/*
 * Tag allocation using scalable bitmaps. Uses active queue tracking to support
 * fairer distribution of tags between multiple submitters when a shared tag map
 * is used.
 *
 * Copyright (C) 2013-2014 Jens Axboe
 */
#include <linux/kernel.h>
#include <linux/module.h>

#include <linux/blk-mq.h>
#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-tag.h"

bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
{
        if (!tags)
                return true;

        return sbitmap_any_bit_clear(&tags->bitmap_tags.sb);
}

/*
 * If a previously inactive queue goes active, bump the active user count.
 */
bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
{
        if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
            !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
                atomic_inc(&hctx->tags->active_queues);

        return true;
}

/*
 * Wakeup all potentially sleeping on tags
 */
void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)
{
        sbitmap_queue_wake_all(&tags->bitmap_tags);
        if (include_reserve)
                sbitmap_queue_wake_all(&tags->breserved_tags);
}

/*
 * If a previously busy queue goes inactive, potential waiters could now
 * be allowed to queue. Wake them up and check.
 */
void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
{
        struct blk_mq_tags *tags = hctx->tags;

        if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
                return;

        atomic_dec(&tags->active_queues);

        blk_mq_tag_wakeup_all(tags, false);
}

/*
 * For shared tag users, we track the number of currently active users
 * and attempt to provide a fair share of the tag depth for each of them.
 */
static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
                                  struct sbitmap_queue *bt)
{
        unsigned int depth, users;

        if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_SHARED))
                return true;
        if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
                return true;

        /*
         * Don't try dividing an ant
         */
        if (bt->sb.depth == 1)
                return true;

        users = atomic_read(&hctx->tags->active_queues);
        if (!users)
                return true;

        /*
         * Allow at least some tags
         */
        depth = max((bt->sb.depth + users - 1) / users, 4U);
        return atomic_read(&hctx->nr_active) < depth;
}

static int __bt_get(struct blk_mq_hw_ctx *hctx, struct sbitmap_queue *bt)
{
        if (!hctx_may_queue(hctx, bt))
                return -1;
        return __sbitmap_queue_get(bt);
}

static int bt_get(struct blk_mq_alloc_data *data, struct sbitmap_queue *bt,
                  struct blk_mq_hw_ctx *hctx, struct blk_mq_tags *tags)
{
        struct sbq_wait_state *ws;
        DEFINE_WAIT(wait);
        int tag;

        tag = __bt_get(hctx, bt);
        if (tag != -1)
                return tag;

        if (data->flags & BLK_MQ_REQ_NOWAIT)
                return -1;

        ws = bt_wait_ptr(bt, hctx);
        do {
                prepare_to_wait(&ws->wait, &wait, TASK_UNINTERRUPTIBLE);

                tag = __bt_get(hctx, bt);
                if (tag != -1)
                        break;

                /*
                 * We're out of tags on this hardware queue, kick any
                 * pending IO submits before going to sleep waiting for
                 * some to complete. Note that hctx can be NULL here for
                 * reserved tag allocation.
                 */
                if (hctx)
                        blk_mq_run_hw_queue(hctx, false);

                /*
                 * Retry tag allocation after running the hardware queue,
                 * as running the queue may also have found completions.
                 */
                tag = __bt_get(hctx, bt);
                if (tag != -1)
                        break;

                blk_mq_put_ctx(data->ctx);

                io_schedule();

                data->ctx = blk_mq_get_ctx(data->q);
                data->hctx = blk_mq_map_queue(data->q, data->ctx->cpu);
                if (data->flags & BLK_MQ_REQ_RESERVED) {
                        bt = &data->hctx->tags->breserved_tags;
                } else {
                        hctx = data->hctx;
                        bt = &hctx->tags->bitmap_tags;
                }
                finish_wait(&ws->wait, &wait);
                ws = bt_wait_ptr(bt, hctx);
        } while (1);

        finish_wait(&ws->wait, &wait);
        return tag;
}

static unsigned int __blk_mq_get_tag(struct blk_mq_alloc_data *data)
{
        int tag;

        tag = bt_get(data, &data->hctx->tags->bitmap_tags, data->hctx,
                     data->hctx->tags);
        if (tag >= 0)
                return tag + data->hctx->tags->nr_reserved_tags;

        return BLK_MQ_TAG_FAIL;
}

static unsigned int __blk_mq_get_reserved_tag(struct blk_mq_alloc_data *data)
{
        int tag;

        if (unlikely(!data->hctx->tags->nr_reserved_tags)) {
                WARN_ON_ONCE(1);
                return BLK_MQ_TAG_FAIL;
        }

        tag = bt_get(data, &data->hctx->tags->breserved_tags, NULL,
                     data->hctx->tags);
        if (tag < 0)
                return BLK_MQ_TAG_FAIL;

        return tag;
}

unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
{
        if (data->flags & BLK_MQ_REQ_RESERVED)
                return __blk_mq_get_reserved_tag(data);
        return __blk_mq_get_tag(data);
}

void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
                    unsigned int tag)
{
        struct blk_mq_tags *tags = hctx->tags;

        if (tag >= tags->nr_reserved_tags) {
                const int real_tag = tag - tags->nr_reserved_tags;

                BUG_ON(real_tag >= tags->nr_tags);
                sbitmap_queue_clear(&tags->bitmap_tags, real_tag, ctx->cpu);
        } else {
                BUG_ON(tag >= tags->nr_reserved_tags);
                sbitmap_queue_clear(&tags->breserved_tags, tag, ctx->cpu);
        }
}

struct bt_iter_data {
        struct blk_mq_hw_ctx *hctx;
        busy_iter_fn *fn;
        void *data;
        bool reserved;
};

static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
{
        struct bt_iter_data *iter_data = data;
        struct blk_mq_hw_ctx *hctx = iter_data->hctx;
        struct blk_mq_tags *tags = hctx->tags;
        bool reserved = iter_data->reserved;
        struct request *rq;

        if (!reserved)
                bitnr += tags->nr_reserved_tags;
        rq = tags->rqs[bitnr];

        if (rq->q == hctx->queue)
                iter_data->fn(hctx, rq, iter_data->data, reserved);
        return true;
}

static void bt_for_each(struct blk_mq_hw_ctx *hctx, struct sbitmap_queue *bt,
                        busy_iter_fn *fn, void *data, bool reserved)
{
        struct bt_iter_data iter_data = {
                .hctx = hctx,
                .fn = fn,
                .data = data,
                .reserved = reserved,
        };

        sbitmap_for_each_set(&bt->sb, bt_iter, &iter_data);
}

struct bt_tags_iter_data {
        struct blk_mq_tags *tags;
        busy_tag_iter_fn *fn;
        void *data;
        bool reserved;
};

static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
{
        struct bt_tags_iter_data *iter_data = data;
        struct blk_mq_tags *tags = iter_data->tags;
        bool reserved = iter_data->reserved;
        struct request *rq;

        if (!reserved)
                bitnr += tags->nr_reserved_tags;
        rq = tags->rqs[bitnr];

        iter_data->fn(rq, iter_data->data, reserved);
        return true;
}

static void bt_tags_for_each(struct blk_mq_tags *tags, struct sbitmap_queue *bt,
                             busy_tag_iter_fn *fn, void *data, bool reserved)
{
        struct bt_tags_iter_data iter_data = {
                .tags = tags,
                .fn = fn,
                .data = data,
                .reserved = reserved,
        };

        if (tags->rqs)
                sbitmap_for_each_set(&bt->sb, bt_tags_iter, &iter_data);
}

static void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags,
                busy_tag_iter_fn *fn, void *priv)
{
        if (tags->nr_reserved_tags)
                bt_tags_for_each(tags, &tags->breserved_tags, fn, priv, true);
        bt_tags_for_each(tags, &tags->bitmap_tags, fn, priv, false);
}

void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
                busy_tag_iter_fn *fn, void *priv)
{
        int i;

        for (i = 0; i < tagset->nr_hw_queues; i++) {
                if (tagset->tags && tagset->tags[i])
                        blk_mq_all_tag_busy_iter(tagset->tags[i], fn, priv);
        }
}
EXPORT_SYMBOL(blk_mq_tagset_busy_iter);

int blk_mq_reinit_tagset(struct blk_mq_tag_set *set)
{
        int i, j, ret = 0;

        if (!set->ops->reinit_request)
                goto out;

        for (i = 0; i < set->nr_hw_queues; i++) {
                struct blk_mq_tags *tags = set->tags[i];

                for (j = 0; j < tags->nr_tags; j++) {
                        if (!tags->rqs[j])
                                continue;

                        ret = set->ops->reinit_request(set->driver_data,
                                                tags->rqs[j]);
                        if (ret)
                                goto out;
                }
        }

out:
        return ret;
}
EXPORT_SYMBOL_GPL(blk_mq_reinit_tagset);

void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
                void *priv)
{
        struct blk_mq_hw_ctx *hctx;
        int i;


        queue_for_each_hw_ctx(q, hctx, i) {
                struct blk_mq_tags *tags = hctx->tags;

                /*
                 * If not software queues are currently mapped to this
                 * hardware queue, there's nothing to check
                 */
                if (!blk_mq_hw_queue_mapped(hctx))
                        continue;

                if (tags->nr_reserved_tags)
                        bt_for_each(hctx, &tags->breserved_tags, fn, priv, true);
                bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false);
        }

}

static unsigned int bt_unused_tags(const struct sbitmap_queue *bt)
{
        return bt->sb.depth - sbitmap_weight(&bt->sb);
}

static int bt_alloc(struct sbitmap_queue *bt, unsigned int depth,
                    bool round_robin, int node)
{
        return sbitmap_queue_init_node(bt, depth, -1, round_robin, GFP_KERNEL,
                                       node);
}

static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
                                                   int node, int alloc_policy)
{
        unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
        bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;

        if (bt_alloc(&tags->bitmap_tags, depth, round_robin, node))
                goto free_tags;
        if (bt_alloc(&tags->breserved_tags, tags->nr_reserved_tags, round_robin,
                     node))
                goto free_bitmap_tags;

        return tags;
free_bitmap_tags:
        sbitmap_queue_free(&tags->bitmap_tags);
free_tags:
        kfree(tags);
        return NULL;
}

struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
                                     unsigned int reserved_tags,
                                     int node, int alloc_policy)
{
        struct blk_mq_tags *tags;

        if (total_tags > BLK_MQ_TAG_MAX) {
                pr_err("blk-mq: tag depth too large\n");
                return NULL;
        }

        tags = kzalloc_node(sizeof(*tags), GFP_KERNEL, node);
        if (!tags)
                return NULL;

        tags->nr_tags = total_tags;
        tags->nr_reserved_tags = reserved_tags;

        return blk_mq_init_bitmap_tags(tags, node, alloc_policy);
}

void blk_mq_free_tags(struct blk_mq_tags *tags)
{
        sbitmap_queue_free(&tags->bitmap_tags);
        sbitmap_queue_free(&tags->breserved_tags);
        kfree(tags);
}

int blk_mq_tag_update_depth(struct blk_mq_tags *tags, unsigned int tdepth)
{
        tdepth -= tags->nr_reserved_tags;
        if (tdepth > tags->nr_tags)
                return -EINVAL;

        /*
         * Don't need (or can't) update reserved tags here, they remain
         * static and should never need resizing.
         */
        sbitmap_queue_resize(&tags->bitmap_tags, tdepth);

        blk_mq_tag_wakeup_all(tags, false);
        return 0;
}

/**
 * blk_mq_unique_tag() - return a tag that is unique queue-wide
 * @rq: request for which to compute a unique tag
 *
 * The tag field in struct request is unique per hardware queue but not over
 * all hardware queues. Hence this function that returns a tag with the
 * hardware context index in the upper bits and the per hardware queue tag in
 * the lower bits.
 *
 * Note: When called for a request that is queued on a non-multiqueue request
 * queue, the hardware context index is set to zero.
 */
u32 blk_mq_unique_tag(struct request *rq)
{
        struct request_queue *q = rq->q;
        struct blk_mq_hw_ctx *hctx;
        int hwq = 0;

        if (q->mq_ops) {
                hctx = blk_mq_map_queue(q, rq->mq_ctx->cpu);
                hwq = hctx->queue_num;
        }

        return (hwq << BLK_MQ_UNIQUE_TAG_BITS) |
                (rq->tag & BLK_MQ_UNIQUE_TAG_MASK);
}
EXPORT_SYMBOL(blk_mq_unique_tag);

ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page)
{
        char *orig_page = page;
        unsigned int free, res;

        if (!tags)
                return 0;

        page += sprintf(page, "nr_tags=%u, reserved_tags=%u, "
                        "bits_per_word=%u\n",
                        tags->nr_tags, tags->nr_reserved_tags,
                        1U << tags->bitmap_tags.sb.shift);

        free = bt_unused_tags(&tags->bitmap_tags);
        res = bt_unused_tags(&tags->breserved_tags);

        page += sprintf(page, "nr_free=%u, nr_reserved=%u\n", free, res);
        page += sprintf(page, "active_queues=%u\n", atomic_read(&tags->active_queues));

        return page - orig_page;
}