// SPDX-License-Identifier: GPL-2.0
/*
 * bcache journalling code, for btree insertions
 *
 * Copyright 2012 Google, Inc.
 */

#include "bcache.h"
#include "btree.h"
#include "debug.h"
#include "extents.h"

#include <trace/events/bcache.h>

/*
 * Journal replay/recovery:
 *
 * This code is all driven from run_cache_set(); we first read the journal
 * entries, do some other stuff, then we mark all the keys in the journal
 * entries (same as garbage collection would), then we replay them - reinserting
 * them into the cache in precisely the same order as they appear in the
 * journal.
 *
 * We only journal keys that go in leaf nodes, which simplifies things quite a
 * bit.
 */

static void journal_read_endio(struct bio *bio)
{
        struct closure *cl = bio->bi_private;
        closure_put(cl);
}

static int journal_read_bucket(struct cache *ca, struct list_head *list,
                               unsigned bucket_index)
{
        struct journal_device *ja = &ca->journal;
        struct bio *bio = &ja->bio;

        struct journal_replay *i;
        struct jset *j, *data = ca->set->journal.w[0].data;
        struct closure cl;
        unsigned len, left, offset = 0;
        int ret = 0;
        sector_t bucket = bucket_to_sector(ca->set, ca->sb.d[bucket_index]);

        closure_init_stack(&cl);

        pr_debug("reading %u", bucket_index);

        while (offset < ca->sb.bucket_size) {
reread:         left = ca->sb.bucket_size - offset;
                len = min_t(unsigned, left, PAGE_SECTORS << JSET_BITS);

                bio_reset(bio);
                bio->bi_iter.bi_sector  = bucket + offset;
                bio_set_dev(bio, ca->bdev);
                bio->bi_iter.bi_size    = len << 9;

                bio->bi_end_io  = journal_read_endio;
                bio->bi_private = &cl;
                bio_set_op_attrs(bio, REQ_OP_READ, 0);
                bch_bio_map(bio, data);

                closure_bio_submit(ca->set, bio, &cl);
                closure_sync(&cl);

                /* This function could be simpler now since we no longer write
                 * journal entries that overlap bucket boundaries; this means
                 * the start of a bucket will always have a valid journal entry
                 * if it has any journal entries at all.
                 */

                j = data;
                while (len) {
                        struct list_head *where;
                        size_t blocks, bytes = set_bytes(j);

                        if (j->magic != jset_magic(&ca->sb)) {
                                pr_debug("%u: bad magic", bucket_index);
                                return ret;
                        }

                        if (bytes > left << 9 ||
                            bytes > PAGE_SIZE << JSET_BITS) {
                                pr_info("%u: too big, %zu bytes, offset %u",
                                        bucket_index, bytes, offset);
                                return ret;
                        }

                        if (bytes > len << 9)
                                goto reread;

                        if (j->csum != csum_set(j)) {
                                pr_info("%u: bad csum, %zu bytes, offset %u",
                                        bucket_index, bytes, offset);
                                return ret;
                        }

                        blocks = set_blocks(j, block_bytes(ca->set));

                        while (!list_empty(list)) {
                                i = list_first_entry(list,
                                        struct journal_replay, list);
                                if (i->j.seq >= j->last_seq)
                                        break;
                                list_del(&i->list);
                                kfree(i);
                        }

                        list_for_each_entry_reverse(i, list, list) {
                                if (j->seq == i->j.seq)
                                        goto next_set;

                                if (j->seq < i->j.last_seq)
                                        goto next_set;

                                if (j->seq > i->j.seq) {
                                        where = &i->list;
                                        goto add;
                                }
                        }

                        where = list;
add:
                        i = kmalloc(offsetof(struct journal_replay, j) +
                                    bytes, GFP_KERNEL);
                        if (!i)
                                return -ENOMEM;
                        memcpy(&i->j, j, bytes);
                        list_add(&i->list, where);
                        ret = 1;

                        ja->seq[bucket_index] = j->seq;
next_set:
                        offset  += blocks * ca->sb.block_size;
                        len     -= blocks * ca->sb.block_size;
                        j = ((void *) j) + blocks * block_bytes(ca);
                }
        }

        return ret;
}

int bch_journal_read(struct cache_set *c, struct list_head *list)
{
#define read_bucket(b)                                                  \
        ({                                                              \
                int ret = journal_read_bucket(ca, list, b);             \
                __set_bit(b, bitmap);                                   \
                if (ret < 0)                                            \
                        return ret;                                     \
                ret;                                                    \
        })

        struct cache *ca;
        unsigned iter;

        for_each_cache(ca, c, iter) {
                struct journal_device *ja = &ca->journal;
                DECLARE_BITMAP(bitmap, SB_JOURNAL_BUCKETS);
                unsigned i, l, r, m;
                uint64_t seq;

                bitmap_zero(bitmap, SB_JOURNAL_BUCKETS);
                pr_debug("%u journal buckets", ca->sb.njournal_buckets);

                /*
                 * Read journal buckets ordered by golden ratio hash to quickly
                 * find a sequence of buckets with valid journal entries
                 */
                for (i = 0; i < ca->sb.njournal_buckets; i++) {
                        /*
                         * We must try the index l with ZERO first for
                         * correctness due to the scenario that the journal
                         * bucket is circular buffer which might have wrapped
                         */
                        l = (i * 2654435769U) % ca->sb.njournal_buckets;

                        if (test_bit(l, bitmap))
                                break;

                        if (read_bucket(l))
                                goto bsearch;
                }

                /*
                 * If that fails, check all the buckets we haven't checked
                 * already
                 */
                pr_debug("falling back to linear search");

                for (l = find_first_zero_bit(bitmap, ca->sb.njournal_buckets);
                     l < ca->sb.njournal_buckets;
                     l = find_next_zero_bit(bitmap, ca->sb.njournal_buckets, l + 1))
                        if (read_bucket(l))
                                goto bsearch;

                /* no journal entries on this device? */
                if (l == ca->sb.njournal_buckets)
                        continue;
bsearch:
                BUG_ON(list_empty(list));

                /* Binary search */
                m = l;
                r = find_next_bit(bitmap, ca->sb.njournal_buckets, l + 1);
                pr_debug("starting binary search, l %u r %u", l, r);

                while (l + 1 < r) {
                        seq = list_entry(list->prev, struct journal_replay,
                                         list)->j.seq;

                        m = (l + r) >> 1;
                        read_bucket(m);

                        if (seq != list_entry(list->prev, struct journal_replay,
                                              list)->j.seq)
                                l = m;
                        else
                                r = m;
                }

                /*
                 * Read buckets in reverse order until we stop finding more
                 * journal entries
                 */
                pr_debug("finishing up: m %u njournal_buckets %u",
                         m, ca->sb.njournal_buckets);
                l = m;

                while (1) {
                        if (!l--)
                                l = ca->sb.njournal_buckets - 1;

                        if (l == m)
                                break;

                        if (test_bit(l, bitmap))
                                continue;

                        if (!read_bucket(l))
                                break;
                }

                seq = 0;

                for (i = 0; i < ca->sb.njournal_buckets; i++)
                        if (ja->seq[i] > seq) {
                                seq = ja->seq[i];
                                /*
                                 * When journal_reclaim() goes to allocate for
                                 * the first time, it'll use the bucket after
                                 * ja->cur_idx
                                 */
                                ja->cur_idx = i;
                                ja->last_idx = ja->discard_idx = (i + 1) %
                                        ca->sb.njournal_buckets;

                        }
        }

        if (!list_empty(list))
                c->journal.seq = list_entry(list->prev,
                                            struct journal_replay,
                                            list)->j.seq;

        return 0;
#undef read_bucket
}

void bch_journal_mark(struct cache_set *c, struct list_head *list)
{
        atomic_t p = { 0 };
        struct bkey *k;
        struct journal_replay *i;
        struct journal *j = &c->journal;
        uint64_t last = j->seq;

        /*
         * journal.pin should never fill up - we never write a journal
         * entry when it would fill up. But if for some reason it does, we
         * iterate over the list in reverse order so that we can just skip that
         * refcount instead of bugging.
         */

        list_for_each_entry_reverse(i, list, list) {
                BUG_ON(last < i->j.seq);
                i->pin = NULL;

                while (last-- != i->j.seq)
                        if (fifo_free(&j->pin) > 1) {
                                fifo_push_front(&j->pin, p);
                                atomic_set(&fifo_front(&j->pin), 0);
                        }

                if (fifo_free(&j->pin) > 1) {
                        fifo_push_front(&j->pin, p);
                        i->pin = &fifo_front(&j->pin);
                        atomic_set(i->pin, 1);
                }

                for (k = i->j.start;
                     k < bset_bkey_last(&i->j);
                     k = bkey_next(k))
                        if (!__bch_extent_invalid(c, k)) {
                                unsigned j;

                                for (j = 0; j < KEY_PTRS(k); j++)
                                        if (ptr_available(c, k, j))
                                                atomic_inc(&PTR_BUCKET(c, k, j)->pin);

                                bch_initial_mark_key(c, 0, k);
                        }
        }
}

int bch_journal_replay(struct cache_set *s, struct list_head *list)
{
        int ret = 0, keys = 0, entries = 0;
        struct bkey *k;
        struct journal_replay *i =
                list_entry(list->prev, struct journal_replay, list);

        uint64_t start = i->j.last_seq, end = i->j.seq, n = start;
        struct keylist keylist;

        list_for_each_entry(i, list, list) {
                BUG_ON(i->pin && atomic_read(i->pin) != 1);

                cache_set_err_on(n != i->j.seq, s,
"bcache: journal entries %llu-%llu missing! (replaying %llu-%llu)",
                                 n, i->j.seq - 1, start, end);

                for (k = i->j.start;
                     k < bset_bkey_last(&i->j);
                     k = bkey_next(k)) {
                        trace_bcache_journal_replay_key(k);

                        bch_keylist_init_single(&keylist, k);

                        ret = bch_btree_insert(s, &keylist, i->pin, NULL);
                        if (ret)
                                goto err;

                        BUG_ON(!bch_keylist_empty(&keylist));
                        keys++;

                        cond_resched();
                }

                if (i->pin)
                        atomic_dec(i->pin);
                n = i->j.seq + 1;
                entries++;
        }

        pr_info("journal replay done, %i keys in %i entries, seq %llu",
                keys, entries, end);
err:
        while (!list_empty(list)) {
                i = list_first_entry(list, struct journal_replay, list);
                list_del(&i->list);
                kfree(i);
        }

        return ret;
}

/* Journalling */
#define journal_max_cmp(l, r) \
        (fifo_idx(&c->journal.pin, btree_current_write(l)->journal) < \
         fifo_idx(&(c)->journal.pin, btree_current_write(r)->journal))
#define journal_min_cmp(l, r) \
        (fifo_idx(&c->journal.pin, btree_current_write(l)->journal) > \
         fifo_idx(&(c)->journal.pin, btree_current_write(r)->journal))

static void btree_flush_write(struct cache_set *c)
{
        /*
         * Try to find the btree node with that references the oldest journal
         * entry, best is our current candidate and is locked if non NULL:
         */
        struct btree *b;
        int i;

        atomic_long_inc(&c->flush_write);

retry:
        spin_lock(&c->journal.lock);
        if (heap_empty(&c->flush_btree)) {
                for_each_cached_btree(b, c, i)
                        if (btree_current_write(b)->journal) {
                                if (!heap_full(&c->flush_btree))
                                        heap_add(&c->flush_btree, b,
                                                 journal_max_cmp);
                                else if (journal_max_cmp(b,
                                         heap_peek(&c->flush_btree))) {
                                        c->flush_btree.data[0] = b;
                                        heap_sift(&c->flush_btree, 0,
                                                  journal_max_cmp);
                                }
                        }

                for (i = c->flush_btree.used / 2 - 1; i >= 0; --i)
                        heap_sift(&c->flush_btree, i, journal_min_cmp);
        }

        b = NULL;
        heap_pop(&c->flush_btree, b, journal_min_cmp);
        spin_unlock(&c->journal.lock);

        if (b) {
                mutex_lock(&b->write_lock);
                if (!btree_current_write(b)->journal) {
                        mutex_unlock(&b->write_lock);
                        /* We raced */
                        atomic_long_inc(&c->retry_flush_write);
                        goto retry;
                }

                __bch_btree_node_write(b, NULL);
                mutex_unlock(&b->write_lock);
        }
}

#define last_seq(j)     ((j)->seq - fifo_used(&(j)->pin) + 1)

static void journal_discard_endio(struct bio *bio)
{
        struct journal_device *ja =
                container_of(bio, struct journal_device, discard_bio);
        struct cache *ca = container_of(ja, struct cache, journal);

        atomic_set(&ja->discard_in_flight, DISCARD_DONE);

        closure_wake_up(&ca->set->journal.wait);
        closure_put(&ca->set->cl);
}

static void journal_discard_work(struct work_struct *work)
{
        struct journal_device *ja =
                container_of(work, struct journal_device, discard_work);

        submit_bio(&ja->discard_bio);
}

static void do_journal_discard(struct cache *ca)
{
        struct journal_device *ja = &ca->journal;
        struct bio *bio = &ja->discard_bio;

        if (!ca->discard) {
                ja->discard_idx = ja->last_idx;
                return;
        }

        switch (atomic_read(&ja->discard_in_flight)) {
        case DISCARD_IN_FLIGHT:
                return;

        case DISCARD_DONE:
                ja->discard_idx = (ja->discard_idx + 1) %
                        ca->sb.njournal_buckets;

                atomic_set(&ja->discard_in_flight, DISCARD_READY);
                /* fallthrough */

        case DISCARD_READY:
                if (ja->discard_idx == ja->last_idx)
                        return;

                atomic_set(&ja->discard_in_flight, DISCARD_IN_FLIGHT);

                bio_init(bio, bio->bi_inline_vecs, 1);
                bio_set_op_attrs(bio, REQ_OP_DISCARD, 0);
                bio->bi_iter.bi_sector  = bucket_to_sector(ca->set,
                                                ca->sb.d[ja->discard_idx]);
                bio_set_dev(bio, ca->bdev);
                bio->bi_iter.bi_size    = bucket_bytes(ca);
                bio->bi_end_io          = journal_discard_endio;

                closure_get(&ca->set->cl);
                INIT_WORK(&ja->discard_work, journal_discard_work);
                schedule_work(&ja->discard_work);
        }
}

static void journal_reclaim(struct cache_set *c)
{
        struct bkey *k = &c->journal.key;
        struct cache *ca;
        uint64_t last_seq;
        unsigned iter, n = 0;
        atomic_t p __maybe_unused;

        atomic_long_inc(&c->reclaim);

        while (!atomic_read(&fifo_front(&c->journal.pin)))
                fifo_pop(&c->journal.pin, p);

        last_seq = last_seq(&c->journal);

        /* Update last_idx */

        for_each_cache(ca, c, iter) {
                struct journal_device *ja = &ca->journal;

                while (ja->last_idx != ja->cur_idx &&
                       ja->seq[ja->last_idx] < last_seq)
                        ja->last_idx = (ja->last_idx + 1) %
                                ca->sb.njournal_buckets;
        }

        for_each_cache(ca, c, iter)
                do_journal_discard(ca);

        if (c->journal.blocks_free)
                goto out;

        /*
         * Allocate:
         * XXX: Sort by free journal space
         */

        for_each_cache(ca, c, iter) {
                struct journal_device *ja = &ca->journal;
                unsigned next = (ja->cur_idx + 1) % ca->sb.njournal_buckets;

                /* No space available on this device */
                if (next == ja->discard_idx)
                        continue;

                ja->cur_idx = next;
                k->ptr[n++] = MAKE_PTR(0,
                                  bucket_to_sector(c, ca->sb.d[ja->cur_idx]),
                                  ca->sb.nr_this_dev);
        }

        bkey_init(k);
        SET_KEY_PTRS(k, n);

        if (n)
                c->journal.blocks_free = c->sb.bucket_size >> c->block_bits;
out:
        if (!journal_full(&c->journal))
                __closure_wake_up(&c->journal.wait);
}

void bch_journal_next(struct journal *j)
{
        atomic_t p = { 1 };

        j->cur = (j->cur == j->w)
                ? &j->w[1]
                : &j->w[0];

        /*
         * The fifo_push() needs to happen at the same time as j->seq is
         * incremented for last_seq() to be calculated correctly
         */
        BUG_ON(!fifo_push(&j->pin, p));
        atomic_set(&fifo_back(&j->pin), 1);

        j->cur->data->seq       = ++j->seq;
        j->cur->dirty           = false;
        j->cur->need_write      = false;
        j->cur->data->keys      = 0;

        if (fifo_full(&j->pin))
                pr_debug("journal_pin full (%zu)", fifo_used(&j->pin));
}

static void journal_write_endio(struct bio *bio)
{
        struct journal_write *w = bio->bi_private;

        cache_set_err_on(bio->bi_status, w->c, "journal io error");
        closure_put(&w->c->journal.io);
}

static void journal_write(struct closure *);

static void journal_write_done(struct closure *cl)
{
        struct journal *j = container_of(cl, struct journal, io);
        struct journal_write *w = (j->cur == j->w)
                ? &j->w[1]
                : &j->w[0];

        __closure_wake_up(&w->wait);
        continue_at_nobarrier(cl, journal_write, system_wq);
}

static void journal_write_unlock(struct closure *cl)
        __releases(&c->journal.lock)
{
        struct cache_set *c = container_of(cl, struct cache_set, journal.io);

        c->journal.io_in_flight = 0;
        spin_unlock(&c->journal.lock);
}

static void journal_write_unlocked(struct closure *cl)
        __releases(c->journal.lock)
{
        struct cache_set *c = container_of(cl, struct cache_set, journal.io);
        struct cache *ca;
        struct journal_write *w = c->journal.cur;
        struct bkey *k = &c->journal.key;
        unsigned i, sectors = set_blocks(w->data, block_bytes(c)) *
                c->sb.block_size;

        struct bio *bio;
        struct bio_list list;
        bio_list_init(&list);

        if (!w->need_write) {
                closure_return_with_destructor(cl, journal_write_unlock);
                return;
        } else if (journal_full(&c->journal)) {
                journal_reclaim(c);
                spin_unlock(&c->journal.lock);

                btree_flush_write(c);
                continue_at(cl, journal_write, system_wq);
                return;
        }

        c->journal.blocks_free -= set_blocks(w->data, block_bytes(c));

        w->data->btree_level = c->root->level;

        bkey_copy(&w->data->btree_root, &c->root->key);
        bkey_copy(&w->data->uuid_bucket, &c->uuid_bucket);

        for_each_cache(ca, c, i)
                w->data->prio_bucket[ca->sb.nr_this_dev] = ca->prio_buckets[0];

        w->data->magic          = jset_magic(&c->sb);
        w->data->version        = BCACHE_JSET_VERSION;
        w->data->last_seq       = last_seq(&c->journal);
        w->data->csum           = csum_set(w->data);

        for (i = 0; i < KEY_PTRS(k); i++) {
                ca = PTR_CACHE(c, k, i);
                bio = &ca->journal.bio;

                atomic_long_add(sectors, &ca->meta_sectors_written);

                bio_reset(bio);
                bio->bi_iter.bi_sector  = PTR_OFFSET(k, i);
                bio_set_dev(bio, ca->bdev);
                bio->bi_iter.bi_size = sectors << 9;

                bio->bi_end_io  = journal_write_endio;
                bio->bi_private = w;
                bio_set_op_attrs(bio, REQ_OP_WRITE,
                                 REQ_SYNC|REQ_META|REQ_PREFLUSH|REQ_FUA);
                bch_bio_map(bio, w->data);

                trace_bcache_journal_write(bio);
                bio_list_add(&list, bio);

                SET_PTR_OFFSET(k, i, PTR_OFFSET(k, i) + sectors);

                ca->journal.seq[ca->journal.cur_idx] = w->data->seq;
        }

        atomic_dec_bug(&fifo_back(&c->journal.pin));
        bch_journal_next(&c->journal);
        journal_reclaim(c);

        spin_unlock(&c->journal.lock);

        while ((bio = bio_list_pop(&list)))
                closure_bio_submit(c, bio, cl);

        continue_at(cl, journal_write_done, NULL);
}

static void journal_write(struct closure *cl)
{
        struct cache_set *c = container_of(cl, struct cache_set, journal.io);

        spin_lock(&c->journal.lock);
        journal_write_unlocked(cl);
}

static void journal_try_write(struct cache_set *c)
        __releases(c->journal.lock)
{
        struct closure *cl = &c->journal.io;
        struct journal_write *w = c->journal.cur;

        w->need_write = true;

        if (!c->journal.io_in_flight) {
                c->journal.io_in_flight = 1;
                closure_call(cl, journal_write_unlocked, NULL, &c->cl);
        } else {
                spin_unlock(&c->journal.lock);
        }
}

static struct journal_write *journal_wait_for_write(struct cache_set *c,
                                                    unsigned nkeys)
        __acquires(&c->journal.lock)
{
        size_t sectors;
        struct closure cl;
        bool wait = false;

        closure_init_stack(&cl);

        spin_lock(&c->journal.lock);

        while (1) {
                struct journal_write *w = c->journal.cur;

                sectors = __set_blocks(w->data, w->data->keys + nkeys,
                                       block_bytes(c)) * c->sb.block_size;

                if (sectors <= min_t(size_t,
                                     c->journal.blocks_free * c->sb.block_size,
                                     PAGE_SECTORS << JSET_BITS))
                        return w;

                if (wait)
                        closure_wait(&c->journal.wait, &cl);

                if (!journal_full(&c->journal)) {
                        if (wait)
                                trace_bcache_journal_entry_full(c);

                        /*
                         * XXX: If we were inserting so many keys that they
                         * won't fit in an _empty_ journal write, we'll
                         * deadlock. For now, handle this in
                         * bch_keylist_realloc() - but something to think about.
                         */
                        BUG_ON(!w->data->keys);

                        journal_try_write(c); /* unlocks */
                } else {
                        if (wait)
                                trace_bcache_journal_full(c);

                        journal_reclaim(c);
                        spin_unlock(&c->journal.lock);

                        btree_flush_write(c);
                }

                closure_sync(&cl);
                spin_lock(&c->journal.lock);
                wait = true;
        }
}

static void journal_write_work(struct work_struct *work)
{
        struct cache_set *c = container_of(to_delayed_work(work),
                                           struct cache_set,
                                           journal.work);
        spin_lock(&c->journal.lock);
        if (c->journal.cur->dirty)
                journal_try_write(c);
        else
                spin_unlock(&c->journal.lock);
}

/*
 * Entry point to the journalling code - bio_insert() and btree_invalidate()
 * pass bch_journal() a list of keys to be journalled, and then
 * bch_journal() hands those same keys off to btree_insert_async()
 */

atomic_t *bch_journal(struct cache_set *c,
                      struct keylist *keys,
                      struct closure *parent)
{
        struct journal_write *w;
        atomic_t *ret;

        if (!CACHE_SYNC(&c->sb))
                return NULL;

        w = journal_wait_for_write(c, bch_keylist_nkeys(keys));

        memcpy(bset_bkey_last(w->data), keys->keys, bch_keylist_bytes(keys));
        w->data->keys += bch_keylist_nkeys(keys);

        ret = &fifo_back(&c->journal.pin);
        atomic_inc(ret);

        if (parent) {
                closure_wait(&w->wait, parent);
                journal_try_write(c);
        } else if (!w->dirty) {
                w->dirty = true;
                schedule_delayed_work(&c->journal.work,
                                      msecs_to_jiffies(c->journal_delay_ms));
                spin_unlock(&c->journal.lock);
        } else {
                spin_unlock(&c->journal.lock);
        }


        return ret;
}

void bch_journal_meta(struct cache_set *c, struct closure *cl)
{
        struct keylist keys;
        atomic_t *ref;

        bch_keylist_init(&keys);

        ref = bch_journal(c, &keys, cl);
        if (ref)
                atomic_dec_bug(ref);
}

void bch_journal_free(struct cache_set *c)
{
        free_pages((unsigned long) c->journal.w[1].data, JSET_BITS);
        free_pages((unsigned long) c->journal.w[0].data, JSET_BITS);
        free_fifo(&c->journal.pin);
}

int bch_journal_alloc(struct cache_set *c)
{
        struct journal *j = &c->journal;

        spin_lock_init(&j->lock);
        INIT_DELAYED_WORK(&j->work, journal_write_work);

        c->journal_delay_ms = 100;

        j->w[0].c = c;
        j->w[1].c = c;

        if (!(init_heap(&c->flush_btree, 128, GFP_KERNEL)) ||
            !(init_fifo(&j->pin, JOURNAL_PIN, GFP_KERNEL)) ||
            !(j->w[0].data = (void *) __get_free_pages(GFP_KERNEL, JSET_BITS)) ||
            !(j->w[1].data = (void *) __get_free_pages(GFP_KERNEL, JSET_BITS)))
                return -ENOMEM;

        return 0;
}