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

// SPDX-License-Identifier: GPL-2.0
/*
 * 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_background.h"
#include "alloc_foreground.h"
#include "bkey_sort.h"
#include "btree_cache.h"
#include "btree_gc.h"
#include "btree_journal_iter.h"
#include "btree_key_cache.h"
#include "btree_update_interior.h"
#include "btree_io.h"
#include "btree_write_buffer.h"
#include "buckets_waiting_for_journal.h"
#include "chardev.h"
#include "checksum.h"
#include "clock.h"
#include "compress.h"
#include "counters.h"
#include "debug.h"
#include "disk_groups.h"
#include "ec.h"
#include "errcode.h"
#include "error.h"
#include "fs.h"
#include "fs-io.h"
#include "fs-io-buffered.h"
#include "fs-io-direct.h"
#include "fsck.h"
#include "inode.h"
#include "io_read.h"
#include "io_write.h"
#include "journal.h"
#include "journal_reclaim.h"
#include "journal_seq_blacklist.h"
#include "move.h"
#include "migrate.h"
#include "movinggc.h"
#include "nocow_locking.h"
#include "quota.h"
#include "rebalance.h"
#include "recovery.h"
#include "replicas.h"
#include "sb-clean.h"
#include "sb-errors.h"
#include "sb-members.h"
#include "snapshot.h"
#include "subvolume.h"
#include "super.h"
#include "super-io.h"
#include "sysfs.h"
#include "trace.h"

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

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

const char * const bch2_fs_flag_strs[] = {
#define x(n)            #n,
        BCH_FS_FLAGS()
#undef x
        NULL
};

#define KTYPE(type)                                                     \
static const struct attribute_group type ## _group = {                  \
        .attrs = type ## _files                                         \
};                                                                      \
                                                                        \
static const struct attribute_group *type ## _groups[] = {              \
        &type ## _group,                                                \
        NULL                                                            \
};                                                                      \
                                                                        \
static const struct kobj_type type ## _ktype = {                        \
        .release        = type ## _release,                             \
        .sysfs_ops      = &type ## _sysfs_ops,                          \
        .default_groups = type ## _groups                               \
}

static void bch2_fs_release(struct kobject *);
static void bch2_dev_release(struct kobject *);
static void bch2_fs_counters_release(struct kobject *k)
{
}

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)
{
}

KTYPE(bch2_fs);
KTYPE(bch2_fs_counters);
KTYPE(bch2_fs_internal);
KTYPE(bch2_fs_opts_dir);
KTYPE(bch2_fs_time_stats);
KTYPE(bch2_dev);

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

DECLARE_WAIT_QUEUE_HEAD(bch2_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_fs *, struct bch_dev *);
static void __bch2_dev_read_only(struct bch_fs *, struct bch_dev *);

struct bch_fs *bch2_dev_to_fs(dev_t dev)
{
        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 && ca->disk_sb.bdev->bd_dev == dev) {
                                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_t 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.sb->uuid, &uuid, sizeof(uuid)))
                        return c;

        return NULL;
}

struct bch_fs *bch2_uuid_to_fs(__uuid_t 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;
}

static void bch2_dev_usage_journal_reserve(struct bch_fs *c)
{
        struct bch_dev *ca;
        unsigned i, nr = 0, u64s =
                ((sizeof(struct jset_entry_dev_usage) +
                  sizeof(struct jset_entry_dev_usage_type) * BCH_DATA_NR)) /
                sizeof(u64);

        rcu_read_lock();
        for_each_member_device_rcu(ca, c, i, NULL)
                nr++;
        rcu_read_unlock();

        bch2_journal_entry_res_resize(&c->journal,
                        &c->dev_usage_journal_res, u64s * nr);
}

/* Filesystem RO/RW: */

/*
 * For startup/shutdown of RW stuff, the dependencies are:
 *
 * - foreground writes depend on copygc and rebalance (to free up space)
 *
 * - copygc and rebalance 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, clean_passes = 0;
        u64 seq = 0;

        bch2_fs_ec_stop(c);
        bch2_open_buckets_stop(c, NULL, true);
        bch2_rebalance_stop(c);
        bch2_copygc_stop(c);
        bch2_gc_thread_stop(c);
        bch2_fs_ec_flush(c);

        bch_verbose(c, "flushing journal and stopping allocators, journal seq %llu",
                    journal_cur_seq(&c->journal));

        do {
                clean_passes++;

                if (bch2_btree_interior_updates_flush(c) ||
                    bch2_journal_flush_all_pins(&c->journal) ||
                    bch2_btree_flush_all_writes(c) ||
                    seq != atomic64_read(&c->journal.seq)) {
                        seq = atomic64_read(&c->journal.seq);
                        clean_passes = 0;
                }
        } while (clean_passes < 2);

        bch_verbose(c, "flushing journal and stopping allocators complete, journal seq %llu",
                    journal_cur_seq(&c->journal));

        if (test_bit(JOURNAL_REPLAY_DONE, &c->journal.flags) &&
            !test_bit(BCH_FS_emergency_ro, &c->flags))
                set_bit(BCH_FS_clean_shutdown, &c->flags);
        bch2_fs_journal_stop(&c->journal);

        /*
         * After stopping journal:
         */
        for_each_member_device(ca, c, i)
                bch2_dev_allocator_remove(c, ca);
}

#ifndef BCH_WRITE_REF_DEBUG
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(&bch2_read_only_wait);
}
#endif

void bch2_fs_read_only(struct bch_fs *c)
{
        if (!test_bit(BCH_FS_rw, &c->flags)) {
                bch2_journal_reclaim_stop(&c->journal);
                return;
        }

        BUG_ON(test_bit(BCH_FS_write_disable_complete, &c->flags));

        bch_verbose(c, "going read-only");

        /*
         * Block new foreground-end write operations from starting - any new
         * writes will return -EROFS:
         */
        set_bit(BCH_FS_going_ro, &c->flags);
#ifndef BCH_WRITE_REF_DEBUG
        percpu_ref_kill(&c->writes);
#else
        for (unsigned i = 0; i < BCH_WRITE_REF_NR; i++)
                bch2_write_ref_put(c, i);
#endif

        /*
         * 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(bch2_read_only_wait,
                   test_bit(BCH_FS_write_disable_complete, &c->flags) ||
                   test_bit(BCH_FS_emergency_ro, &c->flags));

        bool writes_disabled = test_bit(BCH_FS_write_disable_complete, &c->flags);
        if (writes_disabled)
                bch_verbose(c, "finished waiting for writes to stop");

        __bch2_fs_read_only(c);

        wait_event(bch2_read_only_wait,
                   test_bit(BCH_FS_write_disable_complete, &c->flags));

        if (!writes_disabled)
                bch_verbose(c, "finished waiting for writes to stop");

        clear_bit(BCH_FS_write_disable_complete, &c->flags);
        clear_bit(BCH_FS_going_ro, &c->flags);
        clear_bit(BCH_FS_rw, &c->flags);

        if (!bch2_journal_error(&c->journal) &&
            !test_bit(BCH_FS_error, &c->flags) &&
            !test_bit(BCH_FS_emergency_ro, &c->flags) &&
            test_bit(BCH_FS_started, &c->flags) &&
            test_bit(BCH_FS_clean_shutdown, &c->flags) &&
            !c->opts.norecovery) {
                BUG_ON(c->journal.last_empty_seq != journal_cur_seq(&c->journal));
                BUG_ON(atomic_read(&c->btree_cache.dirty));
                BUG_ON(atomic_long_read(&c->btree_key_cache.nr_dirty));
                BUG_ON(c->btree_write_buffer.state.nr);

                bch_verbose(c, "marking filesystem clean");
                bch2_fs_mark_clean(c);
        } else {
                bch_verbose(c, "done going read-only, filesystem not clean");
        }
}

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

        down_write(&c->state_lock);
        bch2_fs_read_only(c);
        up_write(&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_journal_halt(&c->journal);
        bch2_fs_read_only_async(c);

        wake_up(&bch2_read_only_wait);
        return ret;
}

static int bch2_fs_read_write_late(struct bch_fs *c)
{
        int ret;

        /*
         * Data move operations can't run until after check_snapshots has
         * completed, and bch2_snapshot_is_ancestor() is available.
         *
         * Ideally we'd start copygc/rebalance earlier instead of waiting for
         * all of recovery/fsck to complete:
         */
        ret = bch2_copygc_start(c);
        if (ret) {
                bch_err(c, "error starting copygc thread");
                return ret;
        }

        ret = bch2_rebalance_start(c);
        if (ret) {
                bch_err(c, "error starting rebalance thread");
                return ret;
        }

        return 0;
}

static int __bch2_fs_read_write(struct bch_fs *c, bool early)
{
        struct bch_dev *ca;
        unsigned i;
        int ret;

        if (test_bit(BCH_FS_initial_gc_unfixed, &c->flags)) {
                bch_err(c, "cannot go rw, unfixed btree errors");
                return -BCH_ERR_erofs_unfixed_errors;
        }

        if (test_bit(BCH_FS_rw, &c->flags))
                return 0;

        if (c->opts.norecovery)
                return -BCH_ERR_erofs_norecovery;

        /*
         * nochanges is used for fsck -n mode - we have to allow going rw
         * during recovery for that to work:
         */
        if (c->opts.nochanges && (!early || c->opts.read_only))
                return -BCH_ERR_erofs_nochanges;

        bch_info(c, "going read-write");

        ret = bch2_sb_members_v2_init(c);
        if (ret)
                goto err;

        ret = bch2_fs_mark_dirty(c);
        if (ret)
                goto err;

        clear_bit(BCH_FS_clean_shutdown, &c->flags);

        /*
         * First journal write must be a flush write: after a clean shutdown we
         * don't read the journal, so the first journal write may end up
         * overwriting whatever was there previously, and there must always be
         * at least one non-flush write in the journal or recovery will fail:
         */
        set_bit(JOURNAL_NEED_FLUSH_WRITE, &c->journal.flags);

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

        set_bit(BCH_FS_rw, &c->flags);
        set_bit(BCH_FS_was_rw, &c->flags);

#ifndef BCH_WRITE_REF_DEBUG
        percpu_ref_reinit(&c->writes);
#else
        for (i = 0; i < BCH_WRITE_REF_NR; i++) {
                BUG_ON(atomic_long_read(&c->writes[i]));
                atomic_long_inc(&c->writes[i]);
        }
#endif

        ret = bch2_gc_thread_start(c);
        if (ret) {
                bch_err(c, "error starting gc thread");
                return ret;
        }

        ret = bch2_journal_reclaim_start(&c->journal);
        if (ret)
                goto err;

        if (!early) {
                ret = bch2_fs_read_write_late(c);
                if (ret)
                        goto err;
        }

        bch2_do_discards(c);
        bch2_do_invalidates(c);
        bch2_do_stripe_deletes(c);
        bch2_do_pending_node_rewrites(c);
        return 0;
err:
        if (test_bit(BCH_FS_rw, &c->flags))
                bch2_fs_read_only(c);
        else
                __bch2_fs_read_only(c);
        return ret;
}

int bch2_fs_read_write(struct bch_fs *c)
{
        return __bch2_fs_read_write(c, false);
}

int bch2_fs_read_write_early(struct bch_fs *c)
{
        lockdep_assert_held(&c->state_lock);

        return __bch2_fs_read_write(c, true);
}

/* Filesystem startup/shutdown: */

static void __bch2_fs_free(struct bch_fs *c)
{
        unsigned i;

        for (i = 0; i < BCH_TIME_STAT_NR; i++)
                bch2_time_stats_exit(&c->times[i]);

        bch2_free_pending_node_rewrites(c);
        bch2_fs_sb_errors_exit(c);
        bch2_fs_counters_exit(c);
        bch2_fs_snapshots_exit(c);
        bch2_fs_quota_exit(c);
        bch2_fs_fs_io_direct_exit(c);
        bch2_fs_fs_io_buffered_exit(c);
        bch2_fs_fsio_exit(c);
        bch2_fs_ec_exit(c);
        bch2_fs_encryption_exit(c);
        bch2_fs_nocow_locking_exit(c);
        bch2_fs_io_write_exit(c);
        bch2_fs_io_read_exit(c);
        bch2_fs_buckets_waiting_for_journal_exit(c);
        bch2_fs_btree_interior_update_exit(c);
        bch2_fs_btree_iter_exit(c);
        bch2_fs_btree_key_cache_exit(&c->btree_key_cache);
        bch2_fs_btree_cache_exit(c);
        bch2_fs_replicas_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);
        bch2_journal_keys_put_initial(c);
        BUG_ON(atomic_read(&c->journal_keys.ref));
        bch2_fs_btree_write_buffer_exit(c);
        percpu_free_rwsem(&c->mark_lock);
        free_percpu(c->online_reserved);

        darray_exit(&c->btree_roots_extra);
        free_percpu(c->pcpu);
        mempool_exit(&c->large_bkey_pool);
        mempool_exit(&c->btree_bounce_pool);
        bioset_exit(&c->btree_bio);
        mempool_exit(&c->fill_iter);
#ifndef BCH_WRITE_REF_DEBUG
        percpu_ref_exit(&c->writes);
#endif
        kfree(rcu_dereference_protected(c->disk_groups, 1));
        kfree(c->journal_seq_blacklist_table);
        kfree(c->unused_inode_hints);

        if (c->write_ref_wq)
                destroy_workqueue(c->write_ref_wq);
        if (c->io_complete_wq)
                destroy_workqueue(c->io_complete_wq);
        if (c->copygc_wq)
                destroy_workqueue(c->copygc_wq);
        if (c->btree_io_complete_wq)
                destroy_workqueue(c->btree_io_complete_wq);
        if (c->btree_update_wq)
                destroy_workqueue(c->btree_update_wq);

        bch2_free_super(&c->disk_sb);
        kvpfree(c, sizeof(*c));
        module_put(THIS_MODULE);
}

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)
{
        struct bch_dev *ca;
        unsigned i;

        bch_verbose(c, "shutting down");

        set_bit(BCH_FS_stopping, &c->flags);

        cancel_work_sync(&c->journal_seq_blacklist_gc_work);

        down_write(&c->state_lock);
        bch2_fs_read_only(c);
        up_write(&c->state_lock);

        for_each_member_device(ca, c, i)
                if (ca->kobj.state_in_sysfs &&
                    ca->disk_sb.bdev)
                        sysfs_remove_link(bdev_kobj(ca->disk_sb.bdev), "bcachefs");

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

        bch2_fs_debug_exit(c);
        bch2_fs_chardev_exit(c);

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

        /* btree prefetch might have kicked off reads in the background: */
        bch2_btree_flush_all_reads(c);

        for_each_member_device(ca, c, i)
                cancel_work_sync(&ca->io_error_work);

        cancel_work_sync(&c->read_only_work);
}

void bch2_fs_free(struct bch_fs *c)
{
        unsigned i;

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

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

        for (i = 0; i < c->sb.nr_devices; i++) {
                struct bch_dev *ca = rcu_dereference_protected(c->devs[i], true);

                if (ca) {
                        bch2_free_super(&ca->disk_sb);
                        bch2_dev_free(ca);
                }
        }

        bch_verbose(c, "shutdown complete");

        kobject_put(&c->kobj);
}

void bch2_fs_stop(struct bch_fs *c)
{
        __bch2_fs_stop(c);
        bch2_fs_free(c);
}

static int bch2_fs_online(struct bch_fs *c)
{
        struct bch_dev *ca;
        unsigned i;
        int ret = 0;

        lockdep_assert_held(&bch_fs_list_lock);

        if (__bch2_uuid_to_fs(c->sb.uuid)) {
                bch_err(c, "filesystem UUID already open");
                return -EINVAL;
        }

        ret = bch2_fs_chardev_init(c);
        if (ret) {
                bch_err(c, "error creating character device");
                return ret;
        }

        bch2_fs_debug_init(c);

        ret = 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") ?:
#ifndef CONFIG_BCACHEFS_NO_LATENCY_ACCT
            kobject_add(&c->time_stats, &c->kobj, "time_stats") ?:
#endif
            kobject_add(&c->counters_kobj, &c->kobj, "counters") ?:
            bch2_opts_create_sysfs_files(&c->opts_dir);
        if (ret) {
                bch_err(c, "error creating sysfs objects");
                return ret;
        }

        down_write(&c->state_lock);

        for_each_member_device(ca, c, i) {
                ret = bch2_dev_sysfs_online(c, ca);
                if (ret) {
                        bch_err(c, "error creating sysfs objects");
                        percpu_ref_put(&ca->ref);
                        goto err;
                }
        }

        BUG_ON(!list_empty(&c->list));
        list_add(&c->list, &bch_fs_list);
err:
        up_write(&c->state_lock);
        return ret;
}

static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
{
        struct bch_fs *c;
        struct printbuf name = PRINTBUF;
        unsigned i, iter_size;
        int ret = 0;

        c = kvpmalloc(sizeof(struct bch_fs), GFP_KERNEL|__GFP_ZERO);
        if (!c) {
                c = ERR_PTR(-BCH_ERR_ENOMEM_fs_alloc);
                goto out;
        }

        __module_get(THIS_MODULE);

        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);
        kobject_init(&c->counters_kobj, &bch2_fs_counters_ktype);

        c->minor                = -1;
        c->disk_sb.fs_sb        = true;

        init_rwsem(&c->state_lock);
        mutex_init(&c->sb_lock);
        mutex_init(&c->replicas_gc_lock);
        mutex_init(&c->btree_root_lock);
        INIT_WORK(&c->read_only_work, bch2_fs_read_only_work);

        init_rwsem(&c->gc_lock);
        mutex_init(&c->gc_gens_lock);
        atomic_set(&c->journal_keys.ref, 1);
        c->journal_keys.initial_ref_held = true;

        for (i = 0; i < BCH_TIME_STAT_NR; i++)
                bch2_time_stats_init(&c->times[i]);

        bch2_fs_copygc_init(c);
        bch2_fs_btree_key_cache_init_early(&c->btree_key_cache);
        bch2_fs_btree_interior_update_init_early(c);
        bch2_fs_allocator_background_init(c);
        bch2_fs_allocator_foreground_init(c);
        bch2_fs_rebalance_init(c);
        bch2_fs_quota_init(c);
        bch2_fs_ec_init_early(c);
        bch2_fs_move_init(c);
        bch2_fs_sb_errors_init_early(c);

        INIT_LIST_HEAD(&c->list);

        mutex_init(&c->usage_scratch_lock);

        mutex_init(&c->bio_bounce_pages_lock);
        mutex_init(&c->snapshot_table_lock);
        init_rwsem(&c->snapshot_create_lock);

        spin_lock_init(&c->btree_write_error_lock);

        INIT_WORK(&c->journal_seq_blacklist_gc_work,
                  bch2_blacklist_entries_gc);

        INIT_LIST_HEAD(&c->journal_iters);

        INIT_LIST_HEAD(&c->fsck_error_msgs);
        mutex_init(&c->fsck_error_msgs_lock);

        seqcount_init(&c->gc_pos_lock);

        seqcount_init(&c->usage_lock);

        sema_init(&c->io_in_flight, 128);

        INIT_LIST_HEAD(&c->vfs_inodes_list);
        mutex_init(&c->vfs_inodes_lock);

        c->copy_gc_enabled              = 1;
        c->rebalance.enabled            = 1;
        c->promote_whole_extents        = true;

        c->journal.flush_write_time     = &c->times[BCH_TIME_journal_flush_write];
        c->journal.noflush_write_time   = &c->times[BCH_TIME_journal_noflush_write];
        c->journal.flush_seq_time       = &c->times[BCH_TIME_journal_flush_seq];

        bch2_fs_btree_cache_init_early(&c->btree_cache);

        mutex_init(&c->sectors_available_lock);

        ret = percpu_init_rwsem(&c->mark_lock);
        if (ret)
                goto err;

        mutex_lock(&c->sb_lock);
        ret = bch2_sb_to_fs(c, sb);
        mutex_unlock(&c->sb_lock);

        if (ret)
                goto err;

        pr_uuid(&name, c->sb.user_uuid.b);
        strscpy(c->name, name.buf, sizeof(c->name));
        printbuf_exit(&name);

        ret = name.allocation_failure ? -BCH_ERR_ENOMEM_fs_name_alloc : 0;
        if (ret)
                goto err;

        /* Compat: */
        if (le16_to_cpu(sb->version) <= bcachefs_metadata_version_inode_v2 &&
            !BCH_SB_JOURNAL_FLUSH_DELAY(sb))
                SET_BCH_SB_JOURNAL_FLUSH_DELAY(sb, 1000);

        if (le16_to_cpu(sb->version) <= bcachefs_metadata_version_inode_v2 &&
            !BCH_SB_JOURNAL_RECLAIM_DELAY(sb))
                SET_BCH_SB_JOURNAL_RECLAIM_DELAY(sb, 100);

        c->opts = bch2_opts_default;
        ret = bch2_opts_from_sb(&c->opts, sb);
        if (ret)
                goto err;

        bch2_opts_apply(&c->opts, opts);

        c->btree_key_cache_btrees |= 1U << BTREE_ID_alloc;
        if (c->opts.inodes_use_key_cache)
                c->btree_key_cache_btrees |= 1U << BTREE_ID_inodes;
        c->btree_key_cache_btrees |= 1U << BTREE_ID_logged_ops;

        c->block_bits           = ilog2(block_sectors(c));
        c->btree_foreground_merge_threshold = BTREE_FOREGROUND_MERGE_THRESHOLD(c);

        if (bch2_fs_init_fault("fs_alloc")) {
                bch_err(c, "fs_alloc fault injected");
                ret = -EFAULT;
                goto err;
        }

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

        c->inode_shard_bits = ilog2(roundup_pow_of_two(num_possible_cpus()));

        if (!(c->btree_update_wq = alloc_workqueue("bcachefs",
                                WQ_FREEZABLE|WQ_UNBOUND|WQ_MEM_RECLAIM, 512)) ||
            !(c->btree_io_complete_wq = alloc_workqueue("bcachefs_btree_io",
                                WQ_FREEZABLE|WQ_MEM_RECLAIM, 1)) ||
            !(c->copygc_wq = alloc_workqueue("bcachefs_copygc",
                                WQ_FREEZABLE|WQ_MEM_RECLAIM|WQ_CPU_INTENSIVE, 1)) ||
            !(c->io_complete_wq = alloc_workqueue("bcachefs_io",
                                WQ_FREEZABLE|WQ_HIGHPRI|WQ_MEM_RECLAIM, 1)) ||
            !(c->write_ref_wq = alloc_workqueue("bcachefs_write_ref",
                                WQ_FREEZABLE, 0)) ||
#ifndef BCH_WRITE_REF_DEBUG
            percpu_ref_init(&c->writes, bch2_writes_disabled,
                            PERCPU_REF_INIT_DEAD, GFP_KERNEL) ||
#endif
            mempool_init_kmalloc_pool(&c->fill_iter, 1, iter_size) ||
            bioset_init(&c->btree_bio, 1,
                        max(offsetof(struct btree_read_bio, bio),
                            offsetof(struct btree_write_bio, wbio.bio)),
                        BIOSET_NEED_BVECS) ||
            !(c->pcpu = alloc_percpu(struct bch_fs_pcpu)) ||
            !(c->online_reserved = alloc_percpu(u64)) ||
            mempool_init_kvpmalloc_pool(&c->btree_bounce_pool, 1,
                                        btree_bytes(c)) ||
            mempool_init_kmalloc_pool(&c->large_bkey_pool, 1, 2048) ||
            !(c->unused_inode_hints = kcalloc(1U << c->inode_shard_bits,
                                              sizeof(u64), GFP_KERNEL))) {
                ret = -BCH_ERR_ENOMEM_fs_other_alloc;
                goto err;
        }

        ret = bch2_fs_counters_init(c) ?:
            bch2_fs_sb_errors_init(c) ?:
            bch2_io_clock_init(&c->io_clock[READ]) ?:
            bch2_io_clock_init(&c->io_clock[WRITE]) ?:
            bch2_fs_journal_init(&c->journal) ?:
            bch2_fs_replicas_init(c) ?:
            bch2_fs_btree_cache_init(c) ?:
            bch2_fs_btree_key_cache_init(&c->btree_key_cache) ?:
            bch2_fs_btree_iter_init(c) ?:
            bch2_fs_btree_interior_update_init(c) ?:
            bch2_fs_buckets_waiting_for_journal_init(c) ?:
            bch2_fs_btree_write_buffer_init(c) ?:
            bch2_fs_subvolumes_init(c) ?:
            bch2_fs_io_read_init(c) ?:
            bch2_fs_io_write_init(c) ?:
            bch2_fs_nocow_locking_init(c) ?:
            bch2_fs_encryption_init(c) ?:
            bch2_fs_compress_init(c) ?:
            bch2_fs_ec_init(c) ?:
            bch2_fs_fsio_init(c) ?:
            bch2_fs_fs_io_buffered_init(c) ?:
            bch2_fs_fs_io_direct_init(c);
        if (ret)
                goto err;

        for (i = 0; i < c->sb.nr_devices; i++)
                if (bch2_dev_exists(c->disk_sb.sb, i) &&
                    bch2_dev_alloc(c, i)) {
                        ret = -EEXIST;
                        goto err;
                }

        bch2_journal_entry_res_resize(&c->journal,
                        &c->btree_root_journal_res,
                        BTREE_ID_NR * (JSET_KEYS_U64s + BKEY_BTREE_PTR_U64s_MAX));
        bch2_dev_usage_journal_reserve(c);
        bch2_journal_entry_res_resize(&c->journal,
                        &c->clock_journal_res,
                        (sizeof(struct jset_entry_clock) / sizeof(u64)) * 2);

        mutex_lock(&bch_fs_list_lock);
        ret = bch2_fs_online(c);
        mutex_unlock(&bch_fs_list_lock);

        if (ret)
                goto err;
out:
        return c;
err:
        bch2_fs_free(c);
        c = ERR_PTR(ret);
        goto out;
}

noinline_for_stack
static void print_mount_opts(struct bch_fs *c)
{
        enum bch_opt_id i;
        struct printbuf p = PRINTBUF;
        bool first = true;

        prt_str(&p, "mounting version ");
        bch2_version_to_text(&p, c->sb.version);

        if (c->opts.read_only) {
                prt_str(&p, " opts=");
                first = false;
                prt_printf(&p, "ro");
        }

        for (i = 0; i < bch2_opts_nr; i++) {
                const struct bch_option *opt = &bch2_opt_table[i];
                u64 v = bch2_opt_get_by_id(&c->opts, i);

                if (!(opt->flags & OPT_MOUNT))
                        continue;

                if (v == bch2_opt_get_by_id(&bch2_opts_default, i))
                        continue;

                prt_str(&p, first ? " opts=" : ",");
                first = false;
                bch2_opt_to_text(&p, c, c->disk_sb.sb, opt, v, OPT_SHOW_MOUNT_STYLE);
        }

        bch_info(c, "%s", p.buf);
        printbuf_exit(&p);
}

int bch2_fs_start(struct bch_fs *c)
{
        struct bch_dev *ca;
        time64_t now = ktime_get_real_seconds();
        unsigned i;
        int ret;

        print_mount_opts(c);

        down_write(&c->state_lock);

        BUG_ON(test_bit(BCH_FS_started, &c->flags));

        mutex_lock(&c->sb_lock);

        ret = bch2_sb_members_v2_init(c);
        if (ret) {
                mutex_unlock(&c->sb_lock);
                goto err;
        }

        for_each_online_member(ca, c, i)
                bch2_members_v2_get_mut(c->disk_sb.sb, i)->last_mount = cpu_to_le64(now);

        mutex_unlock(&c->sb_lock);

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

        ret = BCH_SB_INITIALIZED(c->disk_sb.sb)
                ? bch2_fs_recovery(c)
                : bch2_fs_initialize(c);
        if (ret)
                goto err;

        ret = bch2_opts_check_may_set(c);
        if (ret)
                goto err;

        if (bch2_fs_init_fault("fs_start")) {
                bch_err(c, "fs_start fault injected");
                ret = -EINVAL;
                goto err;
        }

        set_bit(BCH_FS_started, &c->flags);

        if (c->opts.read_only || c->opts.nochanges) {
                bch2_fs_read_only(c);
        } else {
                ret = !test_bit(BCH_FS_rw, &c->flags)
                        ? bch2_fs_read_write(c)
                        : bch2_fs_read_write_late(c);
                if (ret)
                        goto err;
        }

        ret = 0;
out:
        up_write(&c->state_lock);
        return ret;
err:
        bch_err_msg(c, ret, "starting filesystem");
        goto out;
}

static int bch2_dev_may_add(struct bch_sb *sb, struct bch_fs *c)
{
        struct bch_member m = bch2_sb_member_get(sb, sb->dev_idx);

        if (le16_to_cpu(sb->block_size) != block_sectors(c))
                return -BCH_ERR_mismatched_block_size;

        if (le16_to_cpu(m.bucket_size) <
            BCH_SB_BTREE_NODE_SIZE(c->disk_sb.sb))
                return -BCH_ERR_bucket_size_too_small;

        return 0;
}

static int 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;

        if (!uuid_equal(&fs->uuid, &sb->uuid))
                return -BCH_ERR_device_not_a_member_of_filesystem;

        if (!bch2_dev_exists(newest, sb->dev_idx))
                return -BCH_ERR_device_has_been_removed;

        if (fs->block_size != sb->block_size)
                return -BCH_ERR_mismatched_block_size;

        return 0;
}

/* 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)
{
        cancel_work_sync(&ca->io_error_work);

        if (ca->kobj.state_in_sysfs &&
            ca->disk_sb.bdev)
                sysfs_remove_link(bdev_kobj(ca->disk_sb.bdev), "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);
        bch2_dev_buckets_free(ca);
        free_page((unsigned long) ca->sb_read_scratch);

        bch2_time_stats_exit(&ca->io_latency[WRITE]);
        bch2_time_stats_exit(&ca->io_latency[READ]);

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

static void __bch2_dev_offline(struct bch_fs *c, struct bch_dev *ca)
{

        lockdep_assert_held(&c->state_lock);

        if (percpu_ref_is_zero(&ca->io_ref))
                return;

        __bch2_dev_read_only(c, ca);

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

        if (ca->kobj.state_in_sysfs) {
                sysfs_remove_link(bdev_kobj(ca->disk_sb.bdev), "bcachefs");
                sysfs_remove_link(&ca->kobj, "block");
        }

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

static void bch2_dev_ref_complete(struct percpu_ref *ref)
{
        struct bch_dev *ca = container_of(ref, struct bch_dev, ref);

        complete(&ca->ref_completion);
}

static void bch2_dev_io_ref_complete(struct percpu_ref *ref)
{
        struct bch_dev *ca = container_of(ref, struct bch_dev, io_ref);

        complete(&ca->io_ref_completion);
}

static int bch2_dev_sysfs_online(struct bch_fs *c, struct bch_dev *ca)
{
        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 = bdev_kobj(ca->disk_sb.bdev);

                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 struct bch_dev *__bch2_dev_alloc(struct bch_fs *c,
                                        struct bch_member *member)
{
        struct bch_dev *ca;
        unsigned i;

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

        kobject_init(&ca->kobj, &bch2_dev_ktype);
        init_completion(&ca->ref_completion);
        init_completion(&ca->io_ref_completion);

        init_rwsem(&ca->bucket_lock);

        INIT_WORK(&ca->io_error_work, bch2_io_error_work);

        bch2_time_stats_init(&ca->io_latency[READ]);
        bch2_time_stats_init(&ca->io_latency[WRITE]);

        ca->mi = bch2_mi_to_cpu(member);

        for (i = 0; i < ARRAY_SIZE(member->errors); i++)
                atomic64_set(&ca->errors[i], le64_to_cpu(member->errors[i]));

        ca->uuid = member->uuid;

        ca->nr_btree_reserve = DIV_ROUND_UP(BTREE_NODE_RESERVE,
                             ca->mi.bucket_size / btree_sectors(c));

        if (percpu_ref_init(&ca->ref, bch2_dev_ref_complete,
                            0, GFP_KERNEL) ||
            percpu_ref_init(&ca->io_ref, bch2_dev_io_ref_complete,
                            PERCPU_REF_INIT_DEAD, GFP_KERNEL) ||
            !(ca->sb_read_scratch = (void *) __get_free_page(GFP_KERNEL)) ||
            bch2_dev_buckets_alloc(c, ca) ||
            bioset_init(&ca->replica_set, 4,
                        offsetof(struct bch_write_bio, bio), 0) ||
            !(ca->io_done       = alloc_percpu(*ca->io_done)))
                goto err;

        return ca;
err:
        bch2_dev_free(ca);
        return NULL;
}

static void bch2_dev_attach(struct bch_fs *c, struct bch_dev *ca,
                            unsigned dev_idx)
{
        ca->dev_idx = dev_idx;
        __set_bit(ca->dev_idx, ca->self.d);
        scnprintf(ca->name, sizeof(ca->name), "dev-%u", dev_idx);

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

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

static int bch2_dev_alloc(struct bch_fs *c, unsigned dev_idx)
{
        struct bch_member member = bch2_sb_member_get(c->disk_sb.sb, dev_idx);
        struct bch_dev *ca = NULL;
        int ret = 0;

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

        ca = __bch2_dev_alloc(c, &member);
        if (!ca)
                goto err;

        ca->fs = c;

        bch2_dev_attach(c, ca, dev_idx);
        return ret;
err:
        if (ca)
                bch2_dev_free(ca);
        return -BCH_ERR_ENOMEM_dev_alloc;
}

static int __bch2_dev_attach_bdev(struct bch_dev *ca, struct bch_sb_handle *sb)
{
        unsigned ret;

        if (bch2_dev_is_online(ca)) {
                bch_err(ca, "already have device online in slot %u",
                        sb->sb->dev_idx);
                return -BCH_ERR_device_already_online;
        }

        if (get_capacity(sb->bdev->bd_disk) <
            ca->mi.bucket_size * ca->mi.nbuckets) {
                bch_err(ca, "cannot online: device too small");
                return -BCH_ERR_device_size_too_small;
        }

        BUG_ON(!percpu_ref_is_zero(&ca->io_ref));

        ret = bch2_dev_journal_init(ca, sb->sb);
        if (ret)
                return ret;

        /* Commit: */
        ca->disk_sb = *sb;
        memset(sb, 0, sizeof(*sb));

        ca->dev = ca->disk_sb.bdev->bd_dev;

        percpu_ref_reinit(&ca->io_ref);

        return 0;
}

static int bch2_dev_attach_bdev(struct bch_fs *c, struct bch_sb_handle *sb)
{
        struct bch_dev *ca;
        int ret;

        lockdep_assert_held(&c->state_lock);

        if (le64_to_cpu(sb->sb->seq) >
            le64_to_cpu(c->disk_sb.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 = bch_dev_locked(c, sb->sb->dev_idx);

        ret = __bch2_dev_attach_bdev(ca, sb);
        if (ret)
                return ret;

        bch2_dev_sysfs_online(c, ca);

        if (c->sb.nr_devices == 1)
                snprintf(c->name, sizeof(c->name), "%pg", ca->disk_sb.bdev);
        snprintf(ca->name, sizeof(ca->name), "%pg", ca->disk_sb.bdev);

        rebalance_wakeup(c);
        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 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)
                        if (ca2 != ca)
                                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 >= 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);

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

static bool bch2_fs_may_start(struct bch_fs *c)
{
        struct bch_dev *ca;
        unsigned i, flags = 0;

        if (c->opts.very_degraded)
                flags |= BCH_FORCE_IF_DEGRADED|BCH_FORCE_IF_LOST;

        if (c->opts.degraded)
                flags |= BCH_FORCE_IF_DEGRADED;

        if (!c->opts.degraded &&
            !c->opts.very_degraded) {
                mutex_lock(&c->sb_lock);

                for (i = 0; i < c->disk_sb.sb->nr_devices; i++) {
                        if (!bch2_dev_exists(c->disk_sb.sb, i))
                                continue;

                        ca = bch_dev_locked(c, i);

                        if (!bch2_dev_is_online(ca) &&
                            (ca->mi.state == BCH_MEMBER_STATE_rw ||
                             ca->mi.state == BCH_MEMBER_STATE_ro)) {
                                mutex_unlock(&c->sb_lock);
                                return false;
                        }
                }
                mutex_unlock(&c->sb_lock);
        }

        return bch2_have_enough_devs(c, bch2_online_devs(c), flags, true);
}

static void __bch2_dev_read_only(struct bch_fs *c, struct bch_dev *ca)
{
        /*
         * The allocator thread itself allocates btree nodes, so stop it first:
         */
        bch2_dev_allocator_remove(c, ca);
        bch2_dev_journal_stop(&c->journal, ca);
}

static void __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);
}

int __bch2_dev_set_state(struct bch_fs *c, struct bch_dev *ca,
                         enum bch_member_state new_state, int flags)
{
        struct bch_member *m;
        int ret = 0;

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

        if (!bch2_dev_state_allowed(c, ca, new_state, flags))
                return -BCH_ERR_device_state_not_allowed;

        if (new_state != BCH_MEMBER_STATE_rw)
                __bch2_dev_read_only(c, ca);

        bch_notice(ca, "%s", bch2_member_states[new_state]);

        mutex_lock(&c->sb_lock);
        m = bch2_members_v2_get_mut(c->disk_sb.sb, ca->dev_idx);
        SET_BCH_MEMBER_STATE(m, new_state);
        bch2_write_super(c);
        mutex_unlock(&c->sb_lock);

        if (new_state == BCH_MEMBER_STATE_rw)
                __bch2_dev_read_write(c, ca);

        rebalance_wakeup(c);

        return ret;
}

int bch2_dev_set_state(struct bch_fs *c, struct bch_dev *ca,
                       enum bch_member_state new_state, int flags)
{
        int ret;

        down_write(&c->state_lock);
        ret = __bch2_dev_set_state(c, ca, new_state, flags);
        up_write(&c->state_lock);

        return ret;
}

/* Device add/removal: */

static int bch2_dev_remove_alloc(struct bch_fs *c, struct bch_dev *ca)
{
        struct bpos start       = POS(ca->dev_idx, 0);
        struct bpos end         = POS(ca->dev_idx, U64_MAX);
        int ret;

        /*
         * We clear the LRU and need_discard btrees first so that we don't race
         * with bch2_do_invalidates() and bch2_do_discards()
         */
        ret =   bch2_btree_delete_range(c, BTREE_ID_lru, start, end,
                                        BTREE_TRIGGER_NORUN, NULL) ?:
                bch2_btree_delete_range(c, BTREE_ID_need_discard, start, end,
                                        BTREE_TRIGGER_NORUN, NULL) ?:
                bch2_btree_delete_range(c, BTREE_ID_freespace, start, end,
                                        BTREE_TRIGGER_NORUN, NULL) ?:
                bch2_btree_delete_range(c, BTREE_ID_backpointers, start, end,
                                        BTREE_TRIGGER_NORUN, NULL) ?:
                bch2_btree_delete_range(c, BTREE_ID_alloc, start, end,
                                        BTREE_TRIGGER_NORUN, NULL) ?:
                bch2_btree_delete_range(c, BTREE_ID_bucket_gens, start, end,
                                        BTREE_TRIGGER_NORUN, NULL);
        if (ret)
                bch_err_msg(c, ret, "removing dev alloc info");

        return ret;
}

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

        down_write(&c->state_lock);

        /*
         * We consume a reference to ca->ref, regardless of whether we succeed
         * or fail:
         */
        percpu_ref_put(&ca->ref);

        if (!bch2_dev_state_allowed(c, ca, BCH_MEMBER_STATE_failed, flags)) {
                bch_err(ca, "Cannot remove without losing data");
                ret = -BCH_ERR_device_state_not_allowed;
                goto err;
        }

        __bch2_dev_read_only(c, ca);

        ret = bch2_dev_data_drop(c, ca->dev_idx, flags);
        if (ret) {
                bch_err_msg(ca, ret, "dropping data");
                goto err;
        }

        ret = bch2_dev_remove_alloc(c, ca);
        if (ret) {
                bch_err_msg(ca, ret, "deleting alloc info");
                goto err;
        }

        ret = bch2_journal_flush_device_pins(&c->journal, ca->dev_idx);
        if (ret) {
                bch_err_msg(ca, ret, "flushing journal");
                goto err;
        }

        ret = bch2_journal_flush(&c->journal);
        if (ret) {
                bch_err(ca, "journal error");
                goto err;
        }

        ret = bch2_replicas_gc2(c);
        if (ret) {
                bch_err_msg(ca, ret, "in replicas_gc2()");
                goto err;
        }

        data = bch2_dev_has_data(c, ca);
        if (data) {
                struct printbuf data_has = PRINTBUF;

                prt_bitflags(&data_has, bch2_data_types, data);
                bch_err(ca, "Remove failed, still has data (%s)", data_has.buf);
                printbuf_exit(&data_has);
                ret = -EBUSY;
                goto err;
        }

        __bch2_dev_offline(c, ca);

        mutex_lock(&c->sb_lock);
        rcu_assign_pointer(c->devs[ca->dev_idx], NULL);
        mutex_unlock(&c->sb_lock);

        percpu_ref_kill(&ca->ref);
        wait_for_completion(&ca->ref_completion);

        bch2_dev_free(ca);

        /*
         * At this point the device object has been removed in-core, but the
         * on-disk journal might still refer to the device index via sb device
         * usage entries. Recovery fails if it sees usage information for an
         * invalid device. Flush journal pins to push the back of the journal
         * past now invalid device index references before we update the
         * superblock, but after the device object has been removed so any
         * further journal writes elide usage info for the device.
         */
        bch2_journal_flush_all_pins(&c->journal);

        /*
         * Free this device's slot in the bch_member array - all pointers to
         * this device must be gone:
         */
        mutex_lock(&c->sb_lock);
        m = bch2_members_v2_get_mut(c->disk_sb.sb, dev_idx);
        memset(&m->uuid, 0, sizeof(m->uuid));

        bch2_write_super(c);

        mutex_unlock(&c->sb_lock);
        up_write(&c->state_lock);

        bch2_dev_usage_journal_reserve(c);
        return 0;
err:
        if (ca->mi.state == BCH_MEMBER_STATE_rw &&
            !percpu_ref_is_zero(&ca->io_ref))
                __bch2_dev_read_write(c, ca);
        up_write(&c->state_lock);
        return ret;
}

/* Add new device to running filesystem: */
int bch2_dev_add(struct bch_fs *c, const char *path)
{
        struct bch_opts opts = bch2_opts_empty();
        struct bch_sb_handle sb;
        struct bch_dev *ca = NULL;
        struct bch_sb_field_members_v2 *mi;
        struct bch_member dev_mi;
        unsigned dev_idx, nr_devices, u64s;
        struct printbuf errbuf = PRINTBUF;
        struct printbuf label = PRINTBUF;
        int ret;

        ret = bch2_read_super(path, &opts, &sb);
        if (ret) {
                bch_err_msg(c, ret, "reading super");
                goto err;
        }

        dev_mi = bch2_sb_member_get(sb.sb, sb.sb->dev_idx);

        if (BCH_MEMBER_GROUP(&dev_mi)) {
                bch2_disk_path_to_text_sb(&label, sb.sb, BCH_MEMBER_GROUP(&dev_mi) - 1);
                if (label.allocation_failure) {
                        ret = -ENOMEM;
                        goto err;
                }
        }

        ret = bch2_dev_may_add(sb.sb, c);
        if (ret) {
                bch_err_fn(c, ret);
                goto err;
        }

        ca = __bch2_dev_alloc(c, &dev_mi);
        if (!ca) {
                ret = -ENOMEM;
                goto err;
        }

        bch2_dev_usage_init(ca);

        ret = __bch2_dev_attach_bdev(ca, &sb);
        if (ret)
                goto err;

        ret = bch2_dev_journal_alloc(ca);
        if (ret) {
                bch_err_msg(c, ret, "allocating journal");
                goto err;
        }

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

        ret = bch2_sb_from_fs(c, ca);
        if (ret) {
                bch_err_msg(c, ret, "setting up new superblock");
                goto err_unlock;
        }

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

        for (dev_idx = 0; dev_idx < BCH_SB_MEMBERS_MAX; dev_idx++)
                if (!bch2_dev_exists(c->disk_sb.sb, dev_idx))
                        goto have_slot;
no_slot:
        ret = -BCH_ERR_ENOSPC_sb_members;
        bch_err_msg(c, ret, "setting up new superblock");
        goto err_unlock;

have_slot:
        nr_devices = max_t(unsigned, dev_idx + 1, c->sb.nr_devices);

        mi = bch2_sb_field_get(c->disk_sb.sb, members_v2);
        u64s = DIV_ROUND_UP(sizeof(struct bch_sb_field_members_v2) +
                            le16_to_cpu(mi->member_bytes) * nr_devices, sizeof(u64));

        mi = bch2_sb_field_resize(&c->disk_sb, members_v2, u64s);
        if (!mi) {
                ret = -BCH_ERR_ENOSPC_sb_members;
                bch_err_msg(c, ret, "setting up new superblock");
                goto err_unlock;
        }
        struct bch_member *m = bch2_members_v2_get_mut(c->disk_sb.sb, dev_idx);

        /* success: */

        *m = dev_mi;
        m->last_mount = cpu_to_le64(ktime_get_real_seconds());
        c->disk_sb.sb->nr_devices       = nr_devices;

        ca->disk_sb.sb->dev_idx = dev_idx;
        bch2_dev_attach(c, ca, dev_idx);

        if (BCH_MEMBER_GROUP(&dev_mi)) {
                ret = __bch2_dev_group_set(c, ca, label.buf);
                if (ret) {
                        bch_err_msg(c, ret, "creating new label");
                        goto err_unlock;
                }
        }

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

        bch2_dev_usage_journal_reserve(c);

        ret = bch2_trans_mark_dev_sb(c, ca);
        if (ret) {
                bch_err_msg(ca, ret, "marking new superblock");
                goto err_late;
        }

        ret = bch2_fs_freespace_init(c);
        if (ret) {
                bch_err_msg(ca, ret, "initializing free space");
                goto err_late;
        }

        ca->new_fs_bucket_idx = 0;

        if (ca->mi.state == BCH_MEMBER_STATE_rw)
                __bch2_dev_read_write(c, ca);

        up_write(&c->state_lock);
        return 0;

err_unlock:
        mutex_unlock(&c->sb_lock);
        up_write(&c->state_lock);
err:
        if (ca)
                bch2_dev_free(ca);
        bch2_free_super(&sb);
        printbuf_exit(&label);
        printbuf_exit(&errbuf);
        return ret;
err_late:
        up_write(&c->state_lock);
        ca = NULL;
        goto err;
}

/* Hot add existing device to running filesystem: */
int bch2_dev_online(struct bch_fs *c, const char *path)
{
        struct bch_opts opts = bch2_opts_empty();
        struct bch_sb_handle sb = { NULL };
        struct bch_dev *ca;
        unsigned dev_idx;
        int ret;

        down_write(&c->state_lock);

        ret = bch2_read_super(path, &opts, &sb);
        if (ret) {
                up_write(&c->state_lock);
                return ret;
        }

        dev_idx = sb.sb->dev_idx;

        ret = bch2_dev_in_fs(c->disk_sb.sb, sb.sb);
        if (ret) {
                bch_err_msg(c, ret, "bringing %s online", path);
                goto err;
        }

        ret = bch2_dev_attach_bdev(c, &sb);
        if (ret)
                goto err;

        ca = bch_dev_locked(c, dev_idx);

        ret = bch2_trans_mark_dev_sb(c, ca);
        if (ret) {
                bch_err_msg(c, ret, "bringing %s online: error from bch2_trans_mark_dev_sb", path);
                goto err;
        }

        if (ca->mi.state == BCH_MEMBER_STATE_rw)
                __bch2_dev_read_write(c, ca);

        if (!ca->mi.freespace_initialized) {
                ret = bch2_dev_freespace_init(c, ca, 0, ca->mi.nbuckets);
                bch_err_msg(ca, ret, "initializing free space");
                if (ret)
                        goto err;
        }

        if (!ca->journal.nr) {
                ret = bch2_dev_journal_alloc(ca);
                bch_err_msg(ca, ret, "allocating journal");
                if (ret)
                        goto err;
        }

        mutex_lock(&c->sb_lock);
        bch2_members_v2_get_mut(c->disk_sb.sb, ca->dev_idx)->last_mount =
                cpu_to_le64(ktime_get_real_seconds());
        bch2_write_super(c);
        mutex_unlock(&c->sb_lock);

        up_write(&c->state_lock);
        return 0;
err:
        up_write(&c->state_lock);
        bch2_free_super(&sb);
        return ret;
}

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

        if (!bch2_dev_is_online(ca)) {
                bch_err(ca, "Already offline");
                up_write(&c->state_lock);
                return 0;
        }

        if (!bch2_dev_state_allowed(c, ca, BCH_MEMBER_STATE_failed, flags)) {
                bch_err(ca, "Cannot offline required disk");
                up_write(&c->state_lock);
                return -BCH_ERR_device_state_not_allowed;
        }

        __bch2_dev_offline(c, ca);

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

int bch2_dev_resize(struct bch_fs *c, struct bch_dev *ca, u64 nbuckets)
{
        struct bch_member *m;
        u64 old_nbuckets;
        int ret = 0;

        down_write(&c->state_lock);
        old_nbuckets = ca->mi.nbuckets;

        if (nbuckets < ca->mi.nbuckets) {
                bch_err(ca, "Cannot shrink yet");
                ret = -EINVAL;
                goto err;
        }

        if (bch2_dev_is_online(ca) &&
            get_capacity(ca->disk_sb.bdev->bd_disk) <
            ca->mi.bucket_size * nbuckets) {
                bch_err(ca, "New size larger than device");
                ret = -BCH_ERR_device_size_too_small;
                goto err;
        }

        ret = bch2_dev_buckets_resize(c, ca, nbuckets);
        if (ret) {
                bch_err_msg(ca, ret, "resizing buckets");
                goto err;
        }

        ret = bch2_trans_mark_dev_sb(c, ca);
        if (ret)
                goto err;

        mutex_lock(&c->sb_lock);
        m = bch2_members_v2_get_mut(c->disk_sb.sb, ca->dev_idx);
        m->nbuckets = cpu_to_le64(nbuckets);

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

        if (ca->mi.freespace_initialized) {
                ret = bch2_dev_freespace_init(c, ca, old_nbuckets, nbuckets);
                if (ret)
                        goto err;

                /*
                 * XXX: this is all wrong transactionally - we'll be able to do
                 * this correctly after the disk space accounting rewrite
                 */
                ca->usage_base->d[BCH_DATA_free].buckets += nbuckets - old_nbuckets;
        }

        bch2_recalc_capacity(c);
err:
        up_write(&c->state_lock);
        return ret;
}

/* return with ref on ca->ref: */
struct bch_dev *bch2_dev_lookup(struct bch_fs *c, const char *name)
{
        struct bch_dev *ca;
        unsigned i;

        rcu_read_lock();
        for_each_member_device_rcu(ca, c, i, NULL)
                if (!strcmp(name, ca->name))
                        goto found;
        ca = ERR_PTR(-BCH_ERR_ENOENT_dev_not_found);
found:
        rcu_read_unlock();

        return ca;
}

/* Filesystem open: */

struct bch_fs *bch2_fs_open(char * const *devices, unsigned nr_devices,
                            struct bch_opts opts)
{
        DARRAY(struct bch_sb_handle) sbs = { 0 };
        struct bch_fs *c = NULL;
        struct bch_sb_handle *sb, *best = NULL;
        struct printbuf errbuf = PRINTBUF;
        int ret = 0;

        if (!try_module_get(THIS_MODULE))
                return ERR_PTR(-ENODEV);

        if (!nr_devices) {
                ret = -EINVAL;
                goto err;
        }

        ret = darray_make_room(&sbs, nr_devices);
        if (ret)
                goto err;

        for (unsigned i = 0; i < nr_devices; i++) {
                struct bch_sb_handle sb = { NULL };

                ret = bch2_read_super(devices[i], &opts, &sb);
                if (ret)
                        goto err;

                BUG_ON(darray_push(&sbs, sb));
        }

        darray_for_each(sbs, sb)
                if (!best || le64_to_cpu(sb->sb->seq) > le64_to_cpu(best->sb->seq))
                        best = sb;

        darray_for_each_reverse(sbs, sb) {
                if (sb != best && !bch2_dev_exists(best->sb, sb->sb->dev_idx)) {
                        pr_info("%pg has been removed, skipping", sb->bdev);
                        bch2_free_super(sb);
                        darray_remove_item(&sbs, sb);
                        best -= best > sb;
                        continue;
                }

                ret = bch2_dev_in_fs(best->sb, sb->sb);
                if (ret)
                        goto err_print;
        }

        c = bch2_fs_alloc(best->sb, opts);
        ret = PTR_ERR_OR_ZERO(c);
        if (ret)
                goto err;

        down_write(&c->state_lock);
        darray_for_each(sbs, sb) {
                ret = bch2_dev_attach_bdev(c, sb);
                if (ret) {
                        up_write(&c->state_lock);
                        goto err;
                }
        }
        up_write(&c->state_lock);

        if (!bch2_fs_may_start(c)) {
                ret = -BCH_ERR_insufficient_devices_to_start;
                goto err_print;
        }

        if (!c->opts.nostart) {
                ret = bch2_fs_start(c);
                if (ret)
                        goto err;
        }
out:
        darray_for_each(sbs, sb)
                bch2_free_super(sb);
        darray_exit(&sbs);
        printbuf_exit(&errbuf);
        module_put(THIS_MODULE);
        return c;
err_print:
        pr_err("bch_fs_open err opening %s: %s",
               devices[0], bch2_err_str(ret));
err:
        if (!IS_ERR_OR_NULL(c))
                bch2_fs_stop(c);
        c = ERR_PTR(ret);
        goto out;
}

/* Global interfaces/init */

static void bcachefs_exit(void)
{
        bch2_debug_exit();
        bch2_vfs_exit();
        bch2_chardev_exit();
        bch2_btree_key_cache_exit();
        if (bcachefs_kset)
                kset_unregister(bcachefs_kset);
}

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

        if (!(bcachefs_kset = kset_create_and_add("bcachefs", NULL, fs_kobj)) ||
            bch2_btree_key_cache_init() ||
            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

__maybe_unused
static unsigned bch2_metadata_version = bcachefs_metadata_version_current;
module_param_named(version, bch2_metadata_version, uint, 0400);

module_exit(bcachefs_exit);
module_init(bcachefs_init);