/*
 * blk-mq scheduling framework
 *
 * Copyright (C) 2016 Jens Axboe
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/blk-mq.h>

#include <trace/events/block.h>

#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-debugfs.h"
#include "blk-mq-sched.h"
#include "blk-mq-tag.h"
#include "blk-wbt.h"

void blk_mq_sched_free_hctx_data(struct request_queue *q,
                                 void (*exit)(struct blk_mq_hw_ctx *))
{
        struct blk_mq_hw_ctx *hctx;
        int i;

        queue_for_each_hw_ctx(q, hctx, i) {
                if (exit && hctx->sched_data)
                        exit(hctx);
                kfree(hctx->sched_data);
                hctx->sched_data = NULL;
        }
}
EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);

void blk_mq_sched_assign_ioc(struct request *rq, struct bio *bio)
{
        struct request_queue *q = rq->q;
        struct io_context *ioc = rq_ioc(bio);
        struct io_cq *icq;

        spin_lock_irq(q->queue_lock);
        icq = ioc_lookup_icq(ioc, q);
        spin_unlock_irq(q->queue_lock);

        if (!icq) {
                icq = ioc_create_icq(ioc, q, GFP_ATOMIC);
                if (!icq)
                        return;
        }
        get_io_context(icq->ioc);
        rq->elv.icq = icq;
}

/*
 * Mark a hardware queue as needing a restart. For shared queues, maintain
 * a count of how many hardware queues are marked for restart.
 */
static void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
{
        if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
                return;

        if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
                struct request_queue *q = hctx->queue;

                if (!test_and_set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
                        atomic_inc(&q->shared_hctx_restart);
        } else
                set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
}

static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx)
{
        if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
                return false;

        if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
                struct request_queue *q = hctx->queue;

                if (test_and_clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
                        atomic_dec(&q->shared_hctx_restart);
        } else
                clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);

        return blk_mq_run_hw_queue(hctx, true);
}

/*
 * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
 * its queue by itself in its completion handler, so we don't need to
 * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
 */
static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
{
        struct request_queue *q = hctx->queue;
        struct elevator_queue *e = q->elevator;
        LIST_HEAD(rq_list);

        do {
                struct request *rq;

                if (e->type->ops.mq.has_work &&
                                !e->type->ops.mq.has_work(hctx))
                        break;

                if (!blk_mq_get_dispatch_budget(hctx))
                        break;

                rq = e->type->ops.mq.dispatch_request(hctx);
                if (!rq) {
                        blk_mq_put_dispatch_budget(hctx);
                        break;
                }

                /*
                 * Now this rq owns the budget which has to be released
                 * if this rq won't be queued to driver via .queue_rq()
                 * in blk_mq_dispatch_rq_list().
                 */
                list_add(&rq->queuelist, &rq_list);
        } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
}

static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
                                          struct blk_mq_ctx *ctx)
{
        unsigned idx = ctx->index_hw;

        if (++idx == hctx->nr_ctx)
                idx = 0;

        return hctx->ctxs[idx];
}

/*
 * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
 * its queue by itself in its completion handler, so we don't need to
 * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
 */
static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
{
        struct request_queue *q = hctx->queue;
        LIST_HEAD(rq_list);
        struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);

        do {
                struct request *rq;

                if (!sbitmap_any_bit_set(&hctx->ctx_map))
                        break;

                if (!blk_mq_get_dispatch_budget(hctx))
                        break;

                rq = blk_mq_dequeue_from_ctx(hctx, ctx);
                if (!rq) {
                        blk_mq_put_dispatch_budget(hctx);
                        break;
                }

                /*
                 * Now this rq owns the budget which has to be released
                 * if this rq won't be queued to driver via .queue_rq()
                 * in blk_mq_dispatch_rq_list().
                 */
                list_add(&rq->queuelist, &rq_list);

                /* round robin for fair dispatch */
                ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);

        } while (blk_mq_dispatch_rq_list(q, &rq_list, true));

        WRITE_ONCE(hctx->dispatch_from, ctx);
}

void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
{
        struct request_queue *q = hctx->queue;
        struct elevator_queue *e = q->elevator;
        const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request;
        LIST_HEAD(rq_list);

        /* RCU or SRCU read lock is needed before checking quiesced flag */
        if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
                return;

        hctx->run++;

        /*
         * If we have previous entries on our dispatch list, grab them first for
         * more fair dispatch.
         */
        if (!list_empty_careful(&hctx->dispatch)) {
                spin_lock(&hctx->lock);
                if (!list_empty(&hctx->dispatch))
                        list_splice_init(&hctx->dispatch, &rq_list);
                spin_unlock(&hctx->lock);
        }

        /*
         * Only ask the scheduler for requests, if we didn't have residual
         * requests from the dispatch list. This is to avoid the case where
         * we only ever dispatch a fraction of the requests available because
         * of low device queue depth. Once we pull requests out of the IO
         * scheduler, we can no longer merge or sort them. So it's best to
         * leave them there for as long as we can. Mark the hw queue as
         * needing a restart in that case.
         *
         * We want to dispatch from the scheduler if there was nothing
         * on the dispatch list or we were able to dispatch from the
         * dispatch list.
         */
        if (!list_empty(&rq_list)) {
                blk_mq_sched_mark_restart_hctx(hctx);
                if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
                        if (has_sched_dispatch)
                                blk_mq_do_dispatch_sched(hctx);
                        else
                                blk_mq_do_dispatch_ctx(hctx);
                }
        } else if (has_sched_dispatch) {
                blk_mq_do_dispatch_sched(hctx);
        } else if (q->mq_ops->get_budget) {
                /*
                 * If we need to get budget before queuing request, we
                 * dequeue request one by one from sw queue for avoiding
                 * to mess up I/O merge when dispatch runs out of resource.
                 *
                 * TODO: get more budgets, and dequeue more requests in
                 * one time.
                 */
                blk_mq_do_dispatch_ctx(hctx);
        } else {
                blk_mq_flush_busy_ctxs(hctx, &rq_list);
                blk_mq_dispatch_rq_list(q, &rq_list, false);
        }
}

bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
                            struct request **merged_request)
{
        struct request *rq;

        switch (elv_merge(q, &rq, bio)) {
        case ELEVATOR_BACK_MERGE:
                if (!blk_mq_sched_allow_merge(q, rq, bio))
                        return false;
                if (!bio_attempt_back_merge(q, rq, bio))
                        return false;
                *merged_request = attempt_back_merge(q, rq);
                if (!*merged_request)
                        elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
                return true;
        case ELEVATOR_FRONT_MERGE:
                if (!blk_mq_sched_allow_merge(q, rq, bio))
                        return false;
                if (!bio_attempt_front_merge(q, rq, bio))
                        return false;
                *merged_request = attempt_front_merge(q, rq);
                if (!*merged_request)
                        elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
                return true;
        case ELEVATOR_DISCARD_MERGE:
                return bio_attempt_discard_merge(q, rq, bio);
        default:
                return false;
        }
}
EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);

/*
 * Reverse check our software queue for entries that we could potentially
 * merge with. Currently includes a hand-wavy stop count of 8, to not spend
 * too much time checking for merges.
 */
static bool blk_mq_attempt_merge(struct request_queue *q,
                                 struct blk_mq_ctx *ctx, struct bio *bio)
{
        struct request *rq;
        int checked = 8;

        lockdep_assert_held(&ctx->lock);

        list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
                bool merged = false;

                if (!checked--)
                        break;

                if (!blk_rq_merge_ok(rq, bio))
                        continue;

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

                if (merged)
                        ctx->rq_merged++;
                return merged;
        }

        return false;
}

bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
{
        struct elevator_queue *e = q->elevator;
        struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
        struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
        bool ret = false;

        if (e && e->type->ops.mq.bio_merge) {
                blk_mq_put_ctx(ctx);
                return e->type->ops.mq.bio_merge(hctx, bio);
        }

        if (hctx->flags & BLK_MQ_F_SHOULD_MERGE) {
                /* default per sw-queue merge */
                spin_lock(&ctx->lock);
                ret = blk_mq_attempt_merge(q, ctx, bio);
                spin_unlock(&ctx->lock);
        }

        blk_mq_put_ctx(ctx);
        return ret;
}

bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
{
        return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
}
EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);

void blk_mq_sched_request_inserted(struct request *rq)
{
        trace_block_rq_insert(rq->q, rq);
}
EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);

static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
                                       bool has_sched,
                                       struct request *rq)
{
        /* dispatch flush rq directly */
        if (rq->rq_flags & RQF_FLUSH_SEQ) {
                spin_lock(&hctx->lock);
                list_add(&rq->queuelist, &hctx->dispatch);
                spin_unlock(&hctx->lock);
                return true;
        }

        if (has_sched)
                rq->rq_flags |= RQF_SORTED;

        return false;
}

/**
 * list_for_each_entry_rcu_rr - iterate in a round-robin fashion over rcu list
 * @pos:    loop cursor.
 * @skip:   the list element that will not be examined. Iteration starts at
 *          @skip->next.
 * @head:   head of the list to examine. This list must have at least one
 *          element, namely @skip.
 * @member: name of the list_head structure within typeof(*pos).
 */
#define list_for_each_entry_rcu_rr(pos, skip, head, member)             \
        for ((pos) = (skip);                                            \
             (pos = (pos)->member.next != (head) ? list_entry_rcu(      \
                        (pos)->member.next, typeof(*pos), member) :     \
              list_entry_rcu((pos)->member.next->next, typeof(*pos), member)), \
             (pos) != (skip); )

/*
 * Called after a driver tag has been freed to check whether a hctx needs to
 * be restarted. Restarts @hctx if its tag set is not shared. Restarts hardware
 * queues in a round-robin fashion if the tag set of @hctx is shared with other
 * hardware queues.
 */
void blk_mq_sched_restart(struct blk_mq_hw_ctx *const hctx)
{
        struct blk_mq_tags *const tags = hctx->tags;
        struct blk_mq_tag_set *const set = hctx->queue->tag_set;
        struct request_queue *const queue = hctx->queue, *q;
        struct blk_mq_hw_ctx *hctx2;
        unsigned int i, j;

        if (set->flags & BLK_MQ_F_TAG_SHARED) {
                /*
                 * If this is 0, then we know that no hardware queues
                 * have RESTART marked. We're done.
                 */
                if (!atomic_read(&queue->shared_hctx_restart))
                        return;

                rcu_read_lock();
                list_for_each_entry_rcu_rr(q, queue, &set->tag_list,
                                           tag_set_list) {
                        queue_for_each_hw_ctx(q, hctx2, i)
                                if (hctx2->tags == tags &&
                                    blk_mq_sched_restart_hctx(hctx2))
                                        goto done;
                }
                j = hctx->queue_num + 1;
                for (i = 0; i < queue->nr_hw_queues; i++, j++) {
                        if (j == queue->nr_hw_queues)
                                j = 0;
                        hctx2 = queue->queue_hw_ctx[j];
                        if (hctx2->tags == tags &&
                            blk_mq_sched_restart_hctx(hctx2))
                                break;
                }
done:
                rcu_read_unlock();
        } else {
                blk_mq_sched_restart_hctx(hctx);
        }
}

void blk_mq_sched_insert_request(struct request *rq, bool at_head,
                                 bool run_queue, bool async)
{
        struct request_queue *q = rq->q;
        struct elevator_queue *e = q->elevator;
        struct blk_mq_ctx *ctx = rq->mq_ctx;
        struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);

        /* flush rq in flush machinery need to be dispatched directly */
        if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
                blk_insert_flush(rq);
                goto run;
        }

        WARN_ON(e && (rq->tag != -1));

        if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
                goto run;

        if (e && e->type->ops.mq.insert_requests) {
                LIST_HEAD(list);

                list_add(&rq->queuelist, &list);
                e->type->ops.mq.insert_requests(hctx, &list, at_head);
        } else {
                spin_lock(&ctx->lock);
                __blk_mq_insert_request(hctx, rq, at_head);
                spin_unlock(&ctx->lock);
        }

run:
        if (run_queue)
                blk_mq_run_hw_queue(hctx, async);
}

void blk_mq_sched_insert_requests(struct request_queue *q,
                                  struct blk_mq_ctx *ctx,
                                  struct list_head *list, bool run_queue_async)
{
        struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
        struct elevator_queue *e = hctx->queue->elevator;

        if (e && e->type->ops.mq.insert_requests)
                e->type->ops.mq.insert_requests(hctx, list, false);
        else
                blk_mq_insert_requests(hctx, ctx, list);

        blk_mq_run_hw_queue(hctx, run_queue_async);
}

static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
                                   struct blk_mq_hw_ctx *hctx,
                                   unsigned int hctx_idx)
{
        if (hctx->sched_tags) {
                blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
                blk_mq_free_rq_map(hctx->sched_tags);
                hctx->sched_tags = NULL;
        }
}

static int blk_mq_sched_alloc_tags(struct request_queue *q,
                                   struct blk_mq_hw_ctx *hctx,
                                   unsigned int hctx_idx)
{
        struct blk_mq_tag_set *set = q->tag_set;
        int ret;

        hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
                                               set->reserved_tags);
        if (!hctx->sched_tags)
                return -ENOMEM;

        ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
        if (ret)
                blk_mq_sched_free_tags(set, hctx, hctx_idx);

        return ret;
}

static void blk_mq_sched_tags_teardown(struct request_queue *q)
{
        struct blk_mq_tag_set *set = q->tag_set;
        struct blk_mq_hw_ctx *hctx;
        int i;

        queue_for_each_hw_ctx(q, hctx, i)
                blk_mq_sched_free_tags(set, hctx, i);
}

int blk_mq_sched_init_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
                           unsigned int hctx_idx)
{
        struct elevator_queue *e = q->elevator;
        int ret;

        if (!e)
                return 0;

        ret = blk_mq_sched_alloc_tags(q, hctx, hctx_idx);
        if (ret)
                return ret;

        if (e->type->ops.mq.init_hctx) {
                ret = e->type->ops.mq.init_hctx(hctx, hctx_idx);
                if (ret) {
                        blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
                        return ret;
                }
        }

        blk_mq_debugfs_register_sched_hctx(q, hctx);

        return 0;
}

void blk_mq_sched_exit_hctx(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
                            unsigned int hctx_idx)
{
        struct elevator_queue *e = q->elevator;

        if (!e)
                return;

        blk_mq_debugfs_unregister_sched_hctx(hctx);

        if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
                e->type->ops.mq.exit_hctx(hctx, hctx_idx);
                hctx->sched_data = NULL;
        }

        blk_mq_sched_free_tags(q->tag_set, hctx, hctx_idx);
}

int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
{
        struct blk_mq_hw_ctx *hctx;
        struct elevator_queue *eq;
        unsigned int i;
        int ret;

        if (!e) {
                q->elevator = NULL;
                return 0;
        }

        /*
         * Default to double of smaller one between hw queue_depth and 128,
         * since we don't split into sync/async like the old code did.
         * Additionally, this is a per-hw queue depth.
         */
        q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
                                   BLKDEV_MAX_RQ);

        queue_for_each_hw_ctx(q, hctx, i) {
                ret = blk_mq_sched_alloc_tags(q, hctx, i);
                if (ret)
                        goto err;
        }

        ret = e->ops.mq.init_sched(q, e);
        if (ret)
                goto err;

        blk_mq_debugfs_register_sched(q);

        queue_for_each_hw_ctx(q, hctx, i) {
                if (e->ops.mq.init_hctx) {
                        ret = e->ops.mq.init_hctx(hctx, i);
                        if (ret) {
                                eq = q->elevator;
                                blk_mq_exit_sched(q, eq);
                                kobject_put(&eq->kobj);
                                return ret;
                        }
                }
                blk_mq_debugfs_register_sched_hctx(q, hctx);
        }

        return 0;

err:
        blk_mq_sched_tags_teardown(q);
        q->elevator = NULL;
        return ret;
}

void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
{
        struct blk_mq_hw_ctx *hctx;
        unsigned int i;

        queue_for_each_hw_ctx(q, hctx, i) {
                blk_mq_debugfs_unregister_sched_hctx(hctx);
                if (e->type->ops.mq.exit_hctx && hctx->sched_data) {
                        e->type->ops.mq.exit_hctx(hctx, i);
                        hctx->sched_data = NULL;
                }
        }
        blk_mq_debugfs_unregister_sched(q);
        if (e->type->ops.mq.exit_sched)
                e->type->ops.mq.exit_sched(e);
        blk_mq_sched_tags_teardown(q);
        q->elevator = NULL;
}

int blk_mq_sched_init(struct request_queue *q)
{
        int ret;

        mutex_lock(&q->sysfs_lock);
        ret = elevator_init(q, NULL);
        mutex_unlock(&q->sysfs_lock);

        return ret;
}