[bcachefs-tools-debian] / libbcache / super.c

/*
 * 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 "blockdev.h"
#include "alloc.h"
#include "btree_cache.h"
#include "btree_gc.h"
#include "btree_update.h"
#include "btree_io.h"
#include "chardev.h"
#include "checksum.h"
#include "clock.h"
#include "compress.h"
#include "debug.h"
#include "error.h"
#include "fs.h"
#include "fs-gc.h"
#include "inode.h"
#include "io.h"
#include "journal.h"
#include "keylist.h"
#include "move.h"
#include "migrate.h"
#include "movinggc.h"
#include "notify.h"
#include "stats.h"
#include "super.h"
#include "super-io.h"
#include "tier.h"
#include "writeback.h"

#include <linux/backing-dev.h>
#include <linux/blkdev.h>
#include <linux/debugfs.h>
#include <linux/device.h>
#include <linux/genhd.h>
#include <linux/idr.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/random.h>
#include <linux/reboot.h>
#include <linux/sysfs.h>
#include <crypto/hash.h>

#include <trace/events/bcache.h>

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

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

static struct kset *bcache_kset;
static LIST_HEAD(bch_fs_list);
static DEFINE_MUTEX(bch_fs_list_lock);

static DECLARE_WAIT_QUEUE_HEAD(bch_read_only_wait);
struct workqueue_struct *bcache_io_wq;
struct crypto_shash *bch_sha256;

static void bch_dev_free(struct bch_dev *);
static int bch_dev_alloc(struct bch_fs *, unsigned);
static int bch_dev_sysfs_online(struct bch_dev *);
static void __bch_dev_read_only(struct bch_fs *, struct bch_dev *);

struct bch_fs *bch_bdev_to_fs(struct block_device *bdev)
{
        struct bch_fs *c;
        struct bch_dev *ca;
        unsigned i;

        mutex_lock(&bch_fs_list_lock);
        rcu_read_lock();

        list_for_each_entry(c, &bch_fs_list, list)
                for_each_member_device_rcu(ca, c, i)
                        if (ca->disk_sb.bdev == bdev) {
                                closure_get(&c->cl);
                                goto found;
                        }
        c = NULL;
found:
        rcu_read_unlock();
        mutex_unlock(&bch_fs_list_lock);

        return c;
}

static struct bch_fs *__bch_uuid_to_fs(uuid_le uuid)
{
        struct bch_fs *c;

        lockdep_assert_held(&bch_fs_list_lock);

        list_for_each_entry(c, &bch_fs_list, list)
                if (!memcmp(&c->disk_sb->uuid, &uuid, sizeof(uuid_le)))
                        return c;

        return NULL;
}

struct bch_fs *bch_uuid_to_fs(uuid_le uuid)
{
        struct bch_fs *c;

        mutex_lock(&bch_fs_list_lock);
        c = __bch_uuid_to_fs(uuid);
        if (c)
                closure_get(&c->cl);
        mutex_unlock(&bch_fs_list_lock);

        return c;
}

int bch_congested(struct bch_fs *c, int bdi_bits)
{
        struct backing_dev_info *bdi;
        struct bch_dev *ca;
        unsigned i;
        int ret = 0;

        if (bdi_bits & (1 << WB_sync_congested)) {
                /* Reads - check all devices: */
                for_each_readable_member(ca, c, i) {
                        bdi = blk_get_backing_dev_info(ca->disk_sb.bdev);

                        if (bdi_congested(bdi, bdi_bits)) {
                                ret = 1;
                                break;
                        }
                }
        } else {
                /* Writes prefer fastest tier: */
                struct bch_tier *tier = READ_ONCE(c->fastest_tier);
                struct dev_group *grp = tier ? &tier->devs : &c->all_devs;

                rcu_read_lock();
                group_for_each_dev(ca, grp, i) {
                        bdi = blk_get_backing_dev_info(ca->disk_sb.bdev);

                        if (bdi_congested(bdi, bdi_bits)) {
                                ret = 1;
                                break;
                        }
                }
                rcu_read_unlock();
        }

        return ret;
}

static int bch_congested_fn(void *data, int bdi_bits)
{
        struct bch_fs *c = data;

        return bch_congested(c, bdi_bits);
}

/* Filesystem RO/RW: */

/*
 * For startup/shutdown of RW stuff, the dependencies are:
 *
 * - foreground writes depend on copygc and tiering (to free up space)
 *
 * - copygc and tiering depend on mark and sweep gc (they actually probably
 *   don't because they either reserve ahead of time or don't block if
 *   allocations fail, but allocations can require mark and sweep gc to run
 *   because of generation number wraparound)
 *
 * - all of the above depends on the allocator threads
 *
 * - allocator depends on the journal (when it rewrites prios and gens)
 */

static void __bch_fs_read_only(struct bch_fs *c)
{
        struct bch_dev *ca;
        unsigned i;

        bch_tiering_stop(c);

        for_each_member_device(ca, c, i)
                bch_moving_gc_stop(ca);

        bch_gc_thread_stop(c);

        bch_btree_flush(c);

        for_each_member_device(ca, c, i)
                bch_dev_allocator_stop(ca);

        bch_fs_journal_stop(&c->journal);
}

static void bch_writes_disabled(struct percpu_ref *writes)
{
        struct bch_fs *c = container_of(writes, struct bch_fs, writes);

        set_bit(BCH_FS_WRITE_DISABLE_COMPLETE, &c->flags);
        wake_up(&bch_read_only_wait);
}

void bch_fs_read_only(struct bch_fs *c)
{
        mutex_lock(&c->state_lock);
        if (c->state != BCH_FS_STARTING &&
            c->state != BCH_FS_RW)
                goto out;

        if (test_bit(BCH_FS_ERROR, &c->flags))
                goto out;

        trace_fs_read_only(c);

        /*
         * Block new foreground-end write operations from starting - any new
         * writes will return -EROFS:
         *
         * (This is really blocking new _allocations_, writes to previously
         * allocated space can still happen until stopping the allocator in
         * bch_dev_allocator_stop()).
         */
        percpu_ref_kill(&c->writes);

        del_timer(&c->foreground_write_wakeup);
        cancel_delayed_work(&c->pd_controllers_update);

        c->foreground_write_pd.rate.rate = UINT_MAX;
        bch_wake_delayed_writes((unsigned long) c);

        /*
         * If we're not doing an emergency shutdown, we want to wait on
         * outstanding writes to complete so they don't see spurious errors due
         * to shutting down the allocator:
         *
         * If we are doing an emergency shutdown outstanding writes may
         * hang until we shutdown the allocator so we don't want to wait
         * on outstanding writes before shutting everything down - but
         * we do need to wait on them before returning and signalling
         * that going RO is complete:
         */
        wait_event(bch_read_only_wait,
                   test_bit(BCH_FS_WRITE_DISABLE_COMPLETE, &c->flags) ||
                   test_bit(BCH_FS_EMERGENCY_RO, &c->flags));

        __bch_fs_read_only(c);

        wait_event(bch_read_only_wait,
                   test_bit(BCH_FS_WRITE_DISABLE_COMPLETE, &c->flags));

        clear_bit(BCH_FS_WRITE_DISABLE_COMPLETE, &c->flags);

        if (!bch_journal_error(&c->journal) &&
            !test_bit(BCH_FS_ERROR, &c->flags)) {
                mutex_lock(&c->sb_lock);
                SET_BCH_SB_CLEAN(c->disk_sb, true);
                bch_write_super(c);
                mutex_unlock(&c->sb_lock);
        }

        c->state = BCH_FS_RO;
        bch_notify_fs_read_only(c);
        trace_fs_read_only_done(c);
out:
        mutex_unlock(&c->state_lock);
}

static void bch_fs_read_only_work(struct work_struct *work)
{
        struct bch_fs *c =
                container_of(work, struct bch_fs, read_only_work);

        bch_fs_read_only(c);
}

static void bch_fs_read_only_async(struct bch_fs *c)
{
        queue_work(system_long_wq, &c->read_only_work);
}

bool bch_fs_emergency_read_only(struct bch_fs *c)
{
        bool ret = !test_and_set_bit(BCH_FS_EMERGENCY_RO, &c->flags);

        bch_fs_read_only_async(c);
        bch_journal_halt(&c->journal);

        wake_up(&bch_read_only_wait);
        return ret;
}

const char *bch_fs_read_write(struct bch_fs *c)
{
        struct bch_dev *ca;
        const char *err = NULL;
        unsigned i;

        mutex_lock(&c->state_lock);
        if (c->state != BCH_FS_STARTING &&
            c->state != BCH_FS_RO)
                goto out;

        err = "error starting allocator thread";
        for_each_rw_member(ca, c, i)
                if (bch_dev_allocator_start(ca)) {
                        percpu_ref_put(&ca->io_ref);
                        goto err;
                }

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

        err = "error starting moving GC thread";
        for_each_rw_member(ca, c, i)
                if (bch_moving_gc_start(ca)) {
                        percpu_ref_put(&ca->io_ref);
                        goto err;
                }

        err = "error starting tiering thread";
        if (bch_tiering_start(c))
                goto err;

        schedule_delayed_work(&c->pd_controllers_update, 5 * HZ);

        if (c->state != BCH_FS_STARTING)
                percpu_ref_reinit(&c->writes);

        c->state = BCH_FS_RW;
        err = NULL;
out:
        mutex_unlock(&c->state_lock);
        return err;
err:
        __bch_fs_read_only(c);
        goto out;
}

/* Filesystem startup/shutdown: */

static void bch_fs_free(struct bch_fs *c)
{
        bch_fs_encryption_exit(c);
        bch_fs_btree_exit(c);
        bch_fs_journal_exit(&c->journal);
        bch_io_clock_exit(&c->io_clock[WRITE]);
        bch_io_clock_exit(&c->io_clock[READ]);
        bch_fs_compress_exit(c);
        bch_fs_blockdev_exit(c);
        bdi_destroy(&c->bdi);
        lg_lock_free(&c->usage_lock);
        free_percpu(c->usage_percpu);
        mempool_exit(&c->btree_bounce_pool);
        mempool_exit(&c->bio_bounce_pages);
        bioset_exit(&c->bio_write);
        bioset_exit(&c->bio_read_split);
        bioset_exit(&c->bio_read);
        bioset_exit(&c->btree_read_bio);
        mempool_exit(&c->btree_interior_update_pool);
        mempool_exit(&c->btree_reserve_pool);
        mempool_exit(&c->fill_iter);
        percpu_ref_exit(&c->writes);

        if (c->copygc_wq)
                destroy_workqueue(c->copygc_wq);
        if (c->wq)
                destroy_workqueue(c->wq);

        free_pages((unsigned long) c->disk_sb, c->disk_sb_order);
        kfree(c);
        module_put(THIS_MODULE);
}

static void bch_fs_exit(struct bch_fs *c)
{
        unsigned i;

        del_timer_sync(&c->foreground_write_wakeup);
        cancel_delayed_work_sync(&c->pd_controllers_update);
        cancel_work_sync(&c->read_only_work);
        cancel_work_sync(&c->bio_submit_work);
        cancel_work_sync(&c->read_retry_work);

        for (i = 0; i < c->sb.nr_devices; i++)
                if (c->devs[i])
                        bch_dev_free(c->devs[i]);

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

static void bch_fs_offline(struct bch_fs *c)
{
        struct bch_dev *ca;
        unsigned i;

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

        for_each_member_device(ca, c, i)
                if (ca->kobj.state_in_sysfs &&
                    ca->disk_sb.bdev)
                        sysfs_remove_link(&part_to_dev(ca->disk_sb.bdev->bd_part)->kobj,
                                          "bcache");

        if (c->kobj.state_in_sysfs)
                kobject_del(&c->kobj);

        bch_fs_debug_exit(c);
        bch_fs_chardev_exit(c);

        bch_cache_accounting_destroy(&c->accounting);

        kobject_put(&c->time_stats);
        kobject_put(&c->opts_dir);
        kobject_put(&c->internal);

        __bch_fs_read_only(c);
}

/*
 * should be __bch_fs_stop4 - block devices are closed, now we can finally
 * free it
 */
void bch_fs_release(struct kobject *kobj)
{
        struct bch_fs *c = container_of(kobj, struct bch_fs, kobj);

        bch_notify_fs_stopped(c);
        bch_fs_free(c);
}

/*
 * All activity on the filesystem should have stopped now - close devices:
 */
static void __bch_fs_stop3(struct closure *cl)
{
        struct bch_fs *c = container_of(cl, struct bch_fs, cl);

        bch_fs_exit(c);
}

/*
 * Openers (i.e. block devices) should have exited, shutdown all userspace
 * interfaces and wait for &c->cl to hit 0
 */
static void __bch_fs_stop2(struct closure *cl)
{
        struct bch_fs *c = container_of(cl, struct bch_fs, caching);

        bch_fs_offline(c);

        closure_return(cl);
}

/*
 * First phase of the shutdown process that's kicked off by bch_fs_stop_async();
 * we haven't waited for anything to stop yet, we're just punting to process
 * context to shut down block devices:
 */
static void __bch_fs_stop1(struct closure *cl)
{
        struct bch_fs *c = container_of(cl, struct bch_fs, caching);

        bch_blockdevs_stop(c);

        continue_at(cl, __bch_fs_stop2, system_wq);
}

void bch_fs_stop_async(struct bch_fs *c)
{
        mutex_lock(&c->state_lock);
        if (c->state != BCH_FS_STOPPING) {
                c->state = BCH_FS_STOPPING;
                closure_queue(&c->caching);
        }
        mutex_unlock(&c->state_lock);
}

void bch_fs_stop(struct bch_fs *c)
{
        mutex_lock(&c->state_lock);
        BUG_ON(c->state == BCH_FS_STOPPING);
        c->state = BCH_FS_STOPPING;
        mutex_unlock(&c->state_lock);

        bch_blockdevs_stop(c);

        closure_sync(&c->caching);
        closure_debug_destroy(&c->caching);

        bch_fs_offline(c);

        closure_put(&c->cl);
        closure_sync(&c->cl);

        bch_fs_exit(c);
}

/* Stop, detaching from backing devices: */
void bch_fs_detach(struct bch_fs *c)
{
        if (!test_and_set_bit(BCH_FS_DETACHING, &c->flags))
                bch_fs_stop_async(c);
}

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

static struct bch_fs *bch_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
{
        struct bch_sb_field_members *mi;
        struct bch_fs *c;
        unsigned i, iter_size, journal_entry_bytes;

        c = kzalloc(sizeof(struct bch_fs), GFP_KERNEL);
        if (!c)
                return NULL;

        __module_get(THIS_MODULE);

        c->minor                = -1;

        mutex_init(&c->state_lock);
        mutex_init(&c->sb_lock);
        INIT_RADIX_TREE(&c->devices, GFP_KERNEL);
        mutex_init(&c->btree_cache_lock);
        mutex_init(&c->bucket_lock);
        mutex_init(&c->btree_root_lock);
        INIT_WORK(&c->read_only_work, bch_fs_read_only_work);

        init_rwsem(&c->gc_lock);

#define BCH_TIME_STAT(name, frequency_units, duration_units)            \
        spin_lock_init(&c->name##_time.lock);
        BCH_TIME_STATS()
#undef BCH_TIME_STAT

        bch_fs_allocator_init(c);
        bch_fs_tiering_init(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->btree_interior_update_list);
        mutex_init(&c->btree_reserve_cache_lock);
        mutex_init(&c->btree_interior_update_lock);

        mutex_init(&c->bio_bounce_pages_lock);
        INIT_WORK(&c->bio_submit_work, bch_bio_submit_work);
        spin_lock_init(&c->bio_submit_lock);
        bio_list_init(&c->read_retry_list);
        spin_lock_init(&c->read_retry_lock);
        INIT_WORK(&c->read_retry_work, bch_read_retry_work);
        mutex_init(&c->zlib_workspace_lock);

        seqcount_init(&c->gc_pos_lock);

        c->prio_clock[READ].hand = 1;
        c->prio_clock[READ].min_prio = 0;
        c->prio_clock[WRITE].hand = 1;
        c->prio_clock[WRITE].min_prio = 0;

        c->congested_read_threshold_us  = 2000;
        c->congested_write_threshold_us = 20000;
        c->error_limit  = 16 << IO_ERROR_SHIFT;
        init_waitqueue_head(&c->writeback_wait);

        c->writeback_pages_max = (256 << 10) / PAGE_SIZE;

        c->copy_gc_enabled = 1;
        c->tiering_enabled = 1;
        c->tiering_percent = 10;

        c->foreground_target_percent = 20;

        c->journal.write_time   = &c->journal_write_time;
        c->journal.delay_time   = &c->journal_delay_time;
        c->journal.blocked_time = &c->journal_blocked_time;
        c->journal.flush_seq_time = &c->journal_flush_seq_time;

        mutex_init(&c->uevent_lock);

        mutex_lock(&c->sb_lock);

        if (bch_sb_to_fs(c, sb)) {
                mutex_unlock(&c->sb_lock);
                goto err;
        }

        mutex_unlock(&c->sb_lock);

        scnprintf(c->name, sizeof(c->name), "%pU", &c->sb.user_uuid);

        bch_opts_apply(&c->opts, bch_sb_opts(sb));
        bch_opts_apply(&c->opts, opts);

        c->opts.nochanges       |= c->opts.noreplay;
        c->opts.read_only       |= c->opts.nochanges;

        c->block_bits           = ilog2(c->sb.block_size);

        if (bch_fs_init_fault("fs_alloc"))
                goto err;

        iter_size = (btree_blocks(c) + 1) * 2 *
                sizeof(struct btree_node_iter_set);

        journal_entry_bytes = 512U << BCH_SB_JOURNAL_ENTRY_SIZE(sb);

        if (!(c->wq = alloc_workqueue("bcache",
                                WQ_FREEZABLE|WQ_MEM_RECLAIM|WQ_HIGHPRI, 1)) ||
            !(c->copygc_wq = alloc_workqueue("bcache_copygc",
                                WQ_FREEZABLE|WQ_MEM_RECLAIM|WQ_HIGHPRI, 1)) ||
            percpu_ref_init(&c->writes, bch_writes_disabled, 0, GFP_KERNEL) ||
            mempool_init_kmalloc_pool(&c->btree_reserve_pool, 1,
                                      sizeof(struct btree_reserve)) ||
            mempool_init_kmalloc_pool(&c->btree_interior_update_pool, 1,
                                      sizeof(struct btree_interior_update)) ||
            mempool_init_kmalloc_pool(&c->fill_iter, 1, iter_size) ||
            bioset_init(&c->btree_read_bio, 1, 0) ||
            bioset_init(&c->bio_read, 1, offsetof(struct bch_read_bio, bio)) ||
            bioset_init(&c->bio_read_split, 1, offsetof(struct bch_read_bio, bio)) ||
            bioset_init(&c->bio_write, 1, offsetof(struct bch_write_bio, bio)) ||
            mempool_init_page_pool(&c->bio_bounce_pages,
                                   max_t(unsigned,
                                         c->sb.btree_node_size,
                                         BCH_ENCODED_EXTENT_MAX) /
                                   PAGE_SECTORS, 0) ||
            !(c->usage_percpu = alloc_percpu(struct bch_fs_usage)) ||
            lg_lock_init(&c->usage_lock) ||
            mempool_init_page_pool(&c->btree_bounce_pool, 1,
                                   ilog2(btree_pages(c))) ||
            bdi_setup_and_register(&c->bdi, "bcache") ||
            bch_fs_blockdev_init(c) ||
            bch_io_clock_init(&c->io_clock[READ]) ||
            bch_io_clock_init(&c->io_clock[WRITE]) ||
            bch_fs_journal_init(&c->journal, journal_entry_bytes) ||
            bch_fs_btree_init(c) ||
            bch_fs_encryption_init(c) ||
            bch_fs_compress_init(c) ||
            bch_check_set_has_compressed_data(c, c->opts.compression))
                goto err;

        c->bdi.ra_pages         = VM_MAX_READAHEAD * 1024 / PAGE_SIZE;
        c->bdi.congested_fn     = bch_congested_fn;
        c->bdi.congested_data   = c;

        mi = bch_sb_get_members(c->disk_sb);
        for (i = 0; i < c->sb.nr_devices; i++)
                if (!bch_is_zero(mi->members[i].uuid.b, sizeof(uuid_le)) &&
                    bch_dev_alloc(c, i))
                        goto err;

        /*
         * Now that all allocations have succeeded, init various refcounty
         * things that let us shutdown:
         */
        closure_init(&c->cl, NULL);

        c->kobj.kset = bcache_kset;
        kobject_init(&c->kobj, &bch_fs_ktype);
        kobject_init(&c->internal, &bch_fs_internal_ktype);
        kobject_init(&c->opts_dir, &bch_fs_opts_dir_ktype);
        kobject_init(&c->time_stats, &bch_fs_time_stats_ktype);

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

        closure_init(&c->caching, &c->cl);
        set_closure_fn(&c->caching, __bch_fs_stop1, system_wq);

        closure_get(&c->cl);
        continue_at_noreturn(&c->cl, __bch_fs_stop3, system_wq);
        return c;
err:
        bch_fs_free(c);
        return NULL;
}

static const char *__bch_fs_online(struct bch_fs *c)
{
        struct bch_dev *ca;
        const char *err = NULL;
        unsigned i;
        int ret;

        lockdep_assert_held(&bch_fs_list_lock);

        if (!list_empty(&c->list))
                return NULL;

        if (__bch_uuid_to_fs(c->sb.uuid))
                return "filesystem UUID already open";

        ret = bch_fs_chardev_init(c);
        if (ret)
                return "error creating character device";

        bch_fs_debug_init(c);

        if (kobject_add(&c->kobj, NULL, "%pU", c->sb.user_uuid.b) ||
            kobject_add(&c->internal, &c->kobj, "internal") ||
            kobject_add(&c->opts_dir, &c->kobj, "options") ||
            kobject_add(&c->time_stats, &c->kobj, "time_stats") ||
            bch_cache_accounting_add_kobjs(&c->accounting, &c->kobj))
                return "error creating sysfs objects";

        mutex_lock(&c->state_lock);

        err = "error creating sysfs objects";
        __for_each_member_device(ca, c, i)
                if (bch_dev_sysfs_online(ca))
                        goto err;

        err = "can't bring up blockdev volumes";
        if (bch_blockdev_volumes_start(c))
                goto err;

        bch_attach_backing_devs(c);

        list_add(&c->list, &bch_fs_list);
        err = NULL;
err:
        mutex_unlock(&c->state_lock);
        return err;
}

static const char *bch_fs_online(struct bch_fs *c)
{
        const char *err;

        mutex_lock(&bch_fs_list_lock);
        err = __bch_fs_online(c);
        mutex_unlock(&bch_fs_list_lock);

        return err;
}

static const char *__bch_fs_start(struct bch_fs *c)
{
        const char *err = "cannot allocate memory";
        struct bch_sb_field_members *mi;
        struct bch_dev *ca;
        unsigned i, id;
        time64_t now;
        LIST_HEAD(journal);
        struct jset *j;
        int ret = -EINVAL;

        BUG_ON(c->state != BCH_FS_STARTING);

        mutex_lock(&c->sb_lock);
        for_each_online_member(ca, c, i)
                bch_sb_from_fs(c, ca);
        mutex_unlock(&c->sb_lock);

        if (BCH_SB_INITIALIZED(c->disk_sb)) {
                ret = bch_journal_read(c, &journal);
                if (ret)
                        goto err;

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

                c->prio_clock[READ].hand = le16_to_cpu(j->read_clock);
                c->prio_clock[WRITE].hand = le16_to_cpu(j->write_clock);

                err = "error reading priorities";
                for_each_readable_member(ca, c, i) {
                        ret = bch_prio_read(ca);
                        if (ret) {
                                percpu_ref_put(&ca->io_ref);
                                goto err;
                        }
                }

                for (id = 0; id < BTREE_ID_NR; id++) {
                        unsigned level;
                        struct bkey_i *k;

                        err = "bad btree root";
                        k = bch_journal_find_btree_root(c, j, id, &level);
                        if (!k && id == BTREE_ID_EXTENTS)
                                goto err;
                        if (!k) {
                                pr_debug("missing btree root: %d", id);
                                continue;
                        }

                        err = "error reading btree root";
                        if (bch_btree_root_read(c, id, k, level))
                                goto err;
                }

                bch_verbose(c, "starting mark and sweep:");

                err = "error in recovery";
                if (bch_initial_gc(c, &journal))
                        goto err;

                if (c->opts.noreplay)
                        goto recovery_done;

                bch_verbose(c, "mark and sweep done");

                /*
                 * bch_journal_start() can't happen sooner, or btree_gc_finish()
                 * will give spurious errors about oldest_gen > bucket_gen -
                 * this is a hack but oh well.
                 */
                bch_journal_start(c);

                err = "error starting allocator thread";
                for_each_rw_member(ca, c, i)
                        if (bch_dev_allocator_start(ca)) {
                                percpu_ref_put(&ca->io_ref);
                                goto err;
                        }

                bch_verbose(c, "starting journal replay:");

                err = "journal replay failed";
                ret = bch_journal_replay(c, &journal);
                if (ret)
                        goto err;

                bch_verbose(c, "journal replay done");

                if (c->opts.norecovery)
                        goto recovery_done;

                bch_verbose(c, "starting fsck:");
                err = "error in fsck";
                ret = bch_fsck(c, !c->opts.nofsck);
                if (ret)
                        goto err;

                bch_verbose(c, "fsck done");
        } else {
                struct bch_inode_unpacked inode;
                struct bkey_inode_buf packed_inode;
                struct closure cl;

                closure_init_stack(&cl);

                bch_notice(c, "initializing new filesystem");

                bch_initial_gc(c, NULL);

                err = "unable to allocate journal buckets";
                for_each_rw_member(ca, c, i)
                        if (bch_dev_journal_alloc(ca)) {
                                percpu_ref_put(&ca->io_ref);
                                goto err;
                        }

                /*
                 * journal_res_get() will crash if called before this has
                 * set up the journal.pin FIFO and journal.cur pointer:
                 */
                bch_journal_start(c);
                bch_journal_set_replay_done(&c->journal);

                err = "error starting allocator thread";
                for_each_rw_member(ca, c, i)
                        if (bch_dev_allocator_start(ca)) {
                                percpu_ref_put(&ca->io_ref);
                                goto err;
                        }

                err = "cannot allocate new btree root";
                for (id = 0; id < BTREE_ID_NR; id++)
                        if (bch_btree_root_alloc(c, id, &cl)) {
                                closure_sync(&cl);
                                goto err;
                        }

                /* Wait for new btree roots to be written: */
                closure_sync(&cl);

                bch_inode_init(c, &inode, 0, 0,
                               S_IFDIR|S_IRWXU|S_IRUGO|S_IXUGO, 0);
                inode.inum = BCACHE_ROOT_INO;

                bch_inode_pack(&packed_inode, &inode);

                err = "error creating root directory";
                if (bch_btree_insert(c, BTREE_ID_INODES,
                                     &packed_inode.inode.k_i,
                                     NULL, NULL, NULL, 0))
                        goto err;

                err = "error writing first journal entry";
                if (bch_journal_meta(&c->journal))
                        goto err;
        }
recovery_done:
        err = "dynamic fault";
        if (bch_fs_init_fault("fs_start"))
                goto err;

        if (c->opts.read_only) {
                bch_fs_read_only(c);
        } else {
                err = bch_fs_read_write(c);
                if (err)
                        goto err;
        }

        mutex_lock(&c->sb_lock);
        mi = bch_sb_get_members(c->disk_sb);
        now = ktime_get_seconds();

        for_each_member_device(ca, c, i)
                mi->members[ca->dev_idx].last_mount = cpu_to_le64(now);

        SET_BCH_SB_INITIALIZED(c->disk_sb, true);
        SET_BCH_SB_CLEAN(c->disk_sb, false);
        c->disk_sb->version = BCACHE_SB_VERSION_CDEV;

        bch_write_super(c);
        mutex_unlock(&c->sb_lock);

        err = NULL;
out:
        bch_journal_entries_free(&journal);
        return err;
err:
        switch (ret) {
        case BCH_FSCK_ERRORS_NOT_FIXED:
                bch_err(c, "filesystem contains errors: please report this to the developers");
                pr_cont("mount with -o fix_errors to repair");
                err = "fsck error";
                break;
        case BCH_FSCK_REPAIR_UNIMPLEMENTED:
                bch_err(c, "filesystem contains errors: please report this to the developers");
                pr_cont("repair unimplemented: inform the developers so that it can be added");
                err = "fsck error";
                break;
        case BCH_FSCK_REPAIR_IMPOSSIBLE:
                bch_err(c, "filesystem contains errors, but repair impossible");
                err = "fsck error";
                break;
        case BCH_FSCK_UNKNOWN_VERSION:
                err = "unknown metadata version";;
                break;
        case -ENOMEM:
                err = "cannot allocate memory";
                break;
        case -EIO:
                err = "IO error";
                break;
        }

        BUG_ON(!err);
        set_bit(BCH_FS_ERROR, &c->flags);
        goto out;
}

const char *bch_fs_start(struct bch_fs *c)
{
        return __bch_fs_start(c) ?: bch_fs_online(c);
}

static const char *bch_dev_may_add(struct bch_sb *sb, struct bch_fs *c)
{
        struct bch_sb_field_members *sb_mi;

        sb_mi = bch_sb_get_members(sb);
        if (!sb_mi)
                return "Invalid superblock: member info area missing";

        if (le16_to_cpu(sb->block_size) != c->sb.block_size)
                return "mismatched block size";

        if (le16_to_cpu(sb_mi->members[sb->dev_idx].bucket_size) <
            BCH_SB_BTREE_NODE_SIZE(c->disk_sb))
                return "new cache bucket size is too small";

        return NULL;
}

static const char *bch_dev_in_fs(struct bch_sb *fs, struct bch_sb *sb)
{
        struct bch_sb *newest =
                le64_to_cpu(fs->seq) > le64_to_cpu(sb->seq) ? fs : sb;
        struct bch_sb_field_members *mi = bch_sb_get_members(newest);

        if (uuid_le_cmp(fs->uuid, sb->uuid))
                return "device not a member of filesystem";

        if (sb->dev_idx >= newest->nr_devices)
                return "device has invalid dev_idx";

        if (bch_is_zero(mi->members[sb->dev_idx].uuid.b, sizeof(uuid_le)))
                return "device has been removed";

        if (fs->block_size != sb->block_size)
                return "mismatched block size";

        return NULL;
}

/* Device startup/shutdown: */

void bch_dev_release(struct kobject *kobj)
{
        struct bch_dev *ca = container_of(kobj, struct bch_dev, kobj);

        kfree(ca);
}

static void bch_dev_free(struct bch_dev *ca)
{
        unsigned i;

        cancel_work_sync(&ca->io_error_work);

        if (ca->kobj.state_in_sysfs &&
            ca->disk_sb.bdev)
                sysfs_remove_link(&part_to_dev(ca->disk_sb.bdev->bd_part)->kobj,
                                  "bcache");

        if (ca->kobj.state_in_sysfs)
                kobject_del(&ca->kobj);

        bch_free_super(&ca->disk_sb);
        bch_dev_journal_exit(ca);

        free_percpu(ca->sectors_written);
        bioset_exit(&ca->replica_set);
        free_percpu(ca->usage_percpu);
        free_pages((unsigned long) ca->disk_buckets, ilog2(bucket_pages(ca)));
        kfree(ca->prio_buckets);
        kfree(ca->bio_prio);
        vfree(ca->buckets);
        vfree(ca->oldest_gens);
        free_heap(&ca->heap);
        free_fifo(&ca->free_inc);

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

        percpu_ref_exit(&ca->io_ref);
        percpu_ref_exit(&ca->ref);
        kobject_put(&ca->kobj);
}

static void bch_dev_io_ref_release(struct percpu_ref *ref)
{
        struct bch_dev *ca = container_of(ref, struct bch_dev, io_ref);

        complete(&ca->offline_complete);
}

static void __bch_dev_offline(struct bch_dev *ca)
{
        struct bch_fs *c = ca->fs;

        lockdep_assert_held(&c->state_lock);

        __bch_dev_read_only(ca->fs, ca);

        reinit_completion(&ca->offline_complete);
        percpu_ref_kill(&ca->io_ref);
        wait_for_completion(&ca->offline_complete);

        if (ca->kobj.state_in_sysfs) {
                struct kobject *block =
                        &part_to_dev(ca->disk_sb.bdev->bd_part)->kobj;

                sysfs_remove_link(block, "bcache");
                sysfs_remove_link(&ca->kobj, "block");
        }

        bch_free_super(&ca->disk_sb);
        bch_dev_journal_exit(ca);
}

static void bch_dev_ref_release(struct percpu_ref *ref)
{
        struct bch_dev *ca = container_of(ref, struct bch_dev, ref);

        complete(&ca->stop_complete);
}

static void bch_dev_stop(struct bch_dev *ca)
{
        struct bch_fs *c = ca->fs;

        lockdep_assert_held(&c->state_lock);

        BUG_ON(rcu_access_pointer(c->devs[ca->dev_idx]) != ca);
        rcu_assign_pointer(c->devs[ca->dev_idx], NULL);

        synchronize_rcu();

        reinit_completion(&ca->stop_complete);
        percpu_ref_kill(&ca->ref);
        wait_for_completion(&ca->stop_complete);
}

static int bch_dev_sysfs_online(struct bch_dev *ca)
{
        struct bch_fs *c = ca->fs;
        int ret;

        if (!c->kobj.state_in_sysfs)
                return 0;

        if (!ca->kobj.state_in_sysfs) {
                ret = kobject_add(&ca->kobj, &ca->fs->kobj,
                                  "dev-%u", ca->dev_idx);
                if (ret)
                        return ret;
        }

        if (ca->disk_sb.bdev) {
                struct kobject *block =
                        &part_to_dev(ca->disk_sb.bdev->bd_part)->kobj;

                ret = sysfs_create_link(block, &ca->kobj, "bcache");
                if (ret)
                        return ret;
                ret = sysfs_create_link(&ca->kobj, block, "block");
                if (ret)
                        return ret;
        }

        return 0;
}

static int bch_dev_alloc(struct bch_fs *c, unsigned dev_idx)
{
        struct bch_member *member;
        size_t reserve_none, movinggc_reserve, free_inc_reserve, total_reserve;
        size_t heap_size;
        unsigned i;
        struct bch_dev *ca;

        if (bch_fs_init_fault("dev_alloc"))
                return -ENOMEM;

        ca = kzalloc(sizeof(*ca), GFP_KERNEL);
        if (!ca)
                return -ENOMEM;

        kobject_init(&ca->kobj, &bch_dev_ktype);
        init_completion(&ca->stop_complete);
        init_completion(&ca->offline_complete);

        spin_lock_init(&ca->self.lock);
        ca->self.nr = 1;
        rcu_assign_pointer(ca->self.d[0].dev, ca);
        ca->dev_idx = dev_idx;

        spin_lock_init(&ca->freelist_lock);
        spin_lock_init(&ca->prio_buckets_lock);
        mutex_init(&ca->heap_lock);
        bch_dev_moving_gc_init(ca);

        INIT_WORK(&ca->io_error_work, bch_nonfatal_io_error_work);

        if (bch_fs_init_fault("dev_alloc"))
                goto err;

        member = bch_sb_get_members(c->disk_sb)->members + dev_idx;

        ca->mi = bch_mi_to_cpu(member);
        ca->uuid = member->uuid;
        ca->bucket_bits = ilog2(ca->mi.bucket_size);
        scnprintf(ca->name, sizeof(ca->name), "dev-%u", dev_idx);

        /* XXX: tune these */
        movinggc_reserve = max_t(size_t, 16, ca->mi.nbuckets >> 7);
        reserve_none = max_t(size_t, 4, ca->mi.nbuckets >> 9);
        /*
         * free_inc must be smaller than the copygc reserve: if it was bigger,
         * one copygc iteration might not make enough buckets available to fill
         * up free_inc and allow the allocator to make forward progress
         */
        free_inc_reserve = movinggc_reserve / 2;
        heap_size = movinggc_reserve * 8;

        if (percpu_ref_init(&ca->ref, bch_dev_ref_release,
                            0, GFP_KERNEL) ||
            percpu_ref_init(&ca->io_ref, bch_dev_io_ref_release,
                            PERCPU_REF_INIT_DEAD, GFP_KERNEL) ||
            !init_fifo(&ca->free[RESERVE_PRIO], prio_buckets(ca), GFP_KERNEL) ||
            !init_fifo(&ca->free[RESERVE_BTREE], BTREE_NODE_RESERVE, GFP_KERNEL) ||
            !init_fifo(&ca->free[RESERVE_MOVINGGC],
                       movinggc_reserve, GFP_KERNEL) ||
            !init_fifo(&ca->free[RESERVE_NONE], reserve_none, GFP_KERNEL) ||
            !init_fifo(&ca->free_inc,   free_inc_reserve, GFP_KERNEL) ||
            !init_heap(&ca->heap,       heap_size, GFP_KERNEL) ||
            !(ca->oldest_gens   = vzalloc(sizeof(u8) *
                                          ca->mi.nbuckets)) ||
            !(ca->buckets       = vzalloc(sizeof(struct bucket) *
                                          ca->mi.nbuckets)) ||
            !(ca->prio_buckets  = kzalloc(sizeof(u64) * prio_buckets(ca) *
                                          2, GFP_KERNEL)) ||
            !(ca->disk_buckets  = alloc_bucket_pages(GFP_KERNEL, ca)) ||
            !(ca->usage_percpu = alloc_percpu(struct bch_dev_usage)) ||
            !(ca->bio_prio = bio_kmalloc(GFP_NOIO, bucket_pages(ca))) ||
            bioset_init(&ca->replica_set, 4,
                        offsetof(struct bch_write_bio, bio)) ||
            !(ca->sectors_written = alloc_percpu(*ca->sectors_written)))
                goto err;

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

        total_reserve = ca->free_inc.size;
        for (i = 0; i < RESERVE_NR; i++)
                total_reserve += ca->free[i].size;

        ca->copygc_write_point.group = &ca->self;
        ca->tiering_write_point.group = &ca->self;

        ca->fs = c;
        rcu_assign_pointer(c->devs[ca->dev_idx], ca);

        if (bch_dev_sysfs_online(ca))
                pr_warn("error creating sysfs objects");

        return 0;
err:
        bch_dev_free(ca);
        return -ENOMEM;
}

static int __bch_dev_online(struct bch_fs *c, struct bcache_superblock *sb)
{
        struct bch_dev *ca;
        int ret;

        lockdep_assert_held(&c->sb_lock);

        if (le64_to_cpu(sb->sb->seq) >
            le64_to_cpu(c->disk_sb->seq))
                bch_sb_to_fs(c, sb->sb);

        BUG_ON(sb->sb->dev_idx >= c->sb.nr_devices ||
               !c->devs[sb->sb->dev_idx]);

        ca = c->devs[sb->sb->dev_idx];
        if (ca->disk_sb.bdev) {
                bch_err(c, "already have device online in slot %u",
                        sb->sb->dev_idx);
                return -EINVAL;
        }

        ret = bch_dev_journal_init(ca, sb->sb);
        if (ret)
                return ret;

        /*
         * Increase journal write timeout if flushes to this device are
         * expensive:
         */
        if (!blk_queue_nonrot(bdev_get_queue(sb->bdev)) &&
            journal_flushes_device(ca))
                c->journal.write_delay_ms =
                        max(c->journal.write_delay_ms, 1000U);

        /* Commit: */
        ca->disk_sb = *sb;
        if (sb->mode & FMODE_EXCL)
                ca->disk_sb.bdev->bd_holder = ca;
        memset(sb, 0, sizeof(*sb));

        if (c->sb.nr_devices == 1)
                bdevname(ca->disk_sb.bdev, c->name);
        bdevname(ca->disk_sb.bdev, ca->name);

        if (bch_dev_sysfs_online(ca))
                pr_warn("error creating sysfs objects");

        lg_local_lock(&c->usage_lock);
        if (!gc_will_visit(c, gc_phase(GC_PHASE_SB_METADATA)))
                bch_mark_dev_metadata(ca->fs, ca);
        lg_local_unlock(&c->usage_lock);

        percpu_ref_reinit(&ca->io_ref);
        return 0;
}

/* Device management: */

bool bch_fs_may_start(struct bch_fs *c, int flags)
{
        struct bch_sb_field_members *mi;
        unsigned meta_missing = 0;
        unsigned data_missing = 0;
        bool degraded = false;
        unsigned i;

        mutex_lock(&c->sb_lock);
        mi = bch_sb_get_members(c->disk_sb);

        for (i = 0; i < c->disk_sb->nr_devices; i++)
                if (!c->devs[i] &&
                    !bch_is_zero(mi->members[i].uuid.b, sizeof(uuid_le))) {
                        degraded = true;
                        if (BCH_MEMBER_HAS_METADATA(&mi->members[i]))
                                meta_missing++;
                        if (BCH_MEMBER_HAS_DATA(&mi->members[i]))
                                data_missing++;
                }
        mutex_unlock(&c->sb_lock);

        if (degraded &&
            !(flags & BCH_FORCE_IF_DEGRADED))
                return false;

        if (meta_missing &&
            !(flags & BCH_FORCE_IF_METADATA_DEGRADED))
                return false;

        if (meta_missing >= BCH_SB_META_REPLICAS_HAVE(c->disk_sb) &&
            !(flags & BCH_FORCE_IF_METADATA_LOST))
                return false;

        if (data_missing && !(flags & BCH_FORCE_IF_DATA_DEGRADED))
                return false;

        if (data_missing >= BCH_SB_DATA_REPLICAS_HAVE(c->disk_sb) &&
            !(flags & BCH_FORCE_IF_DATA_LOST))
                return false;

        return true;
}

bool bch_dev_state_allowed(struct bch_fs *c, struct bch_dev *ca,
                           enum bch_member_state new_state, int flags)
{
        lockdep_assert_held(&c->state_lock);

        if (new_state == BCH_MEMBER_STATE_RW)
                return true;

        if (ca->mi.has_data &&
            !(flags & BCH_FORCE_IF_DATA_DEGRADED))
                return false;

        if (ca->mi.has_data &&
            c->sb.data_replicas_have <= 1 &&
            !(flags & BCH_FORCE_IF_DATA_LOST))
                return false;

        if (ca->mi.has_metadata &&
            !(flags & BCH_FORCE_IF_METADATA_DEGRADED))
                return false;

        if (ca->mi.has_metadata &&
            c->sb.meta_replicas_have <= 1 &&
            !(flags & BCH_FORCE_IF_METADATA_LOST))
                return false;

        return true;
}

static void __bch_dev_read_only(struct bch_fs *c, struct bch_dev *ca)
{
        bch_moving_gc_stop(ca);

        /*
         * This stops new data writes (e.g. to existing open data
         * buckets) and then waits for all existing writes to
         * complete.
         */
        bch_dev_allocator_stop(ca);

        bch_dev_group_remove(&c->journal.devs, ca);
}

static const char *__bch_dev_read_write(struct bch_fs *c, struct bch_dev *ca)
{
        lockdep_assert_held(&c->state_lock);

        BUG_ON(ca->mi.state != BCH_MEMBER_STATE_RW);

        trace_bcache_cache_read_write(ca);

        if (bch_dev_allocator_start(ca))
                return "error starting allocator thread";

        if (bch_moving_gc_start(ca))
                return "error starting moving GC thread";

        if (bch_tiering_start(c))
                return "error starting tiering thread";

        bch_notify_dev_read_write(ca);
        trace_bcache_cache_read_write_done(ca);

        return NULL;
}

int __bch_dev_set_state(struct bch_fs *c, struct bch_dev *ca,
                        enum bch_member_state new_state, int flags)
{
        struct bch_sb_field_members *mi;

        if (ca->mi.state == new_state)
                return 0;

        if (!bch_dev_state_allowed(c, ca, new_state, flags))
                return -EINVAL;

        if (new_state == BCH_MEMBER_STATE_RW) {
                if (__bch_dev_read_write(c, ca))
                        return -ENOMEM;
        } else {
                __bch_dev_read_only(c, ca);
        }

        bch_notice(ca, "%s", bch_dev_state[new_state]);

        mutex_lock(&c->sb_lock);
        mi = bch_sb_get_members(c->disk_sb);
        SET_BCH_MEMBER_STATE(&mi->members[ca->dev_idx], new_state);
        bch_write_super(c);
        mutex_unlock(&c->sb_lock);

        return 0;
}

int bch_dev_set_state(struct bch_fs *c, struct bch_dev *ca,
                      enum bch_member_state new_state, int flags)
{
        int ret;

        mutex_lock(&c->state_lock);
        ret = __bch_dev_set_state(c, ca, new_state, flags);
        mutex_unlock(&c->state_lock);

        return ret;
}

#if 0
int bch_dev_migrate_from(struct bch_fs *c, struct bch_dev *ca)
{
        /* First, go RO before we try to migrate data off: */
        ret = bch_dev_set_state(c, ca, BCH_MEMBER_STATE_RO, flags);
        if (ret)
                return ret;

        bch_notify_dev_removing(ca);

        /* Migrate data, metadata off device: */

        ret = bch_move_data_off_device(ca);
        if (ret && !(flags & BCH_FORCE_IF_DATA_LOST)) {
                bch_err(c, "Remove of %s failed, unable to migrate data off",
                        name);
                return ret;
        }

        if (ret)
                ret = bch_flag_data_bad(ca);
        if (ret) {
                bch_err(c, "Remove of %s failed, unable to migrate data off",
                        name);
                return ret;
        }

        ret = bch_move_metadata_off_device(ca);
        if (ret)
                return ret;
}
#endif

/* Device add/removal: */

static int __bch_dev_remove(struct bch_fs *c, struct bch_dev *ca, int flags)
{
        struct bch_sb_field_members *mi;
        unsigned dev_idx = ca->dev_idx;
        int ret;

        if (ca->mi.state == BCH_MEMBER_STATE_RW) {
                bch_err(ca, "Cannot remove RW device");
                bch_notify_dev_remove_failed(ca);
                return -EINVAL;
        }

        if (!bch_dev_state_allowed(c, ca, BCH_MEMBER_STATE_FAILED, flags)) {
                bch_err(ca, "Cannot remove without losing data");
                bch_notify_dev_remove_failed(ca);
                return -EINVAL;
        }

        /*
         * XXX: verify that dev_idx is really not in use anymore, anywhere
         *
         * flag_data_bad() does not check btree pointers
         */
        ret = bch_flag_data_bad(ca);
        if (ret) {
                bch_err(ca, "Remove failed");
                return ret;
        }

        if (ca->mi.has_data || ca->mi.has_metadata) {
                bch_err(ca, "Can't remove, still has data");
                return ret;
        }

        /*
         * Ok, really doing the remove:
         * Drop device's prio pointer before removing it from superblock:
         */
        bch_notify_dev_removed(ca);

        spin_lock(&c->journal.lock);
        c->journal.prio_buckets[dev_idx] = 0;
        spin_unlock(&c->journal.lock);

        bch_journal_meta(&c->journal);

        __bch_dev_offline(ca);
        bch_dev_stop(ca);
        bch_dev_free(ca);

        /*
         * Free this device's slot in the bch_member array - all pointers to
         * this device must be gone:
         */
        mutex_lock(&c->sb_lock);
        mi = bch_sb_get_members(c->disk_sb);
        memset(&mi->members[dev_idx].uuid, 0, sizeof(mi->members[dev_idx].uuid));

        bch_write_super(c);

        mutex_unlock(&c->sb_lock);

        return 0;
}

int bch_dev_remove(struct bch_fs *c, struct bch_dev *ca, int flags)
{
        int ret;

        mutex_lock(&c->state_lock);
        percpu_ref_put(&ca->ref);
        ret = __bch_dev_remove(c, ca, flags);
        mutex_unlock(&c->state_lock);

        return ret;
}

int bch_dev_add(struct bch_fs *c, const char *path)
{
        struct bcache_superblock sb;
        const char *err;
        struct bch_dev *ca = NULL;
        struct bch_sb_field_members *mi, *dev_mi;
        struct bch_member saved_mi;
        unsigned dev_idx, nr_devices, u64s;
        int ret = -EINVAL;

        err = bch_read_super(&sb, bch_opts_empty(), path);
        if (err)
                return -EINVAL;

        err = bch_validate_cache_super(&sb);
        if (err)
                return -EINVAL;

        err = bch_dev_may_add(sb.sb, c);
        if (err)
                return -EINVAL;

        mutex_lock(&c->state_lock);
        mutex_lock(&c->sb_lock);

        /*
         * Preserve the old cache member information (esp. tier)
         * before we start bashing the disk stuff.
         */
        dev_mi = bch_sb_get_members(sb.sb);
        saved_mi = dev_mi->members[sb.sb->dev_idx];
        saved_mi.last_mount = cpu_to_le64(ktime_get_seconds());

        if (dynamic_fault("bcache:add:no_slot"))
                goto no_slot;

        mi = bch_sb_get_members(c->disk_sb);
        for (dev_idx = 0; dev_idx < BCH_SB_MEMBERS_MAX; dev_idx++)
                if (dev_idx >= c->sb.nr_devices ||
                    bch_is_zero(mi->members[dev_idx].uuid.b,
                                 sizeof(uuid_le)))
                        goto have_slot;
no_slot:
        err = "no slots available in superblock";
        ret = -ENOSPC;
        goto err_unlock;

have_slot:
        nr_devices = max_t(unsigned, dev_idx + 1, c->sb.nr_devices);
        u64s = (sizeof(struct bch_sb_field_members) +
                sizeof(struct bch_member) * nr_devices) / sizeof(u64);
        err = "no space in superblock for member info";

        mi = bch_fs_sb_resize_members(c, u64s);
        if (!mi)
                goto err_unlock;

        dev_mi = bch_sb_resize_members(&sb, u64s);
        if (!dev_mi)
                goto err_unlock;

        memcpy(dev_mi, mi, u64s * sizeof(u64));
        dev_mi->members[dev_idx] = saved_mi;

        sb.sb->uuid             = c->disk_sb->uuid;
        sb.sb->dev_idx          = dev_idx;
        sb.sb->nr_devices       = nr_devices;

        /* commit new member info */
        memcpy(mi, dev_mi, u64s * sizeof(u64));
        c->disk_sb->nr_devices  = nr_devices;
        c->sb.nr_devices        = nr_devices;

        if (bch_dev_alloc(c, dev_idx)) {
                err = "cannot allocate memory";
                ret = -ENOMEM;
                goto err_unlock;
        }

        if (__bch_dev_online(c, &sb)) {
                err = "bch_dev_online() error";
                ret = -ENOMEM;
                goto err_unlock;
        }

        bch_write_super(c);
        mutex_unlock(&c->sb_lock);

        ca = c->devs[dev_idx];
        if (ca->mi.state == BCH_MEMBER_STATE_RW) {
                err = "journal alloc failed";
                if (bch_dev_journal_alloc(ca))
                        goto err;

                err = __bch_dev_read_write(c, ca);
                if (err)
                        goto err;
        }

        bch_notify_dev_added(ca);
        mutex_unlock(&c->state_lock);
        return 0;
err_unlock:
        mutex_unlock(&c->sb_lock);
err:
        mutex_unlock(&c->state_lock);
        bch_free_super(&sb);

        bch_err(c, "Unable to add device: %s", err);
        return ret ?: -EINVAL;
}

int bch_dev_online(struct bch_fs *c, const char *path)
{
        struct bcache_superblock sb = { 0 };
        const char *err;

        mutex_lock(&c->state_lock);

        err = bch_read_super(&sb, bch_opts_empty(), path);
        if (err)
                goto err;

        err = bch_dev_in_fs(c->disk_sb, sb.sb);
        if (err)
                goto err;

        mutex_lock(&c->sb_lock);
        if (__bch_dev_online(c, &sb)) {
                mutex_unlock(&c->sb_lock);
                goto err;
        }
        mutex_unlock(&c->sb_lock);

        mutex_unlock(&c->state_lock);
        return 0;
err:
        mutex_unlock(&c->state_lock);
        bch_free_super(&sb);
        bch_err(c, "error bringing %s online: %s", path, err);
        return -EINVAL;
}

int bch_dev_offline(struct bch_fs *c, struct bch_dev *ca, int flags)
{
        mutex_lock(&c->state_lock);

        if (!bch_dev_state_allowed(c, ca, BCH_MEMBER_STATE_FAILED, flags)) {
                bch_err(ca, "Cannot offline required disk");
                mutex_unlock(&c->state_lock);
                return -EINVAL;
        }

        __bch_dev_read_only(c, ca);
        __bch_dev_offline(ca);

        mutex_unlock(&c->state_lock);
        return 0;
}

int bch_dev_migrate(struct bch_fs *c, struct bch_dev *ca)
{
        int ret;

        mutex_lock(&c->state_lock);

        if (ca->mi.state == BCH_MEMBER_STATE_RW) {
                bch_err(ca, "Cannot migrate data off RW device");
                mutex_unlock(&c->state_lock);
                return -EINVAL;
        }

        mutex_unlock(&c->state_lock);

        ret = bch_move_data_off_device(ca);
        if (ret) {
                bch_err(ca, "Error migrating data: %i", ret);
                return ret;
        }

        ret = bch_move_metadata_off_device(ca);
        if (ret) {
                bch_err(ca, "Error migrating metadata: %i", ret);
                return ret;
        }

        if (ca->mi.has_data || ca->mi.has_metadata) {
                bch_err(ca, "Migrate error: data still present");
                return -EINVAL;
        }

        return 0;
}

/* Filesystem open: */

const char *bch_fs_open(char * const *devices, unsigned nr_devices,
                        struct bch_opts opts, struct bch_fs **ret)
{
        const char *err;
        struct bch_fs *c = NULL;
        struct bcache_superblock *sb;
        unsigned i, best_sb = 0;

        if (!nr_devices)
                return "need at least one device";

        if (!try_module_get(THIS_MODULE))
                return "module unloading";

        err = "cannot allocate memory";
        sb = kcalloc(nr_devices, sizeof(*sb), GFP_KERNEL);
        if (!sb)
                goto err;

        for (i = 0; i < nr_devices; i++) {
                err = bch_read_super(&sb[i], opts, devices[i]);
                if (err)
                        goto err;

                err = "attempting to register backing device";
                if (__SB_IS_BDEV(le64_to_cpu(sb[i].sb->version)))
                        goto err;

                err = bch_validate_cache_super(&sb[i]);
                if (err)
                        goto err;
        }

        for (i = 1; i < nr_devices; i++)
                if (le64_to_cpu(sb[i].sb->seq) >
                    le64_to_cpu(sb[best_sb].sb->seq))
                        best_sb = i;

        for (i = 0; i < nr_devices; i++) {
                err = bch_dev_in_fs(sb[best_sb].sb, sb[i].sb);
                if (err)
                        goto err;
        }

        err = "cannot allocate memory";
        c = bch_fs_alloc(sb[best_sb].sb, opts);
        if (!c)
                goto err;

        err = "bch_dev_online() error";
        mutex_lock(&c->sb_lock);
        for (i = 0; i < nr_devices; i++)
                if (__bch_dev_online(c, &sb[i])) {
                        mutex_unlock(&c->sb_lock);
                        goto err;
                }
        mutex_unlock(&c->sb_lock);

        err = "insufficient devices";
        if (!bch_fs_may_start(c, 0))
                goto err;

        if (!c->opts.nostart) {
                err = __bch_fs_start(c);
                if (err)
                        goto err;
        }

        err = bch_fs_online(c);
        if (err)
                goto err;

        if (ret)
                *ret = c;
        else
                closure_put(&c->cl);

        err = NULL;
out:
        kfree(sb);
        module_put(THIS_MODULE);
        if (err)
                c = NULL;
        return err;
err:
        if (c)
                bch_fs_stop(c);

        for (i = 0; i < nr_devices; i++)
                bch_free_super(&sb[i]);
        goto out;
}

static const char *__bch_fs_open_incremental(struct bcache_superblock *sb,
                                             struct bch_opts opts)
{
        const char *err;
        struct bch_fs *c;
        bool allocated_fs = false;

        err = bch_validate_cache_super(sb);
        if (err)
                return err;

        mutex_lock(&bch_fs_list_lock);
        c = __bch_uuid_to_fs(sb->sb->uuid);
        if (c) {
                closure_get(&c->cl);

                err = bch_dev_in_fs(c->disk_sb, sb->sb);
                if (err)
                        goto err;
        } else {
                c = bch_fs_alloc(sb->sb, opts);
                err = "cannot allocate memory";
                if (!c)
                        goto err;

                allocated_fs = true;
        }

        err = "bch_dev_online() error";

        mutex_lock(&c->sb_lock);
        if (__bch_dev_online(c, sb)) {
                mutex_unlock(&c->sb_lock);
                goto err;
        }
        mutex_unlock(&c->sb_lock);

        if (!c->opts.nostart && bch_fs_may_start(c, 0)) {
                err = __bch_fs_start(c);
                if (err)
                        goto err;
        }

        err = __bch_fs_online(c);
        if (err)
                goto err;

        closure_put(&c->cl);
        mutex_unlock(&bch_fs_list_lock);

        return NULL;
err:
        mutex_unlock(&bch_fs_list_lock);

        if (allocated_fs)
                bch_fs_stop(c);
        else if (c)
                closure_put(&c->cl);

        return err;
}

const char *bch_fs_open_incremental(const char *path)
{
        struct bcache_superblock sb;
        struct bch_opts opts = bch_opts_empty();
        const char *err;

        err = bch_read_super(&sb, opts, path);
        if (err)
                return err;

        if (__SB_IS_BDEV(le64_to_cpu(sb.sb->version))) {
                mutex_lock(&bch_fs_list_lock);
                err = bch_backing_dev_register(&sb);
                mutex_unlock(&bch_fs_list_lock);
        } else {
                err = __bch_fs_open_incremental(&sb, opts);
        }

        bch_free_super(&sb);

        return err;
}

/* Global interfaces/init */

#define kobj_attribute_write(n, fn)                                     \
        static struct kobj_attribute ksysfs_##n = __ATTR(n, S_IWUSR, NULL, fn)

#define kobj_attribute_rw(n, show, store)                               \
        static struct kobj_attribute ksysfs_##n =                       \
                __ATTR(n, S_IWUSR|S_IRUSR, show, store)

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 ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
                               const char *buffer, size_t size)
{
        ssize_t ret = -EINVAL;
        const char *err = "cannot allocate memory";
        char *path = NULL;

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

        if (!(path = kstrndup(skip_spaces(buffer), size, GFP_KERNEL)))
                goto err;

        err = bch_fs_open_incremental(strim(path));
        if (err)
                goto err;

        ret = size;
out:
        kfree(path);
        module_put(THIS_MODULE);
        return ret;
err:
        pr_err("error opening %s: %s", path, err);
        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) {
                struct bch_fs *c;

                mutex_lock(&bch_fs_list_lock);

                if (!list_empty(&bch_fs_list))
                        pr_info("Setting all devices read only:");

                list_for_each_entry(c, &bch_fs_list, list)
                        bch_fs_read_only_async(c);

                list_for_each_entry(c, &bch_fs_list, list)
                        bch_fs_read_only(c);

                mutex_unlock(&bch_fs_list_lock);
        }

        return NOTIFY_DONE;
}

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

static ssize_t reboot_test(struct kobject *k, struct kobj_attribute *attr,
                           const char *buffer, size_t size)
{
        bcache_reboot(NULL, SYS_DOWN, NULL);
        return size;
}

kobj_attribute_write(reboot,            reboot_test);

static void bcache_exit(void)
{
        bch_debug_exit();
        bch_vfs_exit();
        bch_blockdev_exit();
        bch_chardev_exit();
        if (bcache_kset)
                kset_unregister(bcache_kset);
        if (bcache_io_wq)
                destroy_workqueue(bcache_io_wq);
        if (!IS_ERR_OR_NULL(bch_sha256))
                crypto_free_shash(bch_sha256);
        unregister_reboot_notifier(&reboot);
}

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

        register_reboot_notifier(&reboot);
        closure_debug_init();
        bkey_pack_test();

        bch_sha256 = crypto_alloc_shash("sha256", 0, 0);
        if (IS_ERR(bch_sha256))
                goto err;

        if (!(bcache_io_wq = create_freezable_workqueue("bcache_io")) ||
            !(bcache_kset = kset_create_and_add("bcache", NULL, fs_kobj)) ||
            sysfs_create_files(&bcache_kset->kobj, files) ||
            bch_chardev_init() ||
            bch_blockdev_init() ||
            bch_vfs_init() ||
            bch_debug_init())
                goto err;

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

#define BCH_DEBUG_PARAM(name, description)                      \
        bool bch_##name;                                        \
        module_param_named(name, bch_##name, bool, 0644);       \
        MODULE_PARM_DESC(name, description);
BCH_DEBUG_PARAMS()
#undef BCH_DEBUG_PARAM

module_exit(bcache_exit);
module_init(bcache_init);