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