// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2017 Red Hat. All rights reserved.
 *
 * This file is released under the GPL.
 */

#include "dm-cache-background-tracker.h"

/*----------------------------------------------------------------*/

#define DM_MSG_PREFIX "dm-background-tracker"

struct background_tracker {
        unsigned int max_work;
        atomic_t pending_promotes;
        atomic_t pending_writebacks;
        atomic_t pending_demotes;

        struct list_head issued;
        struct list_head queued;
        struct rb_root pending;
};

struct kmem_cache *btracker_work_cache = NULL;

struct background_tracker *btracker_create(unsigned int max_work)
{
        struct background_tracker *b = kmalloc_obj(*b);

        if (!b) {
                DMERR("couldn't create background_tracker");
                return NULL;
        }

        b->max_work = max_work;
        atomic_set(&b->pending_promotes, 0);
        atomic_set(&b->pending_writebacks, 0);
        atomic_set(&b->pending_demotes, 0);

        INIT_LIST_HEAD(&b->issued);
        INIT_LIST_HEAD(&b->queued);

        b->pending = RB_ROOT;

        return b;
}
EXPORT_SYMBOL_GPL(btracker_create);

void btracker_destroy(struct background_tracker *b)
{
        struct bt_work *w, *tmp;

        BUG_ON(!list_empty(&b->issued));
        list_for_each_entry_safe (w, tmp, &b->queued, list) {
                list_del(&w->list);
                kmem_cache_free(btracker_work_cache, w);
        }

        kfree(b);
}
EXPORT_SYMBOL_GPL(btracker_destroy);

static int cmp_oblock(dm_oblock_t lhs, dm_oblock_t rhs)
{
        if (from_oblock(lhs) < from_oblock(rhs))
                return -1;

        if (from_oblock(rhs) < from_oblock(lhs))
                return 1;

        return 0;
}

static bool __insert_pending(struct background_tracker *b,
                             struct bt_work *nw)
{
        int cmp;
        struct bt_work *w;
        struct rb_node **new = &b->pending.rb_node, *parent = NULL;

        while (*new) {
                w = container_of(*new, struct bt_work, node);

                parent = *new;
                cmp = cmp_oblock(w->work.oblock, nw->work.oblock);
                if (cmp < 0)
                        new = &((*new)->rb_left);

                else if (cmp > 0)
                        new = &((*new)->rb_right);

                else
                        /* already present */
                        return false;
        }

        rb_link_node(&nw->node, parent, new);
        rb_insert_color(&nw->node, &b->pending);

        return true;
}

static struct bt_work *__find_pending(struct background_tracker *b,
                                      dm_oblock_t oblock)
{
        int cmp;
        struct bt_work *w;
        struct rb_node **new = &b->pending.rb_node;

        while (*new) {
                w = container_of(*new, struct bt_work, node);

                cmp = cmp_oblock(w->work.oblock, oblock);
                if (cmp < 0)
                        new = &((*new)->rb_left);

                else if (cmp > 0)
                        new = &((*new)->rb_right);

                else
                        break;
        }

        return *new ? w : NULL;
}


static void update_stats(struct background_tracker *b, struct policy_work *w, int delta)
{
        switch (w->op) {
        case POLICY_PROMOTE:
                atomic_add(delta, &b->pending_promotes);
                break;

        case POLICY_DEMOTE:
                atomic_add(delta, &b->pending_demotes);
                break;

        case POLICY_WRITEBACK:
                atomic_add(delta, &b->pending_writebacks);
                break;
        }
}

unsigned int btracker_nr_demotions_queued(struct background_tracker *b)
{
        return atomic_read(&b->pending_demotes);
}
EXPORT_SYMBOL_GPL(btracker_nr_demotions_queued);

static bool max_work_reached(struct background_tracker *b)
{
        return atomic_read(&b->pending_promotes) +
                atomic_read(&b->pending_writebacks) +
                atomic_read(&b->pending_demotes) >= b->max_work;
}

static struct bt_work *alloc_work(struct background_tracker *b)
{
        if (max_work_reached(b))
                return NULL;

        return kmem_cache_alloc(btracker_work_cache, GFP_NOWAIT);
}

int btracker_queue(struct background_tracker *b,
                   struct policy_work *work,
                   struct policy_work **pwork)
{
        struct bt_work *w;

        if (pwork)
                *pwork = NULL;

        w = alloc_work(b);
        if (!w)
                return -ENOMEM;

        memcpy(&w->work, work, sizeof(*work));

        if (!__insert_pending(b, w)) {
                /*
                 * There was a race, we'll just ignore this second
                 * bit of work for the same oblock.
                 */
                kmem_cache_free(btracker_work_cache, w);
                return -EINVAL;
        }

        if (pwork) {
                *pwork = &w->work;
                list_add(&w->list, &b->issued);
        } else
                list_add(&w->list, &b->queued);
        update_stats(b, &w->work, 1);

        return 0;
}
EXPORT_SYMBOL_GPL(btracker_queue);

/*
 * Returns -ENODATA if there's no work.
 */
int btracker_issue(struct background_tracker *b, struct policy_work **work)
{
        struct bt_work *w;

        if (list_empty(&b->queued))
                return -ENODATA;

        w = list_first_entry(&b->queued, struct bt_work, list);
        list_move(&w->list, &b->issued);
        *work = &w->work;

        return 0;
}
EXPORT_SYMBOL_GPL(btracker_issue);

void btracker_complete(struct background_tracker *b,
                       struct policy_work *op)
{
        struct bt_work *w = container_of(op, struct bt_work, work);

        update_stats(b, &w->work, -1);
        rb_erase(&w->node, &b->pending);
        list_del(&w->list);
        kmem_cache_free(btracker_work_cache, w);
}
EXPORT_SYMBOL_GPL(btracker_complete);

bool btracker_promotion_already_present(struct background_tracker *b,
                                        dm_oblock_t oblock)
{
        return __find_pending(b, oblock) != NULL;
}
EXPORT_SYMBOL_GPL(btracker_promotion_already_present);

/*----------------------------------------------------------------*/