blk-core.c

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/*
 * Copyright (C) 1991, 1992 Linus Torvalds
 * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
 * Elevator latency, (C) 2000  Andrea Arcangeli <[email protected]> SuSE
 * Queue request tables / lock, selectable elevator, Jens Axboe <[email protected]>
 * kernel-doc documentation started by NeilBrown <[email protected]>
 *  -  July2000
 * bio rewrite, highmem i/o, etc, Jens Axboe <[email protected]> - may 2001
 */

/*
 * This handles all read/write requests to block devices
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/backing-dev.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/highmem.h>
#include <linux/mm.h>
#include <linux/kernel_stat.h>
#include <linux/string.h>
#include <linux/init.h>
#include <linux/completion.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/fault-inject.h>
#include <linux/list_sort.h>
#include <linux/delay.h>
#include <linux/ratelimit.h>

#define CREATE_TRACE_POINTS
#include <trace/events/block.h>

#include "blk.h"
#include "blk-cgroup.h"

EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);
EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_complete);

DEFINE_IDA(blk_queue_ida);

/*
 * For the allocated request tables
 */
static struct kmem_cache *request_cachep;

/*
 * For queue allocation
 */
struct kmem_cache *blk_requestq_cachep;

/*
 * Controlling structure to kblockd
 */
static struct workqueue_struct *kblockd_workqueue;

static void drive_stat_acct(struct request *rq, int new_io)
{
    struct hd_struct *part;
    int rw = rq_data_dir(rq);
    int cpu;

    if (!blk_do_io_stat(rq))
        return;

    cpu = part_stat_lock();

    if (!new_io) {
        part = rq->part;
        part_stat_inc(cpu, part, merges[rw]);
    } else {
        part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
        if (!hd_struct_try_get(part)) {
            /*
             * The partition is already being removed,
             * the request will be accounted on the disk only
             *
             * We take a reference on disk->part0 although that
             * partition will never be deleted, so we can treat
             * it as any other partition.
             */
            part = &rq->rq_disk->part0;
            hd_struct_get(part);
        }
        part_round_stats(cpu, part);
        part_inc_in_flight(part, rw);
        rq->part = part;
    }

    part_stat_unlock();
}

void blk_queue_congestion_threshold(struct request_queue *q)
{
    int nr;

    nr = q->nr_requests - (q->nr_requests / 8) + 1;
    if (nr > q->nr_requests)
        nr = q->nr_requests;
    q->nr_congestion_on = nr;

    nr = q->nr_requests - (q->nr_requests / 8) - (q->nr_requests / 16) - 1;
    if (nr < 1)
        nr = 1;
    q->nr_congestion_off = nr;
}

struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
{
    struct backing_dev_info *ret = NULL;
    struct request_queue *q = bdev_get_queue(bdev);

    if (q)
        ret = &q->backing_dev_info;
    return ret;
}
EXPORT_SYMBOL(blk_get_backing_dev_info);

void blk_rq_init(struct request_queue *q, struct request *rq)
{
    memset(rq, 0, sizeof(*rq));

    INIT_LIST_HEAD(&rq->queuelist);
    INIT_LIST_HEAD(&rq->timeout_list);
    rq->cpu = -1;
    rq->q = q;
    rq->__sector = (sector_t) -1;
    INIT_HLIST_NODE(&rq->hash);
    RB_CLEAR_NODE(&rq->rb_node);
    rq->cmd = rq->__cmd;
    rq->cmd_len = BLK_MAX_CDB;
    rq->tag = -1;
    rq->ref_count = 1;
    rq->start_time = jiffies;
    set_start_time_ns(rq);
    rq->part = NULL;
}
EXPORT_SYMBOL(blk_rq_init);

static void req_bio_endio(struct request *rq, struct bio *bio,
              unsigned int nbytes, int error)
{
    if (error)
        clear_bit(BIO_UPTODATE, &bio->bi_flags);
    else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
        error = -EIO;

    if (unlikely(nbytes > bio->bi_size)) {
        printk(KERN_ERR "%s: want %u bytes done, %u left\n",
               __func__, nbytes, bio->bi_size);
        nbytes = bio->bi_size;
    }

    if (unlikely(rq->cmd_flags & REQ_QUIET))
        set_bit(BIO_QUIET, &bio->bi_flags);

    bio->bi_size -= nbytes;
    bio->bi_sector += (nbytes >> 9);

    if (bio_integrity(bio))
        bio_integrity_advance(bio, nbytes);

    /* don't actually finish bio if it's part of flush sequence */
    if (bio->bi_size == 0 && !(rq->cmd_flags & REQ_FLUSH_SEQ))
        bio_endio(bio, error);
}

void blk_dump_rq_flags(struct request *rq, char *msg)
{
    int bit;

    printk(KERN_INFO "%s: dev %s: type=%x, flags=%x\n", msg,
        rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->cmd_type,
        rq->cmd_flags);

    printk(KERN_INFO "  sector %llu, nr/cnr %u/%u\n",
           (unsigned long long)blk_rq_pos(rq),
           blk_rq_sectors(rq), blk_rq_cur_sectors(rq));
    printk(KERN_INFO "  bio %p, biotail %p, buffer %p, len %u\n",
           rq->bio, rq->biotail, rq->buffer, blk_rq_bytes(rq));

    if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {
        printk(KERN_INFO "  cdb: ");
        for (bit = 0; bit < BLK_MAX_CDB; bit++)
            printk("%02x ", rq->cmd[bit]);
        printk("\n");
    }
}
EXPORT_SYMBOL(blk_dump_rq_flags);

static void blk_delay_work(struct work_struct *work)
{
    struct request_queue *q;

    q = container_of(work, struct request_queue, delay_work.work);
    spin_lock_irq(q->queue_lock);
    __blk_run_queue(q);
    spin_unlock_irq(q->queue_lock);
}

void blk_delay_queue(struct request_queue *q, unsigned long msecs)
{
    queue_delayed_work(kblockd_workqueue, &q->delay_work,
                msecs_to_jiffies(msecs));
}
EXPORT_SYMBOL(blk_delay_queue);

void blk_start_queue(struct request_queue *q)
{
    WARN_ON(!irqs_disabled());

    queue_flag_clear(QUEUE_FLAG_STOPPED, q);
    __blk_run_queue(q);
}
EXPORT_SYMBOL(blk_start_queue);

void blk_stop_queue(struct request_queue *q)
{
    cancel_delayed_work(&q->delay_work);
    queue_flag_set(QUEUE_FLAG_STOPPED, q);
}
EXPORT_SYMBOL(blk_stop_queue);

void blk_sync_queue(struct request_queue *q)
{
    del_timer_sync(&q->timeout);
    cancel_delayed_work_sync(&q->delay_work);
}
EXPORT_SYMBOL(blk_sync_queue);

void __blk_run_queue(struct request_queue *q)
{
    if (unlikely(blk_queue_stopped(q)))
        return;

    q->request_fn(q);
}
EXPORT_SYMBOL(__blk_run_queue);

void blk_run_queue_async(struct request_queue *q)
{
    if (likely(!blk_queue_stopped(q)))
        mod_delayed_work(kblockd_workqueue, &q->delay_work, 0);
}
EXPORT_SYMBOL(blk_run_queue_async);

void blk_run_queue(struct request_queue *q)
{
    unsigned long flags;

    spin_lock_irqsave(q->queue_lock, flags);
    __blk_run_queue(q);
    spin_unlock_irqrestore(q->queue_lock, flags);
}
EXPORT_SYMBOL(blk_run_queue);

void blk_put_queue(struct request_queue *q)
{
    kobject_put(&q->kobj);
}
EXPORT_SYMBOL(blk_put_queue);

void blk_drain_queue(struct request_queue *q, bool drain_all)
{
    int i;

    while (true) {
        bool drain = false;

        spin_lock_irq(q->queue_lock);

        /*
         * The caller might be trying to drain @q before its
         * elevator is initialized.
         */
        if (q->elevator)
            elv_drain_elevator(q);

        blkcg_drain_queue(q);

        /*
         * This function might be called on a queue which failed
         * driver init after queue creation or is not yet fully
         * active yet.  Some drivers (e.g. fd and loop) get unhappy
         * in such cases.  Kick queue iff dispatch queue has
         * something on it and @q has request_fn set.
         */
        if (!list_empty(&q->queue_head) && q->request_fn)
            __blk_run_queue(q);

        drain |= q->nr_rqs_elvpriv;

        /*
         * Unfortunately, requests are queued at and tracked from
         * multiple places and there's no single counter which can
         * be drained.  Check all the queues and counters.
         */
        if (drain_all) {
            drain |= !list_empty(&q->queue_head);
            for (i = 0; i < 2; i++) {
                drain |= q->nr_rqs[i];
                drain |= q->in_flight[i];
                drain |= !list_empty(&q->flush_queue[i]);
            }
        }

        spin_unlock_irq(q->queue_lock);

        if (!drain)
            break;
        msleep(10);
    }

    /*
     * With queue marked dead, any woken up waiter will fail the
     * allocation path, so the wakeup chaining is lost and we're
     * left with hung waiters. We need to wake up those waiters.
     */
    if (q->request_fn) {
        struct request_list *rl;

        spin_lock_irq(q->queue_lock);

        blk_queue_for_each_rl(rl, q)
            for (i = 0; i < ARRAY_SIZE(rl->wait); i++)
                wake_up_all(&rl->wait[i]);

        spin_unlock_irq(q->queue_lock);
    }
}

void blk_queue_bypass_start(struct request_queue *q)
{
    bool drain;

    spin_lock_irq(q->queue_lock);
    drain = !q->bypass_depth++;
    queue_flag_set(QUEUE_FLAG_BYPASS, q);
    spin_unlock_irq(q->queue_lock);

    if (drain) {
        blk_drain_queue(q, false);
        /* ensure blk_queue_bypass() is %true inside RCU read lock */
        synchronize_rcu();
    }
}
EXPORT_SYMBOL_GPL(blk_queue_bypass_start);

void blk_queue_bypass_end(struct request_queue *q)
{
    spin_lock_irq(q->queue_lock);
    if (!--q->bypass_depth)
        queue_flag_clear(QUEUE_FLAG_BYPASS, q);
    WARN_ON_ONCE(q->bypass_depth < 0);
    spin_unlock_irq(q->queue_lock);
}
EXPORT_SYMBOL_GPL(blk_queue_bypass_end);

void blk_cleanup_queue(struct request_queue *q)
{
    spinlock_t *lock = q->queue_lock;

    /* mark @q DEAD, no new request or merges will be allowed afterwards */
    mutex_lock(&q->sysfs_lock);
    queue_flag_set_unlocked(QUEUE_FLAG_DEAD, q);
    spin_lock_irq(lock);

    /*
     * Dead queue is permanently in bypass mode till released.  Note
     * that, unlike blk_queue_bypass_start(), we aren't performing
     * synchronize_rcu() after entering bypass mode to avoid the delay
     * as some drivers create and destroy a lot of queues while
     * probing.  This is still safe because blk_release_queue() will be
     * called only after the queue refcnt drops to zero and nothing,
     * RCU or not, would be traversing the queue by then.
     */
    q->bypass_depth++;
    queue_flag_set(QUEUE_FLAG_BYPASS, q);

    queue_flag_set(QUEUE_FLAG_NOMERGES, q);
    queue_flag_set(QUEUE_FLAG_NOXMERGES, q);
    queue_flag_set(QUEUE_FLAG_DEAD, q);
    spin_unlock_irq(lock);
    mutex_unlock(&q->sysfs_lock);

    /* drain all requests queued before DEAD marking */
    blk_drain_queue(q, true);

    /* @q won't process any more request, flush async actions */
    del_timer_sync(&q->backing_dev_info.laptop_mode_wb_timer);
    blk_sync_queue(q);

    spin_lock_irq(lock);
    if (q->queue_lock != &q->__queue_lock)
        q->queue_lock = &q->__queue_lock;
    spin_unlock_irq(lock);

    /* @q is and will stay empty, shutdown and put */
    blk_put_queue(q);
}
EXPORT_SYMBOL(blk_cleanup_queue);

int blk_init_rl(struct request_list *rl, struct request_queue *q,
        gfp_t gfp_mask)
{
    if (unlikely(rl->rq_pool))
        return 0;

    rl->q = q;
    rl->count[BLK_RW_SYNC] = rl->count[BLK_RW_ASYNC] = 0;
    rl->starved[BLK_RW_SYNC] = rl->starved[BLK_RW_ASYNC] = 0;
    init_waitqueue_head(&rl->wait[BLK_RW_SYNC]);
    init_waitqueue_head(&rl->wait[BLK_RW_ASYNC]);

    rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
                      mempool_free_slab, request_cachep,
                      gfp_mask, q->node);
    if (!rl->rq_pool)
        return -ENOMEM;

    return 0;
}

void blk_exit_rl(struct request_list *rl)
{
    if (rl->rq_pool)
        mempool_destroy(rl->rq_pool);
}

struct request_queue *blk_alloc_queue(gfp_t gfp_mask)
{
    return blk_alloc_queue_node(gfp_mask, -1);
}
EXPORT_SYMBOL(blk_alloc_queue);

struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
{
    struct request_queue *q;
    int err;

    q = kmem_cache_alloc_node(blk_requestq_cachep,
                gfp_mask | __GFP_ZERO, node_id);
    if (!q)
        return NULL;

    q->id = ida_simple_get(&blk_queue_ida, 0, 0, gfp_mask);
    if (q->id < 0)
        goto fail_q;

    q->backing_dev_info.ra_pages =
            (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
    q->backing_dev_info.state = 0;
    q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
    q->backing_dev_info.name = "block";
    q->node = node_id;

    err = bdi_init(&q->backing_dev_info);
    if (err)
        goto fail_id;

    setup_timer(&q->backing_dev_info.laptop_mode_wb_timer,
            laptop_mode_timer_fn, (unsigned long) q);
    setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q);
    INIT_LIST_HEAD(&q->queue_head);
    INIT_LIST_HEAD(&q->timeout_list);
    INIT_LIST_HEAD(&q->icq_list);
#ifdef CONFIG_BLK_CGROUP
    INIT_LIST_HEAD(&q->blkg_list);
#endif
    INIT_LIST_HEAD(&q->flush_queue[0]);
    INIT_LIST_HEAD(&q->flush_queue[1]);
    INIT_LIST_HEAD(&q->flush_data_in_flight);
    INIT_DELAYED_WORK(&q->delay_work, blk_delay_work);

    kobject_init(&q->kobj, &blk_queue_ktype);

    mutex_init(&q->sysfs_lock);
    spin_lock_init(&q->__queue_lock);

    /*
     * By default initialize queue_lock to internal lock and driver can
     * override it later if need be.
     */
    q->queue_lock = &q->__queue_lock;

    /*
     * A queue starts its life with bypass turned on to avoid
     * unnecessary bypass on/off overhead and nasty surprises during
     * init.  The initial bypass will be finished when the queue is
     * registered by blk_register_queue().
     */
    q->bypass_depth = 1;
    __set_bit(QUEUE_FLAG_BYPASS, &q->queue_flags);

    if (blkcg_init_queue(q))
        goto fail_id;

    return q;

fail_id:
    ida_simple_remove(&blk_queue_ida, q->id);
fail_q:
    kmem_cache_free(blk_requestq_cachep, q);
    return NULL;
}
EXPORT_SYMBOL(blk_alloc_queue_node);

struct request_queue *blk_init_queue(request_fn_proc *rfn, spinlock_t *lock)
{
    return blk_init_queue_node(rfn, lock, -1);
}
EXPORT_SYMBOL(blk_init_queue);

struct request_queue *
blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
{
    struct request_queue *uninit_q, *q;

    uninit_q = blk_alloc_queue_node(GFP_KERNEL, node_id);
    if (!uninit_q)
        return NULL;

    q = blk_init_allocated_queue(uninit_q, rfn, lock);
    if (!q)
        blk_cleanup_queue(uninit_q);

    return q;
}
EXPORT_SYMBOL(blk_init_queue_node);

struct request_queue *
blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
             spinlock_t *lock)
{
    if (!q)
        return NULL;

    if (blk_init_rl(&q->root_rl, q, GFP_KERNEL))
        return NULL;

    q->request_fn       = rfn;
    q->prep_rq_fn       = NULL;
    q->unprep_rq_fn     = NULL;
    q->queue_flags      |= QUEUE_FLAG_DEFAULT;

    /* Override internal queue lock with supplied lock pointer */
    if (lock)
        q->queue_lock       = lock;

    /*
     * This also sets hw/phys segments, boundary and size
     */
    blk_queue_make_request(q, blk_queue_bio);

    q->sg_reserved_size = INT_MAX;

    /* init elevator */
    if (elevator_init(q, NULL))
        return NULL;
    return q;
}
EXPORT_SYMBOL(blk_init_allocated_queue);

bool blk_get_queue(struct request_queue *q)
{
    if (likely(!blk_queue_dead(q))) {
        __blk_get_queue(q);
        return true;
    }

    return false;
}
EXPORT_SYMBOL(blk_get_queue);

static inline void blk_free_request(struct request_list *rl, struct request *rq)
{
    if (rq->cmd_flags & REQ_ELVPRIV) {
        elv_put_request(rl->q, rq);
        if (rq->elv.icq)
            put_io_context(rq->elv.icq->ioc);
    }

    mempool_free(rq, rl->rq_pool);
}

/*
 * ioc_batching returns true if the ioc is a valid batching request and
 * should be given priority access to a request.
 */
static inline int ioc_batching(struct request_queue *q, struct io_context *ioc)
{
    if (!ioc)
        return 0;

    /*
     * Make sure the process is able to allocate at least 1 request
     * even if the batch times out, otherwise we could theoretically
     * lose wakeups.
     */
    return ioc->nr_batch_requests == q->nr_batching ||
        (ioc->nr_batch_requests > 0
        && time_before(jiffies, ioc->last_waited + BLK_BATCH_TIME));
}

/*
 * ioc_set_batching sets ioc to be a new "batcher" if it is not one. This
 * will cause the process to be a "batcher" on all queues in the system. This
 * is the behaviour we want though - once it gets a wakeup it should be given
 * a nice run.
 */
static void ioc_set_batching(struct request_queue *q, struct io_context *ioc)
{
    if (!ioc || ioc_batching(q, ioc))
        return;

    ioc->nr_batch_requests = q->nr_batching;
    ioc->last_waited = jiffies;
}

static void __freed_request(struct request_list *rl, int sync)
{
    struct request_queue *q = rl->q;

    /*
     * bdi isn't aware of blkcg yet.  As all async IOs end up root
     * blkcg anyway, just use root blkcg state.
     */
    if (rl == &q->root_rl &&
        rl->count[sync] < queue_congestion_off_threshold(q))
        blk_clear_queue_congested(q, sync);

    if (rl->count[sync] + 1 <= q->nr_requests) {
        if (waitqueue_active(&rl->wait[sync]))
            wake_up(&rl->wait[sync]);

        blk_clear_rl_full(rl, sync);
    }
}

/*
 * A request has just been released.  Account for it, update the full and
 * congestion status, wake up any waiters.   Called under q->queue_lock.
 */
static void freed_request(struct request_list *rl, unsigned int flags)
{
    struct request_queue *q = rl->q;
    int sync = rw_is_sync(flags);

    q->nr_rqs[sync]--;
    rl->count[sync]--;
    if (flags & REQ_ELVPRIV)
        q->nr_rqs_elvpriv--;

    __freed_request(rl, sync);

    if (unlikely(rl->starved[sync ^ 1]))
        __freed_request(rl, sync ^ 1);
}

/*
 * Determine if elevator data should be initialized when allocating the
 * request associated with @bio.
 */
static bool blk_rq_should_init_elevator(struct bio *bio)
{
    if (!bio)
        return true;

    /*
     * Flush requests do not use the elevator so skip initialization.
     * This allows a request to share the flush and elevator data.
     */
    if (bio->bi_rw & (REQ_FLUSH | REQ_FUA))
        return false;

    return true;
}

static struct io_context *rq_ioc(struct bio *bio)
{
#ifdef CONFIG_BLK_CGROUP
    if (bio && bio->bi_ioc)
        return bio->bi_ioc;
#endif
    return current->io_context;
}

static struct request *__get_request(struct request_list *rl, int rw_flags,
                     struct bio *bio, gfp_t gfp_mask)
{
    struct request_queue *q = rl->q;
    struct request *rq;
    struct elevator_type *et = q->elevator->type;
    struct io_context *ioc = rq_ioc(bio);
    struct io_cq *icq = NULL;
    const bool is_sync = rw_is_sync(rw_flags) != 0;
    int may_queue;

    if (unlikely(blk_queue_dead(q)))
        return NULL;

    may_queue = elv_may_queue(q, rw_flags);
    if (may_queue == ELV_MQUEUE_NO)
        goto rq_starved;

    if (rl->count[is_sync]+1 >= queue_congestion_on_threshold(q)) {
        if (rl->count[is_sync]+1 >= q->nr_requests) {
            /*
             * The queue will fill after this allocation, so set
             * it as full, and mark this process as "batching".
             * This process will be allowed to complete a batch of
             * requests, others will be blocked.
             */
            if (!blk_rl_full(rl, is_sync)) {
                ioc_set_batching(q, ioc);
                blk_set_rl_full(rl, is_sync);
            } else {
                if (may_queue != ELV_MQUEUE_MUST
                        && !ioc_batching(q, ioc)) {
                    /*
                     * The queue is full and the allocating
                     * process is not a "batcher", and not
                     * exempted by the IO scheduler
                     */
                    return NULL;
                }
            }
        }
        /*
         * bdi isn't aware of blkcg yet.  As all async IOs end up
         * root blkcg anyway, just use root blkcg state.
         */
        if (rl == &q->root_rl)
            blk_set_queue_congested(q, is_sync);
    }

    /*
     * Only allow batching queuers to allocate up to 50% over the defined
     * limit of requests, otherwise we could have thousands of requests
     * allocated with any setting of ->nr_requests
     */
    if (rl->count[is_sync] >= (3 * q->nr_requests / 2))
        return NULL;

    q->nr_rqs[is_sync]++;
    rl->count[is_sync]++;
    rl->starved[is_sync] = 0;

    /*
     * Decide whether the new request will be managed by elevator.  If
     * so, mark @rw_flags and increment elvpriv.  Non-zero elvpriv will
     * prevent the current elevator from being destroyed until the new
     * request is freed.  This guarantees icq's won't be destroyed and
     * makes creating new ones safe.
     *
     * Also, lookup icq while holding queue_lock.  If it doesn't exist,
     * it will be created after releasing queue_lock.
     */
    if (blk_rq_should_init_elevator(bio) && !blk_queue_bypass(q)) {
        rw_flags |= REQ_ELVPRIV;
        q->nr_rqs_elvpriv++;
        if (et->icq_cache && ioc)
            icq = ioc_lookup_icq(ioc, q);
    }

    if (blk_queue_io_stat(q))
        rw_flags |= REQ_IO_STAT;
    spin_unlock_irq(q->queue_lock);

    /* allocate and init request */
    rq = mempool_alloc(rl->rq_pool, gfp_mask);
    if (!rq)
        goto fail_alloc;

    blk_rq_init(q, rq);
    blk_rq_set_rl(rq, rl);
    rq->cmd_flags = rw_flags | REQ_ALLOCED;

    /* init elvpriv */
    if (rw_flags & REQ_ELVPRIV) {
        if (unlikely(et->icq_cache && !icq)) {
            if (ioc)
                icq = ioc_create_icq(ioc, q, gfp_mask);
            if (!icq)
                goto fail_elvpriv;
        }

        rq->elv.icq = icq;
        if (unlikely(elv_set_request(q, rq, bio, gfp_mask)))
            goto fail_elvpriv;

        /* @rq->elv.icq holds io_context until @rq is freed */
        if (icq)
            get_io_context(icq->ioc);
    }
out:
    /*
     * ioc may be NULL here, and ioc_batching will be false. That's
     * OK, if the queue is under the request limit then requests need
     * not count toward the nr_batch_requests limit. There will always
     * be some limit enforced by BLK_BATCH_TIME.
     */
    if (ioc_batching(q, ioc))
        ioc->nr_batch_requests--;

    trace_block_getrq(q, bio, rw_flags & 1);
    return rq;

fail_elvpriv:
    /*
     * elvpriv init failed.  ioc, icq and elvpriv aren't mempool backed
     * and may fail indefinitely under memory pressure and thus
     * shouldn't stall IO.  Treat this request as !elvpriv.  This will
     * disturb iosched and blkcg but weird is bettern than dead.
     */
    printk_ratelimited(KERN_WARNING "%s: request aux data allocation failed, iosched may be disturbed\n",
               dev_name(q->backing_dev_info.dev));

    rq->cmd_flags &= ~REQ_ELVPRIV;
    rq->elv.icq = NULL;

    spin_lock_irq(q->queue_lock);
    q->nr_rqs_elvpriv--;
    spin_unlock_irq(q->queue_lock);
    goto out;

fail_alloc:
    /*
     * Allocation failed presumably due to memory. Undo anything we
     * might have messed up.
     *
     * Allocating task should really be put onto the front of the wait
     * queue, but this is pretty rare.
     */
    spin_lock_irq(q->queue_lock);
    freed_request(rl, rw_flags);

    /*
     * in the very unlikely event that allocation failed and no
     * requests for this direction was pending, mark us starved so that
     * freeing of a request in the other direction will notice
     * us. another possible fix would be to split the rq mempool into
     * READ and WRITE
     */
rq_starved:
    if (unlikely(rl->count[is_sync] == 0))
        rl->starved[is_sync] = 1;
    return NULL;
}

static struct request *get_request(struct request_queue *q, int rw_flags,
                   struct bio *bio, gfp_t gfp_mask)
{
    const bool is_sync = rw_is_sync(rw_flags) != 0;
    DEFINE_WAIT(wait);
    struct request_list *rl;
    struct request *rq;

    rl = blk_get_rl(q, bio);    /* transferred to @rq on success */
retry:
    rq = __get_request(rl, rw_flags, bio, gfp_mask);
    if (rq)
        return rq;

    if (!(gfp_mask & __GFP_WAIT) || unlikely(blk_queue_dead(q))) {
        blk_put_rl(rl);
        return NULL;
    }

    /* wait on @rl and retry */
    prepare_to_wait_exclusive(&rl->wait[is_sync], &wait,
                  TASK_UNINTERRUPTIBLE);

    trace_block_sleeprq(q, bio, rw_flags & 1);

    spin_unlock_irq(q->queue_lock);
    io_schedule();

    /*
     * After sleeping, we become a "batching" process and will be able
     * to allocate at least one request, and up to a big batch of them
     * for a small period time.  See ioc_batching, ioc_set_batching
     */
    ioc_set_batching(q, current->io_context);

    spin_lock_irq(q->queue_lock);
    finish_wait(&rl->wait[is_sync], &wait);

    goto retry;
}

struct request *blk_get_request(struct request_queue *q, int rw, gfp_t gfp_mask)
{
    struct request *rq;

    BUG_ON(rw != READ && rw != WRITE);

    /* create ioc upfront */
    create_io_context(gfp_mask, q->node);

    spin_lock_irq(q->queue_lock);
    rq = get_request(q, rw, NULL, gfp_mask);
    if (!rq)
        spin_unlock_irq(q->queue_lock);
    /* q->queue_lock is unlocked at this point */

    return rq;
}
EXPORT_SYMBOL(blk_get_request);

struct request *blk_make_request(struct request_queue *q, struct bio *bio,
                 gfp_t gfp_mask)
{
    struct request *rq = blk_get_request(q, bio_data_dir(bio), gfp_mask);

    if (unlikely(!rq))
        return ERR_PTR(-ENOMEM);

    for_each_bio(bio) {
        struct bio *bounce_bio = bio;
        int ret;

        blk_queue_bounce(q, &bounce_bio);
        ret = blk_rq_append_bio(q, rq, bounce_bio);
        if (unlikely(ret)) {
            blk_put_request(rq);
            return ERR_PTR(ret);
        }
    }

    return rq;
}
EXPORT_SYMBOL(blk_make_request);

void blk_requeue_request(struct request_queue *q, struct request *rq)
{
    blk_delete_timer(rq);
    blk_clear_rq_complete(rq);
    trace_block_rq_requeue(q, rq);

    if (blk_rq_tagged(rq))
        blk_queue_end_tag(q, rq);

    BUG_ON(blk_queued_rq(rq));

    elv_requeue_request(q, rq);
}
EXPORT_SYMBOL(blk_requeue_request);

static void add_acct_request(struct request_queue *q, struct request *rq,
                 int where)
{
    drive_stat_acct(rq, 1);
    __elv_add_request(q, rq, where);
}

static void part_round_stats_single(int cpu, struct hd_struct *part,
                    unsigned long now)
{
    if (now == part->stamp)
        return;

    if (part_in_flight(part)) {
        __part_stat_add(cpu, part, time_in_queue,
                part_in_flight(part) * (now - part->stamp));
        __part_stat_add(cpu, part, io_ticks, (now - part->stamp));
    }
    part->stamp = now;
}

void part_round_stats(int cpu, struct hd_struct *part)
{
    unsigned long now = jiffies;

    if (part->partno)
        part_round_stats_single(cpu, &part_to_disk(part)->part0, now);
    part_round_stats_single(cpu, part, now);
}
EXPORT_SYMBOL_GPL(part_round_stats);

/*
 * queue lock must be held
 */
void __blk_put_request(struct request_queue *q, struct request *req)
{
    if (unlikely(!q))
        return;
    if (unlikely(--req->ref_count))
        return;

    elv_completed_request(q, req);

    /* this is a bio leak */
    WARN_ON(req->bio != NULL);

    /*
     * Request may not have originated from ll_rw_blk. if not,
     * it didn't come out of our reserved rq pools
     */
    if (req->cmd_flags & REQ_ALLOCED) {
        unsigned int flags = req->cmd_flags;
        struct request_list *rl = blk_rq_rl(req);

        BUG_ON(!list_empty(&req->queuelist));
        BUG_ON(!hlist_unhashed(&req->hash));

        blk_free_request(rl, req);
        freed_request(rl, flags);
        blk_put_rl(rl);
    }
}
EXPORT_SYMBOL_GPL(__blk_put_request);

void blk_put_request(struct request *req)
{
    unsigned long flags;
    struct request_queue *q = req->q;

    spin_lock_irqsave(q->queue_lock, flags);
    __blk_put_request(q, req);
    spin_unlock_irqrestore(q->queue_lock, flags);
}
EXPORT_SYMBOL(blk_put_request);

void blk_add_request_payload(struct request *rq, struct page *page,
        unsigned int len)
{
    struct bio *bio = rq->bio;

    bio->bi_io_vec->bv_page = page;
    bio->bi_io_vec->bv_offset = 0;
    bio->bi_io_vec->bv_len = len;

    bio->bi_size = len;
    bio->bi_vcnt = 1;
    bio->bi_phys_segments = 1;

    rq->__data_len = rq->resid_len = len;
    rq->nr_phys_segments = 1;
    rq->buffer = bio_data(bio);
}
EXPORT_SYMBOL_GPL(blk_add_request_payload);

static bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
                   struct bio *bio)
{
    const int ff = bio->bi_rw & REQ_FAILFAST_MASK;

    if (!ll_back_merge_fn(q, req, bio))
        return false;

    trace_block_bio_backmerge(q, bio);

    if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
        blk_rq_set_mixed_merge(req);

    req->biotail->bi_next = bio;
    req->biotail = bio;
    req->__data_len += bio->bi_size;
    req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));

    drive_stat_acct(req, 0);
    return true;
}

static bool bio_attempt_front_merge(struct request_queue *q,
                    struct request *req, struct bio *bio)
{
    const int ff = bio->bi_rw & REQ_FAILFAST_MASK;

    if (!ll_front_merge_fn(q, req, bio))
        return false;

    trace_block_bio_frontmerge(q, bio);

    if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
        blk_rq_set_mixed_merge(req);

    bio->bi_next = req->bio;
    req->bio = bio;

    /*
     * may not be valid. if the low level driver said
     * it didn't need a bounce buffer then it better
     * not touch req->buffer either...
     */
    req->buffer = bio_data(bio);
    req->__sector = bio->bi_sector;
    req->__data_len += bio->bi_size;
    req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));

    drive_stat_acct(req, 0);
    return true;
}

static bool attempt_plug_merge(struct request_queue *q, struct bio *bio,
                   unsigned int *request_count)
{
    struct blk_plug *plug;
    struct request *rq;
    bool ret = false;

    plug = current->plug;
    if (!plug)
        goto out;
    *request_count = 0;

    list_for_each_entry_reverse(rq, &plug->list, queuelist) {
        int el_ret;

        if (rq->q == q)
            (*request_count)++;

        if (rq->q != q || !blk_rq_merge_ok(rq, bio))
            continue;

        el_ret = blk_try_merge(rq, bio);
        if (el_ret == ELEVATOR_BACK_MERGE) {
            ret = bio_attempt_back_merge(q, rq, bio);
            if (ret)
                break;
        } else if (el_ret == ELEVATOR_FRONT_MERGE) {
            ret = bio_attempt_front_merge(q, rq, bio);
            if (ret)
                break;
        }
    }
out:
    return ret;
}

void init_request_from_bio(struct request *req, struct bio *bio)
{
    req->cmd_type = REQ_TYPE_FS;

    req->cmd_flags |= bio->bi_rw & REQ_COMMON_MASK;
    if (bio->bi_rw & REQ_RAHEAD)
        req->cmd_flags |= REQ_FAILFAST_MASK;

    req->errors = 0;
    req->__sector = bio->bi_sector;
    req->ioprio = bio_prio(bio);
    blk_rq_bio_prep(req->q, req, bio);
}

void blk_queue_bio(struct request_queue *q, struct bio *bio)
{
    const bool sync = !!(bio->bi_rw & REQ_SYNC);
    struct blk_plug *plug;
    int el_ret, rw_flags, where = ELEVATOR_INSERT_SORT;
    struct request *req;
    unsigned int request_count = 0;

    /*
     * low level driver can indicate that it wants pages above a
     * certain limit bounced to low memory (ie for highmem, or even
     * ISA dma in theory)
     */
    blk_queue_bounce(q, &bio);

    if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
        spin_lock_irq(q->queue_lock);
        where = ELEVATOR_INSERT_FLUSH;
        goto get_rq;
    }

    /*
     * Check if we can merge with the plugged list before grabbing
     * any locks.
     */
    if (attempt_plug_merge(q, bio, &request_count))
        return;

    spin_lock_irq(q->queue_lock);

    el_ret = elv_merge(q, &req, bio);
    if (el_ret == ELEVATOR_BACK_MERGE) {
        if (bio_attempt_back_merge(q, req, bio)) {
            elv_bio_merged(q, req, bio);
            if (!attempt_back_merge(q, req))
                elv_merged_request(q, req, el_ret);
            goto out_unlock;
        }
    } else if (el_ret == ELEVATOR_FRONT_MERGE) {
        if (bio_attempt_front_merge(q, req, bio)) {
            elv_bio_merged(q, req, bio);
            if (!attempt_front_merge(q, req))
                elv_merged_request(q, req, el_ret);
            goto out_unlock;
        }
    }

get_rq:
    /*
     * This sync check and mask will be re-done in init_request_from_bio(),
     * but we need to set it earlier to expose the sync flag to the
     * rq allocator and io schedulers.
     */
    rw_flags = bio_data_dir(bio);
    if (sync)
        rw_flags |= REQ_SYNC;

    /*
     * Grab a free request. This is might sleep but can not fail.
     * Returns with the queue unlocked.
     */
    req = get_request(q, rw_flags, bio, GFP_NOIO);
    if (unlikely(!req)) {
        bio_endio(bio, -ENODEV);    /* @q is dead */
        goto out_unlock;
    }

    /*
     * After dropping the lock and possibly sleeping here, our request
     * may now be mergeable after it had proven unmergeable (above).
     * We don't worry about that case for efficiency. It won't happen
     * often, and the elevators are able to handle it.
     */
    init_request_from_bio(req, bio);

    if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags))
        req->cpu = raw_smp_processor_id();

    plug = current->plug;
    if (plug) {
        /*
         * If this is the first request added after a plug, fire
         * of a plug trace. If others have been added before, check
         * if we have multiple devices in this plug. If so, make a
         * note to sort the list before dispatch.
         */
        if (list_empty(&plug->list))
            trace_block_plug(q);
        else {
            if (!plug->should_sort) {
                struct request *__rq;

                __rq = list_entry_rq(plug->list.prev);
                if (__rq->q != q)
                    plug->should_sort = 1;
            }
            if (request_count >= BLK_MAX_REQUEST_COUNT) {
                blk_flush_plug_list(plug, false);
                trace_block_plug(q);
            }
        }
        list_add_tail(&req->queuelist, &plug->list);
        drive_stat_acct(req, 1);
    } else {
        spin_lock_irq(q->queue_lock);
        add_acct_request(q, req, where);
        __blk_run_queue(q);
out_unlock:
        spin_unlock_irq(q->queue_lock);
    }
}
EXPORT_SYMBOL_GPL(blk_queue_bio);   /* for device mapper only */

/*
 * If bio->bi_dev is a partition, remap the location
 */
static inline void blk_partition_remap(struct bio *bio)
{
    struct block_device *bdev = bio->bi_bdev;

    if (bio_sectors(bio) && bdev != bdev->bd_contains) {
        struct hd_struct *p = bdev->bd_part;

        bio->bi_sector += p->start_sect;
        bio->bi_bdev = bdev->bd_contains;

        trace_block_bio_remap(bdev_get_queue(bio->bi_bdev), bio,
                      bdev->bd_dev,
                      bio->bi_sector - p->start_sect);
    }
}

static void handle_bad_sector(struct bio *bio)
{
    char b[BDEVNAME_SIZE];

    printk(KERN_INFO "attempt to access beyond end of device\n");
    printk(KERN_INFO "%s: rw=%ld, want=%Lu, limit=%Lu\n",
            bdevname(bio->bi_bdev, b),
            bio->bi_rw,
            (unsigned long long)bio->bi_sector + bio_sectors(bio),
            (long long)(i_size_read(bio->bi_bdev->bd_inode) >> 9));

    set_bit(BIO_EOF, &bio->bi_flags);
}

#ifdef CONFIG_FAIL_MAKE_REQUEST

static DECLARE_FAULT_ATTR(fail_make_request);

static int __init setup_fail_make_request(char *str)
{
    return setup_fault_attr(&fail_make_request, str);
}
__setup("fail_make_request=", setup_fail_make_request);

static bool should_fail_request(struct hd_struct *part, unsigned int bytes)
{
    return part->make_it_fail && should_fail(&fail_make_request, bytes);
}

static int __init fail_make_request_debugfs(void)
{
    struct dentry *dir = fault_create_debugfs_attr("fail_make_request",
                        NULL, &fail_make_request);

    return IS_ERR(dir) ? PTR_ERR(dir) : 0;
}

late_initcall(fail_make_request_debugfs);

#else /* CONFIG_FAIL_MAKE_REQUEST */

static inline bool should_fail_request(struct hd_struct *part,
                    unsigned int bytes)
{
    return false;
}

#endif /* CONFIG_FAIL_MAKE_REQUEST */

/*
 * Check whether this bio extends beyond the end of the device.
 */
static inline int bio_check_eod(struct bio *bio, unsigned int nr_sectors)
{
    sector_t maxsector;

    if (!nr_sectors)
        return 0;

    /* Test device or partition size, when known. */
    maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
    if (maxsector) {
        sector_t sector = bio->bi_sector;

        if (maxsector < nr_sectors || maxsector - nr_sectors < sector) {
            /*
             * This may well happen - the kernel calls bread()
             * without checking the size of the device, e.g., when
             * mounting a device.
             */
            handle_bad_sector(bio);
            return 1;
        }
    }

    return 0;
}

static noinline_for_stack bool
generic_make_request_checks(struct bio *bio)
{
    struct request_queue *q;
    int nr_sectors = bio_sectors(bio);
    int err = -EIO;
    char b[BDEVNAME_SIZE];
    struct hd_struct *part;

    might_sleep();

    if (bio_check_eod(bio, nr_sectors))
        goto end_io;

    q = bdev_get_queue(bio->bi_bdev);
    if (unlikely(!q)) {
        printk(KERN_ERR
               "generic_make_request: Trying to access "
            "nonexistent block-device %s (%Lu)\n",
            bdevname(bio->bi_bdev, b),
            (long long) bio->bi_sector);
        goto end_io;
    }

    if (likely(bio_is_rw(bio) &&
           nr_sectors > queue_max_hw_sectors(q))) {
        printk(KERN_ERR "bio too big device %s (%u > %u)\n",
               bdevname(bio->bi_bdev, b),
               bio_sectors(bio),
               queue_max_hw_sectors(q));
        goto end_io;
    }

    part = bio->bi_bdev->bd_part;
    if (should_fail_request(part, bio->bi_size) ||
        should_fail_request(&part_to_disk(part)->part0,
                bio->bi_size))
        goto end_io;

    /*
     * If this device has partitions, remap block n
     * of partition p to block n+start(p) of the disk.
     */
    blk_partition_remap(bio);

    if (bio_integrity_enabled(bio) && bio_integrity_prep(bio))
        goto end_io;

    if (bio_check_eod(bio, nr_sectors))
        goto end_io;

    /*
     * Filter flush bio's early so that make_request based
     * drivers without flush support don't have to worry
     * about them.
     */
    if ((bio->bi_rw & (REQ_FLUSH | REQ_FUA)) && !q->flush_flags) {
        bio->bi_rw &= ~(REQ_FLUSH | REQ_FUA);
        if (!nr_sectors) {
            err = 0;
            goto end_io;
        }
    }

    if ((bio->bi_rw & REQ_DISCARD) &&
        (!blk_queue_discard(q) ||
         ((bio->bi_rw & REQ_SECURE) && !blk_queue_secdiscard(q)))) {
        err = -EOPNOTSUPP;
        goto end_io;
    }

    if (bio->bi_rw & REQ_WRITE_SAME && !bdev_write_same(bio->bi_bdev)) {
        err = -EOPNOTSUPP;
        goto end_io;
    }

    /*
     * Various block parts want %current->io_context and lazy ioc
     * allocation ends up trading a lot of pain for a small amount of
     * memory.  Just allocate it upfront.  This may fail and block
     * layer knows how to live with it.
     */
    create_io_context(GFP_ATOMIC, q->node);

    if (blk_throtl_bio(q, bio))
        return false;   /* throttled, will be resubmitted later */

    trace_block_bio_queue(q, bio);
    return true;

end_io:
    bio_endio(bio, err);
    return false;
}

void generic_make_request(struct bio *bio)
{
    struct bio_list bio_list_on_stack;

    if (!generic_make_request_checks(bio))
        return;

    /*
     * We only want one ->make_request_fn to be active at a time, else
     * stack usage with stacked devices could be a problem.  So use
     * current->bio_list to keep a list of requests submited by a
     * make_request_fn function.  current->bio_list is also used as a
     * flag to say if generic_make_request is currently active in this
     * task or not.  If it is NULL, then no make_request is active.  If
     * it is non-NULL, then a make_request is active, and new requests
     * should be added at the tail
     */
    if (current->bio_list) {
        bio_list_add(current->bio_list, bio);
        return;
    }

    /* following loop may be a bit non-obvious, and so deserves some
     * explanation.
     * Before entering the loop, bio->bi_next is NULL (as all callers
     * ensure that) so we have a list with a single bio.
     * We pretend that we have just taken it off a longer list, so
     * we assign bio_list to a pointer to the bio_list_on_stack,
     * thus initialising the bio_list of new bios to be
     * added.  ->make_request() may indeed add some more bios
     * through a recursive call to generic_make_request.  If it
     * did, we find a non-NULL value in bio_list and re-enter the loop
     * from the top.  In this case we really did just take the bio
     * of the top of the list (no pretending) and so remove it from
     * bio_list, and call into ->make_request() again.
     */
    BUG_ON(bio->bi_next);
    bio_list_init(&bio_list_on_stack);
    current->bio_list = &bio_list_on_stack;
    do {
        struct request_queue *q = bdev_get_queue(bio->bi_bdev);

        q->make_request_fn(q, bio);

        bio = bio_list_pop(current->bio_list);
    } while (bio);
    current->bio_list = NULL; /* deactivate */
}
EXPORT_SYMBOL(generic_make_request);

void submit_bio(int rw, struct bio *bio)
{
    bio->bi_rw |= rw;

    /*
     * If it's a regular read/write or a barrier with data attached,
     * go through the normal accounting stuff before submission.
     */
    if (bio_has_data(bio)) {
        unsigned int count;

        if (unlikely(rw & REQ_WRITE_SAME))
            count = bdev_logical_block_size(bio->bi_bdev) >> 9;
        else
            count = bio_sectors(bio);

        if (rw & WRITE) {
            count_vm_events(PGPGOUT, count);
        } else {
            task_io_account_read(bio->bi_size);
            count_vm_events(PGPGIN, count);
        }

        if (unlikely(block_dump)) {
            char b[BDEVNAME_SIZE];
            printk(KERN_DEBUG "%s(%d): %s block %Lu on %s (%u sectors)\n",
            current->comm, task_pid_nr(current),
                (rw & WRITE) ? "WRITE" : "READ",
                (unsigned long long)bio->bi_sector,
                bdevname(bio->bi_bdev, b),
                count);
        }
    }

    generic_make_request(bio);
}
EXPORT_SYMBOL(submit_bio);

int blk_rq_check_limits(struct request_queue *q, struct request *rq)
{
    if (!rq_mergeable(rq))
        return 0;

    if (blk_rq_sectors(rq) > blk_queue_get_max_sectors(q, rq->cmd_flags)) {
        printk(KERN_ERR "%s: over max size limit.\n", __func__);
        return -EIO;
    }

    /*
     * queue's settings related to segment counting like q->bounce_pfn
     * may differ from that of other stacking queues.
     * Recalculate it to check the request correctly on this queue's
     * limitation.
     */
    blk_recalc_rq_segments(rq);
    if (rq->nr_phys_segments > queue_max_segments(q)) {
        printk(KERN_ERR "%s: over max segments limit.\n", __func__);
        return -EIO;
    }

    return 0;
}
EXPORT_SYMBOL_GPL(blk_rq_check_limits);

int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
{
    unsigned long flags;
    int where = ELEVATOR_INSERT_BACK;

    if (blk_rq_check_limits(q, rq))
        return -EIO;

    if (rq->rq_disk &&
        should_fail_request(&rq->rq_disk->part0, blk_rq_bytes(rq)))
        return -EIO;

    spin_lock_irqsave(q->queue_lock, flags);
    if (unlikely(blk_queue_dead(q))) {
        spin_unlock_irqrestore(q->queue_lock, flags);
        return -ENODEV;
    }

    /*
     * Submitting request must be dequeued before calling this function
     * because it will be linked to another request_queue
     */
    BUG_ON(blk_queued_rq(rq));

    if (rq->cmd_flags & (REQ_FLUSH|REQ_FUA))
        where = ELEVATOR_INSERT_FLUSH;

    add_acct_request(q, rq, where);
    if (where == ELEVATOR_INSERT_FLUSH)
        __blk_run_queue(q);
    spin_unlock_irqrestore(q->queue_lock, flags);

    return 0;
}
EXPORT_SYMBOL_GPL(blk_insert_cloned_request);

unsigned int blk_rq_err_bytes(const struct request *rq)
{
    unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
    unsigned int bytes = 0;
    struct bio *bio;

    if (!(rq->cmd_flags & REQ_MIXED_MERGE))
        return blk_rq_bytes(rq);

    /*
     * Currently the only 'mixing' which can happen is between
     * different fastfail types.  We can safely fail portions
     * which have all the failfast bits that the first one has -
     * the ones which are at least as eager to fail as the first
     * one.
     */
    for (bio = rq->bio; bio; bio = bio->bi_next) {
        if ((bio->bi_rw & ff) != ff)
            break;
        bytes += bio->bi_size;
    }

    /* this could lead to infinite loop */
    BUG_ON(blk_rq_bytes(rq) && !bytes);
    return bytes;
}
EXPORT_SYMBOL_GPL(blk_rq_err_bytes);

static void blk_account_io_completion(struct request *req, unsigned int bytes)
{
    if (blk_do_io_stat(req)) {
        const int rw = rq_data_dir(req);
        struct hd_struct *part;
        int cpu;

        cpu = part_stat_lock();
        part = req->part;
        part_stat_add(cpu, part, sectors[rw], bytes >> 9);
        part_stat_unlock();
    }
}

static void blk_account_io_done(struct request *req)
{
    /*
     * Account IO completion.  flush_rq isn't accounted as a
     * normal IO on queueing nor completion.  Accounting the
     * containing request is enough.
     */
    if (blk_do_io_stat(req) && !(req->cmd_flags & REQ_FLUSH_SEQ)) {
        unsigned long duration = jiffies - req->start_time;
        const int rw = rq_data_dir(req);
        struct hd_struct *part;
        int cpu;

        cpu = part_stat_lock();
        part = req->part;

        part_stat_inc(cpu, part, ios[rw]);
        part_stat_add(cpu, part, ticks[rw], duration);
        part_round_stats(cpu, part);
        part_dec_in_flight(part, rw);

        hd_struct_put(part);
        part_stat_unlock();
    }
}

struct request *blk_peek_request(struct request_queue *q)
{
    struct request *rq;
    int ret;

    while ((rq = __elv_next_request(q)) != NULL) {
        if (!(rq->cmd_flags & REQ_STARTED)) {
            /*
             * This is the first time the device driver
             * sees this request (possibly after
             * requeueing).  Notify IO scheduler.
             */
            if (rq->cmd_flags & REQ_SORTED)
                elv_activate_rq(q, rq);

            /*
             * just mark as started even if we don't start
             * it, a request that has been delayed should
             * not be passed by new incoming requests
             */
            rq->cmd_flags |= REQ_STARTED;
            trace_block_rq_issue(q, rq);
        }

        if (!q->boundary_rq || q->boundary_rq == rq) {
            q->end_sector = rq_end_sector(rq);
            q->boundary_rq = NULL;
        }

        if (rq->cmd_flags & REQ_DONTPREP)
            break;

        if (q->dma_drain_size && blk_rq_bytes(rq)) {
            /*
             * make sure space for the drain appears we
             * know we can do this because max_hw_segments
             * has been adjusted to be one fewer than the
             * device can handle
             */
            rq->nr_phys_segments++;
        }

        if (!q->prep_rq_fn)
            break;

        ret = q->prep_rq_fn(q, rq);
        if (ret == BLKPREP_OK) {
            break;
        } else if (ret == BLKPREP_DEFER) {
            /*
             * the request may have been (partially) prepped.
             * we need to keep this request in the front to
             * avoid resource deadlock.  REQ_STARTED will
             * prevent other fs requests from passing this one.
             */
            if (q->dma_drain_size && blk_rq_bytes(rq) &&
                !(rq->cmd_flags & REQ_DONTPREP)) {
                /*
                 * remove the space for the drain we added
                 * so that we don't add it again
                 */
                --rq->nr_phys_segments;
            }

            rq = NULL;
            break;
        } else if (ret == BLKPREP_KILL) {
            rq->cmd_flags |= REQ_QUIET;
            /*
             * Mark this request as started so we don't trigger
             * any debug logic in the end I/O path.
             */
            blk_start_request(rq);
            __blk_end_request_all(rq, -EIO);
        } else {
            printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
            break;
        }
    }

    return rq;
}
EXPORT_SYMBOL(blk_peek_request);

void blk_dequeue_request(struct request *rq)
{
    struct request_queue *q = rq->q;

    BUG_ON(list_empty(&rq->queuelist));
    BUG_ON(ELV_ON_HASH(rq));

    list_del_init(&rq->queuelist);

    /*
     * the time frame between a request being removed from the lists
     * and to it is freed is accounted as io that is in progress at
     * the driver side.
     */
    if (blk_account_rq(rq)) {
        q->in_flight[rq_is_sync(rq)]++;
        set_io_start_time_ns(rq);
    }
}

void blk_start_request(struct request *req)
{
    blk_dequeue_request(req);

    /*
     * We are now handing the request to the hardware, initialize
     * resid_len to full count and add the timeout handler.
     */
    req->resid_len = blk_rq_bytes(req);
    if (unlikely(blk_bidi_rq(req)))
        req->next_rq->resid_len = blk_rq_bytes(req->next_rq);

    blk_add_timer(req);
}
EXPORT_SYMBOL(blk_start_request);

struct request *blk_fetch_request(struct request_queue *q)
{
    struct request *rq;

    rq = blk_peek_request(q);
    if (rq)
        blk_start_request(rq);
    return rq;
}
EXPORT_SYMBOL(blk_fetch_request);

bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
{
    int total_bytes, bio_nbytes, next_idx = 0;
    struct bio *bio;

    if (!req->bio)
        return false;

    trace_block_rq_complete(req->q, req);

    /*
     * For fs requests, rq is just carrier of independent bio's
     * and each partial completion should be handled separately.
     * Reset per-request error on each partial completion.
     *
     * TODO: tj: This is too subtle.  It would be better to let
     * low level drivers do what they see fit.
     */
    if (req->cmd_type == REQ_TYPE_FS)
        req->errors = 0;

    if (error && req->cmd_type == REQ_TYPE_FS &&
        !(req->cmd_flags & REQ_QUIET)) {
        char *error_type;

        switch (error) {
        case -ENOLINK:
            error_type = "recoverable transport";
            break;
        case -EREMOTEIO:
            error_type = "critical target";
            break;
        case -EBADE:
            error_type = "critical nexus";
            break;
        case -EIO:
        default:
            error_type = "I/O";
            break;
        }
        printk_ratelimited(KERN_ERR "end_request: %s error, dev %s, sector %llu\n",
                   error_type, req->rq_disk ?
                   req->rq_disk->disk_name : "?",
                   (unsigned long long)blk_rq_pos(req));

    }

    blk_account_io_completion(req, nr_bytes);

    total_bytes = bio_nbytes = 0;
    while ((bio = req->bio) != NULL) {
        int nbytes;

        if (nr_bytes >= bio->bi_size) {
            req->bio = bio->bi_next;
            nbytes = bio->bi_size;
            req_bio_endio(req, bio, nbytes, error);
            next_idx = 0;
            bio_nbytes = 0;
        } else {
            int idx = bio->bi_idx + next_idx;

            if (unlikely(idx >= bio->bi_vcnt)) {
                blk_dump_rq_flags(req, "__end_that");
                printk(KERN_ERR "%s: bio idx %d >= vcnt %d\n",
                       __func__, idx, bio->bi_vcnt);
                break;
            }

            nbytes = bio_iovec_idx(bio, idx)->bv_len;
            BIO_BUG_ON(nbytes > bio->bi_size);

            /*
             * not a complete bvec done
             */
            if (unlikely(nbytes > nr_bytes)) {
                bio_nbytes += nr_bytes;
                total_bytes += nr_bytes;
                break;
            }

            /*
             * advance to the next vector
             */
            next_idx++;
            bio_nbytes += nbytes;
        }

        total_bytes += nbytes;
        nr_bytes -= nbytes;

        bio = req->bio;
        if (bio) {
            /*
             * end more in this run, or just return 'not-done'
             */
            if (unlikely(nr_bytes <= 0))
                break;
        }
    }

    /*
     * completely done
     */
    if (!req->bio) {
        /*
         * Reset counters so that the request stacking driver
         * can find how many bytes remain in the request
         * later.
         */
        req->__data_len = 0;
        return false;
    }

    /*
     * if the request wasn't completed, update state
     */
    if (bio_nbytes) {
        req_bio_endio(req, bio, bio_nbytes, error);
        bio->bi_idx += next_idx;
        bio_iovec(bio)->bv_offset += nr_bytes;
        bio_iovec(bio)->bv_len -= nr_bytes;
    }

    req->__data_len -= total_bytes;
    req->buffer = bio_data(req->bio);

    /* update sector only for requests with clear definition of sector */
    if (req->cmd_type == REQ_TYPE_FS)
        req->__sector += total_bytes >> 9;

    /* mixed attributes always follow the first bio */
    if (req->cmd_flags & REQ_MIXED_MERGE) {
        req->cmd_flags &= ~REQ_FAILFAST_MASK;
        req->cmd_flags |= req->bio->bi_rw & REQ_FAILFAST_MASK;
    }

    /*
     * If total number of sectors is less than the first segment
     * size, something has gone terribly wrong.
     */
    if (blk_rq_bytes(req) < blk_rq_cur_bytes(req)) {
        blk_dump_rq_flags(req, "request botched");
        req->__data_len = blk_rq_cur_bytes(req);
    }

    /* recalculate the number of segments */
    blk_recalc_rq_segments(req);

    return true;
}
EXPORT_SYMBOL_GPL(blk_update_request);

static bool blk_update_bidi_request(struct request *rq, int error,
                    unsigned int nr_bytes,
                    unsigned int bidi_bytes)
{
    if (blk_update_request(rq, error, nr_bytes))
        return true;

    /* Bidi request must be completed as a whole */
    if (unlikely(blk_bidi_rq(rq)) &&
        blk_update_request(rq->next_rq, error, bidi_bytes))
        return true;

    if (blk_queue_add_random(rq->q))
        add_disk_randomness(rq->rq_disk);

    return false;
}

void blk_unprep_request(struct request *req)
{
    struct request_queue *q = req->q;

    req->cmd_flags &= ~REQ_DONTPREP;
    if (q->unprep_rq_fn)
        q->unprep_rq_fn(q, req);
}
EXPORT_SYMBOL_GPL(blk_unprep_request);

/*
 * queue lock must be held
 */
static void blk_finish_request(struct request *req, int error)
{
    if (blk_rq_tagged(req))
        blk_queue_end_tag(req->q, req);

    BUG_ON(blk_queued_rq(req));

    if (unlikely(laptop_mode) && req->cmd_type == REQ_TYPE_FS)
        laptop_io_completion(&req->q->backing_dev_info);

    blk_delete_timer(req);

    if (req->cmd_flags & REQ_DONTPREP)
        blk_unprep_request(req);


    blk_account_io_done(req);

    if (req->end_io)
        req->end_io(req, error);
    else {
        if (blk_bidi_rq(req))
            __blk_put_request(req->next_rq->q, req->next_rq);

        __blk_put_request(req->q, req);
    }
}

static bool blk_end_bidi_request(struct request *rq, int error,
                 unsigned int nr_bytes, unsigned int bidi_bytes)
{
    struct request_queue *q = rq->q;
    unsigned long flags;

    if (blk_update_bidi_request(rq, error, nr_bytes, bidi_bytes))
        return true;

    spin_lock_irqsave(q->queue_lock, flags);
    blk_finish_request(rq, error);
    spin_unlock_irqrestore(q->queue_lock, flags);

    return false;
}

bool __blk_end_bidi_request(struct request *rq, int error,
                   unsigned int nr_bytes, unsigned int bidi_bytes)
{
    if (blk_update_bidi_request(rq, error, nr_bytes, bidi_bytes))
        return true;

    blk_finish_request(rq, error);

    return false;
}

bool blk_end_request(struct request *rq, int error, unsigned int nr_bytes)
{
    return blk_end_bidi_request(rq, error, nr_bytes, 0);
}
EXPORT_SYMBOL(blk_end_request);

void blk_end_request_all(struct request *rq, int error)
{
    bool pending;
    unsigned int bidi_bytes = 0;

    if (unlikely(blk_bidi_rq(rq)))
        bidi_bytes = blk_rq_bytes(rq->next_rq);

    pending = blk_end_bidi_request(rq, error, blk_rq_bytes(rq), bidi_bytes);
    BUG_ON(pending);
}
EXPORT_SYMBOL(blk_end_request_all);

bool blk_end_request_cur(struct request *rq, int error)
{
    return blk_end_request(rq, error, blk_rq_cur_bytes(rq));
}
EXPORT_SYMBOL(blk_end_request_cur);

bool blk_end_request_err(struct request *rq, int error)
{
    WARN_ON(error >= 0);
    return blk_end_request(rq, error, blk_rq_err_bytes(rq));
}
EXPORT_SYMBOL_GPL(blk_end_request_err);

bool __blk_end_request(struct request *rq, int error, unsigned int nr_bytes)
{
    return __blk_end_bidi_request(rq, error, nr_bytes, 0);
}
EXPORT_SYMBOL(__blk_end_request);

void __blk_end_request_all(struct request *rq, int error)
{
    bool pending;
    unsigned int bidi_bytes = 0;

    if (unlikely(blk_bidi_rq(rq)))
        bidi_bytes = blk_rq_bytes(rq->next_rq);

    pending = __blk_end_bidi_request(rq, error, blk_rq_bytes(rq), bidi_bytes);
    BUG_ON(pending);
}
EXPORT_SYMBOL(__blk_end_request_all);

bool __blk_end_request_cur(struct request *rq, int error)
{
    return __blk_end_request(rq, error, blk_rq_cur_bytes(rq));
}
EXPORT_SYMBOL(__blk_end_request_cur);

bool __blk_end_request_err(struct request *rq, int error)
{
    WARN_ON(error >= 0);
    return __blk_end_request(rq, error, blk_rq_err_bytes(rq));
}
EXPORT_SYMBOL_GPL(__blk_end_request_err);

void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
             struct bio *bio)
{
    /* Bit 0 (R/W) is identical in rq->cmd_flags and bio->bi_rw */
    rq->cmd_flags |= bio->bi_rw & REQ_WRITE;

    if (bio_has_data(bio)) {
        rq->nr_phys_segments = bio_phys_segments(q, bio);
        rq->buffer = bio_data(bio);
    }
    rq->__data_len = bio->bi_size;
    rq->bio = rq->biotail = bio;

    if (bio->bi_bdev)
        rq->rq_disk = bio->bi_bdev->bd_disk;
}

#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE

void rq_flush_dcache_pages(struct request *rq)
{
    struct req_iterator iter;
    struct bio_vec *bvec;

    rq_for_each_segment(bvec, rq, iter)
        flush_dcache_page(bvec->bv_page);
}
EXPORT_SYMBOL_GPL(rq_flush_dcache_pages);
#endif

int blk_lld_busy(struct request_queue *q)
{
    if (q->lld_busy_fn)
        return q->lld_busy_fn(q);

    return 0;
}
EXPORT_SYMBOL_GPL(blk_lld_busy);

void blk_rq_unprep_clone(struct request *rq)
{
    struct bio *bio;

    while ((bio = rq->bio) != NULL) {
        rq->bio = bio->bi_next;

        bio_put(bio);
    }
}
EXPORT_SYMBOL_GPL(blk_rq_unprep_clone);

/*
 * Copy attributes of the original request to the clone request.
 * The actual data parts (e.g. ->cmd, ->buffer, ->sense) are not copied.
 */
static void __blk_rq_prep_clone(struct request *dst, struct request *src)
{
    dst->cpu = src->cpu;
    dst->cmd_flags = (src->cmd_flags & REQ_CLONE_MASK) | REQ_NOMERGE;
    dst->cmd_type = src->cmd_type;
    dst->__sector = blk_rq_pos(src);
    dst->__data_len = blk_rq_bytes(src);
    dst->nr_phys_segments = src->nr_phys_segments;
    dst->ioprio = src->ioprio;
    dst->extra_len = src->extra_len;
}

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)
{
    struct bio *bio, *bio_src;

    if (!bs)
        bs = fs_bio_set;

    blk_rq_init(NULL, rq);

    __rq_for_each_bio(bio_src, rq_src) {
        bio = bio_clone_bioset(bio_src, gfp_mask, bs);
        if (!bio)
            goto free_and_out;

        if (bio_ctr && bio_ctr(bio, bio_src, data))
            goto free_and_out;

        if (rq->bio) {
            rq->biotail->bi_next = bio;
            rq->biotail = bio;
        } else
            rq->bio = rq->biotail = bio;
    }

    __blk_rq_prep_clone(rq, rq_src);

    return 0;

free_and_out:
    if (bio)
        bio_put(bio);
    blk_rq_unprep_clone(rq);

    return -ENOMEM;
}
EXPORT_SYMBOL_GPL(blk_rq_prep_clone);

int kblockd_schedule_work(struct request_queue *q, struct work_struct *work)
{
    return queue_work(kblockd_workqueue, work);
}
EXPORT_SYMBOL(kblockd_schedule_work);

int kblockd_schedule_delayed_work(struct request_queue *q,
            struct delayed_work *dwork, unsigned long delay)
{
    return queue_delayed_work(kblockd_workqueue, dwork, delay);
}
EXPORT_SYMBOL(kblockd_schedule_delayed_work);

#define PLUG_MAGIC  0x91827364

void blk_start_plug(struct blk_plug *plug)
{
    struct task_struct *tsk = current;

    plug->magic = PLUG_MAGIC;
    INIT_LIST_HEAD(&plug->list);
    INIT_LIST_HEAD(&plug->cb_list);
    plug->should_sort = 0;

    /*
     * If this is a nested plug, don't actually assign it. It will be
     * flushed on its own.
     */
    if (!tsk->plug) {
        /*
         * Store ordering should not be needed here, since a potential
         * preempt will imply a full memory barrier
         */
        tsk->plug = plug;
    }
}
EXPORT_SYMBOL(blk_start_plug);

static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
{
    struct request *rqa = container_of(a, struct request, queuelist);
    struct request *rqb = container_of(b, struct request, queuelist);

    return !(rqa->q < rqb->q ||
        (rqa->q == rqb->q && blk_rq_pos(rqa) < blk_rq_pos(rqb)));
}

/*
 * If 'from_schedule' is true, then postpone the dispatch of requests
 * until a safe kblockd context. We due this to avoid accidental big
 * additional stack usage in driver dispatch, in places where the originally
 * plugger did not intend it.
 */
static void queue_unplugged(struct request_queue *q, unsigned int depth,
                bool from_schedule)
    __releases(q->queue_lock)
{
    trace_block_unplug(q, depth, !from_schedule);

    /*
     * Don't mess with dead queue.
     */
    if (unlikely(blk_queue_dead(q))) {
        spin_unlock(q->queue_lock);
        return;
    }

    /*
     * If we are punting this to kblockd, then we can safely drop
     * the queue_lock before waking kblockd (which needs to take
     * this lock).
     */
    if (from_schedule) {
        spin_unlock(q->queue_lock);
        blk_run_queue_async(q);
    } else {
        __blk_run_queue(q);
        spin_unlock(q->queue_lock);
    }

}

static void flush_plug_callbacks(struct blk_plug *plug, bool from_schedule)
{
    LIST_HEAD(callbacks);

    while (!list_empty(&plug->cb_list)) {
        list_splice_init(&plug->cb_list, &callbacks);

        while (!list_empty(&callbacks)) {
            struct blk_plug_cb *cb = list_first_entry(&callbacks,
                              struct blk_plug_cb,
                              list);
            list_del(&cb->list);
            cb->callback(cb, from_schedule);
        }
    }
}

struct blk_plug_cb *blk_check_plugged(blk_plug_cb_fn unplug, void *data,
                      int size)
{
    struct blk_plug *plug = current->plug;
    struct blk_plug_cb *cb;

    if (!plug)
        return NULL;

    list_for_each_entry(cb, &plug->cb_list, list)
        if (cb->callback == unplug && cb->data == data)
            return cb;

    /* Not currently on the callback list */
    BUG_ON(size < sizeof(*cb));
    cb = kzalloc(size, GFP_ATOMIC);
    if (cb) {
        cb->data = data;
        cb->callback = unplug;
        list_add(&cb->list, &plug->cb_list);
    }
    return cb;
}
EXPORT_SYMBOL(blk_check_plugged);

void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
{
    struct request_queue *q;
    unsigned long flags;
    struct request *rq;
    LIST_HEAD(list);
    unsigned int depth;

    BUG_ON(plug->magic != PLUG_MAGIC);

    flush_plug_callbacks(plug, from_schedule);
    if (list_empty(&plug->list))
        return;

    list_splice_init(&plug->list, &list);

    if (plug->should_sort) {
        list_sort(NULL, &list, plug_rq_cmp);
        plug->should_sort = 0;
    }

    q = NULL;
    depth = 0;

    /*
     * Save and disable interrupts here, to avoid doing it for every
     * queue lock we have to take.
     */
    local_irq_save(flags);
    while (!list_empty(&list)) {
        rq = list_entry_rq(list.next);
        list_del_init(&rq->queuelist);
        BUG_ON(!rq->q);
        if (rq->q != q) {
            /*
             * This drops the queue lock
             */
            if (q)
                queue_unplugged(q, depth, from_schedule);
            q = rq->q;
            depth = 0;
            spin_lock(q->queue_lock);
        }

        /*
         * Short-circuit if @q is dead
         */
        if (unlikely(blk_queue_dead(q))) {
            __blk_end_request_all(rq, -ENODEV);
            continue;
        }

        /*
         * rq is already accounted, so use raw insert
         */
        if (rq->cmd_flags & (REQ_FLUSH | REQ_FUA))
            __elv_add_request(q, rq, ELEVATOR_INSERT_FLUSH);
        else
            __elv_add_request(q, rq, ELEVATOR_INSERT_SORT_MERGE);

        depth++;
    }

    /*
     * This drops the queue lock
     */
    if (q)
        queue_unplugged(q, depth, from_schedule);

    local_irq_restore(flags);
}

void blk_finish_plug(struct blk_plug *plug)
{
    blk_flush_plug_list(plug, false);

    if (plug == current->plug)
        current->plug = NULL;
}
EXPORT_SYMBOL(blk_finish_plug);

int __init blk_dev_init(void)
{
    BUILD_BUG_ON(__REQ_NR_BITS > 8 *
            sizeof(((struct request *)0)->cmd_flags));

    /* used for unplugging and affects IO latency/throughput - HIGHPRI */
    kblockd_workqueue = alloc_workqueue("kblockd",
                        WQ_MEM_RECLAIM | WQ_HIGHPRI, 0);
    if (!kblockd_workqueue)
        panic("Failed to create kblockd\n");

    request_cachep = kmem_cache_create("blkdev_requests",
            sizeof(struct request), 0, SLAB_PANIC, NULL);

    blk_requestq_cachep = kmem_cache_create("blkdev_queue",
            sizeof(struct request_queue), 0, SLAB_PANIC, NULL);

    return 0;
}