pack-bitmap-write.c

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