pack-bitmap-write.c

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