Update bcachefs sources to 661faf58db bcachefs: fix a deadlock in journal replay...

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

/*
 * bcachefs 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 "bcachefs.h"
#include "alloc.h"
#include "btree_cache.h"
#include "btree_gc.h"
#include "btree_update.h"
#include "btree_update_interior.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 "fsck.h"
#include "inode.h"
#include "io.h"
#include "journal.h"
#include "keylist.h"
#include "move.h"
#include "migrate.h"
#include "movinggc.h"
#include "super.h"
#include "super-io.h"
#include "sysfs.h"
#include "tier.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/sysfs.h>
#include <crypto/hash.h>

#include <trace/events/bcachefs.h>

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

#define KTYPE(type)                                                     \
struct kobj_type type ## _ktype = {                                     \
        .release        = type ## _release,                             \
        .sysfs_ops      = &type ## _sysfs_ops,                          \
        .default_attrs  = type ## _files                                \
}

static void bch2_fs_release(struct kobject *);
static void bch2_dev_release(struct kobject *);

static void bch2_fs_internal_release(struct kobject *k)
{
}

static void bch2_fs_opts_dir_release(struct kobject *k)
{
}

static void bch2_fs_time_stats_release(struct kobject *k)
{
}

static KTYPE(bch2_fs);
static KTYPE(bch2_fs_internal);
static KTYPE(bch2_fs_opts_dir);
static KTYPE(bch2_fs_time_stats);
static KTYPE(bch2_dev);

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

static DECLARE_WAIT_QUEUE_HEAD(bch_read_only_wait);

static void bch2_dev_free(struct bch_dev *);
static int bch2_dev_alloc(struct bch_fs *, unsigned);
static int bch2_dev_sysfs_online(struct bch_dev *);
static void __bch2_dev_read_only(struct bch_fs *, struct bch_dev *);

struct bch_fs *bch2_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, NULL)
                        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 *__bch2_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 *bch2_uuid_to_fs(uuid_le uuid)
{
        struct bch_fs *c;

        mutex_lock(&bch_fs_list_lock);
        c = __bch2_uuid_to_fs(uuid);
        if (c)
                closure_get(&c->cl);
        mutex_unlock(&bch_fs_list_lock);

        return c;
}

int bch2_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 = ca->disk_sb.bdev->bd_bdi;

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

                rcu_read_lock();
                for_each_member_device_rcu(ca, c, i, devs) {
                        bdi = ca->disk_sb.bdev->bd_bdi;

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

        return ret;
}

static int bch2_congested_fn(void *data, int bdi_bits)
{
        struct bch_fs *c = data;

        return bch2_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 __bch2_fs_read_only(struct bch_fs *c)
{
        struct bch_dev *ca;
        unsigned i;

        bch2_tiering_stop(c);

        for_each_member_device(ca, c, i)
                bch2_moving_gc_stop(ca);

        bch2_gc_thread_stop(c);

        /*
         * Flush journal before stopping allocators, because flushing journal
         * blacklist entries involves allocating new btree nodes:
         */
        bch2_journal_flush_pins(&c->journal, U64_MAX);

        if (!bch2_journal_error(&c->journal))
                bch2_btree_verify_flushed(c);

        for_each_member_device(ca, c, i)
                bch2_dev_allocator_stop(ca);

        bch2_fs_journal_stop(&c->journal);

        for_each_member_device(ca, c, i)
                bch2_dev_allocator_remove(c, ca);
}

static void bch2_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 bch2_fs_read_only(struct bch_fs *c)
{
        if (c->state != BCH_FS_STARTING &&
            c->state != BCH_FS_RW)
                return;

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

        /*
         * 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
         * bch2_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;
        bch2_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));

        __bch2_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 (!bch2_journal_error(&c->journal) &&
            !test_bit(BCH_FS_ERROR, &c->flags)) {
                mutex_lock(&c->sb_lock);
                SET_BCH_SB_CLEAN(c->disk_sb, true);
                bch2_write_super(c);
                mutex_unlock(&c->sb_lock);
        }

        c->state = BCH_FS_RO;
}

static void bch2_fs_read_only_work(struct work_struct *work)
{
        struct bch_fs *c =
                container_of(work, struct bch_fs, read_only_work);

        mutex_lock(&c->state_lock);
        bch2_fs_read_only(c);
        mutex_unlock(&c->state_lock);
}

static void bch2_fs_read_only_async(struct bch_fs *c)
{
        queue_work(system_long_wq, &c->read_only_work);
}

bool bch2_fs_emergency_read_only(struct bch_fs *c)
{
        bool ret = !test_and_set_bit(BCH_FS_EMERGENCY_RO, &c->flags);

        bch2_fs_read_only_async(c);
        bch2_journal_halt(&c->journal);

        wake_up(&bch_read_only_wait);
        return ret;
}

const char *bch2_fs_read_write(struct bch_fs *c)
{
        struct bch_dev *ca;
        const char *err = NULL;
        unsigned i;

        if (c->state != BCH_FS_STARTING &&
            c->state != BCH_FS_RO)
                return NULL;

        for_each_rw_member(ca, c, i)
                bch2_dev_allocator_add(c, ca);
        bch2_recalc_capacity(c);

        err = "error starting allocator thread";
        for_each_rw_member(ca, c, i)
                if (bch2_dev_allocator_start(ca)) {
                        percpu_ref_put(&ca->io_ref);
                        goto err;
                }

        err = "error starting btree GC thread";
        if (bch2_gc_thread_start(c))
                goto err;

        err = "error starting moving GC thread";
        for_each_rw_member(ca, c, i)
                if (bch2_moving_gc_start(ca)) {
                        percpu_ref_put(&ca->io_ref);
                        goto err;
                }

        err = "error starting tiering thread";
        if (bch2_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;
        return NULL;
err:
        __bch2_fs_read_only(c);
        return err;
}

/* Filesystem startup/shutdown: */

static void bch2_fs_free(struct bch_fs *c)
{
        bch2_fs_encryption_exit(c);
        bch2_fs_btree_exit(c);
        bch2_fs_journal_exit(&c->journal);
        bch2_io_clock_exit(&c->io_clock[WRITE]);
        bch2_io_clock_exit(&c->io_clock[READ]);
        bch2_fs_compress_exit(c);
        if (c->bdi.bdi_list.next)
                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);
        kfree(c->replicas);

        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 bch2_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);

        for (i = 0; i < c->sb.nr_devices; i++)
                if (c->devs[i])
                        bch2_dev_free(c->devs[i]);

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

static void bch2_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,
                                          "bcachefs");

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

        bch2_fs_debug_exit(c);
        bch2_fs_chardev_exit(c);

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

        mutex_lock(&c->state_lock);
        __bch2_fs_read_only(c);
        mutex_unlock(&c->state_lock);
}

static void bch2_fs_release(struct kobject *kobj)
{
        struct bch_fs *c = container_of(kobj, struct bch_fs, kobj);

        bch2_fs_free(c);
}

void bch2_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);

        bch2_fs_offline(c);

        closure_sync(&c->cl);

        bch2_fs_exit(c);
}

static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
{
        struct bch_sb_field_members *mi;
        struct bch_fs *c;
        unsigned i, iter_size;

        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);
        mutex_init(&c->replicas_gc_lock);
        mutex_init(&c->btree_cache_lock);
        mutex_init(&c->bucket_lock);
        mutex_init(&c->btree_root_lock);
        INIT_WORK(&c->read_only_work, bch2_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

        bch2_fs_allocator_init(c);
        bch2_fs_tiering_init(c);

        INIT_LIST_HEAD(&c->list);
        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);
        mutex_init(&c->zlib_workspace_lock);

        bio_list_init(&c->btree_write_error_list);
        spin_lock_init(&c->btree_write_error_lock);
        INIT_WORK(&c->btree_write_error_work, bch2_btree_write_error_work);

        INIT_LIST_HEAD(&c->fsck_errors);
        mutex_init(&c->fsck_error_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;

        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_lock(&c->sb_lock);

        if (bch2_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);

        c->opts = bch2_opts_default;
        bch2_opts_apply(&c->opts, bch2_opts_from_sb(sb));
        bch2_opts_apply(&c->opts, opts);

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

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

        if (bch2_fs_init_fault("fs_alloc"))
                goto err;

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

        if (!(c->wq = alloc_workqueue("bcachefs",
                                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, bch2_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_update)) ||
            mempool_init_kmalloc_pool(&c->fill_iter, 1, iter_size) ||
            bioset_init(&c->btree_read_bio, 1,
                        offsetof(struct btree_read_bio, bio)) ||
            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->opts.btree_node_size,
                                         c->sb.encoded_extent_max) /
                                   PAGE_SECTORS, 0) ||
            !(c->usage_percpu = alloc_percpu(struct bch_fs_usage)) ||
            lg_lock_init(&c->usage_lock) ||
            mempool_init_vp_pool(&c->btree_bounce_pool, 1, btree_bytes(c)) ||
            bdi_setup_and_register(&c->bdi, "bcachefs") ||
            bch2_io_clock_init(&c->io_clock[READ]) ||
            bch2_io_clock_init(&c->io_clock[WRITE]) ||
            bch2_fs_journal_init(&c->journal) ||
            bch2_fs_btree_init(c) ||
            bch2_fs_encryption_init(c) ||
            bch2_fs_compress_init(c) ||
            bch2_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     = bch2_congested_fn;
        c->bdi.congested_data   = c;

        mi = bch2_sb_get_members(c->disk_sb);
        for (i = 0; i < c->sb.nr_devices; i++)
                if (bch2_dev_exists(c->disk_sb, mi, i) &&
                    bch2_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 = bcachefs_kset;
        kobject_init(&c->kobj, &bch2_fs_ktype);
        kobject_init(&c->internal, &bch2_fs_internal_ktype);
        kobject_init(&c->opts_dir, &bch2_fs_opts_dir_ktype);
        kobject_init(&c->time_stats, &bch2_fs_time_stats_ktype);
        return c;
err:
        bch2_fs_free(c);
        return NULL;
}

static const char *__bch2_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 (__bch2_uuid_to_fs(c->sb.uuid))
                return "filesystem UUID already open";

        ret = bch2_fs_chardev_init(c);
        if (ret)
                return "error creating character device";

        bch2_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") ||
            bch2_opts_create_sysfs_files(&c->opts_dir))
                return "error creating sysfs objects";

        mutex_lock(&c->state_lock);

        err = "error creating sysfs objects";
        __for_each_member_device(ca, c, i, NULL)
                if (bch2_dev_sysfs_online(ca))
                        goto err;

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

static const char *bch2_fs_online(struct bch_fs *c)
{
        const char *err;

        mutex_lock(&bch_fs_list_lock);
        err = __bch2_fs_online(c);
        mutex_unlock(&bch_fs_list_lock);

        return err;
}

static const char *__bch2_fs_start(struct bch_fs *c)
{
        const char *err = "cannot allocate memory";
        struct bch_sb_field_members *mi;
        struct bch_dev *ca;
        LIST_HEAD(journal);
        struct jset *j;
        struct closure cl;
        time64_t now;
        unsigned i;
        int ret = -EINVAL;

        closure_init_stack(&cl);

        mutex_lock(&c->state_lock);

        BUG_ON(c->state != BCH_FS_STARTING);

        mutex_lock(&c->sb_lock);
        for_each_online_member(ca, c, i)
                bch2_sb_from_fs(c, ca);
        mutex_unlock(&c->sb_lock);

        for_each_rw_member(ca, c, i)
                bch2_dev_allocator_add(c, ca);
        bch2_recalc_capacity(c);

        if (BCH_SB_INITIALIZED(c->disk_sb)) {
                ret = bch2_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);

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

                        err = "missing btree root";
                        k = bch2_journal_find_btree_root(c, j, i, &level);
                        if (!k && i < BTREE_ID_ALLOC)
                                goto err;

                        if (!k)
                                continue;

                        err = "error reading btree root";
                        if (bch2_btree_root_read(c, i, k, level))
                                goto err;
                }

                err = "error reading allocation information";
                ret = bch2_alloc_read(c, &journal);
                if (ret)
                        goto err;

                set_bit(BCH_FS_ALLOC_READ_DONE, &c->flags);

                bch_verbose(c, "starting mark and sweep:");
                err = "error in recovery";
                ret = bch2_initial_gc(c, &journal);
                if (ret)
                        goto err;
                bch_verbose(c, "mark and sweep done");

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

                err = "cannot allocate new btree root";
                for (i = 0; i < BTREE_ID_NR; i++)
                        if (!c->btree_roots[i].b &&
                            bch2_btree_root_alloc(c, i, &cl))
                                goto err;

                closure_sync(&cl);

                /*
                 * bch2_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.
                 */
                bch2_journal_start(c);

                err = "error starting allocator thread";
                for_each_rw_member(ca, c, i)
                        if (bch2_dev_allocator_start(ca)) {
                                percpu_ref_put(&ca->io_ref);
                                goto err;
                        }

                bch_verbose(c, "starting journal replay:");
                err = "journal replay failed";
                ret = bch2_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 = bch2_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;

                bch_notice(c, "initializing new filesystem");

                set_bit(BCH_FS_ALLOC_READ_DONE, &c->flags);

                ret = bch2_initial_gc(c, &journal);
                if (ret)
                        goto err;

                err = "unable to allocate journal buckets";
                for_each_rw_member(ca, c, i)
                        if (bch2_dev_journal_alloc(ca)) {
                                percpu_ref_put(&ca->io_ref);
                                goto err;
                        }

                err = "cannot allocate new btree root";
                for (i = 0; i < BTREE_ID_NR; i++)
                        if (bch2_btree_root_alloc(c, i, &cl))
                                goto err;

                /*
                 * journal_res_get() will crash if called before this has
                 * set up the journal.pin FIFO and journal.cur pointer:
                 */
                bch2_journal_start(c);
                bch2_journal_set_replay_done(&c->journal);

                err = "error starting allocator thread";
                for_each_rw_member(ca, c, i)
                        if (bch2_dev_allocator_start(ca)) {
                                percpu_ref_put(&ca->io_ref);
                                goto err;
                        }

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

                bch2_inode_init(c, &inode, 0, 0,
                               S_IFDIR|S_IRWXU|S_IRUGO|S_IXUGO, 0);
                inode.bi_inum = BCACHEFS_ROOT_INO;

                bch2_inode_pack(&packed_inode, &inode);

                err = "error creating root directory";
                if (bch2_btree_insert(c, BTREE_ID_INODES,
                                     &packed_inode.inode.k_i,
                                     NULL, NULL, NULL, 0))
                        goto err;

                err = "error writing first journal entry";
                if (bch2_journal_meta(&c->journal))
                        goto err;
        }
recovery_done:
        err = "dynamic fault";
        if (bch2_fs_init_fault("fs_start"))
                goto err;

        if (c->opts.read_only) {
                bch2_fs_read_only(c);
        } else {
                err = bch2_fs_read_write(c);
                if (err)
                        goto err;
        }

        mutex_lock(&c->sb_lock);
        mi = bch2_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);

        bch2_write_super(c);
        mutex_unlock(&c->sb_lock);

        err = NULL;
out:
        mutex_unlock(&c->state_lock);
        bch2_journal_entries_free(&journal);
        return err;
err:
        closure_sync(&cl);

        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\n");
                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\n");
                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 *bch2_fs_start(struct bch_fs *c)
{
        return __bch2_fs_start(c) ?: bch2_fs_online(c);
}

static const char *bch2_dev_may_add(struct bch_sb *sb, struct bch_fs *c)
{
        struct bch_sb_field_members *sb_mi;

        sb_mi = bch2_sb_get_members(sb);
        if (!sb_mi)
                return "Invalid superblock: member info area missing";

        if (le16_to_cpu(sb->block_size) != c->opts.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 *bch2_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 = bch2_sb_get_members(newest);

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

        if (!bch2_dev_exists(newest, mi, sb->dev_idx))
                return "device has been removed";

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

        return NULL;
}

/* Device startup/shutdown: */

static void bch2_dev_release(struct kobject *kobj)
{
        struct bch_dev *ca = container_of(kobj, struct bch_dev, kobj);

        kfree(ca);
}

static void bch2_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,
                                  "bcachefs");

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

        bch2_free_super(&ca->disk_sb);
        bch2_dev_journal_exit(ca);

        free_percpu(ca->io_done);
        bioset_exit(&ca->replica_set);
        free_percpu(ca->usage_percpu);
        kvpfree(ca->bucket_dirty, BITS_TO_LONGS(ca->mi.nbuckets) * sizeof(unsigned long));
        kvpfree(ca->buckets,     ca->mi.nbuckets * sizeof(struct bucket));
        kvpfree(ca->oldest_gens, ca->mi.nbuckets * sizeof(u8));
        free_heap(&ca->copygc_heap);
        free_heap(&ca->alloc_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 bch2_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 __bch2_dev_offline(struct bch_dev *ca)
{
        struct bch_fs *c = ca->fs;

        lockdep_assert_held(&c->state_lock);

        __bch2_dev_read_only(c, 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, "bcachefs");
                sysfs_remove_link(&ca->kobj, "block");
        }

        bch2_free_super(&ca->disk_sb);
        bch2_dev_journal_exit(ca);
}

static void bch2_dev_ref_release(struct percpu_ref *ref)
{
        struct bch_dev *ca = container_of(ref, struct bch_dev, ref);

        complete(&ca->stop_complete);
}

static void bch2_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 bch2_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, &c->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, "bcachefs");
                if (ret)
                        return ret;
                ret = sysfs_create_link(&ca->kobj, block, "block");
                if (ret)
                        return ret;
        }

        return 0;
}

static int bch2_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, btree_node_reserve_buckets;
        struct bch_dev *ca;

        if (bch2_fs_init_fault("dev_alloc"))
                return -ENOMEM;

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

        kobject_init(&ca->kobj, &bch2_dev_ktype);
        init_completion(&ca->stop_complete);
        init_completion(&ca->offline_complete);

        ca->dev_idx = dev_idx;
        __set_bit(ca->dev_idx, ca->self.d);

        ca->copygc_write_point.type = BCH_DATA_USER;

        spin_lock_init(&ca->freelist_lock);
        bch2_dev_moving_gc_init(ca);

        INIT_WORK(&ca->io_error_work, bch2_io_error_work);

        if (bch2_fs_init_fault("dev_alloc"))
                goto err;

        member = bch2_sb_get_members(c->disk_sb)->members + dev_idx;

        ca->mi = bch2_mi_to_cpu(member);
        ca->uuid = member->uuid;
        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;

        btree_node_reserve_buckets =
                DIV_ROUND_UP(BTREE_NODE_RESERVE,
                             ca->mi.bucket_size / c->opts.btree_node_size);

        if (percpu_ref_init(&ca->ref, bch2_dev_ref_release,
                            0, GFP_KERNEL) ||
            percpu_ref_init(&ca->io_ref, bch2_dev_io_ref_release,
                            PERCPU_REF_INIT_DEAD, GFP_KERNEL) ||
            !init_fifo(&ca->free[RESERVE_BTREE], btree_node_reserve_buckets,
                       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->alloc_heap, free_inc_reserve, GFP_KERNEL) ||
            !init_heap(&ca->copygc_heap,heap_size, GFP_KERNEL) ||
            !(ca->oldest_gens   = kvpmalloc(ca->mi.nbuckets *
                                            sizeof(u8),
                                            GFP_KERNEL|__GFP_ZERO)) ||
            !(ca->buckets       = kvpmalloc(ca->mi.nbuckets *
                                            sizeof(struct bucket),
                                            GFP_KERNEL|__GFP_ZERO)) ||
            !(ca->bucket_dirty  = kvpmalloc(BITS_TO_LONGS(ca->mi.nbuckets) *
                                            sizeof(unsigned long),
                                            GFP_KERNEL|__GFP_ZERO)) ||
            !(ca->usage_percpu = alloc_percpu(struct bch_dev_usage)) ||
            bioset_init(&ca->replica_set, 4,
                        offsetof(struct bch_write_bio, bio)) ||
            !(ca->io_done       = alloc_percpu(*ca->io_done)))
                goto err;

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

        if (bch2_dev_sysfs_online(ca))
                pr_warn("error creating sysfs objects");

        return 0;
err:
        bch2_dev_free(ca);
        return -ENOMEM;
}

static int __bch2_dev_online(struct bch_fs *c, struct bch_sb_handle *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))
                bch2_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 = bch2_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 (bch2_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)))
                bch2_mark_dev_metadata(c, ca);
        lg_local_unlock(&c->usage_lock);

        if (ca->mi.state == BCH_MEMBER_STATE_RW)
                bch2_dev_allocator_add(c, ca);

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

/* Device management: */

/*
 * Note: this function is also used by the error paths - when a particular
 * device sees an error, we call it to determine whether we can just set the
 * device RO, or - if this function returns false - we'll set the whole
 * filesystem RO:
 *
 * XXX: maybe we should be more explicit about whether we're changing state
 * because we got an error or what have you?
 */
bool bch2_dev_state_allowed(struct bch_fs *c, struct bch_dev *ca,
                            enum bch_member_state new_state, int flags)
{
        struct bch_devs_mask new_online_devs;
        struct replicas_status s;
        struct bch_dev *ca2;
        int i, nr_rw = 0, required;

        lockdep_assert_held(&c->state_lock);

        switch (new_state) {
        case BCH_MEMBER_STATE_RW:
                return true;
        case BCH_MEMBER_STATE_RO:
                if (ca->mi.state != BCH_MEMBER_STATE_RW)
                        return true;

                /* do we have enough devices to write to?  */
                for_each_member_device(ca2, c, i)
                        nr_rw += ca2->mi.state == BCH_MEMBER_STATE_RW;

                required = max(!(flags & BCH_FORCE_IF_METADATA_DEGRADED)
                               ? c->opts.metadata_replicas
                               : c->opts.metadata_replicas_required,
                               !(flags & BCH_FORCE_IF_DATA_DEGRADED)
                               ? c->opts.data_replicas
                               : c->opts.data_replicas_required);

                return nr_rw - 1 <= required;
        case BCH_MEMBER_STATE_FAILED:
        case BCH_MEMBER_STATE_SPARE:
                if (ca->mi.state != BCH_MEMBER_STATE_RW &&
                    ca->mi.state != BCH_MEMBER_STATE_RO)
                        return true;

                /* do we have enough devices to read from?  */
                new_online_devs = bch2_online_devs(c);
                __clear_bit(ca->dev_idx, new_online_devs.d);

                s = __bch2_replicas_status(c, new_online_devs);

                return bch2_have_enough_devs(c, s, flags);
        default:
                BUG();
        }
}

static bool bch2_fs_may_start(struct bch_fs *c)
{
        struct replicas_status s;
        struct bch_sb_field_members *mi;
        unsigned i, flags = c->opts.degraded
                ? BCH_FORCE_IF_DEGRADED
                : 0;

        if (!c->opts.degraded) {
                mutex_lock(&c->sb_lock);
                mi = bch2_sb_get_members(c->disk_sb);

                for (i = 0; i < c->disk_sb->nr_devices; i++)
                        if (bch2_dev_exists(c->disk_sb, mi, i) &&
                            !bch2_dev_is_online(c->devs[i]) &&
                            (c->devs[i]->mi.state == BCH_MEMBER_STATE_RW ||
                             c->devs[i]->mi.state == BCH_MEMBER_STATE_RO)) {
                                mutex_unlock(&c->sb_lock);
                                return false;
                        }
                mutex_unlock(&c->sb_lock);
        }

        s = bch2_replicas_status(c);

        return bch2_have_enough_devs(c, s, flags);
}

static void __bch2_dev_read_only(struct bch_fs *c, struct bch_dev *ca)
{
        bch2_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.
         */
        bch2_dev_allocator_stop(ca);
        bch2_dev_allocator_remove(c, ca);
}

static const char *__bch2_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);

        bch2_dev_allocator_add(c, ca);
        bch2_recalc_capacity(c);

        if (bch2_dev_allocator_start(ca))
                return "error starting allocator thread";

        if (bch2_moving_gc_start(ca))
                return "error starting moving GC thread";

        if (bch2_tiering_start(c))
                return "error starting tiering thread";

        return NULL;
}

int __bch2_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 (!bch2_dev_state_allowed(c, ca, new_state, flags))
                return -EINVAL;

        if (new_state == BCH_MEMBER_STATE_RW) {
                if (__bch2_dev_read_write(c, ca))
                        return -ENOMEM;
        } else {
                __bch2_dev_read_only(c, ca);
        }

        bch_notice(ca, "%s", bch2_dev_state[new_state]);

        mutex_lock(&c->sb_lock);
        mi = bch2_sb_get_members(c->disk_sb);
        SET_BCH_MEMBER_STATE(&mi->members[ca->dev_idx], new_state);
        bch2_write_super(c);
        mutex_unlock(&c->sb_lock);

        return 0;
}

int bch2_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 = __bch2_dev_set_state(c, ca, new_state, flags);
        mutex_unlock(&c->state_lock);

        return ret;
}

/* Device add/removal: */

int bch2_dev_remove(struct bch_fs *c, struct bch_dev *ca, int flags)
{
        struct bch_sb_field_members *mi;
        unsigned dev_idx = ca->dev_idx, data;
        int ret = -EINVAL;

        mutex_lock(&c->state_lock);

        percpu_ref_put(&ca->ref); /* XXX */

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

        if (!bch2_dev_state_allowed(c, ca, BCH_MEMBER_STATE_FAILED, flags)) {
                bch_err(ca, "Cannot remove without losing data");
                goto err;
        }

        /*
         * XXX: verify that dev_idx is really not in use anymore, anywhere
         *
         * flag_data_bad() does not check btree pointers
         */
        ret = bch2_flag_data_bad(ca);
        if (ret) {
                bch_err(ca, "Remove failed");
                goto err;
        }

        data = bch2_dev_has_data(c, ca);
        if (data) {
                bch_err(ca, "Remove failed, still has data (%x)", data);
                goto err;
        }

        bch2_journal_meta(&c->journal);

        __bch2_dev_offline(ca);
        bch2_dev_stop(ca);
        bch2_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 = bch2_sb_get_members(c->disk_sb);
        memset(&mi->members[dev_idx].uuid, 0, sizeof(mi->members[dev_idx].uuid));

        bch2_write_super(c);

        mutex_unlock(&c->sb_lock);
        mutex_unlock(&c->state_lock);
        return 0;
err:
        mutex_unlock(&c->state_lock);
        return ret;
}

/* Add new device to running filesystem: */
int bch2_dev_add(struct bch_fs *c, const char *path)
{
        struct bch_sb_handle 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 = bch2_read_super(path, bch2_opts_empty(), &sb);
        if (err)
                return -EINVAL;

        err = bch2_sb_validate(&sb);
        if (err)
                return -EINVAL;

        err = bch2_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 = bch2_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("bcachefs:add:no_slot"))
                goto no_slot;

        mi = bch2_sb_get_members(c->disk_sb);
        for (dev_idx = 0; dev_idx < BCH_SB_MEMBERS_MAX; dev_idx++)
                if (!bch2_dev_exists(c->disk_sb, mi, dev_idx))
                        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 = bch2_fs_sb_resize_members(c, u64s);
        if (!mi)
                goto err_unlock;

        dev_mi = bch2_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 (bch2_dev_alloc(c, dev_idx)) {
                err = "cannot allocate memory";
                ret = -ENOMEM;
                goto err_unlock;
        }

        if (__bch2_dev_online(c, &sb)) {
                err = "bch2_dev_online() error";
                ret = -ENOMEM;
                goto err_unlock;
        }

        bch2_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 (bch2_dev_journal_alloc(ca))
                        goto err;

                err = __bch2_dev_read_write(c, ca);
                if (err)
                        goto err;
        }

        mutex_unlock(&c->state_lock);
        return 0;
err_unlock:
        mutex_unlock(&c->sb_lock);
err:
        mutex_unlock(&c->state_lock);
        bch2_free_super(&sb);

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

/* Hot add existing device to running filesystem: */
int bch2_dev_online(struct bch_fs *c, const char *path)
{
        struct bch_sb_handle sb = { 0 };
        struct bch_dev *ca;
        unsigned dev_idx;
        const char *err;

        mutex_lock(&c->state_lock);

        err = bch2_read_super(path, bch2_opts_empty(), &sb);
        if (err)
                goto err;

        dev_idx = sb.sb->dev_idx;

        err = bch2_dev_in_fs(c->disk_sb, sb.sb);
        if (err)
                goto err;

        mutex_lock(&c->sb_lock);
        if (__bch2_dev_online(c, &sb)) {
                err = "__bch2_dev_online() error";
                mutex_unlock(&c->sb_lock);
                goto err;
        }
        mutex_unlock(&c->sb_lock);

        ca = c->devs[dev_idx];
        if (ca->mi.state == BCH_MEMBER_STATE_RW) {
                err = __bch2_dev_read_write(c, ca);
                if (err)
                        goto err;
        }

        mutex_unlock(&c->state_lock);
        return 0;
err:
        mutex_unlock(&c->state_lock);
        bch2_free_super(&sb);
        bch_err(c, "error bringing %s online: %s", path, err);
        return -EINVAL;
}

int bch2_dev_offline(struct bch_fs *c, struct bch_dev *ca, int flags)
{
        mutex_lock(&c->state_lock);

        if (!bch2_dev_state_allowed(c, ca, BCH_MEMBER_STATE_FAILED, flags)) {
                bch_err(ca, "Cannot offline required disk");
                mutex_unlock(&c->state_lock);
                return -EINVAL;
        }

        __bch2_dev_read_only(c, ca);
        __bch2_dev_offline(ca);

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

int bch2_dev_evacuate(struct bch_fs *c, struct bch_dev *ca)
{
        unsigned data;
        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 = bch2_move_data_off_device(ca);
        if (ret) {
                bch_err(ca, "Error migrating data: %i", ret);
                return ret;
        }

        ret = bch2_move_metadata_off_device(ca);
        if (ret) {
                bch_err(ca, "Error migrating metadata: %i", ret);
                return ret;
        }

        data = bch2_dev_has_data(c, ca);
        if (data) {
                bch_err(ca, "Migrate error: data still present (%x)", data);
                return -EINVAL;
        }

        return 0;
}

/* Filesystem open: */

const char *bch2_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 bch_sb_handle *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 = bch2_read_super(devices[i], opts, &sb[i]);
                if (err)
                        goto err;

                err = bch2_sb_validate(&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 = bch2_dev_in_fs(sb[best_sb].sb, sb[i].sb);
                if (err)
                        goto err;
        }

        err = "cannot allocate memory";
        c = bch2_fs_alloc(sb[best_sb].sb, opts);
        if (!c)
                goto err;

        err = "bch2_dev_online() error";
        mutex_lock(&c->sb_lock);
        for (i = 0; i < nr_devices; i++)
                if (__bch2_dev_online(c, &sb[i])) {
                        mutex_unlock(&c->sb_lock);
                        goto err;
                }
        mutex_unlock(&c->sb_lock);

        err = "insufficient devices";
        if (!bch2_fs_may_start(c))
                goto err;

        if (!c->opts.nostart) {
                err = __bch2_fs_start(c);
                if (err)
                        goto err;
        }

        err = bch2_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)
                bch2_fs_stop(c);

        for (i = 0; i < nr_devices; i++)
                bch2_free_super(&sb[i]);
        goto out;
}

static const char *__bch2_fs_open_incremental(struct bch_sb_handle *sb,
                                              struct bch_opts opts)
{
        const char *err;
        struct bch_fs *c;
        bool allocated_fs = false;

        err = bch2_sb_validate(sb);
        if (err)
                return err;

        mutex_lock(&bch_fs_list_lock);
        c = __bch2_uuid_to_fs(sb->sb->uuid);
        if (c) {
                closure_get(&c->cl);

                err = bch2_dev_in_fs(c->disk_sb, sb->sb);
                if (err)
                        goto err;
        } else {
                c = bch2_fs_alloc(sb->sb, opts);
                err = "cannot allocate memory";
                if (!c)
                        goto err;

                allocated_fs = true;
        }

        err = "bch2_dev_online() error";

        mutex_lock(&c->sb_lock);
        if (__bch2_dev_online(c, sb)) {
                mutex_unlock(&c->sb_lock);
                goto err;
        }
        mutex_unlock(&c->sb_lock);

        if (!c->opts.nostart && bch2_fs_may_start(c)) {
                err = __bch2_fs_start(c);
                if (err)
                        goto err;
        }

        err = __bch2_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)
                bch2_fs_stop(c);
        else if (c)
                closure_put(&c->cl);

        return err;
}

const char *bch2_fs_open_incremental(const char *path)
{
        struct bch_sb_handle sb;
        struct bch_opts opts = bch2_opts_empty();
        const char *err;

        err = bch2_read_super(path, opts, &sb);
        if (err)
                return err;

        err = __bch2_fs_open_incremental(&sb, opts);
        bch2_free_super(&sb);

        return err;
}

/* Global interfaces/init */

static void bcachefs_exit(void)
{
        bch2_debug_exit();
        bch2_vfs_exit();
        bch2_chardev_exit();
        if (bcachefs_kset)
                kset_unregister(bcachefs_kset);
}

static int __init bcachefs_init(void)
{
        bch2_bkey_pack_test();
        bch2_inode_pack_test();

        if (!(bcachefs_kset = kset_create_and_add("bcachefs", NULL, fs_kobj)) ||
            bch2_chardev_init() ||
            bch2_vfs_init() ||
            bch2_debug_init())
                goto err;

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

#define BCH_DEBUG_PARAM(name, description)                      \
        bool bch2_##name;                                       \
        module_param_named(name, bch2_##name, bool, 0644);      \
        MODULE_PARM_DESC(name, description);
BCH_DEBUG_PARAMS()
#undef BCH_DEBUG_PARAM

module_exit(bcachefs_exit);
module_init(bcachefs_init);