cur(struct request *rq, int error);
  extern bool blk_end_request_err(struct request *rq, int error);
  extern bool __blk_end_request(struct request *rq, int error,
  			      unsigned int nr_bytes);
  extern void __blk_end_request_all(struct request *rq, int error);
  extern bool __blk_end_request_cur(struct request *rq, int error);
  extern bool __blk_end_request_err(struct request *rq, int error);
  
  extern void blk_complete_request(struct request *);
  extern void __blk_complete_request(struct request *);
  extern void blk_abort_request(struct request *);
  extern void blk_unprep_request(struct request *);
  
  /*
   * 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 struct request_queue *blk_init_allocated_queue(struct request_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_hw_sectors(struct request_queue *, unsigned int);
  extern void blk_queue_chunk_sectors(struct request_queue *, unsigned int);
  extern void blk_queue_max_segments(struct request_queue *, unsigned short);
  extern void blk_queue_max_segment_size(struct request_queue *, unsigned int);
  extern void blk_queue_max_discard_sectors(struct request_queue *q,
  		unsigned int max_discard_sectors);
  extern void blk_queue_max_write_same_sectors(struct request_queue *q,
  		unsigned int max_write_same_sectors);
  extern void blk_queue_logical_block_size(struct request_queue *, unsigned short);
  extern void blk_queue_physical_block_size(struct request_queue *, unsigned int);
  extern void blk_queue_alignment_offset(struct request_queue *q,
  				       unsigned int alignment);
  extern void blk_limits_io_min(struct queue_limits *limits, unsigned int min);
  extern void blk_queue_io_min(struct request_queue *q, unsigned int min);
  extern void blk_limits_io_opt(struct queue_limits *limits, unsigned int opt);
  extern void blk_queue_io_opt(struct request_queue *q, unsigned int opt);
  extern void blk_set_default_limits(struct queue_limits *lim);
  extern void blk_set_stacking_limits(struct queue_limits *lim);
  extern int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
  			    sector_t offset);
  extern int bdev_stack_limits(struct queue_limits *t, struct block_device *bdev,
  			    sector_t offset);
  extern void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
  			      sector_t offset);
  extern void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b);
  extern void blk_queue_dma_pad(struct request_queue *, unsigned int);
  extern void blk_queue_update_dma_pad(struct request_queue *, unsigned int);
  extern int blk_queue_dma_drain(struct request_queue *q,
  			       dma_drain_needed_fn *dma_drain_needed,
  			       void *buf, unsigned int size);
  extern void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn);
  extern void blk_queue_segment_boundary(struct request_queue *, unsigned long);
  extern void blk_queue_virt_boundary(struct request_queue *, unsigned long);
  extern void blk_queue_prep_rq(struct request_queue *, prep_rq_fn *pfn);
  extern void blk_queue_unprep_rq(struct request_queue *, unprep_rq_fn *ufn);
  extern void blk_queue_dma_alignment(struct request_queue *, int);
  extern void blk_queue_update_dma_alignment(struct request_queue *, int);
  extern void blk_queue_softirq_done(struct request_queue *, softirq_done_fn *);
  extern void blk_queue_rq_timed_out(struct request_queue *, rq_timed_out_fn *);
  extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);
  extern void blk_queue_flush(struct request_queue *q, unsigned int flush);
  extern void blk_queue_flush_queueable(struct request_queue *q, bool queueable);
  extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
  
  extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
  extern void blk_dump_rq_flags(struct request *, char *);
  extern long nr_blockdev_pages(void);
  
  bool __must_check 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 *);
  extern void blk_set_queue_dying(struct request_queue *);
  
  /*
   * block layer runtime pm functions
   */
  #ifdef CONFIG_PM
  extern void blk_pm_runtime_init(struct request_queue *q, struct device *dev);
  extern int blk_pre_runtime_suspend(struct request_queue *q);
  extern void blk_post_runtime_suspend(struct request_queue *q, int err);
  extern void blk_pre_runtime_resume(struct request_queue *q);
  extern void blk_post_runtime_resume(struct request_queue *q, int err);
  #else
  static inline void blk_pm_runtime_init(struct request_queue *q,
  	struct device *dev) {}
  static inline int blk_pre_runtime_suspend(struct request_queue *q)
  {
  	return -ENOSYS;
  }
  static inline void blk_post_runtime_suspend(struct request_queue *q, int err) {}
  static inline void blk_pre_runtime_resume(struct request_queue *q) {}
  static inline void blk_post_runtime_resume(struct request_queue *q, int err) {}
  #endif
  
  /*
   * blk_plug permits building a queue of related requests by holding the I/O
   * fragments for a short period. This allows merging of sequential requests
   * into single larger request. As the requests are moved from a per-task list to
   * the device's request_queue in a batch, this results in improved scalability
   * as the lock contention for request_queue lock is reduced.
   *
   * It is ok not to disable preemption when adding the request to the plug list
   * or when attempting a merge, because blk_schedule_flush_list() will only flush
   * the plug list when the task sleeps by itself. For details, please see
   * schedule() where blk_schedule_flush_plug() is called.
   */
  struct blk_plug {
  	struct list_head list; /* requests */
  	struct list_head mq_list; /* blk-mq requests */
  	struct list_head cb_list; /* md requires an unplug callback */
  };
  #define BLK_MAX_REQUEST_COUNT 16
  
  struct blk_plug_cb;
  typedef void (*blk_plug_cb_fn)(struct blk_plug_cb *, bool);
  struct blk_plug_cb {
  	struct list_head list;
  	blk_plug_cb_fn callback;
  	void *data;
  };
  extern struct blk_plug_cb *blk_check_plugged(blk_plug_cb_fn unplug,
  					     void *data, int size);
  extern void blk_start_plug(struct blk_plug *);
  extern void blk_finish_plug(struct blk_plug *);
  extern void blk_flush_plug_list(struct blk_plug *, bool);
  
  static inline void blk_flush_plug(struct task_struct *tsk)
  {
  	struct blk_plug *plug = tsk->plug;
  
  	if (plug)
  		blk_flush_plug_list(plug, false);
  }
  
  static inline void blk_schedule_flush_plug(struct task_struct *tsk)
  {
  	struct blk_plug *plug = tsk->plug;
  
  	if (plug)
  		blk_flush_plug_list(plug, true);
  }
  
  static inline bool blk_needs_flush_plug(struct task_struct *tsk)
  {
  	struct blk_plug *plug = tsk->plug;
  
  	return plug &&
  		(!list_empty(&plug->list) ||
  		 !list_empty(&plug->mq_list) ||
  		 !list_empty(&plug->cb_list));
  }
  
  /*
   * tag stuff
   */
  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 *, int);
  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, 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];
  }
  
  #define BLKDEV_DISCARD_SECURE  0x01    /* secure discard */
  
  extern int blkdev_issue_flush(struct block_device *, gfp_t, sector_t *);
  extern int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
  		sector_t nr_sects, gfp_t gfp_mask, unsigned long flags);
  extern int blkdev_issue_write_same(struct block_device *bdev, sector_t sector,
  		sector_t nr_sects, gfp_t gfp_mask, struct page *page);
  extern int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
  		sector_t nr_sects, gfp_t gfp_mask, bool discard);
  static inline int sb_issue_discard(struct super_block *sb, sector_t block,
  		sector_t nr_blocks, gfp_t gfp_mask, unsigned long flags)
  {
  	return blkdev_issue_discard(sb->s_bdev, block << (sb->s_blocksize_bits - 9),
  				    nr_blocks << (sb->s_blocksize_bits - 9),
  				    gfp_mask, flags);
  }
  static inline int sb_issue_zeroout(struct super_block *sb, sector_t block,
  		sector_t nr_blocks, gfp_t gfp_mask)
  {
  	return blkdev_issue_zeroout(sb->s_bdev,
  				    block << (sb->s_blocksize_bits - 9),
  				    nr_blocks << (sb->s_blocksize_bits - 9),
  				    gfp_mask, true);
  }
  
  extern int blk_verify_command(unsigned char *cmd, fmode_t has_write_perm);
  
  enum blk_default_limits {
  	BLK_MAX_SEGMENTS	= 128,
  	BLK_SAFE_MAX_SECTORS	= 255,
  	BLK_DEF_MAX_SECTORS	= 2560,
  	BLK_MAX_SEGMENT_SIZE	= 65536,
  	BLK_SEG_BOUNDARY_MASK	= 0xFFFFFFFFUL,
  };
  
  #define blkdev_entry_to_request(entry) list_entry((entry), struct request, queuelist)
  
  static inline unsigned long queue_bounce_pfn(struct request_queue *q)
  {
  	return q->limits.bounce_pfn;
  }
  
  static inline unsigned long queue_segment_boundary(struct request_queue *q)
  {
  	return q->limits.seg_boundary_mask;
  }
  
  static inline unsigned long queue_virt_boundary(struct request_queue *q)
  {
  	return q->limits.virt_boundary_mask;
  }
  
  static inline unsigned int queue_max_sectors(struct request_queue *q)
  {
  	return q->limits.max_sectors;
  }
  
  static inline unsigned int queue_max_hw_sectors(struct request_queue *q)
  {
  	return q->limits.max_hw_sectors;
  }
  
  static inline unsigned short queue_max_segments(struct request_queue *q)
  {
  	return q->limits.max_segments;
  }
  
  static inline unsigned int queue_max_segment_size(struct request_queue *q)
  {
  	return q->limits.max_segment_size;
  }
  
  static inline unsigned short queue_logical_block_size(struct request_queue *q)
  {
  	int retval = 512;
  
  	if (q && q->limits.logical_block_size)
  		retval = q->limits.logical_block_size;
  
  	return retval;
  }
  
  static inline unsigned short bdev_logical_block_size(struct block_device *bdev)
  {
  	return queue_logical_block_size(bdev_get_queue(bdev));
  }
  
  static inline unsigned int queue_physical_block_size(struct request_queue *q)
  {
  	return q->limits.physical_block_size;
  }
  
  static inline unsigned int bdev_physical_block_size(struct block_device *bdev)
  {
  	return queue_physical_block_size(bdev_get_queue(bdev));
  }
  
  static inline unsigned int queue_io_min(struct request_queue *q)
  {
  	return q->limits.io_min;
  }
  
  static inline int bdev_io_min(struct block_device *bdev)
  {
  	return queue_io_min(bdev_get_queue(bdev));
  }
  
  static inline unsigned int queue_io_opt(struct request_queue *q)
  {
  	return q->limits.io_opt;
  }
  
  static inline int bdev_io_opt(struct block_device *bdev)
  {
  	return queue_io_opt(bdev_get_queue(bdev));
  }
  
  static inline int queue_alignment_offset(struct request_queue *q)
  {
  	if (q->limits.misaligned)
  		return -1;
  
  	return q->limits.alignment_offset;
  }
  
  static inline int queue_limit_alignment_offset(struct queue_limits *lim, sector_t sector)
  {
  	unsigned int granularity = max(lim->physical_block_size, lim->io_min);
  	unsigned int alignment = sector_div(sector, granularity >> 9) << 9;
  
  	return (granularity + lim->alignment_offset - alignment) % granularity;
  }
  
  static inline int bdev_alignment_offset(struct block_device *bdev)
  {
  	struct request_queue *q = bdev_get_queue(bdev);
  
  	if (q->limits.misaligned)
  		return -1;
  
  	if (bdev != bdev->bd_contains)
  		return bdev->bd_part->alignment_offset;
  
  	return q->limits.alignment_offset;
  }
  
  static inline int queue_discard_alignment(struct request_queue *q)
  {
  	if (q->limits.discard_misaligned)
  		return -1;
  
  	return q->limits.discard_alignment;
  }
  
  static inline int queue_limit_discard_alignment(struct queue_limits *lim, sector_t sector)
  {
  	unsigned int alignment, granularity, offset;
  
  	if (!lim->max_discard_sectors)
  		return 0;
  
  	/* Why are these in bytes, not sectors? */
  	alignment = lim->discard_alignment >> 9;
  	granularity = lim->discard_granularity >> 9;
  	if (!granularity)
  		return 0;
  
  	/* Offset of the partition start in 'granularity' sectors */
  	offset = sector_div(sector, granularity);
  
  	/* And why do we do this modulus *again* in blkdev_issue_discard()? */
  	offset = (granularity + alignment - offset) % granularity;
  
  	/* Turn it back into bytes, gaah */
  	return offset << 9;
  }
  
  static inline int bdev_discard_alignment(struct block_device *bdev)
  {
  	struct request_queue *q = bdev_get_queue(bdev);
  
  	if (bdev != bdev->bd_contains)
  		return bdev->bd_part->discard_alignment;
  
  	return q->limits.discard_alignment;
  }
  
  static inline unsigned int queue_discard_zeroes_data(struct request_queue *q)
  {
  	if (q->limits.max_discard_sectors && q->limits.discard_zeroes_data == 1)
  		return 1;
  
  	return 0;
  }
  
  static inline unsigned int bdev_discard_zeroes_data(struct block_device *bdev)
  {
  	return queue_discard_zeroes_data(bdev_get_queue(bdev));
  }
  
  static inline unsigned int bdev_write_same(struct block_device *bdev)
  {
  	struct request_queue *q = bdev_get_queue(bdev);
  
  	if (q)
  		return q->limits.max_write_same_sectors;
  
  	return 0;
  }
  
  static inline int queue_dma_alignment(struct request_queue *q)
  {
  	return q ? q->dma_alignment : 511;
  }
  
  static inline int blk_rq_aligned(struct request_queue *q, unsigned long addr,
  				 unsigned int len)
  {
  	unsigned int alignment = queue_dma_alignment(q) | q->dma_pad_mask;
  	return !(addr & alignment) && !(len & alignment);
  }
  
  /* 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;
  }
  
  static inline bool queue_flush_queueable(struct request_queue *q)
  {
  	return !q->flush_not_queueable;
  }
  
  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);
  }
  
  static inline bool __bvec_gap_to_prev(struct request_queue *q,
  				struct bio_vec *bprv, unsigned int offset)
  {
  	return offset ||
  		((bprv->bv_offset + bprv->bv_len) & queue_virt_boundary(q));
  }
  
  /*
   * Check if adding a bio_vec after bprv with offset would create a gap in
   * the SG list. Most drivers don't care about this, but some do.
   */
  static inline bool bvec_gap_to_prev(struct request_queue *q,
  				struct bio_vec *bprv, unsigned int offset)
  {
  	if (!queue_virt_boundary(q))
  		return false;
  	return __bvec_gap_to_prev(q, bprv, offset);
  }
  
  static inline bool bio_will_gap(struct request_queue *q, struct bio *prev,
  			 struct bio *next)
  {
  	if (bio_has_data(prev) && queue_virt_boundary(q)) {
  		struct bio_vec pb, nb;
  
  		bio_get_last_bvec(prev, &pb);
  		bio_get_first_bvec(next, &nb);
  
  		return __bvec_gap_to_prev(q, &pb, nb.bv_offset);
  	}
  
  	return false;
  }
  
  static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
  {
  	return bio_will_gap(req->q, req->biotail, bio);
  }
  
  static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
  {
  	return bio_will_gap(req->q, bio, req->bio);
  }
  
  struct work_struct;
  int kblockd_schedule_work(struct work_struct *work);
  int kblockd_schedule_delayed_work(struct delayed_work *dwork, unsigned long delay);
  int kblockd_schedule_delayed_work_on(int cpu, struct delayed_work *dwork, unsigned long delay);
  
  #ifdef CONFIG_BLK_CGROUP
  /*
   * This should not be using sched_clock(). A real patch is in progress
   * to fix this up, until that is in place we need to disable preemption
   * around sched_clock() in this function and set_io_start_time_ns().
   */
  static inline void set_start_time_ns(struct request *req)
  {
  	preempt_disable();
  	req->start_time_ns = sched_clock();
  	preempt_enable();
  }
  
  static inline void set_io_start_time_ns(struct request *req)
  {
  	preempt_disable();
  	req->io_start_time_ns = sched_clock();
  	preempt_enable();
  }
  
  static inline uint64_t rq_start_time_ns(struct request *req)
  {
          return req->start_time_ns;
  }
  
  static inline uint64_t rq_io_start_time_ns(struct request *req)
  {
          return req->io_start_time_ns;
  }
  #else
  static inline void set_start_time_ns(struct request *req) {}
  static inline void set_io_start_time_ns(struct request *req) {}
  static inline uint64_t rq_start_time_ns(struct request *req)
  {
  	return 0;
  }
  static inline uint64_t rq_io_start_time_ns(struct request *req)
  {
  	return 0;
  }
  #endif
  
  #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) "-*")
  
  #if defined(CONFIG_BLK_DEV_INTEGRITY)
  
  enum blk_integrity_flags {
  	BLK_INTEGRITY_VERIFY		= 1 << 0,
  	BLK_INTEGRITY_GENERATE		= 1 << 1,
  	BLK_INTEGRITY_DEVICE_CAPABLE	= 1 << 2,
  	BLK_INTEGRITY_IP_CHECKSUM	= 1 << 3,
  };
  
  struct blk_integrity_iter {
  	void			*prot_buf;
  	void			*data_buf;
  	sector_t		seed;
  	unsigned int		data_size;
  	unsigned short		interval;
  	const char		*disk_name;
  };
  
  typedef int (integrity_processing_fn) (struct blk_integrity_iter *);
  
  struct blk_integrity_profile {
  	integrity_processing_fn		*generate_fn;
  	integrity_processing_fn		*verify_fn;
  	const char			*name;
  };
  
  extern void blk_integrity_register(struct gendisk *, struct blk_integrity *);
  extern void blk_integrity_unregister(struct gendisk *);
  extern int blk_integrity_compare(struct gendisk *, struct gendisk *);
  extern int blk_rq_map_integrity_sg(struct request_queue *, struct bio *,
  				   struct scatterlist *);
  extern int blk_rq_count_integrity_sg(struct request_queue *, struct bio *);
  extern bool blk_integrity_merge_rq(struct request_queue *, struct request *,
  				   struct request *);
  extern bool blk_integrity_merge_bio(struct request_queue *, struct request *,
  				    struct bio *);
  
  static inline struct blk_integrity *blk_get_integrity(struct gendisk *disk)
  {
  	struct blk_integrity *bi = &disk->queue->integrity;
  
  	if (!bi->profile)
  		return NULL;
  
  	return bi;
  }
  
  static inline
  struct blk_integrity *bdev_get_integrity(struct block_device *bdev)
  {
  	return blk_get_integrity(bdev->bd_disk);
  }
  
  static inline bool blk_integrity_rq(struct request *rq)
  {
  	return rq->cmd_flags & REQ_INTEGRITY;
  }
  
  static inline void blk_queue_max_integrity_segments(struct request_queue *q,
  						    unsigned int segs)
  {
  	q->limits.max_integrity_segments = segs;
  }
  
  static inline unsigned short
  queue_max_integrity_segments(struct request_queue *q)
  {
  	return q->limits.max_integrity_segments;
  }
  
  static inline bool integrity_req_gap_back_merge(struct request *req,
  						struct bio *next)
  {
  	struct bio_integrity_payload *bip = bio_integrity(req->bio);
  	struct bio_integrity_payload *bip_next = bio_integrity(next);
  
  	return bvec_gap_to_prev(req->q, &bip->bip_vec[bip->bip_vcnt - 1],
  				bip_next->bip_vec[0].bv_offset);
  }
  
  static inline bool integrity_req_gap_front_merge(struct request *req,
  						 struct bio *bio)
  {
  	struct bio_integrity_payload *bip = bio_integrity(bio);
  	struct bio_integrity_payload *bip_next = bio_integrity(req->bio);
  
  	return bvec_gap_to_prev(req->q, &bip->bip_vec[bip->bip_vcnt - 1],
  				bip_next->bip_vec[0].bv_offset);
  }
  
  #else /* CONFIG_BLK_DEV_INTEGRITY */
  
  struct bio;
  struct block_device;
  struct gendisk;
  struct blk_integrity;
  
  static inline int blk_integrity_rq(struct request *rq)
  {
  	return 0;
  }
  static inline int blk_rq_count_integrity_sg(struct request_queue *q,
  					    struct bio *b)
  {
  	return 0;
  }
  static inline int blk_rq_map_integrity_sg(struct request_queue *q,
  					  struct bio *b,
  					  struct scatterlist *s)
  {
  	return 0;
  }
  static inline struct blk_integrity *bdev_get_integrity(struct block_device *b)
  {
  	return NULL;
  }
  static inline struct blk_integrity *blk_get_integrity(struct gendisk *disk)
  {
  	return NULL;
  }
  static inline int blk_integrity_compare(struct gendisk *a, struct gendisk *b)
  {
  	return 0;
  }
  static inline void blk_integrity_register(struct gendisk *d,
  					 struct blk_integrity *b)
  {
  }
  static inline void blk_integrity_unregister(struct gendisk *d)
  {
  }
  static inline void blk_queue_max_integrity_segments(struct request_queue *q,
  						    unsigned int segs)
  {
  }
  static inline unsigned short queue_max_integrity_segments(struct request_queue *q)
  {
  	return 0;
  }
  static inline bool blk_integrity_merge_rq(struct request_queue *rq,
  					  struct request *r1,
  					  struct request *r2)
  {
  	return true;
  }
  static inline bool blk_integrity_merge_bio(struct request_queue *rq,
  					   struct request *r,
  					   struct bio *b)
  {
  	return true;
  }
  
  static inline bool integrity_req_gap_back_merge(struct request *req,
  						struct bio *next)
  {
  	return false;
  }
  static inline bool integrity_req_gap_front_merge(struct request *req,
  						 struct bio *bio)
  {
  	return false;
  }
  
  #endif /* CONFIG_BLK_DEV_INTEGRITY */
  
  struct block_device_operations {
  	int (*open) (struct block_device *, fmode_t);
  	void (*release) (struct gendisk *, fmode_t);
  	int (*rw_page)(struct block_device *, sector_t, struct page *, int rw);
  	int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
  	int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
  	long (*direct_access)(struct block_device *, sector_t, void __pmem **,
  			unsigned long *pfn);
  	unsigned int (*check_events) (struct gendisk *disk,
  				      unsigned int clearing);
  	/* ->media_changed() is DEPRECATED, use ->check_events() instead */
  	int (*media_changed) (struct gendisk *);
  	void (*unlock_native_capacity) (struct gendisk *);
  	int (*revalidate_disk) (struct gendisk *);
  	int (*getgeo)(struct block_device *, struct hd_geometry *);
  	/* this callback is with swap_lock and sometimes page table lock held */
  	void (*swap_slot_free_notify) (struct block_device *, unsigned long);
  	struct module *owner;
  	const struct pr_ops *pr_ops;
  };
  
  extern int __blkdev_driver_ioctl(struct block_device *, fmode_t, unsigned int,
  				 unsigned long);
  extern int bdev_read_page(struct block_device *, sector_t, struct page *);
  extern int bdev_write_page(struct block_device *, sector_t, struct page *,
  						struct writeback_control *);
  extern long bdev_direct_access(struct block_device *, sector_t,
  		void __pmem **addr, unsigned long *pfn, long size);
  #else /* CONFIG_BLOCK */
  
  struct block_device;
  
  /*
   * stubs for when the block layer is configured out
   */
  #define buffer_heads_over_limit 0
  
  static inline long nr_blockdev_pages(void)
  {
  	return 0;
  }
  
  struct blk_plug {
  };
  
  static inline void blk_start_plug(struct blk_plug *plug)
  {
  }
  
  static inline void blk_finish_plug(struct blk_plug *plug)
  {
  }
  
  static inline void blk_flush_plug(struct task_struct *task)
  {
  }
  
  static inline void blk_schedule_flush_plug(struct task_struct *task)
  {
  }
  
  
  static inline bool blk_needs_flush_plug(struct task_struct *tsk)
  {
  	return false;
  }
  
  static inline int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
  				     sector_t *error_sector)
  {
  	return 0;
  }
  
  #endif /* CONFIG_BLOCK */
  
  #endif
  