/*
 * 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-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);

int blk_mq_sched_init_hctx_data(struct request_queue *q, size_t size,
                                int (*init)(struct blk_mq_hw_ctx *),
                                void (*exit)(struct blk_mq_hw_ctx *))
{
        struct blk_mq_hw_ctx *hctx;
        int ret;
        int i;

        queue_for_each_hw_ctx(q, hctx, i) {
                hctx->sched_data = kmalloc_node(size, GFP_KERNEL, hctx->numa_node);
                if (!hctx->sched_data) {
                        ret = -ENOMEM;
                        goto error;
                }

                if (init) {
                        ret = init(hctx);
                        if (ret) {
                                /*
                                 * We don't want to give exit() a partially
                                 * initialized sched_data. init() must clean up
                                 * if it fails.
                                 */
                                kfree(hctx->sched_data);
                                hctx->sched_data = NULL;
                                goto error;
                        }
                }
        }

        return 0;
error:
        blk_mq_sched_free_hctx_data(q, exit);
        return ret;
}
EXPORT_SYMBOL_GPL(blk_mq_sched_init_hctx_data);

static void __blk_mq_sched_assign_ioc(struct request_queue *q,
                                      struct request *rq,
                                      struct bio *bio,
                                      struct io_context *ioc)
{
        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;
        }

        rq->elv.icq = icq;
        if (!blk_mq_sched_get_rq_priv(q, rq, bio)) {
                rq->rq_flags |= RQF_ELVPRIV;
                get_io_context(icq->ioc);
                return;
        }

        rq->elv.icq = NULL;
}

static void blk_mq_sched_assign_ioc(struct request_queue *q,
                                    struct request *rq, struct bio *bio)
{
        struct io_context *ioc;

        ioc = rq_ioc(bio);
        if (ioc)
                __blk_mq_sched_assign_ioc(q, rq, bio, ioc);
}

struct request *blk_mq_sched_get_request(struct request_queue *q,
                                         struct bio *bio,
                                         unsigned int op,
                                         struct blk_mq_alloc_data *data)
{
        struct elevator_queue *e = q->elevator;
        struct request *rq;

        blk_queue_enter_live(q);
        data->q = q;
        if (likely(!data->ctx))
                data->ctx = blk_mq_get_ctx(q);
        if (likely(!data->hctx))
                data->hctx = blk_mq_map_queue(q, data->ctx->cpu);

        if (e) {
                data->flags |= BLK_MQ_REQ_INTERNAL;

                /*
                 * Flush requests are special and go directly to the
                 * dispatch list.
                 */
                if (!op_is_flush(op) && e->type->ops.mq.get_request) {
                        rq = e->type->ops.mq.get_request(q, op, data);
                        if (rq)
                                rq->rq_flags |= RQF_QUEUED;
                } else
                        rq = __blk_mq_alloc_request(data, op);
        } else {
                rq = __blk_mq_alloc_request(data, op);
        }

        if (rq) {
                if (!op_is_flush(op)) {
                        rq->elv.icq = NULL;
                        if (e && e->type->icq_cache)
                                blk_mq_sched_assign_ioc(q, rq, bio);
                }
                data->hctx->queued++;
                return rq;
        }

        blk_queue_exit(q);
        return NULL;
}

void blk_mq_sched_put_request(struct request *rq)
{
        struct request_queue *q = rq->q;
        struct elevator_queue *e = q->elevator;

        if (rq->rq_flags & RQF_ELVPRIV) {
                blk_mq_sched_put_rq_priv(rq->q, rq);
                if (rq->elv.icq) {
                        put_io_context(rq->elv.icq->ioc);
                        rq->elv.icq = NULL;
                }
        }

        if ((rq->rq_flags & RQF_QUEUED) && e && e->type->ops.mq.put_request)
                e->type->ops.mq.put_request(rq);
        else
                blk_mq_finish_request(rq);
}

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;
        bool did_work = false;
        LIST_HEAD(rq_list);

        if (unlikely(blk_mq_hctx_stopped(hctx)))
                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.
         */
        if (!list_empty(&rq_list)) {
                blk_mq_sched_mark_restart_hctx(hctx);
                did_work = blk_mq_dispatch_rq_list(q, &rq_list);
        } else if (!has_sched_dispatch) {
                blk_mq_flush_busy_ctxs(hctx, &rq_list);
                blk_mq_dispatch_rq_list(q, &rq_list);
        }

        /*
         * We want to dispatch from the scheduler if we had no work left
         * on the dispatch list, OR if we did have work but weren't able
         * to make progress.
         */
        if (!did_work && has_sched_dispatch) {
                do {
                        struct request *rq;

                        rq = e->type->ops.mq.dispatch_request(hctx);
                        if (!rq)
                                break;
                        list_add(&rq->queuelist, &rq_list);
                } while (blk_mq_dispatch_rq_list(q, &rq_list));
        }
}

void blk_mq_sched_move_to_dispatch(struct blk_mq_hw_ctx *hctx,
                                   struct list_head *rq_list,
                                   struct request *(*get_rq)(struct blk_mq_hw_ctx *))
{
        do {
                struct request *rq;

                rq = get_rq(hctx);
                if (!rq)
                        break;

                list_add_tail(&rq->queuelist, rq_list);
        } while (1);
}
EXPORT_SYMBOL_GPL(blk_mq_sched_move_to_dispatch);

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;
        default:
                return false;
        }
}
EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);

bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
{
        struct elevator_queue *e = q->elevator;

        if (e->type->ops.mq.bio_merge) {
                struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
                struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);

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

        return false;
}

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,
                                       struct request *rq)
{
        if (rq->tag == -1) {
                rq->rq_flags |= RQF_SORTED;
                return false;
        }

        /*
         * If we already have a real request tag, send directly to
         * the dispatch list.
         */
        spin_lock(&hctx->lock);
        list_add(&rq->queuelist, &hctx->dispatch);
        spin_unlock(&hctx->lock);
        return true;
}

static bool blk_mq_sched_restart_hctx(struct blk_mq_hw_ctx *hctx)
{
        if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state)) {
                clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
                if (blk_mq_hctx_has_pending(hctx)) {
                        blk_mq_run_hw_queue(hctx, true);
                        return true;
                }
        }
        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) {
                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);
        }
}

/*
 * Add flush/fua to the queue. If we fail getting a driver tag, then
 * punt to the requeue list. Requeue will re-invoke us from a context
 * that's safe to block from.
 */
static void blk_mq_sched_insert_flush(struct blk_mq_hw_ctx *hctx,
                                      struct request *rq, bool can_block)
{
        if (blk_mq_get_driver_tag(rq, &hctx, can_block)) {
                blk_insert_flush(rq);
                blk_mq_run_hw_queue(hctx, true);
        } else
                blk_mq_add_to_requeue_list(rq, false, true);
}

void blk_mq_sched_insert_request(struct request *rq, bool at_head,
                                 bool run_queue, bool async, bool can_block)
{
        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);

        if (rq->tag == -1 && op_is_flush(rq->cmd_flags)) {
                blk_mq_sched_insert_flush(hctx, rq, can_block);
                return;
        }

        if (e && blk_mq_sched_bypass_insert(hctx, 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) {
                struct request *rq, *next;

                /*
                 * We bypass requests that already have a driver tag assigned,
                 * which should only be flushes. Flushes are only ever inserted
                 * as single requests, so we shouldn't ever hit the
                 * WARN_ON_ONCE() below (but let's handle it just in case).
                 */
                list_for_each_entry_safe(rq, next, list, queuelist) {
                        if (WARN_ON_ONCE(rq->tag != -1)) {
                                list_del_init(&rq->queuelist);
                                blk_mq_sched_bypass_insert(hctx, rq);
                        }
                }
        }

        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;

        if (!e)
                return 0;

        return blk_mq_sched_alloc_tags(q, hctx, hctx_idx);
}

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_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;
        unsigned int i;
        int ret;

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

        /*
         * Default to 256, 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 * 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;

        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)
{
        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;
}