// SPDX-License-Identifier: GPL-2.0
/*
 * Main bcache entry point - handle a read or a write request and decide what to
 * do with it; the make_request functions are called by the block layer.
 *
 * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
 * Copyright 2012 Google, Inc.
 */

#include "bcache.h"
#include "btree.h"
#include "debug.h"
#include "request.h"
#include "writeback.h"

#include <linux/module.h>
#include <linux/hash.h>
#include <linux/random.h>
#include <linux/backing-dev.h>

#include <trace/events/bcache.h>

#define CUTOFF_CACHE_ADD        95
#define CUTOFF_CACHE_READA      90

struct kmem_cache *bch_search_cache;

static void bch_data_insert_start(struct closure *cl);

static unsigned int cache_mode(struct cached_dev *dc)
{
        return BDEV_CACHE_MODE(&dc->sb);
}

static bool verify(struct cached_dev *dc)
{
        return dc->verify;
}

static void bio_csum(struct bio *bio, struct bkey *k)
{
        struct bio_vec bv;
        struct bvec_iter iter;
        uint64_t csum = 0;

        bio_for_each_segment(bv, bio, iter) {
                void *d = kmap(bv.bv_page) + bv.bv_offset;

                csum = bch_crc64_update(csum, d, bv.bv_len);
                kunmap(bv.bv_page);
        }

        k->ptr[KEY_PTRS(k)] = csum & (~0ULL >> 1);
}

/* Insert data into cache */

static void bch_data_insert_keys(struct closure *cl)
{
        struct data_insert_op *op = container_of(cl, struct data_insert_op, cl);
        atomic_t *journal_ref = NULL;
        struct bkey *replace_key = op->replace ? &op->replace_key : NULL;
        int ret;

        if (!op->replace)
                journal_ref = bch_journal(op->c, &op->insert_keys,
                                          op->flush_journal ? cl : NULL);

        ret = bch_btree_insert(op->c, &op->insert_keys,
                               journal_ref, replace_key);
        if (ret == -ESRCH) {
                op->replace_collision = true;
        } else if (ret) {
                op->status              = BLK_STS_RESOURCE;
                op->insert_data_done    = true;
        }

        if (journal_ref)
                atomic_dec_bug(journal_ref);

        if (!op->insert_data_done) {
                continue_at(cl, bch_data_insert_start, op->wq);
                return;
        }

        bch_keylist_free(&op->insert_keys);
        closure_return(cl);
}

static int bch_keylist_realloc(struct keylist *l, unsigned int u64s,
                               struct cache_set *c)
{
        size_t oldsize = bch_keylist_nkeys(l);
        size_t newsize = oldsize + u64s;

        /*
         * The journalling code doesn't handle the case where the keys to insert
         * is bigger than an empty write: If we just return -ENOMEM here,
         * bch_data_insert_keys() will insert the keys created so far
         * and finish the rest when the keylist is empty.
         */
        if (newsize * sizeof(uint64_t) > block_bytes(c->cache) - sizeof(struct jset))
                return -ENOMEM;

        return __bch_keylist_realloc(l, u64s);
}

static void bch_data_invalidate(struct closure *cl)
{
        struct data_insert_op *op = container_of(cl, struct data_insert_op, cl);
        struct bio *bio = op->bio;

        pr_debug("invalidating %i sectors from %llu\n",
                 bio_sectors(bio), (uint64_t) bio->bi_iter.bi_sector);

        while (bio_sectors(bio)) {
                unsigned int sectors = min(bio_sectors(bio),
                                       1U << (KEY_SIZE_BITS - 1));

                if (bch_keylist_realloc(&op->insert_keys, 2, op->c))
                        goto out;

                bio->bi_iter.bi_sector  += sectors;
                bio->bi_iter.bi_size    -= sectors << 9;

                bch_keylist_add(&op->insert_keys,
                                &KEY(op->inode,
                                     bio->bi_iter.bi_sector,
                                     sectors));
        }

        op->insert_data_done = true;
        /* get in bch_data_insert() */
        bio_put(bio);
out:
        continue_at(cl, bch_data_insert_keys, op->wq);
}

static void bch_data_insert_error(struct closure *cl)
{
        struct data_insert_op *op = container_of(cl, struct data_insert_op, cl);

        /*
         * Our data write just errored, which means we've got a bunch of keys to
         * insert that point to data that wasn't successfully written.
         *
         * We don't have to insert those keys but we still have to invalidate
         * that region of the cache - so, if we just strip off all the pointers
         * from the keys we'll accomplish just that.
         */

        struct bkey *src = op->insert_keys.keys, *dst = op->insert_keys.keys;

        while (src != op->insert_keys.top) {
                struct bkey *n = bkey_next(src);

                SET_KEY_PTRS(src, 0);
                memmove(dst, src, bkey_bytes(src));

                dst = bkey_next(dst);
                src = n;
        }

        op->insert_keys.top = dst;

        bch_data_insert_keys(cl);
}

static void bch_data_insert_endio(struct bio *bio)
{
        struct closure *cl = bio->bi_private;
        struct data_insert_op *op = container_of(cl, struct data_insert_op, cl);

        if (bio->bi_status) {
                /* TODO: We could try to recover from this. */
                if (op->writeback)
                        op->status = bio->bi_status;
                else if (!op->replace)
                        set_closure_fn(cl, bch_data_insert_error, op->wq);
                else
                        set_closure_fn(cl, NULL, NULL);
        }

        bch_bbio_endio(op->c, bio, bio->bi_status, "writing data to cache");
}

static void bch_data_insert_start(struct closure *cl)
{
        struct data_insert_op *op = container_of(cl, struct data_insert_op, cl);
        struct bio *bio = op->bio, *n;

        if (op->bypass)
                return bch_data_invalidate(cl);

        if (atomic_sub_return(bio_sectors(bio), &op->c->sectors_to_gc) < 0)
                wake_up_gc(op->c);

        /*
         * Journal writes are marked REQ_PREFLUSH; if the original write was a
         * flush, it'll wait on the journal write.
         */
        bio->bi_opf &= ~(REQ_PREFLUSH|REQ_FUA);

        do {
                unsigned int i;
                struct bkey *k;
                struct bio_set *split = &op->c->bio_split;

                /* 1 for the device pointer and 1 for the chksum */
                if (bch_keylist_realloc(&op->insert_keys,
                                        3 + (op->csum ? 1 : 0),
                                        op->c)) {
                        continue_at(cl, bch_data_insert_keys, op->wq);
                        return;
                }

                k = op->insert_keys.top;
                bkey_init(k);
                SET_KEY_INODE(k, op->inode);
                SET_KEY_OFFSET(k, bio->bi_iter.bi_sector);

                if (!bch_alloc_sectors(op->c, k, bio_sectors(bio),
                                       op->write_point, op->write_prio,
                                       op->writeback))
                        goto err;

                n = bio_next_split(bio, KEY_SIZE(k), GFP_NOIO, split);

                n->bi_end_io    = bch_data_insert_endio;
                n->bi_private   = cl;

                if (op->writeback) {
                        SET_KEY_DIRTY(k, true);

                        for (i = 0; i < KEY_PTRS(k); i++)
                                SET_GC_MARK(PTR_BUCKET(op->c, k, i),
                                            GC_MARK_DIRTY);
                }

                SET_KEY_CSUM(k, op->csum);
                if (KEY_CSUM(k))
                        bio_csum(n, k);

                trace_bcache_cache_insert(k);
                bch_keylist_push(&op->insert_keys);

                bio_set_op_attrs(n, REQ_OP_WRITE, 0);
                bch_submit_bbio(n, op->c, k, 0);
        } while (n != bio);

        op->insert_data_done = true;
        continue_at(cl, bch_data_insert_keys, op->wq);
        return;
err:
        /* bch_alloc_sectors() blocks if s->writeback = true */
        BUG_ON(op->writeback);

        /*
         * But if it's not a writeback write we'd rather just bail out if
         * there aren't any buckets ready to write to - it might take awhile and
         * we might be starving btree writes for gc or something.
         */

        if (!op->replace) {
                /*
                 * Writethrough write: We can't complete the write until we've
                 * updated the index. But we don't want to delay the write while
                 * we wait for buckets to be freed up, so just invalidate the
                 * rest of the write.
                 */
                op->bypass = true;
                return bch_data_invalidate(cl);
        } else {
                /*
                 * From a cache miss, we can just insert the keys for the data
                 * we have written or bail out if we didn't do anything.
                 */
                op->insert_data_done = true;
                bio_put(bio);

                if (!bch_keylist_empty(&op->insert_keys))
                        continue_at(cl, bch_data_insert_keys, op->wq);
                else
                        closure_return(cl);
        }
}

/**
 * bch_data_insert - stick some data in the cache
 * @cl: closure pointer.
 *
 * This is the starting point for any data to end up in a cache device; it could
 * be from a normal write, or a writeback write, or a write to a flash only
 * volume - it's also used by the moving garbage collector to compact data in
 * mostly empty buckets.
 *
 * It first writes the data to the cache, creating a list of keys to be inserted
 * (if the data had to be fragmented there will be multiple keys); after the
 * data is written it calls bch_journal, and after the keys have been added to
 * the next journal write they're inserted into the btree.
 *
 * It inserts the data in op->bio; bi_sector is used for the key offset,
 * and op->inode is used for the key inode.
 *
 * If op->bypass is true, instead of inserting the data it invalidates the
 * region of the cache represented by op->bio and op->inode.
 */
void bch_data_insert(struct closure *cl)
{
        struct data_insert_op *op = container_of(cl, struct data_insert_op, cl);

        trace_bcache_write(op->c, op->inode, op->bio,
                           op->writeback, op->bypass);

        bch_keylist_init(&op->insert_keys);
        bio_get(op->bio);
        bch_data_insert_start(cl);
}

/*
 * Congested?  Return 0 (not congested) or the limit (in sectors)
 * beyond which we should bypass the cache due to congestion.
 */
unsigned int bch_get_congested(const struct cache_set *c)
{
        int i;

        if (!c->congested_read_threshold_us &&
            !c->congested_write_threshold_us)
                return 0;

        i = (local_clock_us() - c->congested_last_us) / 1024;
        if (i < 0)
                return 0;

        i += atomic_read(&c->congested);
        if (i >= 0)
                return 0;

        i += CONGESTED_MAX;

        if (i > 0)
                i = fract_exp_two(i, 6);

        i -= hweight32(get_random_u32());

        return i > 0 ? i : 1;
}

static void add_sequential(struct task_struct *t)
{
        ewma_add(t->sequential_io_avg,
                 t->sequential_io, 8, 0);

        t->sequential_io = 0;
}

static struct hlist_head *iohash(struct cached_dev *dc, uint64_t k)
{
        return &dc->io_hash[hash_64(k, RECENT_IO_BITS)];
}

static bool check_should_bypass(struct cached_dev *dc, struct bio *bio)
{
        struct cache_set *c = dc->disk.c;
        unsigned int mode = cache_mode(dc);
        unsigned int sectors, congested;
        struct task_struct *task = current;
        struct io *i;

        if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
            c->gc_stats.in_use > CUTOFF_CACHE_ADD ||
            (bio_op(bio) == REQ_OP_DISCARD))
                goto skip;

        if (mode == CACHE_MODE_NONE ||
            (mode == CACHE_MODE_WRITEAROUND &&
             op_is_write(bio_op(bio))))
                goto skip;

        /*
         * If the bio is for read-ahead or background IO, bypass it or
         * not depends on the following situations,
         * - If the IO is for meta data, always cache it and no bypass
         * - If the IO is not meta data, check dc->cache_reada_policy,
         *      BCH_CACHE_READA_ALL: cache it and not bypass
         *      BCH_CACHE_READA_META_ONLY: not cache it and bypass
         * That is, read-ahead request for metadata always get cached
         * (eg, for gfs2 or xfs).
         */
        if ((bio->bi_opf & (REQ_RAHEAD|REQ_BACKGROUND))) {
                if (!(bio->bi_opf & (REQ_META|REQ_PRIO)) &&
                    (dc->cache_readahead_policy != BCH_CACHE_READA_ALL))
                        goto skip;
        }

        if (bio->bi_iter.bi_sector & (c->cache->sb.block_size - 1) ||
            bio_sectors(bio) & (c->cache->sb.block_size - 1)) {
                pr_debug("skipping unaligned io\n");
                goto skip;
        }

        if (bypass_torture_test(dc)) {
                if ((get_random_int() & 3) == 3)
                        goto skip;
                else
                        goto rescale;
        }

        congested = bch_get_congested(c);
        if (!congested && !dc->sequential_cutoff)
                goto rescale;

        spin_lock(&dc->io_lock);

        hlist_for_each_entry(i, iohash(dc, bio->bi_iter.bi_sector), hash)
                if (i->last == bio->bi_iter.bi_sector &&
                    time_before(jiffies, i->jiffies))
                        goto found;

        i = list_first_entry(&dc->io_lru, struct io, lru);

        add_sequential(task);
        i->sequential = 0;
found:
        if (i->sequential + bio->bi_iter.bi_size > i->sequential)
                i->sequential   += bio->bi_iter.bi_size;

        i->last                  = bio_end_sector(bio);
        i->jiffies               = jiffies + msecs_to_jiffies(5000);
        task->sequential_io      = i->sequential;

        hlist_del(&i->hash);
        hlist_add_head(&i->hash, iohash(dc, i->last));
        list_move_tail(&i->lru, &dc->io_lru);

        spin_unlock(&dc->io_lock);

        sectors = max(task->sequential_io,
                      task->sequential_io_avg) >> 9;

        if (dc->sequential_cutoff &&
            sectors >= dc->sequential_cutoff >> 9) {
                trace_bcache_bypass_sequential(bio);
                goto skip;
        }

        if (congested && sectors >= congested) {
                trace_bcache_bypass_congested(bio);
                goto skip;
        }

rescale:
        bch_rescale_priorities(c, bio_sectors(bio));
        return false;
skip:
        bch_mark_sectors_bypassed(c, dc, bio_sectors(bio));
        return true;
}

/* Cache lookup */

struct search {
        /* Stack frame for bio_complete */
        struct closure          cl;

        struct bbio             bio;
        struct bio              *orig_bio;
        struct bio              *cache_miss;
        struct bcache_device    *d;

        unsigned int            insert_bio_sectors;
        unsigned int            recoverable:1;
        unsigned int            write:1;
        unsigned int            read_dirty_data:1;
        unsigned int            cache_missed:1;

        struct block_device     *orig_bdev;
        unsigned long           start_time;

        struct btree_op         op;
        struct data_insert_op   iop;
};

static void bch_cache_read_endio(struct bio *bio)
{
        struct bbio *b = container_of(bio, struct bbio, bio);
        struct closure *cl = bio->bi_private;
        struct search *s = container_of(cl, struct search, cl);

        /*
         * If the bucket was reused while our bio was in flight, we might have
         * read the wrong data. Set s->error but not error so it doesn't get
         * counted against the cache device, but we'll still reread the data
         * from the backing device.
         */

        if (bio->bi_status)
                s->iop.status = bio->bi_status;
        else if (!KEY_DIRTY(&b->key) &&
                 ptr_stale(s->iop.c, &b->key, 0)) {
                atomic_long_inc(&s->iop.c->cache_read_races);
                s->iop.status = BLK_STS_IOERR;
        }

        bch_bbio_endio(s->iop.c, bio, bio->bi_status, "reading from cache");
}

/*
 * Read from a single key, handling the initial cache miss if the key starts in
 * the middle of the bio
 */
static int cache_lookup_fn(struct btree_op *op, struct btree *b, struct bkey *k)
{
        struct search *s = container_of(op, struct search, op);
        struct bio *n, *bio = &s->bio.bio;
        struct bkey *bio_key;
        unsigned int ptr;

        if (bkey_cmp(k, &KEY(s->iop.inode, bio->bi_iter.bi_sector, 0)) <= 0)
                return MAP_CONTINUE;

        if (KEY_INODE(k) != s->iop.inode ||
            KEY_START(k) > bio->bi_iter.bi_sector) {
                unsigned int bio_sectors = bio_sectors(bio);
                unsigned int sectors = KEY_INODE(k) == s->iop.inode
                        ? min_t(uint64_t, INT_MAX,
                                KEY_START(k) - bio->bi_iter.bi_sector)
                        : INT_MAX;
                int ret = s->d->cache_miss(b, s, bio, sectors);

                if (ret != MAP_CONTINUE)
                        return ret;

                /* if this was a complete miss we shouldn't get here */
                BUG_ON(bio_sectors <= sectors);
        }

        if (!KEY_SIZE(k))
                return MAP_CONTINUE;

        /* XXX: figure out best pointer - for multiple cache devices */
        ptr = 0;

        PTR_BUCKET(b->c, k, ptr)->prio = INITIAL_PRIO;

        if (KEY_DIRTY(k))
                s->read_dirty_data = true;

        n = bio_next_split(bio, min_t(uint64_t, INT_MAX,
                                      KEY_OFFSET(k) - bio->bi_iter.bi_sector),
                           GFP_NOIO, &s->d->bio_split);

        bio_key = &container_of(n, struct bbio, bio)->key;
        bch_bkey_copy_single_ptr(bio_key, k, ptr);

        bch_cut_front(&KEY(s->iop.inode, n->bi_iter.bi_sector, 0), bio_key);
        bch_cut_back(&KEY(s->iop.inode, bio_end_sector(n), 0), bio_key);

        n->bi_end_io    = bch_cache_read_endio;
        n->bi_private   = &s->cl;

        /*
         * The bucket we're reading from might be reused while our bio
         * is in flight, and we could then end up reading the wrong
         * data.
         *
         * We guard against this by checking (in cache_read_endio()) if
         * the pointer is stale again; if so, we treat it as an error
         * and reread from the backing device (but we don't pass that
         * error up anywhere).
         */

        __bch_submit_bbio(n, b->c);
        return n == bio ? MAP_DONE : MAP_CONTINUE;
}

static void cache_lookup(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, iop.cl);
        struct bio *bio = &s->bio.bio;
        struct cached_dev *dc;
        int ret;

        bch_btree_op_init(&s->op, -1);

        ret = bch_btree_map_keys(&s->op, s->iop.c,
                                 &KEY(s->iop.inode, bio->bi_iter.bi_sector, 0),
                                 cache_lookup_fn, MAP_END_KEY);
        if (ret == -EAGAIN) {
                continue_at(cl, cache_lookup, bcache_wq);
                return;
        }

        /*
         * We might meet err when searching the btree, If that happens, we will
         * get negative ret, in this scenario we should not recover data from
         * backing device (when cache device is dirty) because we don't know
         * whether bkeys the read request covered are all clean.
         *
         * And after that happened, s->iop.status is still its initial value
         * before we submit s->bio.bio
         */
        if (ret < 0) {
                BUG_ON(ret == -EINTR);
                if (s->d && s->d->c &&
                                !UUID_FLASH_ONLY(&s->d->c->uuids[s->d->id])) {
                        dc = container_of(s->d, struct cached_dev, disk);
                        if (dc && atomic_read(&dc->has_dirty))
                                s->recoverable = false;
                }
                if (!s->iop.status)
                        s->iop.status = BLK_STS_IOERR;
        }

        closure_return(cl);
}

/* Common code for the make_request functions */

static void request_endio(struct bio *bio)
{
        struct closure *cl = bio->bi_private;

        if (bio->bi_status) {
                struct search *s = container_of(cl, struct search, cl);

                s->iop.status = bio->bi_status;
                /* Only cache read errors are recoverable */
                s->recoverable = false;
        }

        bio_put(bio);
        closure_put(cl);
}

static void backing_request_endio(struct bio *bio)
{
        struct closure *cl = bio->bi_private;

        if (bio->bi_status) {
                struct search *s = container_of(cl, struct search, cl);
                struct cached_dev *dc = container_of(s->d,
                                                     struct cached_dev, disk);
                /*
                 * If a bio has REQ_PREFLUSH for writeback mode, it is
                 * speically assembled in cached_dev_write() for a non-zero
                 * write request which has REQ_PREFLUSH. we don't set
                 * s->iop.status by this failure, the status will be decided
                 * by result of bch_data_insert() operation.
                 */
                if (unlikely(s->iop.writeback &&
                             bio->bi_opf & REQ_PREFLUSH)) {
                        pr_err("Can't flush %s: returned bi_status %i\n",
                                dc->backing_dev_name, bio->bi_status);
                } else {
                        /* set to orig_bio->bi_status in bio_complete() */
                        s->iop.status = bio->bi_status;
                }
                s->recoverable = false;
                /* should count I/O error for backing device here */
                bch_count_backing_io_errors(dc, bio);
        }

        bio_put(bio);
        closure_put(cl);
}

static void bio_complete(struct search *s)
{
        if (s->orig_bio) {
                /* Count on bcache device */
                bio_end_io_acct_remapped(s->orig_bio, s->start_time,
                                         s->orig_bdev);
                trace_bcache_request_end(s->d, s->orig_bio);
                s->orig_bio->bi_status = s->iop.status;
                bio_endio(s->orig_bio);
                s->orig_bio = NULL;
        }
}

static void do_bio_hook(struct search *s,
                        struct bio *orig_bio,
                        bio_end_io_t *end_io_fn)
{
        struct bio *bio = &s->bio.bio;

        bio_init(bio, NULL, 0);
        __bio_clone_fast(bio, orig_bio);
        /*
         * bi_end_io can be set separately somewhere else, e.g. the
         * variants in,
         * - cache_bio->bi_end_io from cached_dev_cache_miss()
         * - n->bi_end_io from cache_lookup_fn()
         */
        bio->bi_end_io          = end_io_fn;
        bio->bi_private         = &s->cl;

        bio_cnt_set(bio, 3);
}

static void search_free(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);

        atomic_dec(&s->iop.c->search_inflight);

        if (s->iop.bio)
                bio_put(s->iop.bio);

        bio_complete(s);
        closure_debug_destroy(cl);
        mempool_free(s, &s->iop.c->search);
}

static inline struct search *search_alloc(struct bio *bio,
                struct bcache_device *d, struct block_device *orig_bdev,
                unsigned long start_time)
{
        struct search *s;

        s = mempool_alloc(&d->c->search, GFP_NOIO);

        closure_init(&s->cl, NULL);
        do_bio_hook(s, bio, request_endio);
        atomic_inc(&d->c->search_inflight);

        s->orig_bio             = bio;
        s->cache_miss           = NULL;
        s->cache_missed         = 0;
        s->d                    = d;
        s->recoverable          = 1;
        s->write                = op_is_write(bio_op(bio));
        s->read_dirty_data      = 0;
        /* Count on the bcache device */
        s->orig_bdev            = orig_bdev;
        s->start_time           = start_time;
        s->iop.c                = d->c;
        s->iop.bio              = NULL;
        s->iop.inode            = d->id;
        s->iop.write_point      = hash_long((unsigned long) current, 16);
        s->iop.write_prio       = 0;
        s->iop.status           = 0;
        s->iop.flags            = 0;
        s->iop.flush_journal    = op_is_flush(bio->bi_opf);
        s->iop.wq               = bcache_wq;

        return s;
}

/* Cached devices */

static void cached_dev_bio_complete(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);
        struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);

        cached_dev_put(dc);
        search_free(cl);
}

/* Process reads */

static void cached_dev_read_error_done(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);

        if (s->iop.replace_collision)
                bch_mark_cache_miss_collision(s->iop.c, s->d);

        if (s->iop.bio)
                bio_free_pages(s->iop.bio);

        cached_dev_bio_complete(cl);
}

static void cached_dev_read_error(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);
        struct bio *bio = &s->bio.bio;

        /*
         * If read request hit dirty data (s->read_dirty_data is true),
         * then recovery a failed read request from cached device may
         * get a stale data back. So read failure recovery is only
         * permitted when read request hit clean data in cache device,
         * or when cache read race happened.
         */
        if (s->recoverable && !s->read_dirty_data) {
                /* Retry from the backing device: */
                trace_bcache_read_retry(s->orig_bio);

                s->iop.status = 0;
                do_bio_hook(s, s->orig_bio, backing_request_endio);

                /* XXX: invalidate cache */

                /* I/O request sent to backing device */
                closure_bio_submit(s->iop.c, bio, cl);
        }

        continue_at(cl, cached_dev_read_error_done, NULL);
}

static void cached_dev_cache_miss_done(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);
        struct bcache_device *d = s->d;

        if (s->iop.replace_collision)
                bch_mark_cache_miss_collision(s->iop.c, s->d);

        if (s->iop.bio)
                bio_free_pages(s->iop.bio);

        cached_dev_bio_complete(cl);
        closure_put(&d->cl);
}

static void cached_dev_read_done(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);
        struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);

        /*
         * We had a cache miss; cache_bio now contains data ready to be inserted
         * into the cache.
         *
         * First, we copy the data we just read from cache_bio's bounce buffers
         * to the buffers the original bio pointed to:
         */

        if (s->iop.bio) {
                bio_reset(s->iop.bio);
                s->iop.bio->bi_iter.bi_sector =
                        s->cache_miss->bi_iter.bi_sector;
                bio_copy_dev(s->iop.bio, s->cache_miss);
                s->iop.bio->bi_iter.bi_size = s->insert_bio_sectors << 9;
                bch_bio_map(s->iop.bio, NULL);

                bio_copy_data(s->cache_miss, s->iop.bio);

                bio_put(s->cache_miss);
                s->cache_miss = NULL;
        }

        if (verify(dc) && s->recoverable && !s->read_dirty_data)
                bch_data_verify(dc, s->orig_bio);

        closure_get(&dc->disk.cl);
        bio_complete(s);

        if (s->iop.bio &&
            !test_bit(CACHE_SET_STOPPING, &s->iop.c->flags)) {
                BUG_ON(!s->iop.replace);
                closure_call(&s->iop.cl, bch_data_insert, NULL, cl);
        }

        continue_at(cl, cached_dev_cache_miss_done, NULL);
}

static void cached_dev_read_done_bh(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);
        struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);

        bch_mark_cache_accounting(s->iop.c, s->d,
                                  !s->cache_missed, s->iop.bypass);
        trace_bcache_read(s->orig_bio, !s->cache_missed, s->iop.bypass);

        if (s->iop.status)
                continue_at_nobarrier(cl, cached_dev_read_error, bcache_wq);
        else if (s->iop.bio || verify(dc))
                continue_at_nobarrier(cl, cached_dev_read_done, bcache_wq);
        else
                continue_at_nobarrier(cl, cached_dev_bio_complete, NULL);
}

static int cached_dev_cache_miss(struct btree *b, struct search *s,
                                 struct bio *bio, unsigned int sectors)
{
        int ret = MAP_CONTINUE;
        struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
        struct bio *miss, *cache_bio;
        unsigned int size_limit;

        s->cache_missed = 1;

        if (s->cache_miss || s->iop.bypass) {
                miss = bio_next_split(bio, sectors, GFP_NOIO, &s->d->bio_split);
                ret = miss == bio ? MAP_DONE : MAP_CONTINUE;
                goto out_submit;
        }

        /* Limitation for valid replace key size and cache_bio bvecs number */
        size_limit = min_t(unsigned int, BIO_MAX_VECS * PAGE_SECTORS,
                           (1 << KEY_SIZE_BITS) - 1);
        s->insert_bio_sectors = min3(size_limit, sectors, bio_sectors(bio));

        s->iop.replace_key = KEY(s->iop.inode,
                                 bio->bi_iter.bi_sector + s->insert_bio_sectors,
                                 s->insert_bio_sectors);

        ret = bch_btree_insert_check_key(b, &s->op, &s->iop.replace_key);
        if (ret)
                return ret;

        s->iop.replace = true;

        miss = bio_next_split(bio, s->insert_bio_sectors, GFP_NOIO,
                              &s->d->bio_split);

        /* btree_search_recurse()'s btree iterator is no good anymore */
        ret = miss == bio ? MAP_DONE : -EINTR;

        cache_bio = bio_alloc_bioset(GFP_NOWAIT,
                        DIV_ROUND_UP(s->insert_bio_sectors, PAGE_SECTORS),
                        &dc->disk.bio_split);
        if (!cache_bio)
                goto out_submit;

        cache_bio->bi_iter.bi_sector    = miss->bi_iter.bi_sector;
        bio_copy_dev(cache_bio, miss);
        cache_bio->bi_iter.bi_size      = s->insert_bio_sectors << 9;

        cache_bio->bi_end_io    = backing_request_endio;
        cache_bio->bi_private   = &s->cl;

        bch_bio_map(cache_bio, NULL);
        if (bch_bio_alloc_pages(cache_bio, __GFP_NOWARN|GFP_NOIO))
                goto out_put;

        s->cache_miss   = miss;
        s->iop.bio      = cache_bio;
        bio_get(cache_bio);
        /* I/O request sent to backing device */
        closure_bio_submit(s->iop.c, cache_bio, &s->cl);

        return ret;
out_put:
        bio_put(cache_bio);
out_submit:
        miss->bi_end_io         = backing_request_endio;
        miss->bi_private        = &s->cl;
        /* I/O request sent to backing device */
        closure_bio_submit(s->iop.c, miss, &s->cl);
        return ret;
}

static void cached_dev_read(struct cached_dev *dc, struct search *s)
{
        struct closure *cl = &s->cl;

        closure_call(&s->iop.cl, cache_lookup, NULL, cl);
        continue_at(cl, cached_dev_read_done_bh, NULL);
}

/* Process writes */

static void cached_dev_write_complete(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);
        struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);

        up_read_non_owner(&dc->writeback_lock);
        cached_dev_bio_complete(cl);
}

static void cached_dev_write(struct cached_dev *dc, struct search *s)
{
        struct closure *cl = &s->cl;
        struct bio *bio = &s->bio.bio;
        struct bkey start = KEY(dc->disk.id, bio->bi_iter.bi_sector, 0);
        struct bkey end = KEY(dc->disk.id, bio_end_sector(bio), 0);

        bch_keybuf_check_overlapping(&s->iop.c->moving_gc_keys, &start, &end);

        down_read_non_owner(&dc->writeback_lock);
        if (bch_keybuf_check_overlapping(&dc->writeback_keys, &start, &end)) {
                /*
                 * We overlap with some dirty data undergoing background
                 * writeback, force this write to writeback
                 */
                s->iop.bypass = false;
                s->iop.writeback = true;
        }

        /*
         * Discards aren't _required_ to do anything, so skipping if
         * check_overlapping returned true is ok
         *
         * But check_overlapping drops dirty keys for which io hasn't started,
         * so we still want to call it.
         */
        if (bio_op(bio) == REQ_OP_DISCARD)
                s->iop.bypass = true;

        if (should_writeback(dc, s->orig_bio,
                             cache_mode(dc),
                             s->iop.bypass)) {

                s->iop.bypass = false;
                s->iop.writeback = true;
        }

        if (s->iop.bypass) {
                s->iop.bio = s->orig_bio;
                bio_get(s->iop.bio);

                if (bio_op(bio) == REQ_OP_DISCARD &&
                    !blk_queue_discard(bdev_get_queue(dc->bdev)))
                        goto insert_data;

                /* I/O request sent to backing device */
                bio->bi_end_io = backing_request_endio;
                closure_bio_submit(s->iop.c, bio, cl);

        } else if (s->iop.writeback) {
                bch_writeback_add(dc);
                s->iop.bio = bio;

                if (bio->bi_opf & REQ_PREFLUSH) {
                        /*
                         * Also need to send a flush to the backing
                         * device.
                         */
                        struct bio *flush;

                        flush = bio_alloc_bioset(GFP_NOIO, 0,
                                                 &dc->disk.bio_split);
                        if (!flush) {
                                s->iop.status = BLK_STS_RESOURCE;
                                goto insert_data;
                        }
                        bio_copy_dev(flush, bio);
                        flush->bi_end_io = backing_request_endio;
                        flush->bi_private = cl;
                        flush->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
                        /* I/O request sent to backing device */
                        closure_bio_submit(s->iop.c, flush, cl);
                }
        } else {
                s->iop.bio = bio_clone_fast(bio, GFP_NOIO, &dc->disk.bio_split);
                /* I/O request sent to backing device */
                bio->bi_end_io = backing_request_endio;
                closure_bio_submit(s->iop.c, bio, cl);
        }

insert_data:
        closure_call(&s->iop.cl, bch_data_insert, NULL, cl);
        continue_at(cl, cached_dev_write_complete, NULL);
}

static void cached_dev_nodata(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);
        struct bio *bio = &s->bio.bio;

        if (s->iop.flush_journal)
                bch_journal_meta(s->iop.c, cl);

        /* If it's a flush, we send the flush to the backing device too */
        bio->bi_end_io = backing_request_endio;
        closure_bio_submit(s->iop.c, bio, cl);

        continue_at(cl, cached_dev_bio_complete, NULL);
}

struct detached_dev_io_private {
        struct bcache_device    *d;
        unsigned long           start_time;
        bio_end_io_t            *bi_end_io;
        void                    *bi_private;
        struct block_device     *orig_bdev;
};

static void detached_dev_end_io(struct bio *bio)
{
        struct detached_dev_io_private *ddip;

        ddip = bio->bi_private;
        bio->bi_end_io = ddip->bi_end_io;
        bio->bi_private = ddip->bi_private;

        /* Count on the bcache device */
        bio_end_io_acct_remapped(bio, ddip->start_time, ddip->orig_bdev);

        if (bio->bi_status) {
                struct cached_dev *dc = container_of(ddip->d,
                                                     struct cached_dev, disk);
                /* should count I/O error for backing device here */
                bch_count_backing_io_errors(dc, bio);
        }

        kfree(ddip);
        bio->bi_end_io(bio);
}

static void detached_dev_do_request(struct bcache_device *d, struct bio *bio,
                struct block_device *orig_bdev, unsigned long start_time)
{
        struct detached_dev_io_private *ddip;
        struct cached_dev *dc = container_of(d, struct cached_dev, disk);

        /*
         * no need to call closure_get(&dc->disk.cl),
         * because upper layer had already opened bcache device,
         * which would call closure_get(&dc->disk.cl)
         */
        ddip = kzalloc(sizeof(struct detached_dev_io_private), GFP_NOIO);
        ddip->d = d;
        /* Count on the bcache device */
        ddip->orig_bdev = orig_bdev;
        ddip->start_time = start_time;
        ddip->bi_end_io = bio->bi_end_io;
        ddip->bi_private = bio->bi_private;
        bio->bi_end_io = detached_dev_end_io;
        bio->bi_private = ddip;

        if ((bio_op(bio) == REQ_OP_DISCARD) &&
            !blk_queue_discard(bdev_get_queue(dc->bdev)))
                bio->bi_end_io(bio);
        else
                submit_bio_noacct(bio);
}

static void quit_max_writeback_rate(struct cache_set *c,
                                    struct cached_dev *this_dc)
{
        int i;
        struct bcache_device *d;
        struct cached_dev *dc;

        /*
         * mutex bch_register_lock may compete with other parallel requesters,
         * or attach/detach operations on other backing device. Waiting to
         * the mutex lock may increase I/O request latency for seconds or more.
         * To avoid such situation, if mutext_trylock() failed, only writeback
         * rate of current cached device is set to 1, and __update_write_back()
         * will decide writeback rate of other cached devices (remember now
         * c->idle_counter is 0 already).
         */
        if (mutex_trylock(&bch_register_lock)) {
                for (i = 0; i < c->devices_max_used; i++) {
                        if (!c->devices[i])
                                continue;

                        if (UUID_FLASH_ONLY(&c->uuids[i]))
                                continue;

                        d = c->devices[i];
                        dc = container_of(d, struct cached_dev, disk);
                        /*
                         * set writeback rate to default minimum value,
                         * then let update_writeback_rate() to decide the
                         * upcoming rate.
                         */
                        atomic_long_set(&dc->writeback_rate.rate, 1);
                }
                mutex_unlock(&bch_register_lock);
        } else
                atomic_long_set(&this_dc->writeback_rate.rate, 1);
}

/* Cached devices - read & write stuff */

blk_qc_t cached_dev_submit_bio(struct bio *bio)
{
        struct search *s;
        struct block_device *orig_bdev = bio->bi_bdev;
        struct bcache_device *d = orig_bdev->bd_disk->private_data;
        struct cached_dev *dc = container_of(d, struct cached_dev, disk);
        unsigned long start_time;
        int rw = bio_data_dir(bio);

        if (unlikely((d->c && test_bit(CACHE_SET_IO_DISABLE, &d->c->flags)) ||
                     dc->io_disable)) {
                bio->bi_status = BLK_STS_IOERR;
                bio_endio(bio);
                return BLK_QC_T_NONE;
        }

        if (likely(d->c)) {
                if (atomic_read(&d->c->idle_counter))
                        atomic_set(&d->c->idle_counter, 0);
                /*
                 * If at_max_writeback_rate of cache set is true and new I/O
                 * comes, quit max writeback rate of all cached devices
                 * attached to this cache set, and set at_max_writeback_rate
                 * to false.
                 */
                if (unlikely(atomic_read(&d->c->at_max_writeback_rate) == 1)) {
                        atomic_set(&d->c->at_max_writeback_rate, 0);
                        quit_max_writeback_rate(d->c, dc);
                }
        }

        start_time = bio_start_io_acct(bio);

        bio_set_dev(bio, dc->bdev);
        bio->bi_iter.bi_sector += dc->sb.data_offset;

        if (cached_dev_get(dc)) {
                s = search_alloc(bio, d, orig_bdev, start_time);
                trace_bcache_request_start(s->d, bio);

                if (!bio->bi_iter.bi_size) {
                        /*
                         * can't call bch_journal_meta from under
                         * submit_bio_noacct
                         */
                        continue_at_nobarrier(&s->cl,
                                              cached_dev_nodata,
                                              bcache_wq);
                } else {
                        s->iop.bypass = check_should_bypass(dc, bio);

                        if (rw)
                                cached_dev_write(dc, s);
                        else
                                cached_dev_read(dc, s);
                }
        } else
                /* I/O request sent to backing device */
                detached_dev_do_request(d, bio, orig_bdev, start_time);

        return BLK_QC_T_NONE;
}

static int cached_dev_ioctl(struct bcache_device *d, fmode_t mode,
                            unsigned int cmd, unsigned long arg)
{
        struct cached_dev *dc = container_of(d, struct cached_dev, disk);

        if (dc->io_disable)
                return -EIO;
        if (!dc->bdev->bd_disk->fops->ioctl)
                return -ENOTTY;
        return dc->bdev->bd_disk->fops->ioctl(dc->bdev, mode, cmd, arg);
}

void bch_cached_dev_request_init(struct cached_dev *dc)
{
        dc->disk.cache_miss                     = cached_dev_cache_miss;
        dc->disk.ioctl                          = cached_dev_ioctl;
}

/* Flash backed devices */

static int flash_dev_cache_miss(struct btree *b, struct search *s,
                                struct bio *bio, unsigned int sectors)
{
        unsigned int bytes = min(sectors, bio_sectors(bio)) << 9;

        swap(bio->bi_iter.bi_size, bytes);
        zero_fill_bio(bio);
        swap(bio->bi_iter.bi_size, bytes);

        bio_advance(bio, bytes);

        if (!bio->bi_iter.bi_size)
                return MAP_DONE;

        return MAP_CONTINUE;
}

static void flash_dev_nodata(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);

        if (s->iop.flush_journal)
                bch_journal_meta(s->iop.c, cl);

        continue_at(cl, search_free, NULL);
}

blk_qc_t flash_dev_submit_bio(struct bio *bio)
{
        struct search *s;
        struct closure *cl;
        struct bcache_device *d = bio->bi_bdev->bd_disk->private_data;

        if (unlikely(d->c && test_bit(CACHE_SET_IO_DISABLE, &d->c->flags))) {
                bio->bi_status = BLK_STS_IOERR;
                bio_endio(bio);
                return BLK_QC_T_NONE;
        }

        s = search_alloc(bio, d, bio->bi_bdev, bio_start_io_acct(bio));
        cl = &s->cl;
        bio = &s->bio.bio;

        trace_bcache_request_start(s->d, bio);

        if (!bio->bi_iter.bi_size) {
                /*
                 * can't call bch_journal_meta from under submit_bio_noacct
                 */
                continue_at_nobarrier(&s->cl,
                                      flash_dev_nodata,
                                      bcache_wq);
                return BLK_QC_T_NONE;
        } else if (bio_data_dir(bio)) {
                bch_keybuf_check_overlapping(&s->iop.c->moving_gc_keys,
                                        &KEY(d->id, bio->bi_iter.bi_sector, 0),
                                        &KEY(d->id, bio_end_sector(bio), 0));

                s->iop.bypass           = (bio_op(bio) == REQ_OP_DISCARD) != 0;
                s->iop.writeback        = true;
                s->iop.bio              = bio;

                closure_call(&s->iop.cl, bch_data_insert, NULL, cl);
        } else {
                closure_call(&s->iop.cl, cache_lookup, NULL, cl);
        }

        continue_at(cl, search_free, NULL);
        return BLK_QC_T_NONE;
}

static int flash_dev_ioctl(struct bcache_device *d, fmode_t mode,
                           unsigned int cmd, unsigned long arg)
{
        return -ENOTTY;
}

void bch_flash_dev_request_init(struct bcache_device *d)
{
        d->cache_miss                           = flash_dev_cache_miss;
        d->ioctl                                = flash_dev_ioctl;
}

void bch_request_exit(void)
{
        kmem_cache_destroy(bch_search_cache);
}

int __init bch_request_init(void)
{
        bch_search_cache = KMEM_CACHE(search, 0);
        if (!bch_search_cache)
                return -ENOMEM;

        return 0;
}