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 #include "object-store.h"
  13
  14 #define GRAPH_SIGNATURE 0x43475048 /* "CGPH" */
  15 #define GRAPH_CHUNKID_OIDFANOUT 0x4f494446 /* "OIDF" */
  16 #define GRAPH_CHUNKID_OIDLOOKUP 0x4f49444c /* "OIDL" */
  17 #define GRAPH_CHUNKID_DATA 0x43444154 /* "CDAT" */
  18 #define GRAPH_CHUNKID_LARGEEDGES 0x45444745 /* "EDGE" */
  19
  20 #define GRAPH_DATA_WIDTH 36
  21
  22 #define GRAPH_VERSION_1 0x1
  23 #define GRAPH_VERSION GRAPH_VERSION_1
  24
  25 #define GRAPH_OID_VERSION_SHA1 1
  26 #define GRAPH_OID_LEN_SHA1 GIT_SHA1_RAWSZ
  27 #define GRAPH_OID_VERSION GRAPH_OID_VERSION_SHA1
  28 #define GRAPH_OID_LEN GRAPH_OID_LEN_SHA1
  29
  30 #define GRAPH_OCTOPUS_EDGES_NEEDED 0x80000000
  31 #define GRAPH_PARENT_MISSING 0x7fffffff
  32 #define GRAPH_EDGE_LAST_MASK 0x7fffffff
  33 #define GRAPH_PARENT_NONE 0x70000000
  34
  35 #define GRAPH_LAST_EDGE 0x80000000
  36
  37 #define GRAPH_FANOUT_SIZE (4 * 256)
  38 #define GRAPH_CHUNKLOOKUP_WIDTH 12
  39 #define GRAPH_MIN_SIZE (5 * GRAPH_CHUNKLOOKUP_WIDTH + GRAPH_FANOUT_SIZE + \
  40                         GRAPH_OID_LEN + 8)
  41
  42 char *get_commit_graph_filename(const char *obj_dir)
  43 {
  44         return xstrfmt("%s/info/commit-graph", obj_dir);
  45 }
  46
  47 static struct commit_graph *alloc_commit_graph(void)
  48 {
  49         struct commit_graph *g = xcalloc(1, sizeof(*g));
  50         g->graph_fd = -1;
  51
  52         return g;
  53 }
  54
  55 struct commit_graph *load_commit_graph_one(const char *graph_file)
  56 {
  57         void *graph_map;
  58         const unsigned char *data, *chunk_lookup;
  59         size_t graph_size;
  60         struct stat st;
  61         uint32_t i;
  62         struct commit_graph *graph;
  63         int fd = git_open(graph_file);
  64         uint64_t last_chunk_offset;
  65         uint32_t last_chunk_id;
  66         uint32_t graph_signature;
  67         unsigned char graph_version, hash_version;
  68
  69         if (fd < 0)
  70                 return NULL;
  71         if (fstat(fd, &st)) {
  72                 close(fd);
  73                 return NULL;
  74         }
  75         graph_size = xsize_t(st.st_size);
  76
  77         if (graph_size < GRAPH_MIN_SIZE) {
  78                 close(fd);
  79                 die("graph file %s is too small", graph_file);
  80         }
  81         graph_map = xmmap(NULL, graph_size, PROT_READ, MAP_PRIVATE, fd, 0);
  82         data = (const unsigned char *)graph_map;
  83
  84         graph_signature = get_be32(data);
  85         if (graph_signature != GRAPH_SIGNATURE) {
  86                 error("graph signature %X does not match signature %X",
  87                       graph_signature, GRAPH_SIGNATURE);
  88                 goto cleanup_fail;
  89         }
  90
  91         graph_version = *(unsigned char*)(data + 4);
  92         if (graph_version != GRAPH_VERSION) {
  93                 error("graph version %X does not match version %X",
  94                       graph_version, GRAPH_VERSION);
  95                 goto cleanup_fail;
  96         }
  97
  98         hash_version = *(unsigned char*)(data + 5);
  99         if (hash_version != GRAPH_OID_VERSION) {
 100                 error("hash version %X does not match version %X",
 101                       hash_version, GRAPH_OID_VERSION);
 102                 goto cleanup_fail;
 103         }
 104
 105         graph = alloc_commit_graph();
 106
 107         graph->hash_len = GRAPH_OID_LEN;
 108         graph->num_chunks = *(unsigned char*)(data + 6);
 109         graph->graph_fd = fd;
 110         graph->data = graph_map;
 111         graph->data_len = graph_size;
 112
 113         last_chunk_id = 0;
 114         last_chunk_offset = 8;
 115         chunk_lookup = data + 8;
 116         for (i = 0; i < graph->num_chunks; i++) {
 117                 uint32_t chunk_id = get_be32(chunk_lookup + 0);
 118                 uint64_t chunk_offset = get_be64(chunk_lookup + 4);
 119                 int chunk_repeated = 0;
 120
 121                 chunk_lookup += GRAPH_CHUNKLOOKUP_WIDTH;
 122
 123                 if (chunk_offset > graph_size - GIT_MAX_RAWSZ) {
 124                         error("improper chunk offset %08x%08x", (uint32_t)(chunk_offset >> 32),
 125                               (uint32_t)chunk_offset);
 126                         goto cleanup_fail;
 127                 }
 128
 129                 switch (chunk_id) {
 130                 case GRAPH_CHUNKID_OIDFANOUT:
 131                         if (graph->chunk_oid_fanout)
 132                                 chunk_repeated = 1;
 133                         else
 134                                 graph->chunk_oid_fanout = (uint32_t*)(data + chunk_offset);
 135                         break;
 136
 137                 case GRAPH_CHUNKID_OIDLOOKUP:
 138                         if (graph->chunk_oid_lookup)
 139                                 chunk_repeated = 1;
 140                         else
 141                                 graph->chunk_oid_lookup = data + chunk_offset;
 142                         break;
 143
 144                 case GRAPH_CHUNKID_DATA:
 145                         if (graph->chunk_commit_data)
 146                                 chunk_repeated = 1;
 147                         else
 148                                 graph->chunk_commit_data = data + chunk_offset;
 149                         break;
 150
 151                 case GRAPH_CHUNKID_LARGEEDGES:
 152                         if (graph->chunk_large_edges)
 153                                 chunk_repeated = 1;
 154                         else
 155                                 graph->chunk_large_edges = data + chunk_offset;
 156                         break;
 157                 }
 158
 159                 if (chunk_repeated) {
 160                         error("chunk id %08x appears multiple times", chunk_id);
 161                         goto cleanup_fail;
 162                 }
 163
 164                 if (last_chunk_id == GRAPH_CHUNKID_OIDLOOKUP)
 165                 {
 166                         graph->num_commits = (chunk_offset - last_chunk_offset)
 167                                              / graph->hash_len;
 168                 }
 169
 170                 last_chunk_id = chunk_id;
 171                 last_chunk_offset = chunk_offset;
 172         }
 173
 174         return graph;
 175
 176 cleanup_fail:
 177         munmap(graph_map, graph_size);
 178         close(fd);
 179         exit(1);
 180 }
 181
 182 /* global storage */
 183 static struct commit_graph *commit_graph = NULL;
 184
 185 static void prepare_commit_graph_one(const char *obj_dir)
 186 {
 187         char *graph_name;
 188
 189         if (commit_graph)
 190                 return;
 191
 192         graph_name = get_commit_graph_filename(obj_dir);
 193         commit_graph = load_commit_graph_one(graph_name);
 194
 195         FREE_AND_NULL(graph_name);
 196 }
 197
 198 static int prepare_commit_graph_run_once = 0;
 199 static void prepare_commit_graph(void)
 200 {
 201         struct alternate_object_database *alt;
 202         char *obj_dir;
 203
 204         if (prepare_commit_graph_run_once)
 205                 return;
 206         prepare_commit_graph_run_once = 1;
 207
 208         obj_dir = get_object_directory();
 209         prepare_commit_graph_one(obj_dir);
 210         prepare_alt_odb(the_repository);
 211         for (alt = the_repository->objects->alt_odb_list;
 212              !commit_graph && alt;
 213              alt = alt->next)
 214                 prepare_commit_graph_one(alt->path);
 215 }
 216
 217 static void close_commit_graph(void)
 218 {
 219         if (!commit_graph)
 220                 return;
 221
 222         if (commit_graph->graph_fd >= 0) {
 223                 munmap((void *)commit_graph->data, commit_graph->data_len);
 224                 commit_graph->data = NULL;
 225                 close(commit_graph->graph_fd);
 226         }
 227
 228         FREE_AND_NULL(commit_graph);
 229 }
 230
 231 static int bsearch_graph(struct commit_graph *g, struct object_id *oid, uint32_t *pos)
 232 {
 233         return bsearch_hash(oid->hash, g->chunk_oid_fanout,
 234                             g->chunk_oid_lookup, g->hash_len, pos);
 235 }
 236
 237 static struct commit_list **insert_parent_or_die(struct commit_graph *g,
 238                                                  uint64_t pos,
 239                                                  struct commit_list **pptr)
 240 {
 241         struct commit *c;
 242         struct object_id oid;
 243         hashcpy(oid.hash, g->chunk_oid_lookup + g->hash_len * pos);
 244         c = lookup_commit(&oid);
 245         if (!c)
 246                 die("could not find commit %s", oid_to_hex(&oid));
 247         c->graph_pos = pos;
 248         return &commit_list_insert(c, pptr)->next;
 249 }
 250
 251 static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uint32_t pos)
 252 {
 253         uint32_t edge_value;
 254         uint32_t *parent_data_ptr;
 255         uint64_t date_low, date_high;
 256         struct commit_list **pptr;
 257         const unsigned char *commit_data = g->chunk_commit_data + (g->hash_len + 16) * pos;
 258
 259         item->object.parsed = 1;
 260         item->graph_pos = pos;
 261
 262         item->maybe_tree = NULL;
 263
 264         date_high = get_be32(commit_data + g->hash_len + 8) & 0x3;
 265         date_low = get_be32(commit_data + g->hash_len + 12);
 266         item->date = (timestamp_t)((date_high << 32) | date_low);
 267
 268         pptr = &item->parents;
 269
 270         edge_value = get_be32(commit_data + g->hash_len);
 271         if (edge_value == GRAPH_PARENT_NONE)
 272                 return 1;
 273         pptr = insert_parent_or_die(g, edge_value, pptr);
 274
 275         edge_value = get_be32(commit_data + g->hash_len + 4);
 276         if (edge_value == GRAPH_PARENT_NONE)
 277                 return 1;
 278         if (!(edge_value & GRAPH_OCTOPUS_EDGES_NEEDED)) {
 279                 pptr = insert_parent_or_die(g, edge_value, pptr);
 280                 return 1;
 281         }
 282
 283         parent_data_ptr = (uint32_t*)(g->chunk_large_edges +
 284                           4 * (uint64_t)(edge_value & GRAPH_EDGE_LAST_MASK));
 285         do {
 286                 edge_value = get_be32(parent_data_ptr);
 287                 pptr = insert_parent_or_die(g,
 288                                             edge_value & GRAPH_EDGE_LAST_MASK,
 289                                             pptr);
 290                 parent_data_ptr++;
 291         } while (!(edge_value & GRAPH_LAST_EDGE));
 292
 293         return 1;
 294 }
 295
 296 int parse_commit_in_graph(struct commit *item)
 297 {
 298         if (!core_commit_graph)
 299                 return 0;
 300         if (item->object.parsed)
 301                 return 1;
 302
 303         prepare_commit_graph();
 304         if (commit_graph) {
 305                 uint32_t pos;
 306                 int found;
 307                 if (item->graph_pos != COMMIT_NOT_FROM_GRAPH) {
 308                         pos = item->graph_pos;
 309                         found = 1;
 310                 } else {
 311                         found = bsearch_graph(commit_graph, &(item->object.oid), &pos);
 312                 }
 313
 314                 if (found)
 315                         return fill_commit_in_graph(item, commit_graph, pos);
 316         }
 317
 318         return 0;
 319 }
 320
 321 static struct tree *load_tree_for_commit(struct commit_graph *g, struct commit *c)
 322 {
 323         struct object_id oid;
 324         const unsigned char *commit_data = g->chunk_commit_data +
 325                                            GRAPH_DATA_WIDTH * (c->graph_pos);
 326
 327         hashcpy(oid.hash, commit_data);
 328         c->maybe_tree = lookup_tree(&oid);
 329
 330         return c->maybe_tree;
 331 }
 332
 333 struct tree *get_commit_tree_in_graph(const struct commit *c)
 334 {
 335         if (c->maybe_tree)
 336                 return c->maybe_tree;
 337         if (c->graph_pos == COMMIT_NOT_FROM_GRAPH)
 338                 BUG("get_commit_tree_in_graph called from non-commit-graph commit");
 339
 340         return load_tree_for_commit(commit_graph, (struct commit *)c);
 341 }
 342
 343 static void write_graph_chunk_fanout(struct hashfile *f,
 344                                      struct commit **commits,
 345                                      int nr_commits)
 346 {
 347         int i, count = 0;
 348         struct commit **list = commits;
 349
 350         /*
 351          * Write the first-level table (the list is sorted,
 352          * but we use a 256-entry lookup to be able to avoid
 353          * having to do eight extra binary search iterations).
 354          */
 355         for (i = 0; i < 256; i++) {
 356                 while (count < nr_commits) {
 357                         if ((*list)->object.oid.hash[0] != i)
 358                                 break;
 359                         count++;
 360                         list++;
 361                 }
 362
 363                 hashwrite_be32(f, count);
 364         }
 365 }
 366
 367 static void write_graph_chunk_oids(struct hashfile *f, int hash_len,
 368                                    struct commit **commits, int nr_commits)
 369 {
 370         struct commit **list = commits;
 371         int count;
 372         for (count = 0; count < nr_commits; count++, list++)
 373                 hashwrite(f, (*list)->object.oid.hash, (int)hash_len);
 374 }
 375
 376 static const unsigned char *commit_to_sha1(size_t index, void *table)
 377 {
 378         struct commit **commits = table;
 379         return commits[index]->object.oid.hash;
 380 }
 381
 382 static void write_graph_chunk_data(struct hashfile *f, int hash_len,
 383                                    struct commit **commits, int nr_commits)
 384 {
 385         struct commit **list = commits;
 386         struct commit **last = commits + nr_commits;
 387         uint32_t num_extra_edges = 0;
 388
 389         while (list < last) {
 390                 struct commit_list *parent;
 391                 int edge_value;
 392                 uint32_t packedDate[2];
 393
 394                 parse_commit(*list);
 395                 hashwrite(f, get_commit_tree_oid(*list)->hash, hash_len);
 396
 397                 parent = (*list)->parents;
 398
 399                 if (!parent)
 400                         edge_value = GRAPH_PARENT_NONE;
 401                 else {
 402                         edge_value = sha1_pos(parent->item->object.oid.hash,
 403                                               commits,
 404                                               nr_commits,
 405                                               commit_to_sha1);
 406
 407                         if (edge_value < 0)
 408                                 edge_value = GRAPH_PARENT_MISSING;
 409                 }
 410
 411                 hashwrite_be32(f, edge_value);
 412
 413                 if (parent)
 414                         parent = parent->next;
 415
 416                 if (!parent)
 417                         edge_value = GRAPH_PARENT_NONE;
 418                 else if (parent->next)
 419                         edge_value = GRAPH_OCTOPUS_EDGES_NEEDED | num_extra_edges;
 420                 else {
 421                         edge_value = sha1_pos(parent->item->object.oid.hash,
 422                                               commits,
 423                                               nr_commits,
 424                                               commit_to_sha1);
 425                         if (edge_value < 0)
 426                                 edge_value = GRAPH_PARENT_MISSING;
 427                 }
 428
 429                 hashwrite_be32(f, edge_value);
 430
 431                 if (edge_value & GRAPH_OCTOPUS_EDGES_NEEDED) {
 432                         do {
 433                                 num_extra_edges++;
 434                                 parent = parent->next;
 435                         } while (parent);
 436                 }
 437
 438                 if (sizeof((*list)->date) > 4)
 439                         packedDate[0] = htonl(((*list)->date >> 32) & 0x3);
 440                 else
 441                         packedDate[0] = 0;
 442
 443                 packedDate[1] = htonl((*list)->date);
 444                 hashwrite(f, packedDate, 8);
 445
 446                 list++;
 447         }
 448 }
 449
 450 static void write_graph_chunk_large_edges(struct hashfile *f,
 451                                           struct commit **commits,
 452                                           int nr_commits)
 453 {
 454         struct commit **list = commits;
 455         struct commit **last = commits + nr_commits;
 456         struct commit_list *parent;
 457
 458         while (list < last) {
 459                 int num_parents = 0;
 460                 for (parent = (*list)->parents; num_parents < 3 && parent;
 461                      parent = parent->next)
 462                         num_parents++;
 463
 464                 if (num_parents <= 2) {
 465                         list++;
 466                         continue;
 467                 }
 468
 469                 /* Since num_parents > 2, this initializer is safe. */
 470                 for (parent = (*list)->parents->next; parent; parent = parent->next) {
 471                         int edge_value = sha1_pos(parent->item->object.oid.hash,
 472                                                   commits,
 473                                                   nr_commits,
 474                                                   commit_to_sha1);
 475
 476                         if (edge_value < 0)
 477                                 edge_value = GRAPH_PARENT_MISSING;
 478                         else if (!parent->next)
 479                                 edge_value |= GRAPH_LAST_EDGE;
 480
 481                         hashwrite_be32(f, edge_value);
 482                 }
 483
 484                 list++;
 485         }
 486 }
 487
 488 static int commit_compare(const void *_a, const void *_b)
 489 {
 490         const struct object_id *a = (const struct object_id *)_a;
 491         const struct object_id *b = (const struct object_id *)_b;
 492         return oidcmp(a, b);
 493 }
 494
 495 struct packed_commit_list {
 496         struct commit **list;
 497         int nr;
 498         int alloc;
 499 };
 500
 501 struct packed_oid_list {
 502         struct object_id *list;
 503         int nr;
 504         int alloc;
 505 };
 506
 507 static int add_packed_commits(const struct object_id *oid,
 508                               struct packed_git *pack,
 509                               uint32_t pos,
 510                               void *data)
 511 {
 512         struct packed_oid_list *list = (struct packed_oid_list*)data;
 513         enum object_type type;
 514         off_t offset = nth_packed_object_offset(pack, pos);
 515         struct object_info oi = OBJECT_INFO_INIT;
 516
 517         oi.typep = &type;
 518         if (packed_object_info(the_repository, pack, offset, &oi) < 0)
 519                 die("unable to get type of object %s", oid_to_hex(oid));
 520
 521         if (type != OBJ_COMMIT)
 522                 return 0;
 523
 524         ALLOC_GROW(list->list, list->nr + 1, list->alloc);
 525         oidcpy(&(list->list[list->nr]), oid);
 526         list->nr++;
 527
 528         return 0;
 529 }
 530
 531 static void add_missing_parents(struct packed_oid_list *oids, struct commit *commit)
 532 {
 533         struct commit_list *parent;
 534         for (parent = commit->parents; parent; parent = parent->next) {
 535                 if (!(parent->item->object.flags & UNINTERESTING)) {
 536                         ALLOC_GROW(oids->list, oids->nr + 1, oids->alloc);
 537                         oidcpy(&oids->list[oids->nr], &(parent->item->object.oid));
 538                         oids->nr++;
 539                         parent->item->object.flags |= UNINTERESTING;
 540                 }
 541         }
 542 }
 543
 544 static void close_reachable(struct packed_oid_list *oids)
 545 {
 546         int i;
 547         struct commit *commit;
 548
 549         for (i = 0; i < oids->nr; i++) {
 550                 commit = lookup_commit(&oids->list[i]);
 551                 if (commit)
 552                         commit->object.flags |= UNINTERESTING;
 553         }
 554
 555         /*
 556          * As this loop runs, oids->nr may grow, but not more
 557          * than the number of missing commits in the reachable
 558          * closure.
 559          */
 560         for (i = 0; i < oids->nr; i++) {
 561                 commit = lookup_commit(&oids->list[i]);
 562
 563                 if (commit && !parse_commit(commit))
 564                         add_missing_parents(oids, commit);
 565         }
 566
 567         for (i = 0; i < oids->nr; i++) {
 568                 commit = lookup_commit(&oids->list[i]);
 569
 570                 if (commit)
 571                         commit->object.flags &= ~UNINTERESTING;
 572         }
 573 }
 574
 575 void write_commit_graph(const char *obj_dir,
 576                         const char **pack_indexes,
 577                         int nr_packs,
 578                         const char **commit_hex,
 579                         int nr_commits,
 580                         int append)
 581 {
 582         struct packed_oid_list oids;
 583         struct packed_commit_list commits;
 584         struct hashfile *f;
 585         uint32_t i, count_distinct = 0;
 586         char *graph_name;
 587         int fd;
 588         struct lock_file lk = LOCK_INIT;
 589         uint32_t chunk_ids[5];
 590         uint64_t chunk_offsets[5];
 591         int num_chunks;
 592         int num_extra_edges;
 593         struct commit_list *parent;
 594
 595         oids.nr = 0;
 596         oids.alloc = approximate_object_count() / 4;
 597
 598         if (append) {
 599                 prepare_commit_graph_one(obj_dir);
 600                 if (commit_graph)
 601                         oids.alloc += commit_graph->num_commits;
 602         }
 603
 604         if (oids.alloc < 1024)
 605                 oids.alloc = 1024;
 606         ALLOC_ARRAY(oids.list, oids.alloc);
 607
 608         if (append && commit_graph) {
 609                 for (i = 0; i < commit_graph->num_commits; i++) {
 610                         const unsigned char *hash = commit_graph->chunk_oid_lookup +
 611                                 commit_graph->hash_len * i;
 612                         hashcpy(oids.list[oids.nr++].hash, hash);
 613                 }
 614         }
 615
 616         if (pack_indexes) {
 617                 struct strbuf packname = STRBUF_INIT;
 618                 int dirlen;
 619                 strbuf_addf(&packname, "%s/pack/", obj_dir);
 620                 dirlen = packname.len;
 621                 for (i = 0; i < nr_packs; i++) {
 622                         struct packed_git *p;
 623                         strbuf_setlen(&packname, dirlen);
 624                         strbuf_addstr(&packname, pack_indexes[i]);
 625                         p = add_packed_git(packname.buf, packname.len, 1);
 626                         if (!p)
 627                                 die("error adding pack %s", packname.buf);
 628                         if (open_pack_index(p))
 629                                 die("error opening index for %s", packname.buf);
 630                         for_each_object_in_pack(p, add_packed_commits, &oids);
 631                         close_pack(p);
 632                 }
 633                 strbuf_release(&packname);
 634         }
 635
 636         if (commit_hex) {
 637                 for (i = 0; i < nr_commits; i++) {
 638                         const char *end;
 639                         struct object_id oid;
 640                         struct commit *result;
 641
 642                         if (commit_hex[i] && parse_oid_hex(commit_hex[i], &oid, &end))
 643                                 continue;
 644
 645                         result = lookup_commit_reference_gently(&oid, 1);
 646
 647                         if (result) {
 648                                 ALLOC_GROW(oids.list, oids.nr + 1, oids.alloc);
 649                                 oidcpy(&oids.list[oids.nr], &(result->object.oid));
 650                                 oids.nr++;
 651                         }
 652                 }
 653         }
 654
 655         if (!pack_indexes && !commit_hex)
 656                 for_each_packed_object(add_packed_commits, &oids, 0);
 657
 658         close_reachable(&oids);
 659
 660         QSORT(oids.list, oids.nr, commit_compare);
 661
 662         count_distinct = 1;
 663         for (i = 1; i < oids.nr; i++) {
 664                 if (oidcmp(&oids.list[i-1], &oids.list[i]))
 665                         count_distinct++;
 666         }
 667
 668         if (count_distinct >= GRAPH_PARENT_MISSING)
 669                 die(_("the commit graph format cannot write %d commits"), count_distinct);
 670
 671         commits.nr = 0;
 672         commits.alloc = count_distinct;
 673         ALLOC_ARRAY(commits.list, commits.alloc);
 674
 675         num_extra_edges = 0;
 676         for (i = 0; i < oids.nr; i++) {
 677                 int num_parents = 0;
 678                 if (i > 0 && !oidcmp(&oids.list[i-1], &oids.list[i]))
 679                         continue;
 680
 681                 commits.list[commits.nr] = lookup_commit(&oids.list[i]);
 682                 parse_commit(commits.list[commits.nr]);
 683
 684                 for (parent = commits.list[commits.nr]->parents;
 685                      parent; parent = parent->next)
 686                         num_parents++;
 687
 688                 if (num_parents > 2)
 689                         num_extra_edges += num_parents - 1;
 690
 691                 commits.nr++;
 692         }
 693         num_chunks = num_extra_edges ? 4 : 3;
 694
 695         if (commits.nr >= GRAPH_PARENT_MISSING)
 696                 die(_("too many commits to write graph"));
 697
 698         graph_name = get_commit_graph_filename(obj_dir);
 699         fd = hold_lock_file_for_update(&lk, graph_name, 0);
 700
 701         if (fd < 0) {
 702                 struct strbuf folder = STRBUF_INIT;
 703                 strbuf_addstr(&folder, graph_name);
 704                 strbuf_setlen(&folder, strrchr(folder.buf, '/') - folder.buf);
 705
 706                 if (mkdir(folder.buf, 0777) < 0)
 707                         die_errno(_("cannot mkdir %s"), folder.buf);
 708                 strbuf_release(&folder);
 709
 710                 fd = hold_lock_file_for_update(&lk, graph_name, LOCK_DIE_ON_ERROR);
 711
 712                 if (fd < 0)
 713                         die_errno("unable to create '%s'", graph_name);
 714         }
 715
 716         f = hashfd(lk.tempfile->fd, lk.tempfile->filename.buf);
 717
 718         hashwrite_be32(f, GRAPH_SIGNATURE);
 719
 720         hashwrite_u8(f, GRAPH_VERSION);
 721         hashwrite_u8(f, GRAPH_OID_VERSION);
 722         hashwrite_u8(f, num_chunks);
 723         hashwrite_u8(f, 0); /* unused padding byte */
 724
 725         chunk_ids[0] = GRAPH_CHUNKID_OIDFANOUT;
 726         chunk_ids[1] = GRAPH_CHUNKID_OIDLOOKUP;
 727         chunk_ids[2] = GRAPH_CHUNKID_DATA;
 728         if (num_extra_edges)
 729                 chunk_ids[3] = GRAPH_CHUNKID_LARGEEDGES;
 730         else
 731                 chunk_ids[3] = 0;
 732         chunk_ids[4] = 0;
 733
 734         chunk_offsets[0] = 8 + (num_chunks + 1) * GRAPH_CHUNKLOOKUP_WIDTH;
 735         chunk_offsets[1] = chunk_offsets[0] + GRAPH_FANOUT_SIZE;
 736         chunk_offsets[2] = chunk_offsets[1] + GRAPH_OID_LEN * commits.nr;
 737         chunk_offsets[3] = chunk_offsets[2] + (GRAPH_OID_LEN + 16) * commits.nr;
 738         chunk_offsets[4] = chunk_offsets[3] + 4 * num_extra_edges;
 739
 740         for (i = 0; i <= num_chunks; i++) {
 741                 uint32_t chunk_write[3];
 742
 743                 chunk_write[0] = htonl(chunk_ids[i]);
 744                 chunk_write[1] = htonl(chunk_offsets[i] >> 32);
 745                 chunk_write[2] = htonl(chunk_offsets[i] & 0xffffffff);
 746                 hashwrite(f, chunk_write, 12);
 747         }
 748
 749         write_graph_chunk_fanout(f, commits.list, commits.nr);
 750         write_graph_chunk_oids(f, GRAPH_OID_LEN, commits.list, commits.nr);
 751         write_graph_chunk_data(f, GRAPH_OID_LEN, commits.list, commits.nr);
 752         write_graph_chunk_large_edges(f, commits.list, commits.nr);
 753
 754         close_commit_graph();
 755         finalize_hashfile(f, NULL, CSUM_HASH_IN_STREAM | CSUM_FSYNC);
 756         commit_lock_file(&lk);
 757
 758         free(oids.list);
 759         oids.alloc = 0;
 760         oids.nr = 0;
 761 }