summaryrefslogtreecommitdiff
path: root/pack-bitmap.c
blob: 57fec38f3f328ac4462cf188519828fc6626787d (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
#include "cache.h"
#include "commit.h"
#include "tag.h"
#include "diff.h"
#include "revision.h"
#include "progress.h"
#include "list-objects.h"
#include "pack.h"
#include "pack-bitmap.h"
#include "pack-revindex.h"
#include "pack-objects.h"
#include "packfile.h"
#include "repository.h"
#include "object-store.h"

/*
 * An entry on the bitmap index, representing the bitmap for a given
 * commit.
 */
struct stored_bitmap {
	unsigned char sha1[20];
	struct ewah_bitmap *root;
	struct stored_bitmap *xor;
	int flags;
};

/*
 * The currently active bitmap index. By design, repositories only have
 * a single bitmap index available (the index for the biggest packfile in
 * the repository), since bitmap indexes need full closure.
 *
 * If there is more than one bitmap index available (e.g. because of alternates),
 * the active bitmap index is the largest one.
 */
static struct bitmap_index {
	/* Packfile to which this bitmap index belongs to */
	struct packed_git *pack;

	/*
	 * Mark the first `reuse_objects` in the packfile as reused:
	 * they will be sent as-is without using them for repacking
	 * calculations
	 */
	uint32_t reuse_objects;

	/* mmapped buffer of the whole bitmap index */
	unsigned char *map;
	size_t map_size; /* size of the mmaped buffer */
	size_t map_pos; /* current position when loading the index */

	/*
	 * Type indexes.
	 *
	 * Each bitmap marks which objects in the packfile  are of the given
	 * type. This provides type information when yielding the objects from
	 * the packfile during a walk, which allows for better delta bases.
	 */
	struct ewah_bitmap *commits;
	struct ewah_bitmap *trees;
	struct ewah_bitmap *blobs;
	struct ewah_bitmap *tags;

	/* Map from SHA1 -> `stored_bitmap` for all the bitmapped commits */
	khash_sha1 *bitmaps;

	/* Number of bitmapped commits */
	uint32_t entry_count;

	/* Name-hash cache (or NULL if not present). */
	uint32_t *hashes;

	/*
	 * Extended index.
	 *
	 * When trying to perform bitmap operations with objects that are not
	 * packed in `pack`, these objects are added to this "fake index" and
	 * are assumed to appear at the end of the packfile for all operations
	 */
	struct eindex {
		struct object **objects;
		uint32_t *hashes;
		uint32_t count, alloc;
		khash_sha1_pos *positions;
	} ext_index;

	/* Bitmap result of the last performed walk */
	struct bitmap *result;

	/* Version of the bitmap index */
	unsigned int version;

	unsigned loaded : 1;

} bitmap_git;

static struct ewah_bitmap *lookup_stored_bitmap(struct stored_bitmap *st)
{
	struct ewah_bitmap *parent;
	struct ewah_bitmap *composed;

	if (st->xor == NULL)
		return st->root;

	composed = ewah_pool_new();
	parent = lookup_stored_bitmap(st->xor);
	ewah_xor(st->root, parent, composed);

	ewah_pool_free(st->root);
	st->root = composed;
	st->xor = NULL;

	return composed;
}

/*
 * Read a bitmap from the current read position on the mmaped
 * index, and increase the read position accordingly
 */
static struct ewah_bitmap *read_bitmap_1(struct bitmap_index *index)
{
	struct ewah_bitmap *b = ewah_pool_new();

	int bitmap_size = ewah_read_mmap(b,
		index->map + index->map_pos,
		index->map_size - index->map_pos);

	if (bitmap_size < 0) {
		error("Failed to load bitmap index (corrupted?)");
		ewah_pool_free(b);
		return NULL;
	}

	index->map_pos += bitmap_size;
	return b;
}

static int load_bitmap_header(struct bitmap_index *index)
{
	struct bitmap_disk_header *header = (void *)index->map;

	if (index->map_size < sizeof(*header) + 20)
		return error("Corrupted bitmap index (missing header data)");

	if (memcmp(header->magic, BITMAP_IDX_SIGNATURE, sizeof(BITMAP_IDX_SIGNATURE)) != 0)
		return error("Corrupted bitmap index file (wrong header)");

	index->version = ntohs(header->version);
	if (index->version != 1)
		return error("Unsupported version for bitmap index file (%d)", index->version);

	/* Parse known bitmap format options */
	{
		uint32_t flags = ntohs(header->options);

		if ((flags & BITMAP_OPT_FULL_DAG) == 0)
			return error("Unsupported options for bitmap index file "
				"(Git requires BITMAP_OPT_FULL_DAG)");

		if (flags & BITMAP_OPT_HASH_CACHE) {
			unsigned char *end = index->map + index->map_size - 20;
			index->hashes = ((uint32_t *)end) - index->pack->num_objects;
		}
	}

	index->entry_count = ntohl(header->entry_count);
	index->map_pos += sizeof(*header);
	return 0;
}

static struct stored_bitmap *store_bitmap(struct bitmap_index *index,
					  struct ewah_bitmap *root,
					  const unsigned char *sha1,
					  struct stored_bitmap *xor_with,
					  int flags)
{
	struct stored_bitmap *stored;
	khiter_t hash_pos;
	int ret;

	stored = xmalloc(sizeof(struct stored_bitmap));
	stored->root = root;
	stored->xor = xor_with;
	stored->flags = flags;
	hashcpy(stored->sha1, sha1);

	hash_pos = kh_put_sha1(index->bitmaps, stored->sha1, &ret);

	/* a 0 return code means the insertion succeeded with no changes,
	 * because the SHA1 already existed on the map. this is bad, there
	 * shouldn't be duplicated commits in the index */
	if (ret == 0) {
		error("Duplicate entry in bitmap index: %s", sha1_to_hex(sha1));
		return NULL;
	}

	kh_value(index->bitmaps, hash_pos) = stored;
	return stored;
}

static inline uint32_t read_be32(const unsigned char *buffer, size_t *pos)
{
	uint32_t result = get_be32(buffer + *pos);
	(*pos) += sizeof(result);
	return result;
}

static inline uint8_t read_u8(const unsigned char *buffer, size_t *pos)
{
	return buffer[(*pos)++];
}

#define MAX_XOR_OFFSET 160

static int load_bitmap_entries_v1(struct bitmap_index *index)
{
	uint32_t i;
	struct stored_bitmap *recent_bitmaps[MAX_XOR_OFFSET] = { NULL };

	for (i = 0; i < index->entry_count; ++i) {
		int xor_offset, flags;
		struct ewah_bitmap *bitmap = NULL;
		struct stored_bitmap *xor_bitmap = NULL;
		uint32_t commit_idx_pos;
		const unsigned char *sha1;

		commit_idx_pos = read_be32(index->map, &index->map_pos);
		xor_offset = read_u8(index->map, &index->map_pos);
		flags = read_u8(index->map, &index->map_pos);

		sha1 = nth_packed_object_sha1(index->pack, commit_idx_pos);

		bitmap = read_bitmap_1(index);
		if (!bitmap)
			return -1;

		if (xor_offset > MAX_XOR_OFFSET || xor_offset > i)
			return error("Corrupted bitmap pack index");

		if (xor_offset > 0) {
			xor_bitmap = recent_bitmaps[(i - xor_offset) % MAX_XOR_OFFSET];

			if (xor_bitmap == NULL)
				return error("Invalid XOR offset in bitmap pack index");
		}

		recent_bitmaps[i % MAX_XOR_OFFSET] = store_bitmap(
			index, bitmap, sha1, xor_bitmap, flags);
	}

	return 0;
}

static char *pack_bitmap_filename(struct packed_git *p)
{
	size_t len;

	if (!strip_suffix(p->pack_name, ".pack", &len))
		die("BUG: pack_name does not end in .pack");
	return xstrfmt("%.*s.bitmap", (int)len, p->pack_name);
}

static int open_pack_bitmap_1(struct packed_git *packfile)
{
	int fd;
	struct stat st;
	char *idx_name;

	if (open_pack_index(packfile))
		return -1;

	idx_name = pack_bitmap_filename(packfile);
	fd = git_open(idx_name);
	free(idx_name);

	if (fd < 0)
		return -1;

	if (fstat(fd, &st)) {
		close(fd);
		return -1;
	}

	if (bitmap_git.pack) {
		warning("ignoring extra bitmap file: %s", packfile->pack_name);
		close(fd);
		return -1;
	}

	bitmap_git.pack = packfile;
	bitmap_git.map_size = xsize_t(st.st_size);
	bitmap_git.map = xmmap(NULL, bitmap_git.map_size, PROT_READ, MAP_PRIVATE, fd, 0);
	bitmap_git.map_pos = 0;
	close(fd);

	if (load_bitmap_header(&bitmap_git) < 0) {
		munmap(bitmap_git.map, bitmap_git.map_size);
		bitmap_git.map = NULL;
		bitmap_git.map_size = 0;
		return -1;
	}

	return 0;
}

static int load_pack_bitmap(void)
{
	assert(bitmap_git.map && !bitmap_git.loaded);

	bitmap_git.bitmaps = kh_init_sha1();
	bitmap_git.ext_index.positions = kh_init_sha1_pos();
	load_pack_revindex(bitmap_git.pack);

	if (!(bitmap_git.commits = read_bitmap_1(&bitmap_git)) ||
		!(bitmap_git.trees = read_bitmap_1(&bitmap_git)) ||
		!(bitmap_git.blobs = read_bitmap_1(&bitmap_git)) ||
		!(bitmap_git.tags = read_bitmap_1(&bitmap_git)))
		goto failed;

	if (load_bitmap_entries_v1(&bitmap_git) < 0)
		goto failed;

	bitmap_git.loaded = 1;
	return 0;

failed:
	munmap(bitmap_git.map, bitmap_git.map_size);
	bitmap_git.map = NULL;
	bitmap_git.map_size = 0;
	return -1;
}

static int open_pack_bitmap(void)
{
	struct packed_git *p;
	int ret = -1;

	assert(!bitmap_git.map && !bitmap_git.loaded);

	prepare_packed_git(the_repository);
	for (p = get_packed_git(the_repository); p; p = p->next) {
		if (open_pack_bitmap_1(p) == 0)
			ret = 0;
	}

	return ret;
}

int prepare_bitmap_git(void)
{
	if (bitmap_git.loaded)
		return 0;

	if (!open_pack_bitmap())
		return load_pack_bitmap();

	return -1;
}

struct include_data {
	struct bitmap *base;
	struct bitmap *seen;
};

static inline int bitmap_position_extended(const unsigned char *sha1)
{
	khash_sha1_pos *positions = bitmap_git.ext_index.positions;
	khiter_t pos = kh_get_sha1_pos(positions, sha1);

	if (pos < kh_end(positions)) {
		int bitmap_pos = kh_value(positions, pos);
		return bitmap_pos + bitmap_git.pack->num_objects;
	}

	return -1;
}

static inline int bitmap_position_packfile(const unsigned char *sha1)
{
	off_t offset = find_pack_entry_one(sha1, bitmap_git.pack);
	if (!offset)
		return -1;

	return find_revindex_position(bitmap_git.pack, offset);
}

static int bitmap_position(const unsigned char *sha1)
{
	int pos = bitmap_position_packfile(sha1);
	return (pos >= 0) ? pos : bitmap_position_extended(sha1);
}

static int ext_index_add_object(struct object *object, const char *name)
{
	struct eindex *eindex = &bitmap_git.ext_index;

	khiter_t hash_pos;
	int hash_ret;
	int bitmap_pos;

	hash_pos = kh_put_sha1_pos(eindex->positions, object->oid.hash, &hash_ret);
	if (hash_ret > 0) {
		if (eindex->count >= eindex->alloc) {
			eindex->alloc = (eindex->alloc + 16) * 3 / 2;
			REALLOC_ARRAY(eindex->objects, eindex->alloc);
			REALLOC_ARRAY(eindex->hashes, eindex->alloc);
		}

		bitmap_pos = eindex->count;
		eindex->objects[eindex->count] = object;
		eindex->hashes[eindex->count] = pack_name_hash(name);
		kh_value(eindex->positions, hash_pos) = bitmap_pos;
		eindex->count++;
	} else {
		bitmap_pos = kh_value(eindex->positions, hash_pos);
	}

	return bitmap_pos + bitmap_git.pack->num_objects;
}

static void show_object(struct object *object, const char *name, void *data)
{
	struct bitmap *base = data;
	int bitmap_pos;

	bitmap_pos = bitmap_position(object->oid.hash);

	if (bitmap_pos < 0)
		bitmap_pos = ext_index_add_object(object, name);

	bitmap_set(base, bitmap_pos);
}

static void show_commit(struct commit *commit, void *data)
{
}

static int add_to_include_set(struct include_data *data,
			      const unsigned char *sha1,
			      int bitmap_pos)
{
	khiter_t hash_pos;

	if (data->seen && bitmap_get(data->seen, bitmap_pos))
		return 0;

	if (bitmap_get(data->base, bitmap_pos))
		return 0;

	hash_pos = kh_get_sha1(bitmap_git.bitmaps, sha1);
	if (hash_pos < kh_end(bitmap_git.bitmaps)) {
		struct stored_bitmap *st = kh_value(bitmap_git.bitmaps, hash_pos);
		bitmap_or_ewah(data->base, lookup_stored_bitmap(st));
		return 0;
	}

	bitmap_set(data->base, bitmap_pos);
	return 1;
}

static int should_include(struct commit *commit, void *_data)
{
	struct include_data *data = _data;
	int bitmap_pos;

	bitmap_pos = bitmap_position(commit->object.oid.hash);
	if (bitmap_pos < 0)
		bitmap_pos = ext_index_add_object((struct object *)commit, NULL);

	if (!add_to_include_set(data, commit->object.oid.hash, bitmap_pos)) {
		struct commit_list *parent = commit->parents;

		while (parent) {
			parent->item->object.flags |= SEEN;
			parent = parent->next;
		}

		return 0;
	}

	return 1;
}

static struct bitmap *find_objects(struct rev_info *revs,
				   struct object_list *roots,
				   struct bitmap *seen)
{
	struct bitmap *base = NULL;
	int needs_walk = 0;

	struct object_list *not_mapped = NULL;

	/*
	 * Go through all the roots for the walk. The ones that have bitmaps
	 * on the bitmap index will be `or`ed together to form an initial
	 * global reachability analysis.
	 *
	 * The ones without bitmaps in the index will be stored in the
	 * `not_mapped_list` for further processing.
	 */
	while (roots) {
		struct object *object = roots->item;
		roots = roots->next;

		if (object->type == OBJ_COMMIT) {
			khiter_t pos = kh_get_sha1(bitmap_git.bitmaps, object->oid.hash);

			if (pos < kh_end(bitmap_git.bitmaps)) {
				struct stored_bitmap *st = kh_value(bitmap_git.bitmaps, pos);
				struct ewah_bitmap *or_with = lookup_stored_bitmap(st);

				if (base == NULL)
					base = ewah_to_bitmap(or_with);
				else
					bitmap_or_ewah(base, or_with);

				object->flags |= SEEN;
				continue;
			}
		}

		object_list_insert(object, &not_mapped);
	}

	/*
	 * Best case scenario: We found bitmaps for all the roots,
	 * so the resulting `or` bitmap has the full reachability analysis
	 */
	if (not_mapped == NULL)
		return base;

	roots = not_mapped;

	/*
	 * Let's iterate through all the roots that don't have bitmaps to
	 * check if we can determine them to be reachable from the existing
	 * global bitmap.
	 *
	 * If we cannot find them in the existing global bitmap, we'll need
	 * to push them to an actual walk and run it until we can confirm
	 * they are reachable
	 */
	while (roots) {
		struct object *object = roots->item;
		int pos;

		roots = roots->next;
		pos = bitmap_position(object->oid.hash);

		if (pos < 0 || base == NULL || !bitmap_get(base, pos)) {
			object->flags &= ~UNINTERESTING;
			add_pending_object(revs, object, "");
			needs_walk = 1;
		} else {
			object->flags |= SEEN;
		}
	}

	if (needs_walk) {
		struct include_data incdata;

		if (base == NULL)
			base = bitmap_new();

		incdata.base = base;
		incdata.seen = seen;

		revs->include_check = should_include;
		revs->include_check_data = &incdata;

		if (prepare_revision_walk(revs))
			die("revision walk setup failed");

		traverse_commit_list(revs, show_commit, show_object, base);
	}

	return base;
}

static void show_extended_objects(struct bitmap *objects,
				  show_reachable_fn show_reach)
{
	struct eindex *eindex = &bitmap_git.ext_index;
	uint32_t i;

	for (i = 0; i < eindex->count; ++i) {
		struct object *obj;

		if (!bitmap_get(objects, bitmap_git.pack->num_objects + i))
			continue;

		obj = eindex->objects[i];
		show_reach(&obj->oid, obj->type, 0, eindex->hashes[i], NULL, 0);
	}
}

static void show_objects_for_type(
	struct bitmap *objects,
	struct ewah_bitmap *type_filter,
	enum object_type object_type,
	show_reachable_fn show_reach)
{
	size_t pos = 0, i = 0;
	uint32_t offset;

	struct ewah_iterator it;
	eword_t filter;

	if (bitmap_git.reuse_objects == bitmap_git.pack->num_objects)
		return;

	ewah_iterator_init(&it, type_filter);

	while (i < objects->word_alloc && ewah_iterator_next(&filter, &it)) {
		eword_t word = objects->words[i] & filter;

		for (offset = 0; offset < BITS_IN_EWORD; ++offset) {
			struct object_id oid;
			struct revindex_entry *entry;
			uint32_t hash = 0;

			if ((word >> offset) == 0)
				break;

			offset += ewah_bit_ctz64(word >> offset);

			if (pos + offset < bitmap_git.reuse_objects)
				continue;

			entry = &bitmap_git.pack->revindex[pos + offset];
			nth_packed_object_oid(&oid, bitmap_git.pack, entry->nr);

			if (bitmap_git.hashes)
				hash = get_be32(bitmap_git.hashes + entry->nr);

			show_reach(&oid, object_type, 0, hash, bitmap_git.pack, entry->offset);
		}

		pos += BITS_IN_EWORD;
		i++;
	}
}

static int in_bitmapped_pack(struct object_list *roots)
{
	while (roots) {
		struct object *object = roots->item;
		roots = roots->next;

		if (find_pack_entry_one(object->oid.hash, bitmap_git.pack) > 0)
			return 1;
	}

	return 0;
}

int prepare_bitmap_walk(struct rev_info *revs)
{
	unsigned int i;

	struct object_list *wants = NULL;
	struct object_list *haves = NULL;

	struct bitmap *wants_bitmap = NULL;
	struct bitmap *haves_bitmap = NULL;

	if (!bitmap_git.loaded) {
		/* try to open a bitmapped pack, but don't parse it yet
		 * because we may not need to use it */
		if (open_pack_bitmap() < 0)
			return -1;
	}

	for (i = 0; i < revs->pending.nr; ++i) {
		struct object *object = revs->pending.objects[i].item;

		if (object->type == OBJ_NONE)
			parse_object_or_die(&object->oid, NULL);

		while (object->type == OBJ_TAG) {
			struct tag *tag = (struct tag *) object;

			if (object->flags & UNINTERESTING)
				object_list_insert(object, &haves);
			else
				object_list_insert(object, &wants);

			if (!tag->tagged)
				die("bad tag");
			object = parse_object_or_die(&tag->tagged->oid, NULL);
		}

		if (object->flags & UNINTERESTING)
			object_list_insert(object, &haves);
		else
			object_list_insert(object, &wants);
	}

	/*
	 * if we have a HAVES list, but none of those haves is contained
	 * in the packfile that has a bitmap, we don't have anything to
	 * optimize here
	 */
	if (haves && !in_bitmapped_pack(haves))
		return -1;

	/* if we don't want anything, we're done here */
	if (!wants)
		return -1;

	/*
	 * now we're going to use bitmaps, so load the actual bitmap entries
	 * from disk. this is the point of no return; after this the rev_list
	 * becomes invalidated and we must perform the revwalk through bitmaps
	 */
	if (!bitmap_git.loaded && load_pack_bitmap() < 0)
		return -1;

	object_array_clear(&revs->pending);

	if (haves) {
		revs->ignore_missing_links = 1;
		haves_bitmap = find_objects(revs, haves, NULL);
		reset_revision_walk();
		revs->ignore_missing_links = 0;

		if (haves_bitmap == NULL)
			die("BUG: failed to perform bitmap walk");
	}

	wants_bitmap = find_objects(revs, wants, haves_bitmap);

	if (!wants_bitmap)
		die("BUG: failed to perform bitmap walk");

	if (haves_bitmap)
		bitmap_and_not(wants_bitmap, haves_bitmap);

	bitmap_git.result = wants_bitmap;

	bitmap_free(haves_bitmap);
	return 0;
}

int reuse_partial_packfile_from_bitmap(struct packed_git **packfile,
				       uint32_t *entries,
				       off_t *up_to)
{
	/*
	 * Reuse the packfile content if we need more than
	 * 90% of its objects
	 */
	static const double REUSE_PERCENT = 0.9;

	struct bitmap *result = bitmap_git.result;
	uint32_t reuse_threshold;
	uint32_t i, reuse_objects = 0;

	assert(result);

	for (i = 0; i < result->word_alloc; ++i) {
		if (result->words[i] != (eword_t)~0) {
			reuse_objects += ewah_bit_ctz64(~result->words[i]);
			break;
		}

		reuse_objects += BITS_IN_EWORD;
	}

#ifdef GIT_BITMAP_DEBUG
	{
		const unsigned char *sha1;
		struct revindex_entry *entry;

		entry = &bitmap_git.reverse_index->revindex[reuse_objects];
		sha1 = nth_packed_object_sha1(bitmap_git.pack, entry->nr);

		fprintf(stderr, "Failed to reuse at %d (%016llx)\n",
			reuse_objects, result->words[i]);
		fprintf(stderr, " %s\n", sha1_to_hex(sha1));
	}
#endif

	if (!reuse_objects)
		return -1;

	if (reuse_objects >= bitmap_git.pack->num_objects) {
		bitmap_git.reuse_objects = *entries = bitmap_git.pack->num_objects;
		*up_to = -1; /* reuse the full pack */
		*packfile = bitmap_git.pack;
		return 0;
	}

	reuse_threshold = bitmap_popcount(bitmap_git.result) * REUSE_PERCENT;

	if (reuse_objects < reuse_threshold)
		return -1;

	bitmap_git.reuse_objects = *entries = reuse_objects;
	*up_to = bitmap_git.pack->revindex[reuse_objects].offset;
	*packfile = bitmap_git.pack;

	return 0;
}

void traverse_bitmap_commit_list(show_reachable_fn show_reachable)
{
	assert(bitmap_git.result);

	show_objects_for_type(bitmap_git.result, bitmap_git.commits,
		OBJ_COMMIT, show_reachable);
	show_objects_for_type(bitmap_git.result, bitmap_git.trees,
		OBJ_TREE, show_reachable);
	show_objects_for_type(bitmap_git.result, bitmap_git.blobs,
		OBJ_BLOB, show_reachable);
	show_objects_for_type(bitmap_git.result, bitmap_git.tags,
		OBJ_TAG, show_reachable);

	show_extended_objects(bitmap_git.result, show_reachable);

	bitmap_free(bitmap_git.result);
	bitmap_git.result = NULL;
}

static uint32_t count_object_type(struct bitmap *objects,
				  enum object_type type)
{
	struct eindex *eindex = &bitmap_git.ext_index;

	uint32_t i = 0, count = 0;
	struct ewah_iterator it;
	eword_t filter;

	switch (type) {
	case OBJ_COMMIT:
		ewah_iterator_init(&it, bitmap_git.commits);
		break;

	case OBJ_TREE:
		ewah_iterator_init(&it, bitmap_git.trees);
		break;

	case OBJ_BLOB:
		ewah_iterator_init(&it, bitmap_git.blobs);
		break;

	case OBJ_TAG:
		ewah_iterator_init(&it, bitmap_git.tags);
		break;

	default:
		return 0;
	}

	while (i < objects->word_alloc && ewah_iterator_next(&filter, &it)) {
		eword_t word = objects->words[i++] & filter;
		count += ewah_bit_popcount64(word);
	}

	for (i = 0; i < eindex->count; ++i) {
		if (eindex->objects[i]->type == type &&
			bitmap_get(objects, bitmap_git.pack->num_objects + i))
			count++;
	}

	return count;
}

void count_bitmap_commit_list(uint32_t *commits, uint32_t *trees,
			      uint32_t *blobs, uint32_t *tags)
{
	assert(bitmap_git.result);

	if (commits)
		*commits = count_object_type(bitmap_git.result, OBJ_COMMIT);

	if (trees)
		*trees = count_object_type(bitmap_git.result, OBJ_TREE);

	if (blobs)
		*blobs = count_object_type(bitmap_git.result, OBJ_BLOB);

	if (tags)
		*tags = count_object_type(bitmap_git.result, OBJ_TAG);
}

struct bitmap_test_data {
	struct bitmap *base;
	struct progress *prg;
	size_t seen;
};

static void test_show_object(struct object *object, const char *name,
			     void *data)
{
	struct bitmap_test_data *tdata = data;
	int bitmap_pos;

	bitmap_pos = bitmap_position(object->oid.hash);
	if (bitmap_pos < 0)
		die("Object not in bitmap: %s\n", oid_to_hex(&object->oid));

	bitmap_set(tdata->base, bitmap_pos);
	display_progress(tdata->prg, ++tdata->seen);
}

static void test_show_commit(struct commit *commit, void *data)
{
	struct bitmap_test_data *tdata = data;
	int bitmap_pos;

	bitmap_pos = bitmap_position(commit->object.oid.hash);
	if (bitmap_pos < 0)
		die("Object not in bitmap: %s\n", oid_to_hex(&commit->object.oid));

	bitmap_set(tdata->base, bitmap_pos);
	display_progress(tdata->prg, ++tdata->seen);
}

void test_bitmap_walk(struct rev_info *revs)
{
	struct object *root;
	struct bitmap *result = NULL;
	khiter_t pos;
	size_t result_popcnt;
	struct bitmap_test_data tdata;

	if (prepare_bitmap_git())
		die("failed to load bitmap indexes");

	if (revs->pending.nr != 1)
		die("you must specify exactly one commit to test");

	fprintf(stderr, "Bitmap v%d test (%d entries loaded)\n",
		bitmap_git.version, bitmap_git.entry_count);

	root = revs->pending.objects[0].item;
	pos = kh_get_sha1(bitmap_git.bitmaps, root->oid.hash);

	if (pos < kh_end(bitmap_git.bitmaps)) {
		struct stored_bitmap *st = kh_value(bitmap_git.bitmaps, pos);
		struct ewah_bitmap *bm = lookup_stored_bitmap(st);

		fprintf(stderr, "Found bitmap for %s. %d bits / %08x checksum\n",
			oid_to_hex(&root->oid), (int)bm->bit_size, ewah_checksum(bm));

		result = ewah_to_bitmap(bm);
	}

	if (result == NULL)
		die("Commit %s doesn't have an indexed bitmap", oid_to_hex(&root->oid));

	revs->tag_objects = 1;
	revs->tree_objects = 1;
	revs->blob_objects = 1;

	result_popcnt = bitmap_popcount(result);

	if (prepare_revision_walk(revs))
		die("revision walk setup failed");

	tdata.base = bitmap_new();
	tdata.prg = start_progress("Verifying bitmap entries", result_popcnt);
	tdata.seen = 0;

	traverse_commit_list(revs, &test_show_commit, &test_show_object, &tdata);

	stop_progress(&tdata.prg);

	if (bitmap_equals(result, tdata.base))
		fprintf(stderr, "OK!\n");
	else
		fprintf(stderr, "Mismatch!\n");

	bitmap_free(result);
}

static int rebuild_bitmap(uint32_t *reposition,
			  struct ewah_bitmap *source,
			  struct bitmap *dest)
{
	uint32_t pos = 0;
	struct ewah_iterator it;
	eword_t word;

	ewah_iterator_init(&it, source);

	while (ewah_iterator_next(&word, &it)) {
		uint32_t offset, bit_pos;

		for (offset = 0; offset < BITS_IN_EWORD; ++offset) {
			if ((word >> offset) == 0)
				break;

			offset += ewah_bit_ctz64(word >> offset);

			bit_pos = reposition[pos + offset];
			if (bit_pos > 0)
				bitmap_set(dest, bit_pos - 1);
			else /* can't reuse, we don't have the object */
				return -1;
		}

		pos += BITS_IN_EWORD;
	}
	return 0;
}

int rebuild_existing_bitmaps(struct packing_data *mapping,
			     khash_sha1 *reused_bitmaps,
			     int show_progress)
{
	uint32_t i, num_objects;
	uint32_t *reposition;
	struct bitmap *rebuild;
	struct stored_bitmap *stored;
	struct progress *progress = NULL;

	khiter_t hash_pos;
	int hash_ret;

	if (prepare_bitmap_git() < 0)
		return -1;

	num_objects = bitmap_git.pack->num_objects;
	reposition = xcalloc(num_objects, sizeof(uint32_t));

	for (i = 0; i < num_objects; ++i) {
		const unsigned char *sha1;
		struct revindex_entry *entry;
		struct object_entry *oe;

		entry = &bitmap_git.pack->revindex[i];
		sha1 = nth_packed_object_sha1(bitmap_git.pack, entry->nr);
		oe = packlist_find(mapping, sha1, NULL);

		if (oe)
			reposition[i] = oe->in_pack_pos + 1;
	}

	rebuild = bitmap_new();
	i = 0;

	if (show_progress)
		progress = start_progress("Reusing bitmaps", 0);

	kh_foreach_value(bitmap_git.bitmaps, stored, {
		if (stored->flags & BITMAP_FLAG_REUSE) {
			if (!rebuild_bitmap(reposition,
					    lookup_stored_bitmap(stored),
					    rebuild)) {
				hash_pos = kh_put_sha1(reused_bitmaps,
						       stored->sha1,
						       &hash_ret);
				kh_value(reused_bitmaps, hash_pos) =
					bitmap_to_ewah(rebuild);
			}
			bitmap_reset(rebuild);
			display_progress(progress, ++i);
		}
	});

	stop_progress(&progress);

	free(reposition);
	bitmap_free(rebuild);
	return 0;
}