git/commit-graph.c

#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"

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_EXTRAEDGES 0x45444745 /* "EDGE" */
#define GRAPH_CHUNKID_BLOOMINDEXES 0x42494458 /* "BIDX" */
#define GRAPH_CHUNKID_BLOOMDATA 0x42444154 /* "BDAT" */
#define GRAPH_CHUNKID_BASE 0x42415345 /* "BASE" */
#define MAX_NUM_CHUNKS 7

#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_CHUNKLOOKUP_WIDTH 12
#define GRAPH_MIN_SIZE (GRAPH_HEADER_SIZE + 4 * GRAPH_CHUNKLOOKUP_WIDTH \
			+ GRAPH_FANOUT_SIZE + the_hash_algo->rawsz)

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

/* 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);

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;
}

uint32_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;
}

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;

	uint32_t generation_a = commit_graph_generation(a);
	uint32_t generation_b = commit_graph_generation(b);
	/* 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 uint8_t oid_version(void)
{
	switch (hash_algo_by_ptr(the_hash_algo)) {
	case GIT_HASH_SHA1:
		return 1;
	case GIT_HASH_SHA256:
		return 2;
	default:
		die(_("invalid hash version"));
	}
}

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);
	ret = parse_commit_graph(r, 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;
}

struct commit_graph *parse_commit_graph(struct repository *r,
					void *graph_map, size_t graph_size)
{
	const unsigned char *data, *chunk_lookup;
	uint32_t i;
	struct commit_graph *graph;
	uint64_t next_chunk_offset;
	uint32_t graph_signature;
	unsigned char graph_version, hash_version;

	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()) {
		error(_("commit-graph hash version %X does not match version %X"),
		      hash_version, oid_version());
		return NULL;
	}

	prepare_repo_settings(r);

	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) * GRAPH_CHUNKLOOKUP_WIDTH +
			 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;
	}

	chunk_lookup = data + 8;
	next_chunk_offset = get_be64(chunk_lookup + 4);
	for (i = 0; i < graph->num_chunks; i++) {
		uint32_t chunk_id;
		uint64_t chunk_offset = next_chunk_offset;
		int chunk_repeated = 0;

		chunk_id = get_be32(chunk_lookup + 0);

		chunk_lookup += GRAPH_CHUNKLOOKUP_WIDTH;
		next_chunk_offset = get_be64(chunk_lookup + 4);

		if (chunk_offset > graph_size - the_hash_algo->rawsz) {
			error(_("commit-graph improper chunk offset %08x%08x"), (uint32_t)(chunk_offset >> 32),
			      (uint32_t)chunk_offset);
			goto free_and_return;
		}

		switch (chunk_id) {
		case GRAPH_CHUNKID_OIDFANOUT:
			if (graph->chunk_oid_fanout)
				chunk_repeated = 1;
			else
				graph->chunk_oid_fanout = (uint32_t*)(data + chunk_offset);
			break;

		case GRAPH_CHUNKID_OIDLOOKUP:
			if (graph->chunk_oid_lookup)
				chunk_repeated = 1;
			else {
				graph->chunk_oid_lookup = data + chunk_offset;
				graph->num_commits = (next_chunk_offset - chunk_offset)
						     / graph->hash_len;
			}
			break;

		case GRAPH_CHUNKID_DATA:
			if (graph->chunk_commit_data)
				chunk_repeated = 1;
			else
				graph->chunk_commit_data = data + chunk_offset;
			break;

		case GRAPH_CHUNKID_EXTRAEDGES:
			if (graph->chunk_extra_edges)
				chunk_repeated = 1;
			else
				graph->chunk_extra_edges = data + chunk_offset;
			break;

		case GRAPH_CHUNKID_BASE:
			if (graph->chunk_base_graphs)
				chunk_repeated = 1;
			else
				graph->chunk_base_graphs = data + chunk_offset;
			break;

		case GRAPH_CHUNKID_BLOOMINDEXES:
			if (graph->chunk_bloom_indexes)
				chunk_repeated = 1;
			else if (r->settings.commit_graph_read_changed_paths)
				graph->chunk_bloom_indexes = data + chunk_offset;
			break;

		case GRAPH_CHUNKID_BLOOMDATA:
			if (graph->chunk_bloom_data)
				chunk_repeated = 1;
			else if (r->settings.commit_graph_read_changed_paths) {
				uint32_t hash_version;
				graph->chunk_bloom_data = data + chunk_offset;
				hash_version = get_be32(data + chunk_offset);

				if (hash_version != 1)
					break;

				graph->bloom_filter_settings = xmalloc(sizeof(struct bloom_filter_settings));
				graph->bloom_filter_settings->hash_version = hash_version;
				graph->bloom_filter_settings->num_hashes = get_be32(data + chunk_offset + 4);
				graph->bloom_filter_settings->bits_per_entry = get_be32(data + chunk_offset + 8);
				graph->bloom_filter_settings->max_changed_paths = DEFAULT_BLOOM_MAX_CHANGES;
			}
			break;
		}

		if (chunk_repeated) {
			error(_("commit-graph chunk id %08x appears multiple times"), chunk_id);
			goto free_and_return;
		}
	}

	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);
	}

	hashcpy(graph->oid.hash, graph->data + graph->data_len - graph->hash_len);

	if (verify_commit_graph_lite(graph))
		goto free_and_return;

	return graph;

free_and_return:
	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 ||
	    stat_res ||
	    st.st_size <= the_hash_algo->hexsz)
		return NULL;

	count = st.st_size / (the_hash_algo->hexsz + 1);
	oids = xcalloc(count, sizeof(struct object_id));

	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;
}