commit-graph.c

   1 #include "cache.h"
   2 #include "config.h"
   3 #include "git-compat-util.h"
   4 #include "lockfile.h"
   5 #include "pack.h"
   6 #include "packfile.h"
   7 #include "commit.h"
   8 #include "object.h"
   9 #include "revision.h"
  10 #include "sha1-lookup.h"
  11 #include "commit-graph.h"
  12
  13 #define GRAPH_SIGNATURE 0x43475048 /* "CGPH" */
  14 #define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
  15 #define GRAPH_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
  16 #define GRAPH_CHUNKID_DATA 0x43444154 /* "CDAT" */
  17 #define GRAPH_CHUNKID_LARGEEDGES 0x45444745 /* "EDGE" */
  18
  19 #define GRAPH_DATA_WIDTH 36
  20
  21 #define GRAPH_VERSION_1 0x1
  22 #define GRAPH_VERSION GRAPH_VERSION_1
  23
  24 #define GRAPH_OID_VERSION_SHA1 1
  25 #define GRAPH_OID_LEN_SHA1 GIT_SHA1_RAWSZ
  26 #define GRAPH_OID_VERSION GRAPH_OID_VERSION_SHA1
  27 #define GRAPH_OID_LEN GRAPH_OID_LEN_SHA1
  28
  29 #define GRAPH_OCTOPUS_EDGES_NEEDED 0x80000000
  30 #define GRAPH_PARENT_MISSING 0x7fffffff
  31 #define GRAPH_EDGE_LAST_MASK 0x7fffffff
  32 #define GRAPH_PARENT_NONE 0x70000000
  33
  34 #define GRAPH_LAST_EDGE 0x80000000
  35
  36 #define GRAPH_FANOUT_SIZE (4 * 256)
  37 #define GRAPH_CHUNKLOOKUP_WIDTH 12
  38 #define GRAPH_MIN_SIZE (5 * GRAPH_CHUNKLOOKUP_WIDTH + GRAPH_FANOUT_SIZE + \
  39                         GRAPH_OID_LEN + 8)
  40
  41 char *get_commit_graph_filename(const char *obj_dir)
  42 {
  43         return xstrfmt("%s/info/commit-graph", obj_dir);
  44 }
  45
  46 static struct commit_graph *alloc_commit_graph(void)
  47 {
  48         struct commit_graph *g = xcalloc(1, sizeof(*g));
  49         g->graph_fd = -1;
  50
  51         return g;
  52 }
  53
  54 struct commit_graph *load_commit_graph_one(const char *graph_file)
  55 {
  56         void *graph_map;
  57         const unsigned char *data, *chunk_lookup;
  58         size_t graph_size;
  59         struct stat st;
  60         uint32_t i;
  61         struct commit_graph *graph;
  62         int fd = git_open(graph_file);
  63         uint64_t last_chunk_offset;
  64         uint32_t last_chunk_id;
  65         uint32_t graph_signature;
  66         unsigned char graph_version, hash_version;
  67
  68         if (fd < 0)
  69                 return NULL;
  70         if (fstat(fd, &st)) {
  71                 close(fd);
  72                 return NULL;
  73         }
  74         graph_size = xsize_t(st.st_size);
  75
  76         if (graph_size < GRAPH_MIN_SIZE) {
  77                 close(fd);
  78                 die("graph file %s is too small", graph_file);
  79         }
  80         graph_map = xmmap(NULL, graph_size, PROT_READ, MAP_PRIVATE, fd, 0);
  81         data = (const unsigned char *)graph_map;
  82
  83         graph_signature = get_be32(data);
  84         if (graph_signature != GRAPH_SIGNATURE) {
  85                 error("graph signature %X does not match signature %X",
  86                       graph_signature, GRAPH_SIGNATURE);
  87                 goto cleanup_fail;
  88         }
  89
  90         graph_version = *(unsigned char*)(data + 4);
  91         if (graph_version != GRAPH_VERSION) {
  92                 error("graph version %X does not match version %X",
  93                       graph_version, GRAPH_VERSION);
  94                 goto cleanup_fail;
  95         }
  96
  97         hash_version = *(unsigned char*)(data + 5);
  98         if (hash_version != GRAPH_OID_VERSION) {
  99                 error("hash version %X does not match version %X",
 100                       hash_version, GRAPH_OID_VERSION);
 101                 goto cleanup_fail;
 102         }
 103
 104         graph = alloc_commit_graph();
 105
 106         graph->hash_len = GRAPH_OID_LEN;
 107         graph->num_chunks = *(unsigned char*)(data + 6);
 108         graph->graph_fd = fd;
 109         graph->data = graph_map;
 110         graph->data_len = graph_size;
 111
 112         last_chunk_id = 0;
 113         last_chunk_offset = 8;
 114         chunk_lookup = data + 8;
 115         for (i = 0; i < graph->num_chunks; i++) {
 116                 uint32_t chunk_id = get_be32(chunk_lookup + 0);
 117                 uint64_t chunk_offset = get_be64(chunk_lookup + 4);
 118                 int chunk_repeated = 0;
 119
 120                 chunk_lookup += GRAPH_CHUNKLOOKUP_WIDTH;
 121
 122                 if (chunk_offset > graph_size - GIT_MAX_RAWSZ) {
 123                         error("improper chunk offset %08x%08x", (uint32_t)(chunk_offset >> 32),
 124                               (uint32_t)chunk_offset);
 125                         goto cleanup_fail;
 126                 }
 127
 128                 switch (chunk_id) {
 129                 case GRAPH_CHUNKID_OIDFANOUT:
 130                         if (graph->chunk_oid_fanout)
 131                                 chunk_repeated = 1;
 132                         else
 133                                 graph->chunk_oid_fanout = (uint32_t*)(data + chunk_offset);
 134                         break;
 135
 136                 case GRAPH_CHUNKID_OIDLOOKUP:
 137                         if (graph->chunk_oid_lookup)
 138                                 chunk_repeated = 1;
 139                         else
 140                                 graph->chunk_oid_lookup = data + chunk_offset;
 141                         break;
 142
 143                 case GRAPH_CHUNKID_DATA:
 144                         if (graph->chunk_commit_data)
 145                                 chunk_repeated = 1;
 146                         else
 147                                 graph->chunk_commit_data = data + chunk_offset;
 148                         break;
 149
 150                 case GRAPH_CHUNKID_LARGEEDGES:
 151                         if (graph->chunk_large_edges)
 152                                 chunk_repeated = 1;
 153                         else
 154                                 graph->chunk_large_edges = data + chunk_offset;
 155                         break;
 156                 }
 157
 158                 if (chunk_repeated) {
 159                         error("chunk id %08x appears multiple times", chunk_id);
 160                         goto cleanup_fail;
 161                 }
 162
 163                 if (last_chunk_id == GRAPH_CHUNKID_OIDLOOKUP)
 164                 {
 165                         graph->num_commits = (chunk_offset - last_chunk_offset)
 166                                              / graph->hash_len;
 167                 }
 168
 169                 last_chunk_id = chunk_id;
 170                 last_chunk_offset = chunk_offset;
 171         }
 172
 173         return graph;
 174
 175 cleanup_fail:
 176         munmap(graph_map, graph_size);
 177         close(fd);
 178         exit(1);
 179 }
 180
 181 /* global storage */
 182 static struct commit_graph *commit_graph = NULL;
 183
 184 static void prepare_commit_graph_one(const char *obj_dir)
 185 {
 186         char *graph_name;
 187
 188         if (commit_graph)
 189                 return;
 190
 191         graph_name = get_commit_graph_filename(obj_dir);
 192         commit_graph = load_commit_graph_one(graph_name);
 193
 194         FREE_AND_NULL(graph_name);
 195 }
 196
 197 static int prepare_commit_graph_run_once = 0;
 198 static void prepare_commit_graph(void)
 199 {
 200         struct alternate_object_database *alt;
 201         char *obj_dir;
 202
 203         if (prepare_commit_graph_run_once)
 204                 return;
 205         prepare_commit_graph_run_once = 1;
 206
 207         obj_dir = get_object_directory();
 208         prepare_commit_graph_one(obj_dir);
 209         prepare_alt_odb();
 210         for (alt = alt_odb_list; !commit_graph && alt; alt = alt->next)
 211                 prepare_commit_graph_one(alt->path);
 212 }
 213
 214 static void close_commit_graph(void)
 215 {
 216         if (!commit_graph)
 217                 return;
 218
 219         if (commit_graph->graph_fd >= 0) {
 220                 munmap((void *)commit_graph->data, commit_graph->data_len);
 221                 commit_graph->data = NULL;
 222                 close(commit_graph->graph_fd);
 223         }
 224
 225         FREE_AND_NULL(commit_graph);
 226 }
 227
 228 static int bsearch_graph(struct commit_graph *g, struct object_id *oid, uint32_t *pos)
 229 {
 230         return bsearch_hash(oid->hash, g->chunk_oid_fanout,
 231                             g->chunk_oid_lookup, g->hash_len, pos);
 232 }
 233
 234 static struct commit_list **insert_parent_or_die(struct commit_graph *g,
 235                                                  uint64_t pos,
 236                                                  struct commit_list **pptr)
 237 {
 238         struct commit *c;
 239         struct object_id oid;
 240         hashcpy(oid.hash, g->chunk_oid_lookup + g->hash_len * pos);
 241         c = lookup_commit(&oid);
 242         if (!c)
 243                 die("could not find commit %s", oid_to_hex(&oid));
 244         c->graph_pos = pos;
 245         return &commit_list_insert(c, pptr)->next;
 246 }
 247
 248 static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uint32_t pos)
 249 {
 250         uint32_t edge_value;
 251         uint32_t *parent_data_ptr;
 252         uint64_t date_low, date_high;
 253         struct commit_list **pptr;
 254         const unsigned char *commit_data = g->chunk_commit_data + (g->hash_len + 16) * pos;
 255
 256         item->object.parsed = 1;
 257         item->graph_pos = pos;
 258
 259         item->maybe_tree = NULL;
 260
 261         date_high = get_be32(commit_data + g->hash_len + 8) & 0x3;
 262         date_low = get_be32(commit_data + g->hash_len + 12);
 263         item->date = (timestamp_t)((date_high << 32) | date_low);
 264
 265         pptr = &item->parents;
 266
 267         edge_value = get_be32(commit_data + g->hash_len);
 268         if (edge_value == GRAPH_PARENT_NONE)
 269                 return 1;
 270         pptr = insert_parent_or_die(g, edge_value, pptr);
 271
 272         edge_value = get_be32(commit_data + g->hash_len + 4);
 273         if (edge_value == GRAPH_PARENT_NONE)
 274                 return 1;
 275         if (!(edge_value & GRAPH_OCTOPUS_EDGES_NEEDED)) {
 276                 pptr = insert_parent_or_die(g, edge_value, pptr);
 277                 return 1;
 278         }
 279
 280         parent_data_ptr = (uint32_t*)(g->chunk_large_edges +
 281                           4 * (uint64_t)(edge_value & GRAPH_EDGE_LAST_MASK));
 282         do {
 283                 edge_value = get_be32(parent_data_ptr);
 284                 pptr = insert_parent_or_die(g,
 285                                             edge_value & GRAPH_EDGE_LAST_MASK,
 286                                             pptr);
 287                 parent_data_ptr++;
 288         } while (!(edge_value & GRAPH_LAST_EDGE));
 289
 290         return 1;
 291 }
 292
 293 int parse_commit_in_graph(struct commit *item)
 294 {
 295         if (!core_commit_graph)
 296                 return 0;
 297         if (item->object.parsed)
 298                 return 1;
 299
 300         prepare_commit_graph();
 301         if (commit_graph) {
 302                 uint32_t pos;
 303                 int found;
 304                 if (item->graph_pos != COMMIT_NOT_FROM_GRAPH) {
 305                         pos = item->graph_pos;
 306                         found = 1;
 307                 } else {
 308                         found = bsearch_graph(commit_graph, &(item->object.oid), &pos);
 309                 }
 310
 311                 if (found)
 312                         return fill_commit_in_graph(item, commit_graph, pos);
 313         }
 314
 315         return 0;
 316 }
 317
 318 static struct tree *load_tree_for_commit(struct commit_graph *g, struct commit *c)
 319 {
 320         struct object_id oid;
 321         const unsigned char *commit_data = g->chunk_commit_data +
 322                                            GRAPH_DATA_WIDTH * (c->graph_pos);
 323
 324         hashcpy(oid.hash, commit_data);
 325         c->maybe_tree = lookup_tree(&oid);
 326
 327         return c->maybe_tree;
 328 }
 329
 330 struct tree *get_commit_tree_in_graph(const struct commit *c)
 331 {
 332         if (c->maybe_tree)
 333                 return c->maybe_tree;
 334         if (c->graph_pos == COMMIT_NOT_FROM_GRAPH)
 335                 BUG("get_commit_tree_in_graph called from non-commit-graph commit");
 336
 337         return load_tree_for_commit(commit_graph, (struct commit *)c);
 338 }
 339
 340 static void write_graph_chunk_fanout(struct hashfile *f,
 341                                      struct commit **commits,
 342                                      int nr_commits)
 343 {
 344         int i, count = 0;
 345         struct commit **list = commits;
 346
 347         /*
 348          * Write the first-level table (the list is sorted,
 349          * but we use a 256-entry lookup to be able to avoid
 350          * having to do eight extra binary search iterations).
 351          */
 352         for (i = 0; i < 256; i++) {
 353                 while (count < nr_commits) {
 354                         if ((*list)->object.oid.hash[0] != i)
 355                                 break;
 356                         count++;
 357                         list++;
 358                 }
 359
 360                 hashwrite_be32(f, count);
 361         }
 362 }
 363
 364 static void write_graph_chunk_oids(struct hashfile *f, int hash_len,
 365                                    struct commit **commits, int nr_commits)
 366 {
 367         struct commit **list = commits;
 368         int count;
 369         for (count = 0; count < nr_commits; count++, list++)
 370                 hashwrite(f, (*list)->object.oid.hash, (int)hash_len);
 371 }
 372
 373 static const unsigned char *commit_to_sha1(size_t index, void *table)
 374 {
 375         struct commit **commits = table;
 376         return commits[index]->object.oid.hash;
 377 }
 378
 379 static void write_graph_chunk_data(struct hashfile *f, int hash_len,
 380                                    struct commit **commits, int nr_commits)
 381 {
 382         struct commit **list = commits;
 383         struct commit **last = commits + nr_commits;
 384         uint32_t num_extra_edges = 0;
 385
 386         while (list < last) {
 387                 struct commit_list *parent;
 388                 int edge_value;
 389                 uint32_t packedDate[2];
 390
 391                 parse_commit(*list);
 392                 hashwrite(f, get_commit_tree_oid(*list)->hash, hash_len);
 393
 394                 parent = (*list)->parents;
 395
 396                 if (!parent)
 397                         edge_value = GRAPH_PARENT_NONE;
 398                 else {
 399                         edge_value = sha1_pos(parent->item->object.oid.hash,
 400                                               commits,
 401                                               nr_commits,
 402                                               commit_to_sha1);
 403
 404                         if (edge_value < 0)
 405                                 edge_value = GRAPH_PARENT_MISSING;
 406                 }
 407
 408                 hashwrite_be32(f, edge_value);
 409
 410                 if (parent)
 411                         parent = parent->next;
 412
 413                 if (!parent)
 414                         edge_value = GRAPH_PARENT_NONE;
 415                 else if (parent->next)
 416                         edge_value = GRAPH_OCTOPUS_EDGES_NEEDED | num_extra_edges;
 417                 else {
 418                         edge_value = sha1_pos(parent->item->object.oid.hash,
 419                                               commits,
 420                                               nr_commits,
 421                                               commit_to_sha1);
 422                         if (edge_value < 0)
 423                                 edge_value = GRAPH_PARENT_MISSING;
 424                 }
 425
 426                 hashwrite_be32(f, edge_value);
 427
 428                 if (edge_value & GRAPH_OCTOPUS_EDGES_NEEDED) {
 429                         do {
 430                                 num_extra_edges++;
 431                                 parent = parent->next;
 432                         } while (parent);
 433                 }
 434
 435                 if (sizeof((*list)->date) > 4)
 436                         packedDate[0] = htonl(((*list)->date >> 32) & 0x3);
 437                 else
 438                         packedDate[0] = 0;
 439
 440                 packedDate[1] = htonl((*list)->date);
 441                 hashwrite(f, packedDate, 8);
 442
 443                 list++;
 444         }
 445 }
 446
 447 static void write_graph_chunk_large_edges(struct hashfile *f,
 448                                           struct commit **commits,
 449                                           int nr_commits)
 450 {
 451         struct commit **list = commits;
 452         struct commit **last = commits + nr_commits;
 453         struct commit_list *parent;
 454
 455         while (list < last) {
 456                 int num_parents = 0;
 457                 for (parent = (*list)->parents; num_parents < 3 && parent;
 458                      parent = parent->next)
 459                         num_parents++;
 460
 461                 if (num_parents <= 2) {
 462                         list++;
 463                         continue;
 464                 }
 465
 466                 /* Since num_parents > 2, this initializer is safe. */
 467                 for (parent = (*list)->parents->next; parent; parent = parent->next) {
 468                         int edge_value = sha1_pos(parent->item->object.oid.hash,
 469                                                   commits,
 470                                                   nr_commits,
 471                                                   commit_to_sha1);
 472
 473                         if (edge_value < 0)
 474                                 edge_value = GRAPH_PARENT_MISSING;
 475                         else if (!parent->next)
 476                                 edge_value |= GRAPH_LAST_EDGE;
 477
 478                         hashwrite_be32(f, edge_value);
 479                 }
 480
 481                 list++;
 482         }
 483 }
 484
 485 static int commit_compare(const void *_a, const void *_b)
 486 {
 487         const struct object_id *a = (const struct object_id *)_a;
 488         const struct object_id *b = (const struct object_id *)_b;
 489         return oidcmp(a, b);
 490 }
 491
 492 struct packed_commit_list {
 493         struct commit **list;
 494         int nr;
 495         int alloc;
 496 };
 497
 498 struct packed_oid_list {
 499         struct object_id *list;
 500         int nr;
 501         int alloc;
 502 };
 503
 504 static int add_packed_commits(const struct object_id *oid,
 505                               struct packed_git *pack,
 506                               uint32_t pos,
 507                               void *data)
 508 {
 509         struct packed_oid_list *list = (struct packed_oid_list*)data;
 510         enum object_type type;
 511         off_t offset = nth_packed_object_offset(pack, pos);
 512         struct object_info oi = OBJECT_INFO_INIT;
 513
 514         oi.typep = &type;
 515         if (packed_object_info(pack, offset, &oi) < 0)
 516                 die("unable to get type of object %s", oid_to_hex(oid));
 517
 518         if (type != OBJ_COMMIT)
 519                 return 0;
 520
 521         ALLOC_GROW(list->list, list->nr + 1, list->alloc);
 522         oidcpy(&(list->list[list->nr]), oid);
 523         list->nr++;
 524
 525         return 0;
 526 }
 527
 528 static void add_missing_parents(struct packed_oid_list *oids, struct commit *commit)
 529 {
 530         struct commit_list *parent;
 531         for (parent = commit->parents; parent; parent = parent->next) {
 532                 if (!(parent->item->object.flags & UNINTERESTING)) {
 533                         ALLOC_GROW(oids->list, oids->nr + 1, oids->alloc);
 534                         oidcpy(&oids->list[oids->nr], &(parent->item->object.oid));
 535                         oids->nr++;
 536                         parent->item->object.flags |= UNINTERESTING;
 537                 }
 538         }
 539 }
 540
 541 static void close_reachable(struct packed_oid_list *oids)
 542 {
 543         int i;
 544         struct commit *commit;
 545
 546         for (i = 0; i < oids->nr; i++) {
 547                 commit = lookup_commit(&oids->list[i]);
 548                 if (commit)
 549                         commit->object.flags |= UNINTERESTING;
 550         }
 551
 552         /*
 553          * As this loop runs, oids->nr may grow, but not more
 554          * than the number of missing commits in the reachable
 555          * closure.
 556          */
 557         for (i = 0; i < oids->nr; i++) {
 558                 commit = lookup_commit(&oids->list[i]);
 559
 560                 if (commit && !parse_commit(commit))
 561                         add_missing_parents(oids, commit);
 562         }
 563
 564         for (i = 0; i < oids->nr; i++) {
 565                 commit = lookup_commit(&oids->list[i]);
 566
 567                 if (commit)
 568                         commit->object.flags &= ~UNINTERESTING;
 569         }
 570 }
 571
 572 void write_commit_graph(const char *obj_dir,
 573                         const char **pack_indexes,
 574                         int nr_packs,
 575                         const char **commit_hex,
 576                         int nr_commits,
 577                         int append)
 578 {
 579         struct packed_oid_list oids;
 580         struct packed_commit_list commits;
 581         struct hashfile *f;
 582         uint32_t i, count_distinct = 0;
 583         char *graph_name;
 584         int fd;
 585         struct lock_file lk = LOCK_INIT;
 586         uint32_t chunk_ids[5];
 587         uint64_t chunk_offsets[5];
 588         int num_chunks;
 589         int num_extra_edges;
 590         struct commit_list *parent;
 591
 592         oids.nr = 0;
 593         oids.alloc = approximate_object_count() / 4;
 594
 595         if (append) {
 596                 prepare_commit_graph_one(obj_dir);
 597                 if (commit_graph)
 598                         oids.alloc += commit_graph->num_commits;
 599         }
 600
 601         if (oids.alloc < 1024)
 602                 oids.alloc = 1024;
 603         ALLOC_ARRAY(oids.list, oids.alloc);
 604
 605         if (append && commit_graph) {
 606                 for (i = 0; i < commit_graph->num_commits; i++) {
 607                         const unsigned char *hash = commit_graph->chunk_oid_lookup +
 608                                 commit_graph->hash_len * i;
 609                         hashcpy(oids.list[oids.nr++].hash, hash);
 610                 }
 611         }
 612
 613         if (pack_indexes) {
 614                 struct strbuf packname = STRBUF_INIT;
 615                 int dirlen;
 616                 strbuf_addf(&packname, "%s/pack/", obj_dir);
 617                 dirlen = packname.len;
 618                 for (i = 0; i < nr_packs; i++) {
 619                         struct packed_git *p;
 620                         strbuf_setlen(&packname, dirlen);
 621                         strbuf_addstr(&packname, pack_indexes[i]);
 622                         p = add_packed_git(packname.buf, packname.len, 1);
 623                         if (!p)
 624                                 die("error adding pack %s", packname.buf);
 625                         if (open_pack_index(p))
 626                                 die("error opening index for %s", packname.buf);
 627                         for_each_object_in_pack(p, add_packed_commits, &oids);
 628                         close_pack(p);
 629                 }
 630                 strbuf_release(&packname);
 631         }
 632
 633         if (commit_hex) {
 634                 for (i = 0; i < nr_commits; i++) {
 635                         const char *end;
 636                         struct object_id oid;
 637                         struct commit *result;
 638
 639                         if (commit_hex[i] && parse_oid_hex(commit_hex[i], &oid, &end))
 640                                 continue;
 641
 642                         result = lookup_commit_reference_gently(&oid, 1);
 643
 644                         if (result) {
 645                                 ALLOC_GROW(oids.list, oids.nr + 1, oids.alloc);
 646                                 oidcpy(&oids.list[oids.nr], &(result->object.oid));
 647                                 oids.nr++;
 648                         }
 649                 }
 650         }
 651
 652         if (!pack_indexes && !commit_hex)
 653                 for_each_packed_object(add_packed_commits, &oids, 0);
 654
 655         close_reachable(&oids);
 656
 657         QSORT(oids.list, oids.nr, commit_compare);
 658
 659         count_distinct = 1;
 660         for (i = 1; i < oids.nr; i++) {
 661                 if (oidcmp(&oids.list[i-1], &oids.list[i]))
 662                         count_distinct++;
 663         }
 664
 665         if (count_distinct >= GRAPH_PARENT_MISSING)
 666                 die(_("the commit graph format cannot write %d commits"), count_distinct);
 667
 668         commits.nr = 0;
 669         commits.alloc = count_distinct;
 670         ALLOC_ARRAY(commits.list, commits.alloc);
 671
 672         num_extra_edges = 0;
 673         for (i = 0; i < oids.nr; i++) {
 674                 int num_parents = 0;
 675                 if (i > 0 && !oidcmp(&oids.list[i-1], &oids.list[i]))
 676                         continue;
 677
 678                 commits.list[commits.nr] = lookup_commit(&oids.list[i]);
 679                 parse_commit(commits.list[commits.nr]);
 680
 681                 for (parent = commits.list[commits.nr]->parents;
 682                      parent; parent = parent->next)
 683                         num_parents++;
 684
 685                 if (num_parents > 2)
 686                         num_extra_edges += num_parents - 1;
 687
 688                 commits.nr++;
 689         }
 690         num_chunks = num_extra_edges ? 4 : 3;
 691
 692         if (commits.nr >= GRAPH_PARENT_MISSING)
 693                 die(_("too many commits to write graph"));
 694
 695         graph_name = get_commit_graph_filename(obj_dir);
 696         fd = hold_lock_file_for_update(&lk, graph_name, 0);
 697
 698         if (fd < 0) {
 699                 struct strbuf folder = STRBUF_INIT;
 700                 strbuf_addstr(&folder, graph_name);
 701                 strbuf_setlen(&folder, strrchr(folder.buf, '/') - folder.buf);
 702
 703                 if (mkdir(folder.buf, 0777) < 0)
 704                         die_errno(_("cannot mkdir %s"), folder.buf);
 705                 strbuf_release(&folder);
 706
 707                 fd = hold_lock_file_for_update(&lk, graph_name, LOCK_DIE_ON_ERROR);
 708
 709                 if (fd < 0)
 710                         die_errno("unable to create '%s'", graph_name);
 711         }
 712
 713         f = hashfd(lk.tempfile->fd, lk.tempfile->filename.buf);
 714
 715         hashwrite_be32(f, GRAPH_SIGNATURE);
 716
 717         hashwrite_u8(f, GRAPH_VERSION);
 718         hashwrite_u8(f, GRAPH_OID_VERSION);
 719         hashwrite_u8(f, num_chunks);
 720         hashwrite_u8(f, 0); /* unused padding byte */
 721
 722         chunk_ids[0] = GRAPH_CHUNKID_OIDFANOUT;
 723         chunk_ids[1] = GRAPH_CHUNKID_OIDLOOKUP;
 724         chunk_ids[2] = GRAPH_CHUNKID_DATA;
 725         if (num_extra_edges)
 726                 chunk_ids[3] = GRAPH_CHUNKID_LARGEEDGES;
 727         else
 728                 chunk_ids[3] = 0;
 729         chunk_ids[4] = 0;
 730
 731         chunk_offsets[0] = 8 + (num_chunks + 1) * GRAPH_CHUNKLOOKUP_WIDTH;
 732         chunk_offsets[1] = chunk_offsets[0] + GRAPH_FANOUT_SIZE;
 733         chunk_offsets[2] = chunk_offsets[1] + GRAPH_OID_LEN * commits.nr;
 734         chunk_offsets[3] = chunk_offsets[2] + (GRAPH_OID_LEN + 16) * commits.nr;
 735         chunk_offsets[4] = chunk_offsets[3] + 4 * num_extra_edges;
 736
 737         for (i = 0; i <= num_chunks; i++) {
 738                 uint32_t chunk_write[3];
 739
 740                 chunk_write[0] = htonl(chunk_ids[i]);
 741                 chunk_write[1] = htonl(chunk_offsets[i] >> 32);
 742                 chunk_write[2] = htonl(chunk_offsets[i] & 0xffffffff);
 743                 hashwrite(f, chunk_write, 12);
 744         }
 745
 746         write_graph_chunk_fanout(f, commits.list, commits.nr);
 747         write_graph_chunk_oids(f, GRAPH_OID_LEN, commits.list, commits.nr);
 748         write_graph_chunk_data(f, GRAPH_OID_LEN, commits.list, commits.nr);
 749         write_graph_chunk_large_edges(f, commits.list, commits.nr);
 750
 751         close_commit_graph();
 752         finalize_hashfile(f, NULL, CSUM_HASH_IN_STREAM | CSUM_FSYNC);
 753         commit_lock_file(&lk);
 754
 755         free(oids.list);
 756         oids.alloc = 0;
 757         oids.nr = 0;
 758 }