2b07fdff330a3dfe23631dd6e98a3effb399e428
[ccan] / ccan / tdb2 / free.c
1  /* 
2    Trivial Database 2: free list/block 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 <ccan/likely/likely.h>
20 #include <ccan/ilog/ilog.h>
21 #include <time.h>
22 #include <assert.h>
23 #include <limits.h>
24
25 static unsigned fls64(uint64_t val)
26 {
27         return ilog64(val);
28 }
29
30 /* In which bucket would we find a particular record size? (ignoring header) */
31 unsigned int size_to_bucket(unsigned int zone_bits, tdb_len_t data_len)
32 {
33         unsigned int bucket;
34
35         /* We can't have records smaller than this. */
36         assert(data_len >= TDB_MIN_DATA_LEN);
37
38         /* Ignoring the header... */
39         if (data_len - TDB_MIN_DATA_LEN <= 64) {
40                 /* 0 in bucket 0, 8 in bucket 1... 64 in bucket 8. */
41                 bucket = (data_len - TDB_MIN_DATA_LEN) / 8;
42         } else {
43                 /* After that we go power of 2. */
44                 bucket = fls64(data_len - TDB_MIN_DATA_LEN) + 2;
45         }
46
47         if (unlikely(bucket > BUCKETS_FOR_ZONE(zone_bits)))
48                 bucket = BUCKETS_FOR_ZONE(zone_bits);
49         return bucket;
50 }
51
52 /* Subtract 1-byte tailer and header.  Then round up to next power of 2. */
53 static unsigned max_zone_bits(struct tdb_context *tdb)
54 {
55         return fls64(tdb->map_size-1-sizeof(struct tdb_header)-1) + 1;
56 }
57
58 /* Start by using a random zone to spread the load: returns the offset. */
59 static uint64_t random_zone(struct tdb_context *tdb)
60 {
61         struct free_zone_header zhdr;
62         tdb_off_t off = sizeof(struct tdb_header);
63         tdb_len_t half_bits;
64         uint64_t randbits = 0;
65         unsigned int i;
66
67         for (i = 0; i < 64; i += fls64(RAND_MAX)) 
68                 randbits ^= ((uint64_t)random()) << i;
69
70         /* FIXME: Does this work?  Test! */
71         half_bits = max_zone_bits(tdb) - 1;
72         do {
73                 /* Pick left or right side (not outside file) */
74                 if ((randbits & 1)
75                     && !tdb->methods->oob(tdb, off + (1ULL << half_bits)
76                                           + sizeof(zhdr), true)) {
77                         off += 1ULL << half_bits;
78                 }
79                 randbits >>= 1;
80
81                 if (tdb_read_convert(tdb, off, &zhdr, sizeof(zhdr)) == -1) 
82                         return TDB_OFF_ERR;
83
84                 if (zhdr.zone_bits == half_bits)
85                         return off;
86
87                 half_bits--;
88         } while (half_bits >= INITIAL_ZONE_BITS);
89
90         tdb->ecode = TDB_ERR_CORRUPT;
91         tdb->log(tdb, TDB_DEBUG_FATAL, tdb->log_priv,
92                  "random_zone: zone at %llu smaller than %u bits?",
93                  (long long)off, INITIAL_ZONE_BITS);
94         return TDB_OFF_ERR;
95 }
96
97 int tdb_zone_init(struct tdb_context *tdb)
98 {
99         tdb->zone_off = random_zone(tdb);
100         if (tdb->zone_off == TDB_OFF_ERR)
101                 return -1;
102         if (tdb_read_convert(tdb, tdb->zone_off,
103                              &tdb->zhdr, sizeof(tdb->zhdr)) == -1) 
104                 return -1;
105         return 0;
106 }
107
108 /* Where's the header, given a zone size of 1 << zone_bits? */
109 static tdb_off_t zone_off(tdb_off_t off, unsigned int zone_bits)
110 {
111         off -= sizeof(struct tdb_header);
112         return (off & ~((1ULL << zone_bits) - 1)) + sizeof(struct tdb_header);
113 }
114
115 /* Offset of a given bucket. */
116 /* FIXME: bucket can be "unsigned" everywhere, or even uint8/16. */
117 tdb_off_t bucket_off(tdb_off_t zone_off, tdb_off_t bucket)
118 {
119         return zone_off
120                 + sizeof(struct free_zone_header)
121                 + bucket * sizeof(tdb_off_t);
122 }
123
124 /* Returns free_buckets + 1, or list number to search. */
125 static tdb_off_t find_free_head(struct tdb_context *tdb, tdb_off_t bucket)
126 {
127         /* Speculatively search for a non-zero bucket. */
128         return tdb_find_nonzero_off(tdb, bucket_off(tdb->zone_off, 0),
129                                     bucket,
130                                     BUCKETS_FOR_ZONE(tdb->zhdr.zone_bits) + 1);
131 }
132
133 /* Remove from free bucket. */
134 static int remove_from_list(struct tdb_context *tdb,
135                             tdb_off_t b_off, tdb_off_t r_off,
136                             struct tdb_free_record *r)
137 {
138         tdb_off_t off;
139
140         /* Front of list? */
141         if (r->prev == 0) {
142                 off = b_off;
143         } else {
144                 off = r->prev + offsetof(struct tdb_free_record, next);
145         }
146
147 #ifdef DEBUG
148         if (tdb_read_off(tdb, off) != r_off) {
149                 tdb->log(tdb, TDB_DEBUG_FATAL, tdb->log_priv,
150                          "remove_from_list: %llu bad prev in list %llu\n",
151                          (long long)r_off, (long long)b_off);
152                 return -1;
153         }
154 #endif
155
156         /* r->prev->next = r->next */
157         if (tdb_write_off(tdb, off, r->next)) {
158                 return -1;
159         }
160
161         if (r->next != 0) {
162                 off = r->next + offsetof(struct tdb_free_record, prev);
163                 /* r->next->prev = r->prev */
164
165 #ifdef DEBUG
166                 if (tdb_read_off(tdb, off) != r_off) {
167                         tdb->log(tdb, TDB_DEBUG_FATAL, tdb->log_priv,
168                                  "remove_from_list: %llu bad list %llu\n",
169                                  (long long)r_off, (long long)b_off);
170                         return -1;
171                 }
172 #endif
173
174                 if (tdb_write_off(tdb, off, r->prev)) {
175                         return -1;
176                 }
177         }
178         return 0;
179 }
180
181 /* Enqueue in this free bucket. */
182 static int enqueue_in_free(struct tdb_context *tdb,
183                            tdb_off_t b_off,
184                            tdb_off_t off,
185                            struct tdb_free_record *new)
186 {
187         new->prev = 0;
188         /* new->next = head. */
189         new->next = tdb_read_off(tdb, b_off);
190         if (new->next == TDB_OFF_ERR)
191                 return -1;
192
193         if (new->next) {
194 #ifdef DEBUG
195                 if (tdb_read_off(tdb,
196                                  new->next
197                                  + offsetof(struct tdb_free_record, prev))
198                     != 0) {
199                         tdb->log(tdb, TDB_DEBUG_FATAL, tdb->log_priv,
200                                  "enqueue_in_free: %llu bad head prev %llu\n",
201                                  (long long)new->next, (long long)b_off);
202                         return -1;
203                 }
204 #endif
205                 /* next->prev = new. */
206                 if (tdb_write_off(tdb, new->next
207                                   + offsetof(struct tdb_free_record, prev),
208                                   off) != 0)
209                         return -1;
210         }
211         /* head = new */
212         if (tdb_write_off(tdb, b_off, off) != 0)
213                 return -1;
214
215         return tdb_write_convert(tdb, off, new, sizeof(*new));
216 }
217
218 /* List need not be locked. */
219 int add_free_record(struct tdb_context *tdb,
220                     unsigned int zone_bits,
221                     tdb_off_t off, tdb_len_t len_with_header)
222 {
223         struct tdb_free_record new;
224         tdb_off_t b_off;
225         int ret;
226
227         assert(len_with_header >= sizeof(new));
228         assert(zone_bits < (1 << 6));
229
230         new.magic_and_meta = TDB_FREE_MAGIC | zone_bits;
231         new.data_len = len_with_header - sizeof(struct tdb_used_record);
232
233         b_off = bucket_off(zone_off(off, zone_bits),
234                            size_to_bucket(zone_bits, new.data_len));
235         if (tdb_lock_free_bucket(tdb, b_off, TDB_LOCK_WAIT) != 0)
236                 return -1;
237
238         ret = enqueue_in_free(tdb, b_off, off, &new);
239         tdb_unlock_free_bucket(tdb, b_off);
240         return ret;
241 }
242
243 static size_t adjust_size(size_t keylen, size_t datalen, bool want_extra)
244 {
245         size_t size = keylen + datalen;
246
247         /* We want at least 50% growth for data. */
248         if (want_extra)
249                 size += datalen/2;
250
251         if (size < TDB_MIN_DATA_LEN)
252                 size = TDB_MIN_DATA_LEN;
253
254         /* Round to next uint64_t boundary. */
255         return (size + (sizeof(uint64_t) - 1ULL)) & ~(sizeof(uint64_t) - 1ULL);
256 }
257
258 /* If we have enough left over to be useful, split that off. */
259 static int to_used_record(struct tdb_context *tdb,
260                           unsigned int zone_bits,
261                           tdb_off_t off,
262                           tdb_len_t needed,
263                           tdb_len_t total_len,
264                           tdb_len_t *actual)
265 {
266         struct tdb_used_record used;
267         tdb_len_t leftover;
268
269         leftover = total_len - needed;
270         if (leftover < sizeof(struct tdb_free_record))
271                 leftover = 0;
272
273         *actual = total_len - leftover;
274
275         if (leftover) {
276                 if (add_free_record(tdb, zone_bits,
277                                     off + sizeof(used) + *actual,
278                                     total_len - needed))
279                         return -1;
280         }
281         return 0;
282 }
283
284 /* Note: we unlock the current bucket if we coalesce or fail. */
285 static int coalesce(struct tdb_context *tdb,
286                     tdb_off_t zone_off, unsigned zone_bits,
287                     tdb_off_t off, tdb_off_t b_off, tdb_len_t data_len)
288 {
289         struct tdb_free_record pad, *r;
290         tdb_off_t end = off + sizeof(struct tdb_used_record) + data_len;
291
292         while (end < (zone_off + (1ULL << zone_bits))) {
293                 tdb_off_t nb_off;
294
295                 /* FIXME: do tdb_get here and below really win? */
296                 r = tdb_get(tdb, end, &pad, sizeof(pad));
297                 if (!r)
298                         goto err;
299
300                 if (frec_magic(r) != TDB_FREE_MAGIC)
301                         break;
302
303                 nb_off = bucket_off(zone_off,
304                                     size_to_bucket(zone_bits, r->data_len));
305
306                 /* We may be violating lock order here, so best effort. */
307                 if (tdb_lock_free_bucket(tdb, nb_off, TDB_LOCK_NOWAIT) == -1)
308                         break;
309
310                 /* Now we have lock, re-check. */
311                 r = tdb_get(tdb, end, &pad, sizeof(pad));
312                 if (!r) {
313                         tdb_unlock_free_bucket(tdb, nb_off);
314                         goto err;
315                 }
316
317                 if (unlikely(frec_magic(r) != TDB_FREE_MAGIC)) {
318                         tdb_unlock_free_bucket(tdb, nb_off);
319                         break;
320                 }
321
322                 if (remove_from_list(tdb, nb_off, end, r) == -1) {
323                         tdb_unlock_free_bucket(tdb, nb_off);
324                         goto err;
325                 }
326
327                 end += sizeof(struct tdb_used_record) + r->data_len;
328                 tdb_unlock_free_bucket(tdb, nb_off);
329         }
330
331         /* Didn't find any adjacent free? */
332         if (end == off + sizeof(struct tdb_used_record) + data_len)
333                 return 0;
334
335         /* OK, expand record */
336         r = tdb_get(tdb, off, &pad, sizeof(pad));
337         if (!r)
338                 goto err;
339
340         if (r->data_len != data_len) {
341                 tdb->ecode = TDB_ERR_CORRUPT;
342                 tdb->log(tdb, TDB_DEBUG_FATAL, tdb->log_priv,
343                          "coalesce: expected data len %llu not %llu\n",
344                          (long long)data_len, (long long)r->data_len);
345                 goto err;
346         }
347
348         if (remove_from_list(tdb, b_off, off, r) == -1)
349                 goto err;
350
351         /* We have to drop this to avoid deadlocks. */
352         tdb_unlock_free_bucket(tdb, b_off);
353
354         if (add_free_record(tdb, zone_bits, off, end - off) == -1)
355                 return -1;
356         return 1;
357
358 err:
359         /* To unify error paths, we *always* unlock bucket on error. */
360         tdb_unlock_free_bucket(tdb, b_off);
361         return -1;
362 }
363
364 /* We need size bytes to put our key and data in. */
365 static tdb_off_t lock_and_alloc(struct tdb_context *tdb,
366                                 tdb_off_t zone_off,
367                                 unsigned zone_bits,
368                                 tdb_off_t bucket,
369                                 size_t size,
370                                 tdb_len_t *actual)
371 {
372         tdb_off_t off, b_off,best_off;
373         struct tdb_free_record pad, best = { 0 }, *r;
374         double multiplier;
375
376 again:
377         b_off = bucket_off(zone_off, bucket);
378
379         /* FIXME: Try non-blocking wait first, to measure contention.
380          * If we're contented, try switching zones, and don't enlarge zone
381          * next time (we want more zones). */
382         /* Lock this bucket. */
383         if (tdb_lock_free_bucket(tdb, b_off, TDB_LOCK_WAIT) == -1) {
384                 return TDB_OFF_ERR;
385         }
386
387         best.data_len = -1ULL;
388         best_off = 0;
389         /* FIXME: Start with larger multiplier if we're growing. */
390         multiplier = 1.0;
391
392         /* Walk the list to see if any are large enough, getting less fussy
393          * as we go. */
394         off = tdb_read_off(tdb, b_off);
395         if (unlikely(off == TDB_OFF_ERR))
396                 goto unlock_err;
397
398         while (off) {
399                 /* FIXME: Does tdb_get win anything here? */
400                 r = tdb_get(tdb, off, &pad, sizeof(*r));
401                 if (!r)
402                         goto unlock_err;
403
404                 if (frec_magic(r) != TDB_FREE_MAGIC) {
405                         tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
406                                  "lock_and_alloc: %llu non-free 0x%llx\n",
407                                  (long long)off, (long long)r->magic_and_meta);
408                         goto unlock_err;
409                 }
410
411                 if (r->data_len >= size && r->data_len < best.data_len) {
412                         best_off = off;
413                         best = *r;
414                 }
415
416                 if (best.data_len < size * multiplier && best_off)
417                         goto use_best;
418
419                 multiplier *= 1.01;
420
421                 /* Since we're going slow anyway, try coalescing here. */
422                 switch (coalesce(tdb, zone_off, zone_bits, off, b_off,
423                                  r->data_len)) {
424                 case -1:
425                         /* This has already unlocked on error. */
426                         return -1;
427                 case 1:
428                         /* This has unlocked list, restart. */
429                         goto again;
430                 }
431                 off = r->next;
432         }
433
434         /* If we found anything at all, use it. */
435         if (best_off) {
436         use_best:
437                 /* We're happy with this size: take it. */
438                 if (remove_from_list(tdb, b_off, best_off, &best) != 0)
439                         goto unlock_err;
440                 tdb_unlock_free_bucket(tdb, b_off);
441
442                 if (to_used_record(tdb, zone_bits, best_off, size,
443                                    best.data_len, actual)) {
444                         return -1;
445                 }
446                 return best_off;
447         }
448
449         tdb_unlock_free_bucket(tdb, b_off);
450         return 0;
451
452 unlock_err:
453         tdb_unlock_free_bucket(tdb, b_off);
454         return TDB_OFF_ERR;
455 }
456
457 static bool next_zone(struct tdb_context *tdb)
458 {
459         tdb_off_t next = tdb->zone_off + (1ULL << tdb->zhdr.zone_bits);
460
461         /* We must have a header. */
462         if (tdb->methods->oob(tdb, next + sizeof(tdb->zhdr), true))
463                 return false;
464
465         tdb->zone_off = next;
466         return tdb_read_convert(tdb, next, &tdb->zhdr, sizeof(tdb->zhdr)) == 0;
467 }
468
469 /* Offset returned is within current zone (which it may alter). */
470 static tdb_off_t get_free(struct tdb_context *tdb, size_t size,
471                           tdb_len_t *actual)
472 {
473         tdb_off_t start_zone = tdb->zone_off, off;
474         bool wrapped = false;
475
476         /* FIXME: If we don't get a hit in the first bucket we want,
477          * try changing zones for next time.  That should help wear
478          * zones evenly, so we don't need to search all of them before
479          * expanding. */
480         while (!wrapped || tdb->zone_off != start_zone) {
481                 tdb_off_t b;
482
483                 /* Shortcut for really huge allocations... */
484                 if ((size >> tdb->zhdr.zone_bits) != 0)
485                         continue;
486
487                 /* Start at exact size bucket, and search up... */
488                 b = size_to_bucket(tdb->zhdr.zone_bits, size);
489                 for (b = find_free_head(tdb, b);
490                      b <= BUCKETS_FOR_ZONE(tdb->zhdr.zone_bits);
491                      b += find_free_head(tdb, b + 1)) {
492                         /* Try getting one from list. */
493                         off = lock_and_alloc(tdb, tdb->zone_off,
494                                              tdb->zhdr.zone_bits,
495                                              b, size, actual);
496                         if (off == TDB_OFF_ERR)
497                                 return TDB_OFF_ERR;
498                         if (off != 0)
499                                 return off;
500                         /* Didn't work.  Try next bucket. */
501                 }
502
503                 /* Didn't work, try next zone, if it exists. */
504                 if (!next_zone(tdb)) {
505                         wrapped = true;
506                         tdb->zone_off = sizeof(struct tdb_header);
507                         if (tdb_read_convert(tdb, tdb->zone_off,
508                                              &tdb->zhdr, sizeof(tdb->zhdr))) {
509                                 return TDB_OFF_ERR;
510                         }
511                 }
512         }
513         return 0;
514 }
515
516 int set_header(struct tdb_context *tdb,
517                struct tdb_used_record *rec,
518                uint64_t keylen, uint64_t datalen,
519                uint64_t actuallen, uint64_t hash,
520                unsigned int zone_bits)
521 {
522         uint64_t keybits = (fls64(keylen) + 1) / 2;
523
524         /* Use bottom bits of hash, so it's independent of hash table size. */
525         rec->magic_and_meta
526                 = zone_bits
527                 | ((hash & ((1 << 5)-1)) << 6)
528                 | ((actuallen - (keylen + datalen)) << 11)
529                 | (keybits << 43)
530                 | (TDB_MAGIC << 48);
531         rec->key_and_data_len = (keylen | (datalen << (keybits*2)));
532
533         /* Encoding can fail on big values. */
534         if (rec_key_length(rec) != keylen
535             || rec_data_length(rec) != datalen
536             || rec_extra_padding(rec) != actuallen - (keylen + datalen)) {
537                 tdb->ecode = TDB_ERR_IO;
538                 tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
539                          "Could not encode k=%llu,d=%llu,a=%llu\n",
540                          (long long)keylen, (long long)datalen,
541                          (long long)actuallen);
542                 return -1;
543         }
544         return 0;
545 }
546
547 static bool zones_happy(struct tdb_context *tdb)
548 {
549         /* FIXME: look at distribution of zones. */
550         return true;
551 }
552
553 /* Assume we want buckets up to the comfort factor. */
554 static tdb_len_t overhead(unsigned int zone_bits)
555 {
556         return sizeof(struct free_zone_header)
557                 + (BUCKETS_FOR_ZONE(zone_bits) + 1) * sizeof(tdb_off_t);
558 }
559
560 /* Expand the database (by adding a zone). */
561 static int tdb_expand(struct tdb_context *tdb, tdb_len_t size)
562 {
563         uint64_t old_size;
564         tdb_off_t off;
565         uint8_t zone_bits;
566         unsigned int num_buckets;
567         tdb_len_t wanted;
568         struct free_zone_header zhdr;
569         bool enlarge_zone;
570
571         /* We need room for the record header too. */
572         wanted = sizeof(struct tdb_used_record) + size;
573
574         /* Only one person can expand file at a time. */
575         if (tdb_lock_expand(tdb, F_WRLCK) != 0)
576                 return -1;
577
578         /* Someone else may have expanded the file, so retry. */
579         old_size = tdb->map_size;
580         tdb->methods->oob(tdb, tdb->map_size + 1, true);
581         if (tdb->map_size != old_size)
582                 goto success;
583
584         /* FIXME: Tailer is a bogus optimization, remove it. */
585         /* zone bits tailer char is protected by EXPAND lock. */
586         if (tdb->methods->read(tdb, old_size - 1, &zone_bits, 1) == -1)
587                 goto fail;
588
589         /* If zones aren't working well, add larger zone if possible. */
590         enlarge_zone = !zones_happy(tdb);
591
592         /* New zone can be between zone_bits or larger if we're on the right
593          * boundary. */
594         for (;;) {
595                 /* Does this fit the allocation comfortably? */
596                 if ((1ULL << zone_bits) >= overhead(zone_bits) + wanted) {
597                         /* Only let enlarge_zone enlarge us once. */
598                         if (!enlarge_zone)
599                                 break;
600                         enlarge_zone = false;
601                 }
602                 if ((old_size - 1 - sizeof(struct tdb_header))
603                     & (1 << zone_bits))
604                         break;
605                 zone_bits++;
606         }
607
608         zhdr.zone_bits = zone_bits;
609         num_buckets = BUCKETS_FOR_ZONE(zone_bits);
610
611         /* FIXME: I don't think we need to expand to full zone, do we? */
612         if (tdb->methods->expand_file(tdb, 1ULL << zone_bits) == -1)
613                 goto fail;
614
615         /* Write new tailer. */
616         if (tdb->methods->write(tdb, tdb->map_size - 1, &zone_bits, 1) == -1)
617                 goto fail;
618
619         /* Write new zone header (just before old tailer). */
620         off = old_size - 1;
621         if (tdb_write_convert(tdb, off, &zhdr, sizeof(zhdr)) == -1)
622                 goto fail;
623
624         /* Now write empty buckets. */
625         off += sizeof(zhdr);
626         if (zero_out(tdb, off, (num_buckets+1) * sizeof(tdb_off_t)) == -1)
627                 goto fail;
628         off += (num_buckets+1) * sizeof(tdb_off_t);
629
630         /* Now add the rest as our free record. */
631         if (add_free_record(tdb, zone_bits, off, tdb->map_size-1-off) == -1)
632                 goto fail;
633
634         /* Try allocating from this zone now. */
635         tdb->zone_off = old_size - 1;
636         tdb->zhdr = zhdr;
637
638 success:
639         tdb_unlock_expand(tdb, F_WRLCK);
640         return 0;
641
642 fail:
643         tdb_unlock_expand(tdb, F_WRLCK);
644         return -1;
645 }
646
647 /* This won't fail: it will expand the database if it has to. */
648 tdb_off_t alloc(struct tdb_context *tdb, size_t keylen, size_t datalen,
649                 uint64_t hash, bool growing)
650 {
651         tdb_off_t off;
652         tdb_len_t size, actual;
653         struct tdb_used_record rec;
654
655         /* We can't hold pointers during this: we could unmap! */
656         assert(!tdb->direct_access);
657
658         size = adjust_size(keylen, datalen, growing);
659
660 again:
661         off = get_free(tdb, size, &actual);
662         if (unlikely(off == TDB_OFF_ERR))
663                 return off;
664
665         if (unlikely(off == 0)) {
666                 if (tdb_expand(tdb, size) == -1)
667                         return TDB_OFF_ERR;
668                 goto again;
669         }
670
671         /* Some supergiant values can't be encoded. */
672         /* FIXME: Check before, and limit actual in get_free. */
673         if (set_header(tdb, &rec, keylen, datalen, actual, hash,
674                        tdb->zhdr.zone_bits) != 0) {
675                 add_free_record(tdb, tdb->zhdr.zone_bits, off,
676                                 sizeof(rec) + actual);
677                 return TDB_OFF_ERR;
678         }
679
680         if (tdb_write_convert(tdb, off, &rec, sizeof(rec)) != 0)
681                 return TDB_OFF_ERR;
682         
683         return off;
684 }