blkdev.h

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#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/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/stringify.h>
#include <linux/gfp.h>
#include <linux/bsg.h>
#include <linux/smp.h>

#include <asm/scatterlist.h>

struct module;
struct scsi_ioctl_command;

struct request_queue;
struct elevator_queue;
struct request_pm_state;
struct blk_trace;
struct request;
struct sg_io_hdr;
struct bsg_job;
struct blkcg_gq;

#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_SENSE,         /* sense request */
    REQ_TYPE_PM_SUSPEND,        /* suspend request */
    REQ_TYPE_PM_RESUME,     /* resume request */
    REQ_TYPE_PM_SHUTDOWN,       /* shutdown request */
    REQ_TYPE_SPECIAL,       /* driver defined type */
    /*
     * 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_TASKFILE,
    REQ_TYPE_ATA_PC,
};

#define BLK_MAX_CDB 16

/*
 * try to put the fields that are referenced together in the same cacheline.
 * if you modify this structure, be sure to check block/blk-core.c:blk_rq_init()
 * as well!
 */
struct request {
    struct list_head queuelist;
    struct call_single_data csd;

    struct request_queue *q;

    unsigned int cmd_flags;
    enum rq_cmd_type_bits 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;

    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;
    };

    /*
     * 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;

    int ref_count;

    void *special;      /* opaque pointer available for LLD use */
    char *buffer;       /* kaddr of the current segment if available */

    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;
}

/*
 * 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 void (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;
struct bvec_merge_data {
    struct block_device *bi_bdev;
    sector_t bi_sector;
    unsigned bi_size;
    unsigned long bi_rw;
};
typedef int (merge_bvec_fn) (struct request_queue *, struct bvec_merge_data *,
                 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 */
};

#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 int        max_hw_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_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;
};

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;
    merge_bvec_fn       *merge_bvec_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;

    /*
     * 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;

    /*
     * 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];

    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;
    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;

    struct mutex        sysfs_lock;

    int         bypass_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_CGROUP
    struct list_head    all_q_node;
#endif
#ifdef CONFIG_BLK_DEV_THROTTLING
    /* Throttle data */
    struct throtl_data *td;
#endif
};

#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_DEAD     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_DEFAULT  ((1 << QUEUE_FLAG_IO_STAT) |        \
                 (1 << QUEUE_FLAG_STACKABLE)    |   \
                 (1 << QUEUE_FLAG_SAME_COMP)    |   \
                 (1 << QUEUE_FLAG_ADD_RANDOM))

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_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_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_pm_request(rq)  \
    ((rq)->cmd_type == REQ_TYPE_PM_SUSPEND || \
     (rq)->cmd_type == REQ_TYPE_PM_RESUME)

#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)     ((rq)->cmd_flags & 1)

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 {
    int i;
    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.i)

#define rq_iter_last(rq, _iter)                 \
        (_iter.bio->bi_next == NULL && _iter.i == _iter.bio->bi_vcnt-1)

#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 void 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_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_rq_check_limits(struct request_queue *q, struct request *rq);
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_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 void blk_queue_bio(struct request_queue *q, 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 sync)
{
    clear_bdi_congested(&q->backing_dev_info, sync);
}

/*
 * 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 sync)
{
    set_bdi_congested(&q->backing_dev_info, sync);
}

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 *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 *, struct sg_iovec *, int,
                   unsigned int, 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 *);

static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
{
    return bdev->bd_disk->queue;
}

/*
 * 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 q->limits.max_discard_sectors;

    if (unlikely(cmd_flags & REQ_WRITE_SAME))
        return q->limits.max_write_same_sectors;

    return q->limits.max_sectors;
}

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_BLOCK_PC))
        return q->limits.max_hw_sectors;

    return blk_queue_get_max_sectors(q, rq->cmd_flags);
}

/*
 * 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 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_limits_max_hw_sectors(struct queue_limits *, unsigned int);
extern void blk_queue_max_hw_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_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_merge_bvec(struct request_queue *, merge_bvec_fn *);
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 int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
              struct scatterlist *sglist);
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 *);

/*
 * 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 {
    unsigned long magic; /* detect uninitialized use-cases */
    struct list_head list; /* requests */
    struct list_head cb_list; /* md requires an unplug callback */
    unsigned int should_sort; /* list to be sorted before flushing? */
};
#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->cb_list));
}

/*
 * tag stuff
 */
#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];
}

#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);
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);
}

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 = 1024,
    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 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 << 9) & (granularity - 1);

    return (granularity + lim->alignment_offset - alignment)
        & (granularity - 1);
}

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 = (sector << 9) & (lim->discard_granularity - 1);

    if (!lim->max_discard_sectors)
        return 0;

    return (lim->discard_granularity + lim->discard_alignment - alignment)
        & (lim->discard_granularity - 1);
}

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);
}

struct work_struct;
int kblockd_schedule_work(struct request_queue *q, struct work_struct *work);

#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)

#define INTEGRITY_FLAG_READ 2   /* verify data integrity on read */
#define INTEGRITY_FLAG_WRITE    4   /* generate data integrity on write */

struct blk_integrity_exchg {
    void            *prot_buf;
    void            *data_buf;
    sector_t        sector;
    unsigned int        data_size;
    unsigned short      sector_size;
    const char      *disk_name;
};

typedef void (integrity_gen_fn) (struct blk_integrity_exchg *);
typedef int (integrity_vrfy_fn) (struct blk_integrity_exchg *);
typedef void (integrity_set_tag_fn) (void *, void *, unsigned int);
typedef void (integrity_get_tag_fn) (void *, void *, unsigned int);

struct blk_integrity {
    integrity_gen_fn    *generate_fn;
    integrity_vrfy_fn   *verify_fn;
    integrity_set_tag_fn    *set_tag_fn;
    integrity_get_tag_fn    *get_tag_fn;

    unsigned short      flags;
    unsigned short      tuple_size;
    unsigned short      sector_size;
    unsigned short      tag_size;

    const char      *name;

    struct kobject      kobj;
};

extern bool blk_integrity_is_initialized(struct gendisk *);
extern int 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 int blk_integrity_merge_rq(struct request_queue *, struct request *,
                  struct request *);
extern int blk_integrity_merge_bio(struct request_queue *, struct request *,
                   struct bio *);

static inline
struct blk_integrity *bdev_get_integrity(struct block_device *bdev)
{
    return bdev->bd_disk->integrity;
}

static inline struct blk_integrity *blk_get_integrity(struct gendisk *disk)
{
    return disk->integrity;
}

static inline int blk_integrity_rq(struct request *rq)
{
    if (rq->bio == NULL)
        return 0;

    return bio_integrity(rq->bio);
}

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;
}

#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 0;
}
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 int blk_integrity_register(struct gendisk *d,
                     struct blk_integrity *b)
{
    return 0;
}
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 int blk_integrity_merge_rq(struct request_queue *rq,
                     struct request *r1,
                     struct request *r2)
{
    return 0;
}
static inline int blk_integrity_merge_bio(struct request_queue *rq,
                      struct request *r,
                      struct bio *b)
{
    return 0;
}
static inline bool blk_integrity_is_initialized(struct gendisk *g)
{
    return 0;
}

#endif /* CONFIG_BLK_DEV_INTEGRITY */

struct block_device_operations {
    int (*open) (struct block_device *, fmode_t);
    int (*release) (struct gendisk *, fmode_t);
    int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
    int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
    int (*direct_access) (struct block_device *, sector_t,
                        void **, unsigned long *);
    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;
};

extern int __blkdev_driver_ioctl(struct block_device *, fmode_t, unsigned int,
                 unsigned long);
#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;
}

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;
}

#endif /* CONFIG_BLOCK */

#endif