tdb2: remove double-open detection for TDB1 databases.
[ccan] / ccan / tdb2 / hash.c
1  /*
2    Trivial Database 2: hash handling
3    Copyright (C) Rusty Russell 2010
4
5    This library is free software; you can redistribute it and/or
6    modify it under the terms of the GNU Lesser General Public
7    License as published by the Free Software Foundation; either
8    version 3 of the License, or (at your option) any later version.
9
10    This library is distributed in the hope that it will be useful,
11    but WITHOUT ANY WARRANTY; without even the implied warranty of
12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13    Lesser General Public License for more details.
14
15    You should have received a copy of the GNU Lesser General Public
16    License along with this library; if not, see <http://www.gnu.org/licenses/>.
17 */
18 #include "private.h"
19 #include <assert.h>
20
21 uint64_t tdb_hash(struct tdb_context *tdb, const void *ptr, size_t len)
22 {
23         return tdb->hash_fn(ptr, len, tdb->hash_seed, tdb->hash_data);
24 }
25
26 uint64_t hash_record(struct tdb_context *tdb, tdb_off_t off)
27 {
28         const struct tdb_used_record *r;
29         const void *key;
30         uint64_t klen, hash;
31
32         r = tdb_access_read(tdb, off, sizeof(*r), true);
33         if (TDB_PTR_IS_ERR(r)) {
34                 /* FIXME */
35                 return 0;
36         }
37
38         klen = rec_key_length(r);
39         tdb_access_release(tdb, r);
40
41         key = tdb_access_read(tdb, off + sizeof(*r), klen, false);
42         if (TDB_PTR_IS_ERR(key)) {
43                 return 0;
44         }
45
46         hash = tdb_hash(tdb, key, klen);
47         tdb_access_release(tdb, key);
48         return hash;
49 }
50
51 /* Get bits from a value. */
52 static uint32_t bits_from(uint64_t val, unsigned start, unsigned num)
53 {
54         assert(num <= 32);
55         return (val >> start) & ((1U << num) - 1);
56 }
57
58 /* We take bits from the top: that way we can lock whole sections of the hash
59  * by using lock ranges. */
60 static uint32_t use_bits(struct hash_info *h, unsigned num)
61 {
62         h->hash_used += num;
63         return bits_from(h->h, 64 - h->hash_used, num);
64 }
65
66 static tdb_bool_err key_matches(struct tdb_context *tdb,
67                                 const struct tdb_used_record *rec,
68                                 tdb_off_t off,
69                                 const struct tdb_data *key)
70 {
71         tdb_bool_err ret = false;
72         const char *rkey;
73
74         if (rec_key_length(rec) != key->dsize) {
75                 tdb->stats.compare_wrong_keylen++;
76                 return ret;
77         }
78
79         rkey = tdb_access_read(tdb, off + sizeof(*rec), key->dsize, false);
80         if (TDB_PTR_IS_ERR(rkey)) {
81                 return TDB_PTR_ERR(rkey);
82         }
83         if (memcmp(rkey, key->dptr, key->dsize) == 0)
84                 ret = true;
85         else
86                 tdb->stats.compare_wrong_keycmp++;
87         tdb_access_release(tdb, rkey);
88         return ret;
89 }
90
91 /* Does entry match? */
92 static tdb_bool_err match(struct tdb_context *tdb,
93                           struct hash_info *h,
94                           const struct tdb_data *key,
95                           tdb_off_t val,
96                           struct tdb_used_record *rec)
97 {
98         tdb_off_t off;
99         enum TDB_ERROR ecode;
100
101         tdb->stats.compares++;
102         /* Desired bucket must match. */
103         if (h->home_bucket != (val & TDB_OFF_HASH_GROUP_MASK)) {
104                 tdb->stats.compare_wrong_bucket++;
105                 return false;
106         }
107
108         /* Top bits of offset == next bits of hash. */
109         if (bits_from(val, TDB_OFF_HASH_EXTRA_BIT, TDB_OFF_UPPER_STEAL_EXTRA)
110             != bits_from(h->h, 64 - h->hash_used - TDB_OFF_UPPER_STEAL_EXTRA,
111                     TDB_OFF_UPPER_STEAL_EXTRA)) {
112                 tdb->stats.compare_wrong_offsetbits++;
113                 return false;
114         }
115
116         off = val & TDB_OFF_MASK;
117         ecode = tdb_read_convert(tdb, off, rec, sizeof(*rec));
118         if (ecode != TDB_SUCCESS) {
119                 return ecode;
120         }
121
122         if ((h->h & ((1 << 11)-1)) != rec_hash(rec)) {
123                 tdb->stats.compare_wrong_rechash++;
124                 return false;
125         }
126
127         return key_matches(tdb, rec, off, key);
128 }
129
130 static tdb_off_t hbucket_off(tdb_off_t group_start, unsigned bucket)
131 {
132         return group_start
133                 + (bucket % (1 << TDB_HASH_GROUP_BITS)) * sizeof(tdb_off_t);
134 }
135
136 bool is_subhash(tdb_off_t val)
137 {
138         return (val >> TDB_OFF_UPPER_STEAL_SUBHASH_BIT) & 1;
139 }
140
141 /* FIXME: Guess the depth, don't over-lock! */
142 static tdb_off_t hlock_range(tdb_off_t group, tdb_off_t *size)
143 {
144         *size = 1ULL << (64 - (TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS));
145         return group << (64 - (TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS));
146 }
147
148 static tdb_off_t COLD find_in_chain(struct tdb_context *tdb,
149                                     struct tdb_data key,
150                                     tdb_off_t chain,
151                                     struct hash_info *h,
152                                     struct tdb_used_record *rec,
153                                     struct traverse_info *tinfo)
154 {
155         tdb_off_t off, next;
156         enum TDB_ERROR ecode;
157
158         /* In case nothing is free, we set these to zero. */
159         h->home_bucket = h->found_bucket = 0;
160
161         for (off = chain; off; off = next) {
162                 unsigned int i;
163
164                 h->group_start = off;
165                 ecode = tdb_read_convert(tdb, off, h->group, sizeof(h->group));
166                 if (ecode != TDB_SUCCESS) {
167                         return ecode;
168                 }
169
170                 for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
171                         tdb_off_t recoff;
172                         if (!h->group[i]) {
173                                 /* Remember this empty bucket. */
174                                 h->home_bucket = h->found_bucket = i;
175                                 continue;
176                         }
177
178                         /* We can insert extra bits via add_to_hash
179                          * empty bucket logic. */
180                         recoff = h->group[i] & TDB_OFF_MASK;
181                         ecode = tdb_read_convert(tdb, recoff, rec,
182                                                  sizeof(*rec));
183                         if (ecode != TDB_SUCCESS) {
184                                 return ecode;
185                         }
186
187                         ecode = key_matches(tdb, rec, recoff, &key);
188                         if (ecode < 0) {
189                                 return ecode;
190                         }
191                         if (ecode == 1) {
192                                 h->home_bucket = h->found_bucket = i;
193
194                                 if (tinfo) {
195                                         tinfo->levels[tinfo->num_levels]
196                                                 .hashtable = off;
197                                         tinfo->levels[tinfo->num_levels]
198                                                 .total_buckets
199                                                 = 1 << TDB_HASH_GROUP_BITS;
200                                         tinfo->levels[tinfo->num_levels].entry
201                                                 = i;
202                                         tinfo->num_levels++;
203                                 }
204                                 return recoff;
205                         }
206                 }
207                 next = tdb_read_off(tdb, off
208                                     + offsetof(struct tdb_chain, next));
209                 if (TDB_OFF_IS_ERR(next)) {
210                         return next;
211                 }
212                 if (next)
213                         next += sizeof(struct tdb_used_record);
214         }
215         return 0;
216 }
217
218 /* This is the core routine which searches the hashtable for an entry.
219  * On error, no locks are held and -ve is returned.
220  * Otherwise, hinfo is filled in (and the optional tinfo).
221  * If not found, the return value is 0.
222  * If found, the return value is the offset, and *rec is the record. */
223 tdb_off_t find_and_lock(struct tdb_context *tdb,
224                         struct tdb_data key,
225                         int ltype,
226                         struct hash_info *h,
227                         struct tdb_used_record *rec,
228                         struct traverse_info *tinfo)
229 {
230         uint32_t i, group;
231         tdb_off_t hashtable;
232         enum TDB_ERROR ecode;
233
234         h->h = tdb_hash(tdb, key.dptr, key.dsize);
235         h->hash_used = 0;
236         group = use_bits(h, TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS);
237         h->home_bucket = use_bits(h, TDB_HASH_GROUP_BITS);
238
239         h->hlock_start = hlock_range(group, &h->hlock_range);
240         ecode = tdb_lock_hashes(tdb, h->hlock_start, h->hlock_range, ltype,
241                                 TDB_LOCK_WAIT);
242         if (ecode != TDB_SUCCESS) {
243                 return ecode;
244         }
245
246         hashtable = offsetof(struct tdb_header, hashtable);
247         if (tinfo) {
248                 tinfo->toplevel_group = group;
249                 tinfo->num_levels = 1;
250                 tinfo->levels[0].entry = 0;
251                 tinfo->levels[0].hashtable = hashtable
252                         + (group << TDB_HASH_GROUP_BITS) * sizeof(tdb_off_t);
253                 tinfo->levels[0].total_buckets = 1 << TDB_HASH_GROUP_BITS;
254         }
255
256         while (h->hash_used <= 64) {
257                 /* Read in the hash group. */
258                 h->group_start = hashtable
259                         + group * (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
260
261                 ecode = tdb_read_convert(tdb, h->group_start, &h->group,
262                                          sizeof(h->group));
263                 if (ecode != TDB_SUCCESS) {
264                         goto fail;
265                 }
266
267                 /* Pointer to another hash table?  Go down... */
268                 if (is_subhash(h->group[h->home_bucket])) {
269                         hashtable = (h->group[h->home_bucket] & TDB_OFF_MASK)
270                                 + sizeof(struct tdb_used_record);
271                         if (tinfo) {
272                                 /* When we come back, use *next* bucket */
273                                 tinfo->levels[tinfo->num_levels-1].entry
274                                         += h->home_bucket + 1;
275                         }
276                         group = use_bits(h, TDB_SUBLEVEL_HASH_BITS
277                                          - TDB_HASH_GROUP_BITS);
278                         h->home_bucket = use_bits(h, TDB_HASH_GROUP_BITS);
279                         if (tinfo) {
280                                 tinfo->levels[tinfo->num_levels].hashtable
281                                         = hashtable;
282                                 tinfo->levels[tinfo->num_levels].total_buckets
283                                         = 1 << TDB_SUBLEVEL_HASH_BITS;
284                                 tinfo->levels[tinfo->num_levels].entry
285                                         = group << TDB_HASH_GROUP_BITS;
286                                 tinfo->num_levels++;
287                         }
288                         continue;
289                 }
290
291                 /* It's in this group: search (until 0 or all searched) */
292                 for (i = 0, h->found_bucket = h->home_bucket;
293                      i < (1 << TDB_HASH_GROUP_BITS);
294                      i++, h->found_bucket = ((h->found_bucket+1)
295                                              % (1 << TDB_HASH_GROUP_BITS))) {
296                         tdb_bool_err berr;
297                         if (is_subhash(h->group[h->found_bucket]))
298                                 continue;
299
300                         if (!h->group[h->found_bucket])
301                                 break;
302
303                         berr = match(tdb, h, &key, h->group[h->found_bucket],
304                                      rec);
305                         if (berr < 0) {
306                                 ecode = berr;
307                                 goto fail;
308                         }
309                         if (berr) {
310                                 if (tinfo) {
311                                         tinfo->levels[tinfo->num_levels-1].entry
312                                                 += h->found_bucket;
313                                 }
314                                 return h->group[h->found_bucket] & TDB_OFF_MASK;
315                         }
316                 }
317                 /* Didn't find it: h indicates where it would go. */
318                 return 0;
319         }
320
321         return find_in_chain(tdb, key, hashtable, h, rec, tinfo);
322
323 fail:
324         tdb_unlock_hashes(tdb, h->hlock_start, h->hlock_range, ltype);
325         return ecode;
326 }
327
328 /* I wrote a simple test, expanding a hash to 2GB, for the following
329  * cases:
330  * 1) Expanding all the buckets at once,
331  * 2) Expanding the bucket we wanted to place the new entry into.
332  * 3) Expanding the most-populated bucket,
333  *
334  * I measured the worst/average/best density during this process.
335  * 1) 3%/16%/30%
336  * 2) 4%/20%/38%
337  * 3) 6%/22%/41%
338  *
339  * So we figure out the busiest bucket for the moment.
340  */
341 static unsigned fullest_bucket(struct tdb_context *tdb,
342                                const tdb_off_t *group,
343                                unsigned new_bucket)
344 {
345         unsigned counts[1 << TDB_HASH_GROUP_BITS] = { 0 };
346         unsigned int i, best_bucket;
347
348         /* Count the new entry. */
349         counts[new_bucket]++;
350         best_bucket = new_bucket;
351
352         for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
353                 unsigned this_bucket;
354
355                 if (is_subhash(group[i]))
356                         continue;
357                 this_bucket = group[i] & TDB_OFF_HASH_GROUP_MASK;
358                 if (++counts[this_bucket] > counts[best_bucket])
359                         best_bucket = this_bucket;
360         }
361
362         return best_bucket;
363 }
364
365 static bool put_into_group(tdb_off_t *group,
366                            unsigned bucket, tdb_off_t encoded)
367 {
368         unsigned int i;
369
370         for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
371                 unsigned b = (bucket + i) % (1 << TDB_HASH_GROUP_BITS);
372
373                 if (group[b] == 0) {
374                         group[b] = encoded;
375                         return true;
376                 }
377         }
378         return false;
379 }
380
381 static void force_into_group(tdb_off_t *group,
382                              unsigned bucket, tdb_off_t encoded)
383 {
384         if (!put_into_group(group, bucket, encoded))
385                 abort();
386 }
387
388 static tdb_off_t encode_offset(tdb_off_t new_off, struct hash_info *h)
389 {
390         return h->home_bucket
391                 | new_off
392                 | ((uint64_t)bits_from(h->h,
393                                   64 - h->hash_used - TDB_OFF_UPPER_STEAL_EXTRA,
394                                   TDB_OFF_UPPER_STEAL_EXTRA)
395                    << TDB_OFF_HASH_EXTRA_BIT);
396 }
397
398 /* Simply overwrite the hash entry we found before. */
399 enum TDB_ERROR replace_in_hash(struct tdb_context *tdb,
400                                struct hash_info *h,
401                                tdb_off_t new_off)
402 {
403         return tdb_write_off(tdb, hbucket_off(h->group_start, h->found_bucket),
404                              encode_offset(new_off, h));
405 }
406
407 /* We slot in anywhere that's empty in the chain. */
408 static enum TDB_ERROR COLD add_to_chain(struct tdb_context *tdb,
409                                         tdb_off_t subhash,
410                                         tdb_off_t new_off)
411 {
412         tdb_off_t entry;
413         enum TDB_ERROR ecode;
414
415         entry = tdb_find_zero_off(tdb, subhash, 1<<TDB_HASH_GROUP_BITS);
416         if (TDB_OFF_IS_ERR(entry)) {
417                 return entry;
418         }
419
420         if (entry == 1 << TDB_HASH_GROUP_BITS) {
421                 tdb_off_t next;
422
423                 next = tdb_read_off(tdb, subhash
424                                     + offsetof(struct tdb_chain, next));
425                 if (TDB_OFF_IS_ERR(next)) {
426                         return next;
427                 }
428
429                 if (!next) {
430                         next = alloc(tdb, 0, sizeof(struct tdb_chain), 0,
431                                      TDB_CHAIN_MAGIC, false);
432                         if (TDB_OFF_IS_ERR(next))
433                                 return next;
434                         ecode = zero_out(tdb,
435                                          next+sizeof(struct tdb_used_record),
436                                          sizeof(struct tdb_chain));
437                         if (ecode != TDB_SUCCESS) {
438                                 return ecode;
439                         }
440                         ecode = tdb_write_off(tdb, subhash
441                                               + offsetof(struct tdb_chain,
442                                                          next),
443                                               next);
444                         if (ecode != TDB_SUCCESS) {
445                                 return ecode;
446                         }
447                 }
448                 return add_to_chain(tdb, next, new_off);
449         }
450
451         return tdb_write_off(tdb, subhash + entry * sizeof(tdb_off_t),
452                              new_off);
453 }
454
455 /* Add into a newly created subhash. */
456 static enum TDB_ERROR add_to_subhash(struct tdb_context *tdb, tdb_off_t subhash,
457                                      unsigned hash_used, tdb_off_t val)
458 {
459         tdb_off_t off = (val & TDB_OFF_MASK), *group;
460         struct hash_info h;
461         unsigned int gnum;
462
463         h.hash_used = hash_used;
464
465         if (hash_used + TDB_SUBLEVEL_HASH_BITS > 64)
466                 return add_to_chain(tdb, subhash, off);
467
468         h.h = hash_record(tdb, off);
469         gnum = use_bits(&h, TDB_SUBLEVEL_HASH_BITS-TDB_HASH_GROUP_BITS);
470         h.group_start = subhash
471                 + gnum * (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
472         h.home_bucket = use_bits(&h, TDB_HASH_GROUP_BITS);
473
474         group = tdb_access_write(tdb, h.group_start,
475                                  sizeof(*group) << TDB_HASH_GROUP_BITS, true);
476         if (TDB_PTR_IS_ERR(group)) {
477                 return TDB_PTR_ERR(group);
478         }
479         force_into_group(group, h.home_bucket, encode_offset(off, &h));
480         return tdb_access_commit(tdb, group);
481 }
482
483 static enum TDB_ERROR expand_group(struct tdb_context *tdb, struct hash_info *h)
484 {
485         unsigned bucket, num_vals, i, magic;
486         size_t subsize;
487         tdb_off_t subhash;
488         tdb_off_t vals[1 << TDB_HASH_GROUP_BITS];
489         enum TDB_ERROR ecode;
490
491         /* Attach new empty subhash under fullest bucket. */
492         bucket = fullest_bucket(tdb, h->group, h->home_bucket);
493
494         if (h->hash_used == 64) {
495                 tdb->stats.alloc_chain++;
496                 subsize = sizeof(struct tdb_chain);
497                 magic = TDB_CHAIN_MAGIC;
498         } else {
499                 tdb->stats.alloc_subhash++;
500                 subsize = (sizeof(tdb_off_t) << TDB_SUBLEVEL_HASH_BITS);
501                 magic = TDB_HTABLE_MAGIC;
502         }
503
504         subhash = alloc(tdb, 0, subsize, 0, magic, false);
505         if (TDB_OFF_IS_ERR(subhash)) {
506                 return subhash;
507         }
508
509         ecode = zero_out(tdb, subhash + sizeof(struct tdb_used_record),
510                          subsize);
511         if (ecode != TDB_SUCCESS) {
512                 return ecode;
513         }
514
515         /* Remove any which are destined for bucket or are in wrong place. */
516         num_vals = 0;
517         for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
518                 unsigned home_bucket = h->group[i] & TDB_OFF_HASH_GROUP_MASK;
519                 if (!h->group[i] || is_subhash(h->group[i]))
520                         continue;
521                 if (home_bucket == bucket || home_bucket != i) {
522                         vals[num_vals++] = h->group[i];
523                         h->group[i] = 0;
524                 }
525         }
526         /* FIXME: This assert is valid, but we do this during unit test :( */
527         /* assert(num_vals); */
528
529         /* Overwrite expanded bucket with subhash pointer. */
530         h->group[bucket] = subhash | (1ULL << TDB_OFF_UPPER_STEAL_SUBHASH_BIT);
531
532         /* Point to actual contents of record. */
533         subhash += sizeof(struct tdb_used_record);
534
535         /* Put values back. */
536         for (i = 0; i < num_vals; i++) {
537                 unsigned this_bucket = vals[i] & TDB_OFF_HASH_GROUP_MASK;
538
539                 if (this_bucket == bucket) {
540                         ecode = add_to_subhash(tdb, subhash, h->hash_used,
541                                                vals[i]);
542                         if (ecode != TDB_SUCCESS)
543                                 return ecode;
544                 } else {
545                         /* There should be room to put this back. */
546                         force_into_group(h->group, this_bucket, vals[i]);
547                 }
548         }
549         return TDB_SUCCESS;
550 }
551
552 enum TDB_ERROR delete_from_hash(struct tdb_context *tdb, struct hash_info *h)
553 {
554         unsigned int i, num_movers = 0;
555         tdb_off_t movers[1 << TDB_HASH_GROUP_BITS];
556
557         h->group[h->found_bucket] = 0;
558         for (i = 1; i < (1 << TDB_HASH_GROUP_BITS); i++) {
559                 unsigned this_bucket;
560
561                 this_bucket = (h->found_bucket+i) % (1 << TDB_HASH_GROUP_BITS);
562                 /* Empty bucket?  We're done. */
563                 if (!h->group[this_bucket])
564                         break;
565
566                 /* Ignore subhashes. */
567                 if (is_subhash(h->group[this_bucket]))
568                         continue;
569
570                 /* If this one is not happy where it is, we'll move it. */
571                 if ((h->group[this_bucket] & TDB_OFF_HASH_GROUP_MASK)
572                     != this_bucket) {
573                         movers[num_movers++] = h->group[this_bucket];
574                         h->group[this_bucket] = 0;
575                 }
576         }
577
578         /* Put back the ones we erased. */
579         for (i = 0; i < num_movers; i++) {
580                 force_into_group(h->group, movers[i] & TDB_OFF_HASH_GROUP_MASK,
581                                  movers[i]);
582         }
583
584         /* Now we write back the hash group */
585         return tdb_write_convert(tdb, h->group_start,
586                                  h->group, sizeof(h->group));
587 }
588
589 enum TDB_ERROR add_to_hash(struct tdb_context *tdb, struct hash_info *h,
590                            tdb_off_t new_off)
591 {
592         enum TDB_ERROR ecode;
593
594         /* We hit an empty bucket during search?  That's where it goes. */
595         if (!h->group[h->found_bucket]) {
596                 h->group[h->found_bucket] = encode_offset(new_off, h);
597                 /* Write back the modified group. */
598                 return tdb_write_convert(tdb, h->group_start,
599                                          h->group, sizeof(h->group));
600         }
601
602         if (h->hash_used > 64)
603                 return add_to_chain(tdb, h->group_start, new_off);
604
605         /* We're full.  Expand. */
606         ecode = expand_group(tdb, h);
607         if (ecode != TDB_SUCCESS) {
608                 return ecode;
609         }
610
611         if (is_subhash(h->group[h->home_bucket])) {
612                 /* We were expanded! */
613                 tdb_off_t hashtable;
614                 unsigned int gnum;
615
616                 /* Write back the modified group. */
617                 ecode = tdb_write_convert(tdb, h->group_start, h->group,
618                                           sizeof(h->group));
619                 if (ecode != TDB_SUCCESS) {
620                         return ecode;
621                 }
622
623                 /* Move hashinfo down a level. */
624                 hashtable = (h->group[h->home_bucket] & TDB_OFF_MASK)
625                         + sizeof(struct tdb_used_record);
626                 gnum = use_bits(h,TDB_SUBLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS);
627                 h->home_bucket = use_bits(h, TDB_HASH_GROUP_BITS);
628                 h->group_start = hashtable
629                         + gnum * (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
630                 ecode = tdb_read_convert(tdb, h->group_start, &h->group,
631                                          sizeof(h->group));
632                 if (ecode != TDB_SUCCESS) {
633                         return ecode;
634                 }
635         }
636
637         /* Expanding the group must have made room if it didn't choose this
638          * bucket. */
639         if (put_into_group(h->group, h->home_bucket, encode_offset(new_off,h))){
640                 return tdb_write_convert(tdb, h->group_start,
641                                          h->group, sizeof(h->group));
642         }
643
644         /* This can happen if all hashes in group (and us) dropped into same
645          * group in subhash. */
646         return add_to_hash(tdb, h, new_off);
647 }
648
649 /* Traverse support: returns offset of record, or 0 or -ve error. */
650 static tdb_off_t iterate_hash(struct tdb_context *tdb,
651                               struct traverse_info *tinfo)
652 {
653         tdb_off_t off, val, i;
654         struct traverse_level *tlevel;
655
656         tlevel = &tinfo->levels[tinfo->num_levels-1];
657
658 again:
659         for (i = tdb_find_nonzero_off(tdb, tlevel->hashtable,
660                                       tlevel->entry, tlevel->total_buckets);
661              i != tlevel->total_buckets;
662              i = tdb_find_nonzero_off(tdb, tlevel->hashtable,
663                                       i+1, tlevel->total_buckets)) {
664                 if (TDB_OFF_IS_ERR(i)) {
665                         return i;
666                 }
667
668                 val = tdb_read_off(tdb, tlevel->hashtable+sizeof(tdb_off_t)*i);
669                 if (TDB_OFF_IS_ERR(val)) {
670                         return val;
671                 }
672
673                 off = val & TDB_OFF_MASK;
674
675                 /* This makes the delete-all-in-traverse case work
676                  * (and simplifies our logic a little). */
677                 if (off == tinfo->prev)
678                         continue;
679
680                 tlevel->entry = i;
681
682                 if (!is_subhash(val)) {
683                         /* Found one. */
684                         tinfo->prev = off;
685                         return off;
686                 }
687
688                 /* When we come back, we want the next one */
689                 tlevel->entry++;
690                 tinfo->num_levels++;
691                 tlevel++;
692                 tlevel->hashtable = off + sizeof(struct tdb_used_record);
693                 tlevel->entry = 0;
694                 /* Next level is a chain? */
695                 if (unlikely(tinfo->num_levels == TDB_MAX_LEVELS + 1))
696                         tlevel->total_buckets = (1 << TDB_HASH_GROUP_BITS);
697                 else
698                         tlevel->total_buckets = (1 << TDB_SUBLEVEL_HASH_BITS);
699                 goto again;
700         }
701
702         /* Nothing there? */
703         if (tinfo->num_levels == 1)
704                 return 0;
705
706         /* Handle chained entries. */
707         if (unlikely(tinfo->num_levels == TDB_MAX_LEVELS + 1)) {
708                 tlevel->hashtable = tdb_read_off(tdb, tlevel->hashtable
709                                                  + offsetof(struct tdb_chain,
710                                                             next));
711                 if (TDB_OFF_IS_ERR(tlevel->hashtable)) {
712                         return tlevel->hashtable;
713                 }
714                 if (tlevel->hashtable) {
715                         tlevel->hashtable += sizeof(struct tdb_used_record);
716                         tlevel->entry = 0;
717                         goto again;
718                 }
719         }
720
721         /* Go back up and keep searching. */
722         tinfo->num_levels--;
723         tlevel--;
724         goto again;
725 }
726
727 /* Return success if we find something, TDB_ERR_NOEXIST if none. */
728 enum TDB_ERROR next_in_hash(struct tdb_context *tdb,
729                             struct traverse_info *tinfo,
730                             TDB_DATA *kbuf, size_t *dlen)
731 {
732         const unsigned group_bits = TDB_TOPLEVEL_HASH_BITS-TDB_HASH_GROUP_BITS;
733         tdb_off_t hl_start, hl_range, off;
734         enum TDB_ERROR ecode;
735
736         while (tinfo->toplevel_group < (1 << group_bits)) {
737                 hl_start = (tdb_off_t)tinfo->toplevel_group
738                         << (64 - group_bits);
739                 hl_range = 1ULL << group_bits;
740                 ecode = tdb_lock_hashes(tdb, hl_start, hl_range, F_RDLCK,
741                                         TDB_LOCK_WAIT);
742                 if (ecode != TDB_SUCCESS) {
743                         return ecode;
744                 }
745
746                 off = iterate_hash(tdb, tinfo);
747                 if (off) {
748                         struct tdb_used_record rec;
749
750                         if (TDB_OFF_IS_ERR(off)) {
751                                 ecode = off;
752                                 goto fail;
753                         }
754
755                         ecode = tdb_read_convert(tdb, off, &rec, sizeof(rec));
756                         if (ecode != TDB_SUCCESS) {
757                                 goto fail;
758                         }
759                         if (rec_magic(&rec) != TDB_USED_MAGIC) {
760                                 ecode = tdb_logerr(tdb, TDB_ERR_CORRUPT,
761                                                    TDB_LOG_ERROR,
762                                                    "next_in_hash:"
763                                                    " corrupt record at %llu",
764                                                    (long long)off);
765                                 goto fail;
766                         }
767
768                         kbuf->dsize = rec_key_length(&rec);
769
770                         /* They want data as well? */
771                         if (dlen) {
772                                 *dlen = rec_data_length(&rec);
773                                 kbuf->dptr = tdb_alloc_read(tdb,
774                                                             off + sizeof(rec),
775                                                             kbuf->dsize
776                                                             + *dlen);
777                         } else {
778                                 kbuf->dptr = tdb_alloc_read(tdb,
779                                                             off + sizeof(rec),
780                                                             kbuf->dsize);
781                         }
782                         tdb_unlock_hashes(tdb, hl_start, hl_range, F_RDLCK);
783                         if (TDB_PTR_IS_ERR(kbuf->dptr)) {
784                                 return TDB_PTR_ERR(kbuf->dptr);
785                         }
786                         return TDB_SUCCESS;
787                 }
788
789                 tdb_unlock_hashes(tdb, hl_start, hl_range, F_RDLCK);
790
791                 tinfo->toplevel_group++;
792                 tinfo->levels[0].hashtable
793                         += (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
794                 tinfo->levels[0].entry = 0;
795         }
796         return TDB_ERR_NOEXIST;
797
798 fail:
799         tdb_unlock_hashes(tdb, hl_start, hl_range, F_RDLCK);
800         return ecode;
801
802 }
803
804 enum TDB_ERROR first_in_hash(struct tdb_context *tdb,
805                              struct traverse_info *tinfo,
806                              TDB_DATA *kbuf, size_t *dlen)
807 {
808         tinfo->prev = 0;
809         tinfo->toplevel_group = 0;
810         tinfo->num_levels = 1;
811         tinfo->levels[0].hashtable = offsetof(struct tdb_header, hashtable);
812         tinfo->levels[0].entry = 0;
813         tinfo->levels[0].total_buckets = (1 << TDB_HASH_GROUP_BITS);
814
815         return next_in_hash(tdb, tinfo, kbuf, dlen);
816 }
817
818 /* Even if the entry isn't in this hash bucket, you'd have to lock this
819  * bucket to find it. */
820 static enum TDB_ERROR chainlock(struct tdb_context *tdb, const TDB_DATA *key,
821                                 int ltype, enum tdb_lock_flags waitflag,
822                                 const char *func)
823 {
824         enum TDB_ERROR ecode;
825         uint64_t h = tdb_hash(tdb, key->dptr, key->dsize);
826         tdb_off_t lockstart, locksize;
827         unsigned int group, gbits;
828
829         gbits = TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS;
830         group = bits_from(h, 64 - gbits, gbits);
831
832         lockstart = hlock_range(group, &locksize);
833
834         ecode = tdb_lock_hashes(tdb, lockstart, locksize, ltype, waitflag);
835         tdb_trace_1rec(tdb, func, *key);
836         return ecode;
837 }
838
839 /* lock/unlock one hash chain. This is meant to be used to reduce
840    contention - it cannot guarantee how many records will be locked */
841 enum TDB_ERROR tdb_chainlock(struct tdb_context *tdb, TDB_DATA key)
842 {
843         return tdb->last_error = chainlock(tdb, &key, F_WRLCK, TDB_LOCK_WAIT,
844                                            "tdb_chainlock");
845 }
846
847 void tdb_chainunlock(struct tdb_context *tdb, TDB_DATA key)
848 {
849         uint64_t h = tdb_hash(tdb, key.dptr, key.dsize);
850         tdb_off_t lockstart, locksize;
851         unsigned int group, gbits;
852
853         gbits = TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS;
854         group = bits_from(h, 64 - gbits, gbits);
855
856         lockstart = hlock_range(group, &locksize);
857
858         tdb_trace_1rec(tdb, "tdb_chainunlock", key);
859         tdb_unlock_hashes(tdb, lockstart, locksize, F_WRLCK);
860 }
861
862 enum TDB_ERROR tdb_chainlock_read(struct tdb_context *tdb, TDB_DATA key)
863 {
864         return tdb->last_error = chainlock(tdb, &key, F_RDLCK, TDB_LOCK_WAIT,
865                                            "tdb_chainlock_read");
866 }
867
868 void tdb_chainunlock_read(struct tdb_context *tdb, TDB_DATA key)
869 {
870         uint64_t h = tdb_hash(tdb, key.dptr, key.dsize);
871         tdb_off_t lockstart, locksize;
872         unsigned int group, gbits;
873
874         gbits = TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS;
875         group = bits_from(h, 64 - gbits, gbits);
876
877         lockstart = hlock_range(group, &locksize);
878
879         tdb_trace_1rec(tdb, "tdb_chainunlock_read", key);
880         tdb_unlock_hashes(tdb, lockstart, locksize, F_RDLCK);
881 }