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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(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 >= TDB_FREE_BUCKETS))
  48                 bucket = TDB_FREE_BUCKETS - 1;
  49         return bucket;
  50 }
  51
  52 tdb_off_t first_ftable(struct tdb_context *tdb)
  53 {
  54         return tdb_read_off(tdb, offsetof(struct tdb_header, free_table));
  55 }
  56
  57 tdb_off_t next_ftable(struct tdb_context *tdb, tdb_off_t ftable)
  58 {
  59         return tdb_read_off(tdb, ftable + offsetof(struct tdb_freetable,next));
  60 }
  61
  62 int tdb_ftable_init(struct tdb_context *tdb)
  63 {
  64         /* Use reservoir sampling algorithm to select a free list at random. */
  65         unsigned int rnd, max = 0, count = 0;
  66         tdb_off_t off;
  67
  68         tdb->ftable_off = off = first_ftable(tdb);
  69         tdb->ftable = 0;
  70
  71         while (off) {
  72                 if (off == TDB_OFF_ERR)
  73                         return -1;
  74
  75                 rnd = random();
  76                 if (rnd >= max) {
  77                         tdb->ftable_off = off;
  78                         tdb->ftable = count;
  79                         max = rnd;
  80                 }
  81
  82                 off = next_ftable(tdb, off);
  83                 count++;
  84         }
  85         return 0;
  86 }
  87
  88 /* Offset of a given bucket. */
  89 tdb_off_t bucket_off(tdb_off_t ftable_off, unsigned bucket)
  90 {
  91         return ftable_off + offsetof(struct tdb_freetable, buckets)
  92                 + bucket * sizeof(tdb_off_t);
  93 }
  94
  95 /* Returns free_buckets + 1, or list number to search. */
  96 static tdb_off_t find_free_head(struct tdb_context *tdb,
  97                                 tdb_off_t ftable_off,
  98                                 tdb_off_t bucket)
  99 {
 100         /* Speculatively search for a non-zero bucket. */
 101         return tdb_find_nonzero_off(tdb, bucket_off(ftable_off, 0),
 102                                     bucket, TDB_FREE_BUCKETS);
 103 }
 104
 105 /* Remove from free bucket. */
 106 static int remove_from_list(struct tdb_context *tdb,
 107                             tdb_off_t b_off, tdb_off_t r_off,
 108                             const struct tdb_free_record *r)
 109 {
 110         tdb_off_t off;
 111
 112         /* Front of list? */
 113         if (frec_prev(r) == 0) {
 114                 off = b_off;
 115         } else {
 116                 off = frec_prev(r) + offsetof(struct tdb_free_record, next);
 117         }
 118
 119 #ifdef CCAN_TDB2_DEBUG
 120         if (tdb_read_off(tdb, off) != r_off) {
 121                 tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_DEBUG_FATAL,
 122                          "remove_from_list: %llu bad prev in list %llu",
 123                          (long long)r_off, (long long)b_off);
 124                 return -1;
 125         }
 126 #endif
 127
 128         /* r->prev->next = r->next */
 129         if (tdb_write_off(tdb, off, r->next)) {
 130                 return -1;
 131         }
 132
 133         if (r->next != 0) {
 134                 off = r->next + offsetof(struct tdb_free_record,magic_and_prev);
 135                 /* r->next->prev = r->prev */
 136
 137 #ifdef CCAN_TDB2_DEBUG
 138                 if (tdb_read_off(tdb, off) & TDB_OFF_MASK != r_off) {
 139                         tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_DEBUG_FATAL,
 140                                    "remove_from_list: %llu bad list %llu",
 141                                    (long long)r_off, (long long)b_off);
 142                         return -1;
 143                 }
 144 #endif
 145
 146                 if (tdb_write_off(tdb, off, r->magic_and_prev)) {
 147                         return -1;
 148                 }
 149         }
 150         return 0;
 151 }
 152
 153 /* Enqueue in this free bucket. */
 154 static int enqueue_in_free(struct tdb_context *tdb,
 155                            tdb_off_t b_off,
 156                            tdb_off_t off,
 157                            tdb_len_t len)
 158 {
 159         struct tdb_free_record new;
 160         uint64_t magic = (TDB_FREE_MAGIC << (64 - TDB_OFF_UPPER_STEAL));
 161
 162         /* We only need to set ftable_and_len; rest is set in enqueue_in_free */
 163         new.ftable_and_len = ((uint64_t)tdb->ftable << (64 - TDB_OFF_UPPER_STEAL))
 164                 | len;
 165         /* prev = 0. */
 166         new.magic_and_prev = magic;
 167
 168         /* new->next = head. */
 169         new.next = tdb_read_off(tdb, b_off);
 170         if (new.next == TDB_OFF_ERR)
 171                 return -1;
 172
 173         if (new.next) {
 174 #ifdef CCAN_TDB2_DEBUG
 175                 if (tdb_read_off(tdb,
 176                                  new.next + offsetof(struct tdb_free_record,
 177                                                      magic_and_prev))
 178                     != magic) {
 179                         tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_DEBUG_FATAL,
 180                                    "enqueue_in_free: %llu bad head"
 181                                    " prev %llu",
 182                                    (long long)new.next, (long long)b_off);
 183                         return -1;
 184                 }
 185 #endif
 186                 /* next->prev = new. */
 187                 if (tdb_write_off(tdb, new.next
 188                                   + offsetof(struct tdb_free_record,
 189                                              magic_and_prev),
 190                                   off | magic) != 0)
 191                         return -1;
 192         }
 193         /* head = new */
 194         if (tdb_write_off(tdb, b_off, off) != 0)
 195                 return -1;
 196
 197         return tdb_write_convert(tdb, off, &new, sizeof(new));
 198 }
 199
 200 /* List need not be locked. */
 201 int add_free_record(struct tdb_context *tdb,
 202                     tdb_off_t off, tdb_len_t len_with_header)
 203 {
 204         tdb_off_t b_off;
 205         tdb_len_t len;
 206         int ret;
 207
 208         assert(len_with_header >= sizeof(struct tdb_free_record));
 209
 210         len = len_with_header - sizeof(struct tdb_used_record);
 211
 212         b_off = bucket_off(tdb->ftable_off, size_to_bucket(len));
 213         if (tdb_lock_free_bucket(tdb, b_off, TDB_LOCK_WAIT) != 0)
 214                 return -1;
 215
 216         ret = enqueue_in_free(tdb, b_off, off, len);
 217         tdb_unlock_free_bucket(tdb, b_off);
 218         return ret;
 219 }
 220
 221 static size_t adjust_size(size_t keylen, size_t datalen)
 222 {
 223         size_t size = keylen + datalen;
 224
 225         if (size < TDB_MIN_DATA_LEN)
 226                 size = TDB_MIN_DATA_LEN;
 227
 228         /* Round to next uint64_t boundary. */
 229         return (size + (sizeof(uint64_t) - 1ULL)) & ~(sizeof(uint64_t) - 1ULL);
 230 }
 231
 232 /* If we have enough left over to be useful, split that off. */
 233 static size_t record_leftover(size_t keylen, size_t datalen,
 234                               bool want_extra, size_t total_len)
 235 {
 236         ssize_t leftover;
 237
 238         if (want_extra)
 239                 datalen += datalen / 2;
 240         leftover = total_len - adjust_size(keylen, datalen);
 241
 242         if (leftover < (ssize_t)sizeof(struct tdb_free_record))
 243                 return 0;
 244
 245         return leftover;
 246 }
 247
 248 static tdb_off_t ftable_offset(struct tdb_context *tdb, unsigned int ftable)
 249 {
 250         tdb_off_t off;
 251         unsigned int i;
 252
 253         if (likely(tdb->ftable == ftable))
 254                 return tdb->ftable_off;
 255
 256         off = first_ftable(tdb);
 257         for (i = 0; i < ftable; i++)
 258                 off = next_ftable(tdb, off);
 259         return off;
 260 }
 261
 262 /* Note: we unlock the current bucket if we coalesce or fail. */
 263 static int coalesce(struct tdb_context *tdb,
 264                     tdb_off_t off, tdb_off_t b_off, tdb_len_t data_len)
 265 {
 266         tdb_off_t end;
 267         struct tdb_free_record rec;
 268
 269         add_stat(tdb, alloc_coalesce_tried, 1);
 270         end = off + sizeof(struct tdb_used_record) + data_len;
 271
 272         while (end < tdb->map_size) {
 273                 const struct tdb_free_record *r;
 274                 tdb_off_t nb_off;
 275                 unsigned ftable, bucket;
 276
 277                 r = tdb_access_read(tdb, end, sizeof(*r), true);
 278                 if (!r)
 279                         goto err;
 280
 281                 if (frec_magic(r) != TDB_FREE_MAGIC
 282                     || frec_ftable(r) == TDB_FTABLE_NONE) {
 283                         tdb_access_release(tdb, r);
 284                         break;
 285                 }
 286
 287                 ftable = frec_ftable(r);
 288                 bucket = size_to_bucket(frec_len(r));
 289                 nb_off = bucket_off(ftable_offset(tdb, ftable), bucket);
 290                 tdb_access_release(tdb, r);
 291
 292                 /* We may be violating lock order here, so best effort. */
 293                 if (tdb_lock_free_bucket(tdb, nb_off, TDB_LOCK_NOWAIT) == -1) {
 294                         add_stat(tdb, alloc_coalesce_lockfail, 1);
 295                         break;
 296                 }
 297
 298                 /* Now we have lock, re-check. */
 299                 if (tdb_read_convert(tdb, end, &rec, sizeof(rec))) {
 300                         tdb_unlock_free_bucket(tdb, nb_off);
 301                         goto err;
 302                 }
 303
 304                 if (unlikely(frec_magic(&rec) != TDB_FREE_MAGIC)) {
 305                         add_stat(tdb, alloc_coalesce_race, 1);
 306                         tdb_unlock_free_bucket(tdb, nb_off);
 307                         break;
 308                 }
 309
 310                 if (unlikely(frec_ftable(&rec) != ftable)
 311                     || unlikely(size_to_bucket(frec_len(&rec)) != bucket)) {
 312                         add_stat(tdb, alloc_coalesce_race, 1);
 313                         tdb_unlock_free_bucket(tdb, nb_off);
 314                         break;
 315                 }
 316
 317                 if (remove_from_list(tdb, nb_off, end, &rec) == -1) {
 318                         tdb_unlock_free_bucket(tdb, nb_off);
 319                         goto err;
 320                 }
 321
 322                 end += sizeof(struct tdb_used_record) + frec_len(&rec);
 323                 tdb_unlock_free_bucket(tdb, nb_off);
 324                 add_stat(tdb, alloc_coalesce_num_merged, 1);
 325         }
 326
 327         /* Didn't find any adjacent free? */
 328         if (end == off + sizeof(struct tdb_used_record) + data_len)
 329                 return 0;
 330
 331         /* OK, expand initial record */
 332         if (tdb_read_convert(tdb, off, &rec, sizeof(rec)))
 333                 goto err;
 334
 335         if (frec_len(&rec) != data_len) {
 336                 tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_DEBUG_FATAL,
 337                            "coalesce: expected data len %zu not %zu",
 338                            (size_t)data_len, (size_t)frec_len(&rec));
 339                 goto err;
 340         }
 341
 342         if (remove_from_list(tdb, b_off, off, &rec) == -1)
 343                 goto err;
 344
 345         /* We have to drop this to avoid deadlocks, so make sure record
 346          * doesn't get coalesced by someone else! */
 347         rec.ftable_and_len = (TDB_FTABLE_NONE << (64 - TDB_OFF_UPPER_STEAL))
 348                 | (end - off - sizeof(struct tdb_used_record));
 349         if (tdb_write_off(tdb, off + offsetof(struct tdb_free_record,
 350                                               ftable_and_len),
 351                           rec.ftable_and_len) != 0)
 352                 goto err;
 353
 354         add_stat(tdb, alloc_coalesce_succeeded, 1);
 355         tdb_unlock_free_bucket(tdb, b_off);
 356
 357         if (add_free_record(tdb, off, end - off) == -1)
 358                 return -1;
 359         return 1;
 360
 361 err:
 362         /* To unify error paths, we *always* unlock bucket on error. */
 363         tdb_unlock_free_bucket(tdb, b_off);
 364         return -1;
 365 }
 366
 367 /* We need size bytes to put our key and data in. */
 368 static tdb_off_t lock_and_alloc(struct tdb_context *tdb,
 369                                 tdb_off_t ftable_off,
 370                                 tdb_off_t bucket,
 371                                 size_t keylen, size_t datalen,
 372                                 bool want_extra,
 373                                 unsigned magic,
 374                                 unsigned hashlow)
 375 {
 376         tdb_off_t off, b_off,best_off;
 377         struct tdb_free_record best = { 0 };
 378         double multiplier;
 379         size_t size = adjust_size(keylen, datalen);
 380
 381         add_stat(tdb, allocs, 1);
 382 again:
 383         b_off = bucket_off(ftable_off, bucket);
 384
 385         /* FIXME: Try non-blocking wait first, to measure contention. */
 386         /* Lock this bucket. */
 387         if (tdb_lock_free_bucket(tdb, b_off, TDB_LOCK_WAIT) == -1) {
 388                 return TDB_OFF_ERR;
 389         }
 390
 391         best.ftable_and_len = -1ULL;
 392         best_off = 0;
 393
 394         /* Get slack if we're after extra. */
 395         if (want_extra)
 396                 multiplier = 1.5;
 397         else
 398                 multiplier = 1.0;
 399
 400         /* Walk the list to see if any are large enough, getting less fussy
 401          * as we go. */
 402         off = tdb_read_off(tdb, b_off);
 403         if (unlikely(off == TDB_OFF_ERR))
 404                 goto unlock_err;
 405
 406         while (off) {
 407                 const struct tdb_free_record *r;
 408                 tdb_len_t len;
 409                 tdb_off_t next;
 410
 411                 r = tdb_access_read(tdb, off, sizeof(*r), true);
 412                 if (!r)
 413                         goto unlock_err;
 414
 415                 if (frec_magic(r) != TDB_FREE_MAGIC) {
 416                         tdb_access_release(tdb, r);
 417                         tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_DEBUG_FATAL,
 418                                  "lock_and_alloc: %llu non-free 0x%llx",
 419                                  (long long)off, (long long)r->magic_and_prev);
 420                         goto unlock_err;
 421                 }
 422
 423                 if (frec_len(r) >= size && frec_len(r) < frec_len(&best)) {
 424                         best_off = off;
 425                         best = *r;
 426                 }
 427
 428                 if (frec_len(&best) < size * multiplier && best_off) {
 429                         tdb_access_release(tdb, r);
 430                         break;
 431                 }
 432
 433                 multiplier *= 1.01;
 434
 435                 next = r->next;
 436                 len = frec_len(r);
 437                 tdb_access_release(tdb, r);
 438
 439                 /* Since we're going slow anyway, try coalescing here. */
 440                 switch (coalesce(tdb, off, b_off, len)) {
 441                 case -1:
 442                         /* This has already unlocked on error. */
 443                         return -1;
 444                 case 1:
 445                         /* This has unlocked list, restart. */
 446                         goto again;
 447                 }
 448                 off = next;
 449         }
 450
 451         /* If we found anything at all, use it. */
 452         if (best_off) {
 453                 struct tdb_used_record rec;
 454                 size_t leftover;
 455
 456                 /* We're happy with this size: take it. */
 457                 if (remove_from_list(tdb, b_off, best_off, &best) != 0)
 458                         goto unlock_err;
 459
 460                 leftover = record_leftover(keylen, datalen, want_extra,
 461                                            frec_len(&best));
 462
 463                 assert(keylen + datalen + leftover <= frec_len(&best));
 464                 /* We need to mark non-free before we drop lock, otherwise
 465                  * coalesce() could try to merge it! */
 466                 if (set_header(tdb, &rec, magic, keylen, datalen,
 467                                frec_len(&best) - leftover, hashlow) != 0)
 468                         goto unlock_err;
 469
 470                 if (tdb_write_convert(tdb, best_off, &rec, sizeof(rec)) != 0)
 471                         goto unlock_err;
 472
 473                 /* Bucket of leftover will be <= current bucket, so nested
 474                  * locking is allowed. */
 475                 if (leftover) {
 476                         add_stat(tdb, alloc_leftover, 1);
 477                         if (add_free_record(tdb,
 478                                             best_off + sizeof(rec)
 479                                             + frec_len(&best) - leftover,
 480                                             leftover))
 481                                 best_off = TDB_OFF_ERR;
 482                 }
 483                 tdb_unlock_free_bucket(tdb, b_off);
 484
 485                 return best_off;
 486         }
 487
 488         tdb_unlock_free_bucket(tdb, b_off);
 489         return 0;
 490
 491 unlock_err:
 492         tdb_unlock_free_bucket(tdb, b_off);
 493         return TDB_OFF_ERR;
 494 }
 495
 496 /* Get a free block from current free list, or 0 if none. */
 497 static tdb_off_t get_free(struct tdb_context *tdb,
 498                           size_t keylen, size_t datalen, bool want_extra,
 499                           unsigned magic, unsigned hashlow)
 500 {
 501         tdb_off_t off, ftable_off;
 502         unsigned start_b, b, ftable;
 503         bool wrapped = false;
 504
 505         /* If they are growing, add 50% to get to higher bucket. */
 506         if (want_extra)
 507                 start_b = size_to_bucket(adjust_size(keylen,
 508                                                      datalen + datalen / 2));
 509         else
 510                 start_b = size_to_bucket(adjust_size(keylen, datalen));
 511
 512         ftable_off = tdb->ftable_off;
 513         ftable = tdb->ftable;
 514         while (!wrapped || ftable_off != tdb->ftable_off) {
 515                 /* Start at exact size bucket, and search up... */
 516                 for (b = find_free_head(tdb, ftable_off, start_b);
 517                      b < TDB_FREE_BUCKETS;
 518                      b = find_free_head(tdb, ftable_off, b + 1)) {
 519                         /* Try getting one from list. */
 520                         off = lock_and_alloc(tdb, ftable_off,
 521                                              b, keylen, datalen, want_extra,
 522                                              magic, hashlow);
 523                         if (off == TDB_OFF_ERR)
 524                                 return TDB_OFF_ERR;
 525                         if (off != 0) {
 526                                 if (b == start_b)
 527                                         add_stat(tdb, alloc_bucket_exact, 1);
 528                                 if (b == TDB_FREE_BUCKETS - 1)
 529                                         add_stat(tdb, alloc_bucket_max, 1);
 530                                 /* Worked?  Stay using this list. */
 531                                 tdb->ftable_off = ftable_off;
 532                                 tdb->ftable = ftable;
 533                                 return off;
 534                         }
 535                         /* Didn't work.  Try next bucket. */
 536                 }
 537
 538                 /* Hmm, try next table. */
 539                 ftable_off = next_ftable(tdb, ftable_off);
 540                 ftable++;
 541
 542                 if (ftable_off == 0) {
 543                         wrapped = true;
 544                         ftable_off = first_ftable(tdb);
 545                         ftable = 0;
 546                 }
 547         }
 548
 549         return 0;
 550 }
 551
 552 int set_header(struct tdb_context *tdb,
 553                struct tdb_used_record *rec,
 554                unsigned magic, uint64_t keylen, uint64_t datalen,
 555                uint64_t actuallen, unsigned hashlow)
 556 {
 557         uint64_t keybits = (fls64(keylen) + 1) / 2;
 558
 559         /* Use bottom bits of hash, so it's independent of hash table size. */
 560         rec->magic_and_meta = (hashlow & ((1 << 11)-1))
 561                 | ((actuallen - (keylen + datalen)) << 11)
 562                 | (keybits << 43)
 563                 | ((uint64_t)magic << 48);
 564         rec->key_and_data_len = (keylen | (datalen << (keybits*2)));
 565
 566         /* Encoding can fail on big values. */
 567         if (rec_key_length(rec) != keylen
 568             || rec_data_length(rec) != datalen
 569             || rec_extra_padding(rec) != actuallen - (keylen + datalen)) {
 570                 tdb_logerr(tdb, TDB_ERR_IO, TDB_DEBUG_ERROR,
 571                          "Could not encode k=%llu,d=%llu,a=%llu",
 572                          (long long)keylen, (long long)datalen,
 573                          (long long)actuallen);
 574                 return -1;
 575         }
 576         return 0;
 577 }
 578
 579 /* Expand the database. */
 580 static int tdb_expand(struct tdb_context *tdb, tdb_len_t size)
 581 {
 582         uint64_t old_size;
 583         tdb_len_t wanted;
 584
 585         /* We need room for the record header too. */
 586         wanted = sizeof(struct tdb_used_record) + size;
 587
 588         /* Need to hold a hash lock to expand DB: transactions rely on it. */
 589         if (!(tdb->flags & TDB_NOLOCK)
 590             && !tdb->allrecord_lock.count && !tdb_has_hash_locks(tdb)) {
 591                 tdb_logerr(tdb, TDB_ERR_LOCK, TDB_DEBUG_ERROR,
 592                            "tdb_expand: must hold lock during expand");
 593                 return -1;
 594         }
 595
 596         /* always make room for at least 100 more records, and at
 597            least 25% more space. */
 598         if (size * TDB_EXTENSION_FACTOR > tdb->map_size / 4)
 599                 wanted = size * TDB_EXTENSION_FACTOR;
 600         else
 601                 wanted = tdb->map_size / 4;
 602         wanted = adjust_size(0, wanted);
 603
 604         /* Only one person can expand file at a time. */
 605         if (tdb_lock_expand(tdb, F_WRLCK) != 0)
 606                 return -1;
 607
 608         /* Someone else may have expanded the file, so retry. */
 609         old_size = tdb->map_size;
 610         tdb->methods->oob(tdb, tdb->map_size + 1, true);
 611         if (tdb->map_size != old_size) {
 612                 tdb_unlock_expand(tdb, F_WRLCK);
 613                 return 0;
 614         }
 615
 616         if (tdb->methods->expand_file(tdb, wanted) == -1) {
 617                 tdb_unlock_expand(tdb, F_WRLCK);
 618                 return -1;
 619         }
 620
 621         /* We need to drop this lock before adding free record. */
 622         tdb_unlock_expand(tdb, F_WRLCK);
 623
 624         add_stat(tdb, expands, 1);
 625         return add_free_record(tdb, old_size, wanted);
 626 }
 627
 628 /* This won't fail: it will expand the database if it has to. */
 629 tdb_off_t alloc(struct tdb_context *tdb, size_t keylen, size_t datalen,
 630                 uint64_t hash, unsigned magic, bool growing)
 631 {
 632         tdb_off_t off;
 633
 634         /* We can't hold pointers during this: we could unmap! */
 635         assert(!tdb->direct_access);
 636
 637         for (;;) {
 638                 off = get_free(tdb, keylen, datalen, growing, magic, hash);
 639                 if (likely(off != 0))
 640                         break;
 641
 642                 if (tdb_expand(tdb, adjust_size(keylen, datalen)))
 643                         return TDB_OFF_ERR;
 644         }
 645
 646         return off;
 647 }