git/commit-graph.c

#include "cache.h"
#include "config.h"
#include "dir.h"
#include "git-compat-util.h"
#include "lockfile.h"
#include "pack.h"
#include "packfile.h"
#include "commit.h"
#include "object.h"
#include "refs.h"
#include "revision.h"
#include "sha1-lookup.h"
#include "commit-graph.h"
#include "object-store.h"
#include "alloc.h"
#include "hashmap.h"
#include "replace-object.h"
#include "progress.h"

#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_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_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)

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

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

static uint8_t oid_version(void)
{
	return 1;
}

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

	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)
		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(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);
	ret = parse_commit_graph(graph_map, fd, graph_size);

	if (ret)
		ret->odb = odb;
	else {
		munmap(graph_map, graph_size);
		close(fd);
	}

	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(void *graph_map, int fd,
					size_t graph_size)
{
	const unsigned char *data, *chunk_lookup;
	uint32_t i;
	struct commit_graph *graph;
	uint64_t last_chunk_offset;
	uint32_t last_chunk_id;
	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;
	}

	graph = alloc_commit_graph();

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

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

		if (data + graph_size - chunk_lookup <
		    GRAPH_CHUNKLOOKUP_WIDTH) {
			error(_("commit-graph chunk lookup table entry missing; file may be incomplete"));
			free(graph);
			return NULL;
		}

		chunk_id = get_be32(chunk_lookup + 0);
		chunk_offset = get_be64(chunk_lookup + 4);

		chunk_lookup += GRAPH_CHUNKLOOKUP_WIDTH;

		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);
			free(graph);
			return NULL;
		}

		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;
			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;
		}

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

		if (last_chunk_id == GRAPH_CHUNKID_OIDLOOKUP)
		{
			graph->num_commits = (chunk_offset - last_chunk_offset)
					     / graph->hash_len;
		}

		last_chunk_id = chunk_id;
		last_chunk_offset = chunk_offset;
	}

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

	if (verify_commit_graph_lite(graph)) {
		free(graph);
		return NULL;
	}

	return graph;
}

static struct commit_graph *load_commit_graph_one(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(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(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_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(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;
}

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);

	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;

	/*
	 * This must come before the "already attempted?" check below, because
	 * we want to disable even an already-loaded graph file.
	 */
	if (r->commit_graph_disabled)
		return 0;

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

	if (git_env_bool(GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD, 0))
		die("dying as requested by the '%s' variable on commit-graph load!",
		    GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD);

	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;
}

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

	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, 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"));