Merge branch 'jc/test-modernization'

[alt-git.git] / commit-graph.c

#include "git-compat-util.h"
#include "config.h"
#include "gettext.h"
#include "hex.h"
#include "lockfile.h"
#include "pack.h"
#include "packfile.h"
#include "commit.h"
#include "object.h"
#include "refs.h"
#include "revision.h"
#include "hash-lookup.h"
#include "commit-graph.h"
#include "object-file.h"
#include "object-store.h"
#include "oid-array.h"
#include "alloc.h"
#include "hashmap.h"
#include "replace-object.h"
#include "progress.h"
#include "bloom.h"
#include "commit-slab.h"
#include "shallow.h"
#include "json-writer.h"
#include "trace2.h"
#include "tree.h"
#include "chunk-format.h"
#include "wrapper.h"

void git_test_write_commit_graph_or_die(void)
{
        int flags = 0;
        if (!git_env_bool(GIT_TEST_COMMIT_GRAPH, 0))
                return;

        if (git_env_bool(GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS, 0))
                flags = COMMIT_GRAPH_WRITE_BLOOM_FILTERS;

        if (write_commit_graph_reachable(the_repository->objects->odb,
                                         flags, NULL))
                die("failed to write commit-graph under GIT_TEST_COMMIT_GRAPH");
}

#define GRAPH_SIGNATURE 0x43475048 /* "CGPH" */
#define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
#define GRAPH_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
#define GRAPH_CHUNKID_DATA 0x43444154 /* "CDAT" */
#define GRAPH_CHUNKID_GENERATION_DATA 0x47444132 /* "GDA2" */
#define GRAPH_CHUNKID_GENERATION_DATA_OVERFLOW 0x47444f32 /* "GDO2" */
#define GRAPH_CHUNKID_EXTRAEDGES 0x45444745 /* "EDGE" */
#define GRAPH_CHUNKID_BLOOMINDEXES 0x42494458 /* "BIDX" */
#define GRAPH_CHUNKID_BLOOMDATA 0x42444154 /* "BDAT" */
#define GRAPH_CHUNKID_BASE 0x42415345 /* "BASE" */

#define GRAPH_DATA_WIDTH (the_hash_algo->rawsz + 16)

#define GRAPH_VERSION_1 0x1
#define GRAPH_VERSION GRAPH_VERSION_1

#define GRAPH_EXTRA_EDGES_NEEDED 0x80000000
#define GRAPH_EDGE_LAST_MASK 0x7fffffff
#define GRAPH_PARENT_NONE 0x70000000

#define GRAPH_LAST_EDGE 0x80000000

#define GRAPH_HEADER_SIZE 8
#define GRAPH_FANOUT_SIZE (4 * 256)
#define GRAPH_MIN_SIZE (GRAPH_HEADER_SIZE + 4 * CHUNK_TOC_ENTRY_SIZE \
                        + GRAPH_FANOUT_SIZE + the_hash_algo->rawsz)

#define CORRECTED_COMMIT_DATE_OFFSET_OVERFLOW (1ULL << 31)

/* Remember to update object flag allocation in object.h */
#define REACHABLE       (1u<<15)

define_commit_slab(topo_level_slab, uint32_t);

/* Keep track of the order in which commits are added to our list. */
define_commit_slab(commit_pos, int);
static struct commit_pos commit_pos = COMMIT_SLAB_INIT(1, commit_pos);

static void set_commit_pos(struct repository *r, const struct object_id *oid)
{
        static int32_t max_pos;
        struct commit *commit = lookup_commit(r, oid);

        if (!commit)
                return; /* should never happen, but be lenient */

        *commit_pos_at(&commit_pos, commit) = max_pos++;
}

static int commit_pos_cmp(const void *va, const void *vb)
{
        const struct commit *a = *(const struct commit **)va;
        const struct commit *b = *(const struct commit **)vb;
        return commit_pos_at(&commit_pos, a) -
               commit_pos_at(&commit_pos, b);
}

define_commit_slab(commit_graph_data_slab, struct commit_graph_data);
static struct commit_graph_data_slab commit_graph_data_slab =
        COMMIT_SLAB_INIT(1, commit_graph_data_slab);

static int get_configured_generation_version(struct repository *r)
{
        int version = 2;
        repo_config_get_int(r, "commitgraph.generationversion", &version);
        return version;
}

uint32_t commit_graph_position(const struct commit *c)
{
        struct commit_graph_data *data =
                commit_graph_data_slab_peek(&commit_graph_data_slab, c);

        return data ? data->graph_pos : COMMIT_NOT_FROM_GRAPH;
}

timestamp_t commit_graph_generation(const struct commit *c)
{
        struct commit_graph_data *data =
                commit_graph_data_slab_peek(&commit_graph_data_slab, c);

        if (data && data->generation)
                return data->generation;

        return GENERATION_NUMBER_INFINITY;
}

static struct commit_graph_data *commit_graph_data_at(const struct commit *c)
{
        unsigned int i, nth_slab;
        struct commit_graph_data *data =
                commit_graph_data_slab_peek(&commit_graph_data_slab, c);

        if (data)
                return data;

        nth_slab = c->index / commit_graph_data_slab.slab_size;
        data = commit_graph_data_slab_at(&commit_graph_data_slab, c);

        /*
         * commit-slab initializes elements with zero, overwrite this with
         * COMMIT_NOT_FROM_GRAPH for graph_pos.
         *
         * We avoid initializing generation with checking if graph position
         * is not COMMIT_NOT_FROM_GRAPH.
         */
        for (i = 0; i < commit_graph_data_slab.slab_size; i++) {
                commit_graph_data_slab.slab[nth_slab][i].graph_pos =
                        COMMIT_NOT_FROM_GRAPH;
        }

        return data;
}

/*
 * Should be used only while writing commit-graph as it compares
 * generation value of commits by directly accessing commit-slab.
 */
static int commit_gen_cmp(const void *va, const void *vb)
{
        const struct commit *a = *(const struct commit **)va;
        const struct commit *b = *(const struct commit **)vb;

        const timestamp_t generation_a = commit_graph_data_at(a)->generation;
        const timestamp_t generation_b = commit_graph_data_at(b)->generation;
        /* lower generation commits first */
        if (generation_a < generation_b)
                return -1;
        else if (generation_a > generation_b)
                return 1;

        /* use date as a heuristic when generations are equal */
        if (a->date < b->date)
                return -1;
        else if (a->date > b->date)
                return 1;
        return 0;
}

char *get_commit_graph_filename(struct object_directory *obj_dir)
{
        return xstrfmt("%s/info/commit-graph", obj_dir->path);
}

static char *get_split_graph_filename(struct object_directory *odb,
                                      const char *oid_hex)
{
        return xstrfmt("%s/info/commit-graphs/graph-%s.graph", odb->path,
                       oid_hex);
}

char *get_commit_graph_chain_filename(struct object_directory *odb)
{
        return xstrfmt("%s/info/commit-graphs/commit-graph-chain", odb->path);
}

static struct commit_graph *alloc_commit_graph(void)
{
        struct commit_graph *g = xcalloc(1, sizeof(*g));

        return g;
}

extern int read_replace_refs;

static int commit_graph_compatible(struct repository *r)
{
        if (!r->gitdir)
                return 0;

        if (read_replace_refs) {
                prepare_replace_object(r);
                if (hashmap_get_size(&r->objects->replace_map->map))
                        return 0;
        }

        prepare_commit_graft(r);
        if (r->parsed_objects &&
            (r->parsed_objects->grafts_nr || r->parsed_objects->substituted_parent))
                return 0;
        if (is_repository_shallow(r))
                return 0;

        return 1;
}

int open_commit_graph(const char *graph_file, int *fd, struct stat *st)
{
        *fd = git_open(graph_file);
        if (*fd < 0)
                return 0;
        if (fstat(*fd, st)) {
                close(*fd);
                return 0;
        }
        return 1;
}

struct commit_graph *load_commit_graph_one_fd_st(struct repository *r,
                                                 int fd, struct stat *st,
                                                 struct object_directory *odb)
{
        void *graph_map;
        size_t graph_size;
        struct commit_graph *ret;

        graph_size = xsize_t(st->st_size);

        if (graph_size < GRAPH_MIN_SIZE) {
                close(fd);
                error(_("commit-graph file is too small"));
                return NULL;
        }
        graph_map = xmmap(NULL, graph_size, PROT_READ, MAP_PRIVATE, fd, 0);
        close(fd);
        prepare_repo_settings(r);
        ret = parse_commit_graph(&r->settings, graph_map, graph_size);

        if (ret)
                ret->odb = odb;
        else
                munmap(graph_map, graph_size);

        return ret;
}

static int verify_commit_graph_lite(struct commit_graph *g)
{
        /*
         * Basic validation shared between parse_commit_graph()
         * which'll be called every time the graph is used, and the
         * much more expensive verify_commit_graph() used by
         * "commit-graph verify".
         *
         * There should only be very basic checks here to ensure that
         * we don't e.g. segfault in fill_commit_in_graph(), but
         * because this is a very hot codepath nothing that e.g. loops
         * over g->num_commits, or runs a checksum on the commit-graph
         * itself.
         */
        if (!g->chunk_oid_fanout) {
                error("commit-graph is missing the OID Fanout chunk");
                return 1;
        }
        if (!g->chunk_oid_lookup) {
                error("commit-graph is missing the OID Lookup chunk");
                return 1;
        }
        if (!g->chunk_commit_data) {
                error("commit-graph is missing the Commit Data chunk");
                return 1;
        }

        return 0;
}

static int graph_read_oid_lookup(const unsigned char *chunk_start,
                                 size_t chunk_size, void *data)
{
        struct commit_graph *g = data;
        g->chunk_oid_lookup = chunk_start;
        g->num_commits = chunk_size / g->hash_len;
        return 0;
}

static int graph_read_bloom_data(const unsigned char *chunk_start,
                                  size_t chunk_size, void *data)
{
        struct commit_graph *g = data;
        uint32_t hash_version;
        g->chunk_bloom_data = chunk_start;
        hash_version = get_be32(chunk_start);

        if (hash_version != 1)
                return 0;

        g->bloom_filter_settings = xmalloc(sizeof(struct bloom_filter_settings));
        g->bloom_filter_settings->hash_version = hash_version;
        g->bloom_filter_settings->num_hashes = get_be32(chunk_start + 4);
        g->bloom_filter_settings->bits_per_entry = get_be32(chunk_start + 8);
        g->bloom_filter_settings->max_changed_paths = DEFAULT_BLOOM_MAX_CHANGES;

        return 0;
}

struct commit_graph *parse_commit_graph(struct repo_settings *s,
                                        void *graph_map, size_t graph_size)
{
        const unsigned char *data;
        struct commit_graph *graph;
        uint32_t graph_signature;
        unsigned char graph_version, hash_version;
        struct chunkfile *cf = NULL;

        if (!graph_map)
                return NULL;

        if (graph_size < GRAPH_MIN_SIZE)
                return NULL;

        data = (const unsigned char *)graph_map;

        graph_signature = get_be32(data);
        if (graph_signature != GRAPH_SIGNATURE) {
                error(_("commit-graph signature %X does not match signature %X"),
                      graph_signature, GRAPH_SIGNATURE);
                return NULL;
        }

        graph_version = *(unsigned char*)(data + 4);
        if (graph_version != GRAPH_VERSION) {
                error(_("commit-graph version %X does not match version %X"),
                      graph_version, GRAPH_VERSION);
                return NULL;
        }

        hash_version = *(unsigned char*)(data + 5);
        if (hash_version != oid_version(the_hash_algo)) {
                error(_("commit-graph hash version %X does not match version %X"),
                      hash_version, oid_version(the_hash_algo));
                return NULL;
        }

        graph = alloc_commit_graph();

        graph->hash_len = the_hash_algo->rawsz;
        graph->num_chunks = *(unsigned char*)(data + 6);
        graph->data = graph_map;
        graph->data_len = graph_size;

        if (graph_size < GRAPH_HEADER_SIZE +
                         (graph->num_chunks + 1) * CHUNK_TOC_ENTRY_SIZE +
                         GRAPH_FANOUT_SIZE + the_hash_algo->rawsz) {
                error(_("commit-graph file is too small to hold %u chunks"),
                      graph->num_chunks);
                free(graph);
                return NULL;
        }

        cf = init_chunkfile(NULL);

        if (read_table_of_contents(cf, graph->data, graph_size,
                                   GRAPH_HEADER_SIZE, graph->num_chunks))
                goto free_and_return;

        pair_chunk(cf, GRAPH_CHUNKID_OIDFANOUT,
                   (const unsigned char **)&graph->chunk_oid_fanout);
        read_chunk(cf, GRAPH_CHUNKID_OIDLOOKUP, graph_read_oid_lookup, graph);
        pair_chunk(cf, GRAPH_CHUNKID_DATA, &graph->chunk_commit_data);
        pair_chunk(cf, GRAPH_CHUNKID_EXTRAEDGES, &graph->chunk_extra_edges);
        pair_chunk(cf, GRAPH_CHUNKID_BASE, &graph->chunk_base_graphs);

        if (s->commit_graph_generation_version >= 2) {
                pair_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA,
                        &graph->chunk_generation_data);
                pair_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA_OVERFLOW,
                        &graph->chunk_generation_data_overflow);

                if (graph->chunk_generation_data)
                        graph->read_generation_data = 1;
        }

        if (s->commit_graph_read_changed_paths) {
                pair_chunk(cf, GRAPH_CHUNKID_BLOOMINDEXES,
                           &graph->chunk_bloom_indexes);
                read_chunk(cf, GRAPH_CHUNKID_BLOOMDATA,
                           graph_read_bloom_data, graph);
        }

        if (graph->chunk_bloom_indexes && graph->chunk_bloom_data) {
                init_bloom_filters();
        } else {
                /* We need both the bloom chunks to exist together. Else ignore the data */
                graph->chunk_bloom_indexes = NULL;
                graph->chunk_bloom_data = NULL;
                FREE_AND_NULL(graph->bloom_filter_settings);
        }

        oidread(&graph->oid, graph->data + graph->data_len - graph->hash_len);

        if (verify_commit_graph_lite(graph))
                goto free_and_return;

        free_chunkfile(cf);
        return graph;

free_and_return:
        free_chunkfile(cf);
        free(graph->bloom_filter_settings);
        free(graph);
        return NULL;
}

static struct commit_graph *load_commit_graph_one(struct repository *r,
                                                  const char *graph_file,
                                                  struct object_directory *odb)
{

        struct stat st;
        int fd;
        struct commit_graph *g;
        int open_ok = open_commit_graph(graph_file, &fd, &st);

        if (!open_ok)
                return NULL;

        g = load_commit_graph_one_fd_st(r, fd, &st, odb);

        if (g)
                g->filename = xstrdup(graph_file);

        return g;
}

static struct commit_graph *load_commit_graph_v1(struct repository *r,
                                                 struct object_directory *odb)
{
        char *graph_name = get_commit_graph_filename(odb);
        struct commit_graph *g = load_commit_graph_one(r, graph_name, odb);
        free(graph_name);

        return g;
}

static int add_graph_to_chain(struct commit_graph *g,
                              struct commit_graph *chain,
                              struct object_id *oids,
                              int n)
{
        struct commit_graph *cur_g = chain;

        if (n && !g->chunk_base_graphs) {
                warning(_("commit-graph has no base graphs chunk"));
                return 0;
        }

        while (n) {
                n--;

                if (!cur_g ||
                    !oideq(&oids[n], &cur_g->oid) ||
                    !hasheq(oids[n].hash, g->chunk_base_graphs + g->hash_len * n)) {
                        warning(_("commit-graph chain does not match"));
                        return 0;
                }

                cur_g = cur_g->base_graph;
        }

        g->base_graph = chain;

        if (chain)
                g->num_commits_in_base = chain->num_commits + chain->num_commits_in_base;

        return 1;
}

static struct commit_graph *load_commit_graph_chain(struct repository *r,
                                                    struct object_directory *odb)
{
        struct commit_graph *graph_chain = NULL;
        struct strbuf line = STRBUF_INIT;
        struct stat st;
        struct object_id *oids;
        int i = 0, valid = 1, count;
        char *chain_name = get_commit_graph_chain_filename(odb);
        FILE *fp;
        int stat_res;

        fp = fopen(chain_name, "r");
        stat_res = stat(chain_name, &st);
        free(chain_name);

        if (!fp)
                return NULL;
        if (stat_res ||
            st.st_size <= the_hash_algo->hexsz) {
                fclose(fp);
                return NULL;
        }

        count = st.st_size / (the_hash_algo->hexsz + 1);
        CALLOC_ARRAY(oids, count);

        prepare_alt_odb(r);

        for (i = 0; i < count; i++) {
                struct object_directory *odb;

                if (strbuf_getline_lf(&line, fp) == EOF)
                        break;

                if (get_oid_hex(line.buf, &oids[i])) {
                        warning(_("invalid commit-graph chain: line '%s' not a hash"),
                                line.buf);
                        valid = 0;
                        break;
                }

                valid = 0;
                for (odb = r->objects->odb; odb; odb = odb->next) {
                        char *graph_name = get_split_graph_filename(odb, line.buf);
                        struct commit_graph *g = load_commit_graph_one(r, graph_name, odb);

                        free(graph_name);

                        if (g) {
                                if (add_graph_to_chain(g, graph_chain, oids, i)) {
                                        graph_chain = g;
                                        valid = 1;
                                }

                                break;
                        }
                }

                if (!valid) {
                        warning(_("unable to find all commit-graph files"));
                        break;
                }
        }

        free(oids);
        fclose(fp);
        strbuf_release(&line);

        return graph_chain;
}

/*
 * returns 1 if and only if all graphs in the chain have
 * corrected commit dates stored in the generation_data chunk.
 */
static int validate_mixed_generation_chain(struct commit_graph *g)
{
        int read_generation_data = 1;
        struct commit_graph *p = g;

        while (read_generation_data && p) {
                read_generation_data = p->read_generation_data;
                p = p->base_graph;
        }

        if (read_generation_data)
                return 1;

        while (g) {
                g->read_generation_data = 0;
                g = g->base_graph;
        }

        return 0;
}

struct commit_graph *read_commit_graph_one(struct repository *r,
                                           struct object_directory *odb)
{
        struct commit_graph *g = load_commit_graph_v1(r, odb);

        if (!g)
                g = load_commit_graph_chain(r, odb);

        validate_mixed_generation_chain(g);

        return g;
}

static void prepare_commit_graph_one(struct repository *r,
                                     struct object_directory *odb)
{

        if (r->objects->commit_graph)
                return;

        r->objects->commit_graph = read_commit_graph_one(r, odb);
}

/*
 * Return 1 if commit_graph is non-NULL, and 0 otherwise.
 *
 * On the first invocation, this function attempts to load the commit
 * graph if the_repository is configured to have one.
 */
static int prepare_commit_graph(struct repository *r)
{
        struct object_directory *odb;

        /*
         * Early return if there is no git dir or if the commit graph is
         * disabled.
         *
         * This must come before the "already attempted?" check below, because
         * we want to disable even an already-loaded graph file.
         */
        if (!r->gitdir || r->commit_graph_disabled)
                return 0;

        if (r->objects->commit_graph_attempted)
                return !!r->objects->commit_graph;
        r->objects->commit_graph_attempted = 1;

        prepare_repo_settings(r);

        if (!git_env_bool(GIT_TEST_COMMIT_GRAPH, 0) &&
            r->settings.core_commit_graph != 1)
                /*
                 * This repository is not configured to use commit graphs, so
                 * do not load one. (But report commit_graph_attempted anyway
                 * so that commit graph loading is not attempted again for this
                 * repository.)
                 */
                return 0;

        if (!commit_graph_compatible(r))
                return 0;

        prepare_alt_odb(r);
        for (odb = r->objects->odb;
             !r->objects->commit_graph && odb;
             odb = odb->next)
                prepare_commit_graph_one(r, odb);
        return !!r->objects->commit_graph;
}

int generation_numbers_enabled(struct repository *r)
{
        uint32_t first_generation;
        struct commit_graph *g;
        if (!prepare_commit_graph(r))
               return 0;

        g = r->objects->commit_graph;

        if (!g->num_commits)
                return 0;

        first_generation = get_be32(g->chunk_commit_data +
                                    g->hash_len + 8) >> 2;

        return !!first_generation;
}

int corrected_commit_dates_enabled(struct repository *r)
{
        struct commit_graph *g;
        if (!prepare_commit_graph(r))
                return 0;

        g = r->objects->commit_graph;

        if (!g->num_commits)
                return 0;

        return g->read_generation_data;
}

struct bloom_filter_settings *get_bloom_filter_settings(struct repository *r)
{
        struct commit_graph *g = r->objects->commit_graph;
        while (g) {
                if (g->bloom_filter_settings)
                        return g->bloom_filter_settings;
                g = g->base_graph;
        }
        return NULL;
}

static void close_commit_graph_one(struct commit_graph *g)
{
        if (!g)
                return;

        clear_commit_graph_data_slab(&commit_graph_data_slab);
        close_commit_graph_one(g->base_graph);
        free_commit_graph(g);
}

void close_commit_graph(struct raw_object_store *o)
{
        close_commit_graph_one(o->commit_graph);
        o->commit_graph = NULL;
}

static int bsearch_graph(struct commit_graph *g, const struct object_id *oid, uint32_t *pos)
{
        return bsearch_hash(oid->hash, g->chunk_oid_fanout,
                            g->chunk_oid_lookup, g->hash_len, pos);
}

static void load_oid_from_graph(struct commit_graph *g,
                                uint32_t pos,
                                struct object_id *oid)
{
        uint32_t lex_index;

        while (g && pos < g->num_commits_in_base)
                g = g->base_graph;

        if (!g)
                BUG("NULL commit-graph");

        if (pos >= g->num_commits + g->num_commits_in_base)
                die(_("invalid commit position. commit-graph is likely corrupt"));

        lex_index = pos - g->num_commits_in_base;

        oidread(oid, g->chunk_oid_lookup + g->hash_len * lex_index);
}

static struct commit_list **insert_parent_or_die(struct repository *r,
                                                 struct commit_graph *g,
                                                 uint32_t pos,
                                                 struct commit_list **pptr)
{
        struct commit *c;
        struct object_id oid;

        if (pos >= g->num_commits + g->num_commits_in_base)
                die("invalid parent position %"PRIu32, pos);

        load_oid_from_graph(g, pos, &oid);
        c = lookup_commit(r, &oid);
        if (!c)
                die(_("could not find commit %s"), oid_to_hex(&oid));
        commit_graph_data_at(c)->graph_pos = pos;
        return &commit_list_insert(c, pptr)->next;
}

static void fill_commit_graph_info(struct commit *item, struct commit_graph *g, uint32_t pos)
{
        const unsigned char *commit_data;
        struct commit_graph_data *graph_data;
        uint32_t lex_index, offset_pos;
        uint64_t date_high, date_low, offset;

        while (pos < g->num_commits_in_base)
                g = g->base_graph;

        if (pos >= g->num_commits + g->num_commits_in_base)
                die(_("invalid commit position. commit-graph is likely corrupt"));

        lex_index = pos - g->num_commits_in_base;
        commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * lex_index;

        graph_data = commit_graph_data_at(item);
        graph_data->graph_pos = pos;

        date_high = get_be32(commit_data + g->hash_len + 8) & 0x3;
        date_low = get_be32(commit_data + g->hash_len + 12);
        item->date = (timestamp_t)((date_high << 32) | date_low);

        if (g->read_generation_data) {
                offset = (timestamp_t)get_be32(g->chunk_generation_data + sizeof(uint32_t) * lex_index);

                if (offset & CORRECTED_COMMIT_DATE_OFFSET_OVERFLOW) {
                        if (!g->chunk_generation_data_overflow)
                                die(_("commit-graph requires overflow generation data but has none"));

                        offset_pos = offset ^ CORRECTED_COMMIT_DATE_OFFSET_OVERFLOW;
                        graph_data->generation = item->date + get_be64(g->chunk_generation_data_overflow + 8 * offset_pos);
                } else
                        graph_data->generation = item->date + offset;
        } else
                graph_data->generation = get_be32(commit_data + g->hash_len + 8) >> 2;

        if (g->topo_levels)
                *topo_level_slab_at(g->topo_levels, item) = get_be32(commit_data + g->hash_len + 8) >> 2;
}

static inline void set_commit_tree(struct commit *c, struct tree *t)
{
        c->maybe_tree = t;
}

static int fill_commit_in_graph(struct repository *r,
                                struct commit *item,
                                struct commit_graph *g, uint32_t pos)
{
        uint32_t edge_value;
        uint32_t *parent_data_ptr;
        struct commit_list **pptr;
        const unsigned char *commit_data;
        uint32_t lex_index;

        while (pos < g->num_commits_in_base)
                g = g->base_graph;

        fill_commit_graph_info(item, g, pos);

        lex_index = pos - g->num_commits_in_base;
        commit_data = g->chunk_commit_data + (g->hash_len + 16) * lex_index;

        item->object.parsed = 1;

        set_commit_tree(item, NULL);

        pptr = &item->parents;

        edge_value = get_be32(commit_data + g->hash_len);
        if (edge_value == GRAPH_PARENT_NONE)
                return 1;
        pptr = insert_parent_or_die(r, g, edge_value, pptr);

        edge_value = get_be32(commit_data + g->hash_len + 4);
        if (edge_value == GRAPH_PARENT_NONE)
                return 1;
        if (!(edge_value & GRAPH_EXTRA_EDGES_NEEDED)) {
                pptr = insert_parent_or_die(r, g, edge_value, pptr);
                return 1;
        }

        parent_data_ptr = (uint32_t*)(g->chunk_extra_edges +
                          4 * (uint64_t)(edge_value & GRAPH_EDGE_LAST_MASK));
        do {
                edge_value = get_be32(parent_data_ptr);
                pptr = insert_parent_or_die(r, g,
                                            edge_value & GRAPH_EDGE_LAST_MASK,
                                            pptr);
                parent_data_ptr++;
        } while (!(edge_value & GRAPH_LAST_EDGE));

        return 1;
}

static int search_commit_pos_in_graph(const struct object_id *id, struct commit_graph *g, uint32_t *pos)
{
        struct commit_graph *cur_g = g;
        uint32_t lex_index;

        while (cur_g && !bsearch_graph(cur_g, id, &lex_index))
                cur_g = cur_g->base_graph;

        if (cur_g) {
                *pos = lex_index + cur_g->num_commits_in_base;
                return 1;
        }

        return 0;
}

static int find_commit_pos_in_graph(struct commit *item, struct commit_graph *g, uint32_t *pos)
{
        uint32_t graph_pos = commit_graph_position(item);
        if (graph_pos != COMMIT_NOT_FROM_GRAPH) {
                *pos = graph_pos;
                return 1;
        } else {
                return search_commit_pos_in_graph(&item->object.oid, g, pos);
        }
}

int repo_find_commit_pos_in_graph(struct repository *r, struct commit *c,
                                  uint32_t *pos)
{
        if (!prepare_commit_graph(r))
                return 0;
        return find_commit_pos_in_graph(c, r->objects->commit_graph, pos);
}

struct commit *lookup_commit_in_graph(struct repository *repo, const struct object_id *id)
{
        struct commit *commit;
        uint32_t pos;

        if (!prepare_commit_graph(repo))
                return NULL;
        if (!search_commit_pos_in_graph(id, repo->objects->commit_graph, &pos))
                return NULL;
        if (!has_object(repo, id, 0))
                return NULL;

        commit = lookup_commit(repo, id);
        if (!commit)
                return NULL;
        if (commit->object.parsed)
                return commit;

        if (!fill_commit_in_graph(repo, commit, repo->objects->commit_graph, pos))
                return NULL;

        return commit;
}

static int parse_commit_in_graph_one(struct repository *r,
                                     struct commit_graph *g,
                                     struct commit *item)
{
        uint32_t pos;

        if (item->object.parsed)
                return 1;

        if (find_commit_pos_in_graph(item, g, &pos))
                return fill_commit_in_graph(r, item, g, pos);

        return 0;
}

int parse_commit_in_graph(struct repository *r, struct commit *item)
{
        static int checked_env = 0;

        if (!checked_env &&
            git_env_bool(GIT_TEST_COMMIT_GRAPH_DIE_ON_PARSE, 0))
                die("dying as requested by the '%s' variable on commit-graph parse!",
                    GIT_TEST_COMMIT_GRAPH_DIE_ON_PARSE);
        checked_env = 1;

        if (!prepare_commit_graph(r))
                return 0;
        return parse_commit_in_graph_one(r, r->objects->commit_graph, item);
}

void load_commit_graph_info(struct repository *r, struct commit *item)
{
        uint32_t pos;
        if (repo_find_commit_pos_in_graph(r, item, &pos))
                fill_commit_graph_info(item, r->objects->commit_graph, pos);
}

static struct tree *load_tree_for_commit(struct repository *r,
                                         struct commit_graph *g,
                                         struct commit *c)
{
        struct object_id oid;
        const unsigned char *commit_data;
        uint32_t graph_pos = commit_graph_position(c);

        while (graph_pos < g->num_commits_in_base)
                g = g->base_graph;

        commit_data = g->chunk_commit_data +
                        GRAPH_DATA_WIDTH * (graph_pos - g->num_commits_in_base);

        oidread(&oid, commit_data);
        set_commit_tree(c, lookup_tree(r, &oid));

        return c->maybe_tree;
}

static struct tree *get_commit_tree_in_graph_one(struct repository *r,
                                                 struct commit_graph *g,
                                                 const struct commit *c)
{
        if (c->maybe_tree)
                return c->maybe_tree;
        if (commit_graph_position(c) == COMMIT_NOT_FROM_GRAPH)
                BUG("get_commit_tree_in_graph_one called from non-commit-graph commit");

        return load_tree_for_commit(r, g, (struct commit *)c);
}

struct tree *get_commit_tree_in_graph(struct repository *r, const struct commit *c)
{
        return get_commit_tree_in_graph_one(r, r->objects->commit_graph, c);
}

struct packed_commit_list {
        struct commit **list;
        size_t nr;
        size_t alloc;
};

struct write_commit_graph_context {
        struct repository *r;
        struct object_directory *odb;
        char *graph_name;
        struct oid_array oids;
        struct packed_commit_list commits;
        int num_extra_edges;
        int num_generation_data_overflows;
        unsigned long approx_nr_objects;
        struct progress *progress;
        int progress_done;
        uint64_t progress_cnt;

        char *base_graph_name;
        int num_commit_graphs_before;
        int num_commit_graphs_after;
        char **commit_graph_filenames_before;
        char **commit_graph_filenames_after;
        char **commit_graph_hash_after;
        uint32_t new_num_commits_in_base;
        struct commit_graph *new_base_graph;

        unsigned append:1,
                 report_progress:1,
                 split:1,
                 changed_paths:1,
                 order_by_pack:1,
                 write_generation_data:1,
                 trust_generation_numbers:1;

        struct topo_level_slab *topo_levels;
        const struct commit_graph_opts *opts;
        size_t total_bloom_filter_data_size;
        const struct bloom_filter_settings *bloom_settings;

        int count_bloom_filter_computed;
        int count_bloom_filter_not_computed;
        int count_bloom_filter_trunc_empty;
        int count_bloom_filter_trunc_large;
};

static int write_graph_chunk_fanout(struct hashfile *f,
                                    void *data)
{
        struct write_commit_graph_context *ctx = data;
        int i, count = 0;
        struct commit **list = ctx->commits.list;

        /*
         * Write the first-level table (the list is sorted,
         * but we use a 256-entry lookup to be able to avoid
         * having to do eight extra binary search iterations).
         */
        for (i = 0; i < 256; i++) {
                while (count < ctx->commits.nr) {
                        if ((*list)->object.oid.hash[0] != i)
                                break;
                        display_progress(ctx->progress, ++ctx->progress_cnt);
                        count++;
                        list++;
                }

                hashwrite_be32(f, count);
        }

        return 0;
}

static int write_graph_chunk_oids(struct hashfile *f,
                                  void *data)
{
        struct write_commit_graph_context *ctx = data;
        struct commit **list = ctx->commits.list;
        int count;
        for (count = 0; count < ctx->commits.nr; count++, list++) {
                display_progress(ctx->progress, ++ctx->progress_cnt);
                hashwrite(f, (*list)->object.oid.hash, the_hash_algo->rawsz);
        }

        return 0;
}

static const struct object_id *commit_to_oid(size_t index, const void *table)
{
        const struct commit * const *commits = table;
        return &commits[index]->object.oid;
}

static int write_graph_chunk_data(struct hashfile *f,
                                  void *data)
{
        struct write_commit_graph_context *ctx = data;
        struct commit **list = ctx->commits.list;
        struct commit **last = ctx->commits.list + ctx->commits.nr;
        uint32_t num_extra_edges = 0;

        while (list < last) {
                struct commit_list *parent;
                struct object_id *tree;
                int edge_value;
                uint32_t packedDate[2];
                display_progress(ctx->progress, ++ctx->progress_cnt);

                if (repo_parse_commit_no_graph(ctx->r, *list))
                        die(_("unable to parse commit %s"),
                                oid_to_hex(&(*list)->object.oid));
                tree = get_commit_tree_oid(*list);
                hashwrite(f, tree->hash, the_hash_algo->rawsz);

                parent = (*list)->parents;

                if (!parent)
                        edge_value = GRAPH_PARENT_NONE;
                else {
                        edge_value = oid_pos(&parent->item->object.oid,
                                             ctx->commits.list,
                                             ctx->commits.nr,
                                             commit_to_oid);

                        if (edge_value >= 0)
                                edge_value += ctx->new_num_commits_in_base;
                        else if (ctx->new_base_graph) {
                                uint32_t pos;
                                if (find_commit_pos_in_graph(parent->item,
                                                             ctx->new_base_graph,
                                                             &pos))
                                        edge_value = pos;
                        }

                        if (edge_value < 0)
                                BUG("missing parent %s for commit %s",
                                    oid_to_hex(&parent->item->object.oid),
                                    oid_to_hex(&(*list)->object.oid));
                }

                hashwrite_be32(f, edge_value);

                if (parent)
                        parent = parent->next;

                if (!parent)
                        edge_value = GRAPH_PARENT_NONE;
                else if (parent->next)
                        edge_value = GRAPH_EXTRA_EDGES_NEEDED | num_extra_edges;
                else {
                        edge_value = oid_pos(&parent->item->object.oid,
                                             ctx->commits.list,
                                             ctx->commits.nr,
                                             commit_to_oid);

                        if (edge_value >= 0)
                                edge_value += ctx->new_num_commits_in_base;
                        else if (ctx->new_base_graph) {
                                uint32_t pos;
                                if (find_commit_pos_in_graph(parent->item,
                                                             ctx->new_base_graph,
                                                             &pos))
                                        edge_value = pos;
                        }

                        if (edge_value < 0)
                                BUG("missing parent %s for commit %s",
                                    oid_to_hex(&parent->item->object.oid),
                                    oid_to_hex(&(*list)->object.oid));
                }

                hashwrite_be32(f, edge_value);

                if (edge_value & GRAPH_EXTRA_EDGES_NEEDED) {
                        do {
                                num_extra_edges++;
                                parent = parent->next;
                        } while (parent);
                }

                if (sizeof((*list)->date) > 4)
                        packedDate[0] = htonl(((*list)->date >> 32) & 0x3);
                else
                        packedDate[0] = 0;

                packedDate[0] |= htonl(*topo_level_slab_at(ctx->topo_levels, *list) << 2);

                packedDate[1] = htonl((*list)->date);
                hashwrite(f, packedDate, 8);

                list++;
        }

        return 0;
}

static int write_graph_chunk_generation_data(struct hashfile *f,
                                             void *data)
{
        struct write_commit_graph_context *ctx = data;
        int i, num_generation_data_overflows = 0;

        for (i = 0; i < ctx->commits.nr; i++) {
                struct commit *c = ctx->commits.list[i];
                timestamp_t offset;
                repo_parse_commit(ctx->r, c);
                offset = commit_graph_data_at(c)->generation - c->date;
                display_progress(ctx->progress, ++ctx->progress_cnt);

                if (offset > GENERATION_NUMBER_V2_OFFSET_MAX) {
                        offset = CORRECTED_COMMIT_DATE_OFFSET_OVERFLOW | num_generation_data_overflows;
                        num_generation_data_overflows++;
                }

                hashwrite_be32(f, offset);
        }

        return 0;
}

static int write_graph_chunk_generation_data_overflow(struct hashfile *f,
                                                      void *data)
{
        struct write_commit_graph_context *ctx = data;
        int i;
        for (i = 0; i < ctx->commits.nr; i++) {
                struct commit *c = ctx->commits.list[i];
                timestamp_t offset = commit_graph_data_at(c)->generation - c->date;
                display_progress(ctx->progress, ++ctx->progress_cnt);

                if (offset > GENERATION_NUMBER_V2_OFFSET_MAX) {
                        hashwrite_be32(f, offset >> 32);
                        hashwrite_be32(f, (uint32_t) offset);
                }
        }

        return 0;
}

static int write_graph_chunk_extra_edges(struct hashfile *f,
                                         void *data)
{
        struct write_commit_graph_context *ctx = data;
        struct commit **list = ctx->commits.list;
        struct commit **last = ctx->commits.list + ctx->commits.nr;
        struct commit_list *parent;

        while (list < last) {
                int num_parents = 0;

                display_progress(ctx->progress, ++ctx->progress_cnt);

                for (parent = (*list)->parents; num_parents < 3 && parent;
                     parent = parent->next)
                        num_parents++;

                if (num_parents <= 2) {
                        list++;
                        continue;
                }

                /* Since num_parents > 2, this initializer is safe. */
                for (parent = (*list)->parents->next; parent; parent = parent->next) {
                        int edge_value = oid_pos(&parent->item->object.oid,
                                                 ctx->commits.list,
                                                 ctx->commits.nr,
                                                 commit_to_oid);

                        if (edge_value >= 0)
                                edge_value += ctx->new_num_commits_in_base;
                        else if (ctx->new_base_graph) {
                                uint32_t pos;
                                if (find_commit_pos_in_graph(parent->item,
                                                             ctx->new_base_graph,
                                                             &pos))
                                        edge_value = pos;
                        }

                        if (edge_value < 0)
                                BUG("missing parent %s for commit %s",
                                    oid_to_hex(&parent->item->object.oid),
                                    oid_to_hex(&(*list)->object.oid));
                        else if (!parent->next)
                                edge_value |= GRAPH_LAST_EDGE;

                        hashwrite_be32(f, edge_value);
                }

                list++;
        }

        return 0;
}

static int write_graph_chunk_bloom_indexes(struct hashfile *f,
                                           void *data)
{
        struct write_commit_graph_context *ctx = data;
        struct commit **list = ctx->commits.list;
        struct commit **last = ctx->commits.list + ctx->commits.nr;
        uint32_t cur_pos = 0;

        while (list < last) {
                struct bloom_filter *filter = get_bloom_filter(ctx->r, *list);
                size_t len = filter ? filter->len : 0;
                cur_pos += len;
                display_progress(ctx->progress, ++ctx->progress_cnt);
                hashwrite_be32(f, cur_pos);
                list++;
        }

        return 0;
}

static void trace2_bloom_filter_settings(struct write_commit_graph_context *ctx)
{
        struct json_writer jw = JSON_WRITER_INIT;

        jw_object_begin(&jw, 0);
        jw_object_intmax(&jw, "hash_version", ctx->bloom_settings->hash_version);
        jw_object_intmax(&jw, "num_hashes", ctx->bloom_settings->num_hashes);
        jw_object_intmax(&jw, "bits_per_entry", ctx->bloom_settings->bits_per_entry);
        jw_object_intmax(&jw, "max_changed_paths", ctx->bloom_settings->max_changed_paths);
        jw_end(&jw);

        trace2_data_json("bloom", ctx->r, "settings", &jw);

        jw_release(&jw);
}

static int write_graph_chunk_bloom_data(struct hashfile *f,
                                        void *data)
{
        struct write_commit_graph_context *ctx = data;
        struct commit **list = ctx->commits.list;
        struct commit **last = ctx->commits.list + ctx->commits.nr;

        trace2_bloom_filter_settings(ctx);

        hashwrite_be32(f, ctx->bloom_settings->hash_version);
        hashwrite_be32(f, ctx->bloom_settings->num_hashes);
        hashwrite_be32(f, ctx->bloom_settings->bits_per_entry);

        while (list < last) {
                struct bloom_filter *filter = get_bloom_filter(ctx->r, *list);
                size_t len = filter ? filter->len : 0;

                display_progress(ctx->progress, ++ctx->progress_cnt);
                if (len)
                        hashwrite(f, filter->data, len * sizeof(unsigned char));
                list++;
        }

        return 0;
}

static int add_packed_commits(const struct object_id *oid,
                              struct packed_git *pack,
                              uint32_t pos,
                              void *data)
{
        struct write_commit_graph_context *ctx = (struct write_commit_graph_context*)data;
        enum object_type type;
        off_t offset = nth_packed_object_offset(pack, pos);
        struct object_info oi = OBJECT_INFO_INIT;

        if (ctx->progress)
                display_progress(ctx->progress, ++ctx->progress_done);

        oi.typep = &type;
        if (packed_object_info(ctx->r, pack, offset, &oi) < 0)
                die(_("unable to get type of object %s"), oid_to_hex(oid));

        if (type != OBJ_COMMIT)
                return 0;

        oid_array_append(&ctx->oids, oid);
        set_commit_pos(ctx->r, oid);

        return 0;
}

static void add_missing_parents(struct write_commit_graph_context *ctx, struct commit *commit)
{
        struct commit_list *parent;
        for (parent = commit->parents; parent; parent = parent->next) {
                if (!(parent->item->object.flags & REACHABLE)) {
                        oid_array_append(&ctx->oids, &parent->item->object.oid);
                        parent->item->object.flags |= REACHABLE;
                }
        }
}

static void close_reachable(struct write_commit_graph_context *ctx)
{
        int i;
        struct commit *commit;
        enum commit_graph_split_flags flags = ctx->opts ?
                ctx->opts->split_flags : COMMIT_GRAPH_SPLIT_UNSPECIFIED;

        if (ctx->report_progress)
                ctx->progress = start_delayed_progress(
                                        _("Loading known commits in commit graph"),
                                        ctx->oids.nr);
        for (i = 0; i < ctx->oids.nr; i++) {
                display_progress(ctx->progress, i + 1);
                commit = lookup_commit(ctx->r, &ctx->oids.oid[i]);
                if (commit)
                        commit->object.flags |= REACHABLE;
        }
        stop_progress(&ctx->progress);

        /*
         * As this loop runs, ctx->oids.nr may grow, but not more
         * than the number of missing commits in the reachable
         * closure.
         */
        if (ctx->report_progress)
                ctx->progress = start_delayed_progress(
                                        _("Expanding reachable commits in commit graph"),
                                        0);
        for (i = 0; i < ctx->oids.nr; i++) {
                display_progress(ctx->progress, i + 1);
                commit = lookup_commit(ctx->r, &ctx->oids.oid[i]);

                if (!commit)
                        continue;
                if (ctx->split) {
                        if ((!repo_parse_commit(ctx->r, commit) &&
                             commit_graph_position(commit) == COMMIT_NOT_FROM_GRAPH) ||
                            flags == COMMIT_GRAPH_SPLIT_REPLACE)
                                add_missing_parents(ctx, commit);
                } else if (!repo_parse_commit_no_graph(ctx->r, commit))
                        add_missing_parents(ctx, commit);
        }
        stop_progress(&ctx->progress);

        if (ctx->report_progress)
                ctx->progress = start_delayed_progress(
                                        _("Clearing commit marks in commit graph"),
                                        ctx->oids.nr);
        for (i = 0; i < ctx->oids.nr; i++) {
                display_progress(ctx->progress, i + 1);
                commit = lookup_commit(ctx->r, &ctx->oids.oid[i]);

                if (commit)
                        commit->object.flags &= ~REACHABLE;
        }
        stop_progress(&ctx->progress);
}

struct compute_generation_info {
        struct repository *r;
        struct packed_commit_list *commits;
        struct progress *progress;
        int progress_cnt;

        timestamp_t (*get_generation)(struct commit *c, void *data);
        void (*set_generation)(struct commit *c, timestamp_t gen, void *data);
        void *data;
};

static timestamp_t compute_generation_from_max(struct commit *c,
                                               timestamp_t max_gen,
                                               int generation_version)
{
        switch (generation_version) {
        case 1: /* topological levels */
                if (max_gen > GENERATION_NUMBER_V1_MAX - 1)
                        max_gen = GENERATION_NUMBER_V1_MAX - 1;
                return max_gen + 1;

        case 2: /* corrected commit date */
                if (c->date && c->date > max_gen)
                        max_gen = c->date - 1;
                return max_gen + 1;

        default:
                BUG("attempting unimplemented version");
        }
}

static void compute_reachable_generation_numbers(
                        struct compute_generation_info *info,
                        int generation_version)
{
        int i;
        struct commit_list *list = NULL;

        for (i = 0; i < info->commits->nr; i++) {
                struct commit *c = info->commits->list[i];
                timestamp_t gen;
                repo_parse_commit(info->r, c);
                gen = info->get_generation(c, info->data);
                display_progress(info->progress, info->progress_cnt + 1);

                if (gen != GENERATION_NUMBER_ZERO && gen != GENERATION_NUMBER_INFINITY)
                        continue;

                commit_list_insert(c, &list);
                while (list) {
                        struct commit *current = list->item;
                        struct commit_list *parent;
                        int all_parents_computed = 1;
                        uint32_t max_gen = 0;

                        for (parent = current->parents; parent; parent = parent->next) {
                                repo_parse_commit(info->r, parent->item);
                                gen = info->get_generation(parent->item, info->data);

                                if (gen == GENERATION_NUMBER_ZERO) {
                                        all_parents_computed = 0;
                                        commit_list_insert(parent->item, &list);
                                        break;
                                }

                                if (gen > max_gen)
                                        max_gen = gen;
                        }

                        if (all_parents_computed) {
                                pop_commit(&list);
                                gen = compute_generation_from_max(
                                                current, max_gen,
                                                generation_version);
                                info->set_generation(current, gen, info->data);
                        }
                }
        }
}

static timestamp_t get_topo_level(struct commit *c, void *data)
{
        struct write_commit_graph_context *ctx = data;
        return *topo_level_slab_at(ctx->topo_levels, c);
}

static void set_topo_level(struct commit *c, timestamp_t t, void *data)
{
        struct write_commit_graph_context *ctx = data;
        *topo_level_slab_at(ctx->topo_levels, c) = (uint32_t)t;
}

static void compute_topological_levels(struct write_commit_graph_context *ctx)
{
        struct compute_generation_info info = {
                .r = ctx->r,
                .commits = &ctx->commits,
                .get_generation = get_topo_level,
                .set_generation = set_topo_level,
                .data = ctx,
        };

        if (ctx->report_progress)
                info.progress = ctx->progress
                              = start_delayed_progress(
                                        _("Computing commit graph topological levels"),
                                        ctx->commits.nr);

        compute_reachable_generation_numbers(&info, 1);

        stop_progress(&ctx->progress);
}

static timestamp_t get_generation_from_graph_data(struct commit *c, void *data)
{
        return commit_graph_data_at(c)->generation;
}

static void set_generation_v2(struct commit *c, timestamp_t t, void *data)
{
        struct commit_graph_data *g = commit_graph_data_at(c);
        g->generation = t;
}

static void compute_generation_numbers(struct write_commit_graph_context *ctx)
{
        int i;
        struct compute_generation_info info = {
                .r = ctx->r,
                .commits = &ctx->commits,
                .get_generation = get_generation_from_graph_data,
                .set_generation = set_generation_v2,
                .data = ctx,
        };

        if (ctx->report_progress)
                info.progress = ctx->progress
                              = start_delayed_progress(
                                        _("Computing commit graph generation numbers"),
                                        ctx->commits.nr);

        if (!ctx->trust_generation_numbers) {
                for (i = 0; i < ctx->commits.nr; i++) {
                        struct commit *c = ctx->commits.list[i];
                        repo_parse_commit(ctx->r, c);
                        commit_graph_data_at(c)->generation = GENERATION_NUMBER_ZERO;
                }
        }

        compute_reachable_generation_numbers(&info, 2);

        for (i = 0; i < ctx->commits.nr; i++) {
                struct commit *c = ctx->commits.list[i];
                timestamp_t offset = commit_graph_data_at(c)->generation - c->date;
                if (offset > GENERATION_NUMBER_V2_OFFSET_MAX)
                        ctx->num_generation_data_overflows++;
        }
        stop_progress(&ctx->progress);
}

static void set_generation_in_graph_data(struct commit *c, timestamp_t t,
                                         void *data)
{
        commit_graph_data_at(c)->generation = t;
}

/*
 * After this method, all commits reachable from those in the given
 * list will have non-zero, non-infinite generation numbers.
 */
void ensure_generations_valid(struct repository *r,
                              struct commit **commits, size_t nr)
{
        int generation_version = get_configured_generation_version(r);
        struct packed_commit_list list = {
                .list = commits,
                .alloc = nr,
                .nr = nr,
        };
        struct compute_generation_info info = {
                .r = r,
                .commits = &list,
                .get_generation = get_generation_from_graph_data,
                .set_generation = set_generation_in_graph_data,
        };

        compute_reachable_generation_numbers(&info, generation_version);
}

static void trace2_bloom_filter_write_statistics(struct write_commit_graph_context *ctx)
{
        trace2_data_intmax("commit-graph", ctx->r, "filter-computed",
                           ctx->count_bloom_filter_computed);
        trace2_data_intmax("commit-graph", ctx->r, "filter-not-computed",
                           ctx->count_bloom_filter_not_computed);
        trace2_data_intmax("commit-graph", ctx->r, "filter-trunc-empty",
                           ctx->count_bloom_filter_trunc_empty);
        trace2_data_intmax("commit-graph", ctx->r, "filter-trunc-large",
                           ctx->count_bloom_filter_trunc_large);
}

static void compute_bloom_filters(struct write_commit_graph_context *ctx)
{
        int i;
        struct progress *progress = NULL;
        struct commit **sorted_commits;
        int max_new_filters;

        init_bloom_filters();

        if (ctx->report_progress)
                progress = start_delayed_progress(
                        _("Computing commit changed paths Bloom filters"),
                        ctx->commits.nr);

        DUP_ARRAY(sorted_commits, ctx->commits.list, ctx->commits.nr);

        if (ctx->order_by_pack)
                QSORT(sorted_commits, ctx->commits.nr, commit_pos_cmp);
        else
                QSORT(sorted_commits, ctx->commits.nr, commit_gen_cmp);

        max_new_filters = ctx->opts && ctx->opts->max_new_filters >= 0 ?
                ctx->opts->max_new_filters : ctx->commits.nr;

        for (i = 0; i < ctx->commits.nr; i++) {
                enum bloom_filter_computed computed = 0;
                struct commit *c = sorted_commits[i];
                struct bloom_filter *filter = get_or_compute_bloom_filter(
                        ctx->r,
                        c,
                        ctx->count_bloom_filter_computed < max_new_filters,
                        ctx->bloom_settings,
                        &computed);
                if (computed & BLOOM_COMPUTED) {
                        ctx->count_bloom_filter_computed++;
                        if (computed & BLOOM_TRUNC_EMPTY)
                                ctx->count_bloom_filter_trunc_empty++;
                        if (computed & BLOOM_TRUNC_LARGE)
                                ctx->count_bloom_filter_trunc_large++;
                } else if (computed & BLOOM_NOT_COMPUTED)
                        ctx->count_bloom_filter_not_computed++;
                ctx->total_bloom_filter_data_size += filter
                        ? sizeof(unsigned char) * filter->len : 0;
                display_progress(progress, i + 1);
        }

        if (trace2_is_enabled())
                trace2_bloom_filter_write_statistics(ctx);

        free(sorted_commits);
        stop_progress(&progress);
}

struct refs_cb_data {
        struct oidset *commits;
        struct progress *progress;
};

static int add_ref_to_set(const char *refname UNUSED,
                          const struct object_id *oid,
                          int flags UNUSED, void *cb_data)
{
        struct object_id peeled;
        struct refs_cb_data *data = (struct refs_cb_data *)cb_data;

        if (!peel_iterated_oid(oid, &peeled))
                oid = &peeled;
        if (oid_object_info(the_repository, oid, NULL) == OBJ_COMMIT)
                oidset_insert(data->commits, oid);

        display_progress(data->progress, oidset_size(data->commits));

        return 0;
}

int write_commit_graph_reachable(struct object_directory *odb,
                                 enum commit_graph_write_flags flags,
                                 const struct commit_graph_opts *opts)
{
        struct oidset commits = OIDSET_INIT;
        struct refs_cb_data data;
        int result;

        memset(&data, 0, sizeof(data));
        data.commits = &commits;
        if (flags & COMMIT_GRAPH_WRITE_PROGRESS)
                data.progress = start_delayed_progress(
                        _("Collecting referenced commits"), 0);

        for_each_ref(add_ref_to_set, &data);

        stop_progress(&data.progress);

        result = write_commit_graph(odb, NULL, &commits,
                                    flags, opts);

        oidset_clear(&commits);
        return result;
}

static int fill_oids_from_packs(struct write_commit_graph_context *ctx,
                                const struct string_list *pack_indexes)
{
        uint32_t i;
        struct strbuf progress_title = STRBUF_INIT;
        struct strbuf packname = STRBUF_INIT;
        int dirlen;
        int ret = 0;

        strbuf_addf(&packname, "%s/pack/", ctx->odb->path);
        dirlen = packname.len;
        if (ctx->report_progress) {
                strbuf_addf(&progress_title,
                            Q_("Finding commits for commit graph in %"PRIuMAX" pack",
                               "Finding commits for commit graph in %"PRIuMAX" packs",
                               pack_indexes->nr),
                            (uintmax_t)pack_indexes->nr);
                ctx->progress = start_delayed_progress(progress_title.buf, 0);
                ctx->progress_done = 0;
        }
        for (i = 0; i < pack_indexes->nr; i++) {
                struct packed_git *p;
                strbuf_setlen(&packname, dirlen);
                strbuf_addstr(&packname, pack_indexes->items[i].string);
                p = add_packed_git(packname.buf, packname.len, 1);
                if (!p) {
                        ret = error(_("error adding pack %s"), packname.buf);
                        goto cleanup;
                }
                if (open_pack_index(p)) {
                        ret = error(_("error opening index for %s"), packname.buf);
                        goto cleanup;
                }
                for_each_object_in_pack(p, add_packed_commits, ctx,
                                        FOR_EACH_OBJECT_PACK_ORDER);
                close_pack(p);
                free(p);
        }

cleanup:
        stop_progress(&ctx->progress);
        strbuf_release(&progress_title);
        strbuf_release(&packname);

        return ret;
}

static int fill_oids_from_commits(struct write_commit_graph_context *ctx,
                                  struct oidset *commits)
{
        struct oidset_iter iter;
        struct object_id *oid;

        if (!oidset_size(commits))
                return 0;

        oidset_iter_init(commits, &iter);
        while ((oid = oidset_iter_next(&iter))) {
                oid_array_append(&ctx->oids, oid);
        }

        return 0;
}

static void fill_oids_from_all_packs(struct write_commit_graph_context *ctx)
{
        if (ctx->report_progress)
                ctx->progress = start_delayed_progress(
                        _("Finding commits for commit graph among packed objects"),
                        ctx->approx_nr_objects);
        for_each_packed_object(add_packed_commits, ctx,
                               FOR_EACH_OBJECT_PACK_ORDER);
        if (ctx->progress_done < ctx->approx_nr_objects)
                display_progress(ctx->progress, ctx->approx_nr_objects);
        stop_progress(&ctx->progress);
}

static void copy_oids_to_commits(struct write_commit_graph_context *ctx)
{
        uint32_t i;
        enum commit_graph_split_flags flags = ctx->opts ?
                ctx->opts->split_flags : COMMIT_GRAPH_SPLIT_UNSPECIFIED;

        ctx->num_extra_edges = 0;
        if (ctx->report_progress)
                ctx->progress = start_delayed_progress(
                        _("Finding extra edges in commit graph"),
                        ctx->oids.nr);
        oid_array_sort(&ctx->oids);
        for (i = 0; i < ctx->oids.nr; i = oid_array_next_unique(&ctx->oids, i)) {
                unsigned int num_parents;

                display_progress(ctx->progress, i + 1);

                ALLOC_GROW(ctx->commits.list, ctx->commits.nr + 1, ctx->commits.alloc);
                ctx->commits.list[ctx->commits.nr] = lookup_commit(ctx->r, &ctx->oids.oid[i]);

                if (ctx->split && flags != COMMIT_GRAPH_SPLIT_REPLACE &&
                    commit_graph_position(ctx->commits.list[ctx->commits.nr]) != COMMIT_NOT_FROM_GRAPH)
                        continue;

                if (ctx->split && flags == COMMIT_GRAPH_SPLIT_REPLACE)
                        repo_parse_commit(ctx->r, ctx->commits.list[ctx->commits.nr]);
                else
                        repo_parse_commit_no_graph(ctx->r, ctx->commits.list[ctx->commits.nr]);

                num_parents = commit_list_count(ctx->commits.list[ctx->commits.nr]->parents);
                if (num_parents > 2)
                        ctx->num_extra_edges += num_parents - 1;

                ctx->commits.nr++;
        }
        stop_progress(&ctx->progress);
}

static int write_graph_chunk_base_1(struct hashfile *f,
                                    struct commit_graph *g)
{
        int num = 0;

        if (!g)
                return 0;

        num = write_graph_chunk_base_1(f, g->base_graph);
        hashwrite(f, g->oid.hash, the_hash_algo->rawsz);
        return num + 1;
}

static int write_graph_chunk_base(struct hashfile *f,
                                    void *data)
{
        struct write_commit_graph_context *ctx = data;
        int num = write_graph_chunk_base_1(f, ctx->new_base_graph);

        if (num != ctx->num_commit_graphs_after - 1) {
                error(_("failed to write correct number of base graph ids"));
                return -1;
        }

        return 0;
}

static int write_commit_graph_file(struct write_commit_graph_context *ctx)
{
        uint32_t i;
        int fd;
        struct hashfile *f;
        struct lock_file lk = LOCK_INIT;
        const unsigned hashsz = the_hash_algo->rawsz;
        struct strbuf progress_title = STRBUF_INIT;
        struct chunkfile *cf;
        unsigned char file_hash[GIT_MAX_RAWSZ];

        if (ctx->split) {
                struct strbuf tmp_file = STRBUF_INIT;

                strbuf_addf(&tmp_file,
                            "%s/info/commit-graphs/tmp_graph_XXXXXX",
                            ctx->odb->path);
                ctx->graph_name = strbuf_detach(&tmp_file, NULL);
        } else {
                ctx->graph_name = get_commit_graph_filename(ctx->odb);
        }

        if (safe_create_leading_directories(ctx->graph_name)) {
                UNLEAK(ctx->graph_name);
                error(_("unable to create leading directories of %s"),
                        ctx->graph_name);
                return -1;
        }

        if (ctx->split) {
                char *lock_name = get_commit_graph_chain_filename(ctx->odb);

                hold_lock_file_for_update_mode(&lk, lock_name,
                                               LOCK_DIE_ON_ERROR, 0444);
                free(lock_name);

                fd = git_mkstemp_mode(ctx->graph_name, 0444);
                if (fd < 0) {
                        error(_("unable to create temporary graph layer"));
                        return -1;
                }

                if (adjust_shared_perm(ctx->graph_name)) {
                        error(_("unable to adjust shared permissions for '%s'"),
                              ctx->graph_name);
                        return -1;
                }

                f = hashfd(fd, ctx->graph_name);
        } else {
                hold_lock_file_for_update_mode(&lk, ctx->graph_name,
                                               LOCK_DIE_ON_ERROR, 0444);
                fd = get_lock_file_fd(&lk);
                f = hashfd(fd, get_lock_file_path(&lk));
        }

        cf = init_chunkfile(f);

        add_chunk(cf, GRAPH_CHUNKID_OIDFANOUT, GRAPH_FANOUT_SIZE,
                  write_graph_chunk_fanout);
        add_chunk(cf, GRAPH_CHUNKID_OIDLOOKUP, hashsz * ctx->commits.nr,
                  write_graph_chunk_oids);
        add_chunk(cf, GRAPH_CHUNKID_DATA, (hashsz + 16) * ctx->commits.nr,
                  write_graph_chunk_data);

        if (ctx->write_generation_data)
                add_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA,
                          sizeof(uint32_t) * ctx->commits.nr,
                          write_graph_chunk_generation_data);
        if (ctx->num_generation_data_overflows)
                add_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA_OVERFLOW,
                          sizeof(timestamp_t) * ctx->num_generation_data_overflows,
                          write_graph_chunk_generation_data_overflow);
        if (ctx->num_extra_edges)
                add_chunk(cf, GRAPH_CHUNKID_EXTRAEDGES,
                          4 * ctx->num_extra_edges,
                          write_graph_chunk_extra_edges);
        if (ctx->changed_paths) {
                add_chunk(cf, GRAPH_CHUNKID_BLOOMINDEXES,
                          sizeof(uint32_t) * ctx->commits.nr,
                          write_graph_chunk_bloom_indexes);
                add_chunk(cf, GRAPH_CHUNKID_BLOOMDATA,
                          sizeof(uint32_t) * 3
                                + ctx->total_bloom_filter_data_size,
                          write_graph_chunk_bloom_data);
        }
        if (ctx->num_commit_graphs_after > 1)
                add_chunk(cf, GRAPH_CHUNKID_BASE,
                          hashsz * (ctx->num_commit_graphs_after - 1),
                          write_graph_chunk_base);

        hashwrite_be32(f, GRAPH_SIGNATURE);

        hashwrite_u8(f, GRAPH_VERSION);
        hashwrite_u8(f, oid_version(the_hash_algo));
        hashwrite_u8(f, get_num_chunks(cf));
        hashwrite_u8(f, ctx->num_commit_graphs_after - 1);

        if (ctx->report_progress) {
                strbuf_addf(&progress_title,
                            Q_("Writing out commit graph in %d pass",
                               "Writing out commit graph in %d passes",
                               get_num_chunks(cf)),
                            get_num_chunks(cf));
                ctx->progress = start_delayed_progress(
                        progress_title.buf,
                        get_num_chunks(cf) * ctx->commits.nr);
        }

        write_chunkfile(cf, ctx);

        stop_progress(&ctx->progress);
        strbuf_release(&progress_title);

        if (ctx->split && ctx->base_graph_name && ctx->num_commit_graphs_after > 1) {
                char *new_base_hash = xstrdup(oid_to_hex(&ctx->new_base_graph->oid));
                char *new_base_name = get_split_graph_filename(ctx->new_base_graph->odb, new_base_hash);

                free(ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 2]);
                free(ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 2]);
                ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 2] = new_base_name;
                ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 2] = new_base_hash;
        }

        close_commit_graph(ctx->r->objects);
        finalize_hashfile(f, file_hash, FSYNC_COMPONENT_COMMIT_GRAPH,
                          CSUM_HASH_IN_STREAM | CSUM_FSYNC);
        free_chunkfile(cf);

        if (ctx->split) {
                FILE *chainf = fdopen_lock_file(&lk, "w");
                char *final_graph_name;
                int result;

                close(fd);

                if (!chainf) {
                        error(_("unable to open commit-graph chain file"));
                        return -1;
                }

                if (ctx->base_graph_name) {
                        const char *dest;
                        int idx = ctx->num_commit_graphs_after - 1;
                        if (ctx->num_commit_graphs_after > 1)
                                idx--;

                        dest = ctx->commit_graph_filenames_after[idx];

                        if (strcmp(ctx->base_graph_name, dest)) {
                                result = rename(ctx->base_graph_name, dest);

                                if (result) {
                                        error(_("failed to rename base commit-graph file"));
                                        return -1;
                                }
                        }
                } else {
                        char *graph_name = get_commit_graph_filename(ctx->odb);
                        unlink(graph_name);
                        free(graph_name);
                }

                ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 1] = xstrdup(hash_to_hex(file_hash));
                final_graph_name = get_split_graph_filename(ctx->odb,
                                        ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 1]);
                ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 1] = final_graph_name;

                result = rename(ctx->graph_name, final_graph_name);

                for (i = 0; i < ctx->num_commit_graphs_after; i++)
                        fprintf(get_lock_file_fp(&lk), "%s\n", ctx->commit_graph_hash_after[i]);

                if (result) {
                        error(_("failed to rename temporary commit-graph file"));
                        return -1;
                }
        }

        commit_lock_file(&lk);

        return 0;
}

static void split_graph_merge_strategy(struct write_commit_graph_context *ctx)
{
        struct commit_graph *g;
        uint32_t num_commits;
        enum commit_graph_split_flags flags = COMMIT_GRAPH_SPLIT_UNSPECIFIED;
        uint32_t i;

        int max_commits = 0;
        int size_mult = 2;

        if (ctx->opts) {
                max_commits = ctx->opts->max_commits;

                if (ctx->opts->size_multiple)
                        size_mult = ctx->opts->size_multiple;

                flags = ctx->opts->split_flags;
        }

        g = ctx->r->objects->commit_graph;
        num_commits = ctx->commits.nr;
        if (flags == COMMIT_GRAPH_SPLIT_REPLACE)
                ctx->num_commit_graphs_after = 1;
        else
                ctx->num_commit_graphs_after = ctx->num_commit_graphs_before + 1;

        if (flags != COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED &&
            flags != COMMIT_GRAPH_SPLIT_REPLACE) {
                while (g && (g->num_commits <= size_mult * num_commits ||
                            (max_commits && num_commits > max_commits))) {
                        if (g->odb != ctx->odb)
                                break;

                        num_commits += g->num_commits;
                        g = g->base_graph;

                        ctx->num_commit_graphs_after--;
                }
        }

        if (flags != COMMIT_GRAPH_SPLIT_REPLACE)
                ctx->new_base_graph = g;
        else if (ctx->num_commit_graphs_after != 1)
                BUG("split_graph_merge_strategy: num_commit_graphs_after "
                    "should be 1 with --split=replace");

        if (ctx->num_commit_graphs_after == 2) {
                char *old_graph_name = get_commit_graph_filename(g->odb);

                if (!strcmp(g->filename, old_graph_name) &&
                    g->odb != ctx->odb) {
                        ctx->num_commit_graphs_after = 1;
                        ctx->new_base_graph = NULL;
                }

                free(old_graph_name);
        }

        CALLOC_ARRAY(ctx->commit_graph_filenames_after, ctx->num_commit_graphs_after);
        CALLOC_ARRAY(ctx->commit_graph_hash_after, ctx->num_commit_graphs_after);

        for (i = 0; i < ctx->num_commit_graphs_after &&
                    i < ctx->num_commit_graphs_before; i++)
                ctx->commit_graph_filenames_after[i] = xstrdup(ctx->commit_graph_filenames_before[i]);

        i = ctx->num_commit_graphs_before - 1;
        g = ctx->r->objects->commit_graph;

        while (g) {
                if (i < ctx->num_commit_graphs_after)
                        ctx->commit_graph_hash_after[i] = xstrdup(oid_to_hex(&g->oid));

                /*
                 * If the topmost remaining layer has generation data chunk, the
                 * resultant layer also has generation data chunk.
                 */
                if (i == ctx->num_commit_graphs_after - 2)
                        ctx->write_generation_data = !!g->chunk_generation_data;

                i--;
                g = g->base_graph;
        }
}

static void merge_commit_graph(struct write_commit_graph_context *ctx,
                               struct commit_graph *g)
{
        uint32_t i;
        uint32_t offset = g->num_commits_in_base;

        ALLOC_GROW(ctx->commits.list, ctx->commits.nr + g->num_commits, ctx->commits.alloc);

        for (i = 0; i < g->num_commits; i++) {
                struct object_id oid;
                struct commit *result;

                display_progress(ctx->progress, i + 1);

                load_oid_from_graph(g, i + offset, &oid);

                /* only add commits if they still exist in the repo */
                result = lookup_commit_reference_gently(ctx->r, &oid, 1);

                if (result) {
                        ctx->commits.list[ctx->commits.nr] = result;
                        ctx->commits.nr++;
                }
        }
}

static int commit_compare(const void *_a, const void *_b)
{
        const struct commit *a = *(const struct commit **)_a;
        const struct commit *b = *(const struct commit **)_b;
        return oidcmp(&a->object.oid, &b->object.oid);
}

static void sort_and_scan_merged_commits(struct write_commit_graph_context *ctx)
{
        uint32_t i, dedup_i = 0;

        if (ctx->report_progress)
                ctx->progress = start_delayed_progress(
                                        _("Scanning merged commits"),
                                        ctx->commits.nr);

        QSORT(ctx->commits.list, ctx->commits.nr, commit_compare);

        ctx->num_extra_edges = 0;
        for (i = 0; i < ctx->commits.nr; i++) {
                display_progress(ctx->progress, i + 1);

                if (i && oideq(&ctx->commits.list[i - 1]->object.oid,
                          &ctx->commits.list[i]->object.oid)) {
                        /*
                         * Silently ignore duplicates. These were likely
                         * created due to a commit appearing in multiple
                         * layers of the chain, which is unexpected but
                         * not invalid. We should make sure there is a
                         * unique copy in the new layer.
                         */
                } else {
                        unsigned int num_parents;

                        ctx->commits.list[dedup_i] = ctx->commits.list[i];
                        dedup_i++;

                        num_parents = commit_list_count(ctx->commits.list[i]->parents);
                        if (num_parents > 2)
                                ctx->num_extra_edges += num_parents - 1;
                }
        }

        ctx->commits.nr = dedup_i;

        stop_progress(&ctx->progress);
}

static void merge_commit_graphs(struct write_commit_graph_context *ctx)
{
        struct commit_graph *g = ctx->r->objects->commit_graph;
        uint32_t current_graph_number = ctx->num_commit_graphs_before;

        while (g && current_graph_number >= ctx->num_commit_graphs_after) {
                current_graph_number--;

                if (ctx->report_progress)
                        ctx->progress = start_delayed_progress(_("Merging commit-graph"), 0);

                merge_commit_graph(ctx, g);
                stop_progress(&ctx->progress);

                g = g->base_graph;
        }

        if (g) {
                ctx->new_base_graph = g;
                ctx->new_num_commits_in_base = g->num_commits + g->num_commits_in_base;
        }

        if (ctx->new_base_graph)
                ctx->base_graph_name = xstrdup(ctx->new_base_graph->filename);

        sort_and_scan_merged_commits(ctx);
}

static void mark_commit_graphs(struct write_commit_graph_context *ctx)
{
        uint32_t i;
        time_t now = time(NULL);

        for (i = ctx->num_commit_graphs_after - 1; i < ctx->num_commit_graphs_before; i++) {
                struct stat st;
                struct utimbuf updated_time;

                if (stat(ctx->commit_graph_filenames_before[i], &st) < 0)
                        continue;

                updated_time.actime = st.st_atime;
                updated_time.modtime = now;
                utime(ctx->commit_graph_filenames_before[i], &updated_time);
        }
}

static void expire_commit_graphs(struct write_commit_graph_context *ctx)
{
        struct strbuf path = STRBUF_INIT;
        DIR *dir;
        struct dirent *de;
        size_t dirnamelen;
        timestamp_t expire_time = time(NULL);

        if (ctx->opts && ctx->opts->expire_time)
                expire_time = ctx->opts->expire_time;
        if (!ctx->split) {
                char *chain_file_name = get_commit_graph_chain_filename(ctx->odb);
                unlink(chain_file_name);
                free(chain_file_name);
                ctx->num_commit_graphs_after = 0;
        }

        strbuf_addstr(&path, ctx->odb->path);
        strbuf_addstr(&path, "/info/commit-graphs");
        dir = opendir(path.buf);

        if (!dir)
                goto out;

        strbuf_addch(&path, '/');
        dirnamelen = path.len;
        while ((de = readdir(dir)) != NULL) {
                struct stat st;
                uint32_t i, found = 0;

                strbuf_setlen(&path, dirnamelen);
                strbuf_addstr(&path, de->d_name);

                if (stat(path.buf, &st) < 0)
                        continue;

                if (st.st_mtime > expire_time)
                        continue;
                if (path.len < 6 || strcmp(path.buf + path.len - 6, ".graph"))
                        continue;

                for (i = 0; i < ctx->num_commit_graphs_after; i++) {
                        if (!strcmp(ctx->commit_graph_filenames_after[i],
                                    path.buf)) {
                                found = 1;
                                break;
                        }
                }

                if (!found)
                        unlink(path.buf);
        }

out:
        if(dir)
                closedir(dir);
        strbuf_release(&path);
}

int write_commit_graph(struct object_directory *odb,
                       const struct string_list *const pack_indexes,
                       struct oidset *commits,
                       enum commit_graph_write_flags flags,
                       const struct commit_graph_opts *opts)
{
        struct repository *r = the_repository;
        struct write_commit_graph_context *ctx;
        uint32_t i;
        int res = 0;
        int replace = 0;
        struct bloom_filter_settings bloom_settings = DEFAULT_BLOOM_FILTER_SETTINGS;
        struct topo_level_slab topo_levels;

        prepare_repo_settings(r);
        if (!r->settings.core_commit_graph) {
                warning(_("attempting to write a commit-graph, but 'core.commitGraph' is disabled"));
                return 0;
        }
        if (!commit_graph_compatible(r))
                return 0;

        CALLOC_ARRAY(ctx, 1);
        ctx->r = r;
        ctx->odb = odb;
        ctx->append = flags & COMMIT_GRAPH_WRITE_APPEND ? 1 : 0;
        ctx->report_progress = flags & COMMIT_GRAPH_WRITE_PROGRESS ? 1 : 0;
        ctx->split = flags & COMMIT_GRAPH_WRITE_SPLIT ? 1 : 0;
        ctx->opts = opts;
        ctx->total_bloom_filter_data_size = 0;
        ctx->write_generation_data = (get_configured_generation_version(r) == 2);
        ctx->num_generation_data_overflows = 0;

        bloom_settings.bits_per_entry = git_env_ulong("GIT_TEST_BLOOM_SETTINGS_BITS_PER_ENTRY",
                                                      bloom_settings.bits_per_entry);
        bloom_settings.num_hashes = git_env_ulong("GIT_TEST_BLOOM_SETTINGS_NUM_HASHES",
                                                  bloom_settings.num_hashes);
        bloom_settings.max_changed_paths = git_env_ulong("GIT_TEST_BLOOM_SETTINGS_MAX_CHANGED_PATHS",
                                                         bloom_settings.max_changed_paths);
        ctx->bloom_settings = &bloom_settings;

        init_topo_level_slab(&topo_levels);
        ctx->topo_levels = &topo_levels;

        prepare_commit_graph(ctx->r);
        if (ctx->r->objects->commit_graph) {
                struct commit_graph *g = ctx->r->objects->commit_graph;

                while (g) {
                        g->topo_levels = &topo_levels;
                        g = g->base_graph;
                }
        }

        if (flags & COMMIT_GRAPH_WRITE_BLOOM_FILTERS)
                ctx->changed_paths = 1;
        if (!(flags & COMMIT_GRAPH_NO_WRITE_BLOOM_FILTERS)) {
                struct commit_graph *g;

                g = ctx->r->objects->commit_graph;

                /* We have changed-paths already. Keep them in the next graph */
                if (g && g->chunk_bloom_data) {
                        ctx->changed_paths = 1;
                        ctx->bloom_settings = g->bloom_filter_settings;
                }
        }

        if (ctx->split) {
                struct commit_graph *g = ctx->r->objects->commit_graph;

                while (g) {
                        ctx->num_commit_graphs_before++;
                        g = g->base_graph;
                }

                if (ctx->num_commit_graphs_before) {
                        ALLOC_ARRAY(ctx->commit_graph_filenames_before, ctx->num_commit_graphs_before);
                        i = ctx->num_commit_graphs_before;
                        g = ctx->r->objects->commit_graph;

                        while (g) {
                                ctx->commit_graph_filenames_before[--i] = xstrdup(g->filename);
                                g = g->base_graph;
                        }
                }

                if (ctx->opts)
                        replace = ctx->opts->split_flags & COMMIT_GRAPH_SPLIT_REPLACE;
        }

        ctx->approx_nr_objects = repo_approximate_object_count(the_repository);

        if (ctx->append && ctx->r->objects->commit_graph) {
                struct commit_graph *g = ctx->r->objects->commit_graph;
                for (i = 0; i < g->num_commits; i++) {
                        struct object_id oid;
                        oidread(&oid, g->chunk_oid_lookup + g->hash_len * i);
                        oid_array_append(&ctx->oids, &oid);
                }
        }

        if (pack_indexes) {
                ctx->order_by_pack = 1;
                if ((res = fill_oids_from_packs(ctx, pack_indexes)))
                        goto cleanup;
        }

        if (commits) {
                if ((res = fill_oids_from_commits(ctx, commits)))
                        goto cleanup;
        }

        if (!pack_indexes && !commits) {
                ctx->order_by_pack = 1;
                fill_oids_from_all_packs(ctx);
        }

        close_reachable(ctx);

        copy_oids_to_commits(ctx);

        if (ctx->commits.nr >= GRAPH_EDGE_LAST_MASK) {
                error(_("too many commits to write graph"));
                res = -1;
                goto cleanup;
        }

        if (!ctx->commits.nr && !replace)
                goto cleanup;

        if (ctx->split) {
                split_graph_merge_strategy(ctx);

                if (!replace)
                        merge_commit_graphs(ctx);
        } else
                ctx->num_commit_graphs_after = 1;

        ctx->trust_generation_numbers = validate_mixed_generation_chain(ctx->r->objects->commit_graph);

        compute_topological_levels(ctx);
        if (ctx->write_generation_data)
                compute_generation_numbers(ctx);

        if (ctx->changed_paths)
                compute_bloom_filters(ctx);

        res = write_commit_graph_file(ctx);

        if (ctx->split)
                mark_commit_graphs(ctx);

        expire_commit_graphs(ctx);

cleanup:
        free(ctx->graph_name);
        free(ctx->commits.list);
        oid_array_clear(&ctx->oids);
        clear_topo_level_slab(&topo_levels);

        if (ctx->commit_graph_filenames_after) {
                for (i = 0; i < ctx->num_commit_graphs_after; i++) {
                        free(ctx->commit_graph_filenames_after[i]);
                        free(ctx->commit_graph_hash_after[i]);
                }

                for (i = 0; i < ctx->num_commit_graphs_before; i++)
                        free(ctx->commit_graph_filenames_before[i]);

                free(ctx->commit_graph_filenames_after);
                free(ctx->commit_graph_filenames_before);
                free(ctx->commit_graph_hash_after);
        }

        free(ctx);

        return res;
}

#define VERIFY_COMMIT_GRAPH_ERROR_HASH 2
static int verify_commit_graph_error;

__attribute__((format (printf, 1, 2)))
static void graph_report(const char *fmt, ...)
{
        va_list ap;

        verify_commit_graph_error = 1;
        va_start(ap, fmt);
        vfprintf(stderr, fmt, ap);
        fprintf(stderr, "\n");
        va_end(ap);
}

#define GENERATION_ZERO_EXISTS 1
#define GENERATION_NUMBER_EXISTS 2

static int commit_graph_checksum_valid(struct commit_graph *g)
{
        return hashfile_checksum_valid(g->data, g->data_len);
}

int verify_commit_graph(struct repository *r, struct commit_graph *g, int flags)
{
        uint32_t i, cur_fanout_pos = 0;
        struct object_id prev_oid, cur_oid;
        int generation_zero = 0;
        struct progress *progress = NULL;
        int local_error = 0;

        if (!g) {
                graph_report("no commit-graph file loaded");
                return 1;
        }

        verify_commit_graph_error = verify_commit_graph_lite(g);
        if (verify_commit_graph_error)
                return verify_commit_graph_error;

        if (!commit_graph_checksum_valid(g)) {
                graph_report(_("the commit-graph file has incorrect checksum and is likely corrupt"));
                verify_commit_graph_error = VERIFY_COMMIT_GRAPH_ERROR_HASH;
        }

        for (i = 0; i < g->num_commits; i++) {
                struct commit *graph_commit;

                oidread(&cur_oid, g->chunk_oid_lookup + g->hash_len * i);

                if (i && oidcmp(&prev_oid, &cur_oid) >= 0)
                        graph_report(_("commit-graph has incorrect OID order: %s then %s"),
                                     oid_to_hex(&prev_oid),
                                     oid_to_hex(&cur_oid));

                oidcpy(&prev_oid, &cur_oid);

                while (cur_oid.hash[0] > cur_fanout_pos) {
                        uint32_t fanout_value = get_be32(g->chunk_oid_fanout + cur_fanout_pos);

                        if (i != fanout_value)
                                graph_report(_("commit-graph has incorrect fanout value: fanout[%d] = %u != %u"),
                                             cur_fanout_pos, fanout_value, i);
                        cur_fanout_pos++;
                }

                graph_commit = lookup_commit(r, &cur_oid);
                if (!parse_commit_in_graph_one(r, g, graph_commit))
                        graph_report(_("failed to parse commit %s from commit-graph"),
                                     oid_to_hex(&cur_oid));
        }

        while (cur_fanout_pos < 256) {
                uint32_t fanout_value = get_be32(g->chunk_oid_fanout + cur_fanout_pos);

                if (g->num_commits != fanout_value)
                        graph_report(_("commit-graph has incorrect fanout value: fanout[%d] = %u != %u"),
                                     cur_fanout_pos, fanout_value, i);

                cur_fanout_pos++;
        }

        if (verify_commit_graph_error & ~VERIFY_COMMIT_GRAPH_ERROR_HASH)
                return verify_commit_graph_error;

        if (flags & COMMIT_GRAPH_WRITE_PROGRESS)
                progress = start_progress(_("Verifying commits in commit graph"),
                                        g->num_commits);

        for (i = 0; i < g->num_commits; i++) {
                struct commit *graph_commit, *odb_commit;
                struct commit_list *graph_parents, *odb_parents;
                timestamp_t max_generation = 0;
                timestamp_t generation;

                display_progress(progress, i + 1);
                oidread(&cur_oid, g->chunk_oid_lookup + g->hash_len * i);

                graph_commit = lookup_commit(r, &cur_oid);
                odb_commit = (struct commit *)create_object(r, &cur_oid, alloc_commit_node(r));
                if (repo_parse_commit_internal(r, odb_commit, 0, 0)) {
                        graph_report(_("failed to parse commit %s from object database for commit-graph"),
                                     oid_to_hex(&cur_oid));
                        continue;
                }

                if (!oideq(&get_commit_tree_in_graph_one(r, g, graph_commit)->object.oid,
                           get_commit_tree_oid(odb_commit)))
                        graph_report(_("root tree OID for commit %s in commit-graph is %s != %s"),
                                     oid_to_hex(&cur_oid),
                                     oid_to_hex(get_commit_tree_oid(graph_commit)),
                                     oid_to_hex(get_commit_tree_oid(odb_commit)));

                graph_parents = graph_commit->parents;
                odb_parents = odb_commit->parents;

                while (graph_parents) {
                        if (!odb_parents) {
                                graph_report(_("commit-graph parent list for commit %s is too long"),
                                             oid_to_hex(&cur_oid));
                                break;
                        }

                        /* parse parent in case it is in a base graph */
                        parse_commit_in_graph_one(r, g, graph_parents->item);

                        if (!oideq(&graph_parents->item->object.oid, &odb_parents->item->object.oid))
                                graph_report(_("commit-graph parent for %s is %s != %s"),
                                             oid_to_hex(&cur_oid),
                                             oid_to_hex(&graph_parents->item->object.oid),
                                             oid_to_hex(&odb_parents->item->object.oid));

                        generation = commit_graph_generation(graph_parents->item);
                        if (generation > max_generation)
                                max_generation = generation;

                        graph_parents = graph_parents->next;
                        odb_parents = odb_parents->next;
                }

                if (odb_parents)
                        graph_report(_("commit-graph parent list for commit %s terminates early"),
                                     oid_to_hex(&cur_oid));

                if (!commit_graph_generation(graph_commit)) {
                        if (generation_zero == GENERATION_NUMBER_EXISTS)
                                graph_report(_("commit-graph has generation number zero for commit %s, but non-zero elsewhere"),
                                             oid_to_hex(&cur_oid));
                        generation_zero = GENERATION_ZERO_EXISTS;
                } else if (generation_zero == GENERATION_ZERO_EXISTS)
                        graph_report(_("commit-graph has non-zero generation number for commit %s, but zero elsewhere"),
                                     oid_to_hex(&cur_oid));

                if (generation_zero == GENERATION_ZERO_EXISTS)
                        continue;

                /*
                 * If we are using topological level and one of our parents has
                 * generation GENERATION_NUMBER_V1_MAX, then our generation is
                 * also GENERATION_NUMBER_V1_MAX. Decrement to avoid extra logic
                 * in the following condition.
                 */
                if (!g->read_generation_data && max_generation == GENERATION_NUMBER_V1_MAX)
                        max_generation--;

                generation = commit_graph_generation(graph_commit);
                if (generation < max_generation + 1)
                        graph_report(_("commit-graph generation for commit %s is %"PRItime" < %"PRItime),
                                     oid_to_hex(&cur_oid),
                                     generation,
                                     max_generation + 1);

                if (graph_commit->date != odb_commit->date)
                        graph_report(_("commit date for commit %s in commit-graph is %"PRItime" != %"PRItime),
                                     oid_to_hex(&cur_oid),
                                     graph_commit->date,
                                     odb_commit->date);
        }
        stop_progress(&progress);

        local_error = verify_commit_graph_error;

        if (!(flags & COMMIT_GRAPH_VERIFY_SHALLOW) && g->base_graph)
                local_error |= verify_commit_graph(r, g->base_graph, flags);

        return local_error;
}

void free_commit_graph(struct commit_graph *g)
{
        if (!g)
                return;
        if (g->data) {
                munmap((void *)g->data, g->data_len);
                g->data = NULL;
        }
        free(g->filename);
        free(g->bloom_filter_settings);
        free(g);
}

void disable_commit_graph(struct repository *r)
{
        r->commit_graph_disabled = 1;
}