Update bcachefs sources to de3b30303e bcachefs: bucket_gens btree

[bcachefs-tools-debian] / libbcachefs / bcachefs.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _BCACHEFS_H
#define _BCACHEFS_H

/*
 * SOME HIGH LEVEL CODE DOCUMENTATION:
 *
 * Bcache mostly works with cache sets, cache devices, and backing devices.
 *
 * Support for multiple cache devices hasn't quite been finished off yet, but
 * it's about 95% plumbed through. A cache set and its cache devices is sort of
 * like a md raid array and its component devices. Most of the code doesn't care
 * about individual cache devices, the main abstraction is the cache set.
 *
 * Multiple cache devices is intended to give us the ability to mirror dirty
 * cached data and metadata, without mirroring clean cached data.
 *
 * Backing devices are different, in that they have a lifetime independent of a
 * cache set. When you register a newly formatted backing device it'll come up
 * in passthrough mode, and then you can attach and detach a backing device from
 * a cache set at runtime - while it's mounted and in use. Detaching implicitly
 * invalidates any cached data for that backing device.
 *
 * A cache set can have multiple (many) backing devices attached to it.
 *
 * There's also flash only volumes - this is the reason for the distinction
 * between struct cached_dev and struct bcache_device. A flash only volume
 * works much like a bcache device that has a backing device, except the
 * "cached" data is always dirty. The end result is that we get thin
 * provisioning with very little additional code.
 *
 * Flash only volumes work but they're not production ready because the moving
 * garbage collector needs more work. More on that later.
 *
 * BUCKETS/ALLOCATION:
 *
 * Bcache is primarily designed for caching, which means that in normal
 * operation all of our available space will be allocated. Thus, we need an
 * efficient way of deleting things from the cache so we can write new things to
 * it.
 *
 * To do this, we first divide the cache device up into buckets. A bucket is the
 * unit of allocation; they're typically around 1 mb - anywhere from 128k to 2M+
 * works efficiently.
 *
 * Each bucket has a 16 bit priority, and an 8 bit generation associated with
 * it. The gens and priorities for all the buckets are stored contiguously and
 * packed on disk (in a linked list of buckets - aside from the superblock, all
 * of bcache's metadata is stored in buckets).
 *
 * The priority is used to implement an LRU. We reset a bucket's priority when
 * we allocate it or on cache it, and every so often we decrement the priority
 * of each bucket. It could be used to implement something more sophisticated,
 * if anyone ever gets around to it.
 *
 * The generation is used for invalidating buckets. Each pointer also has an 8
 * bit generation embedded in it; for a pointer to be considered valid, its gen
 * must match the gen of the bucket it points into.  Thus, to reuse a bucket all
 * we have to do is increment its gen (and write its new gen to disk; we batch
 * this up).
 *
 * Bcache is entirely COW - we never write twice to a bucket, even buckets that
 * contain metadata (including btree nodes).
 *
 * THE BTREE:
 *
 * Bcache is in large part design around the btree.
 *
 * At a high level, the btree is just an index of key -> ptr tuples.
 *
 * Keys represent extents, and thus have a size field. Keys also have a variable
 * number of pointers attached to them (potentially zero, which is handy for
 * invalidating the cache).
 *
 * The key itself is an inode:offset pair. The inode number corresponds to a
 * backing device or a flash only volume. The offset is the ending offset of the
 * extent within the inode - not the starting offset; this makes lookups
 * slightly more convenient.
 *
 * Pointers contain the cache device id, the offset on that device, and an 8 bit
 * generation number. More on the gen later.
 *
 * Index lookups are not fully abstracted - cache lookups in particular are
 * still somewhat mixed in with the btree code, but things are headed in that
 * direction.
 *
 * Updates are fairly well abstracted, though. There are two different ways of
 * updating the btree; insert and replace.
 *
 * BTREE_INSERT will just take a list of keys and insert them into the btree -
 * overwriting (possibly only partially) any extents they overlap with. This is
 * used to update the index after a write.
 *
 * BTREE_REPLACE is really cmpxchg(); it inserts a key into the btree iff it is
 * overwriting a key that matches another given key. This is used for inserting
 * data into the cache after a cache miss, and for background writeback, and for
 * the moving garbage collector.
 *
 * There is no "delete" operation; deleting things from the index is
 * accomplished by either by invalidating pointers (by incrementing a bucket's
 * gen) or by inserting a key with 0 pointers - which will overwrite anything
 * previously present at that location in the index.
 *
 * This means that there are always stale/invalid keys in the btree. They're
 * filtered out by the code that iterates through a btree node, and removed when
 * a btree node is rewritten.
 *
 * BTREE NODES:
 *
 * Our unit of allocation is a bucket, and we can't arbitrarily allocate and
 * free smaller than a bucket - so, that's how big our btree nodes are.
 *
 * (If buckets are really big we'll only use part of the bucket for a btree node
 * - no less than 1/4th - but a bucket still contains no more than a single
 * btree node. I'd actually like to change this, but for now we rely on the
 * bucket's gen for deleting btree nodes when we rewrite/split a node.)
 *
 * Anyways, btree nodes are big - big enough to be inefficient with a textbook
 * btree implementation.
 *
 * The way this is solved is that btree nodes are internally log structured; we
 * can append new keys to an existing btree node without rewriting it. This
 * means each set of keys we write is sorted, but the node is not.
 *
 * We maintain this log structure in memory - keeping 1Mb of keys sorted would
 * be expensive, and we have to distinguish between the keys we have written and
 * the keys we haven't. So to do a lookup in a btree node, we have to search
 * each sorted set. But we do merge written sets together lazily, so the cost of
 * these extra searches is quite low (normally most of the keys in a btree node
 * will be in one big set, and then there'll be one or two sets that are much
 * smaller).
 *
 * This log structure makes bcache's btree more of a hybrid between a
 * conventional btree and a compacting data structure, with some of the
 * advantages of both.
 *
 * GARBAGE COLLECTION:
 *
 * We can't just invalidate any bucket - it might contain dirty data or
 * metadata. If it once contained dirty data, other writes might overwrite it
 * later, leaving no valid pointers into that bucket in the index.
 *
 * Thus, the primary purpose of garbage collection is to find buckets to reuse.
 * It also counts how much valid data it each bucket currently contains, so that
 * allocation can reuse buckets sooner when they've been mostly overwritten.
 *
 * It also does some things that are really internal to the btree
 * implementation. If a btree node contains pointers that are stale by more than
 * some threshold, it rewrites the btree node to avoid the bucket's generation
 * wrapping around. It also merges adjacent btree nodes if they're empty enough.
 *
 * THE JOURNAL:
 *
 * Bcache's journal is not necessary for consistency; we always strictly
 * order metadata writes so that the btree and everything else is consistent on
 * disk in the event of an unclean shutdown, and in fact bcache had writeback
 * caching (with recovery from unclean shutdown) before journalling was
 * implemented.
 *
 * Rather, the journal is purely a performance optimization; we can't complete a
 * write until we've updated the index on disk, otherwise the cache would be
 * inconsistent in the event of an unclean shutdown. This means that without the
 * journal, on random write workloads we constantly have to update all the leaf
 * nodes in the btree, and those writes will be mostly empty (appending at most
 * a few keys each) - highly inefficient in terms of amount of metadata writes,
 * and it puts more strain on the various btree resorting/compacting code.
 *
 * The journal is just a log of keys we've inserted; on startup we just reinsert
 * all the keys in the open journal entries. That means that when we're updating
 * a node in the btree, we can wait until a 4k block of keys fills up before
 * writing them out.
 *
 * For simplicity, we only journal updates to leaf nodes; updates to parent
 * nodes are rare enough (since our leaf nodes are huge) that it wasn't worth
 * the complexity to deal with journalling them (in particular, journal replay)
 * - updates to non leaf nodes just happen synchronously (see btree_split()).
 */

#undef pr_fmt
#ifdef __KERNEL__
#define pr_fmt(fmt) "bcachefs: %s() " fmt "\n", __func__
#else
#define pr_fmt(fmt) "%s() " fmt "\n", __func__
#endif

#include <linux/backing-dev-defs.h>
#include <linux/bug.h>
#include <linux/bio.h>
#include <linux/closure.h>
#include <linux/kobject.h>
#include <linux/list.h>
#include <linux/math64.h>
#include <linux/mutex.h>
#include <linux/percpu-refcount.h>
#include <linux/percpu-rwsem.h>
#include <linux/rhashtable.h>
#include <linux/rwsem.h>
#include <linux/semaphore.h>
#include <linux/seqlock.h>
#include <linux/shrinker.h>
#include <linux/srcu.h>
#include <linux/types.h>
#include <linux/workqueue.h>
#include <linux/zstd.h>

#include "bcachefs_format.h"
#include "errcode.h"
#include "fifo.h"
#include "nocow_locking.h"
#include "opts.h"
#include "util.h"

#define dynamic_fault(...)              0
#define race_fault(...)                 0

#define trace_and_count(_c, _name, ...)                                 \
do {                                                                    \
        this_cpu_inc((_c)->counters[BCH_COUNTER_##_name]);              \
        trace_##_name(__VA_ARGS__);                                     \
} while (0)

#define bch2_fs_init_fault(name)                                        \
        dynamic_fault("bcachefs:bch_fs_init:" name)
#define bch2_meta_read_fault(name)                                      \
         dynamic_fault("bcachefs:meta:read:" name)
#define bch2_meta_write_fault(name)                                     \
         dynamic_fault("bcachefs:meta:write:" name)

#ifdef __KERNEL__
#define BCACHEFS_LOG_PREFIX
#endif

#ifdef BCACHEFS_LOG_PREFIX

#define bch2_log_msg(_c, fmt)                   "bcachefs (%s): " fmt, ((_c)->name)
#define bch2_fmt_dev(_ca, fmt)                  "bcachefs (%s): " fmt "\n", ((_ca)->name)
#define bch2_fmt_dev_offset(_ca, _offset, fmt)  "bcachefs (%s sector %llu): " fmt "\n", ((_ca)->name), (_offset)
#define bch2_fmt_inum(_c, _inum, fmt)           "bcachefs (%s inum %llu): " fmt "\n", ((_c)->name), (_inum)
#define bch2_fmt_inum_offset(_c, _inum, _offset, fmt)                   \
         "bcachefs (%s inum %llu offset %llu): " fmt "\n", ((_c)->name), (_inum), (_offset)

#else

#define bch2_log_msg(_c, fmt)                   fmt
#define bch2_fmt_dev(_ca, fmt)                  "%s: " fmt "\n", ((_ca)->name)
#define bch2_fmt_dev_offset(_ca, _offset, fmt)  "%s sector %llu: " fmt "\n", ((_ca)->name), (_offset)
#define bch2_fmt_inum(_c, _inum, fmt)           "inum %llu: " fmt "\n", (_inum)
#define bch2_fmt_inum_offset(_c, _inum, _offset, fmt)                           \
         "inum %llu offset %llu: " fmt "\n", (_inum), (_offset)

#endif

#define bch2_fmt(_c, fmt)               bch2_log_msg(_c, fmt "\n")

#define bch_info(c, fmt, ...) \
        printk(KERN_INFO bch2_fmt(c, fmt), ##__VA_ARGS__)
#define bch_notice(c, fmt, ...) \
        printk(KERN_NOTICE bch2_fmt(c, fmt), ##__VA_ARGS__)
#define bch_warn(c, fmt, ...) \
        printk(KERN_WARNING bch2_fmt(c, fmt), ##__VA_ARGS__)
#define bch_warn_ratelimited(c, fmt, ...) \
        printk_ratelimited(KERN_WARNING bch2_fmt(c, fmt), ##__VA_ARGS__)

#define bch_err(c, fmt, ...) \
        printk(KERN_ERR bch2_fmt(c, fmt), ##__VA_ARGS__)
#define bch_err_dev(ca, fmt, ...) \
        printk(KERN_ERR bch2_fmt_dev(ca, fmt), ##__VA_ARGS__)
#define bch_err_dev_offset(ca, _offset, fmt, ...) \
        printk(KERN_ERR bch2_fmt_dev_offset(ca, _offset, fmt), ##__VA_ARGS__)
#define bch_err_inum(c, _inum, fmt, ...) \
        printk(KERN_ERR bch2_fmt_inum(c, _inum, fmt), ##__VA_ARGS__)
#define bch_err_inum_offset(c, _inum, _offset, fmt, ...) \
        printk(KERN_ERR bch2_fmt_inum_offset(c, _inum, _offset, fmt), ##__VA_ARGS__)

#define bch_err_ratelimited(c, fmt, ...) \
        printk_ratelimited(KERN_ERR bch2_fmt(c, fmt), ##__VA_ARGS__)
#define bch_err_dev_ratelimited(ca, fmt, ...) \
        printk_ratelimited(KERN_ERR bch2_fmt_dev(ca, fmt), ##__VA_ARGS__)
#define bch_err_dev_offset_ratelimited(ca, _offset, fmt, ...) \
        printk_ratelimited(KERN_ERR bch2_fmt_dev_offset(ca, _offset, fmt), ##__VA_ARGS__)
#define bch_err_inum_ratelimited(c, _inum, fmt, ...) \
        printk_ratelimited(KERN_ERR bch2_fmt_inum(c, _inum, fmt), ##__VA_ARGS__)
#define bch_err_inum_offset_ratelimited(c, _inum, _offset, fmt, ...) \
        printk_ratelimited(KERN_ERR bch2_fmt_inum_offset(c, _inum, _offset, fmt), ##__VA_ARGS__)

#define bch_verbose(c, fmt, ...)                                        \
do {                                                                    \
        if ((c)->opts.verbose)                                          \
                bch_info(c, fmt, ##__VA_ARGS__);                        \
} while (0)

#define pr_verbose_init(opts, fmt, ...)                                 \
do {                                                                    \
        if (opt_get(opts, verbose))                                     \
                pr_info(fmt, ##__VA_ARGS__);                            \
} while (0)

/* Parameters that are useful for debugging, but should always be compiled in: */
#define BCH_DEBUG_PARAMS_ALWAYS()                                       \
        BCH_DEBUG_PARAM(key_merging_disabled,                           \
                "Disables merging of extents")                          \
        BCH_DEBUG_PARAM(btree_gc_always_rewrite,                        \
                "Causes mark and sweep to compact and rewrite every "   \
                "btree node it traverses")                              \
        BCH_DEBUG_PARAM(btree_gc_rewrite_disabled,                      \
                "Disables rewriting of btree nodes during mark and sweep")\
        BCH_DEBUG_PARAM(btree_shrinker_disabled,                        \
                "Disables the shrinker callback for the btree node cache")\
        BCH_DEBUG_PARAM(verify_btree_ondisk,                            \
                "Reread btree nodes at various points to verify the "   \
                "mergesort in the read path against modifications "     \
                "done in memory")                                       \
        BCH_DEBUG_PARAM(verify_all_btree_replicas,                      \
                "When reading btree nodes, read all replicas and "      \
                "compare them")

/* Parameters that should only be compiled in debug mode: */
#define BCH_DEBUG_PARAMS_DEBUG()                                        \
        BCH_DEBUG_PARAM(expensive_debug_checks,                         \
                "Enables various runtime debugging checks that "        \
                "significantly affect performance")                     \
        BCH_DEBUG_PARAM(debug_check_iterators,                          \
                "Enables extra verification for btree iterators")       \
        BCH_DEBUG_PARAM(debug_check_btree_accounting,                   \
                "Verify btree accounting for keys within a node")       \
        BCH_DEBUG_PARAM(journal_seq_verify,                             \
                "Store the journal sequence number in the version "     \
                "number of every btree key, and verify that btree "     \
                "update ordering is preserved during recovery")         \
        BCH_DEBUG_PARAM(inject_invalid_keys,                            \
                "Store the journal sequence number in the version "     \
                "number of every btree key, and verify that btree "     \
                "update ordering is preserved during recovery")         \
        BCH_DEBUG_PARAM(test_alloc_startup,                             \
                "Force allocator startup to use the slowpath where it"  \
                "can't find enough free buckets without invalidating"   \
                "cached data")                                          \
        BCH_DEBUG_PARAM(force_reconstruct_read,                         \
                "Force reads to use the reconstruct path, when reading" \
                "from erasure coded extents")                           \
        BCH_DEBUG_PARAM(test_restart_gc,                                \
                "Test restarting mark and sweep gc when bucket gens change")

#define BCH_DEBUG_PARAMS_ALL() BCH_DEBUG_PARAMS_ALWAYS() BCH_DEBUG_PARAMS_DEBUG()

#ifdef CONFIG_BCACHEFS_DEBUG
#define BCH_DEBUG_PARAMS() BCH_DEBUG_PARAMS_ALL()
#else
#define BCH_DEBUG_PARAMS() BCH_DEBUG_PARAMS_ALWAYS()
#endif

#define BCH_DEBUG_PARAM(name, description) extern bool bch2_##name;
BCH_DEBUG_PARAMS()
#undef BCH_DEBUG_PARAM

#ifndef CONFIG_BCACHEFS_DEBUG
#define BCH_DEBUG_PARAM(name, description) static const bool bch2_##name;
BCH_DEBUG_PARAMS_DEBUG()
#undef BCH_DEBUG_PARAM
#endif

#define BCH_TIME_STATS()                        \
        x(btree_node_mem_alloc)                 \
        x(btree_node_split)                     \
        x(btree_node_compact)                   \
        x(btree_node_merge)                     \
        x(btree_node_sort)                      \
        x(btree_node_read)                      \
        x(btree_interior_update_foreground)     \
        x(btree_interior_update_total)          \
        x(btree_gc)                             \
        x(data_write)                           \
        x(data_read)                            \
        x(data_promote)                         \
        x(journal_flush_write)                  \
        x(journal_noflush_write)                \
        x(journal_flush_seq)                    \
        x(blocked_journal)                      \
        x(blocked_allocate)                     \
        x(blocked_allocate_open_bucket)         \
        x(nocow_lock_contended)

enum bch_time_stats {
#define x(name) BCH_TIME_##name,
        BCH_TIME_STATS()
#undef x
        BCH_TIME_STAT_NR
};

#include "alloc_types.h"
#include "btree_types.h"
#include "buckets_types.h"
#include "buckets_waiting_for_journal_types.h"
#include "clock_types.h"
#include "ec_types.h"
#include "journal_types.h"
#include "keylist_types.h"
#include "quota_types.h"
#include "rebalance_types.h"
#include "replicas_types.h"
#include "subvolume_types.h"
#include "super_types.h"

/* Number of nodes btree coalesce will try to coalesce at once */
#define GC_MERGE_NODES          4U

/* Maximum number of nodes we might need to allocate atomically: */
#define BTREE_RESERVE_MAX       (BTREE_MAX_DEPTH + (BTREE_MAX_DEPTH - 1))

/* Size of the freelist we allocate btree nodes from: */
#define BTREE_NODE_RESERVE      (BTREE_RESERVE_MAX * 4)

#define BTREE_NODE_OPEN_BUCKET_RESERVE  (BTREE_RESERVE_MAX * BCH_REPLICAS_MAX)

struct btree;

enum gc_phase {
        GC_PHASE_NOT_RUNNING,
        GC_PHASE_START,
        GC_PHASE_SB,

        GC_PHASE_BTREE_stripes,
        GC_PHASE_BTREE_extents,
        GC_PHASE_BTREE_inodes,
        GC_PHASE_BTREE_dirents,
        GC_PHASE_BTREE_xattrs,
        GC_PHASE_BTREE_alloc,
        GC_PHASE_BTREE_quotas,
        GC_PHASE_BTREE_reflink,
        GC_PHASE_BTREE_subvolumes,
        GC_PHASE_BTREE_snapshots,
        GC_PHASE_BTREE_lru,
        GC_PHASE_BTREE_freespace,
        GC_PHASE_BTREE_need_discard,
        GC_PHASE_BTREE_backpointers,
        GC_PHASE_BTREE_bucket_gens,

        GC_PHASE_PENDING_DELETE,
};

struct gc_pos {
        enum gc_phase           phase;
        struct bpos             pos;
        unsigned                level;
};

struct reflink_gc {
        u64             offset;
        u32             size;
        u32             refcount;
};

typedef GENRADIX(struct reflink_gc) reflink_gc_table;

struct io_count {
        u64                     sectors[2][BCH_DATA_NR];
};

struct bch_dev {
        struct kobject          kobj;
        struct percpu_ref       ref;
        struct completion       ref_completion;
        struct percpu_ref       io_ref;
        struct completion       io_ref_completion;

        struct bch_fs           *fs;

        u8                      dev_idx;
        /*
         * Cached version of this device's member info from superblock
         * Committed by bch2_write_super() -> bch_fs_mi_update()
         */
        struct bch_member_cpu   mi;
        uuid_le                 uuid;
        char                    name[BDEVNAME_SIZE];

        struct bch_sb_handle    disk_sb;
        struct bch_sb           *sb_read_scratch;
        int                     sb_write_error;
        dev_t                   dev;
        atomic_t                flush_seq;

        struct bch_devs_mask    self;

        /* biosets used in cloned bios for writing multiple replicas */
        struct bio_set          replica_set;

        /*
         * Buckets:
         * Per-bucket arrays are protected by c->mark_lock, bucket_lock and
         * gc_lock, for device resize - holding any is sufficient for access:
         * Or rcu_read_lock(), but only for ptr_stale():
         */
        struct bucket_array __rcu *buckets_gc;
        struct bucket_gens __rcu *bucket_gens;
        u8                      *oldest_gen;
        unsigned long           *buckets_nouse;
        struct rw_semaphore     bucket_lock;

        struct bch_dev_usage            *usage_base;
        struct bch_dev_usage __percpu   *usage[JOURNAL_BUF_NR];
        struct bch_dev_usage __percpu   *usage_gc;

        /* Allocator: */
        u64                     new_fs_bucket_idx;
        u64                     bucket_alloc_trans_early_cursor;

        unsigned                nr_open_buckets;
        unsigned                nr_btree_reserve;

        open_bucket_idx_t       open_buckets_partial[OPEN_BUCKETS_COUNT];
        open_bucket_idx_t       open_buckets_partial_nr;

        size_t                  inc_gen_needs_gc;
        size_t                  inc_gen_really_needs_gc;
        size_t                  buckets_waiting_on_journal;

        atomic64_t              rebalance_work;

        struct journal_device   journal;
        u64                     prev_journal_sector;

        struct work_struct      io_error_work;

        /* The rest of this all shows up in sysfs */
        atomic64_t              cur_latency[2];
        struct time_stats       io_latency[2];

#define CONGESTED_MAX           1024
        atomic_t                congested;
        u64                     congested_last;

        struct io_count __percpu *io_done;
};

enum {
        /* startup: */
        BCH_FS_STARTED,
        BCH_FS_MAY_GO_RW,
        BCH_FS_RW,
        BCH_FS_WAS_RW,

        /* shutdown: */
        BCH_FS_STOPPING,
        BCH_FS_EMERGENCY_RO,
        BCH_FS_WRITE_DISABLE_COMPLETE,
        BCH_FS_CLEAN_SHUTDOWN,

        /* fsck passes: */
        BCH_FS_TOPOLOGY_REPAIR_DONE,
        BCH_FS_INITIAL_GC_DONE,         /* kill when we enumerate fsck passes */
        BCH_FS_CHECK_LRUS_DONE,
        BCH_FS_CHECK_BACKPOINTERS_DONE,
        BCH_FS_CHECK_ALLOC_TO_LRU_REFS_DONE,
        BCH_FS_FSCK_DONE,
        BCH_FS_INITIAL_GC_UNFIXED,      /* kill when we enumerate fsck errors */
        BCH_FS_NEED_ANOTHER_GC,

        BCH_FS_HAVE_DELETED_SNAPSHOTS,

        /* errors: */
        BCH_FS_ERROR,
        BCH_FS_TOPOLOGY_ERROR,
        BCH_FS_ERRORS_FIXED,
        BCH_FS_ERRORS_NOT_FIXED,
};

struct btree_debug {
        unsigned                id;
};

#define BCH_TRANSACTIONS_NR 128

struct btree_transaction_stats {
        struct mutex            lock;
        struct time_stats       lock_hold_times;
        unsigned                nr_max_paths;
        unsigned                max_mem;
        char                    *max_paths_text;
};

struct bch_fs_pcpu {
        u64                     sectors_available;
};

struct journal_seq_blacklist_table {
        size_t                  nr;
        struct journal_seq_blacklist_table_entry {
                u64             start;
                u64             end;
                bool            dirty;
        }                       entries[0];
};

struct journal_keys {
        struct journal_key {
                u64             journal_seq;
                u32             journal_offset;
                enum btree_id   btree_id:8;
                unsigned        level:8;
                bool            allocated;
                bool            overwritten;
                struct bkey_i   *k;
        }                       *d;
        /*
         * Gap buffer: instead of all the empty space in the array being at the
         * end of the buffer - from @nr to @size - the empty space is at @gap.
         * This means that sequential insertions are O(n) instead of O(n^2).
         */
        size_t                  gap;
        size_t                  nr;
        size_t                  size;
};

struct btree_path_buf {
        struct btree_path       *path;
};

#define REPLICAS_DELTA_LIST_MAX (1U << 16)

struct snapshot_t {
        u32                     parent;
        u32                     children[2];
        u32                     subvol; /* Nonzero only if a subvolume points to this node: */
        u32                     equiv;
};

typedef struct {
        u32             subvol;
        u64             inum;
} subvol_inum;

#define BCACHEFS_ROOT_SUBVOL_INUM                                       \
        ((subvol_inum) { BCACHEFS_ROOT_SUBVOL,  BCACHEFS_ROOT_INO })

struct bch_fs {
        struct closure          cl;

        struct list_head        list;
        struct kobject          kobj;
        struct kobject          counters_kobj;
        struct kobject          internal;
        struct kobject          opts_dir;
        struct kobject          time_stats;
        unsigned long           flags;

        int                     minor;
        struct device           *chardev;
        struct super_block      *vfs_sb;
        dev_t                   dev;
        char                    name[40];

        /* ro/rw, add/remove/resize devices: */
        struct rw_semaphore     state_lock;

        /* Counts outstanding writes, for clean transition to read-only */
        struct percpu_ref       writes;
        struct work_struct      read_only_work;

        struct bch_dev __rcu    *devs[BCH_SB_MEMBERS_MAX];

        struct bch_replicas_cpu replicas;
        struct bch_replicas_cpu replicas_gc;
        struct mutex            replicas_gc_lock;
        mempool_t               replicas_delta_pool;

        struct journal_entry_res btree_root_journal_res;
        struct journal_entry_res replicas_journal_res;
        struct journal_entry_res clock_journal_res;
        struct journal_entry_res dev_usage_journal_res;

        struct bch_disk_groups_cpu __rcu *disk_groups;

        struct bch_opts         opts;

        /* Updated by bch2_sb_update():*/
        struct {
                uuid_le         uuid;
                uuid_le         user_uuid;

                u16             version;
                u16             version_min;

                u8              nr_devices;
                u8              clean;

                u8              encryption_type;

                u64             time_base_lo;
                u32             time_base_hi;
                unsigned        time_units_per_sec;
                unsigned        nsec_per_time_unit;
                u64             features;
                u64             compat;
        }                       sb;


        struct bch_sb_handle    disk_sb;

        unsigned short          block_bits;     /* ilog2(block_size) */

        u16                     btree_foreground_merge_threshold;

        struct closure          sb_write;
        struct mutex            sb_lock;

        /* snapshot.c: */
        GENRADIX(struct snapshot_t) snapshots;
        struct bch_snapshot_table __rcu *snapshot_table;
        struct mutex            snapshot_table_lock;
        struct work_struct      snapshot_delete_work;
        struct work_struct      snapshot_wait_for_pagecache_and_delete_work;
        snapshot_id_list        snapshots_unlinked;
        struct mutex            snapshots_unlinked_lock;

        /* BTREE CACHE */
        struct bio_set          btree_bio;
        struct workqueue_struct *io_complete_wq;

        struct btree_root       btree_roots[BTREE_ID_NR];
        struct mutex            btree_root_lock;

        struct btree_cache      btree_cache;

        /*
         * Cache of allocated btree nodes - if we allocate a btree node and
         * don't use it, if we free it that space can't be reused until going
         * _all_ the way through the allocator (which exposes us to a livelock
         * when allocating btree reserves fail halfway through) - instead, we
         * can stick them here:
         */
        struct btree_alloc      btree_reserve_cache[BTREE_NODE_RESERVE * 2];
        unsigned                btree_reserve_cache_nr;
        struct mutex            btree_reserve_cache_lock;

        mempool_t               btree_interior_update_pool;
        struct list_head        btree_interior_update_list;
        struct list_head        btree_interior_updates_unwritten;
        struct mutex            btree_interior_update_lock;
        struct closure_waitlist btree_interior_update_wait;

        struct workqueue_struct *btree_interior_update_worker;
        struct work_struct      btree_interior_update_work;

        /* btree_io.c: */
        spinlock_t              btree_write_error_lock;
        struct btree_write_stats {
                atomic64_t      nr;
                atomic64_t      bytes;
        }                       btree_write_stats[BTREE_WRITE_TYPE_NR];

        /* btree_iter.c: */
        struct mutex            btree_trans_lock;
        struct list_head        btree_trans_list;
        mempool_t               btree_paths_pool;
        mempool_t               btree_trans_mem_pool;
        struct btree_path_buf  __percpu *btree_paths_bufs;

        struct srcu_struct      btree_trans_barrier;
        bool                    btree_trans_barrier_initialized;

        struct btree_key_cache  btree_key_cache;
        unsigned                btree_key_cache_btrees;

        struct workqueue_struct *btree_update_wq;
        struct workqueue_struct *btree_io_complete_wq;
        /* copygc needs its own workqueue for index updates.. */
        struct workqueue_struct *copygc_wq;

        /* ALLOCATION */
        struct bch_devs_mask    rw_devs[BCH_DATA_NR];

        u64                     capacity; /* sectors */

        /*
         * When capacity _decreases_ (due to a disk being removed), we
         * increment capacity_gen - this invalidates outstanding reservations
         * and forces them to be revalidated
         */
        u32                     capacity_gen;
        unsigned                bucket_size_max;

        atomic64_t              sectors_available;
        struct mutex            sectors_available_lock;

        struct bch_fs_pcpu __percpu     *pcpu;

        struct percpu_rw_semaphore      mark_lock;

        seqcount_t                      usage_lock;
        struct bch_fs_usage             *usage_base;
        struct bch_fs_usage __percpu    *usage[JOURNAL_BUF_NR];
        struct bch_fs_usage __percpu    *usage_gc;
        u64 __percpu            *online_reserved;

        /* single element mempool: */
        struct mutex            usage_scratch_lock;
        struct bch_fs_usage_online *usage_scratch;

        struct io_clock         io_clock[2];

        /* JOURNAL SEQ BLACKLIST */
        struct journal_seq_blacklist_table *
                                journal_seq_blacklist_table;
        struct work_struct      journal_seq_blacklist_gc_work;

        /* ALLOCATOR */
        spinlock_t              freelist_lock;
        struct closure_waitlist freelist_wait;
        u64                     blocked_allocate;
        u64                     blocked_allocate_open_bucket;

        open_bucket_idx_t       open_buckets_freelist;
        open_bucket_idx_t       open_buckets_nr_free;
        struct closure_waitlist open_buckets_wait;
        struct open_bucket      open_buckets[OPEN_BUCKETS_COUNT];
        open_bucket_idx_t       open_buckets_hash[OPEN_BUCKETS_COUNT];

        struct write_point      btree_write_point;
        struct write_point      rebalance_write_point;

        struct write_point      write_points[WRITE_POINT_MAX];
        struct hlist_head       write_points_hash[WRITE_POINT_HASH_NR];
        struct mutex            write_points_hash_lock;
        unsigned                write_points_nr;

        struct buckets_waiting_for_journal buckets_waiting_for_journal;
        struct work_struct      discard_work;
        struct work_struct      invalidate_work;

        /* GARBAGE COLLECTION */
        struct task_struct      *gc_thread;
        atomic_t                kick_gc;
        unsigned long           gc_count;

        enum btree_id           gc_gens_btree;
        struct bpos             gc_gens_pos;

        /*
         * Tracks GC's progress - everything in the range [ZERO_KEY..gc_cur_pos]
         * has been marked by GC.
         *
         * gc_cur_phase is a superset of btree_ids (BTREE_ID_extents etc.)
         *
         * Protected by gc_pos_lock. Only written to by GC thread, so GC thread
         * can read without a lock.
         */
        seqcount_t              gc_pos_lock;
        struct gc_pos           gc_pos;

        /*
         * The allocation code needs gc_mark in struct bucket to be correct, but
         * it's not while a gc is in progress.
         */
        struct rw_semaphore     gc_lock;
        struct mutex            gc_gens_lock;

        /* IO PATH */
        struct bio_set          bio_read;
        struct bio_set          bio_read_split;
        struct bio_set          bio_write;
        struct mutex            bio_bounce_pages_lock;
        mempool_t               bio_bounce_pages;
        struct bucket_nocow_lock_table
                                nocow_locks;
        struct rhashtable       promote_table;

        mempool_t               compression_bounce[2];
        mempool_t               compress_workspace[BCH_COMPRESSION_TYPE_NR];
        mempool_t               decompress_workspace;
        ZSTD_parameters         zstd_params;

        struct crypto_shash     *sha256;
        struct crypto_sync_skcipher *chacha20;
        struct crypto_shash     *poly1305;

        atomic64_t              key_version;

        mempool_t               large_bkey_pool;

        /* REBALANCE */
        struct bch_fs_rebalance rebalance;

        /* COPYGC */
        struct task_struct      *copygc_thread;
        copygc_heap             copygc_heap;
        struct write_point      copygc_write_point;
        s64                     copygc_wait;
        bool                    copygc_running;
        wait_queue_head_t       copygc_running_wq;

        /* DATA PROGRESS STATS */
        struct list_head        data_progress_list;
        struct mutex            data_progress_lock;

        /* STRIPES: */
        GENRADIX(struct stripe) stripes;
        GENRADIX(struct gc_stripe) gc_stripes;

        ec_stripes_heap         ec_stripes_heap;
        spinlock_t              ec_stripes_heap_lock;

        /* ERASURE CODING */
        struct list_head        ec_stripe_head_list;
        struct mutex            ec_stripe_head_lock;

        struct list_head        ec_stripe_new_list;
        struct mutex            ec_stripe_new_lock;

        struct work_struct      ec_stripe_create_work;
        u64                     ec_stripe_hint;

        struct bio_set          ec_bioset;

        struct work_struct      ec_stripe_delete_work;
        struct llist_head       ec_stripe_delete_list;

        /* REFLINK */
        u64                     reflink_hint;
        reflink_gc_table        reflink_gc_table;
        size_t                  reflink_gc_nr;

        /* VFS IO PATH - fs-io.c */
        struct bio_set          writepage_bioset;
        struct bio_set          dio_write_bioset;
        struct bio_set          dio_read_bioset;
        struct bio_set          nocow_flush_bioset;

        /* ERRORS */
        struct list_head        fsck_errors;
        struct mutex            fsck_error_lock;
        bool                    fsck_alloc_err;

        /* QUOTAS */
        struct bch_memquota_type quotas[QTYP_NR];

        /* DEBUG JUNK */
        struct dentry           *fs_debug_dir;
        struct dentry           *btree_debug_dir;
        struct btree_debug      btree_debug[BTREE_ID_NR];
        struct btree            *verify_data;
        struct btree_node       *verify_ondisk;
        struct mutex            verify_lock;

        u64                     *unused_inode_hints;
        unsigned                inode_shard_bits;

        /*
         * A btree node on disk could have too many bsets for an iterator to fit
         * on the stack - have to dynamically allocate them
         */
        mempool_t               fill_iter;

        mempool_t               btree_bounce_pool;

        struct journal          journal;
        GENRADIX(struct journal_replay *) journal_entries;
        u64                     journal_entries_base_seq;
        struct journal_keys     journal_keys;
        struct list_head        journal_iters;

        u64                     last_bucket_seq_cleanup;

        u64                     counters_on_mount[BCH_COUNTER_NR];
        u64 __percpu            *counters;

        unsigned                btree_gc_periodic:1;
        unsigned                copy_gc_enabled:1;
        bool                    promote_whole_extents;

        struct time_stats       times[BCH_TIME_STAT_NR];

        struct btree_transaction_stats btree_transaction_stats[BCH_TRANSACTIONS_NR];
};

static inline void bch2_set_ra_pages(struct bch_fs *c, unsigned ra_pages)
{
#ifndef NO_BCACHEFS_FS
        if (c->vfs_sb)
                c->vfs_sb->s_bdi->ra_pages = ra_pages;
#endif
}

static inline unsigned bucket_bytes(const struct bch_dev *ca)
{
        return ca->mi.bucket_size << 9;
}

static inline unsigned block_bytes(const struct bch_fs *c)
{
        return c->opts.block_size;
}

static inline unsigned block_sectors(const struct bch_fs *c)
{
        return c->opts.block_size >> 9;
}

static inline size_t btree_sectors(const struct bch_fs *c)
{
        return c->opts.btree_node_size >> 9;
}

static inline bool btree_id_cached(const struct bch_fs *c, enum btree_id btree)
{
        return c->btree_key_cache_btrees & (1U << btree);
}

static inline struct timespec64 bch2_time_to_timespec(const struct bch_fs *c, s64 time)
{
        struct timespec64 t;
        s32 rem;

        time += c->sb.time_base_lo;

        t.tv_sec = div_s64_rem(time, c->sb.time_units_per_sec, &rem);
        t.tv_nsec = rem * c->sb.nsec_per_time_unit;
        return t;
}

static inline s64 timespec_to_bch2_time(const struct bch_fs *c, struct timespec64 ts)
{
        return (ts.tv_sec * c->sb.time_units_per_sec +
                (int) ts.tv_nsec / c->sb.nsec_per_time_unit) - c->sb.time_base_lo;
}

static inline s64 bch2_current_time(const struct bch_fs *c)
{
        struct timespec64 now;

        ktime_get_coarse_real_ts64(&now);
        return timespec_to_bch2_time(c, now);
}

static inline bool bch2_dev_exists2(const struct bch_fs *c, unsigned dev)
{
        return dev < c->sb.nr_devices && c->devs[dev];
}

#endif /* _BCACHEFS_H */