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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 <time.h>
  21 #include <assert.h>
  22 #include <limits.h>
  23
  24 /* We have to be able to fit a free record here. */
  25 #define MIN_DATA_LEN    \
  26         (sizeof(struct tdb_free_record) - sizeof(struct tdb_used_record))
  27
  28 static unsigned fls64(uint64_t val)
  29 {
  30 #if HAVE_BUILTIN_CLZL
  31         if (val <= ULONG_MAX) {
  32                 /* This is significantly faster! */
  33                 return val ? sizeof(long) * CHAR_BIT - __builtin_clzl(val) : 0;
  34         } else {
  35 #endif
  36         uint64_t r = 64;
  37
  38         if (!val)
  39                 return 0;
  40         if (!(val & 0xffffffff00000000ull)) {
  41                 val <<= 32;
  42                 r -= 32;
  43         }
  44         if (!(val & 0xffff000000000000ull)) {
  45                 val <<= 16;
  46                 r -= 16;
  47         }
  48         if (!(val & 0xff00000000000000ull)) {
  49                 val <<= 8;
  50                 r -= 8;
  51         }
  52         if (!(val & 0xf000000000000000ull)) {
  53                 val <<= 4;
  54                 r -= 4;
  55         }
  56         if (!(val & 0xc000000000000000ull)) {
  57                 val <<= 2;
  58                 r -= 2;
  59         }
  60         if (!(val & 0x8000000000000000ull)) {
  61                 val <<= 1;
  62                 r -= 1;
  63         }
  64         return r;
  65 #if HAVE_BUILTIN_CLZL
  66         }
  67 #endif
  68 }
  69
  70 /* In which bucket would we find a particular record size? (ignoring header) */
  71 unsigned int size_to_bucket(unsigned int zone_bits, tdb_len_t data_len)
  72 {
  73         unsigned int bucket;
  74
  75         /* We can't have records smaller than this. */
  76         assert(data_len >= MIN_DATA_LEN);
  77
  78         /* Ignoring the header... */
  79         if (data_len - MIN_DATA_LEN <= 64) {
  80                 /* 0 in bucket 0, 8 in bucket 1... 64 in bucket 6. */
  81                 bucket = (data_len - MIN_DATA_LEN) / 8;
  82         } else {
  83                 /* After that we go power of 2. */
  84                 bucket = fls64(data_len - MIN_DATA_LEN) + 2;
  85         }
  86
  87         if (unlikely(bucket > BUCKETS_FOR_ZONE(zone_bits)))
  88                 bucket = BUCKETS_FOR_ZONE(zone_bits);
  89         return bucket;
  90 }
  91
  92 /* Subtract 1-byte tailer and header.  Then round up to next power of 2. */
  93 static unsigned max_zone_bits(struct tdb_context *tdb)
  94 {
  95         return fls64(tdb->map_size-1-sizeof(struct tdb_header)-1) + 1;
  96 }
  97
  98 /* Start by using a random zone to spread the load: returns the offset. */
  99 static uint64_t random_zone(struct tdb_context *tdb)
 100 {
 101         struct free_zone_header zhdr;
 102         tdb_off_t off = sizeof(struct tdb_header);
 103         tdb_len_t half_bits;
 104         uint64_t randbits = 0;
 105         unsigned int i;
 106
 107         for (i = 0; i < 64; i += fls64(RAND_MAX))
 108                 randbits ^= ((uint64_t)random()) << i;
 109
 110         /* FIXME: Does this work?  Test! */
 111         half_bits = max_zone_bits(tdb) - 1;
 112         do {
 113                 /* Pick left or right side (not outside file) */
 114                 if ((randbits & 1)
 115                     && !tdb->methods->oob(tdb, off + (1ULL << half_bits)
 116                                           + sizeof(zhdr), true)) {
 117                         off += 1ULL << half_bits;
 118                 }
 119                 randbits >>= 1;
 120
 121                 if (tdb_read_convert(tdb, off, &zhdr, sizeof(zhdr)) == -1)
 122                         return TDB_OFF_ERR;
 123
 124                 if (zhdr.zone_bits == half_bits)
 125                         return off;
 126
 127                 half_bits--;
 128         } while (half_bits >= INITIAL_ZONE_BITS);
 129
 130         tdb->ecode = TDB_ERR_CORRUPT;
 131         tdb->log(tdb, TDB_DEBUG_FATAL, tdb->log_priv,
 132                  "random_zone: zone at %llu smaller than %u bits?",
 133                  (long long)off, INITIAL_ZONE_BITS);
 134         return TDB_OFF_ERR;
 135 }
 136
 137 int tdb_zone_init(struct tdb_context *tdb)
 138 {
 139         tdb->zone_off = random_zone(tdb);
 140         if (tdb->zone_off == TDB_OFF_ERR)
 141                 return -1;
 142         if (tdb_read_convert(tdb, tdb->zone_off,
 143                              &tdb->zhdr, sizeof(tdb->zhdr)) == -1)
 144                 return -1;
 145         return 0;
 146 }
 147
 148 /* Where's the header, given a zone size of 1 << zone_bits? */
 149 static tdb_off_t zone_off(tdb_off_t off, unsigned int zone_bits)
 150 {
 151         off -= sizeof(struct tdb_header);
 152         return (off & ~((1ULL << zone_bits) - 1)) + sizeof(struct tdb_header);
 153 }
 154
 155 /* Offset of a given bucket. */
 156 /* FIXME: bucket can be "unsigned" everywhere, or even uint8/16. */
 157 tdb_off_t bucket_off(tdb_off_t zone_off, tdb_off_t bucket)
 158 {
 159         return zone_off
 160                 + sizeof(struct free_zone_header)
 161                 + bucket * sizeof(tdb_off_t);
 162 }
 163
 164 /* Returns free_buckets + 1, or list number to search. */
 165 static tdb_off_t find_free_head(struct tdb_context *tdb, tdb_off_t bucket)
 166 {
 167         /* Speculatively search for a non-zero bucket. */
 168         return tdb_find_nonzero_off(tdb, bucket_off(tdb->zone_off, 0),
 169                                     bucket,
 170                                     BUCKETS_FOR_ZONE(tdb->zhdr.zone_bits) + 1);
 171 }
 172
 173 /* Remove from free bucket. */
 174 static int remove_from_list(struct tdb_context *tdb,
 175                             tdb_off_t b_off, struct tdb_free_record *r)
 176 {
 177         tdb_off_t off;
 178
 179         /* Front of list? */
 180         if (r->prev == 0) {
 181                 off = b_off;
 182         } else {
 183                 off = r->prev + offsetof(struct tdb_free_record, next);
 184         }
 185         /* r->prev->next = r->next */
 186         if (tdb_write_off(tdb, off, r->next)) {
 187                 return -1;
 188         }
 189
 190         if (r->next != 0) {
 191                 off = r->next + offsetof(struct tdb_free_record, prev);
 192                 /* r->next->prev = r->prev */
 193                 if (tdb_write_off(tdb, off, r->prev)) {
 194                         return -1;
 195                 }
 196         }
 197         return 0;
 198 }
 199
 200 /* Enqueue in this free bucket. */
 201 static int enqueue_in_free(struct tdb_context *tdb,
 202                            tdb_off_t b_off,
 203                            tdb_off_t off,
 204                            struct tdb_free_record *new)
 205 {
 206         new->prev = 0;
 207         /* new->next = head. */
 208         new->next = tdb_read_off(tdb, b_off);
 209         if (new->next == TDB_OFF_ERR)
 210                 return -1;
 211
 212         if (new->next) {
 213                 /* next->prev = new. */
 214                 if (tdb_write_off(tdb, new->next
 215                                   + offsetof(struct tdb_free_record, prev),
 216                                   off) != 0)
 217                         return -1;
 218         }
 219         /* head = new */
 220         if (tdb_write_off(tdb, b_off, off) != 0)
 221                 return -1;
 222
 223         return tdb_write_convert(tdb, off, new, sizeof(*new));
 224 }
 225
 226 /* List need not be locked. */
 227 int add_free_record(struct tdb_context *tdb,
 228                     unsigned int zone_bits,
 229                     tdb_off_t off, tdb_len_t len_with_header)
 230 {
 231         struct tdb_free_record new;
 232         tdb_off_t b_off;
 233         int ret;
 234
 235         assert(len_with_header >= sizeof(new));
 236         assert(zone_bits < (1 << 6));
 237
 238         new.magic_and_meta = TDB_FREE_MAGIC | zone_bits;
 239         new.data_len = len_with_header - sizeof(struct tdb_used_record);
 240
 241         b_off = bucket_off(zone_off(off, zone_bits),
 242                            size_to_bucket(zone_bits, new.data_len));
 243         if (tdb_lock_free_bucket(tdb, b_off, TDB_LOCK_WAIT) != 0)
 244                 return -1;
 245
 246         ret = enqueue_in_free(tdb, b_off, off, &new);
 247         tdb_unlock_free_bucket(tdb, b_off);
 248         return ret;
 249 }
 250
 251 /* If we have enough left over to be useful, split that off. */
 252 static int to_used_record(struct tdb_context *tdb,
 253                           unsigned int zone_bits,
 254                           tdb_off_t off,
 255                           tdb_len_t needed,
 256                           tdb_len_t total_len,
 257                           tdb_len_t *actual)
 258 {
 259         struct tdb_used_record used;
 260         tdb_len_t leftover;
 261
 262         leftover = total_len - needed;
 263         if (leftover < sizeof(struct tdb_free_record))
 264                 leftover = 0;
 265
 266         *actual = total_len - leftover;
 267
 268         if (leftover) {
 269                 if (add_free_record(tdb, zone_bits,
 270                                     off + sizeof(used) + *actual,
 271                                     total_len - needed))
 272                         return -1;
 273         }
 274         return 0;
 275 }
 276
 277 /* Note: we unlock the current bucket if we coalesce or fail. */
 278 static int coalesce(struct tdb_context *tdb,
 279                     tdb_off_t zone_off, unsigned zone_bits,
 280                     tdb_off_t off, tdb_off_t b_off, tdb_len_t data_len)
 281 {
 282         struct tdb_free_record pad, *r;
 283         tdb_off_t end = off + sizeof(struct tdb_used_record) + data_len;
 284
 285         while (end < (zone_off + (1ULL << zone_bits))) {
 286                 tdb_off_t nb_off;
 287
 288                 /* FIXME: do tdb_get here and below really win? */
 289                 r = tdb_get(tdb, end, &pad, sizeof(pad));
 290                 if (!r)
 291                         goto err;
 292
 293                 if (frec_magic(r) != TDB_FREE_MAGIC)
 294                         break;
 295
 296                 nb_off = bucket_off(zone_off,
 297                                     size_to_bucket(zone_bits, r->data_len));
 298
 299                 /* We may be violating lock order here, so best effort. */
 300                 if (tdb_lock_free_bucket(tdb, nb_off, TDB_LOCK_NOWAIT) == -1)
 301                         break;
 302
 303                 /* Now we have lock, re-check. */
 304                 r = tdb_get(tdb, end, &pad, sizeof(pad));
 305                 if (!r) {
 306                         tdb_unlock_free_bucket(tdb, nb_off);
 307                         goto err;
 308                 }
 309
 310                 if (unlikely(frec_magic(r) != TDB_FREE_MAGIC)) {
 311                         tdb_unlock_free_bucket(tdb, nb_off);
 312                         break;
 313                 }
 314
 315                 if (remove_from_list(tdb, nb_off, r) == -1) {
 316                         tdb_unlock_free_bucket(tdb, nb_off);
 317                         goto err;
 318                 }
 319
 320                 end += sizeof(struct tdb_used_record) + r->data_len;
 321                 tdb_unlock_free_bucket(tdb, nb_off);
 322         }
 323
 324         /* Didn't find any adjacent free? */
 325         if (end == off + sizeof(struct tdb_used_record) + data_len)
 326                 return 0;
 327
 328         /* OK, expand record */
 329         r = tdb_get(tdb, off, &pad, sizeof(pad));
 330         if (!r)
 331                 goto err;
 332
 333         if (r->data_len != data_len) {
 334                 tdb->ecode = TDB_ERR_CORRUPT;
 335                 tdb->log(tdb, TDB_DEBUG_FATAL, tdb->log_priv,
 336                          "coalesce: expected data len %llu not %llu\n",
 337                          (long long)data_len, (long long)r->data_len);
 338                 goto err;
 339         }
 340
 341         if (remove_from_list(tdb, b_off, r) == -1)
 342                 goto err;
 343
 344         /* We have to drop this to avoid deadlocks. */
 345         tdb_unlock_free_bucket(tdb, b_off);
 346
 347         if (add_free_record(tdb, zone_bits, off, end - off) == -1)
 348                 return -1;
 349         return 1;
 350
 351 err:
 352         /* To unify error paths, we *always* unlock bucket on error. */
 353         tdb_unlock_free_bucket(tdb, b_off);
 354         return -1;
 355 }
 356
 357 /* We need size bytes to put our key and data in. */
 358 static tdb_off_t lock_and_alloc(struct tdb_context *tdb,
 359                                 tdb_off_t zone_off,
 360                                 unsigned zone_bits,
 361                                 tdb_off_t bucket,
 362                                 size_t size,
 363                                 tdb_len_t *actual)
 364 {
 365         tdb_off_t off, b_off,best_off;
 366         struct tdb_free_record pad, best = { 0 }, *r;
 367         double multiplier;
 368
 369 again:
 370         b_off = bucket_off(zone_off, bucket);
 371
 372         /* Lock this bucket. */
 373         if (tdb_lock_free_bucket(tdb, b_off, TDB_LOCK_WAIT) == -1) {
 374                 return TDB_OFF_ERR;
 375         }
 376
 377         best.data_len = -1ULL;
 378         best_off = 0;
 379         /* FIXME: Start with larger multiplier if we're growing. */
 380         multiplier = 1.0;
 381
 382         /* Walk the list to see if any are large enough, getting less fussy
 383          * as we go. */
 384         off = tdb_read_off(tdb, b_off);
 385         if (unlikely(off == TDB_OFF_ERR))
 386                 goto unlock_err;
 387
 388         while (off) {
 389                 /* FIXME: Does tdb_get win anything here? */
 390                 r = tdb_get(tdb, off, &pad, sizeof(*r));
 391                 if (!r)
 392                         goto unlock_err;
 393
 394                 if (frec_magic(r) != TDB_FREE_MAGIC) {
 395                         tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
 396                                  "lock_and_alloc: %llu non-free 0x%llx\n",
 397                                  (long long)off, (long long)r->magic_and_meta);
 398                         goto unlock_err;
 399                 }
 400
 401                 if (r->data_len >= size && r->data_len < best.data_len) {
 402                         best_off = off;
 403                         best = *r;
 404                 }
 405
 406                 if (best.data_len < size * multiplier && best_off)
 407                         goto use_best;
 408
 409                 multiplier *= 1.01;
 410
 411                 /* Since we're going slow anyway, try coalescing here. */
 412                 switch (coalesce(tdb, zone_off, zone_bits, off, b_off,
 413                                  r->data_len)) {
 414                 case -1:
 415                         /* This has already unlocked on error. */
 416                         return -1;
 417                 case 1:
 418                         /* This has unlocked list, restart. */
 419                         goto again;
 420                 }
 421                 off = r->next;
 422         }
 423
 424         /* If we found anything at all, use it. */
 425         if (best_off) {
 426         use_best:
 427                 /* We're happy with this size: take it. */
 428                 if (remove_from_list(tdb, b_off, &best) != 0)
 429                         goto unlock_err;
 430                 tdb_unlock_free_bucket(tdb, b_off);
 431
 432                 if (to_used_record(tdb, zone_bits, best_off, size,
 433                                    best.data_len, actual)) {
 434                         return -1;
 435                 }
 436                 return best_off;
 437         }
 438
 439         tdb_unlock_free_bucket(tdb, b_off);
 440         return 0;
 441
 442 unlock_err:
 443         tdb_unlock_free_bucket(tdb, b_off);
 444         return TDB_OFF_ERR;
 445 }
 446
 447 static bool next_zone(struct tdb_context *tdb)
 448 {
 449         tdb_off_t next = tdb->zone_off + (1ULL << tdb->zhdr.zone_bits);
 450
 451         /* We must have a header. */
 452         if (tdb->methods->oob(tdb, next + sizeof(tdb->zhdr), true))
 453                 return false;
 454
 455         tdb->zone_off = next;
 456         return tdb_read_convert(tdb, next, &tdb->zhdr, sizeof(tdb->zhdr)) == 0;
 457 }
 458
 459 /* Offset returned is within current zone (which it may alter). */
 460 static tdb_off_t get_free(struct tdb_context *tdb, size_t size,
 461                           tdb_len_t *actual)
 462 {
 463         tdb_off_t start_zone = tdb->zone_off, off;
 464         bool wrapped = false;
 465
 466         while (!wrapped || tdb->zone_off != start_zone) {
 467                 tdb_off_t b;
 468
 469                 /* Shortcut for really huge allocations... */
 470                 if ((size >> tdb->zhdr.zone_bits) != 0)
 471                         continue;
 472
 473                 /* Start at exact size bucket, and search up... */
 474                 b = size_to_bucket(tdb->zhdr.zone_bits, size);
 475                 for (b = find_free_head(tdb, b);
 476                      b <= BUCKETS_FOR_ZONE(tdb->zhdr.zone_bits);
 477                      b += find_free_head(tdb, b + 1)) {
 478                         /* Try getting one from list. */
 479                         off = lock_and_alloc(tdb, tdb->zone_off,
 480                                              tdb->zhdr.zone_bits,
 481                                              b, size, actual);
 482                         if (off == TDB_OFF_ERR)
 483                                 return TDB_OFF_ERR;
 484                         if (off != 0)
 485                                 return off;
 486                         /* Didn't work.  Try next bucket. */
 487                 }
 488
 489                 /* Didn't work, try next zone, if it exists. */
 490                 if (!next_zone(tdb)) {
 491                         wrapped = true;
 492                         tdb->zone_off = sizeof(struct tdb_header);
 493                         if (tdb_read_convert(tdb, tdb->zone_off,
 494                                              &tdb->zhdr, sizeof(tdb->zhdr))) {
 495                                 return TDB_OFF_ERR;
 496                         }
 497                 }
 498         }
 499         return 0;
 500 }
 501
 502 int set_header(struct tdb_context *tdb,
 503                struct tdb_used_record *rec,
 504                uint64_t keylen, uint64_t datalen,
 505                uint64_t actuallen, uint64_t hash,
 506                unsigned int zone_bits)
 507 {
 508         uint64_t keybits = (fls64(keylen) + 1) / 2;
 509
 510         /* Use bottom bits of hash, so it's independent of hash table size. */
 511         rec->magic_and_meta
 512                 = zone_bits
 513                 | ((hash & ((1 << 5)-1)) << 6)
 514                 | ((actuallen - (keylen + datalen)) << 11)
 515                 | (keybits << 43)
 516                 | (TDB_MAGIC << 48);
 517         rec->key_and_data_len = (keylen | (datalen << (keybits*2)));
 518
 519         /* Encoding can fail on big values. */
 520         if (rec_key_length(rec) != keylen
 521             || rec_data_length(rec) != datalen
 522             || rec_extra_padding(rec) != actuallen - (keylen + datalen)) {
 523                 tdb->ecode = TDB_ERR_IO;
 524                 tdb->log(tdb, TDB_DEBUG_ERROR, tdb->log_priv,
 525                          "Could not encode k=%llu,d=%llu,a=%llu\n",
 526                          (long long)keylen, (long long)datalen,
 527                          (long long)actuallen);
 528                 return -1;
 529         }
 530         return 0;
 531 }
 532
 533 static bool zones_happy(struct tdb_context *tdb)
 534 {
 535         /* FIXME: look at distribution of zones. */
 536         return true;
 537 }
 538
 539 /* Assume we want buckets up to the comfort factor. */
 540 static tdb_len_t overhead(unsigned int zone_bits)
 541 {
 542         return sizeof(struct free_zone_header)
 543                 + (BUCKETS_FOR_ZONE(zone_bits) + 1) * sizeof(tdb_off_t);
 544 }
 545
 546 /* Expand the database (by adding a zone). */
 547 static int tdb_expand(struct tdb_context *tdb, tdb_len_t size)
 548 {
 549         uint64_t old_size;
 550         tdb_off_t off;
 551         uint8_t zone_bits;
 552         unsigned int num_buckets;
 553         tdb_len_t wanted;
 554         struct free_zone_header zhdr;
 555         bool enlarge_zone;
 556
 557         /* We need room for the record header too. */
 558         wanted = sizeof(struct tdb_used_record) + size;
 559
 560         /* Only one person can expand file at a time. */
 561         if (tdb_lock_expand(tdb, F_WRLCK) != 0)
 562                 return -1;
 563
 564         /* Someone else may have expanded the file, so retry. */
 565         old_size = tdb->map_size;
 566         tdb->methods->oob(tdb, tdb->map_size + 1, true);
 567         if (tdb->map_size != old_size)
 568                 goto success;
 569
 570         /* zone bits tailer char is protected by EXPAND lock. */
 571         if (tdb->methods->read(tdb, old_size - 1, &zone_bits, 1) == -1)
 572                 goto fail;
 573
 574         /* If zones aren't working well, add larger zone if possible. */
 575         enlarge_zone = !zones_happy(tdb);
 576
 577         /* New zone can be between zone_bits or larger if we're on the right
 578          * boundary. */
 579         for (;;) {
 580                 /* Does this fit the allocation comfortably? */
 581                 if ((1ULL << zone_bits) >= overhead(zone_bits) + wanted) {
 582                         /* Only let enlarge_zone enlarge us once. */
 583                         if (!enlarge_zone)
 584                                 break;
 585                         enlarge_zone = false;
 586                 }
 587                 if ((old_size - 1 - sizeof(struct tdb_header))
 588                     & (1 << zone_bits))
 589                         break;
 590                 zone_bits++;
 591         }
 592
 593         zhdr.zone_bits = zone_bits;
 594         num_buckets = BUCKETS_FOR_ZONE(zone_bits);
 595
 596         if (tdb->methods->expand_file(tdb, 1ULL << zone_bits) == -1)
 597                 goto fail;
 598
 599         /* Write new tailer. */
 600         if (tdb->methods->write(tdb, tdb->map_size - 1, &zone_bits, 1) == -1)
 601                 goto fail;
 602
 603         /* Write new zone header (just before old tailer). */
 604         off = old_size - 1;
 605         if (tdb_write_convert(tdb, off, &zhdr, sizeof(zhdr)) == -1)
 606                 goto fail;
 607
 608         /* Now write empty buckets. */
 609         off += sizeof(zhdr);
 610         if (zero_out(tdb, off, (num_buckets+1) * sizeof(tdb_off_t)) == -1)
 611                 goto fail;
 612         off += (num_buckets+1) * sizeof(tdb_off_t);
 613
 614         /* Now add the rest as our free record. */
 615         if (add_free_record(tdb, zone_bits, off, tdb->map_size-1-off) == -1)
 616                 goto fail;
 617
 618         /* Try allocating from this zone now. */
 619         tdb->zone_off = old_size - 1;
 620         tdb->zhdr = zhdr;
 621
 622 success:
 623         tdb_unlock_expand(tdb, F_WRLCK);
 624         return 0;
 625
 626 fail:
 627         tdb_unlock_expand(tdb, F_WRLCK);
 628         return -1;
 629 }
 630
 631 static tdb_len_t adjust_size(size_t keylen, size_t datalen, bool growing)
 632 {
 633         tdb_len_t size = keylen + datalen;
 634
 635         if (size < MIN_DATA_LEN)
 636                 size = MIN_DATA_LEN;
 637
 638         /* Overallocate if this is coming from an enlarging store. */
 639         if (growing)
 640                 size += datalen / 2;
 641
 642         /* Round to next uint64_t boundary. */
 643         return (size + (sizeof(uint64_t) - 1ULL)) & ~(sizeof(uint64_t) - 1ULL);
 644 }
 645
 646 /* This won't fail: it will expand the database if it has to. */
 647 tdb_off_t alloc(struct tdb_context *tdb, size_t keylen, size_t datalen,
 648                 uint64_t hash, bool growing)
 649 {
 650         tdb_off_t off;
 651         tdb_len_t size, actual;
 652         struct tdb_used_record rec;
 653
 654         /* We can't hold pointers during this: we could unmap! */
 655         assert(!tdb->direct_access);
 656
 657         size = adjust_size(keylen, datalen, growing);
 658
 659 again:
 660         off = get_free(tdb, size, &actual);
 661         if (unlikely(off == TDB_OFF_ERR))
 662                 return off;
 663
 664         if (unlikely(off == 0)) {
 665                 if (tdb_expand(tdb, size) == -1)
 666                         return TDB_OFF_ERR;
 667                 goto again;
 668         }
 669
 670         /* Some supergiant values can't be encoded. */
 671         /* FIXME: Check before, and limit actual in get_free. */
 672         if (set_header(tdb, &rec, keylen, datalen, actual, hash,
 673                        tdb->zhdr.zone_bits) != 0) {
 674                 add_free_record(tdb, tdb->zhdr.zone_bits, off,
 675                                 sizeof(rec) + actual);
 676                 return TDB_OFF_ERR;
 677         }
 678
 679         if (tdb_write_convert(tdb, off, &rec, sizeof(rec)) != 0)
 680                 return TDB_OFF_ERR;
 681
 682         return off;
 683 }