/src/git/commit-graph.c

Source
#define DISABLE_SIGN_COMPARE_WARNINGS

#include "git-compat-util.h"
#include "config.h"
#include "csum-file.h"
#include "environment.h"
#include "gettext.h"
#include "hex.h"
#include "lockfile.h"
#include "packfile.h"
#include "commit.h"
#include "object.h"
#include "refs.h"
#include "hash-lookup.h"
#include "commit-graph.h"
#include "odb.h"
#include "oid-array.h"
#include "path.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"

void git_test_write_commit_graph_or_die(struct odb_source *source)
{
  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(source, 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_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 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 size_t graph_data_width(const struct git_hash_algo *algop)
{
  return algop->rawsz + 16;
}

static size_t graph_min_size(const struct git_hash_algo *algop)
{
  return GRAPH_HEADER_SIZE + 4 * CHUNK_TOC_ENTRY_SIZE + GRAPH_FANOUT_SIZE + algop->rawsz;
}

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

  if (!data || data->graph_pos == COMMIT_NOT_FROM_GRAPH)
    return GENERATION_NUMBER_INFINITY;
  return data->generation;
}

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 odb_source *source)
{
  return xstrfmt("%s/info/commit-graph", source->path);
}

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

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

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

  return g;
}

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

  if (replace_refs_enabled(r)) {
    prepare_replace_object(r);
    if (oidmap_get_size(&r->objects->replace_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 odb_source *source,
             int fd, struct stat *st)
{
  void *graph_map;
  size_t graph_size;
  struct commit_graph *ret;

  graph_size = xsize_t(st->st_size);

  if (graph_size < graph_min_size(source->odb->repo->hash_algo)) {
    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);

  ret = parse_commit_graph(source->odb->repo, graph_map, graph_size);
  if (ret)
    ret->odb_source = source;
  else
    munmap(graph_map, graph_size);

  return ret;
}

static int graph_read_oid_fanout(const unsigned char *chunk_start,
         size_t chunk_size, void *data)
{
  struct commit_graph *g = data;
  int i;

  if (chunk_size != 256 * sizeof(uint32_t))
    return error(_("commit-graph oid fanout chunk is wrong size"));
  g->chunk_oid_fanout = (const uint32_t *)chunk_start;
  g->num_commits = ntohl(g->chunk_oid_fanout[255]);

  for (i = 0; i < 255; i++) {
    uint32_t oid_fanout1 = ntohl(g->chunk_oid_fanout[i]);
    uint32_t oid_fanout2 = ntohl(g->chunk_oid_fanout[i + 1]);

    if (oid_fanout1 > oid_fanout2) {
      error(_("commit-graph fanout values out of order"));
      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;
  if (chunk_size / g->hash_algo->rawsz != g->num_commits)
    return error(_("commit-graph OID lookup chunk is the wrong size"));
  return 0;
}

static int graph_read_commit_data(const unsigned char *chunk_start,
          size_t chunk_size, void *data)
{
  struct commit_graph *g = data;
  if (chunk_size / graph_data_width(g->hash_algo) != g->num_commits)
    return error(_("commit-graph commit data chunk is wrong size"));
  g->chunk_commit_data = chunk_start;
  return 0;
}

static int graph_read_generation_data(const unsigned char *chunk_start,
              size_t chunk_size, void *data)
{
  struct commit_graph *g = data;
  if (chunk_size / sizeof(uint32_t) != g->num_commits)
    return error(_("commit-graph generations chunk is wrong size"));
  g->chunk_generation_data = chunk_start;
  return 0;
}

static int graph_read_bloom_index(const unsigned char *chunk_start,
          size_t chunk_size, void *data)
{
  struct commit_graph *g = data;
  if (chunk_size / 4 != g->num_commits) {
    warning(_("commit-graph changed-path index chunk is too small"));
    return -1;
  }
  g->chunk_bloom_indexes = chunk_start;
  return 0;
}

static int graph_read_bloom_data(const unsigned char *chunk_start,
          size_t chunk_size, void *data)
{
  struct commit_graph *g = data;

  if (chunk_size < BLOOMDATA_CHUNK_HEADER_SIZE) {
    warning(_("ignoring too-small changed-path chunk"
      " (%"PRIuMAX" < %"PRIuMAX") in commit-graph file"),
      (uintmax_t)chunk_size,
      (uintmax_t)BLOOMDATA_CHUNK_HEADER_SIZE);
    return -1;
  }

  g->chunk_bloom_data = chunk_start;
  g->chunk_bloom_data_size = chunk_size;

  g->bloom_filter_settings = xmalloc(sizeof(struct bloom_filter_settings));
  g->bloom_filter_settings->hash_version = get_be32(chunk_start);
  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 repository *r,
          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(r->hash_algo))
    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(r->hash_algo)) {
    error(_("commit-graph hash version %X does not match version %X"),
          hash_version, oid_version(r->hash_algo));
    return NULL;
  }

  graph = alloc_commit_graph();

  graph->hash_algo = r->hash_algo;
  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 + r->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, 1))
    goto free_and_return;

  if (read_chunk(cf, GRAPH_CHUNKID_OIDFANOUT, graph_read_oid_fanout, graph)) {
    error(_("commit-graph required OID fanout chunk missing or corrupted"));
    goto free_and_return;
  }
  if (read_chunk(cf, GRAPH_CHUNKID_OIDLOOKUP, graph_read_oid_lookup, graph)) {
    error(_("commit-graph required OID lookup chunk missing or corrupted"));
    goto free_and_return;
  }
  if (read_chunk(cf, GRAPH_CHUNKID_DATA, graph_read_commit_data, graph)) {
    error(_("commit-graph required commit data chunk missing or corrupted"));
    goto free_and_return;
  }

  pair_chunk(cf, GRAPH_CHUNKID_EXTRAEDGES, &graph->chunk_extra_edges,
       &graph->chunk_extra_edges_size);
  pair_chunk(cf, GRAPH_CHUNKID_BASE, &graph->chunk_base_graphs,
       &graph->chunk_base_graphs_size);

  prepare_repo_settings(r);

  if (r->settings.commit_graph_generation_version >= 2) {
    read_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA,
         graph_read_generation_data, graph);
    pair_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA_OVERFLOW,
         &graph->chunk_generation_data_overflow,
         &graph->chunk_generation_data_overflow_size);

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

  if (r->settings.commit_graph_changed_paths_version) {
    read_chunk(cf, GRAPH_CHUNKID_BLOOMINDEXES,
         graph_read_bloom_index, graph);
    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_algo->rawsz,
    r->hash_algo);

  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 odb_source *source,
              const char *graph_file)
{
  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(source, fd, &st);
  if (g)
    g->filename = xstrdup(graph_file);

  return g;
}

static struct commit_graph *load_commit_graph_v1(struct odb_source *source)
{
  char *graph_name = get_commit_graph_filename(source);
  struct commit_graph *g = load_commit_graph_one(source, graph_name);
  free(graph_name);

  return g;
}

/*
 * 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;
}

static void validate_mixed_bloom_settings(struct commit_graph *g)
{
  struct bloom_filter_settings *settings = NULL;
  for (; g; g = g->base_graph) {
    if (!g->bloom_filter_settings)
      continue;
    if (!settings) {
      settings = g->bloom_filter_settings;
      continue;
    }

    if (g->bloom_filter_settings->bits_per_entry != settings->bits_per_entry ||
        g->bloom_filter_settings->num_hashes != settings->num_hashes ||
        g->bloom_filter_settings->hash_version != settings->hash_version) {
      g->chunk_bloom_indexes = NULL;
      g->chunk_bloom_data = NULL;
      FREE_AND_NULL(g->bloom_filter_settings);

      warning(_("disabling Bloom filters for commit-graph "
          "layer '%s' due to incompatible settings"),
        oid_to_hex(&g->oid));
    }
  }
}

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;
  }

  if (g->chunk_base_graphs_size / g->hash_algo->rawsz < n) {
    warning(_("commit-graph base graphs chunk is too small"));
    return 0;
  }

  while (n) {
    n--;

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

    cur_g = cur_g->base_graph;
  }

  if (chain) {
    if (unsigned_add_overflows(chain->num_commits,
             chain->num_commits_in_base)) {
      warning(_("commit count in base graph too high: %"PRIuMAX),
        (uintmax_t)chain->num_commits_in_base);
      return 0;
    }
    g->num_commits_in_base = chain->num_commits + chain->num_commits_in_base;
  }

  g->base_graph = chain;

  return 1;
}

int open_commit_graph_chain(const char *chain_file,
          int *fd, struct stat *st,
          const struct git_hash_algo *hash_algo)
{
  *fd = git_open(chain_file);
  if (*fd < 0)
    return 0;
  if (fstat(*fd, st)) {
    close(*fd);
    return 0;
  }
  if (st->st_size < hash_algo->hexsz) {
    close(*fd);
    if (!st->st_size) {
      /* treat empty files the same as missing */
      errno = ENOENT;
    } else {
      warning(_("commit-graph chain file too small"));
      errno = EINVAL;
    }
    return 0;
  }
  return 1;
}

struct commit_graph *load_commit_graph_chain_fd_st(struct object_database *odb,
               int fd, struct stat *st,
               int *incomplete_chain)
{
  struct commit_graph *graph_chain = NULL;
  struct strbuf line = STRBUF_INIT;
  struct object_id *oids;
  int i = 0, valid = 1, count;
  FILE *fp = xfdopen(fd, "r");

  count = st->st_size / (odb->repo->hash_algo->hexsz + 1);
  CALLOC_ARRAY(oids, count);

  odb_prepare_alternates(odb);

  for (i = 0; i < count; i++) {
    struct odb_source *source;

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

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

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

      free(graph_name);

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

        break;
      }
    }

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

  validate_mixed_generation_chain(graph_chain);
  validate_mixed_bloom_settings(graph_chain);

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

  *incomplete_chain = !valid;
  return graph_chain;
}

static struct commit_graph *load_commit_graph_chain(struct odb_source *source)
{
  char *chain_file = get_commit_graph_chain_filename(source);
  struct stat st;
  int fd;
  struct commit_graph *g = NULL;

  if (open_commit_graph_chain(chain_file, &fd, &st, source->odb->repo->hash_algo)) {
    int incomplete;
    /* ownership of fd is taken over by load function */
    g = load_commit_graph_chain_fd_st(source->odb, fd, &st, &incomplete);
  }

  free(chain_file);
  return g;
}

struct commit_graph *read_commit_graph_one(struct odb_source *source)
{
  struct commit_graph *g = load_commit_graph_v1(source);

  if (!g)
    g = load_commit_graph_chain(source);

  return g;
}

/*
 * 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 struct commit_graph *prepare_commit_graph(struct repository *r)
{
  struct odb_source *source;

  /*
   * 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 NULL;

  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 NULL;

  if (!commit_graph_compatible(r))
    return NULL;

  odb_prepare_alternates(r->objects);
  for (source = r->objects->sources; source; source = source->next) {
    r->objects->commit_graph = read_commit_graph_one(source);
    if (r->objects->commit_graph)
      break;
  }

  return r->objects->commit_graph;
}

int generation_numbers_enabled(struct repository *r)
{
  uint32_t first_generation;
  struct commit_graph *g;

  g = prepare_commit_graph(r);
  if (!g || !g->num_commits)
         return 0;

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

  return !!first_generation;
}

int corrected_commit_dates_enabled(struct repository *r)
{
  struct commit_graph *g;

  g = prepare_commit_graph(r);
  if (!g || !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;

  if (!prepare_commit_graph(r))
         return NULL;

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

void close_commit_graph(struct object_database *o)
{
  if (!o->commit_graph)
    return;

  clear_commit_graph_data_slab(&commit_graph_data_slab);
  deinit_bloom_filters();
  free_commit_graph(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_algo->rawsz, 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 + st_mult(g->hash_algo->rawsz, lex_index),
    g->hash_algo);
}

static struct commit_list **insert_parent_or_die(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(g->odb_source->odb->repo, &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 + st_mult(graph_data_width(g->hash_algo), lex_index);

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

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

  if (g->read_generation_data) {
    offset = (timestamp_t)get_be32(g->chunk_generation_data + st_mult(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;
      if (g->chunk_generation_data_overflow_size / sizeof(uint64_t) <= offset_pos)
        die(_("commit-graph overflow generation data is too small"));
      graph_data->generation = item->date +
        get_be64(g->chunk_generation_data_overflow + sizeof(uint64_t) * offset_pos);
    } else
      graph_data->generation = item->date + offset;
  } else
    graph_data->generation = get_be32(commit_data + g->hash_algo->rawsz + 8) >> 2;

  if (g->topo_levels)
    *topo_level_slab_at(g->topo_levels, item) = get_be32(commit_data + g->hash_algo->rawsz + 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 commit *item,
        struct commit_graph *g, uint32_t pos)
{
  uint32_t edge_value;
  uint32_t parent_data_pos;
  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 + st_mult(g->hash_algo->rawsz + 16, lex_index);

  item->object.parsed = 1;

  set_commit_tree(item, NULL);

  pptr = &item->parents;

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

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

  parent_data_pos = edge_value & GRAPH_EDGE_LAST_MASK;
  do {
    if (g->chunk_extra_edges_size / sizeof(uint32_t) <= parent_data_pos) {
      error(_("commit-graph extra-edges pointer out of bounds"));
      free_commit_list(item->parents);
      item->parents = NULL;
      item->object.parsed = 0;
      return 0;
    }
    edge_value = get_be32(g->chunk_extra_edges +
              sizeof(uint32_t) * parent_data_pos);
    pptr = insert_parent_or_die(g,
              edge_value & GRAPH_EDGE_LAST_MASK,
              pptr);
    parent_data_pos++;
  } 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);
  }
}

struct commit_graph *repo_find_commit_pos_in_graph(struct repository *r,
               struct commit *c,
               uint32_t *pos)
{
  struct commit_graph *g = prepare_commit_graph(r);
  if (!g)
    return NULL;
  if (!find_commit_pos_in_graph(c, g, pos))
    return NULL;
  return g;
}

struct commit *lookup_commit_in_graph(struct repository *repo, const struct object_id *id)
{
  static int commit_graph_paranoia = -1;
  struct commit_graph *g;
  struct commit *commit;
  uint32_t pos;

  if (commit_graph_paranoia == -1)
    commit_graph_paranoia = git_env_bool(GIT_COMMIT_GRAPH_PARANOIA, 0);

  g = prepare_commit_graph(repo);
  if (!g)
    return NULL;
  if (!search_commit_pos_in_graph(id, g, &pos))
    return NULL;
  if (commit_graph_paranoia && !odb_has_object(repo->objects, id, 0))
    return NULL;

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

  if (!fill_commit_in_graph(commit, g, pos))
    return NULL;

  return commit;
}

static int parse_commit_in_graph_one(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(item, g, pos);

  return 0;
}

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

  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;

  g = prepare_commit_graph(r);
  if (!g)
    return 0;
  return parse_commit_in_graph_one(g, item);
}

void load_commit_graph_info(struct repository *r, struct commit *item)
{
  struct commit_graph *g;
  uint32_t pos;

  g = repo_find_commit_pos_in_graph(r, item, &pos);
  if (g)
    fill_commit_graph_info(item, g, pos);
}

static struct tree *load_tree_for_commit(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 +
      st_mult(graph_data_width(g->hash_algo),
        graph_pos - g->num_commits_in_base);

  oidread(&oid, commit_data, g->hash_algo);
  set_commit_tree(c, lookup_tree(g->odb_source->odb->repo, &oid));

  return c->maybe_tree;
}

static struct tree *get_commit_tree_in_graph_one(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(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->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 odb_source *odb_source;
  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;
  int count_bloom_filter_upgraded;
};

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, f->algop->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, ctx->r->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(
          ctx->r,
          _("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(
          ctx->r,
          _("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(
          ctx->r,
          _("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);

    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(
          ctx->r,
          _("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 UNUSED)
{
  return commit_graph_data_at(c)->generation;
}

static void set_generation_v2(struct commit *c, timestamp_t t,
            void *data UNUSED)
{
  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,
  };

  if (ctx->report_progress)
    info.progress = ctx->progress
            = start_delayed_progress(
          ctx->r,
          _("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 UNUSED)
{
  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);
  trace2_data_intmax("commit-graph", ctx->r, "filter-upgraded",
         ctx->count_bloom_filter_upgraded);
}

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(
      ctx->r,
      _("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_UPGRADED) {
      ctx->count_bloom_filter_upgraded++;
    } 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 repository *repo;
  struct oidset *commits;
  struct progress *progress;
};

static int add_ref_to_set(const struct reference *ref, void *cb_data)
{
  const struct object_id *maybe_peeled = ref->oid;
  struct object_id peeled;
  struct refs_cb_data *data = (struct refs_cb_data *)cb_data;

  if (!reference_get_peeled_oid(data->repo, ref, &peeled))
    maybe_peeled = &peeled;
  if (odb_read_object_info(data->repo->objects, maybe_peeled, NULL) == OBJ_COMMIT)
    oidset_insert(data->commits, maybe_peeled);

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

  return 0;
}

int write_commit_graph_reachable(struct odb_source *source,
         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.repo = source->odb->repo;
  data.commits = &commits;

  if (flags & COMMIT_GRAPH_WRITE_PROGRESS)
    data.progress = start_delayed_progress(
      source->odb->repo,
      _("Collecting referenced commits"), 0);

  refs_for_each_ref(get_main_ref_store(source->odb->repo), add_ref_to_set,
        &data);

  stop_progress(&data.progress);

  result = write_commit_graph(source, 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_source->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(ctx->r,
                   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(ctx->r, 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);
      close_pack(p);
      free(p);
      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(
      ctx->r,
      _("Finding commits for commit graph among packed objects"),
      ctx->approx_nr_objects);
  for_each_packed_object(ctx->r, 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(
      ctx->r,
      _("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, g->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;
  struct hashfile *f;
  struct tempfile *graph_layer; /* when ctx->split is non-zero */
  struct lock_file lk = LOCK_INIT;
  const unsigned hashsz = ctx->r->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_source->path);
    ctx->graph_name = strbuf_detach(&tmp_file, NULL);
  } else {
    ctx->graph_name = get_commit_graph_filename(ctx->odb_source);
  }

  if (safe_create_leading_directories(ctx->r, 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_source);

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

    graph_layer = mks_tempfile_m(ctx->graph_name, 0444);
    if (!graph_layer) {
      error(_("unable to create temporary graph layer"));
      return -1;
    }

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

    f = hashfd(ctx->r->hash_algo,
         get_tempfile_fd(graph_layer), get_tempfile_path(graph_layer));
  } else {
    hold_lock_file_for_update_mode(&lk, ctx->graph_name,
                 LOCK_DIE_ON_ERROR, 0444);
    f = hashfd(ctx->r->hash_algo,
         get_lock_file_fd(&lk), 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, st_mult(hashsz, ctx->commits.nr),
      write_graph_chunk_oids);
  add_chunk(cf, GRAPH_CHUNKID_DATA, st_mult(hashsz + 16, ctx->commits.nr),
      write_graph_chunk_data);

  if (ctx->write_generation_data)
    add_chunk(cf, GRAPH_CHUNKID_GENERATION_DATA,
        st_mult(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,
        st_mult(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,
        st_mult(4, ctx->num_extra_edges),
        write_graph_chunk_extra_edges);
  if (ctx->changed_paths) {
    add_chunk(cf, GRAPH_CHUNKID_BLOOMINDEXES,
        st_mult(sizeof(uint32_t), ctx->commits.nr),
        write_graph_chunk_bloom_indexes);
    add_chunk(cf, GRAPH_CHUNKID_BLOOMDATA,
        st_add(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,
        st_mult(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(ctx->r->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(
      ctx->r,
      progress_title.buf,
      st_mult(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_source, 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;

    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_source);
      unlink(graph_name);
      free(graph_name);
    }

    free(ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 1]);
    ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 1] =
      xstrdup(hash_to_hex_algop(file_hash, ctx->r->hash_algo));
    final_graph_name = get_split_graph_filename(ctx->odb_source,
          ctx->commit_graph_hash_after[ctx->num_commit_graphs_after - 1]);
    free(ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 1]);
    ctx->commit_graph_filenames_after[ctx->num_commit_graphs_after - 1] = final_graph_name;

    result = rename_tempfile(&graph_layer, 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 *graph_to_merge)
{
  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 = graph_to_merge;
  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 <= st_mult(size_mult, num_commits) ||
          (max_commits && num_commits > max_commits))) {
      if (g->odb_source != ctx->odb_source)
        break;

      if (unsigned_add_overflows(num_commits, g->num_commits))
        die(_("cannot merge graphs with %"PRIuMAX", "
              "%"PRIuMAX" commits"),
            (uintmax_t)num_commits,
            (uintmax_t)g->num_commits);
      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_source);

    if (!strcmp(g->filename, old_graph_name) &&
        g->odb_source != ctx->odb_source) {
      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 = graph_to_merge;

  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;

  if (unsigned_add_overflows(ctx->commits.nr, g->num_commits))
    die(_("cannot merge graph %s, too many commits: %"PRIuMAX),
        oid_to_hex(&g->oid),
        (uintmax_t)st_add(ctx->commits.nr, g->num_commits));

  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(
          ctx->r,
          _("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)
{
  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(ctx->r,
                     _("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_source);
    unlink(chain_file_name);
    free(chain_file_name);
    ctx->num_commit_graphs_after = 0;
  }

  strbuf_addstr(&path, ctx->odb_source->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 odb_source *source,
           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 = source->odb->repo;
  struct write_commit_graph_context ctx = {
    .r = r,
    .odb_source = source,
    .append = flags & COMMIT_GRAPH_WRITE_APPEND ? 1 : 0,
    .report_progress = flags & COMMIT_GRAPH_WRITE_PROGRESS ? 1 : 0,
    .split = flags & COMMIT_GRAPH_WRITE_SPLIT ? 1 : 0,
    .opts = opts,
    .total_bloom_filter_data_size = 0,
    .write_generation_data = (get_configured_generation_version(r) == 2),
    .num_generation_data_overflows = 0,
  };
  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;
  struct commit_graph *g;

  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;
  if (r->settings.commit_graph_changed_paths_version < -1
      || r->settings.commit_graph_changed_paths_version > 2) {
    warning(_("attempting to write a commit-graph, but "
        "'commitGraph.changedPathsVersion' (%d) is not supported"),
      r->settings.commit_graph_changed_paths_version);
    return 0;
  }

  bloom_settings.hash_version = r->settings.commit_graph_changed_paths_version;
  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;

  g = prepare_commit_graph(ctx.r);
  for (struct commit_graph *chain = g; chain; chain = chain->base_graph)
    g->topo_levels = &topo_levels;

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

      /* don't propagate the hash_version unless unspecified */
      if (bloom_settings.hash_version == -1)
        bloom_settings.hash_version = g->bloom_filter_settings->hash_version;
      bloom_settings.bits_per_entry = g->bloom_filter_settings->bits_per_entry;
      bloom_settings.num_hashes = g->bloom_filter_settings->num_hashes;
      bloom_settings.max_changed_paths = g->bloom_filter_settings->max_changed_paths;
    }
  }

  bloom_settings.hash_version = bloom_settings.hash_version == 2 ? 2 : 1;

  if (ctx.split) {
    for (struct commit_graph *chain = g; chain; chain = chain->base_graph)
      ctx.num_commit_graphs_before++;

    if (ctx.num_commit_graphs_before) {
      ALLOC_ARRAY(ctx.commit_graph_filenames_before, ctx.num_commit_graphs_before);
      i = ctx.num_commit_graphs_before;

      for (struct commit_graph *chain = g; chain; chain = chain->base_graph)
        ctx.commit_graph_filenames_before[--i] = xstrdup(chain->filename);
    }

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

  ctx.approx_nr_objects = repo_approximate_object_count(r);

  if (ctx.append && g) {
    for (i = 0; i < g->num_commits; i++) {
      struct object_id oid;
      oidread(&oid, g->chunk_oid_lookup + st_mult(g->hash_algo->rawsz, i),
        r->hash_algo);
      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, g);

    if (!replace)
      merge_commit_graphs(&ctx, g);
  } else {
    ctx.num_commit_graphs_after = 1;
  }

  ctx.trust_generation_numbers = validate_mixed_generation_chain(g);

  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.changed_paths)
    deinit_bloom_filters();

  if (ctx.split)
    mark_commit_graphs(&ctx);

  expire_commit_graphs(&ctx);

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

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

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

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

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

  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);
}

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

static int verify_one_commit_graph(struct commit_graph *g,
           struct progress *progress,
           uint64_t *seen)
{
  struct repository *r = g->odb_source->odb->repo;
  uint32_t i, cur_fanout_pos = 0;
  struct object_id prev_oid, cur_oid;
  struct commit *seen_gen_zero = NULL;
  struct commit *seen_gen_non_zero = NULL;

  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 + st_mult(g->hash_algo->rawsz, i),
      g->hash_algo);

    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(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;

  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, ++(*seen));
    oidread(&cur_oid, g->chunk_oid_lookup + st_mult(g->hash_algo->rawsz, i),
      g->hash_algo);

    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(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(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_from_graph(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_from_graph(graph_commit))
      seen_gen_non_zero = graph_commit;
    else
      seen_gen_zero = graph_commit;

    if (seen_gen_zero)
      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);
  }

  if (seen_gen_zero && seen_gen_non_zero)
    graph_report(_("commit-graph has both zero and non-zero "
             "generations (e.g., commits '%s' and '%s')"),
           oid_to_hex(&seen_gen_zero->object.oid),
           oid_to_hex(&seen_gen_non_zero->object.oid));

  return verify_commit_graph_error;
}

int verify_commit_graph(struct commit_graph *g, int flags)
{
  struct progress *progress = NULL;
  int local_error = 0;
  uint64_t seen = 0;

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

  if (flags & COMMIT_GRAPH_WRITE_PROGRESS) {
    uint64_t total = g->num_commits;
    if (!(flags & COMMIT_GRAPH_VERIFY_SHALLOW))
      total += g->num_commits_in_base;

    progress = start_progress(g->odb_source->odb->repo,
            _("Verifying commits in commit graph"),
            total);
  }

  for (; g; g = g->base_graph) {
    local_error |= verify_one_commit_graph(g, progress, &seen);
    if (flags & COMMIT_GRAPH_VERIFY_SHALLOW)
      break;
  }

  stop_progress(&progress);

  return local_error;
}

void free_commit_graph(struct commit_graph *g)
{
  while (g) {
    struct commit_graph *next = g->base_graph;

    if (g->data)
      munmap((void *)g->data, g->data_len);
    free(g->filename);
    free(g->bloom_filter_settings);
    free(g);

    g = next;
  }
}

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

Coverage Report

Created: 2025-12-31 07:02