/*
 * 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/cgroup.h>
#include <linux/module.h>
#include <linux/hash.h>
#include <linux/random.h>
#include "blk-cgroup.h"

#include <trace/events/bcache.h>

#define CUTOFF_CACHE_ADD        95
#define CUTOFF_CACHE_READA      90

struct kmem_cache *bch_search_cache;

static void check_should_skip(struct cached_dev *, struct search *);

/* Cgroup interface */

#ifdef CONFIG_CGROUP_BCACHE
static struct bch_cgroup bcache_default_cgroup = { .cache_mode = -1 };

static struct bch_cgroup *cgroup_to_bcache(struct cgroup *cgroup)
{
        struct cgroup_subsys_state *css;
        return cgroup &&
                (css = cgroup_subsys_state(cgroup, bcache_subsys_id))
                ? container_of(css, struct bch_cgroup, css)
                : &bcache_default_cgroup;
}

struct bch_cgroup *bch_bio_to_cgroup(struct bio *bio)
{
        struct cgroup_subsys_state *css = bio->bi_css
                ? cgroup_subsys_state(bio->bi_css->cgroup, bcache_subsys_id)
                : task_subsys_state(current, bcache_subsys_id);

        return css
                ? container_of(css, struct bch_cgroup, css)
                : &bcache_default_cgroup;
}

static ssize_t cache_mode_read(struct cgroup *cgrp, struct cftype *cft,
                        struct file *file,
                        char __user *buf, size_t nbytes, loff_t *ppos)
{
        char tmp[1024];
        int len = bch_snprint_string_list(tmp, PAGE_SIZE, bch_cache_modes,
                                          cgroup_to_bcache(cgrp)->cache_mode + 1);

        if (len < 0)
                return len;

        return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}

static int cache_mode_write(struct cgroup *cgrp, struct cftype *cft,
                            const char *buf)
{
        int v = bch_read_string_list(buf, bch_cache_modes);
        if (v < 0)
                return v;

        cgroup_to_bcache(cgrp)->cache_mode = v - 1;
        return 0;
}

static u64 bch_verify_read(struct cgroup *cgrp, struct cftype *cft)
{
        return cgroup_to_bcache(cgrp)->verify;
}

static int bch_verify_write(struct cgroup *cgrp, struct cftype *cft, u64 val)
{
        cgroup_to_bcache(cgrp)->verify = val;
        return 0;
}

static u64 bch_cache_hits_read(struct cgroup *cgrp, struct cftype *cft)
{
        struct bch_cgroup *bcachecg = cgroup_to_bcache(cgrp);
        return atomic_read(&bcachecg->stats.cache_hits);
}

static u64 bch_cache_misses_read(struct cgroup *cgrp, struct cftype *cft)
{
        struct bch_cgroup *bcachecg = cgroup_to_bcache(cgrp);
        return atomic_read(&bcachecg->stats.cache_misses);
}

static u64 bch_cache_bypass_hits_read(struct cgroup *cgrp,
                                         struct cftype *cft)
{
        struct bch_cgroup *bcachecg = cgroup_to_bcache(cgrp);
        return atomic_read(&bcachecg->stats.cache_bypass_hits);
}

static u64 bch_cache_bypass_misses_read(struct cgroup *cgrp,
                                           struct cftype *cft)
{
        struct bch_cgroup *bcachecg = cgroup_to_bcache(cgrp);
        return atomic_read(&bcachecg->stats.cache_bypass_misses);
}

static struct cftype bch_files[] = {
        {
                .name           = "cache_mode",
                .read           = cache_mode_read,
                .write_string   = cache_mode_write,
        },
        {
                .name           = "verify",
                .read_u64       = bch_verify_read,
                .write_u64      = bch_verify_write,
        },
        {
                .name           = "cache_hits",
                .read_u64       = bch_cache_hits_read,
        },
        {
                .name           = "cache_misses",
                .read_u64       = bch_cache_misses_read,
        },
        {
                .name           = "cache_bypass_hits",
                .read_u64       = bch_cache_bypass_hits_read,
        },
        {
                .name           = "cache_bypass_misses",
                .read_u64       = bch_cache_bypass_misses_read,
        },
        { }     /* terminate */
};

static void init_bch_cgroup(struct bch_cgroup *cg)
{
        cg->cache_mode = -1;
}

static struct cgroup_subsys_state *bcachecg_create(struct cgroup *cgroup)
{
        struct bch_cgroup *cg;

        cg = kzalloc(sizeof(*cg), GFP_KERNEL);
        if (!cg)
                return ERR_PTR(-ENOMEM);
        init_bch_cgroup(cg);
        return &cg->css;
}

static void bcachecg_destroy(struct cgroup *cgroup)
{
        struct bch_cgroup *cg = cgroup_to_bcache(cgroup);
        free_css_id(&bcache_subsys, &cg->css);
        kfree(cg);
}

struct cgroup_subsys bcache_subsys = {
        .create         = bcachecg_create,
        .destroy        = bcachecg_destroy,
        .subsys_id      = bcache_subsys_id,
        .name           = "bcache",
        .module         = THIS_MODULE,
};
EXPORT_SYMBOL_GPL(bcache_subsys);
#endif

static unsigned cache_mode(struct cached_dev *dc, struct bio *bio)
{
#ifdef CONFIG_CGROUP_BCACHE
        int r = bch_bio_to_cgroup(bio)->cache_mode;
        if (r >= 0)
                return r;
#endif
        return BDEV_CACHE_MODE(&dc->sb);
}

static bool verify(struct cached_dev *dc, struct bio *bio)
{
#ifdef CONFIG_CGROUP_BCACHE
        if (bch_bio_to_cgroup(bio)->verify)
                return true;
#endif
        return dc->verify;
}

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

        bio_for_each_segment(bv, bio, i) {
                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 bio_invalidate(struct closure *cl)
{
        struct btree_op *op = container_of(cl, struct btree_op, cl);
        struct bio *bio = op->cache_bio;

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

        while (bio_sectors(bio)) {
                unsigned len = min(bio_sectors(bio), 1U << 14);

                if (bch_keylist_realloc(&op->keys, 0, op->c))
                        goto out;

                bio->bi_sector  += len;
                bio->bi_size    -= len << 9;

                bch_keylist_add(&op->keys,
                                &KEY(op->inode, bio->bi_sector, len));
        }

        op->insert_data_done = true;
        bio_put(bio);
out:
        continue_at(cl, bch_journal, bcache_wq);
}

struct open_bucket {
        struct list_head        list;
        struct task_struct      *last;
        unsigned                sectors_free;
        BKEY_PADDED(key);
};

void bch_open_buckets_free(struct cache_set *c)
{
        struct open_bucket *b;

        while (!list_empty(&c->data_buckets)) {
                b = list_first_entry(&c->data_buckets,
                                     struct open_bucket, list);
                list_del(&b->list);
                kfree(b);
        }
}

int bch_open_buckets_alloc(struct cache_set *c)
{
        int i;

        spin_lock_init(&c->data_bucket_lock);

        for (i = 0; i < 6; i++) {
                struct open_bucket *b = kzalloc(sizeof(*b), GFP_KERNEL);
                if (!b)
                        return -ENOMEM;

                list_add(&b->list, &c->data_buckets);
        }

        return 0;
}

/*
 * We keep multiple buckets open for writes, and try to segregate different
 * write streams for better cache utilization: first we look for a bucket where
 * the last write to it was sequential with the current write, and failing that
 * we look for a bucket that was last used by the same task.
 *
 * The ideas is if you've got multiple tasks pulling data into the cache at the
 * same time, you'll get better cache utilization if you try to segregate their
 * data and preserve locality.
 *
 * For example, say you've starting Firefox at the same time you're copying a
 * bunch of files. Firefox will likely end up being fairly hot and stay in the
 * cache awhile, but the data you copied might not be; if you wrote all that
 * data to the same buckets it'd get invalidated at the same time.
 *
 * Both of those tasks will be doing fairly random IO so we can't rely on
 * detecting sequential IO to segregate their data, but going off of the task
 * should be a sane heuristic.
 */
static struct open_bucket *pick_data_bucket(struct cache_set *c,
                                            const struct bkey *search,
                                            struct task_struct *task,
                                            struct bkey *alloc)
{
        struct open_bucket *ret, *ret_task = NULL;

        list_for_each_entry_reverse(ret, &c->data_buckets, list)
                if (!bkey_cmp(&ret->key, search))
                        goto found;
                else if (ret->last == task)
                        ret_task = ret;

        ret = ret_task ?: list_first_entry(&c->data_buckets,
                                           struct open_bucket, list);
found:
        if (!ret->sectors_free && KEY_PTRS(alloc)) {
                ret->sectors_free = c->sb.bucket_size;
                bkey_copy(&ret->key, alloc);
                bkey_init(alloc);
        }

        if (!ret->sectors_free)
                ret = NULL;

        return ret;
}

/*
 * Allocates some space in the cache to write to, and k to point to the newly
 * allocated space, and updates KEY_SIZE(k) and KEY_OFFSET(k) (to point to the
 * end of the newly allocated space).
 *
 * May allocate fewer sectors than @sectors, KEY_SIZE(k) indicates how many
 * sectors were actually allocated.
 *
 * If s->writeback is true, will not fail.
 */
static bool bch_alloc_sectors(struct bkey *k, unsigned sectors,
                              struct search *s)
{
        struct cache_set *c = s->op.c;
        struct open_bucket *b;
        BKEY_PADDED(key) alloc;
        struct closure cl, *w = NULL;
        unsigned i;

        if (s->writeback) {
                closure_init_stack(&cl);
                w = &cl;
        }

        /*
         * We might have to allocate a new bucket, which we can't do with a
         * spinlock held. So if we have to allocate, we drop the lock, allocate
         * and then retry. KEY_PTRS() indicates whether alloc points to
         * allocated bucket(s).
         */

        bkey_init(&alloc.key);
        spin_lock(&c->data_bucket_lock);

        while (!(b = pick_data_bucket(c, k, s->task, &alloc.key))) {
                unsigned watermark = s->op.write_prio
                        ? WATERMARK_MOVINGGC
                        : WATERMARK_NONE;

                spin_unlock(&c->data_bucket_lock);

                if (bch_bucket_alloc_set(c, watermark, &alloc.key, 1, w))
                        return false;

                spin_lock(&c->data_bucket_lock);
        }

        /*
         * If we had to allocate, we might race and not need to allocate the
         * second time we call find_data_bucket(). If we allocated a bucket but
         * didn't use it, drop the refcount bch_bucket_alloc_set() took:
         */
        if (KEY_PTRS(&alloc.key))
                __bkey_put(c, &alloc.key);

        for (i = 0; i < KEY_PTRS(&b->key); i++)
                EBUG_ON(ptr_stale(c, &b->key, i));

        /* Set up the pointer to the space we're allocating: */

        for (i = 0; i < KEY_PTRS(&b->key); i++)
                k->ptr[i] = b->key.ptr[i];

        sectors = min(sectors, b->sectors_free);

        SET_KEY_OFFSET(k, KEY_OFFSET(k) + sectors);
        SET_KEY_SIZE(k, sectors);
        SET_KEY_PTRS(k, KEY_PTRS(&b->key));

        /*
         * Move b to the end of the lru, and keep track of what this bucket was
         * last used for:
         */
        list_move_tail(&b->list, &c->data_buckets);
        bkey_copy_key(&b->key, k);
        b->last = s->task;

        b->sectors_free -= sectors;

        for (i = 0; i < KEY_PTRS(&b->key); i++) {
                SET_PTR_OFFSET(&b->key, i, PTR_OFFSET(&b->key, i) + sectors);

                atomic_long_add(sectors,
                                &PTR_CACHE(c, &b->key, i)->sectors_written);
        }

        if (b->sectors_free < c->sb.block_size)
                b->sectors_free = 0;

        /*
         * k takes refcounts on the buckets it points to until it's inserted
         * into the btree, but if we're done with this bucket we just transfer
         * get_data_bucket()'s refcount.
         */
        if (b->sectors_free)
                for (i = 0; i < KEY_PTRS(&b->key); i++)
                        atomic_inc(&PTR_BUCKET(c, &b->key, i)->pin);

        spin_unlock(&c->data_bucket_lock);
        return true;
}

static void bch_insert_data_error(struct closure *cl)
{
        struct btree_op *op = container_of(cl, struct btree_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 succesfully 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->keys.bottom, *dst = op->keys.bottom;

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

                SET_KEY_PTRS(src, 0);
                bkey_copy(dst, src);

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

        op->keys.top = dst;

        bch_journal(cl);
}

static void bch_insert_data_endio(struct bio *bio, int error)
{
        struct closure *cl = bio->bi_private;
        struct btree_op *op = container_of(cl, struct btree_op, cl);
        struct search *s = container_of(op, struct search, op);

        if (error) {
                /* TODO: We could try to recover from this. */
                if (s->writeback)
                        s->error = error;
                else if (s->write)
                        set_closure_fn(cl, bch_insert_data_error, bcache_wq);
                else
                        set_closure_fn(cl, NULL, NULL);
        }

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

static void bch_insert_data_loop(struct closure *cl)
{
        struct btree_op *op = container_of(cl, struct btree_op, cl);
        struct search *s = container_of(op, struct search, op);
        struct bio *bio = op->cache_bio, *n;

        if (op->skip)
                return bio_invalidate(cl);

        if (atomic_sub_return(bio_sectors(bio), &op->c->sectors_to_gc) < 0) {
                set_gc_sectors(op->c);
                bch_queue_gc(op->c);
        }

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

        do {
                unsigned i;
                struct bkey *k;
                struct bio_set *split = s->d
                        ? s->d->bio_split : op->c->bio_split;

                /* 1 for the device pointer and 1 for the chksum */
                if (bch_keylist_realloc(&op->keys,
                                        1 + (op->csum ? 1 : 0),
                                        op->c))
                        continue_at(cl, bch_journal, bcache_wq);

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

                if (!bch_alloc_sectors(k, bio_sectors(bio), s))
                        goto err;

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

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

                if (s->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->keys);

                n->bi_rw |= REQ_WRITE;
                bch_submit_bbio(n, op->c, k, 0);
        } while (n != bio);

        op->insert_data_done = true;
        continue_at(cl, bch_journal, bcache_wq);
err:
        /* bch_alloc_sectors() blocks if s->writeback = true */
        BUG_ON(s->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 (s->write) {
                /*
                 * 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->skip = true;
                return bio_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->keys))
                        continue_at(cl, bch_journal, bcache_wq);
                else
                        closure_return(cl);
        }
}

/**
 * bch_insert_data - stick some data in the cache
 *
 * 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->cache_bio; bi_sector is used for the key offset,
 * and op->inode is used for the key inode.
 *
 * If op->skip is true, instead of inserting the data it invalidates the region
 * of the cache represented by op->cache_bio and op->inode.
 */
void bch_insert_data(struct closure *cl)
{
        struct btree_op *op = container_of(cl, struct btree_op, cl);

        bch_keylist_init(&op->keys);
        bio_get(op->cache_bio);
        bch_insert_data_loop(cl);
}

void bch_btree_insert_async(struct closure *cl)
{
        struct btree_op *op = container_of(cl, struct btree_op, cl);
        struct search *s = container_of(op, struct search, op);

        if (bch_btree_insert(op, op->c)) {
                s->error                = -ENOMEM;
                op->insert_data_done    = true;
        }

        if (op->insert_data_done) {
                bch_keylist_free(&op->keys);
                closure_return(cl);
        } else
                continue_at(cl, bch_insert_data_loop, bcache_wq);
}

/* Common code for the make_request functions */

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

        if (error) {
                struct search *s = container_of(cl, struct search, cl);
                s->error = error;
                /* Only cache read errors are recoverable */
                s->recoverable = false;
        }

        bio_put(bio);
        closure_put(cl);
}

void bch_cache_read_endio(struct bio *bio, int error)
{
        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 (error)
                s->error = error;
        else if (ptr_stale(s->op.c, &b->key, 0)) {
                atomic_long_inc(&s->op.c->cache_read_races);
                s->error = -EINTR;
        }

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

static void bio_complete(struct search *s)
{
        if (s->orig_bio) {
                int cpu, rw = bio_data_dir(s->orig_bio);
                unsigned long duration = jiffies - s->start_time;

                cpu = part_stat_lock();
                part_round_stats(cpu, &s->d->disk->part0);
                part_stat_add(cpu, &s->d->disk->part0, ticks[rw], duration);
                part_stat_unlock();

                trace_bcache_request_end(s, s->orig_bio);
                bio_endio(s->orig_bio, s->error);
                s->orig_bio = NULL;
        }
}

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

        bio->bi_end_io          = request_endio;
        bio->bi_private         = &s->cl;
        atomic_set(&bio->bi_cnt, 3);
}

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

        if (s->op.cache_bio)
                bio_put(s->op.cache_bio);

        if (s->unaligned_bvec)
                mempool_free(s->bio.bio.bi_io_vec, s->d->unaligned_bvec);

        closure_debug_destroy(cl);
        mempool_free(s, s->d->c->search);
}

static struct search *search_alloc(struct bio *bio, struct bcache_device *d)
{
        struct bio_vec *bv;
        struct search *s = mempool_alloc(d->c->search, GFP_NOIO);
        memset(s, 0, offsetof(struct search, op.keys));

        __closure_init(&s->cl, NULL);

        s->op.inode             = d->id;
        s->op.c                 = d->c;
        s->d                    = d;
        s->op.lock              = -1;
        s->task                 = current;
        s->orig_bio             = bio;
        s->write                = (bio->bi_rw & REQ_WRITE) != 0;
        s->op.flush_journal     = (bio->bi_rw & (REQ_FLUSH|REQ_FUA)) != 0;
        s->op.skip              = (bio->bi_rw & REQ_DISCARD) != 0;
        s->recoverable          = 1;
        s->start_time           = jiffies;
        do_bio_hook(s);

        if (bio->bi_size != bio_segments(bio) * PAGE_SIZE) {
                bv = mempool_alloc(d->unaligned_bvec, GFP_NOIO);
                memcpy(bv, bio_iovec(bio),
                       sizeof(struct bio_vec) * bio_segments(bio));

                s->bio.bio.bi_io_vec    = bv;
                s->unaligned_bvec       = 1;
        }

        return s;
}

static void btree_read_async(struct closure *cl)
{
        struct btree_op *op = container_of(cl, struct btree_op, cl);

        int ret = btree_root(search_recurse, op->c, op);

        if (ret == -EAGAIN)
                continue_at(cl, btree_read_async, bcache_wq);

        closure_return(cl);
}

/* 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);

        search_free(cl);
        cached_dev_put(dc);
}

/* Process reads */

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

        if (s->op.insert_collision)
                bch_mark_cache_miss_collision(s);

        if (s->op.cache_bio) {
                int i;
                struct bio_vec *bv;

                __bio_for_each_segment(bv, s->op.cache_bio, i, 0)
                        __free_page(bv->bv_page);
        }

        cached_dev_bio_complete(cl);
}

static void request_read_error(struct closure *cl)
{
        struct search *s = container_of(cl, struct search, cl);
        struct bio_vec *bv;
        int i;

        if (s->recoverable) {
                /* Retry from the backing device: */
                trace_bcache_read_retry(s->orig_bio);

                s->error = 0;
                bv = s->bio.bio.bi_io_vec;
                do_bio_hook(s);
                s->bio.bio.bi_io_vec = bv;

                if (!s->unaligned_bvec)
                        bio_for_each_segment(bv, s->orig_bio, i)
                                bv->bv_offset = 0, bv->bv_len = PAGE_SIZE;
                else
                        memcpy(s->bio.bio.bi_io_vec,
                               bio_iovec(s->orig_bio),
                               sizeof(struct bio_vec) *
                               bio_segments(s->orig_bio));

                /* XXX: invalidate cache */

                closure_bio_submit(&s->bio.bio, &s->cl, s->d);
        }

        continue_at(cl, cached_dev_read_complete, NULL);
}

static void request_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);

        /*
         * s->cache_bio != NULL implies that 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->op.cache_bio) {
                bio_reset(s->op.cache_bio);
                s->op.cache_bio->bi_sector      = s->cache_miss->bi_sector;
                s->op.cache_bio->bi_bdev        = s->cache_miss->bi_bdev;
                s->op.cache_bio->bi_size        = s->cache_bio_sectors << 9;
                bch_bio_map(s->op.cache_bio, NULL);

                bio_copy_data(s->cache_miss, s->op.cache_bio);

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

        if (verify(dc, &s->bio.bio) && s->recoverable)
                bch_data_verify(s);

        bio_complete(s);

        if (s->op.cache_bio &&
            !test_bit(CACHE_SET_STOPPING, &s->op.c->flags)) {
                s->op.type = BTREE_REPLACE;
                closure_call(&s->op.cl, bch_insert_data, NULL, cl);
        }

        continue_at(cl, cached_dev_read_complete, NULL);
}

static void request_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, !s->cache_miss, s->op.skip);
        trace_bcache_read(s->orig_bio, !s->cache_miss, s->op.skip);

        if (s->error)
                continue_at_nobarrier(cl, request_read_error, bcache_wq);
        else if (s->op.cache_bio || verify(dc, &s->bio.bio))
                continue_at_nobarrier(cl, request_read_done, bcache_wq);
        else
                continue_at_nobarrier(cl, cached_dev_read_complete, NULL);
}

static int cached_dev_cache_miss(struct btree *b, struct search *s,
                                 struct bio *bio, unsigned sectors)
{
        int ret = 0;
        unsigned reada;
        struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
        struct bio *miss;

        miss = bch_bio_split(bio, sectors, GFP_NOIO, s->d->bio_split);
        if (miss == bio)
                s->op.lookup_done = true;

        miss->bi_end_io         = request_endio;
        miss->bi_private        = &s->cl;

        if (s->cache_miss || s->op.skip)
                goto out_submit;

        if (miss != bio ||
            (bio->bi_rw & REQ_RAHEAD) ||
            (bio->bi_rw & REQ_META) ||
            s->op.c->gc_stats.in_use >= CUTOFF_CACHE_READA)
                reada = 0;
        else {
                reada = min(dc->readahead >> 9,
                            sectors - bio_sectors(miss));

                if (bio_end_sector(miss) + reada > bdev_sectors(miss->bi_bdev))
                        reada = bdev_sectors(miss->bi_bdev) -
                                bio_end_sector(miss);
        }

        s->cache_bio_sectors = bio_sectors(miss) + reada;
        s->op.cache_bio = bio_alloc_bioset(GFP_NOWAIT,
                        DIV_ROUND_UP(s->cache_bio_sectors, PAGE_SECTORS),
                        dc->disk.bio_split);

        if (!s->op.cache_bio)
                goto out_submit;

        s->op.cache_bio->bi_sector      = miss->bi_sector;
        s->op.cache_bio->bi_bdev        = miss->bi_bdev;
        s->op.cache_bio->bi_size        = s->cache_bio_sectors << 9;

        s->op.cache_bio->bi_end_io      = request_endio;
        s->op.cache_bio->bi_private     = &s->cl;

        /* btree_search_recurse()'s btree iterator is no good anymore */
        ret = -EINTR;
        if (!bch_btree_insert_check_key(b, &s->op, s->op.cache_bio))
                goto out_put;

        bch_bio_map(s->op.cache_bio, NULL);
        if (bio_alloc_pages(s->op.cache_bio, __GFP_NOWARN|GFP_NOIO))
                goto out_put;

        s->cache_miss = miss;
        bio_get(s->op.cache_bio);

        closure_bio_submit(s->op.cache_bio, &s->cl, s->d);

        return ret;
out_put:
        bio_put(s->op.cache_bio);
        s->op.cache_bio = NULL;
out_submit:
        closure_bio_submit(miss, &s->cl, s->d);
        return ret;
}

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

        check_should_skip(dc, s);
        closure_call(&s->op.cl, btree_read_async, NULL, cl);

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

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

        check_should_skip(dc, s);
        down_read_non_owner(&dc->writeback_lock);

        if (bch_keybuf_check_overlapping(&dc->writeback_keys, &start, &end)) {
                s->op.skip      = false;
                s->writeback    = true;
        }

        if (bio->bi_rw & REQ_DISCARD)
                goto skip;

        if (should_writeback(dc, s->orig_bio,
                             cache_mode(dc, bio),
                             s->op.skip)) {
                s->op.skip = false;
                s->writeback = true;
        }

        if (s->op.skip)
                goto skip;

        trace_bcache_write(s->orig_bio, s->writeback, s->op.skip);

        if (!s->writeback) {
                s->op.cache_bio = bio_clone_bioset(bio, GFP_NOIO,
                                                   dc->disk.bio_split);

                closure_bio_submit(bio, cl, s->d);
        } else {
                bch_writeback_add(dc);

                if (s->op.flush_journal) {

                        /* Also need to send a flush to the backing device */
                        s->op.cache_bio = bio_clone_bioset(bio, GFP_NOIO,
                                                           dc->disk.bio_split);

                        bio->bi_size = 0;
                        bio->bi_vcnt = 0;
                        closure_bio_submit(bio, cl, s->d);
                } else {
                        s->op.cache_bio = bio;
                }
        }
out:
        closure_call(&s->op.cl, bch_insert_data, NULL, cl);
        continue_at(cl, cached_dev_write_complete, NULL);
skip:
        s->op.skip = true;
        s->op.cache_bio = s->orig_bio;
        bio_get(s->op.cache_bio);

        if ((bio->bi_rw & REQ_DISCARD) &&
            !blk_queue_discard(bdev_get_queue(dc->bdev)))
                goto out;

        closure_bio_submit(bio, cl, s->d);
        goto out;
}

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

        if (bio->bi_rw & REQ_DISCARD) {
                request_write(dc, s);
                return;
        }

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

        closure_bio_submit(bio, cl, s->d);

        continue_at(cl, cached_dev_bio_complete, NULL);
}

/* Cached devices - read & write stuff */

unsigned bch_get_congested(struct cache_set *c)
{
        int i;
        long rand;

        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);

        rand = get_random_int();
        i -= bitmap_weight(&rand, BITS_PER_LONG);

        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 void check_should_skip(struct cached_dev *dc, struct search *s)
{
        struct cache_set *c = s->op.c;
        struct bio *bio = &s->bio.bio;
        unsigned mode = cache_mode(dc, bio);
        unsigned sectors, congested = bch_get_congested(c);

        if (atomic_read(&dc->disk.detaching) ||
            c->gc_stats.in_use > CUTOFF_CACHE_ADD ||
            (bio->bi_rw & REQ_DISCARD))
                goto skip;

        if (mode == CACHE_MODE_NONE ||
            (mode == CACHE_MODE_WRITEAROUND &&
             (bio->bi_rw & REQ_WRITE)))
                goto skip;

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

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

        if (!congested &&
            mode == CACHE_MODE_WRITEBACK &&
            (bio->bi_rw & REQ_WRITE) &&
            (bio->bi_rw & REQ_SYNC))
                goto rescale;

        if (dc->sequential_merge) {
                struct io *i;

                spin_lock(&dc->io_lock);

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

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

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

                i->last                  = bio_end_sector(bio);
                i->jiffies               = jiffies + msecs_to_jiffies(5000);
                s->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);
        } else {
                s->task->sequential_io = bio->bi_size;

                add_sequential(s->task);
        }

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

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

        if (congested && sectors >= congested) {
                trace_bcache_bypass_congested(s->orig_bio);
                goto skip;
        }

rescale:
        bch_rescale_priorities(c, bio_sectors(bio));
        return;
skip:
        bch_mark_sectors_bypassed(s, bio_sectors(bio));
        s->op.skip = true;
}

static void cached_dev_make_request(struct request_queue *q, struct bio *bio)
{
        struct search *s;
        struct bcache_device *d = bio->bi_bdev->bd_disk->private_data;
        struct cached_dev *dc = container_of(d, struct cached_dev, disk);
        int cpu, rw = bio_data_dir(bio);

        cpu = part_stat_lock();
        part_stat_inc(cpu, &d->disk->part0, ios[rw]);
        part_stat_add(cpu, &d->disk->part0, sectors[rw], bio_sectors(bio));
        part_stat_unlock();

        bio->bi_bdev = dc->bdev;
        bio->bi_sector += dc->sb.data_offset;

        if (cached_dev_get(dc)) {
                s = search_alloc(bio, d);
                trace_bcache_request_start(s, bio);

                if (!bio_has_data(bio))
                        request_nodata(dc, s);
                else if (rw)
                        request_write(dc, s);
                else
                        request_read(dc, s);
        } else {
                if ((bio->bi_rw & REQ_DISCARD) &&
                    !blk_queue_discard(bdev_get_queue(dc->bdev)))
                        bio_endio(bio, 0);
                else
                        bch_generic_make_request(bio, &d->bio_split_hook);
        }
}

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);
        return __blkdev_driver_ioctl(dc->bdev, mode, cmd, arg);
}

static int cached_dev_congested(void *data, int bits)
{
        struct bcache_device *d = data;
        struct cached_dev *dc = container_of(d, struct cached_dev, disk);
        struct request_queue *q = bdev_get_queue(dc->bdev);
        int ret = 0;

        if (bdi_congested(&q->backing_dev_info, bits))
                return 1;

        if (cached_dev_get(dc)) {
                unsigned i;
                struct cache *ca;

                for_each_cache(ca, d->c, i) {
                        q = bdev_get_queue(ca->bdev);
                        ret |= bdi_congested(&q->backing_dev_info, bits);
                }

                cached_dev_put(dc);
        }

        return ret;
}

void bch_cached_dev_request_init(struct cached_dev *dc)
{
        struct gendisk *g = dc->disk.disk;

        g->queue->make_request_fn               = cached_dev_make_request;
        g->queue->backing_dev_info.congested_fn = cached_dev_congested;
        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 sectors)
{
        struct bio_vec *bv;
        int i;

        /* Zero fill bio */

        bio_for_each_segment(bv, bio, i) {
                unsigned j = min(bv->bv_len >> 9, sectors);

                void *p = kmap(bv->bv_page);
                memset(p + bv->bv_offset, 0, j << 9);
                kunmap(bv->bv_page);

                sectors -= j;
        }

        bio_advance(bio, min(sectors << 9, bio->bi_size));

        if (!bio->bi_size)
                s->op.lookup_done = true;

        return 0;
}

static void flash_dev_make_request(struct request_queue *q, struct bio *bio)
{
        struct search *s;
        struct closure *cl;
        struct bcache_device *d = bio->bi_bdev->bd_disk->private_data;
        int cpu, rw = bio_data_dir(bio);

        cpu = part_stat_lock();
        part_stat_inc(cpu, &d->disk->part0, ios[rw]);
        part_stat_add(cpu, &d->disk->part0, sectors[rw], bio_sectors(bio));
        part_stat_unlock();

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

        trace_bcache_request_start(s, bio);

        if (bio_has_data(bio) && !rw) {
                closure_call(&s->op.cl, btree_read_async, NULL, cl);
        } else if (bio_has_data(bio) || s->op.skip) {
                bch_keybuf_check_overlapping(&s->op.c->moving_gc_keys,
                                        &KEY(d->id, bio->bi_sector, 0),
                                        &KEY(d->id, bio_end_sector(bio), 0));

                s->writeback    = true;
                s->op.cache_bio = bio;

                closure_call(&s->op.cl, bch_insert_data, NULL, cl);
        } else {
                /* No data - probably a cache flush */
                if (s->op.flush_journal)
                        bch_journal_meta(s->op.c, cl);
        }

        continue_at(cl, search_free, NULL);
}

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

static int flash_dev_congested(void *data, int bits)
{
        struct bcache_device *d = data;
        struct request_queue *q;
        struct cache *ca;
        unsigned i;
        int ret = 0;

        for_each_cache(ca, d->c, i) {
                q = bdev_get_queue(ca->bdev);
                ret |= bdi_congested(&q->backing_dev_info, bits);
        }

        return ret;
}

void bch_flash_dev_request_init(struct bcache_device *d)
{
        struct gendisk *g = d->disk;

        g->queue->make_request_fn               = flash_dev_make_request;
        g->queue->backing_dev_info.congested_fn = flash_dev_congested;
        d->cache_miss                           = flash_dev_cache_miss;
        d->ioctl                                = flash_dev_ioctl;
}

void bch_request_exit(void)
{
#ifdef CONFIG_CGROUP_BCACHE
        cgroup_unload_subsys(&bcache_subsys);
#endif
        if (bch_search_cache)
                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;

#ifdef CONFIG_CGROUP_BCACHE
        cgroup_load_subsys(&bcache_subsys);
        init_bch_cgroup(&bcache_default_cgroup);

        cgroup_add_cftypes(&bcache_subsys, bch_files);
#endif
        return 0;
}