drm/bridge: Fix the bridge kernel doc

[linux/fpc-iii.git] / block / blk-core.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 1991, 1992 Linus Torvalds
 * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
 * Elevator latency, (C) 2000  Andrea Arcangeli <andrea@suse.de> SuSE
 * Queue request tables / lock, selectable elevator, Jens Axboe <axboe@suse.de>
 * kernel-doc documentation started by NeilBrown <neilb@cse.unsw.edu.au>
 *      -  July2000
 * bio rewrite, highmem i/o, etc, Jens Axboe <axboe@suse.de> - 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/blk-mq.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>
#include <linux/pm_runtime.h>
#include <linux/blk-cgroup.h>
#include <linux/t10-pi.h>
#include <linux/debugfs.h>
#include <linux/bpf.h>
#include <linux/psi.h>

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

#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-sched.h"
#include "blk-pm.h"
#include "blk-rq-qos.h"

#ifdef CONFIG_DEBUG_FS
struct dentry *blk_debugfs_root;
#endif

EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);
EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_complete);
EXPORT_TRACEPOINT_SYMBOL_GPL(block_split);
EXPORT_TRACEPOINT_SYMBOL_GPL(block_unplug);

DEFINE_IDA(blk_queue_ida);

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

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

/**
 * blk_queue_flag_set - atomically set a queue flag
 * @flag: flag to be set
 * @q: request queue
 */
void blk_queue_flag_set(unsigned int flag, struct request_queue *q)
{
        set_bit(flag, &q->queue_flags);
}
EXPORT_SYMBOL(blk_queue_flag_set);

/**
 * blk_queue_flag_clear - atomically clear a queue flag
 * @flag: flag to be cleared
 * @q: request queue
 */
void blk_queue_flag_clear(unsigned int flag, struct request_queue *q)
{
        clear_bit(flag, &q->queue_flags);
}
EXPORT_SYMBOL(blk_queue_flag_clear);

/**
 * blk_queue_flag_test_and_set - atomically test and set a queue flag
 * @flag: flag to be set
 * @q: request queue
 *
 * Returns the previous value of @flag - 0 if the flag was not set and 1 if
 * the flag was already set.
 */
bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q)
{
        return test_and_set_bit(flag, &q->queue_flags);
}
EXPORT_SYMBOL_GPL(blk_queue_flag_test_and_set);

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

        INIT_LIST_HEAD(&rq->queuelist);
        rq->q = q;
        rq->__sector = (sector_t) -1;
        INIT_HLIST_NODE(&rq->hash);
        RB_CLEAR_NODE(&rq->rb_node);
        rq->tag = -1;
        rq->internal_tag = -1;
        rq->start_time_ns = ktime_get_ns();
        rq->part = NULL;
        refcount_set(&rq->ref, 1);
}
EXPORT_SYMBOL(blk_rq_init);

#define REQ_OP_NAME(name) [REQ_OP_##name] = #name
static const char *const blk_op_name[] = {
        REQ_OP_NAME(READ),
        REQ_OP_NAME(WRITE),
        REQ_OP_NAME(FLUSH),
        REQ_OP_NAME(DISCARD),
        REQ_OP_NAME(SECURE_ERASE),
        REQ_OP_NAME(ZONE_RESET),
        REQ_OP_NAME(ZONE_RESET_ALL),
        REQ_OP_NAME(ZONE_OPEN),
        REQ_OP_NAME(ZONE_CLOSE),
        REQ_OP_NAME(ZONE_FINISH),
        REQ_OP_NAME(WRITE_SAME),
        REQ_OP_NAME(WRITE_ZEROES),
        REQ_OP_NAME(SCSI_IN),
        REQ_OP_NAME(SCSI_OUT),
        REQ_OP_NAME(DRV_IN),
        REQ_OP_NAME(DRV_OUT),
};
#undef REQ_OP_NAME

/**
 * blk_op_str - Return string XXX in the REQ_OP_XXX.
 * @op: REQ_OP_XXX.
 *
 * Description: Centralize block layer function to convert REQ_OP_XXX into
 * string format. Useful in the debugging and tracing bio or request. For
 * invalid REQ_OP_XXX it returns string "UNKNOWN".
 */
inline const char *blk_op_str(unsigned int op)
{
        const char *op_str = "UNKNOWN";

        if (op < ARRAY_SIZE(blk_op_name) && blk_op_name[op])
                op_str = blk_op_name[op];

        return op_str;
}
EXPORT_SYMBOL_GPL(blk_op_str);

static const struct {
        int             errno;
        const char      *name;
} blk_errors[] = {
        [BLK_STS_OK]            = { 0,          "" },
        [BLK_STS_NOTSUPP]       = { -EOPNOTSUPP, "operation not supported" },
        [BLK_STS_TIMEOUT]       = { -ETIMEDOUT, "timeout" },
        [BLK_STS_NOSPC]         = { -ENOSPC,    "critical space allocation" },
        [BLK_STS_TRANSPORT]     = { -ENOLINK,   "recoverable transport" },
        [BLK_STS_TARGET]        = { -EREMOTEIO, "critical target" },
        [BLK_STS_NEXUS]         = { -EBADE,     "critical nexus" },
        [BLK_STS_MEDIUM]        = { -ENODATA,   "critical medium" },
        [BLK_STS_PROTECTION]    = { -EILSEQ,    "protection" },
        [BLK_STS_RESOURCE]      = { -ENOMEM,    "kernel resource" },
        [BLK_STS_DEV_RESOURCE]  = { -EBUSY,     "device resource" },
        [BLK_STS_AGAIN]         = { -EAGAIN,    "nonblocking retry" },

        /* device mapper special case, should not leak out: */
        [BLK_STS_DM_REQUEUE]    = { -EREMCHG, "dm internal retry" },

        /* everything else not covered above: */
        [BLK_STS_IOERR]         = { -EIO,       "I/O" },
};

blk_status_t errno_to_blk_status(int errno)
{
        int i;

        for (i = 0; i < ARRAY_SIZE(blk_errors); i++) {
                if (blk_errors[i].errno == errno)
                        return (__force blk_status_t)i;
        }

        return BLK_STS_IOERR;
}
EXPORT_SYMBOL_GPL(errno_to_blk_status);

int blk_status_to_errno(blk_status_t status)
{
        int idx = (__force int)status;

        if (WARN_ON_ONCE(idx >= ARRAY_SIZE(blk_errors)))
                return -EIO;
        return blk_errors[idx].errno;
}
EXPORT_SYMBOL_GPL(blk_status_to_errno);

static void print_req_error(struct request *req, blk_status_t status,
                const char *caller)
{
        int idx = (__force int)status;

        if (WARN_ON_ONCE(idx >= ARRAY_SIZE(blk_errors)))
                return;

        printk_ratelimited(KERN_ERR
                "%s: %s error, dev %s, sector %llu op 0x%x:(%s) flags 0x%x "
                "phys_seg %u prio class %u\n",
                caller, blk_errors[idx].name,
                req->rq_disk ? req->rq_disk->disk_name : "?",
                blk_rq_pos(req), req_op(req), blk_op_str(req_op(req)),
                req->cmd_flags & ~REQ_OP_MASK,
                req->nr_phys_segments,
                IOPRIO_PRIO_CLASS(req->ioprio));
}

static void req_bio_endio(struct request *rq, struct bio *bio,
                          unsigned int nbytes, blk_status_t error)
{
        if (error)
                bio->bi_status = error;

        if (unlikely(rq->rq_flags & RQF_QUIET))
                bio_set_flag(bio, BIO_QUIET);

        bio_advance(bio, nbytes);

        /* don't actually finish bio if it's part of flush sequence */
        if (bio->bi_iter.bi_size == 0 && !(rq->rq_flags & RQF_FLUSH_SEQ))
                bio_endio(bio);
}

void blk_dump_rq_flags(struct request *rq, char *msg)
{
        printk(KERN_INFO "%s: dev %s: flags=%llx\n", msg,
                rq->rq_disk ? rq->rq_disk->disk_name : "?",
                (unsigned long long) 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, len %u\n",
               rq->bio, rq->biotail, blk_rq_bytes(rq));
}
EXPORT_SYMBOL(blk_dump_rq_flags);

/**
 * blk_sync_queue - cancel any pending callbacks on a queue
 * @q: the queue
 *
 * Description:
 *     The block layer may perform asynchronous callback activity
 *     on a queue, such as calling the unplug function after a timeout.
 *     A block device may call blk_sync_queue to ensure that any
 *     such activity is cancelled, thus allowing it to release resources
 *     that the callbacks might use. The caller must already have made sure
 *     that its ->make_request_fn will not re-add plugging prior to calling
 *     this function.
 *
 *     This function does not cancel any asynchronous activity arising
 *     out of elevator or throttling code. That would require elevator_exit()
 *     and blkcg_exit_queue() to be called with queue lock initialized.
 *
 */
void blk_sync_queue(struct request_queue *q)
{
        del_timer_sync(&q->timeout);
        cancel_work_sync(&q->timeout_work);
}
EXPORT_SYMBOL(blk_sync_queue);

/**
 * blk_set_pm_only - increment pm_only counter
 * @q: request queue pointer
 */
void blk_set_pm_only(struct request_queue *q)
{
        atomic_inc(&q->pm_only);
}
EXPORT_SYMBOL_GPL(blk_set_pm_only);

void blk_clear_pm_only(struct request_queue *q)
{
        int pm_only;

        pm_only = atomic_dec_return(&q->pm_only);
        WARN_ON_ONCE(pm_only < 0);
        if (pm_only == 0)
                wake_up_all(&q->mq_freeze_wq);
}
EXPORT_SYMBOL_GPL(blk_clear_pm_only);

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

void blk_set_queue_dying(struct request_queue *q)
{
        blk_queue_flag_set(QUEUE_FLAG_DYING, q);

        /*
         * When queue DYING flag is set, we need to block new req
         * entering queue, so we call blk_freeze_queue_start() to
         * prevent I/O from crossing blk_queue_enter().
         */
        blk_freeze_queue_start(q);

        if (queue_is_mq(q))
                blk_mq_wake_waiters(q);

        /* Make blk_queue_enter() reexamine the DYING flag. */
        wake_up_all(&q->mq_freeze_wq);
}
EXPORT_SYMBOL_GPL(blk_set_queue_dying);

/**
 * blk_cleanup_queue - shutdown a request queue
 * @q: request queue to shutdown
 *
 * Mark @q DYING, drain all pending requests, mark @q DEAD, destroy and
 * put it.  All future requests will be failed immediately with -ENODEV.
 */
void blk_cleanup_queue(struct request_queue *q)
{
        WARN_ON_ONCE(blk_queue_registered(q));

        /* mark @q DYING, no new request or merges will be allowed afterwards */
        blk_set_queue_dying(q);

        blk_queue_flag_set(QUEUE_FLAG_NOMERGES, q);
        blk_queue_flag_set(QUEUE_FLAG_NOXMERGES, q);
        blk_queue_flag_set(QUEUE_FLAG_DYING, q);

        /*
         * Drain all requests queued before DYING marking. Set DEAD flag to
         * prevent that blk_mq_run_hw_queues() accesses the hardware queues
         * after draining finished.
         */
        blk_freeze_queue(q);

        rq_qos_exit(q);

        blk_queue_flag_set(QUEUE_FLAG_DEAD, q);

        /* for synchronous bio-based driver finish in-flight integrity i/o */
        blk_flush_integrity();

        /* @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);

        if (queue_is_mq(q))
                blk_mq_exit_queue(q);

        /*
         * In theory, request pool of sched_tags belongs to request queue.
         * However, the current implementation requires tag_set for freeing
         * requests, so free the pool now.
         *
         * Queue has become frozen, there can't be any in-queue requests, so
         * it is safe to free requests now.
         */
        mutex_lock(&q->sysfs_lock);
        if (q->elevator)
                blk_mq_sched_free_requests(q);
        mutex_unlock(&q->sysfs_lock);

        percpu_ref_exit(&q->q_usage_counter);

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

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

/**
 * blk_queue_enter() - try to increase q->q_usage_counter
 * @q: request queue pointer
 * @flags: BLK_MQ_REQ_NOWAIT and/or BLK_MQ_REQ_PREEMPT
 */
int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
{
        const bool pm = flags & BLK_MQ_REQ_PREEMPT;

        while (true) {
                bool success = false;

                rcu_read_lock();
                if (percpu_ref_tryget_live(&q->q_usage_counter)) {
                        /*
                         * The code that increments the pm_only counter is
                         * responsible for ensuring that that counter is
                         * globally visible before the queue is unfrozen.
                         */
                        if (pm || !blk_queue_pm_only(q)) {
                                success = true;
                        } else {
                                percpu_ref_put(&q->q_usage_counter);
                        }
                }
                rcu_read_unlock();

                if (success)
                        return 0;

                if (flags & BLK_MQ_REQ_NOWAIT)
                        return -EBUSY;

                /*
                 * read pair of barrier in blk_freeze_queue_start(),
                 * we need to order reading __PERCPU_REF_DEAD flag of
                 * .q_usage_counter and reading .mq_freeze_depth or
                 * queue dying flag, otherwise the following wait may
                 * never return if the two reads are reordered.
                 */
                smp_rmb();

                wait_event(q->mq_freeze_wq,
                           (!q->mq_freeze_depth &&
                            (pm || (blk_pm_request_resume(q),
                                    !blk_queue_pm_only(q)))) ||
                           blk_queue_dying(q));
                if (blk_queue_dying(q))
                        return -ENODEV;
        }
}

void blk_queue_exit(struct request_queue *q)
{
        percpu_ref_put(&q->q_usage_counter);
}

static void blk_queue_usage_counter_release(struct percpu_ref *ref)
{
        struct request_queue *q =
                container_of(ref, struct request_queue, q_usage_counter);

        wake_up_all(&q->mq_freeze_wq);
}

static void blk_rq_timed_out_timer(struct timer_list *t)
{
        struct request_queue *q = from_timer(q, t, timeout);

        kblockd_schedule_work(&q->timeout_work);
}

static void blk_timeout_work(struct work_struct *work)
{
}

/**
 * blk_alloc_queue_node - allocate a request queue
 * @gfp_mask: memory allocation flags
 * @node_id: NUMA node to allocate memory from
 */
struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
{
        struct request_queue *q;
        int ret;

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

        q->last_merge = NULL;

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

        ret = bioset_init(&q->bio_split, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
        if (ret)
                goto fail_id;

        q->backing_dev_info = bdi_alloc_node(gfp_mask, node_id);
        if (!q->backing_dev_info)
                goto fail_split;

        q->stats = blk_alloc_queue_stats();
        if (!q->stats)
                goto fail_stats;

        q->backing_dev_info->ra_pages = VM_READAHEAD_PAGES;
        q->backing_dev_info->capabilities = BDI_CAP_CGROUP_WRITEBACK;
        q->backing_dev_info->name = "block";
        q->node = node_id;

        timer_setup(&q->backing_dev_info->laptop_mode_wb_timer,
                    laptop_mode_timer_fn, 0);
        timer_setup(&q->timeout, blk_rq_timed_out_timer, 0);
        INIT_WORK(&q->timeout_work, blk_timeout_work);
        INIT_LIST_HEAD(&q->icq_list);
#ifdef CONFIG_BLK_CGROUP
        INIT_LIST_HEAD(&q->blkg_list);
#endif

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

#ifdef CONFIG_BLK_DEV_IO_TRACE
        mutex_init(&q->blk_trace_mutex);
#endif
        mutex_init(&q->sysfs_lock);
        mutex_init(&q->sysfs_dir_lock);
        spin_lock_init(&q->queue_lock);

        init_waitqueue_head(&q->mq_freeze_wq);
        mutex_init(&q->mq_freeze_lock);

        /*
         * Init percpu_ref in atomic mode so that it's faster to shutdown.
         * See blk_register_queue() for details.
         */
        if (percpu_ref_init(&q->q_usage_counter,
                                blk_queue_usage_counter_release,
                                PERCPU_REF_INIT_ATOMIC, GFP_KERNEL))
                goto fail_bdi;

        if (blkcg_init_queue(q))
                goto fail_ref;

        return q;

fail_ref:
        percpu_ref_exit(&q->q_usage_counter);
fail_bdi:
        blk_free_queue_stats(q->stats);
fail_stats:
        bdi_put(q->backing_dev_info);
fail_split:
        bioset_exit(&q->bio_split);
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);

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

        return false;
}
EXPORT_SYMBOL(blk_get_queue);

/**
 * blk_get_request - allocate a request
 * @q: request queue to allocate a request for
 * @op: operation (REQ_OP_*) and REQ_* flags, e.g. REQ_SYNC.
 * @flags: BLK_MQ_REQ_* flags, e.g. BLK_MQ_REQ_NOWAIT.
 */
struct request *blk_get_request(struct request_queue *q, unsigned int op,
                                blk_mq_req_flags_t flags)
{
        struct request *req;

        WARN_ON_ONCE(op & REQ_NOWAIT);
        WARN_ON_ONCE(flags & ~(BLK_MQ_REQ_NOWAIT | BLK_MQ_REQ_PREEMPT));

        req = blk_mq_alloc_request(q, op, flags);
        if (!IS_ERR(req) && q->mq_ops->initialize_rq_fn)
                q->mq_ops->initialize_rq_fn(req);

        return req;
}
EXPORT_SYMBOL(blk_get_request);

void blk_put_request(struct request *req)
{
        blk_mq_free_request(req);
}
EXPORT_SYMBOL(blk_put_request);

bool bio_attempt_back_merge(struct request *req, struct bio *bio,
                unsigned int nr_segs)
{
        const int ff = bio->bi_opf & REQ_FAILFAST_MASK;

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

        trace_block_bio_backmerge(req->q, req, bio);
        rq_qos_merge(req->q, req, 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_iter.bi_size;

        blk_account_io_start(req, false);
        return true;
}

bool bio_attempt_front_merge(struct request *req, struct bio *bio,
                unsigned int nr_segs)
{
        const int ff = bio->bi_opf & REQ_FAILFAST_MASK;

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

        trace_block_bio_frontmerge(req->q, req, bio);
        rq_qos_merge(req->q, req, bio);

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

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

        req->__sector = bio->bi_iter.bi_sector;
        req->__data_len += bio->bi_iter.bi_size;

        blk_account_io_start(req, false);
        return true;
}

bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
                struct bio *bio)
{
        unsigned short segments = blk_rq_nr_discard_segments(req);

        if (segments >= queue_max_discard_segments(q))
                goto no_merge;
        if (blk_rq_sectors(req) + bio_sectors(bio) >
            blk_rq_get_max_sectors(req, blk_rq_pos(req)))
                goto no_merge;

        rq_qos_merge(q, req, bio);

        req->biotail->bi_next = bio;
        req->biotail = bio;
        req->__data_len += bio->bi_iter.bi_size;
        req->nr_phys_segments = segments + 1;

        blk_account_io_start(req, false);
        return true;
no_merge:
        req_set_nomerge(q, req);
        return false;
}

/**
 * blk_attempt_plug_merge - try to merge with %current's plugged list
 * @q: request_queue new bio is being queued at
 * @bio: new bio being queued
 * @nr_segs: number of segments in @bio
 * @same_queue_rq: pointer to &struct request that gets filled in when
 * another request associated with @q is found on the plug list
 * (optional, may be %NULL)
 *
 * Determine whether @bio being queued on @q can be merged with a request
 * on %current's plugged list.  Returns %true if merge was successful,
 * otherwise %false.
 *
 * Plugging coalesces IOs from the same issuer for the same purpose without
 * going through @q->queue_lock.  As such it's more of an issuing mechanism
 * than scheduling, and the request, while may have elvpriv data, is not
 * added on the elevator at this point.  In addition, we don't have
 * reliable access to the elevator outside queue lock.  Only check basic
 * merging parameters without querying the elevator.
 *
 * Caller must ensure !blk_queue_nomerges(q) beforehand.
 */
bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
                unsigned int nr_segs, struct request **same_queue_rq)
{
        struct blk_plug *plug;
        struct request *rq;
        struct list_head *plug_list;

        plug = blk_mq_plug(q, bio);
        if (!plug)
                return false;

        plug_list = &plug->mq_list;

        list_for_each_entry_reverse(rq, plug_list, queuelist) {
                bool merged = false;

                if (rq->q == q && same_queue_rq) {
                        /*
                         * Only blk-mq multiple hardware queues case checks the
                         * rq in the same queue, there should be only one such
                         * rq in a queue
                         **/
                        *same_queue_rq = rq;
                }

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

                switch (blk_try_merge(rq, bio)) {
                case ELEVATOR_BACK_MERGE:
                        merged = bio_attempt_back_merge(rq, bio, nr_segs);
                        break;
                case ELEVATOR_FRONT_MERGE:
                        merged = bio_attempt_front_merge(rq, bio, nr_segs);
                        break;
                case ELEVATOR_DISCARD_MERGE:
                        merged = bio_attempt_discard_merge(q, rq, bio);
                        break;
                default:
                        break;
                }

                if (merged)
                        return true;
        }

        return false;
}

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

        printk(KERN_INFO "attempt to access beyond end of device\n");
        printk(KERN_INFO "%s: rw=%d, want=%Lu, limit=%Lu\n",
                        bio_devname(bio, b), bio->bi_opf,
                        (unsigned long long)bio_end_sector(bio),
                        (long long)maxsector);
}

#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 PTR_ERR_OR_ZERO(dir);
}

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 */

static inline bool bio_check_ro(struct bio *bio, struct hd_struct *part)
{
        const int op = bio_op(bio);

        if (part->policy && op_is_write(op)) {
                char b[BDEVNAME_SIZE];

                if (op_is_flush(bio->bi_opf) && !bio_sectors(bio))
                        return false;

                WARN_ONCE(1,
                       "generic_make_request: Trying to write "
                        "to read-only block-device %s (partno %d)\n",
                        bio_devname(bio, b), part->partno);
                /* Older lvm-tools actually trigger this */
                return false;
        }

        return false;
}

static noinline int should_fail_bio(struct bio *bio)
{
        if (should_fail_request(&bio->bi_disk->part0, bio->bi_iter.bi_size))
                return -EIO;
        return 0;
}
ALLOW_ERROR_INJECTION(should_fail_bio, ERRNO);

/*
 * Check whether this bio extends beyond the end of the device or partition.
 * This may well happen - the kernel calls bread() without checking the size of
 * the device, e.g., when mounting a file system.
 */
static inline int bio_check_eod(struct bio *bio, sector_t maxsector)
{
        unsigned int nr_sectors = bio_sectors(bio);

        if (nr_sectors && maxsector &&
            (nr_sectors > maxsector ||
             bio->bi_iter.bi_sector > maxsector - nr_sectors)) {
                handle_bad_sector(bio, maxsector);
                return -EIO;
        }
        return 0;
}

/*
 * Remap block n of partition p to block n+start(p) of the disk.
 */
static inline int blk_partition_remap(struct bio *bio)
{
        struct hd_struct *p;
        int ret = -EIO;

        rcu_read_lock();
        p = __disk_get_part(bio->bi_disk, bio->bi_partno);
        if (unlikely(!p))
                goto out;
        if (unlikely(should_fail_request(p, bio->bi_iter.bi_size)))
                goto out;
        if (unlikely(bio_check_ro(bio, p)))
                goto out;

        if (bio_sectors(bio)) {
                if (bio_check_eod(bio, part_nr_sects_read(p)))
                        goto out;
                bio->bi_iter.bi_sector += p->start_sect;
                trace_block_bio_remap(bio->bi_disk->queue, bio, part_devt(p),
                                      bio->bi_iter.bi_sector - p->start_sect);
        }
        bio->bi_partno = 0;
        ret = 0;
out:
        rcu_read_unlock();
        return ret;
}

static noinline_for_stack bool
generic_make_request_checks(struct bio *bio)
{
        struct request_queue *q;
        int nr_sectors = bio_sectors(bio);
        blk_status_t status = BLK_STS_IOERR;
        char b[BDEVNAME_SIZE];

        might_sleep();

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

        /*
         * Non-mq queues do not honor REQ_NOWAIT, so complete a bio
         * with BLK_STS_AGAIN status in order to catch -EAGAIN and
         * to give a chance to the caller to repeat request gracefully.
         */
        if ((bio->bi_opf & REQ_NOWAIT) && !queue_is_mq(q)) {
                status = BLK_STS_AGAIN;
                goto end_io;
        }

        if (should_fail_bio(bio))
                goto end_io;

        if (bio->bi_partno) {
                if (unlikely(blk_partition_remap(bio)))
                        goto end_io;
        } else {
                if (unlikely(bio_check_ro(bio, &bio->bi_disk->part0)))
                        goto end_io;
                if (unlikely(bio_check_eod(bio, get_capacity(bio->bi_disk))))
                        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 (op_is_flush(bio->bi_opf) &&
            !test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
                bio->bi_opf &= ~(REQ_PREFLUSH | REQ_FUA);
                if (!nr_sectors) {
                        status = BLK_STS_OK;
                        goto end_io;
                }
        }

        if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
                bio->bi_opf &= ~REQ_HIPRI;

        switch (bio_op(bio)) {
        case REQ_OP_DISCARD:
                if (!blk_queue_discard(q))
                        goto not_supported;
                break;
        case REQ_OP_SECURE_ERASE:
                if (!blk_queue_secure_erase(q))
                        goto not_supported;
                break;
        case REQ_OP_WRITE_SAME:
                if (!q->limits.max_write_same_sectors)
                        goto not_supported;
                break;
        case REQ_OP_ZONE_RESET:
        case REQ_OP_ZONE_OPEN:
        case REQ_OP_ZONE_CLOSE:
        case REQ_OP_ZONE_FINISH:
                if (!blk_queue_is_zoned(q))
                        goto not_supported;
                break;
        case REQ_OP_ZONE_RESET_ALL:
                if (!blk_queue_is_zoned(q) || !blk_queue_zone_resetall(q))
                        goto not_supported;
                break;
        case REQ_OP_WRITE_ZEROES:
                if (!q->limits.max_write_zeroes_sectors)
                        goto not_supported;
                break;
        default:
                break;
        }

        /*
         * 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 (!blkcg_bio_issue_check(q, bio))
                return false;

        if (!bio_flagged(bio, BIO_TRACE_COMPLETION)) {
                trace_block_bio_queue(q, bio);
                /* Now that enqueuing has been traced, we need to trace
                 * completion as well.
                 */
                bio_set_flag(bio, BIO_TRACE_COMPLETION);
        }
        return true;

not_supported:
        status = BLK_STS_NOTSUPP;
end_io:
        bio->bi_status = status;
        bio_endio(bio);
        return false;
}

/**
 * generic_make_request - hand a buffer to its device driver for I/O
 * @bio:  The bio describing the location in memory and on the device.
 *
 * generic_make_request() is used to make I/O requests of block
 * devices. It is passed a &struct bio, which describes the I/O that needs
 * to be done.
 *
 * generic_make_request() does not return any status.  The
 * success/failure status of the request, along with notification of
 * completion, is delivered asynchronously through the bio->bi_end_io
 * function described (one day) else where.
 *
 * The caller of generic_make_request must make sure that bi_io_vec
 * are set to describe the memory buffer, and that bi_dev and bi_sector are
 * set to describe the device address, and the
 * bi_end_io and optionally bi_private are set to describe how
 * completion notification should be signaled.
 *
 * generic_make_request and the drivers it calls may use bi_next if this
 * bio happens to be merged with someone else, and may resubmit the bio to
 * a lower device by calling into generic_make_request recursively, which
 * means the bio should NOT be touched after the call to ->make_request_fn.
 */
blk_qc_t generic_make_request(struct bio *bio)
{
        /*
         * bio_list_on_stack[0] contains bios submitted by the current
         * make_request_fn.
         * bio_list_on_stack[1] contains bios that were submitted before
         * the current make_request_fn, but that haven't been processed
         * yet.
         */
        struct bio_list bio_list_on_stack[2];
        blk_qc_t ret = BLK_QC_T_NONE;

        if (!generic_make_request_checks(bio))
                goto out;

        /*
         * 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[0], bio);
                goto out;
        }

        /* 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[0]);
        current->bio_list = bio_list_on_stack;
        do {
                struct request_queue *q = bio->bi_disk->queue;
                blk_mq_req_flags_t flags = bio->bi_opf & REQ_NOWAIT ?
                        BLK_MQ_REQ_NOWAIT : 0;

                if (likely(blk_queue_enter(q, flags) == 0)) {
                        struct bio_list lower, same;

                        /* Create a fresh bio_list for all subordinate requests */
                        bio_list_on_stack[1] = bio_list_on_stack[0];
                        bio_list_init(&bio_list_on_stack[0]);
                        ret = q->make_request_fn(q, bio);

                        blk_queue_exit(q);

                        /* sort new bios into those for a lower level
                         * and those for the same level
                         */
                        bio_list_init(&lower);
                        bio_list_init(&same);
                        while ((bio = bio_list_pop(&bio_list_on_stack[0])) != NULL)
                                if (q == bio->bi_disk->queue)
                                        bio_list_add(&same, bio);
                                else
                                        bio_list_add(&lower, bio);
                        /* now assemble so we handle the lowest level first */
                        bio_list_merge(&bio_list_on_stack[0], &lower);
                        bio_list_merge(&bio_list_on_stack[0], &same);
                        bio_list_merge(&bio_list_on_stack[0], &bio_list_on_stack[1]);
                } else {
                        if (unlikely(!blk_queue_dying(q) &&
                                        (bio->bi_opf & REQ_NOWAIT)))
                                bio_wouldblock_error(bio);
                        else
                                bio_io_error(bio);
                }
                bio = bio_list_pop(&bio_list_on_stack[0]);
        } while (bio);
        current->bio_list = NULL; /* deactivate */

out:
        return ret;
}
EXPORT_SYMBOL(generic_make_request);

/**
 * direct_make_request - hand a buffer directly to its device driver for I/O
 * @bio:  The bio describing the location in memory and on the device.
 *
 * This function behaves like generic_make_request(), but does not protect
 * against recursion.  Must only be used if the called driver is known
 * to not call generic_make_request (or direct_make_request) again from
 * its make_request function.  (Calling direct_make_request again from
 * a workqueue is perfectly fine as that doesn't recurse).
 */
blk_qc_t direct_make_request(struct bio *bio)
{
        struct request_queue *q = bio->bi_disk->queue;
        bool nowait = bio->bi_opf & REQ_NOWAIT;
        blk_qc_t ret;

        if (!generic_make_request_checks(bio))
                return BLK_QC_T_NONE;

        if (unlikely(blk_queue_enter(q, nowait ? BLK_MQ_REQ_NOWAIT : 0))) {
                if (nowait && !blk_queue_dying(q))
                        bio->bi_status = BLK_STS_AGAIN;
                else
                        bio->bi_status = BLK_STS_IOERR;
                bio_endio(bio);
                return BLK_QC_T_NONE;
        }

        ret = q->make_request_fn(q, bio);
        blk_queue_exit(q);
        return ret;
}
EXPORT_SYMBOL_GPL(direct_make_request);

/**
 * submit_bio - submit a bio to the block device layer for I/O
 * @bio: The &struct bio which describes the I/O
 *
 * submit_bio() is very similar in purpose to generic_make_request(), and
 * uses that function to do most of the work. Both are fairly rough
 * interfaces; @bio must be presetup and ready for I/O.
 *
 */
blk_qc_t submit_bio(struct bio *bio)
{
        bool workingset_read = false;
        unsigned long pflags;
        blk_qc_t ret;

        if (blkcg_punt_bio_submit(bio))
                return BLK_QC_T_NONE;

        /*
         * 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(bio_op(bio) == REQ_OP_WRITE_SAME))
                        count = queue_logical_block_size(bio->bi_disk->queue) >> 9;
                else
                        count = bio_sectors(bio);

                if (op_is_write(bio_op(bio))) {
                        count_vm_events(PGPGOUT, count);
                } else {
                        if (bio_flagged(bio, BIO_WORKINGSET))
                                workingset_read = true;
                        task_io_account_read(bio->bi_iter.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),
                                op_is_write(bio_op(bio)) ? "WRITE" : "READ",
                                (unsigned long long)bio->bi_iter.bi_sector,
                                bio_devname(bio, b), count);
                }
        }

        /*
         * If we're reading data that is part of the userspace
         * workingset, count submission time as memory stall. When the
         * device is congested, or the submitting cgroup IO-throttled,
         * submission can be a significant part of overall IO time.
         */
        if (workingset_read)
                psi_memstall_enter(&pflags);

        ret = generic_make_request(bio);

        if (workingset_read)
                psi_memstall_leave(&pflags);

        return ret;
}
EXPORT_SYMBOL(submit_bio);

/**
 * blk_cloned_rq_check_limits - Helper function to check a cloned request
 *                              for new the queue limits
 * @q:  the queue
 * @rq: the request being checked
 *
 * Description:
 *    @rq may have been made based on weaker limitations of upper-level queues
 *    in request stacking drivers, and it may violate the limitation of @q.
 *    Since the block layer and the underlying device driver trust @rq
 *    after it is inserted to @q, it should be checked against @q before
 *    the insertion using this generic function.
 *
 *    Request stacking drivers like request-based dm may change the queue
 *    limits when retrying requests on other queues. Those requests need
 *    to be checked against the new queue limits again during dispatch.
 */
static int blk_cloned_rq_check_limits(struct request_queue *q,
                                      struct request *rq)
{
        if (blk_rq_sectors(rq) > blk_queue_get_max_sectors(q, req_op(rq))) {
                printk(KERN_ERR "%s: over max size limit. (%u > %u)\n",
                        __func__, blk_rq_sectors(rq),
                        blk_queue_get_max_sectors(q, req_op(rq)));
                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.
         */
        rq->nr_phys_segments = blk_recalc_rq_segments(rq);
        if (rq->nr_phys_segments > queue_max_segments(q)) {
                printk(KERN_ERR "%s: over max segments limit. (%hu > %hu)\n",
                        __func__, rq->nr_phys_segments, queue_max_segments(q));
                return -EIO;
        }

        return 0;
}

/**
 * blk_insert_cloned_request - Helper for stacking drivers to submit a request
 * @q:  the queue to submit the request
 * @rq: the request being queued
 */
blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request *rq)
{
        if (blk_cloned_rq_check_limits(q, rq))
                return BLK_STS_IOERR;

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

        if (blk_queue_io_stat(q))
                blk_account_io_start(rq, true);

        /*
         * Since we have a scheduler attached on the top device,
         * bypass a potential scheduler on the bottom device for
         * insert.
         */
        return blk_mq_request_issue_directly(rq, true);
}
EXPORT_SYMBOL_GPL(blk_insert_cloned_request);

/**
 * blk_rq_err_bytes - determine number of bytes till the next failure boundary
 * @rq: request to examine
 *
 * Description:
 *     A request could be merge of IOs which require different failure
 *     handling.  This function determines the number of bytes which
 *     can be failed from the beginning of the request without
 *     crossing into area which need to be retried further.
 *
 * Return:
 *     The number of bytes to fail.
 */
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->rq_flags & RQF_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_opf & ff) != ff)
                        break;
                bytes += bio->bi_iter.bi_size;
        }

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

void blk_account_io_completion(struct request *req, unsigned int bytes)
{
        if (req->part && blk_do_io_stat(req)) {
                const int sgrp = op_stat_group(req_op(req));
                struct hd_struct *part;

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

void blk_account_io_done(struct request *req, u64 now)
{
        /*
         * Account IO completion.  flush_rq isn't accounted as a
         * normal IO on queueing nor completion.  Accounting the
         * containing request is enough.
         */
        if (req->part && blk_do_io_stat(req) &&
            !(req->rq_flags & RQF_FLUSH_SEQ)) {
                const int sgrp = op_stat_group(req_op(req));
                struct hd_struct *part;

                part_stat_lock();
                part = req->part;

                update_io_ticks(part, jiffies);
                part_stat_inc(part, ios[sgrp]);
                part_stat_add(part, nsecs[sgrp], now - req->start_time_ns);
                part_stat_add(part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns));
                part_dec_in_flight(req->q, part, rq_data_dir(req));

                hd_struct_put(part);
                part_stat_unlock();
        }
}

void blk_account_io_start(struct request *rq, bool new_io)
{
        struct hd_struct *part;
        int rw = rq_data_dir(rq);

        if (!blk_do_io_stat(rq))
                return;

        part_stat_lock();

        if (!new_io) {
                part = rq->part;
                part_stat_inc(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_inc_in_flight(rq->q, part, rw);
                rq->part = part;
        }

        update_io_ticks(part, jiffies);

        part_stat_unlock();
}

/*
 * Steal bios from a request and add them to a bio list.
 * The request must not have been partially completed before.
 */
void blk_steal_bios(struct bio_list *list, struct request *rq)
{
        if (rq->bio) {
                if (list->tail)
                        list->tail->bi_next = rq->bio;
                else
                        list->head = rq->bio;
                list->tail = rq->biotail;

                rq->bio = NULL;
                rq->biotail = NULL;
        }

        rq->__data_len = 0;
}
EXPORT_SYMBOL_GPL(blk_steal_bios);

/**
 * blk_update_request - Special helper function for request stacking drivers
 * @req:      the request being processed
 * @error:    block status code
 * @nr_bytes: number of bytes to complete @req
 *
 * Description:
 *     Ends I/O on a number of bytes attached to @req, but doesn't complete
 *     the request structure even if @req doesn't have leftover.
 *     If @req has leftover, sets it up for the next range of segments.
 *
 *     This special helper function is only for request stacking drivers
 *     (e.g. request-based dm) so that they can handle partial completion.
 *     Actual device drivers should use blk_mq_end_request instead.
 *
 *     Passing the result of blk_rq_bytes() as @nr_bytes guarantees
 *     %false return from this function.
 *
 * Note:
 *      The RQF_SPECIAL_PAYLOAD flag is ignored on purpose in both
 *      blk_rq_bytes() and in blk_update_request().
 *
 * Return:
 *     %false - this request doesn't have any more data
 *     %true  - this request has more data
 **/
bool blk_update_request(struct request *req, blk_status_t error,
                unsigned int nr_bytes)
{
        int total_bytes;

        trace_block_rq_complete(req, blk_status_to_errno(error), nr_bytes);

        if (!req->bio)
                return false;

#ifdef CONFIG_BLK_DEV_INTEGRITY
        if (blk_integrity_rq(req) && req_op(req) == REQ_OP_READ &&
            error == BLK_STS_OK)
                req->q->integrity.profile->complete_fn(req, nr_bytes);
#endif

        if (unlikely(error && !blk_rq_is_passthrough(req) &&
                     !(req->rq_flags & RQF_QUIET)))
                print_req_error(req, error, __func__);

        blk_account_io_completion(req, nr_bytes);

        total_bytes = 0;
        while (req->bio) {
                struct bio *bio = req->bio;
                unsigned bio_bytes = min(bio->bi_iter.bi_size, nr_bytes);

                if (bio_bytes == bio->bi_iter.bi_size)
                        req->bio = bio->bi_next;

                /* Completion has already been traced */
                bio_clear_flag(bio, BIO_TRACE_COMPLETION);
                req_bio_endio(req, bio, bio_bytes, error);

                total_bytes += bio_bytes;
                nr_bytes -= bio_bytes;

                if (!nr_bytes)
                        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;
        }

        req->__data_len -= total_bytes;

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

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

        if (!(req->rq_flags & RQF_SPECIAL_PAYLOAD)) {
                /*
                 * 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 */
                req->nr_phys_segments = blk_recalc_rq_segments(req);
        }

        return true;
}
EXPORT_SYMBOL_GPL(blk_update_request);

#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
/**
 * rq_flush_dcache_pages - Helper function to flush all pages in a request
 * @rq: the request to be flushed
 *
 * Description:
 *     Flush all pages in @rq.
 */
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

/**
 * blk_lld_busy - Check if underlying low-level drivers of a device are busy
 * @q : the queue of the device being checked
 *
 * Description:
 *    Check if underlying low-level drivers of a device are busy.
 *    If the drivers want to export their busy state, they must set own
 *    exporting function using blk_queue_lld_busy() first.
 *
 *    Basically, this function is used only by request stacking drivers
 *    to stop dispatching requests to underlying devices when underlying
 *    devices are busy.  This behavior helps more I/O merging on the queue
 *    of the request stacking driver and prevents I/O throughput regression
 *    on burst I/O load.
 *
 * Return:
 *    0 - Not busy (The request stacking driver should dispatch request)
 *    1 - Busy (The request stacking driver should stop dispatching request)
 */
int blk_lld_busy(struct request_queue *q)
{
        if (queue_is_mq(q) && q->mq_ops->busy)
                return q->mq_ops->busy(q);

        return 0;
}
EXPORT_SYMBOL_GPL(blk_lld_busy);

/**
 * blk_rq_unprep_clone - Helper function to free all bios in a cloned request
 * @rq: the clone request to be cleaned up
 *
 * Description:
 *     Free all bios in @rq for a cloned request.
 */
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, ->sense) are not copied.
 */
static void __blk_rq_prep_clone(struct request *dst, struct request *src)
{
        dst->__sector = blk_rq_pos(src);
        dst->__data_len = blk_rq_bytes(src);
        if (src->rq_flags & RQF_SPECIAL_PAYLOAD) {
                dst->rq_flags |= RQF_SPECIAL_PAYLOAD;
                dst->special_vec = src->special_vec;
        }
        dst->nr_phys_segments = src->nr_phys_segments;
        dst->ioprio = src->ioprio;
        dst->extra_len = src->extra_len;
}

/**
 * blk_rq_prep_clone - Helper function to setup clone request
 * @rq: the request to be setup
 * @rq_src: original request to be cloned
 * @bs: bio_set that bios for clone are allocated from
 * @gfp_mask: memory allocation mask for bio
 * @bio_ctr: setup function to be called for each clone bio.
 *           Returns %0 for success, non %0 for failure.
 * @data: private data to be passed to @bio_ctr
 *
 * Description:
 *     Clones bios in @rq_src to @rq, and copies attributes of @rq_src to @rq.
 *     The actual data parts of @rq_src (e.g. ->cmd, ->sense)
 *     are not copied, and copying such parts is the caller's responsibility.
 *     Also, pages which the original bios are pointing to are not copied
 *     and the cloned bios just point same pages.
 *     So cloned bios must be completed before original bios, which means
 *     the caller must complete @rq before @rq_src.
 */
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;

        __rq_for_each_bio(bio_src, rq_src) {
                bio = bio_clone_fast(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 work_struct *work)
{
        return queue_work(kblockd_workqueue, work);
}
EXPORT_SYMBOL(kblockd_schedule_work);

int kblockd_schedule_work_on(int cpu, struct work_struct *work)
{
        return queue_work_on(cpu, kblockd_workqueue, work);
}
EXPORT_SYMBOL(kblockd_schedule_work_on);

int kblockd_mod_delayed_work_on(int cpu, struct delayed_work *dwork,
                                unsigned long delay)
{
        return mod_delayed_work_on(cpu, kblockd_workqueue, dwork, delay);
}
EXPORT_SYMBOL(kblockd_mod_delayed_work_on);

/**
 * blk_start_plug - initialize blk_plug and track it inside the task_struct
 * @plug:       The &struct blk_plug that needs to be initialized
 *
 * Description:
 *   blk_start_plug() indicates to the block layer an intent by the caller
 *   to submit multiple I/O requests in a batch.  The block layer may use
 *   this hint to defer submitting I/Os from the caller until blk_finish_plug()
 *   is called.  However, the block layer may choose to submit requests
 *   before a call to blk_finish_plug() if the number of queued I/Os
 *   exceeds %BLK_MAX_REQUEST_COUNT, or if the size of the I/O is larger than
 *   %BLK_PLUG_FLUSH_SIZE.  The queued I/Os may also be submitted early if
 *   the task schedules (see below).
 *
 *   Tracking blk_plug inside the task_struct will help with auto-flushing the
 *   pending I/O should the task end up blocking between blk_start_plug() and
 *   blk_finish_plug(). This is important from a performance perspective, but
 *   also ensures that we don't deadlock. For instance, if the task is blocking
 *   for a memory allocation, memory reclaim could end up wanting to free a
 *   page belonging to that request that is currently residing in our private
 *   plug. By flushing the pending I/O when the process goes to sleep, we avoid
 *   this kind of deadlock.
 */
void blk_start_plug(struct blk_plug *plug)
{
        struct task_struct *tsk = current;

        /*
         * If this is a nested plug, don't actually assign it.
         */
        if (tsk->plug)
                return;

        INIT_LIST_HEAD(&plug->mq_list);
        INIT_LIST_HEAD(&plug->cb_list);
        plug->rq_count = 0;
        plug->multiple_queues = false;

        /*
         * 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 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)
{
        flush_plug_callbacks(plug, from_schedule);

        if (!list_empty(&plug->mq_list))
                blk_mq_flush_plug_list(plug, from_schedule);
}

/**
 * blk_finish_plug - mark the end of a batch of submitted I/O
 * @plug:       The &struct blk_plug passed to blk_start_plug()
 *
 * Description:
 * Indicate that a batch of I/O submissions is complete.  This function
 * must be paired with an initial call to blk_start_plug().  The intent
 * is to allow the block layer to optimize I/O submission.  See the
 * documentation for blk_start_plug() for more information.
 */
void blk_finish_plug(struct blk_plug *plug)
{
        if (plug != current->plug)
                return;
        blk_flush_plug_list(plug, false);

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

int __init blk_dev_init(void)
{
        BUILD_BUG_ON(REQ_OP_LAST >= (1 << REQ_OP_BITS));
        BUILD_BUG_ON(REQ_OP_BITS + REQ_FLAG_BITS > 8 *
                        sizeof_field(struct request, cmd_flags));
        BUILD_BUG_ON(REQ_OP_BITS + REQ_FLAG_BITS > 8 *
                        sizeof_field(struct bio, bi_opf));

        /* 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");

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

#ifdef CONFIG_DEBUG_FS
        blk_debugfs_root = debugfs_create_dir("block", NULL);
#endif

        return 0;
}