pack-bitmap-write.c

   1 #include "git-compat-util.h"
   2 #include "environment.h"
   3 #include "gettext.h"
   4 #include "hex.h"
   5 #include "object-store-ll.h"
   6 #include "commit.h"
   7 #include "diff.h"
   8 #include "revision.h"
   9 #include "progress.h"
  10 #include "pack.h"
  11 #include "pack-bitmap.h"
  12 #include "hash-lookup.h"
  13 #include "pack-objects.h"
  14 #include "path.h"
  15 #include "commit-reach.h"
  16 #include "prio-queue.h"
  17 #include "trace2.h"
  18 #include "tree.h"
  19 #include "tree-walk.h"
  20
  21 struct bitmapped_commit {
  22         struct commit *commit;
  23         struct ewah_bitmap *bitmap;
  24         struct ewah_bitmap *write_as;
  25         int flags;
  26         int xor_offset;
  27         uint32_t commit_pos;
  28 };
  29
  30 struct bitmap_writer {
  31         struct ewah_bitmap *commits;
  32         struct ewah_bitmap *trees;
  33         struct ewah_bitmap *blobs;
  34         struct ewah_bitmap *tags;
  35
  36         kh_oid_map_t *bitmaps;
  37         struct packing_data *to_pack;
  38
  39         struct bitmapped_commit *selected;
  40         unsigned int selected_nr, selected_alloc;
  41
  42         struct progress *progress;
  43         int show_progress;
  44         unsigned char pack_checksum[GIT_MAX_RAWSZ];
  45 };
  46
  47 static struct bitmap_writer writer;
  48
  49 void bitmap_writer_show_progress(int show)
  50 {
  51         writer.show_progress = show;
  52 }
  53
  54 /**
  55  * Build the initial type index for the packfile or multi-pack-index
  56  */
  57 void bitmap_writer_build_type_index(struct packing_data *to_pack,
  58                                     struct pack_idx_entry **index,
  59                                     uint32_t index_nr)
  60 {
  61         uint32_t i;
  62
  63         writer.commits = ewah_new();
  64         writer.trees = ewah_new();
  65         writer.blobs = ewah_new();
  66         writer.tags = ewah_new();
  67         ALLOC_ARRAY(to_pack->in_pack_pos, to_pack->nr_objects);
  68
  69         for (i = 0; i < index_nr; ++i) {
  70                 struct object_entry *entry = (struct object_entry *)index[i];
  71                 enum object_type real_type;
  72
  73                 oe_set_in_pack_pos(to_pack, entry, i);
  74
  75                 switch (oe_type(entry)) {
  76                 case OBJ_COMMIT:
  77                 case OBJ_TREE:
  78                 case OBJ_BLOB:
  79                 case OBJ_TAG:
  80                         real_type = oe_type(entry);
  81                         break;
  82
  83                 default:
  84                         real_type = oid_object_info(to_pack->repo,
  85                                                     &entry->idx.oid, NULL);
  86                         break;
  87                 }
  88
  89                 switch (real_type) {
  90                 case OBJ_COMMIT:
  91                         ewah_set(writer.commits, i);
  92                         break;
  93
  94                 case OBJ_TREE:
  95                         ewah_set(writer.trees, i);
  96                         break;
  97
  98                 case OBJ_BLOB:
  99                         ewah_set(writer.blobs, i);
 100                         break;
 101
 102                 case OBJ_TAG:
 103                         ewah_set(writer.tags, i);
 104                         break;
 105
 106                 default:
 107                         die("Missing type information for %s (%d/%d)",
 108                             oid_to_hex(&entry->idx.oid), real_type,
 109                             oe_type(entry));
 110                 }
 111         }
 112 }
 113
 114 /**
 115  * Compute the actual bitmaps
 116  */
 117
 118 static inline void push_bitmapped_commit(struct commit *commit)
 119 {
 120         if (writer.selected_nr >= writer.selected_alloc) {
 121                 writer.selected_alloc = (writer.selected_alloc + 32) * 2;
 122                 REALLOC_ARRAY(writer.selected, writer.selected_alloc);
 123         }
 124
 125         writer.selected[writer.selected_nr].commit = commit;
 126         writer.selected[writer.selected_nr].bitmap = NULL;
 127         writer.selected[writer.selected_nr].flags = 0;
 128
 129         writer.selected_nr++;
 130 }
 131
 132 static uint32_t find_object_pos(const struct object_id *oid, int *found)
 133 {
 134         struct object_entry *entry = packlist_find(writer.to_pack, oid);
 135
 136         if (!entry) {
 137                 if (found)
 138                         *found = 0;
 139                 warning("Failed to write bitmap index. Packfile doesn't have full closure "
 140                         "(object %s is missing)", oid_to_hex(oid));
 141                 return 0;
 142         }
 143
 144         if (found)
 145                 *found = 1;
 146         return oe_in_pack_pos(writer.to_pack, entry);
 147 }
 148
 149 static void compute_xor_offsets(void)
 150 {
 151         static const int MAX_XOR_OFFSET_SEARCH = 10;
 152
 153         int i, next = 0;
 154
 155         while (next < writer.selected_nr) {
 156                 struct bitmapped_commit *stored = &writer.selected[next];
 157
 158                 int best_offset = 0;
 159                 struct ewah_bitmap *best_bitmap = stored->bitmap;
 160                 struct ewah_bitmap *test_xor;
 161
 162                 for (i = 1; i <= MAX_XOR_OFFSET_SEARCH; ++i) {
 163                         int curr = next - i;
 164
 165                         if (curr < 0)
 166                                 break;
 167
 168                         test_xor = ewah_pool_new();
 169                         ewah_xor(writer.selected[curr].bitmap, stored->bitmap, test_xor);
 170
 171                         if (test_xor->buffer_size < best_bitmap->buffer_size) {
 172                                 if (best_bitmap != stored->bitmap)
 173                                         ewah_pool_free(best_bitmap);
 174
 175                                 best_bitmap = test_xor;
 176                                 best_offset = i;
 177                         } else {
 178                                 ewah_pool_free(test_xor);
 179                         }
 180                 }
 181
 182                 stored->xor_offset = best_offset;
 183                 stored->write_as = best_bitmap;
 184
 185                 next++;
 186         }
 187 }
 188
 189 struct bb_commit {
 190         struct commit_list *reverse_edges;
 191         struct bitmap *commit_mask;
 192         struct bitmap *bitmap;
 193         unsigned selected:1,
 194                  maximal:1;
 195         unsigned idx; /* within selected array */
 196 };
 197
 198 define_commit_slab(bb_data, struct bb_commit);
 199
 200 struct bitmap_builder {
 201         struct bb_data data;
 202         struct commit **commits;
 203         size_t commits_nr, commits_alloc;
 204 };
 205
 206 static void bitmap_builder_init(struct bitmap_builder *bb,
 207                                 struct bitmap_writer *writer,
 208                                 struct bitmap_index *old_bitmap)
 209 {
 210         struct rev_info revs;
 211         struct commit *commit;
 212         struct commit_list *reusable = NULL;
 213         struct commit_list *r;
 214         unsigned int i, num_maximal = 0;
 215
 216         memset(bb, 0, sizeof(*bb));
 217         init_bb_data(&bb->data);
 218
 219         reset_revision_walk();
 220         repo_init_revisions(writer->to_pack->repo, &revs, NULL);
 221         revs.topo_order = 1;
 222         revs.first_parent_only = 1;
 223
 224         for (i = 0; i < writer->selected_nr; i++) {
 225                 struct commit *c = writer->selected[i].commit;
 226                 struct bb_commit *ent = bb_data_at(&bb->data, c);
 227
 228                 ent->selected = 1;
 229                 ent->maximal = 1;
 230                 ent->idx = i;
 231
 232                 ent->commit_mask = bitmap_new();
 233                 bitmap_set(ent->commit_mask, i);
 234
 235                 add_pending_object(&revs, &c->object, "");
 236         }
 237
 238         if (prepare_revision_walk(&revs))
 239                 die("revision walk setup failed");
 240
 241         while ((commit = get_revision(&revs))) {
 242                 struct commit_list *p = commit->parents;
 243                 struct bb_commit *c_ent;
 244
 245                 parse_commit_or_die(commit);
 246
 247                 c_ent = bb_data_at(&bb->data, commit);
 248
 249                 /*
 250                  * If there is no commit_mask, there is no reason to iterate
 251                  * over this commit; it is not selected (if it were, it would
 252                  * not have a blank commit mask) and all its children have
 253                  * existing bitmaps (see the comment starting with "This commit
 254                  * has an existing bitmap" below), so it does not contribute
 255                  * anything to the final bitmap file or its descendants.
 256                  */
 257                 if (!c_ent->commit_mask)
 258                         continue;
 259
 260                 if (old_bitmap && bitmap_for_commit(old_bitmap, commit)) {
 261                         /*
 262                          * This commit has an existing bitmap, so we can
 263                          * get its bits immediately without an object
 264                          * walk. That is, it is reusable as-is and there is no
 265                          * need to continue walking beyond it.
 266                          *
 267                          * Mark it as such and add it to bb->commits separately
 268                          * to avoid allocating a position in the commit mask.
 269                          */
 270                         commit_list_insert(commit, &reusable);
 271                         goto next;
 272                 }
 273
 274                 if (c_ent->maximal) {
 275                         num_maximal++;
 276                         ALLOC_GROW(bb->commits, bb->commits_nr + 1, bb->commits_alloc);
 277                         bb->commits[bb->commits_nr++] = commit;
 278                 }
 279
 280                 if (p) {
 281                         struct bb_commit *p_ent = bb_data_at(&bb->data, p->item);
 282                         int c_not_p, p_not_c;
 283
 284                         if (!p_ent->commit_mask) {
 285                                 p_ent->commit_mask = bitmap_new();
 286                                 c_not_p = 1;
 287                                 p_not_c = 0;
 288                         } else {
 289                                 c_not_p = bitmap_is_subset(c_ent->commit_mask, p_ent->commit_mask);
 290                                 p_not_c = bitmap_is_subset(p_ent->commit_mask, c_ent->commit_mask);
 291                         }
 292
 293                         if (!c_not_p)
 294                                 continue;
 295
 296                         bitmap_or(p_ent->commit_mask, c_ent->commit_mask);
 297
 298                         if (p_not_c)
 299                                 p_ent->maximal = 1;
 300                         else {
 301                                 p_ent->maximal = 0;
 302                                 free_commit_list(p_ent->reverse_edges);
 303                                 p_ent->reverse_edges = NULL;
 304                         }
 305
 306                         if (c_ent->maximal) {
 307                                 commit_list_insert(commit, &p_ent->reverse_edges);
 308                         } else {
 309                                 struct commit_list *cc = c_ent->reverse_edges;
 310
 311                                 for (; cc; cc = cc->next) {
 312                                         if (!commit_list_contains(cc->item, p_ent->reverse_edges))
 313                                                 commit_list_insert(cc->item, &p_ent->reverse_edges);
 314                                 }
 315                         }
 316                 }
 317
 318 next:
 319                 bitmap_free(c_ent->commit_mask);
 320                 c_ent->commit_mask = NULL;
 321         }
 322
 323         for (r = reusable; r; r = r->next) {
 324                 ALLOC_GROW(bb->commits, bb->commits_nr + 1, bb->commits_alloc);
 325                 bb->commits[bb->commits_nr++] = r->item;
 326         }
 327
 328         trace2_data_intmax("pack-bitmap-write", the_repository,
 329                            "num_selected_commits", writer->selected_nr);
 330         trace2_data_intmax("pack-bitmap-write", the_repository,
 331                            "num_maximal_commits", num_maximal);
 332
 333         release_revisions(&revs);
 334         free_commit_list(reusable);
 335 }
 336
 337 static void bitmap_builder_clear(struct bitmap_builder *bb)
 338 {
 339         clear_bb_data(&bb->data);
 340         free(bb->commits);
 341         bb->commits_nr = bb->commits_alloc = 0;
 342 }
 343
 344 static int fill_bitmap_tree(struct bitmap *bitmap,
 345                             struct tree *tree)
 346 {
 347         int found;
 348         uint32_t pos;
 349         struct tree_desc desc;
 350         struct name_entry entry;
 351
 352         /*
 353          * If our bit is already set, then there is nothing to do. Both this
 354          * tree and all of its children will be set.
 355          */
 356         pos = find_object_pos(&tree->object.oid, &found);
 357         if (!found)
 358                 return -1;
 359         if (bitmap_get(bitmap, pos))
 360                 return 0;
 361         bitmap_set(bitmap, pos);
 362
 363         if (parse_tree(tree) < 0)
 364                 die("unable to load tree object %s",
 365                     oid_to_hex(&tree->object.oid));
 366         init_tree_desc(&desc, tree->buffer, tree->size);
 367
 368         while (tree_entry(&desc, &entry)) {
 369                 switch (object_type(entry.mode)) {
 370                 case OBJ_TREE:
 371                         if (fill_bitmap_tree(bitmap,
 372                                              lookup_tree(the_repository, &entry.oid)) < 0)
 373                                 return -1;
 374                         break;
 375                 case OBJ_BLOB:
 376                         pos = find_object_pos(&entry.oid, &found);
 377                         if (!found)
 378                                 return -1;
 379                         bitmap_set(bitmap, pos);
 380                         break;
 381                 default:
 382                         /* Gitlink, etc; not reachable */
 383                         break;
 384                 }
 385         }
 386
 387         free_tree_buffer(tree);
 388         return 0;
 389 }
 390
 391 static int reused_bitmaps_nr;
 392
 393 static int fill_bitmap_commit(struct bb_commit *ent,
 394                               struct commit *commit,
 395                               struct prio_queue *queue,
 396                               struct prio_queue *tree_queue,
 397                               struct bitmap_index *old_bitmap,
 398                               const uint32_t *mapping)
 399 {
 400         int found;
 401         uint32_t pos;
 402         if (!ent->bitmap)
 403                 ent->bitmap = bitmap_new();
 404
 405         prio_queue_put(queue, commit);
 406
 407         while (queue->nr) {
 408                 struct commit_list *p;
 409                 struct commit *c = prio_queue_get(queue);
 410
 411                 if (old_bitmap && mapping) {
 412                         struct ewah_bitmap *old = bitmap_for_commit(old_bitmap, c);
 413                         struct bitmap *remapped = bitmap_new();
 414                         /*
 415                          * If this commit has an old bitmap, then translate that
 416                          * bitmap and add its bits to this one. No need to walk
 417                          * parents or the tree for this commit.
 418                          */
 419                         if (old && !rebuild_bitmap(mapping, old, remapped)) {
 420                                 bitmap_or(ent->bitmap, remapped);
 421                                 bitmap_free(remapped);
 422                                 reused_bitmaps_nr++;
 423                                 continue;
 424                         }
 425                         bitmap_free(remapped);
 426                 }
 427
 428                 /*
 429                  * Mark ourselves and queue our tree. The commit
 430                  * walk ensures we cover all parents.
 431                  */
 432                 pos = find_object_pos(&c->object.oid, &found);
 433                 if (!found)
 434                         return -1;
 435                 bitmap_set(ent->bitmap, pos);
 436                 prio_queue_put(tree_queue,
 437                                repo_get_commit_tree(the_repository, c));
 438
 439                 for (p = c->parents; p; p = p->next) {
 440                         pos = find_object_pos(&p->item->object.oid, &found);
 441                         if (!found)
 442                                 return -1;
 443                         if (!bitmap_get(ent->bitmap, pos)) {
 444                                 bitmap_set(ent->bitmap, pos);
 445                                 prio_queue_put(queue, p->item);
 446                         }
 447                 }
 448         }
 449
 450         while (tree_queue->nr) {
 451                 if (fill_bitmap_tree(ent->bitmap,
 452                                      prio_queue_get(tree_queue)) < 0)
 453                         return -1;
 454         }
 455         return 0;
 456 }
 457
 458 static void store_selected(struct bb_commit *ent, struct commit *commit)
 459 {
 460         struct bitmapped_commit *stored = &writer.selected[ent->idx];
 461         khiter_t hash_pos;
 462         int hash_ret;
 463
 464         stored->bitmap = bitmap_to_ewah(ent->bitmap);
 465
 466         hash_pos = kh_put_oid_map(writer.bitmaps, commit->object.oid, &hash_ret);
 467         if (hash_ret == 0)
 468                 die("Duplicate entry when writing index: %s",
 469                     oid_to_hex(&commit->object.oid));
 470         kh_value(writer.bitmaps, hash_pos) = stored;
 471 }
 472
 473 int bitmap_writer_build(struct packing_data *to_pack)
 474 {
 475         struct bitmap_builder bb;
 476         size_t i;
 477         int nr_stored = 0; /* for progress */
 478         struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
 479         struct prio_queue tree_queue = { NULL };
 480         struct bitmap_index *old_bitmap;
 481         uint32_t *mapping;
 482         int closed = 1; /* until proven otherwise */
 483
 484         writer.bitmaps = kh_init_oid_map();
 485         writer.to_pack = to_pack;
 486
 487         if (writer.show_progress)
 488                 writer.progress = start_progress("Building bitmaps", writer.selected_nr);
 489         trace2_region_enter("pack-bitmap-write", "building_bitmaps_total",
 490                             the_repository);
 491
 492         old_bitmap = prepare_bitmap_git(to_pack->repo);
 493         if (old_bitmap)
 494                 mapping = create_bitmap_mapping(old_bitmap, to_pack);
 495         else
 496                 mapping = NULL;
 497
 498         bitmap_builder_init(&bb, &writer, old_bitmap);
 499         for (i = bb.commits_nr; i > 0; i--) {
 500                 struct commit *commit = bb.commits[i-1];
 501                 struct bb_commit *ent = bb_data_at(&bb.data, commit);
 502                 struct commit *child;
 503                 int reused = 0;
 504
 505                 if (fill_bitmap_commit(ent, commit, &queue, &tree_queue,
 506                                        old_bitmap, mapping) < 0) {
 507                         closed = 0;
 508                         break;
 509                 }
 510
 511                 if (ent->selected) {
 512                         store_selected(ent, commit);
 513                         nr_stored++;
 514                         display_progress(writer.progress, nr_stored);
 515                 }
 516
 517                 while ((child = pop_commit(&ent->reverse_edges))) {
 518                         struct bb_commit *child_ent =
 519                                 bb_data_at(&bb.data, child);
 520
 521                         if (child_ent->bitmap)
 522                                 bitmap_or(child_ent->bitmap, ent->bitmap);
 523                         else if (reused)
 524                                 child_ent->bitmap = bitmap_dup(ent->bitmap);
 525                         else {
 526                                 child_ent->bitmap = ent->bitmap;
 527                                 reused = 1;
 528                         }
 529                 }
 530                 if (!reused)
 531                         bitmap_free(ent->bitmap);
 532                 ent->bitmap = NULL;
 533         }
 534         clear_prio_queue(&queue);
 535         clear_prio_queue(&tree_queue);
 536         bitmap_builder_clear(&bb);
 537         free_bitmap_index(old_bitmap);
 538         free(mapping);
 539
 540         trace2_region_leave("pack-bitmap-write", "building_bitmaps_total",
 541                             the_repository);
 542         trace2_data_intmax("pack-bitmap-write", the_repository,
 543                            "building_bitmaps_reused", reused_bitmaps_nr);
 544
 545         stop_progress(&writer.progress);
 546
 547         if (closed)
 548                 compute_xor_offsets();
 549         return closed ? 0 : -1;
 550 }
 551
 552 /**
 553  * Select the commits that will be bitmapped
 554  */
 555 static inline unsigned int next_commit_index(unsigned int idx)
 556 {
 557         static const unsigned int MIN_COMMITS = 100;
 558         static const unsigned int MAX_COMMITS = 5000;
 559
 560         static const unsigned int MUST_REGION = 100;
 561         static const unsigned int MIN_REGION = 20000;
 562
 563         unsigned int offset, next;
 564
 565         if (idx <= MUST_REGION)
 566                 return 0;
 567
 568         if (idx <= MIN_REGION) {
 569                 offset = idx - MUST_REGION;
 570                 return (offset < MIN_COMMITS) ? offset : MIN_COMMITS;
 571         }
 572
 573         offset = idx - MIN_REGION;
 574         next = (offset < MAX_COMMITS) ? offset : MAX_COMMITS;
 575
 576         return (next > MIN_COMMITS) ? next : MIN_COMMITS;
 577 }
 578
 579 static int date_compare(const void *_a, const void *_b)
 580 {
 581         struct commit *a = *(struct commit **)_a;
 582         struct commit *b = *(struct commit **)_b;
 583         return (long)b->date - (long)a->date;
 584 }
 585
 586 void bitmap_writer_select_commits(struct commit **indexed_commits,
 587                                   unsigned int indexed_commits_nr,
 588                                   int max_bitmaps)
 589 {
 590         unsigned int i = 0, j, next;
 591
 592         QSORT(indexed_commits, indexed_commits_nr, date_compare);
 593
 594         if (indexed_commits_nr < 100) {
 595                 for (i = 0; i < indexed_commits_nr; ++i)
 596                         push_bitmapped_commit(indexed_commits[i]);
 597                 return;
 598         }
 599
 600         if (writer.show_progress)
 601                 writer.progress = start_progress("Selecting bitmap commits", 0);
 602
 603         for (;;) {
 604                 struct commit *chosen = NULL;
 605
 606                 next = next_commit_index(i);
 607
 608                 if (i + next >= indexed_commits_nr)
 609                         break;
 610
 611                 if (max_bitmaps > 0 && writer.selected_nr >= max_bitmaps) {
 612                         writer.selected_nr = max_bitmaps;
 613                         break;
 614                 }
 615
 616                 if (next == 0) {
 617                         chosen = indexed_commits[i];
 618                 } else {
 619                         chosen = indexed_commits[i + next];
 620
 621                         for (j = 0; j <= next; ++j) {
 622                                 struct commit *cm = indexed_commits[i + j];
 623
 624                                 if ((cm->object.flags & NEEDS_BITMAP) != 0) {
 625                                         chosen = cm;
 626                                         break;
 627                                 }
 628
 629                                 if (cm->parents && cm->parents->next)
 630                                         chosen = cm;
 631                         }
 632                 }
 633
 634                 push_bitmapped_commit(chosen);
 635
 636                 i += next + 1;
 637                 display_progress(writer.progress, i);
 638         }
 639
 640         stop_progress(&writer.progress);
 641 }
 642
 643
 644 static int hashwrite_ewah_helper(void *f, const void *buf, size_t len)
 645 {
 646         /* hashwrite will die on error */
 647         hashwrite(f, buf, len);
 648         return len;
 649 }
 650
 651 /**
 652  * Write the bitmap index to disk
 653  */
 654 static inline void dump_bitmap(struct hashfile *f, struct ewah_bitmap *bitmap)
 655 {
 656         if (ewah_serialize_to(bitmap, hashwrite_ewah_helper, f) < 0)
 657                 die("Failed to write bitmap index");
 658 }
 659
 660 static const struct object_id *oid_access(size_t pos, const void *table)
 661 {
 662         const struct pack_idx_entry * const *index = table;
 663         return &index[pos]->oid;
 664 }
 665
 666 static void write_selected_commits_v1(struct hashfile *f,
 667                                       uint32_t *commit_positions,
 668                                       off_t *offsets)
 669 {
 670         int i;
 671
 672         for (i = 0; i < writer.selected_nr; ++i) {
 673                 struct bitmapped_commit *stored = &writer.selected[i];
 674
 675                 if (offsets)
 676                         offsets[i] = hashfile_total(f);
 677
 678                 hashwrite_be32(f, commit_positions[i]);
 679                 hashwrite_u8(f, stored->xor_offset);
 680                 hashwrite_u8(f, stored->flags);
 681
 682                 dump_bitmap(f, stored->write_as);
 683         }
 684 }
 685
 686 static int table_cmp(const void *_va, const void *_vb, void *_data)
 687 {
 688         uint32_t *commit_positions = _data;
 689         uint32_t a = commit_positions[*(uint32_t *)_va];
 690         uint32_t b = commit_positions[*(uint32_t *)_vb];
 691
 692         if (a > b)
 693                 return 1;
 694         else if (a < b)
 695                 return -1;
 696
 697         return 0;
 698 }
 699
 700 static void write_lookup_table(struct hashfile *f,
 701                                uint32_t *commit_positions,
 702                                off_t *offsets)
 703 {
 704         uint32_t i;
 705         uint32_t *table, *table_inv;
 706
 707         ALLOC_ARRAY(table, writer.selected_nr);
 708         ALLOC_ARRAY(table_inv, writer.selected_nr);
 709
 710         for (i = 0; i < writer.selected_nr; i++)
 711                 table[i] = i;
 712
 713         /*
 714          * At the end of this sort table[j] = i means that the i'th
 715          * bitmap corresponds to j'th bitmapped commit (among the selected
 716          * commits) in lex order of OIDs.
 717          */
 718         QSORT_S(table, writer.selected_nr, table_cmp, commit_positions);
 719
 720         /* table_inv helps us discover that relationship (i'th bitmap
 721          * to j'th commit by j = table_inv[i])
 722          */
 723         for (i = 0; i < writer.selected_nr; i++)
 724                 table_inv[table[i]] = i;
 725
 726         trace2_region_enter("pack-bitmap-write", "writing_lookup_table", the_repository);
 727         for (i = 0; i < writer.selected_nr; i++) {
 728                 struct bitmapped_commit *selected = &writer.selected[table[i]];
 729                 uint32_t xor_offset = selected->xor_offset;
 730                 uint32_t xor_row;
 731
 732                 if (xor_offset) {
 733                         /*
 734                          * xor_index stores the index (in the bitmap entries)
 735                          * of the corresponding xor bitmap. But we need to convert
 736                          * this index into lookup table's index. So, table_inv[xor_index]
 737                          * gives us the index position w.r.t. the lookup table.
 738                          *
 739                          * If "k = table[i] - xor_offset" then the xor base is the k'th
 740                          * bitmap. `table_inv[k]` gives us the position of that bitmap
 741                          * in the lookup table.
 742                          */
 743                         uint32_t xor_index = table[i] - xor_offset;
 744                         xor_row = table_inv[xor_index];
 745                 } else {
 746                         xor_row = 0xffffffff;
 747                 }
 748
 749                 hashwrite_be32(f, commit_positions[table[i]]);
 750                 hashwrite_be64(f, (uint64_t)offsets[table[i]]);
 751                 hashwrite_be32(f, xor_row);
 752         }
 753         trace2_region_leave("pack-bitmap-write", "writing_lookup_table", the_repository);
 754
 755         free(table);
 756         free(table_inv);
 757 }
 758
 759 static void write_hash_cache(struct hashfile *f,
 760                              struct pack_idx_entry **index,
 761                              uint32_t index_nr)
 762 {
 763         uint32_t i;
 764
 765         for (i = 0; i < index_nr; ++i) {
 766                 struct object_entry *entry = (struct object_entry *)index[i];
 767                 hashwrite_be32(f, entry->hash);
 768         }
 769 }
 770
 771 void bitmap_writer_set_checksum(const unsigned char *sha1)
 772 {
 773         hashcpy(writer.pack_checksum, sha1);
 774 }
 775
 776 void bitmap_writer_finish(struct pack_idx_entry **index,
 777                           uint32_t index_nr,
 778                           const char *filename,
 779                           uint16_t options)
 780 {
 781         static uint16_t default_version = 1;
 782         static uint16_t flags = BITMAP_OPT_FULL_DAG;
 783         struct strbuf tmp_file = STRBUF_INIT;
 784         struct hashfile *f;
 785         uint32_t *commit_positions = NULL;
 786         off_t *offsets = NULL;
 787         uint32_t i;
 788
 789         struct bitmap_disk_header header;
 790
 791         int fd = odb_mkstemp(&tmp_file, "pack/tmp_bitmap_XXXXXX");
 792
 793         f = hashfd(fd, tmp_file.buf);
 794
 795         memcpy(header.magic, BITMAP_IDX_SIGNATURE, sizeof(BITMAP_IDX_SIGNATURE));
 796         header.version = htons(default_version);
 797         header.options = htons(flags | options);
 798         header.entry_count = htonl(writer.selected_nr);
 799         hashcpy(header.checksum, writer.pack_checksum);
 800
 801         hashwrite(f, &header, sizeof(header) - GIT_MAX_RAWSZ + the_hash_algo->rawsz);
 802         dump_bitmap(f, writer.commits);
 803         dump_bitmap(f, writer.trees);
 804         dump_bitmap(f, writer.blobs);
 805         dump_bitmap(f, writer.tags);
 806
 807         if (options & BITMAP_OPT_LOOKUP_TABLE)
 808                 CALLOC_ARRAY(offsets, index_nr);
 809
 810         ALLOC_ARRAY(commit_positions, writer.selected_nr);
 811
 812         for (i = 0; i < writer.selected_nr; i++) {
 813                 struct bitmapped_commit *stored = &writer.selected[i];
 814                 int commit_pos = oid_pos(&stored->commit->object.oid, index, index_nr, oid_access);
 815
 816                 if (commit_pos < 0)
 817                         BUG(_("trying to write commit not in index"));
 818
 819                 commit_positions[i] = commit_pos;
 820         }
 821
 822         write_selected_commits_v1(f, commit_positions, offsets);
 823
 824         if (options & BITMAP_OPT_LOOKUP_TABLE)
 825                 write_lookup_table(f, commit_positions, offsets);
 826
 827         if (options & BITMAP_OPT_HASH_CACHE)
 828                 write_hash_cache(f, index, index_nr);
 829
 830         finalize_hashfile(f, NULL, FSYNC_COMPONENT_PACK_METADATA,
 831                           CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
 832
 833         if (adjust_shared_perm(tmp_file.buf))
 834                 die_errno("unable to make temporary bitmap file readable");
 835
 836         if (rename(tmp_file.buf, filename))
 837                 die_errno("unable to rename temporary bitmap file to '%s'", filename);
 838
 839         strbuf_release(&tmp_file);
 840         free(commit_positions);
 841         free(offsets);
 842 }