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 reused_bitmaps_nr;
 388
 389 static int fill_bitmap_commit(struct bb_commit *ent,
 390                               struct commit *commit,
 391                               struct prio_queue *queue,
 392                               struct prio_queue *tree_queue,
 393                               struct bitmap_index *old_bitmap,
 394                               const uint32_t *mapping)
 395 {
 396         int found;
 397         uint32_t pos;
 398         if (!ent->bitmap)
 399                 ent->bitmap = bitmap_new();
 400
 401         prio_queue_put(queue, commit);
 402
 403         while (queue->nr) {
 404                 struct commit_list *p;
 405                 struct commit *c = prio_queue_get(queue);
 406
 407                 if (old_bitmap && mapping) {
 408                         struct ewah_bitmap *old = bitmap_for_commit(old_bitmap, c);
 409                         /*
 410                          * If this commit has an old bitmap, then translate that
 411                          * bitmap and add its bits to this one. No need to walk
 412                          * parents or the tree for this commit.
 413                          */
 414                         if (old && !rebuild_bitmap(mapping, old, ent->bitmap)) {
 415                                 reused_bitmaps_nr++;
 416                                 continue;
 417                         }
 418                 }
 419
 420                 /*
 421                  * Mark ourselves and queue our tree. The commit
 422                  * walk ensures we cover all parents.
 423                  */
 424                 pos = find_object_pos(&c->object.oid, &found);
 425                 if (!found)
 426                         return -1;
 427                 bitmap_set(ent->bitmap, pos);
 428                 prio_queue_put(tree_queue, get_commit_tree(c));
 429
 430                 for (p = c->parents; p; p = p->next) {
 431                         pos = find_object_pos(&p->item->object.oid, &found);
 432                         if (!found)
 433                                 return -1;
 434                         if (!bitmap_get(ent->bitmap, pos)) {
 435                                 bitmap_set(ent->bitmap, pos);
 436                                 prio_queue_put(queue, p->item);
 437                         }
 438                 }
 439         }
 440
 441         while (tree_queue->nr) {
 442                 if (fill_bitmap_tree(ent->bitmap,
 443                                      prio_queue_get(tree_queue)) < 0)
 444                         return -1;
 445         }
 446         return 0;
 447 }
 448
 449 static void store_selected(struct bb_commit *ent, struct commit *commit)
 450 {
 451         struct bitmapped_commit *stored = &writer.selected[ent->idx];
 452         khiter_t hash_pos;
 453         int hash_ret;
 454
 455         stored->bitmap = bitmap_to_ewah(ent->bitmap);
 456
 457         hash_pos = kh_put_oid_map(writer.bitmaps, commit->object.oid, &hash_ret);
 458         if (hash_ret == 0)
 459                 die("Duplicate entry when writing index: %s",
 460                     oid_to_hex(&commit->object.oid));
 461         kh_value(writer.bitmaps, hash_pos) = stored;
 462 }
 463
 464 int bitmap_writer_build(struct packing_data *to_pack)
 465 {
 466         struct bitmap_builder bb;
 467         size_t i;
 468         int nr_stored = 0; /* for progress */
 469         struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
 470         struct prio_queue tree_queue = { NULL };
 471         struct bitmap_index *old_bitmap;
 472         uint32_t *mapping;
 473         int closed = 1; /* until proven otherwise */
 474
 475         writer.bitmaps = kh_init_oid_map();
 476         writer.to_pack = to_pack;
 477
 478         if (writer.show_progress)
 479                 writer.progress = start_progress("Building bitmaps", writer.selected_nr);
 480         trace2_region_enter("pack-bitmap-write", "building_bitmaps_total",
 481                             the_repository);
 482
 483         old_bitmap = prepare_bitmap_git(to_pack->repo);
 484         if (old_bitmap)
 485                 mapping = create_bitmap_mapping(old_bitmap, to_pack);
 486         else
 487                 mapping = NULL;
 488
 489         bitmap_builder_init(&bb, &writer, old_bitmap);
 490         for (i = bb.commits_nr; i > 0; i--) {
 491                 struct commit *commit = bb.commits[i-1];
 492                 struct bb_commit *ent = bb_data_at(&bb.data, commit);
 493                 struct commit *child;
 494                 int reused = 0;
 495
 496                 if (fill_bitmap_commit(ent, commit, &queue, &tree_queue,
 497                                        old_bitmap, mapping) < 0) {
 498                         closed = 0;
 499                         break;
 500                 }
 501
 502                 if (ent->selected) {
 503                         store_selected(ent, commit);
 504                         nr_stored++;
 505                         display_progress(writer.progress, nr_stored);
 506                 }
 507
 508                 while ((child = pop_commit(&ent->reverse_edges))) {
 509                         struct bb_commit *child_ent =
 510                                 bb_data_at(&bb.data, child);
 511
 512                         if (child_ent->bitmap)
 513                                 bitmap_or(child_ent->bitmap, ent->bitmap);
 514                         else if (reused)
 515                                 child_ent->bitmap = bitmap_dup(ent->bitmap);
 516                         else {
 517                                 child_ent->bitmap = ent->bitmap;
 518                                 reused = 1;
 519                         }
 520                 }
 521                 if (!reused)
 522                         bitmap_free(ent->bitmap);
 523                 ent->bitmap = NULL;
 524         }
 525         clear_prio_queue(&queue);
 526         clear_prio_queue(&tree_queue);
 527         bitmap_builder_clear(&bb);
 528         free_bitmap_index(old_bitmap);
 529         free(mapping);
 530
 531         trace2_region_leave("pack-bitmap-write", "building_bitmaps_total",
 532                             the_repository);
 533         trace2_data_intmax("pack-bitmap-write", the_repository,
 534                            "building_bitmaps_reused", reused_bitmaps_nr);
 535
 536         stop_progress(&writer.progress);
 537
 538         if (closed)
 539                 compute_xor_offsets();
 540         return closed ? 0 : -1;
 541 }
 542
 543 /**
 544  * Select the commits that will be bitmapped
 545  */
 546 static inline unsigned int next_commit_index(unsigned int idx)
 547 {
 548         static const unsigned int MIN_COMMITS = 100;
 549         static const unsigned int MAX_COMMITS = 5000;
 550
 551         static const unsigned int MUST_REGION = 100;
 552         static const unsigned int MIN_REGION = 20000;
 553
 554         unsigned int offset, next;
 555
 556         if (idx <= MUST_REGION)
 557                 return 0;
 558
 559         if (idx <= MIN_REGION) {
 560                 offset = idx - MUST_REGION;
 561                 return (offset < MIN_COMMITS) ? offset : MIN_COMMITS;
 562         }
 563
 564         offset = idx - MIN_REGION;
 565         next = (offset < MAX_COMMITS) ? offset : MAX_COMMITS;
 566
 567         return (next > MIN_COMMITS) ? next : MIN_COMMITS;
 568 }
 569
 570 static int date_compare(const void *_a, const void *_b)
 571 {
 572         struct commit *a = *(struct commit **)_a;
 573         struct commit *b = *(struct commit **)_b;
 574         return (long)b->date - (long)a->date;
 575 }
 576
 577 void bitmap_writer_select_commits(struct commit **indexed_commits,
 578                                   unsigned int indexed_commits_nr,
 579                                   int max_bitmaps)
 580 {
 581         unsigned int i = 0, j, next;
 582
 583         QSORT(indexed_commits, indexed_commits_nr, date_compare);
 584
 585         if (indexed_commits_nr < 100) {
 586                 for (i = 0; i < indexed_commits_nr; ++i)
 587                         push_bitmapped_commit(indexed_commits[i]);
 588                 return;
 589         }
 590
 591         if (writer.show_progress)
 592                 writer.progress = start_progress("Selecting bitmap commits", 0);
 593
 594         for (;;) {
 595                 struct commit *chosen = NULL;
 596
 597                 next = next_commit_index(i);
 598
 599                 if (i + next >= indexed_commits_nr)
 600                         break;
 601
 602                 if (max_bitmaps > 0 && writer.selected_nr >= max_bitmaps) {
 603                         writer.selected_nr = max_bitmaps;
 604                         break;
 605                 }
 606
 607                 if (next == 0) {
 608                         chosen = indexed_commits[i];
 609                 } else {
 610                         chosen = indexed_commits[i + next];
 611
 612                         for (j = 0; j <= next; ++j) {
 613                                 struct commit *cm = indexed_commits[i + j];
 614
 615                                 if ((cm->object.flags & NEEDS_BITMAP) != 0) {
 616                                         chosen = cm;
 617                                         break;
 618                                 }
 619
 620                                 if (cm->parents && cm->parents->next)
 621                                         chosen = cm;
 622                         }
 623                 }
 624
 625                 push_bitmapped_commit(chosen);
 626
 627                 i += next + 1;
 628                 display_progress(writer.progress, i);
 629         }
 630
 631         stop_progress(&writer.progress);
 632 }
 633
 634
 635 static int hashwrite_ewah_helper(void *f, const void *buf, size_t len)
 636 {
 637         /* hashwrite will die on error */
 638         hashwrite(f, buf, len);
 639         return len;
 640 }
 641
 642 /**
 643  * Write the bitmap index to disk
 644  */
 645 static inline void dump_bitmap(struct hashfile *f, struct ewah_bitmap *bitmap)
 646 {
 647         if (ewah_serialize_to(bitmap, hashwrite_ewah_helper, f) < 0)
 648                 die("Failed to write bitmap index");
 649 }
 650
 651 static const struct object_id *oid_access(size_t pos, const void *table)
 652 {
 653         const struct pack_idx_entry * const *index = table;
 654         return &index[pos]->oid;
 655 }
 656
 657 static void write_selected_commits_v1(struct hashfile *f,
 658                                       uint32_t *commit_positions,
 659                                       off_t *offsets)
 660 {
 661         int i;
 662
 663         for (i = 0; i < writer.selected_nr; ++i) {
 664                 struct bitmapped_commit *stored = &writer.selected[i];
 665
 666                 if (offsets)
 667                         offsets[i] = hashfile_total(f);
 668
 669                 hashwrite_be32(f, commit_positions[i]);
 670                 hashwrite_u8(f, stored->xor_offset);
 671                 hashwrite_u8(f, stored->flags);
 672
 673                 dump_bitmap(f, stored->write_as);
 674         }
 675 }
 676
 677 static int table_cmp(const void *_va, const void *_vb, void *_data)
 678 {
 679         uint32_t *commit_positions = _data;
 680         uint32_t a = commit_positions[*(uint32_t *)_va];
 681         uint32_t b = commit_positions[*(uint32_t *)_vb];
 682
 683         if (a > b)
 684                 return 1;
 685         else if (a < b)
 686                 return -1;
 687
 688         return 0;
 689 }
 690
 691 static void write_lookup_table(struct hashfile *f,
 692                                uint32_t *commit_positions,
 693                                off_t *offsets)
 694 {
 695         uint32_t i;
 696         uint32_t *table, *table_inv;
 697
 698         ALLOC_ARRAY(table, writer.selected_nr);
 699         ALLOC_ARRAY(table_inv, writer.selected_nr);
 700
 701         for (i = 0; i < writer.selected_nr; i++)
 702                 table[i] = i;
 703
 704         /*
 705          * At the end of this sort table[j] = i means that the i'th
 706          * bitmap corresponds to j'th bitmapped commit (among the selected
 707          * commits) in lex order of OIDs.
 708          */
 709         QSORT_S(table, writer.selected_nr, table_cmp, commit_positions);
 710
 711         /* table_inv helps us discover that relationship (i'th bitmap
 712          * to j'th commit by j = table_inv[i])
 713          */
 714         for (i = 0; i < writer.selected_nr; i++)
 715                 table_inv[table[i]] = i;
 716
 717         trace2_region_enter("pack-bitmap-write", "writing_lookup_table", the_repository);
 718         for (i = 0; i < writer.selected_nr; i++) {
 719                 struct bitmapped_commit *selected = &writer.selected[table[i]];
 720                 uint32_t xor_offset = selected->xor_offset;
 721                 uint32_t xor_row;
 722
 723                 if (xor_offset) {
 724                         /*
 725                          * xor_index stores the index (in the bitmap entries)
 726                          * of the corresponding xor bitmap. But we need to convert
 727                          * this index into lookup table's index. So, table_inv[xor_index]
 728                          * gives us the index position w.r.t. the lookup table.
 729                          *
 730                          * If "k = table[i] - xor_offset" then the xor base is the k'th
 731                          * bitmap. `table_inv[k]` gives us the position of that bitmap
 732                          * in the lookup table.
 733                          */
 734                         uint32_t xor_index = table[i] - xor_offset;
 735                         xor_row = table_inv[xor_index];
 736                 } else {
 737                         xor_row = 0xffffffff;
 738                 }
 739
 740                 hashwrite_be32(f, commit_positions[table[i]]);
 741                 hashwrite_be64(f, (uint64_t)offsets[table[i]]);
 742                 hashwrite_be32(f, xor_row);
 743         }
 744         trace2_region_leave("pack-bitmap-write", "writing_lookup_table", the_repository);
 745
 746         free(table);
 747         free(table_inv);
 748 }
 749
 750 static void write_hash_cache(struct hashfile *f,
 751                              struct pack_idx_entry **index,
 752                              uint32_t index_nr)
 753 {
 754         uint32_t i;
 755
 756         for (i = 0; i < index_nr; ++i) {
 757                 struct object_entry *entry = (struct object_entry *)index[i];
 758                 hashwrite_be32(f, entry->hash);
 759         }
 760 }
 761
 762 void bitmap_writer_set_checksum(const unsigned char *sha1)
 763 {
 764         hashcpy(writer.pack_checksum, sha1);
 765 }
 766
 767 void bitmap_writer_finish(struct pack_idx_entry **index,
 768                           uint32_t index_nr,
 769                           const char *filename,
 770                           uint16_t options)
 771 {
 772         static uint16_t default_version = 1;
 773         static uint16_t flags = BITMAP_OPT_FULL_DAG;
 774         struct strbuf tmp_file = STRBUF_INIT;
 775         struct hashfile *f;
 776         uint32_t *commit_positions = NULL;
 777         off_t *offsets = NULL;
 778         uint32_t i;
 779
 780         struct bitmap_disk_header header;
 781
 782         int fd = odb_mkstemp(&tmp_file, "pack/tmp_bitmap_XXXXXX");
 783
 784         f = hashfd(fd, tmp_file.buf);
 785
 786         memcpy(header.magic, BITMAP_IDX_SIGNATURE, sizeof(BITMAP_IDX_SIGNATURE));
 787         header.version = htons(default_version);
 788         header.options = htons(flags | options);
 789         header.entry_count = htonl(writer.selected_nr);
 790         hashcpy(header.checksum, writer.pack_checksum);
 791
 792         hashwrite(f, &header, sizeof(header) - GIT_MAX_RAWSZ + the_hash_algo->rawsz);
 793         dump_bitmap(f, writer.commits);
 794         dump_bitmap(f, writer.trees);
 795         dump_bitmap(f, writer.blobs);
 796         dump_bitmap(f, writer.tags);
 797
 798         if (options & BITMAP_OPT_LOOKUP_TABLE)
 799                 CALLOC_ARRAY(offsets, index_nr);
 800
 801         ALLOC_ARRAY(commit_positions, writer.selected_nr);
 802
 803         for (i = 0; i < writer.selected_nr; i++) {
 804                 struct bitmapped_commit *stored = &writer.selected[i];
 805                 int commit_pos = oid_pos(&stored->commit->object.oid, index, index_nr, oid_access);
 806
 807                 if (commit_pos < 0)
 808                         BUG(_("trying to write commit not in index"));
 809
 810                 commit_positions[i] = commit_pos;
 811         }
 812
 813         write_selected_commits_v1(f, commit_positions, offsets);
 814
 815         if (options & BITMAP_OPT_LOOKUP_TABLE)
 816                 write_lookup_table(f, commit_positions, offsets);
 817
 818         if (options & BITMAP_OPT_HASH_CACHE)
 819                 write_hash_cache(f, index, index_nr);
 820
 821         finalize_hashfile(f, NULL, FSYNC_COMPONENT_PACK_METADATA,
 822                           CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
 823
 824         if (adjust_shared_perm(tmp_file.buf))
 825                 die_errno("unable to make temporary bitmap file readable");
 826
 827         if (rename(tmp_file.buf, filename))
 828                 die_errno("unable to rename temporary bitmap file to '%s'", filename);
 829
 830         strbuf_release(&tmp_file);
 831         free(commit_positions);
 832         free(offsets);
 833 }