pack-bitmap-write.c

   1 #include "git-compat-util.h"
   2 #include "environment.h"
   3 #include "gettext.h"
   4 #include "hex.h"
   5 #include "object-store-ll.h"
   6 #include "commit.h"
   7 #include "diff.h"
   8 #include "revision.h"
   9 #include "progress.h"
  10 #include "pack.h"
  11 #include "pack-bitmap.h"
  12 #include "hash-lookup.h"
  13 #include "pack-objects.h"
  14 #include "path.h"
  15 #include "commit-reach.h"
  16 #include "prio-queue.h"
  17 #include "trace2.h"
  18 #include "tree.h"
  19 #include "tree-walk.h"
  20
  21 struct bitmapped_commit {
  22         struct commit *commit;
  23         struct ewah_bitmap *bitmap;
  24         struct ewah_bitmap *write_as;
  25         int flags;
  26         int xor_offset;
  27         uint32_t commit_pos;
  28 };
  29
  30 struct bitmap_writer {
  31         struct ewah_bitmap *commits;
  32         struct ewah_bitmap *trees;
  33         struct ewah_bitmap *blobs;
  34         struct ewah_bitmap *tags;
  35
  36         kh_oid_map_t *bitmaps;
  37         struct packing_data *to_pack;
  38
  39         struct bitmapped_commit *selected;
  40         unsigned int selected_nr, selected_alloc;
  41
  42         struct progress *progress;
  43         int show_progress;
  44         unsigned char pack_checksum[GIT_MAX_RAWSZ];
  45 };
  46
  47 static struct bitmap_writer writer;
  48
  49 void bitmap_writer_show_progress(int show)
  50 {
  51         writer.show_progress = show;
  52 }
  53
  54 /**
  55  * Build the initial type index for the packfile or multi-pack-index
  56  */
  57 void bitmap_writer_build_type_index(struct packing_data *to_pack,
  58                                     struct pack_idx_entry **index,
  59                                     uint32_t index_nr)
  60 {
  61         uint32_t i;
  62
  63         writer.commits = ewah_new();
  64         writer.trees = ewah_new();
  65         writer.blobs = ewah_new();
  66         writer.tags = ewah_new();
  67         ALLOC_ARRAY(to_pack->in_pack_pos, to_pack->nr_objects);
  68
  69         for (i = 0; i < index_nr; ++i) {
  70                 struct object_entry *entry = (struct object_entry *)index[i];
  71                 enum object_type real_type;
  72
  73                 oe_set_in_pack_pos(to_pack, entry, i);
  74
  75                 switch (oe_type(entry)) {
  76                 case OBJ_COMMIT:
  77                 case OBJ_TREE:
  78                 case OBJ_BLOB:
  79                 case OBJ_TAG:
  80                         real_type = oe_type(entry);
  81                         break;
  82
  83                 default:
  84                         real_type = oid_object_info(to_pack->repo,
  85                                                     &entry->idx.oid, NULL);
  86                         break;
  87                 }
  88
  89                 switch (real_type) {
  90                 case OBJ_COMMIT:
  91                         ewah_set(writer.commits, i);
  92                         break;
  93
  94                 case OBJ_TREE:
  95                         ewah_set(writer.trees, i);
  96                         break;
  97
  98                 case OBJ_BLOB:
  99                         ewah_set(writer.blobs, i);
 100                         break;
 101
 102                 case OBJ_TAG:
 103                         ewah_set(writer.tags, i);
 104                         break;
 105
 106                 default:
 107                         die("Missing type information for %s (%d/%d)",
 108                             oid_to_hex(&entry->idx.oid), real_type,
 109                             oe_type(entry));
 110                 }
 111         }
 112 }
 113
 114 /**
 115  * Compute the actual bitmaps
 116  */
 117
 118 static inline void push_bitmapped_commit(struct commit *commit)
 119 {
 120         if (writer.selected_nr >= writer.selected_alloc) {
 121                 writer.selected_alloc = (writer.selected_alloc + 32) * 2;
 122                 REALLOC_ARRAY(writer.selected, writer.selected_alloc);
 123         }
 124
 125         writer.selected[writer.selected_nr].commit = commit;
 126         writer.selected[writer.selected_nr].bitmap = NULL;
 127         writer.selected[writer.selected_nr].flags = 0;
 128
 129         writer.selected_nr++;
 130 }
 131
 132 static uint32_t find_object_pos(const struct object_id *oid, int *found)
 133 {
 134         struct object_entry *entry = packlist_find(writer.to_pack, oid);
 135
 136         if (!entry) {
 137                 if (found)
 138                         *found = 0;
 139                 warning("Failed to write bitmap index. Packfile doesn't have full closure "
 140                         "(object %s is missing)", oid_to_hex(oid));
 141                 return 0;
 142         }
 143
 144         if (found)
 145                 *found = 1;
 146         return oe_in_pack_pos(writer.to_pack, entry);
 147 }
 148
 149 static void compute_xor_offsets(void)
 150 {
 151         static const int MAX_XOR_OFFSET_SEARCH = 10;
 152
 153         int i, next = 0;
 154
 155         while (next < writer.selected_nr) {
 156                 struct bitmapped_commit *stored = &writer.selected[next];
 157
 158                 int best_offset = 0;
 159                 struct ewah_bitmap *best_bitmap = stored->bitmap;
 160                 struct ewah_bitmap *test_xor;
 161
 162                 for (i = 1; i <= MAX_XOR_OFFSET_SEARCH; ++i) {
 163                         int curr = next - i;
 164
 165                         if (curr < 0)
 166                                 break;
 167
 168                         test_xor = ewah_pool_new();
 169                         ewah_xor(writer.selected[curr].bitmap, stored->bitmap, test_xor);
 170
 171                         if (test_xor->buffer_size < best_bitmap->buffer_size) {
 172                                 if (best_bitmap != stored->bitmap)
 173                                         ewah_pool_free(best_bitmap);
 174
 175                                 best_bitmap = test_xor;
 176                                 best_offset = i;
 177                         } else {
 178                                 ewah_pool_free(test_xor);
 179                         }
 180                 }
 181
 182                 stored->xor_offset = best_offset;
 183                 stored->write_as = best_bitmap;
 184
 185                 next++;
 186         }
 187 }
 188
 189 struct bb_commit {
 190         struct commit_list *reverse_edges;
 191         struct bitmap *commit_mask;
 192         struct bitmap *bitmap;
 193         unsigned selected:1,
 194                  maximal:1;
 195         unsigned idx; /* within selected array */
 196 };
 197
 198 static void clear_bb_commit(struct bb_commit *commit)
 199 {
 200         free_commit_list(commit->reverse_edges);
 201         bitmap_free(commit->commit_mask);
 202         bitmap_free(commit->bitmap);
 203 }
 204
 205 define_commit_slab(bb_data, struct bb_commit);
 206
 207 struct bitmap_builder {
 208         struct bb_data data;
 209         struct commit **commits;
 210         size_t commits_nr, commits_alloc;
 211 };
 212
 213 static void bitmap_builder_init(struct bitmap_builder *bb,
 214                                 struct bitmap_writer *writer,
 215                                 struct bitmap_index *old_bitmap)
 216 {
 217         struct rev_info revs;
 218         struct commit *commit;
 219         struct commit_list *reusable = NULL;
 220         struct commit_list *r;
 221         unsigned int i, num_maximal = 0;
 222
 223         memset(bb, 0, sizeof(*bb));
 224         init_bb_data(&bb->data);
 225
 226         reset_revision_walk();
 227         repo_init_revisions(writer->to_pack->repo, &revs, NULL);
 228         revs.topo_order = 1;
 229         revs.first_parent_only = 1;
 230
 231         for (i = 0; i < writer->selected_nr; i++) {
 232                 struct commit *c = writer->selected[i].commit;
 233                 struct bb_commit *ent = bb_data_at(&bb->data, c);
 234
 235                 ent->selected = 1;
 236                 ent->maximal = 1;
 237                 ent->idx = i;
 238
 239                 ent->commit_mask = bitmap_new();
 240                 bitmap_set(ent->commit_mask, i);
 241
 242                 add_pending_object(&revs, &c->object, "");
 243         }
 244
 245         if (prepare_revision_walk(&revs))
 246                 die("revision walk setup failed");
 247
 248         while ((commit = get_revision(&revs))) {
 249                 struct commit_list *p = commit->parents;
 250                 struct bb_commit *c_ent;
 251
 252                 parse_commit_or_die(commit);
 253
 254                 c_ent = bb_data_at(&bb->data, commit);
 255
 256                 /*
 257                  * If there is no commit_mask, there is no reason to iterate
 258                  * over this commit; it is not selected (if it were, it would
 259                  * not have a blank commit mask) and all its children have
 260                  * existing bitmaps (see the comment starting with "This commit
 261                  * has an existing bitmap" below), so it does not contribute
 262                  * anything to the final bitmap file or its descendants.
 263                  */
 264                 if (!c_ent->commit_mask)
 265                         continue;
 266
 267                 if (old_bitmap && bitmap_for_commit(old_bitmap, commit)) {
 268                         /*
 269                          * This commit has an existing bitmap, so we can
 270                          * get its bits immediately without an object
 271                          * walk. That is, it is reusable as-is and there is no
 272                          * need to continue walking beyond it.
 273                          *
 274                          * Mark it as such and add it to bb->commits separately
 275                          * to avoid allocating a position in the commit mask.
 276                          */
 277                         commit_list_insert(commit, &reusable);
 278                         goto next;
 279                 }
 280
 281                 if (c_ent->maximal) {
 282                         num_maximal++;
 283                         ALLOC_GROW(bb->commits, bb->commits_nr + 1, bb->commits_alloc);
 284                         bb->commits[bb->commits_nr++] = commit;
 285                 }
 286
 287                 if (p) {
 288                         struct bb_commit *p_ent = bb_data_at(&bb->data, p->item);
 289                         int c_not_p, p_not_c;
 290
 291                         if (!p_ent->commit_mask) {
 292                                 p_ent->commit_mask = bitmap_new();
 293                                 c_not_p = 1;
 294                                 p_not_c = 0;
 295                         } else {
 296                                 c_not_p = bitmap_is_subset(c_ent->commit_mask, p_ent->commit_mask);
 297                                 p_not_c = bitmap_is_subset(p_ent->commit_mask, c_ent->commit_mask);
 298                         }
 299
 300                         if (!c_not_p)
 301                                 continue;
 302
 303                         bitmap_or(p_ent->commit_mask, c_ent->commit_mask);
 304
 305                         if (p_not_c)
 306                                 p_ent->maximal = 1;
 307                         else {
 308                                 p_ent->maximal = 0;
 309                                 free_commit_list(p_ent->reverse_edges);
 310                                 p_ent->reverse_edges = NULL;
 311                         }
 312
 313                         if (c_ent->maximal) {
 314                                 commit_list_insert(commit, &p_ent->reverse_edges);
 315                         } else {
 316                                 struct commit_list *cc = c_ent->reverse_edges;
 317
 318                                 for (; cc; cc = cc->next) {
 319                                         if (!commit_list_contains(cc->item, p_ent->reverse_edges))
 320                                                 commit_list_insert(cc->item, &p_ent->reverse_edges);
 321                                 }
 322                         }
 323                 }
 324
 325 next:
 326                 bitmap_free(c_ent->commit_mask);
 327                 c_ent->commit_mask = NULL;
 328         }
 329
 330         for (r = reusable; r; r = r->next) {
 331                 ALLOC_GROW(bb->commits, bb->commits_nr + 1, bb->commits_alloc);
 332                 bb->commits[bb->commits_nr++] = r->item;
 333         }
 334
 335         trace2_data_intmax("pack-bitmap-write", the_repository,
 336                            "num_selected_commits", writer->selected_nr);
 337         trace2_data_intmax("pack-bitmap-write", the_repository,
 338                            "num_maximal_commits", num_maximal);
 339
 340         release_revisions(&revs);
 341         free_commit_list(reusable);
 342 }
 343
 344 static void bitmap_builder_clear(struct bitmap_builder *bb)
 345 {
 346         deep_clear_bb_data(&bb->data, clear_bb_commit);
 347         free(bb->commits);
 348         bb->commits_nr = bb->commits_alloc = 0;
 349 }
 350
 351 static int fill_bitmap_tree(struct bitmap *bitmap,
 352                             struct tree *tree)
 353 {
 354         int found;
 355         uint32_t pos;
 356         struct tree_desc desc;
 357         struct name_entry entry;
 358
 359         /*
 360          * If our bit is already set, then there is nothing to do. Both this
 361          * tree and all of its children will be set.
 362          */
 363         pos = find_object_pos(&tree->object.oid, &found);
 364         if (!found)
 365                 return -1;
 366         if (bitmap_get(bitmap, pos))
 367                 return 0;
 368         bitmap_set(bitmap, pos);
 369
 370         if (parse_tree(tree) < 0)
 371                 die("unable to load tree object %s",
 372                     oid_to_hex(&tree->object.oid));
 373         init_tree_desc(&desc, tree->buffer, tree->size);
 374
 375         while (tree_entry(&desc, &entry)) {
 376                 switch (object_type(entry.mode)) {
 377                 case OBJ_TREE:
 378                         if (fill_bitmap_tree(bitmap,
 379                                              lookup_tree(the_repository, &entry.oid)) < 0)
 380                                 return -1;
 381                         break;
 382                 case OBJ_BLOB:
 383                         pos = find_object_pos(&entry.oid, &found);
 384                         if (!found)
 385                                 return -1;
 386                         bitmap_set(bitmap, pos);
 387                         break;
 388                 default:
 389                         /* Gitlink, etc; not reachable */
 390                         break;
 391                 }
 392         }
 393
 394         free_tree_buffer(tree);
 395         return 0;
 396 }
 397
 398 static int reused_bitmaps_nr;
 399
 400 static int fill_bitmap_commit(struct bb_commit *ent,
 401                               struct commit *commit,
 402                               struct prio_queue *queue,
 403                               struct prio_queue *tree_queue,
 404                               struct bitmap_index *old_bitmap,
 405                               const uint32_t *mapping)
 406 {
 407         int found;
 408         uint32_t pos;
 409         if (!ent->bitmap)
 410                 ent->bitmap = bitmap_new();
 411
 412         prio_queue_put(queue, commit);
 413
 414         while (queue->nr) {
 415                 struct commit_list *p;
 416                 struct commit *c = prio_queue_get(queue);
 417
 418                 if (old_bitmap && mapping) {
 419                         struct ewah_bitmap *old = bitmap_for_commit(old_bitmap, c);
 420                         struct bitmap *remapped = bitmap_new();
 421                         /*
 422                          * If this commit has an old bitmap, then translate that
 423                          * bitmap and add its bits to this one. No need to walk
 424                          * parents or the tree for this commit.
 425                          */
 426                         if (old && !rebuild_bitmap(mapping, old, remapped)) {
 427                                 bitmap_or(ent->bitmap, remapped);
 428                                 bitmap_free(remapped);
 429                                 reused_bitmaps_nr++;
 430                                 continue;
 431                         }
 432                         bitmap_free(remapped);
 433                 }
 434
 435                 /*
 436                  * Mark ourselves and queue our tree. The commit
 437                  * walk ensures we cover all parents.
 438                  */
 439                 pos = find_object_pos(&c->object.oid, &found);
 440                 if (!found)
 441                         return -1;
 442                 bitmap_set(ent->bitmap, pos);
 443                 prio_queue_put(tree_queue,
 444                                repo_get_commit_tree(the_repository, c));
 445
 446                 for (p = c->parents; p; p = p->next) {
 447                         pos = find_object_pos(&p->item->object.oid, &found);
 448                         if (!found)
 449                                 return -1;
 450                         if (!bitmap_get(ent->bitmap, pos)) {
 451                                 bitmap_set(ent->bitmap, pos);
 452                                 prio_queue_put(queue, p->item);
 453                         }
 454                 }
 455         }
 456
 457         while (tree_queue->nr) {
 458                 if (fill_bitmap_tree(ent->bitmap,
 459                                      prio_queue_get(tree_queue)) < 0)
 460                         return -1;
 461         }
 462         return 0;
 463 }
 464
 465 static void store_selected(struct bb_commit *ent, struct commit *commit)
 466 {
 467         struct bitmapped_commit *stored = &writer.selected[ent->idx];
 468         khiter_t hash_pos;
 469         int hash_ret;
 470
 471         stored->bitmap = bitmap_to_ewah(ent->bitmap);
 472
 473         hash_pos = kh_put_oid_map(writer.bitmaps, commit->object.oid, &hash_ret);
 474         if (hash_ret == 0)
 475                 die("Duplicate entry when writing index: %s",
 476                     oid_to_hex(&commit->object.oid));
 477         kh_value(writer.bitmaps, hash_pos) = stored;
 478 }
 479
 480 int bitmap_writer_build(struct packing_data *to_pack)
 481 {
 482         struct bitmap_builder bb;
 483         size_t i;
 484         int nr_stored = 0; /* for progress */
 485         struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
 486         struct prio_queue tree_queue = { NULL };
 487         struct bitmap_index *old_bitmap;
 488         uint32_t *mapping;
 489         int closed = 1; /* until proven otherwise */
 490
 491         writer.bitmaps = kh_init_oid_map();
 492         writer.to_pack = to_pack;
 493
 494         if (writer.show_progress)
 495                 writer.progress = start_progress("Building bitmaps", writer.selected_nr);
 496         trace2_region_enter("pack-bitmap-write", "building_bitmaps_total",
 497                             the_repository);
 498
 499         old_bitmap = prepare_bitmap_git(to_pack->repo);
 500         if (old_bitmap)
 501                 mapping = create_bitmap_mapping(old_bitmap, to_pack);
 502         else
 503                 mapping = NULL;
 504
 505         bitmap_builder_init(&bb, &writer, old_bitmap);
 506         for (i = bb.commits_nr; i > 0; i--) {
 507                 struct commit *commit = bb.commits[i-1];
 508                 struct bb_commit *ent = bb_data_at(&bb.data, commit);
 509                 struct commit *child;
 510                 int reused = 0;
 511
 512                 if (fill_bitmap_commit(ent, commit, &queue, &tree_queue,
 513                                        old_bitmap, mapping) < 0) {
 514                         closed = 0;
 515                         break;
 516                 }
 517
 518                 if (ent->selected) {
 519                         store_selected(ent, commit);
 520                         nr_stored++;
 521                         display_progress(writer.progress, nr_stored);
 522                 }
 523
 524                 while ((child = pop_commit(&ent->reverse_edges))) {
 525                         struct bb_commit *child_ent =
 526                                 bb_data_at(&bb.data, child);
 527
 528                         if (child_ent->bitmap)
 529                                 bitmap_or(child_ent->bitmap, ent->bitmap);
 530                         else if (reused)
 531                                 child_ent->bitmap = bitmap_dup(ent->bitmap);
 532                         else {
 533                                 child_ent->bitmap = ent->bitmap;
 534                                 reused = 1;
 535                         }
 536                 }
 537                 if (!reused)
 538                         bitmap_free(ent->bitmap);
 539                 ent->bitmap = NULL;
 540         }
 541         clear_prio_queue(&queue);
 542         clear_prio_queue(&tree_queue);
 543         bitmap_builder_clear(&bb);
 544         free_bitmap_index(old_bitmap);
 545         free(mapping);
 546
 547         trace2_region_leave("pack-bitmap-write", "building_bitmaps_total",
 548                             the_repository);
 549         trace2_data_intmax("pack-bitmap-write", the_repository,
 550                            "building_bitmaps_reused", reused_bitmaps_nr);
 551
 552         stop_progress(&writer.progress);
 553
 554         if (closed)
 555                 compute_xor_offsets();
 556         return closed ? 0 : -1;
 557 }
 558
 559 /**
 560  * Select the commits that will be bitmapped
 561  */
 562 static inline unsigned int next_commit_index(unsigned int idx)
 563 {
 564         static const unsigned int MIN_COMMITS = 100;
 565         static const unsigned int MAX_COMMITS = 5000;
 566
 567         static const unsigned int MUST_REGION = 100;
 568         static const unsigned int MIN_REGION = 20000;
 569
 570         unsigned int offset, next;
 571
 572         if (idx <= MUST_REGION)
 573                 return 0;
 574
 575         if (idx <= MIN_REGION) {
 576                 offset = idx - MUST_REGION;
 577                 return (offset < MIN_COMMITS) ? offset : MIN_COMMITS;
 578         }
 579
 580         offset = idx - MIN_REGION;
 581         next = (offset < MAX_COMMITS) ? offset : MAX_COMMITS;
 582
 583         return (next > MIN_COMMITS) ? next : MIN_COMMITS;
 584 }
 585
 586 static int date_compare(const void *_a, const void *_b)
 587 {
 588         struct commit *a = *(struct commit **)_a;
 589         struct commit *b = *(struct commit **)_b;
 590         return (long)b->date - (long)a->date;
 591 }
 592
 593 void bitmap_writer_select_commits(struct commit **indexed_commits,
 594                                   unsigned int indexed_commits_nr,
 595                                   int max_bitmaps)
 596 {
 597         unsigned int i = 0, j, next;
 598
 599         QSORT(indexed_commits, indexed_commits_nr, date_compare);
 600
 601         if (indexed_commits_nr < 100) {
 602                 for (i = 0; i < indexed_commits_nr; ++i)
 603                         push_bitmapped_commit(indexed_commits[i]);
 604                 return;
 605         }
 606
 607         if (writer.show_progress)
 608                 writer.progress = start_progress("Selecting bitmap commits", 0);
 609
 610         for (;;) {
 611                 struct commit *chosen = NULL;
 612
 613                 next = next_commit_index(i);
 614
 615                 if (i + next >= indexed_commits_nr)
 616                         break;
 617
 618                 if (max_bitmaps > 0 && writer.selected_nr >= max_bitmaps) {
 619                         writer.selected_nr = max_bitmaps;
 620                         break;
 621                 }
 622
 623                 if (next == 0) {
 624                         chosen = indexed_commits[i];
 625                 } else {
 626                         chosen = indexed_commits[i + next];
 627
 628                         for (j = 0; j <= next; ++j) {
 629                                 struct commit *cm = indexed_commits[i + j];
 630
 631                                 if ((cm->object.flags & NEEDS_BITMAP) != 0) {
 632                                         chosen = cm;
 633                                         break;
 634                                 }
 635
 636                                 if (cm->parents && cm->parents->next)
 637                                         chosen = cm;
 638                         }
 639                 }
 640
 641                 push_bitmapped_commit(chosen);
 642
 643                 i += next + 1;
 644                 display_progress(writer.progress, i);
 645         }
 646
 647         stop_progress(&writer.progress);
 648 }
 649
 650
 651 static int hashwrite_ewah_helper(void *f, const void *buf, size_t len)
 652 {
 653         /* hashwrite will die on error */
 654         hashwrite(f, buf, len);
 655         return len;
 656 }
 657
 658 /**
 659  * Write the bitmap index to disk
 660  */
 661 static inline void dump_bitmap(struct hashfile *f, struct ewah_bitmap *bitmap)
 662 {
 663         if (ewah_serialize_to(bitmap, hashwrite_ewah_helper, f) < 0)
 664                 die("Failed to write bitmap index");
 665 }
 666
 667 static const struct object_id *oid_access(size_t pos, const void *table)
 668 {
 669         const struct pack_idx_entry * const *index = table;
 670         return &index[pos]->oid;
 671 }
 672
 673 static void write_selected_commits_v1(struct hashfile *f,
 674                                       uint32_t *commit_positions,
 675                                       off_t *offsets)
 676 {
 677         int i;
 678
 679         for (i = 0; i < writer.selected_nr; ++i) {
 680                 struct bitmapped_commit *stored = &writer.selected[i];
 681
 682                 if (offsets)
 683                         offsets[i] = hashfile_total(f);
 684
 685                 hashwrite_be32(f, commit_positions[i]);
 686                 hashwrite_u8(f, stored->xor_offset);
 687                 hashwrite_u8(f, stored->flags);
 688
 689                 dump_bitmap(f, stored->write_as);
 690         }
 691 }
 692
 693 static int table_cmp(const void *_va, const void *_vb, void *_data)
 694 {
 695         uint32_t *commit_positions = _data;
 696         uint32_t a = commit_positions[*(uint32_t *)_va];
 697         uint32_t b = commit_positions[*(uint32_t *)_vb];
 698
 699         if (a > b)
 700                 return 1;
 701         else if (a < b)
 702                 return -1;
 703
 704         return 0;
 705 }
 706
 707 static void write_lookup_table(struct hashfile *f,
 708                                uint32_t *commit_positions,
 709                                off_t *offsets)
 710 {
 711         uint32_t i;
 712         uint32_t *table, *table_inv;
 713
 714         ALLOC_ARRAY(table, writer.selected_nr);
 715         ALLOC_ARRAY(table_inv, writer.selected_nr);
 716
 717         for (i = 0; i < writer.selected_nr; i++)
 718                 table[i] = i;
 719
 720         /*
 721          * At the end of this sort table[j] = i means that the i'th
 722          * bitmap corresponds to j'th bitmapped commit (among the selected
 723          * commits) in lex order of OIDs.
 724          */
 725         QSORT_S(table, writer.selected_nr, table_cmp, commit_positions);
 726
 727         /* table_inv helps us discover that relationship (i'th bitmap
 728          * to j'th commit by j = table_inv[i])
 729          */
 730         for (i = 0; i < writer.selected_nr; i++)
 731                 table_inv[table[i]] = i;
 732
 733         trace2_region_enter("pack-bitmap-write", "writing_lookup_table", the_repository);
 734         for (i = 0; i < writer.selected_nr; i++) {
 735                 struct bitmapped_commit *selected = &writer.selected[table[i]];
 736                 uint32_t xor_offset = selected->xor_offset;
 737                 uint32_t xor_row;
 738
 739                 if (xor_offset) {
 740                         /*
 741                          * xor_index stores the index (in the bitmap entries)
 742                          * of the corresponding xor bitmap. But we need to convert
 743                          * this index into lookup table's index. So, table_inv[xor_index]
 744                          * gives us the index position w.r.t. the lookup table.
 745                          *
 746                          * If "k = table[i] - xor_offset" then the xor base is the k'th
 747                          * bitmap. `table_inv[k]` gives us the position of that bitmap
 748                          * in the lookup table.
 749                          */
 750                         uint32_t xor_index = table[i] - xor_offset;
 751                         xor_row = table_inv[xor_index];
 752                 } else {
 753                         xor_row = 0xffffffff;
 754                 }
 755
 756                 hashwrite_be32(f, commit_positions[table[i]]);
 757                 hashwrite_be64(f, (uint64_t)offsets[table[i]]);
 758                 hashwrite_be32(f, xor_row);
 759         }
 760         trace2_region_leave("pack-bitmap-write", "writing_lookup_table", the_repository);
 761
 762         free(table);
 763         free(table_inv);
 764 }
 765
 766 static void write_hash_cache(struct hashfile *f,
 767                              struct pack_idx_entry **index,
 768                              uint32_t index_nr)
 769 {
 770         uint32_t i;
 771
 772         for (i = 0; i < index_nr; ++i) {
 773                 struct object_entry *entry = (struct object_entry *)index[i];
 774                 hashwrite_be32(f, entry->hash);
 775         }
 776 }
 777
 778 void bitmap_writer_set_checksum(const unsigned char *sha1)
 779 {
 780         hashcpy(writer.pack_checksum, sha1);
 781 }
 782
 783 void bitmap_writer_finish(struct pack_idx_entry **index,
 784                           uint32_t index_nr,
 785                           const char *filename,
 786                           uint16_t options)
 787 {
 788         static uint16_t default_version = 1;
 789         static uint16_t flags = BITMAP_OPT_FULL_DAG;
 790         struct strbuf tmp_file = STRBUF_INIT;
 791         struct hashfile *f;
 792         uint32_t *commit_positions = NULL;
 793         off_t *offsets = NULL;
 794         uint32_t i;
 795
 796         struct bitmap_disk_header header;
 797
 798         int fd = odb_mkstemp(&tmp_file, "pack/tmp_bitmap_XXXXXX");
 799
 800         f = hashfd(fd, tmp_file.buf);
 801
 802         memcpy(header.magic, BITMAP_IDX_SIGNATURE, sizeof(BITMAP_IDX_SIGNATURE));
 803         header.version = htons(default_version);
 804         header.options = htons(flags | options);
 805         header.entry_count = htonl(writer.selected_nr);
 806         hashcpy(header.checksum, writer.pack_checksum);
 807
 808         hashwrite(f, &header, sizeof(header) - GIT_MAX_RAWSZ + the_hash_algo->rawsz);
 809         dump_bitmap(f, writer.commits);
 810         dump_bitmap(f, writer.trees);
 811         dump_bitmap(f, writer.blobs);
 812         dump_bitmap(f, writer.tags);
 813
 814         if (options & BITMAP_OPT_LOOKUP_TABLE)
 815                 CALLOC_ARRAY(offsets, index_nr);
 816
 817         ALLOC_ARRAY(commit_positions, writer.selected_nr);
 818
 819         for (i = 0; i < writer.selected_nr; i++) {
 820                 struct bitmapped_commit *stored = &writer.selected[i];
 821                 int commit_pos = oid_pos(&stored->commit->object.oid, index, index_nr, oid_access);
 822
 823                 if (commit_pos < 0)
 824                         BUG(_("trying to write commit not in index"));
 825
 826                 commit_positions[i] = commit_pos;
 827         }
 828
 829         write_selected_commits_v1(f, commit_positions, offsets);
 830
 831         if (options & BITMAP_OPT_LOOKUP_TABLE)
 832                 write_lookup_table(f, commit_positions, offsets);
 833
 834         if (options & BITMAP_OPT_HASH_CACHE)
 835                 write_hash_cache(f, index, index_nr);
 836
 837         finalize_hashfile(f, NULL, FSYNC_COMPONENT_PACK_METADATA,
 838                           CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
 839
 840         if (adjust_shared_perm(tmp_file.buf))
 841                 die_errno("unable to make temporary bitmap file readable");
 842
 843         if (rename(tmp_file.buf, filename))
 844                 die_errno("unable to rename temporary bitmap file to '%s'", filename);
 845
 846         strbuf_release(&tmp_file);
 847         free(commit_positions);
 848         free(offsets);
 849 }