/*
 * Copyright (C) 2016 Red Hat, Inc. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include "dm-core.h"
#include "dm-rq.h"

#include <linux/elevator.h> /* for rq_end_sector() */
#include <linux/blk-mq.h>

#define DM_MSG_PREFIX "core-rq"

#define DM_MQ_NR_HW_QUEUES 1
#define DM_MQ_QUEUE_DEPTH 2048
static unsigned dm_mq_nr_hw_queues = DM_MQ_NR_HW_QUEUES;
static unsigned dm_mq_queue_depth = DM_MQ_QUEUE_DEPTH;

/*
 * Request-based DM's mempools' reserved IOs set by the user.
 */
#define RESERVED_REQUEST_BASED_IOS      256
static unsigned reserved_rq_based_ios = RESERVED_REQUEST_BASED_IOS;

static bool use_blk_mq = IS_ENABLED(CONFIG_DM_MQ_DEFAULT);

bool dm_use_blk_mq_default(void)
{
        return use_blk_mq;
}

bool dm_use_blk_mq(struct mapped_device *md)
{
        return md->use_blk_mq;
}
EXPORT_SYMBOL_GPL(dm_use_blk_mq);

unsigned dm_get_reserved_rq_based_ios(void)
{
        return __dm_get_module_param(&reserved_rq_based_ios,
                                     RESERVED_REQUEST_BASED_IOS, DM_RESERVED_MAX_IOS);
}
EXPORT_SYMBOL_GPL(dm_get_reserved_rq_based_ios);

static unsigned dm_get_blk_mq_nr_hw_queues(void)
{
        return __dm_get_module_param(&dm_mq_nr_hw_queues, 1, 32);
}

static unsigned dm_get_blk_mq_queue_depth(void)
{
        return __dm_get_module_param(&dm_mq_queue_depth,
                                     DM_MQ_QUEUE_DEPTH, BLK_MQ_MAX_DEPTH);
}

int dm_request_based(struct mapped_device *md)
{
        return blk_queue_stackable(md->queue);
}

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

        spin_lock_irqsave(q->queue_lock, flags);
        if (blk_queue_stopped(q))
                blk_start_queue(q);
        spin_unlock_irqrestore(q->queue_lock, flags);
}

static void dm_mq_start_queue(struct request_queue *q)
{
        blk_mq_unquiesce_queue(q);
        blk_mq_kick_requeue_list(q);
}

void dm_start_queue(struct request_queue *q)
{
        if (!q->mq_ops)
                dm_old_start_queue(q);
        else
                dm_mq_start_queue(q);
}

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

        spin_lock_irqsave(q->queue_lock, flags);
        if (!blk_queue_stopped(q))
                blk_stop_queue(q);
        spin_unlock_irqrestore(q->queue_lock, flags);
}

static void dm_mq_stop_queue(struct request_queue *q)
{
        if (blk_mq_queue_stopped(q))
                return;

        blk_mq_quiesce_queue(q);
}

void dm_stop_queue(struct request_queue *q)
{
        if (!q->mq_ops)
                dm_old_stop_queue(q);
        else
                dm_mq_stop_queue(q);
}

static struct dm_rq_target_io *alloc_old_rq_tio(struct mapped_device *md,
                                                gfp_t gfp_mask)
{
        return mempool_alloc(md->io_pool, gfp_mask);
}

static void free_old_rq_tio(struct dm_rq_target_io *tio)
{
        mempool_free(tio, tio->md->io_pool);
}

static struct request *alloc_old_clone_request(struct mapped_device *md,
                                               gfp_t gfp_mask)
{
        return mempool_alloc(md->rq_pool, gfp_mask);
}

static void free_old_clone_request(struct mapped_device *md, struct request *rq)
{
        mempool_free(rq, md->rq_pool);
}

/*
 * Partial completion handling for request-based dm
 */
static void end_clone_bio(struct bio *clone, int error)
{
        struct dm_rq_clone_bio_info *info =
                container_of(clone, struct dm_rq_clone_bio_info, clone);
        struct dm_rq_target_io *tio = info->tio;
        unsigned int nr_bytes = info->orig->bi_size;
        bool is_last = !clone->bi_next;

        bio_put(clone);

        if (tio->error)
                /*
                 * An error has already been detected on the request.
                 * Once error occurred, just let clone->end_io() handle
                 * the remainder.
                 */
                return;
        else if (error) {
                /*
                 * Don't notice the error to the upper layer yet.
                 * The error handling decision is made by the target driver,
                 * when the request is completed.
                 */
                tio->error = error;
                goto exit;
        }

        /*
         * I/O for the bio successfully completed.
         * Notice the data completion to the upper layer.
         */
        tio->completed += nr_bytes;

        /*
         * Update the original request.
         * Do not use blk_end_request() here, because it may complete
         * the original request before the clone, and break the ordering.
         */
        if (is_last)
exit:
                blk_update_request(tio->orig, 0, tio->completed);
}

static struct dm_rq_target_io *tio_from_request(struct request *rq)
{
        return (rq->q->mq_ops ? blk_mq_rq_to_pdu(rq) : rq->special);
}

static void rq_end_stats(struct mapped_device *md, struct request *orig)
{
        if (unlikely(dm_stats_used(&md->stats))) {
                struct dm_rq_target_io *tio = tio_from_request(orig);
                tio->duration_jiffies = jiffies - tio->duration_jiffies;
                dm_stats_account_io(&md->stats, orig->cmd_flags, blk_rq_pos(orig),
                                    tio->n_sectors, true, tio->duration_jiffies,
                                    &tio->stats_aux);
        }
}

/*
 * Don't touch any member of the md after calling this function because
 * the md may be freed in dm_put() at the end of this function.
 * Or do dm_get() before calling this function and dm_put() later.
 */
static void rq_completed(struct mapped_device *md, int rw, bool run_queue)
{
        struct request_queue *q = md->queue;
        unsigned long flags;

        atomic_dec(&md->pending[rw]);

        /* nudge anyone waiting on suspend queue */
        if (!md_in_flight(md))
                wake_up(&md->wait);

        /*
         * Run this off this callpath, as drivers could invoke end_io while
         * inside their request_fn (and holding the queue lock). Calling
         * back into ->request_fn() could deadlock attempting to grab the
         * queue lock again.
         */
        if (!q->mq_ops && run_queue) {
                spin_lock_irqsave(q->queue_lock, flags);
                blk_run_queue_async(q);
                spin_unlock_irqrestore(q->queue_lock, flags);
        }

        /*
         * dm_put() must be at the end of this function. See the comment above
         */
        dm_put(md);
}

static void free_rq_clone(struct request *clone)
{
        struct dm_rq_target_io *tio = clone->end_io_data;
        struct mapped_device *md = tio->md;

        blk_rq_unprep_clone(clone);

        /*
         * It is possible for a clone_old_rq() allocated clone to
         * get passed in -- it may not yet have a request_queue.
         * This is known to occur if the error target replaces
         * a multipath target that has a request_fn queue stacked
         * on blk-mq queue(s).
         */
        if (clone->q && clone->q->mq_ops)
                /* stacked on blk-mq queue(s) */
                tio->ti->type->release_clone_rq(clone, NULL);
        else if (!md->queue->mq_ops)
                /* request_fn queue stacked on request_fn queue(s) */
                free_old_clone_request(md, clone);

        if (!md->queue->mq_ops)
                free_old_rq_tio(tio);
}

/*
 * Complete the clone and the original request.
 * Must be called without clone's queue lock held,
 * see end_clone_request() for more details.
 */
static void dm_end_request(struct request *clone, int error)
{
        int rw = rq_data_dir(clone);
        struct dm_rq_target_io *tio = clone->end_io_data;
        struct mapped_device *md = tio->md;
        struct request *rq = tio->orig;

        if (rq->cmd_type == REQ_TYPE_BLOCK_PC) {
                rq->errors = clone->errors;
                rq->resid_len = clone->resid_len;

                if (rq->sense)
                        /*
                         * We are using the sense buffer of the original
                         * request.
                         * So setting the length of the sense data is enough.
                         */
                        rq->sense_len = clone->sense_len;
        }

        free_rq_clone(clone);
        rq_end_stats(md, rq);
        if (!rq->q->mq_ops)
                blk_end_request_all(rq, error);
        else
                blk_mq_end_request(rq, error);
        rq_completed(md, rw, true);
}

static void dm_unprep_request(struct request *rq)
{
        struct dm_rq_target_io *tio = tio_from_request(rq);
        struct request *clone = tio->clone;

        if (!rq->q->mq_ops) {
                rq->special = NULL;
                rq->cmd_flags &= ~REQ_DONTPREP;
        }

        if (clone)
                free_rq_clone(clone);
        else if (!tio->md->queue->mq_ops)
                free_old_rq_tio(tio);
}

/*
 * Requeue the original request of a clone.
 */
static void dm_old_requeue_request(struct request *rq, unsigned long delay_ms)
{
        struct request_queue *q = rq->q;
        unsigned long flags;

        spin_lock_irqsave(q->queue_lock, flags);
        blk_requeue_request(q, rq);
        blk_delay_queue(q, delay_ms);
        spin_unlock_irqrestore(q->queue_lock, flags);
}

static void __dm_mq_kick_requeue_list(struct request_queue *q, unsigned long msecs)
{
        blk_mq_delay_kick_requeue_list(q, msecs);
}

void dm_mq_kick_requeue_list(struct mapped_device *md)
{
        __dm_mq_kick_requeue_list(dm_get_md_queue(md), 0);
}
EXPORT_SYMBOL(dm_mq_kick_requeue_list);

static void dm_mq_delay_requeue_request(struct request *rq, unsigned long msecs)
{
        blk_mq_requeue_request(rq, false);
        __dm_mq_kick_requeue_list(rq->q, msecs);
}

static void dm_requeue_original_request(struct dm_rq_target_io *tio, bool delay_requeue)
{
        struct mapped_device *md = tio->md;
        struct request *rq = tio->orig;
        int rw = rq_data_dir(rq);
        unsigned long delay_ms = delay_requeue ? 100 : 0;

        rq_end_stats(md, rq);
        dm_unprep_request(rq);

        if (!rq->q->mq_ops)
                dm_old_requeue_request(rq, delay_ms);
        else
                dm_mq_delay_requeue_request(rq, delay_ms);

        rq_completed(md, rw, false);
}

static void dm_done(struct request *clone, int error, bool mapped)
{
        int r = error;
        struct dm_rq_target_io *tio = clone->end_io_data;
        dm_request_endio_fn rq_end_io = NULL;

        if (tio->ti) {
                rq_end_io = tio->ti->type->rq_end_io;

                if (mapped && rq_end_io)
                        r = rq_end_io(tio->ti, clone, error, &tio->info);
        }

        if (unlikely(r == -EREMOTEIO)) {
                if ((clone->cmd_flags & REQ_DISCARD) &&
                    !clone->q->limits.max_discard_sectors)
                        disable_discard(tio->md);
                else if ((clone->cmd_flags & REQ_WRITE_SAME) &&
                         !clone->q->limits.max_write_same_sectors)
                        disable_write_same(tio->md);
        }

        if (r <= 0)
                /* The target wants to complete the I/O */
                dm_end_request(clone, r);
        else if (r == DM_ENDIO_INCOMPLETE)
                /* The target will handle the I/O */
                return;
        else if (r == DM_ENDIO_REQUEUE)
                /* The target wants to requeue the I/O */
                dm_requeue_original_request(tio, false);
        else {
                DMWARN("unimplemented target endio return value: %d", r);
                BUG();
        }
}

/*
 * Request completion handler for request-based dm
 */
static void dm_softirq_done(struct request *rq)
{
        bool mapped = true;
        struct dm_rq_target_io *tio = tio_from_request(rq);
        struct request *clone = tio->clone;
        int rw;

        if (!clone) {
                rq_end_stats(tio->md, rq);
                rw = rq_data_dir(rq);
                if (!rq->q->mq_ops) {
                        blk_end_request_all(rq, tio->error);
                        rq_completed(tio->md, rw, false);
                        free_old_rq_tio(tio);
                } else {
                        blk_mq_end_request(rq, tio->error);
                        rq_completed(tio->md, rw, false);
                }
                return;
        }

        if (rq->cmd_flags & REQ_FAILED)
                mapped = false;

        dm_done(clone, tio->error, mapped);
}

/*
 * Complete the clone and the original request with the error status
 * through softirq context.
 */
static void dm_complete_request(struct request *rq, int error)
{
        struct dm_rq_target_io *tio = tio_from_request(rq);

        tio->error = error;
        if (!rq->q->mq_ops)
                blk_complete_request(rq);
        else
                blk_mq_complete_request(rq, error);
}

/*
 * Complete the not-mapped clone and the original request with the error status
 * through softirq context.
 * Target's rq_end_io() function isn't called.
 * This may be used when the target's map_rq() or clone_and_map_rq() functions fail.
 */
static void dm_kill_unmapped_request(struct request *rq, int error)
{
        rq->cmd_flags |= REQ_FAILED;
        dm_complete_request(rq, error);
}

/*
 * Called with the clone's queue lock held (in the case of .request_fn)
 */
static void end_clone_request(struct request *clone, int error)
{
        struct dm_rq_target_io *tio = clone->end_io_data;

        if (!clone->q->mq_ops) {
                /*
                 * For just cleaning up the information of the queue in which
                 * the clone was dispatched.
                 * The clone is *NOT* freed actually here because it is alloced
                 * from dm own mempool (REQ_ALLOCED isn't set).
                 */
                __blk_put_request(clone->q, clone);
        }

        /*
         * Actual request completion is done in a softirq context which doesn't
         * hold the clone's queue lock.  Otherwise, deadlock could occur because:
         *     - another request may be submitted by the upper level driver
         *       of the stacking during the completion
         *     - the submission which requires queue lock may be done
         *       against this clone's queue
         */
        dm_complete_request(tio->orig, error);
}

static int dm_dispatch_clone_request(struct request *clone, struct request *rq)
{
        int r;

        if (blk_queue_io_stat(clone->q))
                clone->cmd_flags |= REQ_IO_STAT;

        clone->start_time = jiffies;
        r = blk_insert_cloned_request(clone->q, clone);
        if (r != BLK_MQ_RQ_QUEUE_OK && r != BLK_MQ_RQ_QUEUE_BUSY &&
                        r != BLK_MQ_RQ_QUEUE_DEV_BUSY)
                /* must complete clone in terms of original request */
                dm_complete_request(rq, r);
        return r;
}

static int dm_rq_bio_constructor(struct bio *bio, struct bio *bio_orig,
                                 void *data)
{
        struct dm_rq_target_io *tio = data;
        struct dm_rq_clone_bio_info *info =
                container_of(bio, struct dm_rq_clone_bio_info, clone);

        info->orig = bio_orig;
        info->tio = tio;
        bio->bi_end_io = end_clone_bio;

        return 0;
}

static int setup_clone(struct request *clone, struct request *rq,
                       struct dm_rq_target_io *tio, gfp_t gfp_mask)
{
        int r;

        r = blk_rq_prep_clone(clone, rq, tio->md->bs, gfp_mask,
                              dm_rq_bio_constructor, tio);
        if (r)
                return r;

        clone->cmd = rq->cmd;
        clone->cmd_len = rq->cmd_len;
        clone->sense = rq->sense;
        clone->buffer = rq->buffer;
        clone->end_io = end_clone_request;
        clone->end_io_data = tio;

        tio->clone = clone;

        return 0;
}

static struct request *clone_old_rq(struct request *rq, struct mapped_device *md,
                                    struct dm_rq_target_io *tio, gfp_t gfp_mask)
{
        /*
         * Create clone for use with .request_fn request_queue
         */
        struct request *clone;

        clone = alloc_old_clone_request(md, gfp_mask);
        if (!clone)
                return NULL;

        blk_rq_init(NULL, clone);
        if (setup_clone(clone, rq, tio, gfp_mask)) {
                /* -ENOMEM */
                free_old_clone_request(md, clone);
                return NULL;
        }

        return clone;
}

static void map_tio_request(struct kthread_work *work);

static void init_tio(struct dm_rq_target_io *tio, struct request *rq,
                     struct mapped_device *md)
{
        tio->md = md;
        tio->ti = NULL;
        tio->clone = NULL;
        tio->orig = rq;
        tio->error = 0;
        tio->completed = 0;
        /*
         * Avoid initializing info for blk-mq; it passes
         * target-specific data through info.ptr
         * (see: dm_mq_init_request)
         */
        if (!md->init_tio_pdu)
                memset(&tio->info, 0, sizeof(tio->info));
        if (md->kworker_task)
                init_kthread_work(&tio->work, map_tio_request);
}

static struct dm_rq_target_io *dm_old_prep_tio(struct request *rq,
                                               struct mapped_device *md,
                                               gfp_t gfp_mask)
{
        struct dm_rq_target_io *tio;
        int srcu_idx;
        struct dm_table *table;

        tio = alloc_old_rq_tio(md, gfp_mask);
        if (!tio)
                return NULL;

        init_tio(tio, rq, md);

        table = dm_get_live_table(md, &srcu_idx);
        /*
         * Must clone a request if this .request_fn DM device
         * is stacked on .request_fn device(s).
         */
        if (!dm_table_all_blk_mq_devices(table)) {
                if (!clone_old_rq(rq, md, tio, gfp_mask)) {
                        dm_put_live_table(md, srcu_idx);
                        free_old_rq_tio(tio);
                        return NULL;
                }
        }
        dm_put_live_table(md, srcu_idx);

        return tio;
}

/*
 * Called with the queue lock held.
 */
static int dm_old_prep_fn(struct request_queue *q, struct request *rq)
{
        struct mapped_device *md = q->queuedata;
        struct dm_rq_target_io *tio;

        if (unlikely(rq->special)) {
                DMWARN("Already has something in rq->special.");
                return BLKPREP_KILL;
        }

        tio = dm_old_prep_tio(rq, md, GFP_ATOMIC);
        if (!tio)
                return BLKPREP_DEFER;

        rq->special = tio;
        rq->cmd_flags |= REQ_DONTPREP;

        return BLKPREP_OK;
}

/*
 * Returns:
 * DM_MAPIO_*       : the request has been processed as indicated
 * DM_MAPIO_REQUEUE : the original request needs to be immediately requeued
 * < 0              : the request was completed due to failure
 */
static int map_request(struct dm_rq_target_io *tio)
{
        int r;
        struct dm_target *ti = tio->ti;
        struct mapped_device *md = tio->md;
        struct request *rq = tio->orig;
        struct request *clone = NULL;
        int ret;

        if (tio->clone) {
                clone = tio->clone;
                r = ti->type->map_rq(ti, clone, &tio->info);
                if (r == DM_MAPIO_DELAY_REQUEUE)
                        return DM_MAPIO_REQUEUE; /* .request_fn requeue is always immediate */
        } else {
                r = ti->type->clone_and_map_rq(ti, rq, &tio->info, &clone);
                if (r < 0) {
                        /* The target wants to complete the I/O */
                        dm_kill_unmapped_request(rq, r);
                        return r;
                }
                if (r == DM_MAPIO_REMAPPED &&
                    setup_clone(clone, rq, tio, GFP_ATOMIC)) {
                        /* -ENOMEM */
                        ti->type->release_clone_rq(clone, &tio->info);
                        return DM_MAPIO_REQUEUE;
                }
        }
check_again:
        switch (r) {
        case DM_MAPIO_SUBMITTED:
                /* The target has taken the I/O to submit by itself later */
                break;
        case DM_MAPIO_REMAPPED:
                /* The target has remapped the I/O so dispatch it */
                trace_block_rq_remap(clone->q, clone, disk_devt(dm_disk(md)),
                                     blk_rq_pos(rq));
                ret = dm_dispatch_clone_request(clone, rq);
                if (ret == BLK_MQ_RQ_QUEUE_BUSY || ret == BLK_MQ_RQ_QUEUE_DEV_BUSY) {
                        blk_rq_unprep_clone(clone);
                        blk_mq_cleanup_rq(clone);
                        tio->ti->type->release_clone_rq(clone, &tio->info);
                        tio->clone = NULL;
                        if (!rq->q->mq_ops)
                                r = DM_MAPIO_DELAY_REQUEUE;
                        else
                                r = DM_MAPIO_REQUEUE;
                        goto check_again;
                }
                break;
        case DM_MAPIO_REQUEUE:
                /* The target wants to requeue the I/O */
                break;
        case DM_MAPIO_DELAY_REQUEUE:
                /* The target wants to requeue the I/O after a delay */
                dm_requeue_original_request(tio, true);
                break;
        default:
                if (r > 0) {
                        DMWARN("unimplemented target map return value: %d", r);
                        BUG();
                }

                /* The target wants to complete the I/O */
                dm_kill_unmapped_request(rq, r);
        }

        return r;
}

static void dm_start_request(struct mapped_device *md, struct request *orig)
{
        if (!orig->q->mq_ops)
                blk_start_request(orig);
        else
                blk_mq_start_request(orig);
        atomic_inc(&md->pending[rq_data_dir(orig)]);

        if (md->seq_rq_merge_deadline_usecs) {
                md->last_rq_pos = rq_end_sector(orig);
                md->last_rq_rw = rq_data_dir(orig);
                md->last_rq_start_time = ktime_get();
        }

        if (unlikely(dm_stats_used(&md->stats))) {
                struct dm_rq_target_io *tio = tio_from_request(orig);
                tio->duration_jiffies = jiffies;
                tio->n_sectors = blk_rq_sectors(orig);
                dm_stats_account_io(&md->stats, orig->cmd_flags, blk_rq_pos(orig),
                                    tio->n_sectors, false, 0, &tio->stats_aux);
        }

        /*
         * Hold the md reference here for the in-flight I/O.
         * We can't rely on the reference count by device opener,
         * because the device may be closed during the request completion
         * when all bios are completed.
         * See the comment in rq_completed() too.
         */
        dm_get(md);
}

static void map_tio_request(struct kthread_work *work)
{
        struct dm_rq_target_io *tio = container_of(work, struct dm_rq_target_io, work);

        if (map_request(tio) == DM_MAPIO_REQUEUE)
                dm_requeue_original_request(tio, false);
}

ssize_t dm_attr_rq_based_seq_io_merge_deadline_show(struct mapped_device *md, char *buf)
{
        return sprintf(buf, "%u\n", md->seq_rq_merge_deadline_usecs);
}

#define MAX_SEQ_RQ_MERGE_DEADLINE_USECS 100000

ssize_t dm_attr_rq_based_seq_io_merge_deadline_store(struct mapped_device *md,
                                                     const char *buf, size_t count)
{
        unsigned deadline;

        if (dm_get_md_type(md) != DM_TYPE_REQUEST_BASED)
                return count;

        if (kstrtouint(buf, 10, &deadline))
                return -EINVAL;

        if (deadline > MAX_SEQ_RQ_MERGE_DEADLINE_USECS)
                deadline = MAX_SEQ_RQ_MERGE_DEADLINE_USECS;

        md->seq_rq_merge_deadline_usecs = deadline;

        return count;
}

static bool dm_old_request_peeked_before_merge_deadline(struct mapped_device *md)
{
        ktime_t kt_deadline;

        if (!md->seq_rq_merge_deadline_usecs)
                return false;

        kt_deadline = ns_to_ktime((u64)md->seq_rq_merge_deadline_usecs * NSEC_PER_USEC);
        kt_deadline = ktime_add_safe(md->last_rq_start_time, kt_deadline);

        return !ktime_after(ktime_get(), kt_deadline);
}

/*
 * q->request_fn for old request-based dm.
 * Called with the queue lock held.
 */
static void dm_old_request_fn(struct request_queue *q)
{
        struct mapped_device *md = q->queuedata;
        struct dm_target *ti = md->immutable_target;
        struct request *rq;
        struct dm_rq_target_io *tio;
        sector_t pos = 0;

        if (unlikely(!ti)) {
                int srcu_idx;
                struct dm_table *map = dm_get_live_table(md, &srcu_idx);

                if (unlikely(!map)) {
                        dm_put_live_table(md, srcu_idx);
                        return;
                }
                ti = dm_table_find_target(map, pos);
                dm_put_live_table(md, srcu_idx);
        }

        /*
         * For suspend, check blk_queue_stopped() and increment
         * ->pending within a single queue_lock not to increment the
         * number of in-flight I/Os after the queue is stopped in
         * dm_suspend().
         */
        while (!blk_queue_stopped(q)) {
                rq = blk_peek_request(q);
                if (!rq)
                        return;

                /* always use block 0 to find the target for flushes for now */
                pos = 0;
                if (!(rq->cmd_flags & REQ_FLUSH))
                        pos = blk_rq_pos(rq);

                if ((dm_old_request_peeked_before_merge_deadline(md) &&
                     md_in_flight(md) && rq->bio && rq->bio->bi_vcnt == 1 &&
                     md->last_rq_pos == pos && md->last_rq_rw == rq_data_dir(rq)) ||
                    (ti->type->busy && ti->type->busy(ti))) {
                        blk_delay_queue(q, 10);
                        return;
                }

                dm_start_request(md, rq);

                tio = tio_from_request(rq);
                /* Establish tio->ti before queuing work (map_tio_request) */
                tio->ti = ti;
                queue_kthread_work(&md->kworker, &tio->work);
                BUG_ON(!irqs_disabled());
        }
}

/*
 * Fully initialize a .request_fn request-based queue.
 */
int dm_old_init_request_queue(struct mapped_device *md)
{
        /* Fully initialize the queue */
        md->queue->request_fn = dm_old_request_fn;
        if (blk_init_allocated_queue(md->queue) < 0)
                return -EINVAL;

        /* disable dm_old_request_fn's merge heuristic by default */
        md->seq_rq_merge_deadline_usecs = 0;

        dm_init_normal_md_queue(md);
        blk_queue_softirq_done(md->queue, dm_softirq_done);
        blk_queue_prep_rq(md->queue, dm_old_prep_fn);

        /* Initialize the request-based DM worker thread */
        init_kthread_worker(&md->kworker);
        md->kworker_task = kthread_run(kthread_worker_fn, &md->kworker,
                                       "kdmwork-%s", dm_device_name(md));
        if (IS_ERR(md->kworker_task)) {
                int error = PTR_ERR(md->kworker_task);
                md->kworker_task = NULL;
                return error;
        }

        return 0;
}

static int dm_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,
                unsigned int hctx_idx, unsigned int numa_node)
{
        struct mapped_device *md = set->driver_data;
        struct dm_rq_target_io *tio = blk_mq_rq_to_pdu(rq);

        /*
         * Must initialize md member of tio, otherwise it won't
         * be available in dm_mq_queue_rq.
         */
        tio->md = md;

        if (md->init_tio_pdu) {
                /* target-specific per-io data is immediately after the tio */
                tio->info.ptr = tio + 1;
        }

        return 0;
}

static int dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
                          const struct blk_mq_queue_data *bd)
{
        struct request *rq = bd->rq;
        struct dm_rq_target_io *tio = blk_mq_rq_to_pdu(rq);
        struct mapped_device *md = tio->md;
        struct dm_target *ti = md->immutable_target;

        if (unlikely(!ti)) {
                int srcu_idx;
                struct dm_table *map = dm_get_live_table(md, &srcu_idx);

                ti = dm_table_find_target(map, 0);
                dm_put_live_table(md, srcu_idx);
        }

        if (ti->type->busy && ti->type->busy(ti))
                return BLK_MQ_RQ_QUEUE_BUSY;

        dm_start_request(md, rq);

        /* Init tio using md established in .init_request */
        init_tio(tio, rq, md);

        /*
         * Establish tio->ti before calling map_request().
         */
        tio->ti = ti;

        /* Direct call is fine since .queue_rq allows allocations */
        if (map_request(tio) == DM_MAPIO_REQUEUE) {
                /* Undo dm_start_request() before requeuing */
                rq_end_stats(md, rq);
                rq_completed(md, rq_data_dir(rq), false);
                return BLK_MQ_RQ_QUEUE_BUSY;
        }

        return BLK_MQ_RQ_QUEUE_OK;
}

static struct blk_mq_ops dm_mq_ops = {
        .queue_rq = dm_mq_queue_rq,
        .complete = dm_softirq_done,
        .init_request = dm_mq_init_request,
};

int dm_mq_init_request_queue(struct mapped_device *md, struct dm_table *t)
{
        struct request_queue *q;
        struct dm_target *immutable_tgt;
        int err;

        if (!dm_table_all_blk_mq_devices(t)) {
                DMERR("request-based dm-mq may only be stacked on blk-mq device(s)");
                return -EINVAL;
        }

        md->tag_set = kzalloc_node(sizeof(struct blk_mq_tag_set), GFP_KERNEL, md->numa_node_id);
        if (!md->tag_set)
                return -ENOMEM;

        md->tag_set->ops = &dm_mq_ops;
        md->tag_set->queue_depth = dm_get_blk_mq_queue_depth();
        md->tag_set->numa_node = md->numa_node_id;
        md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
        md->tag_set->nr_hw_queues = dm_get_blk_mq_nr_hw_queues();
        md->tag_set->driver_data = md;

        md->tag_set->cmd_size = sizeof(struct dm_rq_target_io);
        immutable_tgt = dm_table_get_immutable_target(t);
        if (immutable_tgt && immutable_tgt->per_io_data_size) {
                /* any target-specific per-io data is immediately after the tio */
                md->tag_set->cmd_size += immutable_tgt->per_io_data_size;
                md->init_tio_pdu = true;
        }

        err = blk_mq_alloc_tag_set(md->tag_set);
        if (err)
                goto out_kfree_tag_set;

        q = blk_mq_init_allocated_queue(md->tag_set, md->queue);
        if (IS_ERR(q)) {
                err = PTR_ERR(q);
                goto out_tag_set;
        }
        q->front_queue = 1;
        dm_init_md_queue(md);

        return 0;

out_tag_set:
        blk_mq_free_tag_set(md->tag_set);
out_kfree_tag_set:
        kfree(md->tag_set);

        return err;
}

void dm_mq_cleanup_mapped_device(struct mapped_device *md)
{
        if (md->tag_set) {
                blk_mq_free_tag_set(md->tag_set);
                kfree(md->tag_set);
        }
}

module_param(reserved_rq_based_ios, uint, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(reserved_rq_based_ios, "Reserved IOs in request-based mempools");

module_param(use_blk_mq, bool, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(use_blk_mq, "Use block multiqueue for request-based DM devices");

module_param(dm_mq_nr_hw_queues, uint, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(dm_mq_nr_hw_queues, "Number of hardware queues for request-based dm-mq devices");

module_param(dm_mq_queue_depth, uint, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(dm_mq_queue_depth, "Queue depth for request-based dm-mq devices");