Adding upstream version 1:2.39.2.upstream/1%2.39.2upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2657 insertions, 0 deletions

diff --git a/commit-graph.c b/commit-graph.c
new file mode 100644
index 0000000..a7d8755
--- /dev/null
+++ b/commit-graph.c
@@ -0,0 +1,2657 @@
+#include "git-compat-util.h"
+#include "config.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-store.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 "chunk-format.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)
+		return GENERATION_NUMBER_INFINITY;
+	else if (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 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);
+}
+
+static void compute_topological_levels(struct write_commit_graph_context *ctx)
+{
+	int i;
+	struct commit_list *list = NULL;
+
+	if (ctx->report_progress)
+		ctx->progress = start_delayed_progress(
+					_("Computing commit graph topological levels"),
+					ctx->commits.nr);
+	for (i = 0; i < ctx->commits.nr; i++) {
+		struct commit *c = ctx->commits.list[i];
+		uint32_t level;
+
+		repo_parse_commit(ctx->r, c);
+		level = *topo_level_slab_at(ctx->topo_levels, c);
+
+		display_progress(ctx->progress, i + 1);
+		if (level != GENERATION_NUMBER_ZERO)
+			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_level = 0;
+
+			for (parent = current->parents; parent; parent = parent->next) {
+				repo_parse_commit(ctx->r, parent->item);
+				level = *topo_level_slab_at(ctx->topo_levels, parent->item);
+
+				if (level == GENERATION_NUMBER_ZERO) {
+					all_parents_computed = 0;
+					commit_list_insert(parent->item, &list);
+					break;
+				}
+
+				if (level > max_level)
+					max_level = level;
+			}
+
+			if (all_parents_computed) {
+				pop_commit(&list);
+
+				if (max_level > GENERATION_NUMBER_V1_MAX - 1)
+					max_level = GENERATION_NUMBER_V1_MAX - 1;
+				*topo_level_slab_at(ctx->topo_levels, current) = max_level + 1;
+			}
+		}
+	}
+	stop_progress(&ctx->progress);
+}
+
+static void compute_generation_numbers(struct write_commit_graph_context *ctx)
+{
+	int i;
+	struct commit_list *list = NULL;
+
+	if (ctx->report_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;
+		}
+	}
+
+	for (i = 0; i < ctx->commits.nr; i++) {
+		struct commit *c = ctx->commits.list[i];
+		timestamp_t corrected_commit_date;
+
+		repo_parse_commit(ctx->r, c);
+		corrected_commit_date = commit_graph_data_at(c)->generation;
+
+		display_progress(ctx->progress, i + 1);
+		if (corrected_commit_date != GENERATION_NUMBER_ZERO)
+			continue;
+
+		commit_list_insert(c, &list);
+		while (list) {
+			struct commit *current = list->item;
+			struct commit_list *parent;
+			int all_parents_computed = 1;
+			timestamp_t max_corrected_commit_date = 0;
+
+			for (parent = current->parents; parent; parent = parent->next) {
+				repo_parse_commit(ctx->r, parent->item);
+				corrected_commit_date = commit_graph_data_at(parent->item)->generation;
+
+				if (corrected_commit_date == GENERATION_NUMBER_ZERO) {
+					all_parents_computed = 0;
+					commit_list_insert(parent->item, &list);
+					break;
+				}
+
+				if (corrected_commit_date > max_corrected_commit_date)
+					max_corrected_commit_date = corrected_commit_date;
+			}
+
+			if (all_parents_computed) {
+				pop_commit(&list);
+
+				if (current->date && current->date > max_corrected_commit_date)
+					max_corrected_commit_date = current->date - 1;
+				commit_graph_data_at(current)->generation = max_corrected_commit_date + 1;
+			}
+		}
+	}
+
+	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 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);
+
+	ALLOC_ARRAY(sorted_commits, ctx->commits.nr);
+	COPY_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 = approximate_object_count();
+
+	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 (parse_commit_internal(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;
+}