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