/*
 * Copyright (C) 2016 Facebook
 * Copyright (C) 2013-2014 Jens Axboe
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <linux/random.h>
#include <linux/sbitmap.h>

int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
                      gfp_t flags, int node)
{
        unsigned int bits_per_word;
        unsigned int i;

        if (shift < 0) {
                shift = ilog2(BITS_PER_LONG);
                /*
                 * If the bitmap is small, shrink the number of bits per word so
                 * we spread over a few cachelines, at least. If less than 4
                 * bits, just forget about it, it's not going to work optimally
                 * anyway.
                 */
                if (depth >= 4) {
                        while ((4U << shift) > depth)
                                shift--;
                }
        }
        bits_per_word = 1U << shift;
        if (bits_per_word > BITS_PER_LONG)
                return -EINVAL;

        sb->shift = shift;
        sb->depth = depth;
        sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);

        if (depth == 0) {
                sb->map = NULL;
                return 0;
        }

        sb->map = kzalloc_node(sb->map_nr * sizeof(*sb->map), flags, node);
        if (!sb->map)
                return -ENOMEM;

        for (i = 0; i < sb->map_nr; i++) {
                sb->map[i].depth = min(depth, bits_per_word);
                depth -= sb->map[i].depth;
        }
        return 0;
}
EXPORT_SYMBOL_GPL(sbitmap_init_node);

void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
{
        unsigned int bits_per_word = 1U << sb->shift;
        unsigned int i;

        sb->depth = depth;
        sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);

        for (i = 0; i < sb->map_nr; i++) {
                sb->map[i].depth = min(depth, bits_per_word);
                depth -= sb->map[i].depth;
        }
}
EXPORT_SYMBOL_GPL(sbitmap_resize);

static int __sbitmap_get_word(struct sbitmap_word *word, unsigned int hint,
                              bool wrap)
{
        unsigned int orig_hint = hint;
        int nr;

        while (1) {
                nr = find_next_zero_bit(&word->word, word->depth, hint);
                if (unlikely(nr >= word->depth)) {
                        /*
                         * We started with an offset, and we didn't reset the
                         * offset to 0 in a failure case, so start from 0 to
                         * exhaust the map.
                         */
                        if (orig_hint && hint && wrap) {
                                hint = orig_hint = 0;
                                continue;
                        }
                        return -1;
                }

                if (!test_and_set_bit(nr, &word->word))
                        break;

                hint = nr + 1;
                if (hint >= word->depth - 1)
                        hint = 0;
        }

        return nr;
}

int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
{
        unsigned int i, index;
        int nr = -1;

        index = SB_NR_TO_INDEX(sb, alloc_hint);

        for (i = 0; i < sb->map_nr; i++) {
                nr = __sbitmap_get_word(&sb->map[index],
                                        SB_NR_TO_BIT(sb, alloc_hint),
                                        !round_robin);
                if (nr != -1) {
                        nr += index << sb->shift;
                        break;
                }

                /* Jump to next index. */
                index++;
                alloc_hint = index << sb->shift;

                if (index >= sb->map_nr) {
                        index = 0;
                        alloc_hint = 0;
                }
        }

        return nr;
}
EXPORT_SYMBOL_GPL(sbitmap_get);

bool sbitmap_any_bit_set(const struct sbitmap *sb)
{
        unsigned int i;

        for (i = 0; i < sb->map_nr; i++) {
                if (sb->map[i].word)
                        return true;
        }
        return false;
}
EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);

bool sbitmap_any_bit_clear(const struct sbitmap *sb)
{
        unsigned int i;

        for (i = 0; i < sb->map_nr; i++) {
                const struct sbitmap_word *word = &sb->map[i];
                unsigned long ret;

                ret = find_first_zero_bit(&word->word, word->depth);
                if (ret < word->depth)
                        return true;
        }
        return false;
}
EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);

unsigned int sbitmap_weight(const struct sbitmap *sb)
{
        unsigned int i, weight = 0;

        for (i = 0; i < sb->map_nr; i++) {
                const struct sbitmap_word *word = &sb->map[i];

                weight += bitmap_weight(&word->word, word->depth);
        }
        return weight;
}
EXPORT_SYMBOL_GPL(sbitmap_weight);

static unsigned int sbq_calc_wake_batch(unsigned int depth)
{
        unsigned int wake_batch;

        /*
         * For each batch, we wake up one queue. We need to make sure that our
         * batch size is small enough that the full depth of the bitmap is
         * enough to wake up all of the queues.
         */
        wake_batch = SBQ_WAKE_BATCH;
        if (wake_batch > depth / SBQ_WAIT_QUEUES)
                wake_batch = max(1U, depth / SBQ_WAIT_QUEUES);

        return wake_batch;
}

int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
                            int shift, bool round_robin, gfp_t flags, int node)
{
        int ret;
        int i;

        ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
        if (ret)
                return ret;

        sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
        if (!sbq->alloc_hint) {
                sbitmap_free(&sbq->sb);
                return -ENOMEM;
        }

        if (depth && !round_robin) {
                for_each_possible_cpu(i)
                        *per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
        }

        sbq->wake_batch = sbq_calc_wake_batch(depth);
        atomic_set(&sbq->wake_index, 0);

        sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
        if (!sbq->ws) {
                free_percpu(sbq->alloc_hint);
                sbitmap_free(&sbq->sb);
                return -ENOMEM;
        }

        for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
                init_waitqueue_head(&sbq->ws[i].wait);
                atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
        }

        sbq->round_robin = round_robin;
        return 0;
}
EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);

void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
{
        sbq->wake_batch = sbq_calc_wake_batch(depth);
        sbitmap_resize(&sbq->sb, depth);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_resize);

int __sbitmap_queue_get(struct sbitmap_queue *sbq)
{
        unsigned int hint, depth;
        int nr;

        hint = this_cpu_read(*sbq->alloc_hint);
        depth = READ_ONCE(sbq->sb.depth);
        if (unlikely(hint >= depth)) {
                hint = depth ? prandom_u32() % depth : 0;
                this_cpu_write(*sbq->alloc_hint, hint);
        }
        nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);

        if (nr == -1) {
                /* If the map is full, a hint won't do us much good. */
                this_cpu_write(*sbq->alloc_hint, 0);
        } else if (nr == hint || unlikely(sbq->round_robin)) {
                /* Only update the hint if we used it. */
                hint = nr + 1;
                if (hint >= depth - 1)
                        hint = 0;
                this_cpu_write(*sbq->alloc_hint, hint);
        }

        return nr;
}
EXPORT_SYMBOL_GPL(__sbitmap_queue_get);

static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
{
        int i, wake_index;

        wake_index = atomic_read(&sbq->wake_index);
        for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
                struct sbq_wait_state *ws = &sbq->ws[wake_index];

                if (waitqueue_active(&ws->wait)) {
                        int o = atomic_read(&sbq->wake_index);

                        if (wake_index != o)
                                atomic_cmpxchg(&sbq->wake_index, o, wake_index);
                        return ws;
                }

                wake_index = sbq_index_inc(wake_index);
        }

        return NULL;
}

static void sbq_wake_up(struct sbitmap_queue *sbq)
{
        struct sbq_wait_state *ws;
        int wait_cnt;

        /* Ensure that the wait list checks occur after clear_bit(). */
        smp_mb();

        ws = sbq_wake_ptr(sbq);
        if (!ws)
                return;

        wait_cnt = atomic_dec_return(&ws->wait_cnt);
        if (unlikely(wait_cnt < 0))
                wait_cnt = atomic_inc_return(&ws->wait_cnt);
        if (wait_cnt == 0) {
                atomic_add(sbq->wake_batch, &ws->wait_cnt);
                sbq_index_atomic_inc(&sbq->wake_index);
                wake_up(&ws->wait);
        }
}

void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
                         unsigned int cpu)
{
        sbitmap_clear_bit(&sbq->sb, nr);
        sbq_wake_up(sbq);
        if (likely(!sbq->round_robin && nr < sbq->sb.depth))
                *per_cpu_ptr(sbq->alloc_hint, cpu) = nr;
}
EXPORT_SYMBOL_GPL(sbitmap_queue_clear);

void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
{
        int i, wake_index;

        /*
         * Make sure all changes prior to this are visible from other CPUs.
         */
        smp_mb();
        wake_index = atomic_read(&sbq->wake_index);
        for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
                struct sbq_wait_state *ws = &sbq->ws[wake_index];

                if (waitqueue_active(&ws->wait))
                        wake_up(&ws->wait);

                wake_index = sbq_index_inc(wake_index);
        }
}
EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);