pack-bitmap-write.c

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