/*
 * bcache setup/teardown code, and some metadata io - read a superblock and
 * figure out what to do with it.
 *
 * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
 * Copyright 2012 Google, Inc.
 */

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

#include <linux/blkdev.h>
#include <linux/buffer_head.h>
#include <linux/debugfs.h>
#include <linux/genhd.h>
#include <linux/idr.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/random.h>
#include <linux/reboot.h>
#include <linux/sysfs.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Kent Overstreet <kent.overstreet@gmail.com>");

static const char bcache_magic[] = {
        0xc6, 0x85, 0x73, 0xf6, 0x4e, 0x1a, 0x45, 0xca,
        0x82, 0x65, 0xf5, 0x7f, 0x48, 0xba, 0x6d, 0x81
};

static const char invalid_uuid[] = {
        0xa0, 0x3e, 0xf8, 0xed, 0x3e, 0xe1, 0xb8, 0x78,
        0xc8, 0x50, 0xfc, 0x5e, 0xcb, 0x16, 0xcd, 0x99
};

static struct kobject *bcache_kobj;
struct mutex bch_register_lock;
LIST_HEAD(bch_cache_sets);
static LIST_HEAD(uncached_devices);

static int bcache_major;
static DEFINE_IDA(bcache_device_idx);
static wait_queue_head_t unregister_wait;
struct workqueue_struct *bcache_wq;

#define BTREE_MAX_PAGES         (256 * 1024 / PAGE_SIZE)
/* limitation of partitions number on single bcache device */
#define BCACHE_MINORS           128
/* limitation of bcache devices number on single system */
#define BCACHE_DEVICE_IDX_MAX   ((1U << MINORBITS)/BCACHE_MINORS)

/* Superblock */

static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
                              struct page **res)
{
        const char *err;
        struct cache_sb *s;
        struct buffer_head *bh = __bread(bdev, 1, SB_SIZE);
        unsigned i;

        if (!bh)
                return "IO error";

        s = (struct cache_sb *) bh->b_data;

        sb->offset              = le64_to_cpu(s->offset);
        sb->version             = le64_to_cpu(s->version);

        memcpy(sb->magic,       s->magic, 16);
        memcpy(sb->uuid,        s->uuid, 16);
        memcpy(sb->set_uuid,    s->set_uuid, 16);
        memcpy(sb->label,       s->label, SB_LABEL_SIZE);

        sb->flags               = le64_to_cpu(s->flags);
        sb->seq                 = le64_to_cpu(s->seq);
        sb->last_mount          = le32_to_cpu(s->last_mount);
        sb->first_bucket        = le16_to_cpu(s->first_bucket);
        sb->keys                = le16_to_cpu(s->keys);

        for (i = 0; i < SB_JOURNAL_BUCKETS; i++)
                sb->d[i] = le64_to_cpu(s->d[i]);

        pr_debug("read sb version %llu, flags %llu, seq %llu, journal size %u",
                 sb->version, sb->flags, sb->seq, sb->keys);

        err = "Not a bcache superblock";
        if (sb->offset != SB_SECTOR)
                goto err;

        if (memcmp(sb->magic, bcache_magic, 16))
                goto err;

        err = "Too many journal buckets";
        if (sb->keys > SB_JOURNAL_BUCKETS)
                goto err;

        err = "Bad checksum";
        if (s->csum != csum_set(s))
                goto err;

        err = "Bad UUID";
        if (bch_is_zero(sb->uuid, 16))
                goto err;

        sb->block_size  = le16_to_cpu(s->block_size);

        err = "Superblock block size smaller than device block size";
        if (sb->block_size << 9 < bdev_logical_block_size(bdev))
                goto err;

        switch (sb->version) {
        case BCACHE_SB_VERSION_BDEV:
                sb->data_offset = BDEV_DATA_START_DEFAULT;
                break;
        case BCACHE_SB_VERSION_BDEV_WITH_OFFSET:
                sb->data_offset = le64_to_cpu(s->data_offset);

                err = "Bad data offset";
                if (sb->data_offset < BDEV_DATA_START_DEFAULT)
                        goto err;

                break;
        case BCACHE_SB_VERSION_CDEV:
        case BCACHE_SB_VERSION_CDEV_WITH_UUID:
                sb->nbuckets    = le64_to_cpu(s->nbuckets);
                sb->bucket_size = le16_to_cpu(s->bucket_size);

                sb->nr_in_set   = le16_to_cpu(s->nr_in_set);
                sb->nr_this_dev = le16_to_cpu(s->nr_this_dev);

                err = "Too many buckets";
                if (sb->nbuckets > LONG_MAX)
                        goto err;

                err = "Not enough buckets";
                if (sb->nbuckets < 1 << 7)
                        goto err;

                err = "Bad block/bucket size";
                if (!is_power_of_2(sb->block_size) ||
                    sb->block_size > PAGE_SECTORS ||
                    !is_power_of_2(sb->bucket_size) ||
                    sb->bucket_size < PAGE_SECTORS)
                        goto err;

                err = "Invalid superblock: device too small";
                if (get_capacity(bdev->bd_disk) < sb->bucket_size * sb->nbuckets)
                        goto err;

                err = "Bad UUID";
                if (bch_is_zero(sb->set_uuid, 16))
                        goto err;

                err = "Bad cache device number in set";
                if (!sb->nr_in_set ||
                    sb->nr_in_set <= sb->nr_this_dev ||
                    sb->nr_in_set > MAX_CACHES_PER_SET)
                        goto err;

                err = "Journal buckets not sequential";
                for (i = 0; i < sb->keys; i++)
                        if (sb->d[i] != sb->first_bucket + i)
                                goto err;

                err = "Too many journal buckets";
                if (sb->first_bucket + sb->keys > sb->nbuckets)
                        goto err;

                err = "Invalid superblock: first bucket comes before end of super";
                if (sb->first_bucket * sb->bucket_size < 16)
                        goto err;

                break;
        default:
                err = "Unsupported superblock version";
                goto err;
        }

        sb->last_mount = get_seconds();
        err = NULL;

        get_page(bh->b_page);
        *res = bh->b_page;
err:
        put_bh(bh);
        return err;
}

static void write_bdev_super_endio(struct bio *bio)
{
        struct cached_dev *dc = bio->bi_private;
        /* XXX: error checking */

        closure_put(&dc->sb_write);
}

static void __write_super(struct cache_sb *sb, struct bio *bio)
{
        struct cache_sb *out = page_address(bio_first_page_all(bio));
        unsigned i;

        bio->bi_iter.bi_sector  = SB_SECTOR;
        bio->bi_iter.bi_size    = SB_SIZE;
        bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_SYNC|REQ_META);
        bch_bio_map(bio, NULL);

        out->offset             = cpu_to_le64(sb->offset);
        out->version            = cpu_to_le64(sb->version);

        memcpy(out->uuid,       sb->uuid, 16);
        memcpy(out->set_uuid,   sb->set_uuid, 16);
        memcpy(out->label,      sb->label, SB_LABEL_SIZE);

        out->flags              = cpu_to_le64(sb->flags);
        out->seq                = cpu_to_le64(sb->seq);

        out->last_mount         = cpu_to_le32(sb->last_mount);
        out->first_bucket       = cpu_to_le16(sb->first_bucket);
        out->keys               = cpu_to_le16(sb->keys);

        for (i = 0; i < sb->keys; i++)
                out->d[i] = cpu_to_le64(sb->d[i]);

        out->csum = csum_set(out);

        pr_debug("ver %llu, flags %llu, seq %llu",
                 sb->version, sb->flags, sb->seq);

        submit_bio(bio);
}

static void bch_write_bdev_super_unlock(struct closure *cl)
{
        struct cached_dev *dc = container_of(cl, struct cached_dev, sb_write);

        up(&dc->sb_write_mutex);
}

void bch_write_bdev_super(struct cached_dev *dc, struct closure *parent)
{
        struct closure *cl = &dc->sb_write;
        struct bio *bio = &dc->sb_bio;

        down(&dc->sb_write_mutex);
        closure_init(cl, parent);

        bio_reset(bio);
        bio_set_dev(bio, dc->bdev);
        bio->bi_end_io  = write_bdev_super_endio;
        bio->bi_private = dc;

        closure_get(cl);
        /* I/O request sent to backing device */
        __write_super(&dc->sb, bio);

        closure_return_with_destructor(cl, bch_write_bdev_super_unlock);
}

static void write_super_endio(struct bio *bio)
{
        struct cache *ca = bio->bi_private;

        /* is_read = 0 */
        bch_count_io_errors(ca, bio->bi_status, 0,
                            "writing superblock");
        closure_put(&ca->set->sb_write);
}

static void bcache_write_super_unlock(struct closure *cl)
{
        struct cache_set *c = container_of(cl, struct cache_set, sb_write);

        up(&c->sb_write_mutex);
}

void bcache_write_super(struct cache_set *c)
{
        struct closure *cl = &c->sb_write;
        struct cache *ca;
        unsigned i;

        down(&c->sb_write_mutex);
        closure_init(cl, &c->cl);

        c->sb.seq++;

        for_each_cache(ca, c, i) {
                struct bio *bio = &ca->sb_bio;

                ca->sb.version          = BCACHE_SB_VERSION_CDEV_WITH_UUID;
                ca->sb.seq              = c->sb.seq;
                ca->sb.last_mount       = c->sb.last_mount;

                SET_CACHE_SYNC(&ca->sb, CACHE_SYNC(&c->sb));

                bio_reset(bio);
                bio_set_dev(bio, ca->bdev);
                bio->bi_end_io  = write_super_endio;
                bio->bi_private = ca;

                closure_get(cl);
                __write_super(&ca->sb, bio);
        }

        closure_return_with_destructor(cl, bcache_write_super_unlock);
}

/* UUID io */

static void uuid_endio(struct bio *bio)
{
        struct closure *cl = bio->bi_private;
        struct cache_set *c = container_of(cl, struct cache_set, uuid_write);

        cache_set_err_on(bio->bi_status, c, "accessing uuids");
        bch_bbio_free(bio, c);
        closure_put(cl);
}

static void uuid_io_unlock(struct closure *cl)
{
        struct cache_set *c = container_of(cl, struct cache_set, uuid_write);

        up(&c->uuid_write_mutex);
}

static void uuid_io(struct cache_set *c, int op, unsigned long op_flags,
                    struct bkey *k, struct closure *parent)
{
        struct closure *cl = &c->uuid_write;
        struct uuid_entry *u;
        unsigned i;
        char buf[80];

        BUG_ON(!parent);
        down(&c->uuid_write_mutex);
        closure_init(cl, parent);

        for (i = 0; i < KEY_PTRS(k); i++) {
                struct bio *bio = bch_bbio_alloc(c);

                bio->bi_opf = REQ_SYNC | REQ_META | op_flags;
                bio->bi_iter.bi_size = KEY_SIZE(k) << 9;

                bio->bi_end_io  = uuid_endio;
                bio->bi_private = cl;
                bio_set_op_attrs(bio, op, REQ_SYNC|REQ_META|op_flags);
                bch_bio_map(bio, c->uuids);

                bch_submit_bbio(bio, c, k, i);

                if (op != REQ_OP_WRITE)
                        break;
        }

        bch_extent_to_text(buf, sizeof(buf), k);
        pr_debug("%s UUIDs at %s", op == REQ_OP_WRITE ? "wrote" : "read", buf);

        for (u = c->uuids; u < c->uuids + c->nr_uuids; u++)
                if (!bch_is_zero(u->uuid, 16))
                        pr_debug("Slot %zi: %pU: %s: 1st: %u last: %u inv: %u",
                                 u - c->uuids, u->uuid, u->label,
                                 u->first_reg, u->last_reg, u->invalidated);

        closure_return_with_destructor(cl, uuid_io_unlock);
}

static char *uuid_read(struct cache_set *c, struct jset *j, struct closure *cl)
{
        struct bkey *k = &j->uuid_bucket;

        if (__bch_btree_ptr_invalid(c, k))
                return "bad uuid pointer";

        bkey_copy(&c->uuid_bucket, k);
        uuid_io(c, REQ_OP_READ, 0, k, cl);

        if (j->version < BCACHE_JSET_VERSION_UUIDv1) {
                struct uuid_entry_v0    *u0 = (void *) c->uuids;
                struct uuid_entry       *u1 = (void *) c->uuids;
                int i;

                closure_sync(cl);

                /*
                 * Since the new uuid entry is bigger than the old, we have to
                 * convert starting at the highest memory address and work down
                 * in order to do it in place
                 */

                for (i = c->nr_uuids - 1;
                     i >= 0;
                     --i) {
                        memcpy(u1[i].uuid,      u0[i].uuid, 16);
                        memcpy(u1[i].label,     u0[i].label, 32);

                        u1[i].first_reg         = u0[i].first_reg;
                        u1[i].last_reg          = u0[i].last_reg;
                        u1[i].invalidated       = u0[i].invalidated;

                        u1[i].flags     = 0;
                        u1[i].sectors   = 0;
                }
        }

        return NULL;
}

static int __uuid_write(struct cache_set *c)
{
        BKEY_PADDED(key) k;
        struct closure cl;
        closure_init_stack(&cl);

        lockdep_assert_held(&bch_register_lock);

        if (bch_bucket_alloc_set(c, RESERVE_BTREE, &k.key, 1, true))
                return 1;

        SET_KEY_SIZE(&k.key, c->sb.bucket_size);
        uuid_io(c, REQ_OP_WRITE, 0, &k.key, &cl);
        closure_sync(&cl);

        bkey_copy(&c->uuid_bucket, &k.key);
        bkey_put(c, &k.key);
        return 0;
}

int bch_uuid_write(struct cache_set *c)
{
        int ret = __uuid_write(c);

        if (!ret)
                bch_journal_meta(c, NULL);

        return ret;
}

static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid)
{
        struct uuid_entry *u;

        for (u = c->uuids;
             u < c->uuids + c->nr_uuids; u++)
                if (!memcmp(u->uuid, uuid, 16))
                        return u;

        return NULL;
}

static struct uuid_entry *uuid_find_empty(struct cache_set *c)
{
        static const char zero_uuid[16] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
        return uuid_find(c, zero_uuid);
}

/*
 * Bucket priorities/gens:
 *
 * For each bucket, we store on disk its
   * 8 bit gen
   * 16 bit priority
 *
 * See alloc.c for an explanation of the gen. The priority is used to implement
 * lru (and in the future other) cache replacement policies; for most purposes
 * it's just an opaque integer.
 *
 * The gens and the priorities don't have a whole lot to do with each other, and
 * it's actually the gens that must be written out at specific times - it's no
 * big deal if the priorities don't get written, if we lose them we just reuse
 * buckets in suboptimal order.
 *
 * On disk they're stored in a packed array, and in as many buckets are required
 * to fit them all. The buckets we use to store them form a list; the journal
 * header points to the first bucket, the first bucket points to the second
 * bucket, et cetera.
 *
 * This code is used by the allocation code; periodically (whenever it runs out
 * of buckets to allocate from) the allocation code will invalidate some
 * buckets, but it can't use those buckets until their new gens are safely on
 * disk.
 */

static void prio_endio(struct bio *bio)
{
        struct cache *ca = bio->bi_private;

        cache_set_err_on(bio->bi_status, ca->set, "accessing priorities");
        bch_bbio_free(bio, ca->set);
        closure_put(&ca->prio);
}

static void prio_io(struct cache *ca, uint64_t bucket, int op,
                    unsigned long op_flags)
{
        struct closure *cl = &ca->prio;
        struct bio *bio = bch_bbio_alloc(ca->set);

        closure_init_stack(cl);

        bio->bi_iter.bi_sector  = bucket * ca->sb.bucket_size;
        bio_set_dev(bio, ca->bdev);
        bio->bi_iter.bi_size    = bucket_bytes(ca);

        bio->bi_end_io  = prio_endio;
        bio->bi_private = ca;
        bio_set_op_attrs(bio, op, REQ_SYNC|REQ_META|op_flags);
        bch_bio_map(bio, ca->disk_buckets);

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

void bch_prio_write(struct cache *ca)
{
        int i;
        struct bucket *b;
        struct closure cl;

        closure_init_stack(&cl);

        lockdep_assert_held(&ca->set->bucket_lock);

        ca->disk_buckets->seq++;

        atomic_long_add(ca->sb.bucket_size * prio_buckets(ca),
                        &ca->meta_sectors_written);

        //pr_debug("free %zu, free_inc %zu, unused %zu", fifo_used(&ca->free),
        //       fifo_used(&ca->free_inc), fifo_used(&ca->unused));

        for (i = prio_buckets(ca) - 1; i >= 0; --i) {
                long bucket;
                struct prio_set *p = ca->disk_buckets;
                struct bucket_disk *d = p->data;
                struct bucket_disk *end = d + prios_per_bucket(ca);

                for (b = ca->buckets + i * prios_per_bucket(ca);
                     b < ca->buckets + ca->sb.nbuckets && d < end;
                     b++, d++) {
                        d->prio = cpu_to_le16(b->prio);
                        d->gen = b->gen;
                }

                p->next_bucket  = ca->prio_buckets[i + 1];
                p->magic        = pset_magic(&ca->sb);
                p->csum         = bch_crc64(&p->magic, bucket_bytes(ca) - 8);

                bucket = bch_bucket_alloc(ca, RESERVE_PRIO, true);
                BUG_ON(bucket == -1);

                mutex_unlock(&ca->set->bucket_lock);
                prio_io(ca, bucket, REQ_OP_WRITE, 0);
                mutex_lock(&ca->set->bucket_lock);

                ca->prio_buckets[i] = bucket;
                atomic_dec_bug(&ca->buckets[bucket].pin);
        }

        mutex_unlock(&ca->set->bucket_lock);

        bch_journal_meta(ca->set, &cl);
        closure_sync(&cl);

        mutex_lock(&ca->set->bucket_lock);

        /*
         * Don't want the old priorities to get garbage collected until after we
         * finish writing the new ones, and they're journalled
         */
        for (i = 0; i < prio_buckets(ca); i++) {
                if (ca->prio_last_buckets[i])
                        __bch_bucket_free(ca,
                                &ca->buckets[ca->prio_last_buckets[i]]);

                ca->prio_last_buckets[i] = ca->prio_buckets[i];
        }
}

static void prio_read(struct cache *ca, uint64_t bucket)
{
        struct prio_set *p = ca->disk_buckets;
        struct bucket_disk *d = p->data + prios_per_bucket(ca), *end = d;
        struct bucket *b;
        unsigned bucket_nr = 0;

        for (b = ca->buckets;
             b < ca->buckets + ca->sb.nbuckets;
             b++, d++) {
                if (d == end) {
                        ca->prio_buckets[bucket_nr] = bucket;
                        ca->prio_last_buckets[bucket_nr] = bucket;
                        bucket_nr++;

                        prio_io(ca, bucket, REQ_OP_READ, 0);

                        if (p->csum != bch_crc64(&p->magic, bucket_bytes(ca) - 8))
                                pr_warn("bad csum reading priorities");

                        if (p->magic != pset_magic(&ca->sb))
                                pr_warn("bad magic reading priorities");

                        bucket = p->next_bucket;
                        d = p->data;
                }

                b->prio = le16_to_cpu(d->prio);
                b->gen = b->last_gc = d->gen;
        }
}

/* Bcache device */

static int open_dev(struct block_device *b, fmode_t mode)
{
        struct bcache_device *d = b->bd_disk->private_data;
        if (test_bit(BCACHE_DEV_CLOSING, &d->flags))
                return -ENXIO;

        closure_get(&d->cl);
        return 0;
}

static void release_dev(struct gendisk *b, fmode_t mode)
{
        struct bcache_device *d = b->private_data;
        closure_put(&d->cl);
}

static int ioctl_dev(struct block_device *b, fmode_t mode,
                     unsigned int cmd, unsigned long arg)
{
        struct bcache_device *d = b->bd_disk->private_data;
        struct cached_dev *dc = container_of(d, struct cached_dev, disk);

        if (dc->io_disable)
                return -EIO;

        return d->ioctl(d, mode, cmd, arg);
}

static const struct block_device_operations bcache_ops = {
        .open           = open_dev,
        .release        = release_dev,
        .ioctl          = ioctl_dev,
        .owner          = THIS_MODULE,
};

void bcache_device_stop(struct bcache_device *d)
{
        if (!test_and_set_bit(BCACHE_DEV_CLOSING, &d->flags))
                closure_queue(&d->cl);
}

static void bcache_device_unlink(struct bcache_device *d)
{
        lockdep_assert_held(&bch_register_lock);

        if (d->c && !test_and_set_bit(BCACHE_DEV_UNLINK_DONE, &d->flags)) {
                unsigned i;
                struct cache *ca;

                sysfs_remove_link(&d->c->kobj, d->name);
                sysfs_remove_link(&d->kobj, "cache");

                for_each_cache(ca, d->c, i)
                        bd_unlink_disk_holder(ca->bdev, d->disk);
        }
}

static void bcache_device_link(struct bcache_device *d, struct cache_set *c,
                               const char *name)
{
        unsigned i;
        struct cache *ca;

        for_each_cache(ca, d->c, i)
                bd_link_disk_holder(ca->bdev, d->disk);

        snprintf(d->name, BCACHEDEVNAME_SIZE,
                 "%s%u", name, d->id);

        WARN(sysfs_create_link(&d->kobj, &c->kobj, "cache") ||
             sysfs_create_link(&c->kobj, &d->kobj, d->name),
             "Couldn't create device <-> cache set symlinks");

        clear_bit(BCACHE_DEV_UNLINK_DONE, &d->flags);
}

static void bcache_device_detach(struct bcache_device *d)
{
        lockdep_assert_held(&bch_register_lock);

        if (test_bit(BCACHE_DEV_DETACHING, &d->flags)) {
                struct uuid_entry *u = d->c->uuids + d->id;

                SET_UUID_FLASH_ONLY(u, 0);
                memcpy(u->uuid, invalid_uuid, 16);
                u->invalidated = cpu_to_le32(get_seconds());
                bch_uuid_write(d->c);
        }

        bcache_device_unlink(d);

        d->c->devices[d->id] = NULL;
        closure_put(&d->c->caching);
        d->c = NULL;
}

static void bcache_device_attach(struct bcache_device *d, struct cache_set *c,
                                 unsigned id)
{
        d->id = id;
        d->c = c;
        c->devices[id] = d;

        if (id >= c->devices_max_used)
                c->devices_max_used = id + 1;

        closure_get(&c->caching);
}

static inline int first_minor_to_idx(int first_minor)
{
        return (first_minor/BCACHE_MINORS);
}

static inline int idx_to_first_minor(int idx)
{
        return (idx * BCACHE_MINORS);
}

static void bcache_device_free(struct bcache_device *d)
{
        lockdep_assert_held(&bch_register_lock);

        pr_info("%s stopped", d->disk->disk_name);

        if (d->c)
                bcache_device_detach(d);
        if (d->disk && d->disk->flags & GENHD_FL_UP)
                del_gendisk(d->disk);
        if (d->disk && d->disk->queue)
                blk_cleanup_queue(d->disk->queue);
        if (d->disk) {
                ida_simple_remove(&bcache_device_idx,
                                  first_minor_to_idx(d->disk->first_minor));
                put_disk(d->disk);
        }

        bioset_exit(&d->bio_split);
        kvfree(d->full_dirty_stripes);
        kvfree(d->stripe_sectors_dirty);

        closure_debug_destroy(&d->cl);
}

static int bcache_device_init(struct bcache_device *d, unsigned block_size,
                              sector_t sectors)
{
        struct request_queue *q;
        const size_t max_stripes = min_t(size_t, INT_MAX,
                                         SIZE_MAX / sizeof(atomic_t));
        size_t n;
        int idx;

        if (!d->stripe_size)
                d->stripe_size = 1 << 31;

        d->nr_stripes = DIV_ROUND_UP_ULL(sectors, d->stripe_size);

        if (!d->nr_stripes || d->nr_stripes > max_stripes) {
                pr_err("nr_stripes too large or invalid: %u (start sector beyond end of disk?)",
                        (unsigned)d->nr_stripes);
                return -ENOMEM;
        }

        n = d->nr_stripes * sizeof(atomic_t);
        d->stripe_sectors_dirty = kvzalloc(n, GFP_KERNEL);
        if (!d->stripe_sectors_dirty)
                return -ENOMEM;

        n = BITS_TO_LONGS(d->nr_stripes) * sizeof(unsigned long);
        d->full_dirty_stripes = kvzalloc(n, GFP_KERNEL);
        if (!d->full_dirty_stripes)
                return -ENOMEM;

        idx = ida_simple_get(&bcache_device_idx, 0,
                                BCACHE_DEVICE_IDX_MAX, GFP_KERNEL);
        if (idx < 0)
                return idx;

        if (bioset_init(&d->bio_split, 4, offsetof(struct bbio, bio),
                        BIOSET_NEED_BVECS|BIOSET_NEED_RESCUER) ||
            !(d->disk = alloc_disk(BCACHE_MINORS))) {
                ida_simple_remove(&bcache_device_idx, idx);
                return -ENOMEM;
        }

        set_capacity(d->disk, sectors);
        snprintf(d->disk->disk_name, DISK_NAME_LEN, "bcache%i", idx);

        d->disk->major          = bcache_major;
        d->disk->first_minor    = idx_to_first_minor(idx);
        d->disk->fops           = &bcache_ops;
        d->disk->private_data   = d;

        q = blk_alloc_queue(GFP_KERNEL);
        if (!q)
                return -ENOMEM;

        blk_queue_make_request(q, NULL);
        d->disk->queue                  = q;
        q->queuedata                    = d;
        q->backing_dev_info->congested_data = d;
        q->limits.max_hw_sectors        = UINT_MAX;
        q->limits.max_sectors           = UINT_MAX;
        q->limits.max_segment_size      = UINT_MAX;
        q->limits.max_segments          = BIO_MAX_PAGES;
        blk_queue_max_discard_sectors(q, UINT_MAX);
        q->limits.discard_granularity   = 512;
        q->limits.io_min                = block_size;
        q->limits.logical_block_size    = block_size;
        q->limits.physical_block_size   = block_size;
        blk_queue_flag_set(QUEUE_FLAG_NONROT, d->disk->queue);
        blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, d->disk->queue);
        blk_queue_flag_set(QUEUE_FLAG_DISCARD, d->disk->queue);

        blk_queue_write_cache(q, true, true);

        return 0;
}

/* Cached device */

static void calc_cached_dev_sectors(struct cache_set *c)
{
        uint64_t sectors = 0;
        struct cached_dev *dc;

        list_for_each_entry(dc, &c->cached_devs, list)
                sectors += bdev_sectors(dc->bdev);

        c->cached_dev_sectors = sectors;
}

#define BACKING_DEV_OFFLINE_TIMEOUT 5
static int cached_dev_status_update(void *arg)
{
        struct cached_dev *dc = arg;
        struct request_queue *q;

        /*
         * If this delayed worker is stopping outside, directly quit here.
         * dc->io_disable might be set via sysfs interface, so check it
         * here too.
         */
        while (!kthread_should_stop() && !dc->io_disable) {
                q = bdev_get_queue(dc->bdev);
                if (blk_queue_dying(q))
                        dc->offline_seconds++;
                else
                        dc->offline_seconds = 0;

                if (dc->offline_seconds >= BACKING_DEV_OFFLINE_TIMEOUT) {
                        pr_err("%s: device offline for %d seconds",
                               dc->backing_dev_name,
                               BACKING_DEV_OFFLINE_TIMEOUT);
                        pr_err("%s: disable I/O request due to backing "
                               "device offline", dc->disk.name);
                        dc->io_disable = true;
                        /* let others know earlier that io_disable is true */
                        smp_mb();
                        bcache_device_stop(&dc->disk);
                        break;
                }
                schedule_timeout_interruptible(HZ);
        }

        wait_for_kthread_stop();
        return 0;
}


void bch_cached_dev_run(struct cached_dev *dc)
{
        struct bcache_device *d = &dc->disk;
        char buf[SB_LABEL_SIZE + 1];
        char *env[] = {
                "DRIVER=bcache",
                kasprintf(GFP_KERNEL, "CACHED_UUID=%pU", dc->sb.uuid),
                NULL,
                NULL,
        };

        memcpy(buf, dc->sb.label, SB_LABEL_SIZE);
        buf[SB_LABEL_SIZE] = '\0';
        env[2] = kasprintf(GFP_KERNEL, "CACHED_LABEL=%s", buf);

        if (atomic_xchg(&dc->running, 1)) {
                kfree(env[1]);
                kfree(env[2]);
                return;
        }

        if (!d->c &&
            BDEV_STATE(&dc->sb) != BDEV_STATE_NONE) {
                struct closure cl;
                closure_init_stack(&cl);

                SET_BDEV_STATE(&dc->sb, BDEV_STATE_STALE);
                bch_write_bdev_super(dc, &cl);
                closure_sync(&cl);
        }

        add_disk(d->disk);
        bd_link_disk_holder(dc->bdev, dc->disk.disk);
        /* won't show up in the uevent file, use udevadm monitor -e instead
         * only class / kset properties are persistent */
        kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
        kfree(env[1]);
        kfree(env[2]);

        if (sysfs_create_link(&d->kobj, &disk_to_dev(d->disk)->kobj, "dev") ||
            sysfs_create_link(&disk_to_dev(d->disk)->kobj, &d->kobj, "bcache"))
                pr_debug("error creating sysfs link");

        dc->status_update_thread = kthread_run(cached_dev_status_update,
                                               dc, "bcache_status_update");
        if (IS_ERR(dc->status_update_thread)) {
                pr_warn("failed to create bcache_status_update kthread, "
                        "continue to run without monitoring backing "
                        "device status");
        }
}

/*
 * If BCACHE_DEV_RATE_DW_RUNNING is set, it means routine of the delayed
 * work dc->writeback_rate_update is running. Wait until the routine
 * quits (BCACHE_DEV_RATE_DW_RUNNING is clear), then continue to
 * cancel it. If BCACHE_DEV_RATE_DW_RUNNING is not clear after time_out
 * seconds, give up waiting here and continue to cancel it too.
 */
static void cancel_writeback_rate_update_dwork(struct cached_dev *dc)
{
        int time_out = WRITEBACK_RATE_UPDATE_SECS_MAX * HZ;

        do {
                if (!test_bit(BCACHE_DEV_RATE_DW_RUNNING,
                              &dc->disk.flags))
                        break;
                time_out--;
                schedule_timeout_interruptible(1);
        } while (time_out > 0);

        if (time_out == 0)
                pr_warn("give up waiting for dc->writeback_write_update to quit");

        cancel_delayed_work_sync(&dc->writeback_rate_update);
}

static void cached_dev_detach_finish(struct work_struct *w)
{
        struct cached_dev *dc = container_of(w, struct cached_dev, detach);
        struct closure cl;
        closure_init_stack(&cl);

        BUG_ON(!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags));
        BUG_ON(refcount_read(&dc->count));

        mutex_lock(&bch_register_lock);

        if (test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags))
                cancel_writeback_rate_update_dwork(dc);

        if (!IS_ERR_OR_NULL(dc->writeback_thread)) {
                kthread_stop(dc->writeback_thread);
                dc->writeback_thread = NULL;
        }

        memset(&dc->sb.set_uuid, 0, 16);
        SET_BDEV_STATE(&dc->sb, BDEV_STATE_NONE);

        bch_write_bdev_super(dc, &cl);
        closure_sync(&cl);

        bcache_device_detach(&dc->disk);
        list_move(&dc->list, &uncached_devices);

        clear_bit(BCACHE_DEV_DETACHING, &dc->disk.flags);
        clear_bit(BCACHE_DEV_UNLINK_DONE, &dc->disk.flags);

        mutex_unlock(&bch_register_lock);

        pr_info("Caching disabled for %s", dc->backing_dev_name);

        /* Drop ref we took in cached_dev_detach() */
        closure_put(&dc->disk.cl);
}

void bch_cached_dev_detach(struct cached_dev *dc)
{
        lockdep_assert_held(&bch_register_lock);

        if (test_bit(BCACHE_DEV_CLOSING, &dc->disk.flags))
                return;

        if (test_and_set_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))
                return;

        /*
         * Block the device from being closed and freed until we're finished
         * detaching
         */
        closure_get(&dc->disk.cl);

        bch_writeback_queue(dc);

        cached_dev_put(dc);
}

int bch_cached_dev_attach(struct cached_dev *dc, struct cache_set *c,
                          uint8_t *set_uuid)
{
        uint32_t rtime = cpu_to_le32(get_seconds());
        struct uuid_entry *u;
        struct cached_dev *exist_dc, *t;

        if ((set_uuid && memcmp(set_uuid, c->sb.set_uuid, 16)) ||
            (!set_uuid && memcmp(dc->sb.set_uuid, c->sb.set_uuid, 16)))
                return -ENOENT;

        if (dc->disk.c) {
                pr_err("Can't attach %s: already attached",
                       dc->backing_dev_name);
                return -EINVAL;
        }

        if (test_bit(CACHE_SET_STOPPING, &c->flags)) {
                pr_err("Can't attach %s: shutting down",
                       dc->backing_dev_name);
                return -EINVAL;
        }

        if (dc->sb.block_size < c->sb.block_size) {
                /* Will die */
                pr_err("Couldn't attach %s: block size less than set's block size",
                       dc->backing_dev_name);
                return -EINVAL;
        }

        /* Check whether already attached */
        list_for_each_entry_safe(exist_dc, t, &c->cached_devs, list) {
                if (!memcmp(dc->sb.uuid, exist_dc->sb.uuid, 16)) {
                        pr_err("Tried to attach %s but duplicate UUID already attached",
                                dc->backing_dev_name);

                        return -EINVAL;
                }
        }

        u = uuid_find(c, dc->sb.uuid);

        if (u &&
            (BDEV_STATE(&dc->sb) == BDEV_STATE_STALE ||
             BDEV_STATE(&dc->sb) == BDEV_STATE_NONE)) {
                memcpy(u->uuid, invalid_uuid, 16);
                u->invalidated = cpu_to_le32(get_seconds());
                u = NULL;
        }

        if (!u) {
                if (BDEV_STATE(&dc->sb) == BDEV_STATE_DIRTY) {
                        pr_err("Couldn't find uuid for %s in set",
                               dc->backing_dev_name);
                        return -ENOENT;
                }

                u = uuid_find_empty(c);
                if (!u) {
                        pr_err("Not caching %s, no room for UUID",
                               dc->backing_dev_name);
                        return -EINVAL;
                }
        }

        /* Deadlocks since we're called via sysfs...
        sysfs_remove_file(&dc->kobj, &sysfs_attach);
         */

        if (bch_is_zero(u->uuid, 16)) {
                struct closure cl;
                closure_init_stack(&cl);

                memcpy(u->uuid, dc->sb.uuid, 16);
                memcpy(u->label, dc->sb.label, SB_LABEL_SIZE);
                u->first_reg = u->last_reg = rtime;
                bch_uuid_write(c);

                memcpy(dc->sb.set_uuid, c->sb.set_uuid, 16);
                SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);

                bch_write_bdev_super(dc, &cl);
                closure_sync(&cl);
        } else {
                u->last_reg = rtime;
                bch_uuid_write(c);
        }

        bcache_device_attach(&dc->disk, c, u - c->uuids);
        list_move(&dc->list, &c->cached_devs);
        calc_cached_dev_sectors(c);

        smp_wmb();
        /*
         * dc->c must be set before dc->count != 0 - paired with the mb in
         * cached_dev_get()
         */
        refcount_set(&dc->count, 1);

        /* Block writeback thread, but spawn it */
        down_write(&dc->writeback_lock);
        if (bch_cached_dev_writeback_start(dc)) {
                up_write(&dc->writeback_lock);
                return -ENOMEM;
        }

        if (BDEV_STATE(&dc->sb) == BDEV_STATE_DIRTY) {
                bch_sectors_dirty_init(&dc->disk);
                atomic_set(&dc->has_dirty, 1);
                bch_writeback_queue(dc);
        }

        bch_cached_dev_run(dc);
        bcache_device_link(&dc->disk, c, "bdev");

        /* Allow the writeback thread to proceed */
        up_write(&dc->writeback_lock);

        pr_info("Caching %s as %s on set %pU",
                dc->backing_dev_name,
                dc->disk.disk->disk_name,
                dc->disk.c->sb.set_uuid);
        return 0;
}

void bch_cached_dev_release(struct kobject *kobj)
{
        struct cached_dev *dc = container_of(kobj, struct cached_dev,
                                             disk.kobj);
        kfree(dc);
        module_put(THIS_MODULE);
}

static void cached_dev_free(struct closure *cl)
{
        struct cached_dev *dc = container_of(cl, struct cached_dev, disk.cl);

        mutex_lock(&bch_register_lock);

        if (test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags))
                cancel_writeback_rate_update_dwork(dc);

        if (!IS_ERR_OR_NULL(dc->writeback_thread))
                kthread_stop(dc->writeback_thread);
        if (dc->writeback_write_wq)
                destroy_workqueue(dc->writeback_write_wq);
        if (!IS_ERR_OR_NULL(dc->status_update_thread))
                kthread_stop(dc->status_update_thread);

        if (atomic_read(&dc->running))
                bd_unlink_disk_holder(dc->bdev, dc->disk.disk);
        bcache_device_free(&dc->disk);
        list_del(&dc->list);

        mutex_unlock(&bch_register_lock);

        if (!IS_ERR_OR_NULL(dc->bdev))
                blkdev_put(dc->bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);

        wake_up(&unregister_wait);

        kobject_put(&dc->disk.kobj);
}

static void cached_dev_flush(struct closure *cl)
{
        struct cached_dev *dc = container_of(cl, struct cached_dev, disk.cl);
        struct bcache_device *d = &dc->disk;

        mutex_lock(&bch_register_lock);
        bcache_device_unlink(d);
        mutex_unlock(&bch_register_lock);

        bch_cache_accounting_destroy(&dc->accounting);
        kobject_del(&d->kobj);

        continue_at(cl, cached_dev_free, system_wq);
}

static int cached_dev_init(struct cached_dev *dc, unsigned block_size)
{
        int ret;
        struct io *io;
        struct request_queue *q = bdev_get_queue(dc->bdev);

        __module_get(THIS_MODULE);
        INIT_LIST_HEAD(&dc->list);
        closure_init(&dc->disk.cl, NULL);
        set_closure_fn(&dc->disk.cl, cached_dev_flush, system_wq);
        kobject_init(&dc->disk.kobj, &bch_cached_dev_ktype);
        INIT_WORK(&dc->detach, cached_dev_detach_finish);
        sema_init(&dc->sb_write_mutex, 1);
        INIT_LIST_HEAD(&dc->io_lru);
        spin_lock_init(&dc->io_lock);
        bch_cache_accounting_init(&dc->accounting, &dc->disk.cl);

        dc->sequential_cutoff           = 4 << 20;

        for (io = dc->io; io < dc->io + RECENT_IO; io++) {
                list_add(&io->lru, &dc->io_lru);
                hlist_add_head(&io->hash, dc->io_hash + RECENT_IO);
        }

        dc->disk.stripe_size = q->limits.io_opt >> 9;

        if (dc->disk.stripe_size)
                dc->partial_stripes_expensive =
                        q->limits.raid_partial_stripes_expensive;

        ret = bcache_device_init(&dc->disk, block_size,
                         dc->bdev->bd_part->nr_sects - dc->sb.data_offset);
        if (ret)
                return ret;

        dc->disk.disk->queue->backing_dev_info->ra_pages =
                max(dc->disk.disk->queue->backing_dev_info->ra_pages,
                    q->backing_dev_info->ra_pages);

        atomic_set(&dc->io_errors, 0);
        dc->io_disable = false;
        dc->error_limit = DEFAULT_CACHED_DEV_ERROR_LIMIT;
        /* default to auto */
        dc->stop_when_cache_set_failed = BCH_CACHED_DEV_STOP_AUTO;

        bch_cached_dev_request_init(dc);
        bch_cached_dev_writeback_init(dc);
        return 0;
}

/* Cached device - bcache superblock */

static void register_bdev(struct cache_sb *sb, struct page *sb_page,
                                 struct block_device *bdev,
                                 struct cached_dev *dc)
{
        const char *err = "cannot allocate memory";
        struct cache_set *c;

        bdevname(bdev, dc->backing_dev_name);
        memcpy(&dc->sb, sb, sizeof(struct cache_sb));
        dc->bdev = bdev;
        dc->bdev->bd_holder = dc;

        bio_init(&dc->sb_bio, dc->sb_bio.bi_inline_vecs, 1);
        bio_first_bvec_all(&dc->sb_bio)->bv_page = sb_page;
        get_page(sb_page);


        if (cached_dev_init(dc, sb->block_size << 9))
                goto err;

        err = "error creating kobject";
        if (kobject_add(&dc->disk.kobj, &part_to_dev(bdev->bd_part)->kobj,
                        "bcache"))
                goto err;
        if (bch_cache_accounting_add_kobjs(&dc->accounting, &dc->disk.kobj))
                goto err;

        pr_info("registered backing device %s", dc->backing_dev_name);

        list_add(&dc->list, &uncached_devices);
        list_for_each_entry(c, &bch_cache_sets, list)
                bch_cached_dev_attach(dc, c, NULL);

        if (BDEV_STATE(&dc->sb) == BDEV_STATE_NONE ||
            BDEV_STATE(&dc->sb) == BDEV_STATE_STALE)
                bch_cached_dev_run(dc);

        return;
err:
        pr_notice("error %s: %s", dc->backing_dev_name, err);
        bcache_device_stop(&dc->disk);
}

/* Flash only volumes */

void bch_flash_dev_release(struct kobject *kobj)
{
        struct bcache_device *d = container_of(kobj, struct bcache_device,
                                               kobj);
        kfree(d);
}

static void flash_dev_free(struct closure *cl)
{
        struct bcache_device *d = container_of(cl, struct bcache_device, cl);
        mutex_lock(&bch_register_lock);
        bcache_device_free(d);
        mutex_unlock(&bch_register_lock);
        kobject_put(&d->kobj);
}

static void flash_dev_flush(struct closure *cl)
{
        struct bcache_device *d = container_of(cl, struct bcache_device, cl);

        mutex_lock(&bch_register_lock);
        bcache_device_unlink(d);
        mutex_unlock(&bch_register_lock);
        kobject_del(&d->kobj);
        continue_at(cl, flash_dev_free, system_wq);
}

static int flash_dev_run(struct cache_set *c, struct uuid_entry *u)
{
        struct bcache_device *d = kzalloc(sizeof(struct bcache_device),
                                          GFP_KERNEL);
        if (!d)
                return -ENOMEM;

        closure_init(&d->cl, NULL);
        set_closure_fn(&d->cl, flash_dev_flush, system_wq);

        kobject_init(&d->kobj, &bch_flash_dev_ktype);

        if (bcache_device_init(d, block_bytes(c), u->sectors))
                goto err;

        bcache_device_attach(d, c, u - c->uuids);
        bch_sectors_dirty_init(d);
        bch_flash_dev_request_init(d);
        add_disk(d->disk);

        if (kobject_add(&d->kobj, &disk_to_dev(d->disk)->kobj, "bcache"))
                goto err;

        bcache_device_link(d, c, "volume");

        return 0;
err:
        kobject_put(&d->kobj);
        return -ENOMEM;
}

static int flash_devs_run(struct cache_set *c)
{
        int ret = 0;
        struct uuid_entry *u;

        for (u = c->uuids;
             u < c->uuids + c->nr_uuids && !ret;
             u++)
                if (UUID_FLASH_ONLY(u))
                        ret = flash_dev_run(c, u);

        return ret;
}

int bch_flash_dev_create(struct cache_set *c, uint64_t size)
{
        struct uuid_entry *u;

        if (test_bit(CACHE_SET_STOPPING, &c->flags))
                return -EINTR;

        if (!test_bit(CACHE_SET_RUNNING, &c->flags))
                return -EPERM;

        u = uuid_find_empty(c);
        if (!u) {
                pr_err("Can't create volume, no room for UUID");
                return -EINVAL;
        }

        get_random_bytes(u->uuid, 16);
        memset(u->label, 0, 32);
        u->first_reg = u->last_reg = cpu_to_le32(get_seconds());

        SET_UUID_FLASH_ONLY(u, 1);
        u->sectors = size >> 9;

        bch_uuid_write(c);

        return flash_dev_run(c, u);
}

bool bch_cached_dev_error(struct cached_dev *dc)
{
        struct cache_set *c;

        if (!dc || test_bit(BCACHE_DEV_CLOSING, &dc->disk.flags))
                return false;

        dc->io_disable = true;
        /* make others know io_disable is true earlier */
        smp_mb();

        pr_err("stop %s: too many IO errors on backing device %s\n",
                dc->disk.disk->disk_name, dc->backing_dev_name);

        /*
         * If the cached device is still attached to a cache set,
         * even dc->io_disable is true and no more I/O requests
         * accepted, cache device internal I/O (writeback scan or
         * garbage collection) may still prevent bcache device from
         * being stopped. So here CACHE_SET_IO_DISABLE should be
         * set to c->flags too, to make the internal I/O to cache
         * device rejected and stopped immediately.
         * If c is NULL, that means the bcache device is not attached
         * to any cache set, then no CACHE_SET_IO_DISABLE bit to set.
         */
        c = dc->disk.c;
        if (c && test_and_set_bit(CACHE_SET_IO_DISABLE, &c->flags))
                pr_info("CACHE_SET_IO_DISABLE already set");

        bcache_device_stop(&dc->disk);
        return true;
}

/* Cache set */

__printf(2, 3)
bool bch_cache_set_error(struct cache_set *c, const char *fmt, ...)
{
        va_list args;

        if (c->on_error != ON_ERROR_PANIC &&
            test_bit(CACHE_SET_STOPPING, &c->flags))
                return false;

        if (test_and_set_bit(CACHE_SET_IO_DISABLE, &c->flags))
                pr_info("CACHE_SET_IO_DISABLE already set");

        /* XXX: we can be called from atomic context
        acquire_console_sem();
        */

        printk(KERN_ERR "bcache: error on %pU: ", c->sb.set_uuid);

        va_start(args, fmt);
        vprintk(fmt, args);
        va_end(args);

        printk(", disabling caching\n");

        if (c->on_error == ON_ERROR_PANIC)
                panic("panic forced after error\n");

        bch_cache_set_unregister(c);
        return true;
}

void bch_cache_set_release(struct kobject *kobj)
{
        struct cache_set *c = container_of(kobj, struct cache_set, kobj);
        kfree(c);
        module_put(THIS_MODULE);
}

static void cache_set_free(struct closure *cl)
{
        struct cache_set *c = container_of(cl, struct cache_set, cl);
        struct cache *ca;
        unsigned i;

        if (!IS_ERR_OR_NULL(c->debug))
                debugfs_remove(c->debug);

        bch_open_buckets_free(c);
        bch_btree_cache_free(c);
        bch_journal_free(c);

        for_each_cache(ca, c, i)
                if (ca) {
                        ca->set = NULL;
                        c->cache[ca->sb.nr_this_dev] = NULL;
                        kobject_put(&ca->kobj);
                }

        bch_bset_sort_state_free(&c->sort);
        free_pages((unsigned long) c->uuids, ilog2(bucket_pages(c)));

        if (c->moving_gc_wq)
                destroy_workqueue(c->moving_gc_wq);
        bioset_exit(&c->bio_split);
        mempool_exit(&c->fill_iter);
        mempool_exit(&c->bio_meta);
        mempool_exit(&c->search);
        kfree(c->devices);

        mutex_lock(&bch_register_lock);
        list_del(&c->list);
        mutex_unlock(&bch_register_lock);

        pr_info("Cache set %pU unregistered", c->sb.set_uuid);
        wake_up(&unregister_wait);

        closure_debug_destroy(&c->cl);
        kobject_put(&c->kobj);
}

static void cache_set_flush(struct closure *cl)
{
        struct cache_set *c = container_of(cl, struct cache_set, caching);
        struct cache *ca;
        struct btree *b;
        unsigned i;

        bch_cache_accounting_destroy(&c->accounting);

        kobject_put(&c->internal);
        kobject_del(&c->kobj);

        if (c->gc_thread)
                kthread_stop(c->gc_thread);

        if (!IS_ERR_OR_NULL(c->root))
                list_add(&c->root->list, &c->btree_cache);

        /* Should skip this if we're unregistering because of an error */
        list_for_each_entry(b, &c->btree_cache, list) {
                mutex_lock(&b->write_lock);
                if (btree_node_dirty(b))
                        __bch_btree_node_write(b, NULL);
                mutex_unlock(&b->write_lock);
        }

        for_each_cache(ca, c, i)
                if (ca->alloc_thread)
                        kthread_stop(ca->alloc_thread);

        if (c->journal.cur) {
                cancel_delayed_work_sync(&c->journal.work);
                /* flush last journal entry if needed */
                c->journal.work.work.func(&c->journal.work.work);
        }

        closure_return(cl);
}

/*
 * This function is only called when CACHE_SET_IO_DISABLE is set, which means
 * cache set is unregistering due to too many I/O errors. In this condition,
 * the bcache device might be stopped, it depends on stop_when_cache_set_failed
 * value and whether the broken cache has dirty data:
 *
 * dc->stop_when_cache_set_failed    dc->has_dirty   stop bcache device
 *  BCH_CACHED_STOP_AUTO               0               NO
 *  BCH_CACHED_STOP_AUTO               1               YES
 *  BCH_CACHED_DEV_STOP_ALWAYS         0               YES
 *  BCH_CACHED_DEV_STOP_ALWAYS         1               YES
 *
 * The expected behavior is, if stop_when_cache_set_failed is configured to
 * "auto" via sysfs interface, the bcache device will not be stopped if the
 * backing device is clean on the broken cache device.
 */
static void conditional_stop_bcache_device(struct cache_set *c,
                                           struct bcache_device *d,
                                           struct cached_dev *dc)
{
        if (dc->stop_when_cache_set_failed == BCH_CACHED_DEV_STOP_ALWAYS) {
                pr_warn("stop_when_cache_set_failed of %s is \"always\", stop it for failed cache set %pU.",
                        d->disk->disk_name, c->sb.set_uuid);
                bcache_device_stop(d);
        } else if (atomic_read(&dc->has_dirty)) {
                /*
                 * dc->stop_when_cache_set_failed == BCH_CACHED_STOP_AUTO
                 * and dc->has_dirty == 1
                 */
                pr_warn("stop_when_cache_set_failed of %s is \"auto\" and cache is dirty, stop it to avoid potential data corruption.",
                        d->disk->disk_name);
                        /*
                         * There might be a small time gap that cache set is
                         * released but bcache device is not. Inside this time
                         * gap, regular I/O requests will directly go into
                         * backing device as no cache set attached to. This
                         * behavior may also introduce potential inconsistence
                         * data in writeback mode while cache is dirty.
                         * Therefore before calling bcache_device_stop() due
                         * to a broken cache device, dc->io_disable should be
                         * explicitly set to true.
                         */
                        dc->io_disable = true;
                        /* make others know io_disable is true earlier */
                        smp_mb();
                        bcache_device_stop(d);
        } else {
                /*
                 * dc->stop_when_cache_set_failed == BCH_CACHED_STOP_AUTO
                 * and dc->has_dirty == 0
                 */
                pr_warn("stop_when_cache_set_failed of %s is \"auto\" and cache is clean, keep it alive.",
                        d->disk->disk_name);
        }
}

static void __cache_set_unregister(struct closure *cl)
{
        struct cache_set *c = container_of(cl, struct cache_set, caching);
        struct cached_dev *dc;
        struct bcache_device *d;
        size_t i;

        mutex_lock(&bch_register_lock);

        for (i = 0; i < c->devices_max_used; i++) {
                d = c->devices[i];
                if (!d)
                        continue;

                if (!UUID_FLASH_ONLY(&c->uuids[i]) &&
                    test_bit(CACHE_SET_UNREGISTERING, &c->flags)) {
                        dc = container_of(d, struct cached_dev, disk);
                        bch_cached_dev_detach(dc);
                        if (test_bit(CACHE_SET_IO_DISABLE, &c->flags))
                                conditional_stop_bcache_device(c, d, dc);
                } else {
                        bcache_device_stop(d);
                }
        }

        mutex_unlock(&bch_register_lock);

        continue_at(cl, cache_set_flush, system_wq);
}

void bch_cache_set_stop(struct cache_set *c)
{
        if (!test_and_set_bit(CACHE_SET_STOPPING, &c->flags))
                closure_queue(&c->caching);
}

void bch_cache_set_unregister(struct cache_set *c)
{
        set_bit(CACHE_SET_UNREGISTERING, &c->flags);
        bch_cache_set_stop(c);
}

#define alloc_bucket_pages(gfp, c)                      \
        ((void *) __get_free_pages(__GFP_ZERO|gfp, ilog2(bucket_pages(c))))

struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
{
        int iter_size;
        struct cache_set *c = kzalloc(sizeof(struct cache_set), GFP_KERNEL);
        if (!c)
                return NULL;

        __module_get(THIS_MODULE);
        closure_init(&c->cl, NULL);
        set_closure_fn(&c->cl, cache_set_free, system_wq);

        closure_init(&c->caching, &c->cl);
        set_closure_fn(&c->caching, __cache_set_unregister, system_wq);

        /* Maybe create continue_at_noreturn() and use it here? */
        closure_set_stopped(&c->cl);
        closure_put(&c->cl);

        kobject_init(&c->kobj, &bch_cache_set_ktype);
        kobject_init(&c->internal, &bch_cache_set_internal_ktype);

        bch_cache_accounting_init(&c->accounting, &c->cl);

        memcpy(c->sb.set_uuid, sb->set_uuid, 16);
        c->sb.block_size        = sb->block_size;
        c->sb.bucket_size       = sb->bucket_size;
        c->sb.nr_in_set         = sb->nr_in_set;
        c->sb.last_mount        = sb->last_mount;
        c->bucket_bits          = ilog2(sb->bucket_size);
        c->block_bits           = ilog2(sb->block_size);
        c->nr_uuids             = bucket_bytes(c) / sizeof(struct uuid_entry);
        c->devices_max_used     = 0;
        c->btree_pages          = bucket_pages(c);
        if (c->btree_pages > BTREE_MAX_PAGES)
                c->btree_pages = max_t(int, c->btree_pages / 4,
                                       BTREE_MAX_PAGES);

        sema_init(&c->sb_write_mutex, 1);
        mutex_init(&c->bucket_lock);
        init_waitqueue_head(&c->btree_cache_wait);
        init_waitqueue_head(&c->bucket_wait);
        init_waitqueue_head(&c->gc_wait);
        sema_init(&c->uuid_write_mutex, 1);

        spin_lock_init(&c->btree_gc_time.lock);
        spin_lock_init(&c->btree_split_time.lock);
        spin_lock_init(&c->btree_read_time.lock);

        bch_moving_init_cache_set(c);

        INIT_LIST_HEAD(&c->list);
        INIT_LIST_HEAD(&c->cached_devs);
        INIT_LIST_HEAD(&c->btree_cache);
        INIT_LIST_HEAD(&c->btree_cache_freeable);
        INIT_LIST_HEAD(&c->btree_cache_freed);
        INIT_LIST_HEAD(&c->data_buckets);

        iter_size = (sb->bucket_size / sb->block_size + 1) *
                sizeof(struct btree_iter_set);

        if (!(c->devices = kcalloc(c->nr_uuids, sizeof(void *), GFP_KERNEL)) ||
            mempool_init_slab_pool(&c->search, 32, bch_search_cache) ||
            mempool_init_kmalloc_pool(&c->bio_meta, 2,
                                      sizeof(struct bbio) + sizeof(struct bio_vec) *
                                      bucket_pages(c)) ||
            mempool_init_kmalloc_pool(&c->fill_iter, 1, iter_size) ||
            bioset_init(&c->bio_split, 4, offsetof(struct bbio, bio),
                        BIOSET_NEED_BVECS|BIOSET_NEED_RESCUER) ||
            !(c->uuids = alloc_bucket_pages(GFP_KERNEL, c)) ||
            !(c->moving_gc_wq = alloc_workqueue("bcache_gc",
                                                WQ_MEM_RECLAIM, 0)) ||
            bch_journal_alloc(c) ||
            bch_btree_cache_alloc(c) ||
            bch_open_buckets_alloc(c) ||
            bch_bset_sort_state_init(&c->sort, ilog2(c->btree_pages)))
                goto err;

        c->congested_read_threshold_us  = 2000;
        c->congested_write_threshold_us = 20000;
        c->error_limit  = DEFAULT_IO_ERROR_LIMIT;
        WARN_ON(test_and_clear_bit(CACHE_SET_IO_DISABLE, &c->flags));

        return c;
err:
        bch_cache_set_unregister(c);
        return NULL;
}

static void run_cache_set(struct cache_set *c)
{
        const char *err = "cannot allocate memory";
        struct cached_dev *dc, *t;
        struct cache *ca;
        struct closure cl;
        unsigned i;

        closure_init_stack(&cl);

        for_each_cache(ca, c, i)
                c->nbuckets += ca->sb.nbuckets;
        set_gc_sectors(c);

        if (CACHE_SYNC(&c->sb)) {
                LIST_HEAD(journal);
                struct bkey *k;
                struct jset *j;

                err = "cannot allocate memory for journal";
                if (bch_journal_read(c, &journal))
                        goto err;

                pr_debug("btree_journal_read() done");

                err = "no journal entries found";
                if (list_empty(&journal))
                        goto err;

                j = &list_entry(journal.prev, struct journal_replay, list)->j;

                err = "IO error reading priorities";
                for_each_cache(ca, c, i)
                        prio_read(ca, j->prio_bucket[ca->sb.nr_this_dev]);

                /*
                 * If prio_read() fails it'll call cache_set_error and we'll
                 * tear everything down right away, but if we perhaps checked
                 * sooner we could avoid journal replay.
                 */

                k = &j->btree_root;

                err = "bad btree root";
                if (__bch_btree_ptr_invalid(c, k))
                        goto err;

                err = "error reading btree root";
                c->root = bch_btree_node_get(c, NULL, k, j->btree_level, true, NULL);
                if (IS_ERR_OR_NULL(c->root))
                        goto err;

                list_del_init(&c->root->list);
                rw_unlock(true, c->root);

                err = uuid_read(c, j, &cl);
                if (err)
                        goto err;

                err = "error in recovery";
                if (bch_btree_check(c))
                        goto err;

                bch_journal_mark(c, &journal);
                bch_initial_gc_finish(c);
                pr_debug("btree_check() done");

                /*
                 * bcache_journal_next() can't happen sooner, or
                 * btree_gc_finish() will give spurious errors about last_gc >
                 * gc_gen - this is a hack but oh well.
                 */
                bch_journal_next(&c->journal);

                err = "error starting allocator thread";
                for_each_cache(ca, c, i)
                        if (bch_cache_allocator_start(ca))
                                goto err;

                /*
                 * First place it's safe to allocate: btree_check() and
                 * btree_gc_finish() have to run before we have buckets to
                 * allocate, and bch_bucket_alloc_set() might cause a journal
                 * entry to be written so bcache_journal_next() has to be called
                 * first.
                 *
                 * If the uuids were in the old format we have to rewrite them
                 * before the next journal entry is written:
                 */
                if (j->version < BCACHE_JSET_VERSION_UUID)
                        __uuid_write(c);

                bch_journal_replay(c, &journal);
        } else {
                pr_notice("invalidating existing data");

                for_each_cache(ca, c, i) {
                        unsigned j;

                        ca->sb.keys = clamp_t(int, ca->sb.nbuckets >> 7,
                                              2, SB_JOURNAL_BUCKETS);

                        for (j = 0; j < ca->sb.keys; j++)
                                ca->sb.d[j] = ca->sb.first_bucket + j;
                }

                bch_initial_gc_finish(c);

                err = "error starting allocator thread";
                for_each_cache(ca, c, i)
                        if (bch_cache_allocator_start(ca))
                                goto err;

                mutex_lock(&c->bucket_lock);
                for_each_cache(ca, c, i)
                        bch_prio_write(ca);
                mutex_unlock(&c->bucket_lock);

                err = "cannot allocate new UUID bucket";
                if (__uuid_write(c))
                        goto err;

                err = "cannot allocate new btree root";
                c->root = __bch_btree_node_alloc(c, NULL, 0, true, NULL);
                if (IS_ERR_OR_NULL(c->root))
                        goto err;

                mutex_lock(&c->root->write_lock);
                bkey_copy_key(&c->root->key, &MAX_KEY);
                bch_btree_node_write(c->root, &cl);
                mutex_unlock(&c->root->write_lock);

                bch_btree_set_root(c->root);
                rw_unlock(true, c->root);

                /*
                 * We don't want to write the first journal entry until
                 * everything is set up - fortunately journal entries won't be
                 * written until the SET_CACHE_SYNC() here:
                 */
                SET_CACHE_SYNC(&c->sb, true);

                bch_journal_next(&c->journal);
                bch_journal_meta(c, &cl);
        }

        err = "error starting gc thread";
        if (bch_gc_thread_start(c))
                goto err;

        closure_sync(&cl);
        c->sb.last_mount = get_seconds();
        bcache_write_super(c);

        list_for_each_entry_safe(dc, t, &uncached_devices, list)
                bch_cached_dev_attach(dc, c, NULL);

        flash_devs_run(c);

        set_bit(CACHE_SET_RUNNING, &c->flags);
        return;
err:
        closure_sync(&cl);
        /* XXX: test this, it's broken */
        bch_cache_set_error(c, "%s", err);
}

static bool can_attach_cache(struct cache *ca, struct cache_set *c)
{
        return ca->sb.block_size        == c->sb.block_size &&
                ca->sb.bucket_size      == c->sb.bucket_size &&
                ca->sb.nr_in_set        == c->sb.nr_in_set;
}

static const char *register_cache_set(struct cache *ca)
{
        char buf[12];
        const char *err = "cannot allocate memory";
        struct cache_set *c;

        list_for_each_entry(c, &bch_cache_sets, list)
                if (!memcmp(c->sb.set_uuid, ca->sb.set_uuid, 16)) {
                        if (c->cache[ca->sb.nr_this_dev])
                                return "duplicate cache set member";

                        if (!can_attach_cache(ca, c))
                                return "cache sb does not match set";

                        if (!CACHE_SYNC(&ca->sb))
                                SET_CACHE_SYNC(&c->sb, false);

                        goto found;
                }

        c = bch_cache_set_alloc(&ca->sb);
        if (!c)
                return err;

        err = "error creating kobject";
        if (kobject_add(&c->kobj, bcache_kobj, "%pU", c->sb.set_uuid) ||
            kobject_add(&c->internal, &c->kobj, "internal"))
                goto err;

        if (bch_cache_accounting_add_kobjs(&c->accounting, &c->kobj))
                goto err;

        bch_debug_init_cache_set(c);

        list_add(&c->list, &bch_cache_sets);
found:
        sprintf(buf, "cache%i", ca->sb.nr_this_dev);
        if (sysfs_create_link(&ca->kobj, &c->kobj, "set") ||
            sysfs_create_link(&c->kobj, &ca->kobj, buf))
                goto err;

        if (ca->sb.seq > c->sb.seq) {
                c->sb.version           = ca->sb.version;
                memcpy(c->sb.set_uuid, ca->sb.set_uuid, 16);
                c->sb.flags             = ca->sb.flags;
                c->sb.seq               = ca->sb.seq;
                pr_debug("set version = %llu", c->sb.version);
        }

        kobject_get(&ca->kobj);
        ca->set = c;
        ca->set->cache[ca->sb.nr_this_dev] = ca;
        c->cache_by_alloc[c->caches_loaded++] = ca;

        if (c->caches_loaded == c->sb.nr_in_set)
                run_cache_set(c);

        return NULL;
err:
        bch_cache_set_unregister(c);
        return err;
}

/* Cache device */

void bch_cache_release(struct kobject *kobj)
{
        struct cache *ca = container_of(kobj, struct cache, kobj);
        unsigned i;

        if (ca->set) {
                BUG_ON(ca->set->cache[ca->sb.nr_this_dev] != ca);
                ca->set->cache[ca->sb.nr_this_dev] = NULL;
        }

        free_pages((unsigned long) ca->disk_buckets, ilog2(bucket_pages(ca)));
        kfree(ca->prio_buckets);
        vfree(ca->buckets);

        free_heap(&ca->heap);
        free_fifo(&ca->free_inc);

        for (i = 0; i < RESERVE_NR; i++)
                free_fifo(&ca->free[i]);

        if (ca->sb_bio.bi_inline_vecs[0].bv_page)
                put_page(bio_first_page_all(&ca->sb_bio));

        if (!IS_ERR_OR_NULL(ca->bdev))
                blkdev_put(ca->bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);

        kfree(ca);
        module_put(THIS_MODULE);
}

static int cache_alloc(struct cache *ca)
{
        size_t free;
        size_t btree_buckets;
        struct bucket *b;

        __module_get(THIS_MODULE);
        kobject_init(&ca->kobj, &bch_cache_ktype);

        bio_init(&ca->journal.bio, ca->journal.bio.bi_inline_vecs, 8);

        /*
         * when ca->sb.njournal_buckets is not zero, journal exists,
         * and in bch_journal_replay(), tree node may split,
         * so bucket of RESERVE_BTREE type is needed,
         * the worst situation is all journal buckets are valid journal,
         * and all the keys need to replay,
         * so the number of  RESERVE_BTREE type buckets should be as much
         * as journal buckets
         */
        btree_buckets = ca->sb.njournal_buckets ?: 8;
        free = roundup_pow_of_two(ca->sb.nbuckets) >> 10;

        if (!init_fifo(&ca->free[RESERVE_BTREE], btree_buckets, GFP_KERNEL) ||
            !init_fifo_exact(&ca->free[RESERVE_PRIO], prio_buckets(ca), GFP_KERNEL) ||
            !init_fifo(&ca->free[RESERVE_MOVINGGC], free, GFP_KERNEL) ||
            !init_fifo(&ca->free[RESERVE_NONE], free, GFP_KERNEL) ||
            !init_fifo(&ca->free_inc,   free << 2, GFP_KERNEL) ||
            !init_heap(&ca->heap,       free << 3, GFP_KERNEL) ||
            !(ca->buckets       = vzalloc(array_size(sizeof(struct bucket),
                                                     ca->sb.nbuckets))) ||
            !(ca->prio_buckets  = kzalloc(array3_size(sizeof(uint64_t),
                                                      prio_buckets(ca), 2),
                                          GFP_KERNEL)) ||
            !(ca->disk_buckets  = alloc_bucket_pages(GFP_KERNEL, ca)))
                return -ENOMEM;

        ca->prio_last_buckets = ca->prio_buckets + prio_buckets(ca);

        for_each_bucket(b, ca)
                atomic_set(&b->pin, 0);

        return 0;
}

static int register_cache(struct cache_sb *sb, struct page *sb_page,
                                struct block_device *bdev, struct cache *ca)
{
        const char *err = NULL; /* must be set for any error case */
        int ret = 0;

        bdevname(bdev, ca->cache_dev_name);
        memcpy(&ca->sb, sb, sizeof(struct cache_sb));
        ca->bdev = bdev;
        ca->bdev->bd_holder = ca;

        bio_init(&ca->sb_bio, ca->sb_bio.bi_inline_vecs, 1);
        bio_first_bvec_all(&ca->sb_bio)->bv_page = sb_page;
        get_page(sb_page);

        if (blk_queue_discard(bdev_get_queue(bdev)))
                ca->discard = CACHE_DISCARD(&ca->sb);

        ret = cache_alloc(ca);
        if (ret != 0) {
                blkdev_put(bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
                if (ret == -ENOMEM)
                        err = "cache_alloc(): -ENOMEM";
                else
                        err = "cache_alloc(): unknown error";
                goto err;
        }

        if (kobject_add(&ca->kobj, &part_to_dev(bdev->bd_part)->kobj, "bcache")) {
                err = "error calling kobject_add";
                ret = -ENOMEM;
                goto out;
        }

        mutex_lock(&bch_register_lock);
        err = register_cache_set(ca);
        mutex_unlock(&bch_register_lock);

        if (err) {
                ret = -ENODEV;
                goto out;
        }

        pr_info("registered cache device %s", ca->cache_dev_name);

out:
        kobject_put(&ca->kobj);

err:
        if (err)
                pr_notice("error %s: %s", ca->cache_dev_name, err);

        return ret;
}

/* Global interfaces/init */

static ssize_t register_bcache(struct kobject *, struct kobj_attribute *,
                               const char *, size_t);

kobj_attribute_write(register,          register_bcache);
kobj_attribute_write(register_quiet,    register_bcache);

static bool bch_is_open_backing(struct block_device *bdev) {
        struct cache_set *c, *tc;
        struct cached_dev *dc, *t;

        list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
                list_for_each_entry_safe(dc, t, &c->cached_devs, list)
                        if (dc->bdev == bdev)
                                return true;
        list_for_each_entry_safe(dc, t, &uncached_devices, list)
                if (dc->bdev == bdev)
                        return true;
        return false;
}

static bool bch_is_open_cache(struct block_device *bdev) {
        struct cache_set *c, *tc;
        struct cache *ca;
        unsigned i;

        list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
                for_each_cache(ca, c, i)
                        if (ca->bdev == bdev)
                                return true;
        return false;
}

static bool bch_is_open(struct block_device *bdev) {
        return bch_is_open_cache(bdev) || bch_is_open_backing(bdev);
}

static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
                               const char *buffer, size_t size)
{
        ssize_t ret = size;
        const char *err = "cannot allocate memory";
        char *path = NULL;
        struct cache_sb *sb = NULL;
        struct block_device *bdev = NULL;
        struct page *sb_page = NULL;

        if (!try_module_get(THIS_MODULE))
                return -EBUSY;

        if (!(path = kstrndup(buffer, size, GFP_KERNEL)) ||
            !(sb = kmalloc(sizeof(struct cache_sb), GFP_KERNEL)))
                goto err;

        err = "failed to open device";
        bdev = blkdev_get_by_path(strim(path),
                                  FMODE_READ|FMODE_WRITE|FMODE_EXCL,
                                  sb);
        if (IS_ERR(bdev)) {
                if (bdev == ERR_PTR(-EBUSY)) {
                        bdev = lookup_bdev(strim(path));
                        mutex_lock(&bch_register_lock);
                        if (!IS_ERR(bdev) && bch_is_open(bdev))
                                err = "device already registered";
                        else
                                err = "device busy";
                        mutex_unlock(&bch_register_lock);
                        if (!IS_ERR(bdev))
                                bdput(bdev);
                        if (attr == &ksysfs_register_quiet)
                                goto out;
                }
                goto err;
        }

        err = "failed to set blocksize";
        if (set_blocksize(bdev, 4096))
                goto err_close;

        err = read_super(sb, bdev, &sb_page);
        if (err)
                goto err_close;

        err = "failed to register device";
        if (SB_IS_BDEV(sb)) {
                struct cached_dev *dc = kzalloc(sizeof(*dc), GFP_KERNEL);
                if (!dc)
                        goto err_close;

                mutex_lock(&bch_register_lock);
                register_bdev(sb, sb_page, bdev, dc);
                mutex_unlock(&bch_register_lock);
        } else {
                struct cache *ca = kzalloc(sizeof(*ca), GFP_KERNEL);
                if (!ca)
                        goto err_close;

                if (register_cache(sb, sb_page, bdev, ca) != 0)
                        goto err;
        }
out:
        if (sb_page)
                put_page(sb_page);
        kfree(sb);
        kfree(path);
        module_put(THIS_MODULE);
        return ret;

err_close:
        blkdev_put(bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
err:
        pr_info("error %s: %s", path, err);
        ret = -EINVAL;
        goto out;
}

static int bcache_reboot(struct notifier_block *n, unsigned long code, void *x)
{
        if (code == SYS_DOWN ||
            code == SYS_HALT ||
            code == SYS_POWER_OFF) {
                DEFINE_WAIT(wait);
                unsigned long start = jiffies;
                bool stopped = false;

                struct cache_set *c, *tc;
                struct cached_dev *dc, *tdc;

                mutex_lock(&bch_register_lock);

                if (list_empty(&bch_cache_sets) &&
                    list_empty(&uncached_devices))
                        goto out;

                pr_info("Stopping all devices:");

                list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
                        bch_cache_set_stop(c);

                list_for_each_entry_safe(dc, tdc, &uncached_devices, list)
                        bcache_device_stop(&dc->disk);

                /* What's a condition variable? */
                while (1) {
                        long timeout = start + 2 * HZ - jiffies;

                        stopped = list_empty(&bch_cache_sets) &&
                                list_empty(&uncached_devices);

                        if (timeout < 0 || stopped)
                                break;

                        prepare_to_wait(&unregister_wait, &wait,
                                        TASK_UNINTERRUPTIBLE);

                        mutex_unlock(&bch_register_lock);
                        schedule_timeout(timeout);
                        mutex_lock(&bch_register_lock);
                }

                finish_wait(&unregister_wait, &wait);

                if (stopped)
                        pr_info("All devices stopped");
                else
                        pr_notice("Timeout waiting for devices to be closed");
out:
                mutex_unlock(&bch_register_lock);
        }

        return NOTIFY_DONE;
}

static struct notifier_block reboot = {
        .notifier_call  = bcache_reboot,
        .priority       = INT_MAX, /* before any real devices */
};

static void bcache_exit(void)
{
        bch_debug_exit();
        bch_request_exit();
        if (bcache_kobj)
                kobject_put(bcache_kobj);
        if (bcache_wq)
                destroy_workqueue(bcache_wq);
        if (bcache_major)
                unregister_blkdev(bcache_major, "bcache");
        unregister_reboot_notifier(&reboot);
        mutex_destroy(&bch_register_lock);
}

static int __init bcache_init(void)
{
        static const struct attribute *files[] = {
                &ksysfs_register.attr,
                &ksysfs_register_quiet.attr,
                NULL
        };

        mutex_init(&bch_register_lock);
        init_waitqueue_head(&unregister_wait);
        register_reboot_notifier(&reboot);

        bcache_major = register_blkdev(0, "bcache");
        if (bcache_major < 0) {
                unregister_reboot_notifier(&reboot);
                mutex_destroy(&bch_register_lock);
                return bcache_major;
        }

        if (!(bcache_wq = alloc_workqueue("bcache", WQ_MEM_RECLAIM, 0)) ||
            !(bcache_kobj = kobject_create_and_add("bcache", fs_kobj)) ||
            bch_request_init() ||
            bch_debug_init(bcache_kobj) || closure_debug_init() ||
            sysfs_create_files(bcache_kobj, files))
                goto err;

        return 0;
err:
        bcache_exit();
        return -ENOMEM;
}

module_exit(bcache_exit);
module_init(bcache_init);