summaryrefslogtreecommitdiff
path: root/lib/tdb2/hash.c
blob: 56c5086e742552480a23e81a8e2a7baafe583d73 (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
 /*
   Trivial Database 2: hash handling
   Copyright (C) Rusty Russell 2010

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 3 of the License, or (at your option) any later version.

   This library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/
#include "private.h"
#include <ccan/hash/hash.h>
#include <assert.h>

/* Default hash function. */
uint64_t tdb_jenkins_hash(const void *key, size_t length, uint64_t seed,
			  void *unused)
{
	uint64_t ret;
	/* hash64_stable assumes lower bits are more important; they are a
	 * slightly better hash.  We use the upper bits first, so swap them. */
	ret = hash64_stable((const unsigned char *)key, length, seed);
	return (ret >> 32) | (ret << 32);
}

uint64_t tdb_hash(struct tdb_context *tdb, const void *ptr, size_t len)
{
	return tdb->hash_fn(ptr, len, tdb->hash_seed, tdb->hash_data);
}

uint64_t hash_record(struct tdb_context *tdb, tdb_off_t off)
{
	const struct tdb_used_record *r;
	const void *key;
	uint64_t klen, hash;

	r = tdb_access_read(tdb, off, sizeof(*r), true);
	if (TDB_PTR_IS_ERR(r)) {
		/* FIXME */
		return 0;
	}

	klen = rec_key_length(r);
	tdb_access_release(tdb, r);

	key = tdb_access_read(tdb, off + sizeof(*r), klen, false);
	if (TDB_PTR_IS_ERR(key)) {
		return 0;
	}

	hash = tdb_hash(tdb, key, klen);
	tdb_access_release(tdb, key);
	return hash;
}

/* Get bits from a value. */
static uint32_t bits_from(uint64_t val, unsigned start, unsigned num)
{
	assert(num <= 32);
	return (val >> start) & ((1U << num) - 1);
}

/* We take bits from the top: that way we can lock whole sections of the hash
 * by using lock ranges. */
static uint32_t use_bits(struct hash_info *h, unsigned num)
{
	h->hash_used += num;
	return bits_from(h->h, 64 - h->hash_used, num);
}

static tdb_bool_err key_matches(struct tdb_context *tdb,
				const struct tdb_used_record *rec,
				tdb_off_t off,
				const struct tdb_data *key)
{
	tdb_bool_err ret = false;
	const char *rkey;

	if (rec_key_length(rec) != key->dsize) {
		tdb->stats.compare_wrong_keylen++;
		return ret;
	}

	rkey = tdb_access_read(tdb, off + sizeof(*rec), key->dsize, false);
	if (TDB_PTR_IS_ERR(rkey)) {
		return TDB_PTR_ERR(rkey);
	}
	if (memcmp(rkey, key->dptr, key->dsize) == 0)
		ret = true;
	else
		tdb->stats.compare_wrong_keycmp++;
	tdb_access_release(tdb, rkey);
	return ret;
}

/* Does entry match? */
static tdb_bool_err match(struct tdb_context *tdb,
			  struct hash_info *h,
			  const struct tdb_data *key,
			  tdb_off_t val,
			  struct tdb_used_record *rec)
{
	tdb_off_t off;
	enum TDB_ERROR ecode;

	tdb->stats.compares++;
	/* Desired bucket must match. */
	if (h->home_bucket != (val & TDB_OFF_HASH_GROUP_MASK)) {
		tdb->stats.compare_wrong_bucket++;
		return false;
	}

	/* Top bits of offset == next bits of hash. */
	if (bits_from(val, TDB_OFF_HASH_EXTRA_BIT, TDB_OFF_UPPER_STEAL_EXTRA)
	    != bits_from(h->h, 64 - h->hash_used - TDB_OFF_UPPER_STEAL_EXTRA,
		    TDB_OFF_UPPER_STEAL_EXTRA)) {
		tdb->stats.compare_wrong_offsetbits++;
		return false;
	}

	off = val & TDB_OFF_MASK;
	ecode = tdb_read_convert(tdb, off, rec, sizeof(*rec));
	if (ecode != TDB_SUCCESS) {
		return ecode;
	}

	if ((h->h & ((1 << 11)-1)) != rec_hash(rec)) {
		tdb->stats.compare_wrong_rechash++;
		return false;
	}

	return key_matches(tdb, rec, off, key);
}

static tdb_off_t hbucket_off(tdb_off_t group_start, unsigned bucket)
{
	return group_start
		+ (bucket % (1 << TDB_HASH_GROUP_BITS)) * sizeof(tdb_off_t);
}

bool is_subhash(tdb_off_t val)
{
	return (val >> TDB_OFF_UPPER_STEAL_SUBHASH_BIT) & 1;
}

/* FIXME: Guess the depth, don't over-lock! */
static tdb_off_t hlock_range(tdb_off_t group, tdb_off_t *size)
{
	*size = 1ULL << (64 - (TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS));
	return group << (64 - (TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS));
}

static tdb_off_t COLD find_in_chain(struct tdb_context *tdb,
				    struct tdb_data key,
				    tdb_off_t chain,
				    struct hash_info *h,
				    struct tdb_used_record *rec,
				    struct traverse_info *tinfo)
{
	tdb_off_t off, next;
	enum TDB_ERROR ecode;

	/* In case nothing is free, we set these to zero. */
	h->home_bucket = h->found_bucket = 0;

	for (off = chain; off; off = next) {
		unsigned int i;

		h->group_start = off;
		ecode = tdb_read_convert(tdb, off, h->group, sizeof(h->group));
		if (ecode != TDB_SUCCESS) {
			return ecode;
		}

		for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
			tdb_off_t recoff;
			if (!h->group[i]) {
				/* Remember this empty bucket. */
				h->home_bucket = h->found_bucket = i;
				continue;
			}

			/* We can insert extra bits via add_to_hash
			 * empty bucket logic. */
			recoff = h->group[i] & TDB_OFF_MASK;
			ecode = tdb_read_convert(tdb, recoff, rec,
						 sizeof(*rec));
			if (ecode != TDB_SUCCESS) {
				return ecode;
			}

			ecode = key_matches(tdb, rec, recoff, &key);
			if (ecode < 0) {
				return ecode;
			}
			if (ecode == 1) {
				h->home_bucket = h->found_bucket = i;

				if (tinfo) {
					tinfo->levels[tinfo->num_levels]
						.hashtable = off;
					tinfo->levels[tinfo->num_levels]
						.total_buckets
						= 1 << TDB_HASH_GROUP_BITS;
					tinfo->levels[tinfo->num_levels].entry
						= i;
					tinfo->num_levels++;
				}
				return recoff;
			}
		}
		next = tdb_read_off(tdb, off
				    + offsetof(struct tdb_chain, next));
		if (TDB_OFF_IS_ERR(next)) {
			return next;
		}
		if (next)
			next += sizeof(struct tdb_used_record);
	}
	return 0;
}

/* This is the core routine which searches the hashtable for an entry.
 * On error, no locks are held and -ve is returned.
 * Otherwise, hinfo is filled in (and the optional tinfo).
 * If not found, the return value is 0.
 * If found, the return value is the offset, and *rec is the record. */
tdb_off_t find_and_lock(struct tdb_context *tdb,
			struct tdb_data key,
			int ltype,
			struct hash_info *h,
			struct tdb_used_record *rec,
			struct traverse_info *tinfo)
{
	uint32_t i, group;
	tdb_off_t hashtable;
	enum TDB_ERROR ecode;

	h->h = tdb_hash(tdb, key.dptr, key.dsize);
	h->hash_used = 0;
	group = use_bits(h, TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS);
	h->home_bucket = use_bits(h, TDB_HASH_GROUP_BITS);

	h->hlock_start = hlock_range(group, &h->hlock_range);
	ecode = tdb_lock_hashes(tdb, h->hlock_start, h->hlock_range, ltype,
				TDB_LOCK_WAIT);
	if (ecode != TDB_SUCCESS) {
		return ecode;
	}

	hashtable = offsetof(struct tdb_header, hashtable);
	if (tinfo) {
		tinfo->toplevel_group = group;
		tinfo->num_levels = 1;
		tinfo->levels[0].entry = 0;
		tinfo->levels[0].hashtable = hashtable
			+ (group << TDB_HASH_GROUP_BITS) * sizeof(tdb_off_t);
		tinfo->levels[0].total_buckets = 1 << TDB_HASH_GROUP_BITS;
	}

	while (h->hash_used <= 64) {
		/* Read in the hash group. */
		h->group_start = hashtable
			+ group * (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);

		ecode = tdb_read_convert(tdb, h->group_start, &h->group,
					 sizeof(h->group));
		if (ecode != TDB_SUCCESS) {
			goto fail;
		}

		/* Pointer to another hash table?  Go down... */
		if (is_subhash(h->group[h->home_bucket])) {
			hashtable = (h->group[h->home_bucket] & TDB_OFF_MASK)
				+ sizeof(struct tdb_used_record);
			if (tinfo) {
				/* When we come back, use *next* bucket */
				tinfo->levels[tinfo->num_levels-1].entry
					+= h->home_bucket + 1;
			}
			group = use_bits(h, TDB_SUBLEVEL_HASH_BITS
					 - TDB_HASH_GROUP_BITS);
			h->home_bucket = use_bits(h, TDB_HASH_GROUP_BITS);
			if (tinfo) {
				tinfo->levels[tinfo->num_levels].hashtable
					= hashtable;
				tinfo->levels[tinfo->num_levels].total_buckets
					= 1 << TDB_SUBLEVEL_HASH_BITS;
				tinfo->levels[tinfo->num_levels].entry
					= group << TDB_HASH_GROUP_BITS;
				tinfo->num_levels++;
			}
			continue;
		}

		/* It's in this group: search (until 0 or all searched) */
		for (i = 0, h->found_bucket = h->home_bucket;
		     i < (1 << TDB_HASH_GROUP_BITS);
		     i++, h->found_bucket = ((h->found_bucket+1)
					     % (1 << TDB_HASH_GROUP_BITS))) {
			tdb_bool_err berr;
			if (is_subhash(h->group[h->found_bucket]))
				continue;

			if (!h->group[h->found_bucket])
				break;

			berr = match(tdb, h, &key, h->group[h->found_bucket],
				     rec);
			if (berr < 0) {
				ecode = berr;
				goto fail;
			}
			if (berr) {
				if (tinfo) {
					tinfo->levels[tinfo->num_levels-1].entry
						+= h->found_bucket;
				}
				return h->group[h->found_bucket] & TDB_OFF_MASK;
			}
		}
		/* Didn't find it: h indicates where it would go. */
		return 0;
	}

	return find_in_chain(tdb, key, hashtable, h, rec, tinfo);

fail:
	tdb_unlock_hashes(tdb, h->hlock_start, h->hlock_range, ltype);
	return ecode;
}

/* I wrote a simple test, expanding a hash to 2GB, for the following
 * cases:
 * 1) Expanding all the buckets at once,
 * 2) Expanding the bucket we wanted to place the new entry into.
 * 3) Expanding the most-populated bucket,
 *
 * I measured the worst/average/best density during this process.
 * 1) 3%/16%/30%
 * 2) 4%/20%/38%
 * 3) 6%/22%/41%
 *
 * So we figure out the busiest bucket for the moment.
 */
static unsigned fullest_bucket(struct tdb_context *tdb,
			       const tdb_off_t *group,
			       unsigned new_bucket)
{
	unsigned counts[1 << TDB_HASH_GROUP_BITS] = { 0 };
	unsigned int i, best_bucket;

	/* Count the new entry. */
	counts[new_bucket]++;
	best_bucket = new_bucket;

	for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
		unsigned this_bucket;

		if (is_subhash(group[i]))
			continue;
		this_bucket = group[i] & TDB_OFF_HASH_GROUP_MASK;
		if (++counts[this_bucket] > counts[best_bucket])
			best_bucket = this_bucket;
	}

	return best_bucket;
}

static bool put_into_group(tdb_off_t *group,
			   unsigned bucket, tdb_off_t encoded)
{
	unsigned int i;

	for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
		unsigned b = (bucket + i) % (1 << TDB_HASH_GROUP_BITS);

		if (group[b] == 0) {
			group[b] = encoded;
			return true;
		}
	}
	return false;
}

static void force_into_group(tdb_off_t *group,
			     unsigned bucket, tdb_off_t encoded)
{
	if (!put_into_group(group, bucket, encoded))
		abort();
}

static tdb_off_t encode_offset(tdb_off_t new_off, struct hash_info *h)
{
	return h->home_bucket
		| new_off
		| ((uint64_t)bits_from(h->h,
				  64 - h->hash_used - TDB_OFF_UPPER_STEAL_EXTRA,
				  TDB_OFF_UPPER_STEAL_EXTRA)
		   << TDB_OFF_HASH_EXTRA_BIT);
}

/* Simply overwrite the hash entry we found before. */
enum TDB_ERROR replace_in_hash(struct tdb_context *tdb,
			       struct hash_info *h,
			       tdb_off_t new_off)
{
	return tdb_write_off(tdb, hbucket_off(h->group_start, h->found_bucket),
			     encode_offset(new_off, h));
}

/* We slot in anywhere that's empty in the chain. */
static enum TDB_ERROR COLD add_to_chain(struct tdb_context *tdb,
					tdb_off_t subhash,
					tdb_off_t new_off)
{
	tdb_off_t entry;
	enum TDB_ERROR ecode;

	entry = tdb_find_zero_off(tdb, subhash, 1<<TDB_HASH_GROUP_BITS);
	if (TDB_OFF_IS_ERR(entry)) {
		return entry;
	}

	if (entry == 1 << TDB_HASH_GROUP_BITS) {
		tdb_off_t next;

		next = tdb_read_off(tdb, subhash
				    + offsetof(struct tdb_chain, next));
		if (TDB_OFF_IS_ERR(next)) {
			return next;
		}

		if (!next) {
			next = alloc(tdb, 0, sizeof(struct tdb_chain), 0,
				     TDB_CHAIN_MAGIC, false);
			if (TDB_OFF_IS_ERR(next))
				return next;
			ecode = zero_out(tdb,
					 next+sizeof(struct tdb_used_record),
					 sizeof(struct tdb_chain));
			if (ecode != TDB_SUCCESS) {
				return ecode;
			}
			ecode = tdb_write_off(tdb, subhash
					      + offsetof(struct tdb_chain,
							 next),
					      next);
			if (ecode != TDB_SUCCESS) {
				return ecode;
			}
		}
		return add_to_chain(tdb, next, new_off);
	}

	return tdb_write_off(tdb, subhash + entry * sizeof(tdb_off_t),
			     new_off);
}

/* Add into a newly created subhash. */
static enum TDB_ERROR add_to_subhash(struct tdb_context *tdb, tdb_off_t subhash,
				     unsigned hash_used, tdb_off_t val)
{
	tdb_off_t off = (val & TDB_OFF_MASK), *group;
	struct hash_info h;
	unsigned int gnum;

	h.hash_used = hash_used;

	if (hash_used + TDB_SUBLEVEL_HASH_BITS > 64)
		return add_to_chain(tdb, subhash, off);

	h.h = hash_record(tdb, off);
	gnum = use_bits(&h, TDB_SUBLEVEL_HASH_BITS-TDB_HASH_GROUP_BITS);
	h.group_start = subhash
		+ gnum * (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
	h.home_bucket = use_bits(&h, TDB_HASH_GROUP_BITS);

	group = tdb_access_write(tdb, h.group_start,
				 sizeof(*group) << TDB_HASH_GROUP_BITS, true);
	if (TDB_PTR_IS_ERR(group)) {
		return TDB_PTR_ERR(group);
	}
	force_into_group(group, h.home_bucket, encode_offset(off, &h));
	return tdb_access_commit(tdb, group);
}

static enum TDB_ERROR expand_group(struct tdb_context *tdb, struct hash_info *h)
{
	unsigned bucket, num_vals, i, magic;
	size_t subsize;
	tdb_off_t subhash;
	tdb_off_t vals[1 << TDB_HASH_GROUP_BITS];
	enum TDB_ERROR ecode;

	/* Attach new empty subhash under fullest bucket. */
	bucket = fullest_bucket(tdb, h->group, h->home_bucket);

	if (h->hash_used == 64) {
		tdb->stats.alloc_chain++;
		subsize = sizeof(struct tdb_chain);
		magic = TDB_CHAIN_MAGIC;
	} else {
		tdb->stats.alloc_subhash++;
		subsize = (sizeof(tdb_off_t) << TDB_SUBLEVEL_HASH_BITS);
		magic = TDB_HTABLE_MAGIC;
	}

	subhash = alloc(tdb, 0, subsize, 0, magic, false);
	if (TDB_OFF_IS_ERR(subhash)) {
		return subhash;
	}

	ecode = zero_out(tdb, subhash + sizeof(struct tdb_used_record),
			 subsize);
	if (ecode != TDB_SUCCESS) {
		return ecode;
	}

	/* Remove any which are destined for bucket or are in wrong place. */
	num_vals = 0;
	for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
		unsigned home_bucket = h->group[i] & TDB_OFF_HASH_GROUP_MASK;
		if (!h->group[i] || is_subhash(h->group[i]))
			continue;
		if (home_bucket == bucket || home_bucket != i) {
			vals[num_vals++] = h->group[i];
			h->group[i] = 0;
		}
	}
	/* FIXME: This assert is valid, but we do this during unit test :( */
	/* assert(num_vals); */

	/* Overwrite expanded bucket with subhash pointer. */
	h->group[bucket] = subhash | (1ULL << TDB_OFF_UPPER_STEAL_SUBHASH_BIT);

	/* Point to actual contents of record. */
	subhash += sizeof(struct tdb_used_record);

	/* Put values back. */
	for (i = 0; i < num_vals; i++) {
		unsigned this_bucket = vals[i] & TDB_OFF_HASH_GROUP_MASK;

		if (this_bucket == bucket) {
			ecode = add_to_subhash(tdb, subhash, h->hash_used,
					       vals[i]);
			if (ecode != TDB_SUCCESS)
				return ecode;
		} else {
			/* There should be room to put this back. */
			force_into_group(h->group, this_bucket, vals[i]);
		}
	}
	return TDB_SUCCESS;
}

enum TDB_ERROR delete_from_hash(struct tdb_context *tdb, struct hash_info *h)
{
	unsigned int i, num_movers = 0;
	tdb_off_t movers[1 << TDB_HASH_GROUP_BITS];

	h->group[h->found_bucket] = 0;
	for (i = 1; i < (1 << TDB_HASH_GROUP_BITS); i++) {
		unsigned this_bucket;

		this_bucket = (h->found_bucket+i) % (1 << TDB_HASH_GROUP_BITS);
		/* Empty bucket?  We're done. */
		if (!h->group[this_bucket])
			break;

		/* Ignore subhashes. */
		if (is_subhash(h->group[this_bucket]))
			continue;

		/* If this one is not happy where it is, we'll move it. */
		if ((h->group[this_bucket] & TDB_OFF_HASH_GROUP_MASK)
		    != this_bucket) {
			movers[num_movers++] = h->group[this_bucket];
			h->group[this_bucket] = 0;
		}
	}

	/* Put back the ones we erased. */
	for (i = 0; i < num_movers; i++) {
		force_into_group(h->group, movers[i] & TDB_OFF_HASH_GROUP_MASK,
				 movers[i]);
	}

	/* Now we write back the hash group */
	return tdb_write_convert(tdb, h->group_start,
				 h->group, sizeof(h->group));
}

enum TDB_ERROR add_to_hash(struct tdb_context *tdb, struct hash_info *h,
			   tdb_off_t new_off)
{
	enum TDB_ERROR ecode;

	/* We hit an empty bucket during search?  That's where it goes. */
	if (!h->group[h->found_bucket]) {
		h->group[h->found_bucket] = encode_offset(new_off, h);
		/* Write back the modified group. */
		return tdb_write_convert(tdb, h->group_start,
					 h->group, sizeof(h->group));
	}

	if (h->hash_used > 64)
		return add_to_chain(tdb, h->group_start, new_off);

	/* We're full.  Expand. */
	ecode = expand_group(tdb, h);
	if (ecode != TDB_SUCCESS) {
		return ecode;
	}

	if (is_subhash(h->group[h->home_bucket])) {
		/* We were expanded! */
		tdb_off_t hashtable;
		unsigned int gnum;

		/* Write back the modified group. */
		ecode = tdb_write_convert(tdb, h->group_start, h->group,
					  sizeof(h->group));
		if (ecode != TDB_SUCCESS) {
			return ecode;
		}

		/* Move hashinfo down a level. */
		hashtable = (h->group[h->home_bucket] & TDB_OFF_MASK)
			+ sizeof(struct tdb_used_record);
		gnum = use_bits(h,TDB_SUBLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS);
		h->home_bucket = use_bits(h, TDB_HASH_GROUP_BITS);
		h->group_start = hashtable
			+ gnum * (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
		ecode = tdb_read_convert(tdb, h->group_start, &h->group,
					 sizeof(h->group));
		if (ecode != TDB_SUCCESS) {
			return ecode;
		}
	}

	/* Expanding the group must have made room if it didn't choose this
	 * bucket. */
	if (put_into_group(h->group, h->home_bucket, encode_offset(new_off,h))){
		return tdb_write_convert(tdb, h->group_start,
					 h->group, sizeof(h->group));
	}

	/* This can happen if all hashes in group (and us) dropped into same
	 * group in subhash. */
	return add_to_hash(tdb, h, new_off);
}

/* Traverse support: returns offset of record, or 0 or -ve error. */
static tdb_off_t iterate_hash(struct tdb_context *tdb,
			      struct traverse_info *tinfo)
{
	tdb_off_t off, val, i;
	struct traverse_level *tlevel;

	tlevel = &tinfo->levels[tinfo->num_levels-1];

again:
	for (i = tdb_find_nonzero_off(tdb, tlevel->hashtable,
				      tlevel->entry, tlevel->total_buckets);
	     i != tlevel->total_buckets;
	     i = tdb_find_nonzero_off(tdb, tlevel->hashtable,
				      i+1, tlevel->total_buckets)) {
		if (TDB_OFF_IS_ERR(i)) {
			return i;
		}

		val = tdb_read_off(tdb, tlevel->hashtable+sizeof(tdb_off_t)*i);
		if (TDB_OFF_IS_ERR(val)) {
			return val;
		}

		off = val & TDB_OFF_MASK;

		/* This makes the delete-all-in-traverse case work
		 * (and simplifies our logic a little). */
		if (off == tinfo->prev)
			continue;

		tlevel->entry = i;

		if (!is_subhash(val)) {
			/* Found one. */
			tinfo->prev = off;
			return off;
		}

		/* When we come back, we want the next one */
		tlevel->entry++;
		tinfo->num_levels++;
		tlevel++;
		tlevel->hashtable = off + sizeof(struct tdb_used_record);
		tlevel->entry = 0;
		/* Next level is a chain? */
		if (unlikely(tinfo->num_levels == TDB_MAX_LEVELS + 1))
			tlevel->total_buckets = (1 << TDB_HASH_GROUP_BITS);
		else
			tlevel->total_buckets = (1 << TDB_SUBLEVEL_HASH_BITS);
		goto again;
	}

	/* Nothing there? */
	if (tinfo->num_levels == 1)
		return 0;

	/* Handle chained entries. */
	if (unlikely(tinfo->num_levels == TDB_MAX_LEVELS + 1)) {
		tlevel->hashtable = tdb_read_off(tdb, tlevel->hashtable
						 + offsetof(struct tdb_chain,
							    next));
		if (TDB_OFF_IS_ERR(tlevel->hashtable)) {
			return tlevel->hashtable;
		}
		if (tlevel->hashtable) {
			tlevel->hashtable += sizeof(struct tdb_used_record);
			tlevel->entry = 0;
			goto again;
		}
	}

	/* Go back up and keep searching. */
	tinfo->num_levels--;
	tlevel--;
	goto again;
}

/* Return success if we find something, TDB_ERR_NOEXIST if none. */
enum TDB_ERROR next_in_hash(struct tdb_context *tdb,
			    struct traverse_info *tinfo,
			    TDB_DATA *kbuf, size_t *dlen)
{
	const unsigned group_bits = TDB_TOPLEVEL_HASH_BITS-TDB_HASH_GROUP_BITS;
	tdb_off_t hl_start, hl_range, off;
	enum TDB_ERROR ecode;

	while (tinfo->toplevel_group < (1 << group_bits)) {
		hl_start = (tdb_off_t)tinfo->toplevel_group
			<< (64 - group_bits);
		hl_range = 1ULL << group_bits;
		ecode = tdb_lock_hashes(tdb, hl_start, hl_range, F_RDLCK,
					TDB_LOCK_WAIT);
		if (ecode != TDB_SUCCESS) {
			return ecode;
		}

		off = iterate_hash(tdb, tinfo);
		if (off) {
			struct tdb_used_record rec;

			if (TDB_OFF_IS_ERR(off)) {
				ecode = off;
				goto fail;
			}

			ecode = tdb_read_convert(tdb, off, &rec, sizeof(rec));
			if (ecode != TDB_SUCCESS) {
				goto fail;
			}
			if (rec_magic(&rec) != TDB_USED_MAGIC) {
				ecode = tdb_logerr(tdb, TDB_ERR_CORRUPT,
						   TDB_LOG_ERROR,
						   "next_in_hash:"
						   " corrupt record at %llu",
						   (long long)off);
				goto fail;
			}

			kbuf->dsize = rec_key_length(&rec);

			/* They want data as well? */
			if (dlen) {
				*dlen = rec_data_length(&rec);
				kbuf->dptr = tdb_alloc_read(tdb,
							    off + sizeof(rec),
							    kbuf->dsize
							    + *dlen);
			} else {
				kbuf->dptr = tdb_alloc_read(tdb,
							    off + sizeof(rec),
							    kbuf->dsize);
			}
			tdb_unlock_hashes(tdb, hl_start, hl_range, F_RDLCK);
			if (TDB_PTR_IS_ERR(kbuf->dptr)) {
				return TDB_PTR_ERR(kbuf->dptr);
			}
			return TDB_SUCCESS;
		}

		tdb_unlock_hashes(tdb, hl_start, hl_range, F_RDLCK);

		tinfo->toplevel_group++;
		tinfo->levels[0].hashtable
			+= (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
		tinfo->levels[0].entry = 0;
	}
	return TDB_ERR_NOEXIST;

fail:
	tdb_unlock_hashes(tdb, hl_start, hl_range, F_RDLCK);
	return ecode;

}

enum TDB_ERROR first_in_hash(struct tdb_context *tdb,
			     struct traverse_info *tinfo,
			     TDB_DATA *kbuf, size_t *dlen)
{
	tinfo->prev = 0;
	tinfo->toplevel_group = 0;
	tinfo->num_levels = 1;
	tinfo->levels[0].hashtable = offsetof(struct tdb_header, hashtable);
	tinfo->levels[0].entry = 0;
	tinfo->levels[0].total_buckets = (1 << TDB_HASH_GROUP_BITS);

	return next_in_hash(tdb, tinfo, kbuf, dlen);
}

/* Even if the entry isn't in this hash bucket, you'd have to lock this
 * bucket to find it. */
static enum TDB_ERROR chainlock(struct tdb_context *tdb, const TDB_DATA *key,
				int ltype, enum tdb_lock_flags waitflag,
				const char *func)
{
	enum TDB_ERROR ecode;
	uint64_t h = tdb_hash(tdb, key->dptr, key->dsize);
	tdb_off_t lockstart, locksize;
	unsigned int group, gbits;

	gbits = TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS;
	group = bits_from(h, 64 - gbits, gbits);

	lockstart = hlock_range(group, &locksize);

	ecode = tdb_lock_hashes(tdb, lockstart, locksize, ltype, waitflag);
	tdb_trace_1rec(tdb, func, *key);
	return ecode;
}

/* lock/unlock one hash chain. This is meant to be used to reduce
   contention - it cannot guarantee how many records will be locked */
enum TDB_ERROR tdb_chainlock(struct tdb_context *tdb, TDB_DATA key)
{
	return tdb->last_error = chainlock(tdb, &key, F_WRLCK, TDB_LOCK_WAIT,
					   "tdb_chainlock");
}

void tdb_chainunlock(struct tdb_context *tdb, TDB_DATA key)
{
	uint64_t h = tdb_hash(tdb, key.dptr, key.dsize);
	tdb_off_t lockstart, locksize;
	unsigned int group, gbits;

	gbits = TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS;
	group = bits_from(h, 64 - gbits, gbits);

	lockstart = hlock_range(group, &locksize);

	tdb_trace_1rec(tdb, "tdb_chainunlock", key);
	tdb_unlock_hashes(tdb, lockstart, locksize, F_WRLCK);
}

enum TDB_ERROR tdb_chainlock_read(struct tdb_context *tdb, TDB_DATA key)
{
	return tdb->last_error = chainlock(tdb, &key, F_RDLCK, TDB_LOCK_WAIT,
					   "tdb_chainlock_read");
}

void tdb_chainunlock_read(struct tdb_context *tdb, TDB_DATA key)
{
	uint64_t h = tdb_hash(tdb, key.dptr, key.dsize);
	tdb_off_t lockstart, locksize;
	unsigned int group, gbits;

	gbits = TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS;
	group = bits_from(h, 64 - gbits, gbits);

	lockstart = hlock_range(group, &locksize);

	tdb_trace_1rec(tdb, "tdb_chainunlock_read", key);
	tdb_unlock_hashes(tdb, lockstart, locksize, F_RDLCK);
}