git.ozlabs.org Git - ccan/blob - 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(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         enum TDB_ERROR ecode;
 112
 113         /* Front of list? */
 114         if (frec_prev(r) == 0) {
 115                 off = b_off;
 116         } else {
 117                 off = frec_prev(r) + offsetof(struct tdb_free_record, next);
 118         }
 119
 120 #ifdef CCAN_TDB2_DEBUG
 121         if (tdb_read_off(tdb, off) != r_off) {
 122                 tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 123                          "remove_from_list: %llu bad prev in list %llu",
 124                          (long long)r_off, (long long)b_off);
 125                 return -1;
 126         }
 127 #endif
 128
 129         /* r->prev->next = r->next */
 130         ecode = tdb_write_off(tdb, off, r->next);
 131         if (ecode != TDB_SUCCESS) {
 132                 tdb->ecode = ecode;
 133                 return -1;
 134         }
 135
 136         if (r->next != 0) {
 137                 off = r->next + offsetof(struct tdb_free_record,magic_and_prev);
 138                 /* r->next->prev = r->prev */
 139
 140 #ifdef CCAN_TDB2_DEBUG
 141                 if (tdb_read_off(tdb, off) & TDB_OFF_MASK != r_off) {
 142                         tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 143                                    "remove_from_list: %llu bad list %llu",
 144                                    (long long)r_off, (long long)b_off);
 145                         return -1;
 146                 }
 147 #endif
 148
 149                 ecode = tdb_write_off(tdb, off, r->magic_and_prev);
 150                 if (ecode != TDB_SUCCESS) {
 151                         tdb->ecode = ecode;
 152                         return -1;
 153                 }
 154         }
 155         return 0;
 156 }
 157
 158 /* Enqueue in this free bucket. */
 159 static int enqueue_in_free(struct tdb_context *tdb,
 160                            tdb_off_t b_off,
 161                            tdb_off_t off,
 162                            tdb_len_t len)
 163 {
 164         struct tdb_free_record new;
 165         enum TDB_ERROR ecode;
 166         uint64_t magic = (TDB_FREE_MAGIC << (64 - TDB_OFF_UPPER_STEAL));
 167
 168         /* We only need to set ftable_and_len; rest is set in enqueue_in_free */
 169         new.ftable_and_len = ((uint64_t)tdb->ftable << (64 - TDB_OFF_UPPER_STEAL))
 170                 | len;
 171         /* prev = 0. */
 172         new.magic_and_prev = magic;
 173
 174         /* new->next = head. */
 175         new.next = tdb_read_off(tdb, b_off);
 176         if (new.next == TDB_OFF_ERR)
 177                 return -1;
 178
 179         if (new.next) {
 180 #ifdef CCAN_TDB2_DEBUG
 181                 if (tdb_read_off(tdb,
 182                                  new.next + offsetof(struct tdb_free_record,
 183                                                      magic_and_prev))
 184                     != magic) {
 185                         tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 186                                    "enqueue_in_free: %llu bad head"
 187                                    " prev %llu",
 188                                    (long long)new.next, (long long)b_off);
 189                         return -1;
 190                 }
 191 #endif
 192                 /* next->prev = new. */
 193                 ecode = tdb_write_off(tdb, new.next
 194                                       + offsetof(struct tdb_free_record,
 195                                                  magic_and_prev),
 196                                       off | magic);
 197                 if (ecode != TDB_SUCCESS) {
 198                         tdb->ecode = ecode;
 199                         return -1;
 200                 }
 201         }
 202         /* head = new */
 203         ecode = tdb_write_off(tdb, b_off, off);
 204         if (ecode != TDB_SUCCESS) {
 205                 tdb->ecode = ecode;
 206                 return -1;
 207         }
 208
 209         ecode = tdb_write_convert(tdb, off, &new, sizeof(new));
 210         if (ecode != TDB_SUCCESS) {
 211                 tdb->ecode = ecode;
 212                 return -1;
 213         }
 214         return 0;
 215 }
 216
 217 /* List need not be locked. */
 218 int add_free_record(struct tdb_context *tdb,
 219                     tdb_off_t off, tdb_len_t len_with_header)
 220 {
 221         tdb_off_t b_off;
 222         tdb_len_t len;
 223         int ret;
 224         enum TDB_ERROR ecode;
 225
 226         assert(len_with_header >= sizeof(struct tdb_free_record));
 227
 228         len = len_with_header - sizeof(struct tdb_used_record);
 229
 230         b_off = bucket_off(tdb->ftable_off, size_to_bucket(len));
 231         ecode = tdb_lock_free_bucket(tdb, b_off, TDB_LOCK_WAIT);
 232         if (ecode != TDB_SUCCESS) {
 233                 tdb->ecode = ecode;
 234                 return -1;
 235         }
 236
 237         ret = enqueue_in_free(tdb, b_off, off, len);
 238         tdb_unlock_free_bucket(tdb, b_off);
 239         return ret;
 240 }
 241
 242 static size_t adjust_size(size_t keylen, size_t datalen)
 243 {
 244         size_t size = keylen + datalen;
 245
 246         if (size < TDB_MIN_DATA_LEN)
 247                 size = TDB_MIN_DATA_LEN;
 248
 249         /* Round to next uint64_t boundary. */
 250         return (size + (sizeof(uint64_t) - 1ULL)) & ~(sizeof(uint64_t) - 1ULL);
 251 }
 252
 253 /* If we have enough left over to be useful, split that off. */
 254 static size_t record_leftover(size_t keylen, size_t datalen,
 255                               bool want_extra, size_t total_len)
 256 {
 257         ssize_t leftover;
 258
 259         if (want_extra)
 260                 datalen += datalen / 2;
 261         leftover = total_len - adjust_size(keylen, datalen);
 262
 263         if (leftover < (ssize_t)sizeof(struct tdb_free_record))
 264                 return 0;
 265
 266         return leftover;
 267 }
 268
 269 static tdb_off_t ftable_offset(struct tdb_context *tdb, unsigned int ftable)
 270 {
 271         tdb_off_t off;
 272         unsigned int i;
 273
 274         if (likely(tdb->ftable == ftable))
 275                 return tdb->ftable_off;
 276
 277         off = first_ftable(tdb);
 278         for (i = 0; i < ftable; i++)
 279                 off = next_ftable(tdb, off);
 280         return off;
 281 }
 282
 283 /* Note: we unlock the current bucket if we coalesce or fail. */
 284 static int coalesce(struct tdb_context *tdb,
 285                     tdb_off_t off, tdb_off_t b_off, tdb_len_t data_len)
 286 {
 287         tdb_off_t end;
 288         struct tdb_free_record rec;
 289         enum TDB_ERROR ecode;
 290
 291         add_stat(tdb, alloc_coalesce_tried, 1);
 292         end = off + sizeof(struct tdb_used_record) + data_len;
 293
 294         while (end < tdb->map_size) {
 295                 const struct tdb_free_record *r;
 296                 tdb_off_t nb_off;
 297                 unsigned ftable, bucket;
 298
 299                 r = tdb_access_read(tdb, end, sizeof(*r), true);
 300                 if (TDB_PTR_IS_ERR(r)) {
 301                         tdb->ecode = TDB_PTR_ERR(r);
 302                         goto err;
 303                 }
 304
 305                 if (frec_magic(r) != TDB_FREE_MAGIC
 306                     || frec_ftable(r) == TDB_FTABLE_NONE) {
 307                         tdb_access_release(tdb, r);
 308                         break;
 309                 }
 310
 311                 ftable = frec_ftable(r);
 312                 bucket = size_to_bucket(frec_len(r));
 313                 nb_off = bucket_off(ftable_offset(tdb, ftable), bucket);
 314                 tdb_access_release(tdb, r);
 315
 316                 /* We may be violating lock order here, so best effort. */
 317                 if (tdb_lock_free_bucket(tdb, nb_off, TDB_LOCK_NOWAIT)
 318                     != TDB_SUCCESS) {
 319                         add_stat(tdb, alloc_coalesce_lockfail, 1);
 320                         break;
 321                 }
 322
 323                 /* Now we have lock, re-check. */
 324                 ecode = tdb_read_convert(tdb, end, &rec, sizeof(rec));
 325                 if (ecode != TDB_SUCCESS) {
 326                         tdb->ecode = ecode;
 327                         tdb_unlock_free_bucket(tdb, nb_off);
 328                         goto err;
 329                 }
 330
 331                 if (unlikely(frec_magic(&rec) != TDB_FREE_MAGIC)) {
 332                         add_stat(tdb, alloc_coalesce_race, 1);
 333                         tdb_unlock_free_bucket(tdb, nb_off);
 334                         break;
 335                 }
 336
 337                 if (unlikely(frec_ftable(&rec) != ftable)
 338                     || unlikely(size_to_bucket(frec_len(&rec)) != bucket)) {
 339                         add_stat(tdb, alloc_coalesce_race, 1);
 340                         tdb_unlock_free_bucket(tdb, nb_off);
 341                         break;
 342                 }
 343
 344                 if (remove_from_list(tdb, nb_off, end, &rec) == -1) {
 345                         tdb_unlock_free_bucket(tdb, nb_off);
 346                         goto err;
 347                 }
 348
 349                 end += sizeof(struct tdb_used_record) + frec_len(&rec);
 350                 tdb_unlock_free_bucket(tdb, nb_off);
 351                 add_stat(tdb, alloc_coalesce_num_merged, 1);
 352         }
 353
 354         /* Didn't find any adjacent free? */
 355         if (end == off + sizeof(struct tdb_used_record) + data_len)
 356                 return 0;
 357
 358         /* OK, expand initial record */
 359         ecode = tdb_read_convert(tdb, off, &rec, sizeof(rec));
 360         if (ecode != TDB_SUCCESS) {
 361                 tdb->ecode = ecode;
 362                 goto err;
 363         }
 364
 365         if (frec_len(&rec) != data_len) {
 366                 tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 367                            "coalesce: expected data len %zu not %zu",
 368                            (size_t)data_len, (size_t)frec_len(&rec));
 369                 goto err;
 370         }
 371
 372         if (remove_from_list(tdb, b_off, off, &rec) == -1)
 373                 goto err;
 374
 375         /* We have to drop this to avoid deadlocks, so make sure record
 376          * doesn't get coalesced by someone else! */
 377         rec.ftable_and_len = (TDB_FTABLE_NONE << (64 - TDB_OFF_UPPER_STEAL))
 378                 | (end - off - sizeof(struct tdb_used_record));
 379         ecode = tdb_write_off(tdb, off + offsetof(struct tdb_free_record,
 380                                                   ftable_and_len),
 381                               rec.ftable_and_len);
 382         if (ecode != TDB_SUCCESS) {
 383                 tdb->ecode = ecode;
 384                 goto err;
 385         }
 386
 387         add_stat(tdb, alloc_coalesce_succeeded, 1);
 388         tdb_unlock_free_bucket(tdb, b_off);
 389
 390         if (add_free_record(tdb, off, end - off) == -1)
 391                 return -1;
 392         return 1;
 393
 394 err:
 395         /* To unify error paths, we *always* unlock bucket on error. */
 396         tdb_unlock_free_bucket(tdb, b_off);
 397         return -1;
 398 }
 399
 400 /* We need size bytes to put our key and data in. */
 401 static tdb_off_t lock_and_alloc(struct tdb_context *tdb,
 402                                 tdb_off_t ftable_off,
 403                                 tdb_off_t bucket,
 404                                 size_t keylen, size_t datalen,
 405                                 bool want_extra,
 406                                 unsigned magic,
 407                                 unsigned hashlow)
 408 {
 409         tdb_off_t off, b_off,best_off;
 410         struct tdb_free_record best = { 0 };
 411         double multiplier;
 412         size_t size = adjust_size(keylen, datalen);
 413         enum TDB_ERROR ecode;
 414
 415         add_stat(tdb, allocs, 1);
 416 again:
 417         b_off = bucket_off(ftable_off, bucket);
 418
 419         /* FIXME: Try non-blocking wait first, to measure contention. */
 420         /* Lock this bucket. */
 421         ecode = tdb_lock_free_bucket(tdb, b_off, TDB_LOCK_WAIT);
 422         if (ecode != TDB_SUCCESS) {
 423                 tdb->ecode = ecode;
 424                 return TDB_OFF_ERR;
 425         }
 426
 427         best.ftable_and_len = -1ULL;
 428         best_off = 0;
 429
 430         /* Get slack if we're after extra. */
 431         if (want_extra)
 432                 multiplier = 1.5;
 433         else
 434                 multiplier = 1.0;
 435
 436         /* Walk the list to see if any are large enough, getting less fussy
 437          * as we go. */
 438         off = tdb_read_off(tdb, b_off);
 439         if (unlikely(off == TDB_OFF_ERR))
 440                 goto unlock_err;
 441
 442         while (off) {
 443                 const struct tdb_free_record *r;
 444                 tdb_len_t len;
 445                 tdb_off_t next;
 446
 447                 r = tdb_access_read(tdb, off, sizeof(*r), true);
 448                 if (TDB_PTR_IS_ERR(r)) {
 449                         tdb->ecode = TDB_PTR_ERR(r);
 450                         goto unlock_err;
 451                 }
 452
 453                 if (frec_magic(r) != TDB_FREE_MAGIC) {
 454                         tdb_access_release(tdb, r);
 455                         tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 456                                  "lock_and_alloc: %llu non-free 0x%llx",
 457                                  (long long)off, (long long)r->magic_and_prev);
 458                         goto unlock_err;
 459                 }
 460
 461                 if (frec_len(r) >= size && frec_len(r) < frec_len(&best)) {
 462                         best_off = off;
 463                         best = *r;
 464                 }
 465
 466                 if (frec_len(&best) < size * multiplier && best_off) {
 467                         tdb_access_release(tdb, r);
 468                         break;
 469                 }
 470
 471                 multiplier *= 1.01;
 472
 473                 next = r->next;
 474                 len = frec_len(r);
 475                 tdb_access_release(tdb, r);
 476
 477                 /* Since we're going slow anyway, try coalescing here. */
 478                 switch (coalesce(tdb, off, b_off, len)) {
 479                 case -1:
 480                         /* This has already unlocked on error. */
 481                         return -1;
 482                 case 1:
 483                         /* This has unlocked list, restart. */
 484                         goto again;
 485                 }
 486                 off = next;
 487         }
 488
 489         /* If we found anything at all, use it. */
 490         if (best_off) {
 491                 struct tdb_used_record rec;
 492                 size_t leftover;
 493
 494                 /* We're happy with this size: take it. */
 495                 if (remove_from_list(tdb, b_off, best_off, &best) != 0)
 496                         goto unlock_err;
 497
 498                 leftover = record_leftover(keylen, datalen, want_extra,
 499                                            frec_len(&best));
 500
 501                 assert(keylen + datalen + leftover <= frec_len(&best));
 502                 /* We need to mark non-free before we drop lock, otherwise
 503                  * coalesce() could try to merge it! */
 504                 if (set_header(tdb, &rec, magic, keylen, datalen,
 505                                frec_len(&best) - leftover, hashlow) != 0)
 506                         goto unlock_err;
 507
 508                 ecode = tdb_write_convert(tdb, best_off, &rec, sizeof(rec));
 509                 if (ecode != TDB_SUCCESS) {
 510                         tdb->ecode = ecode;
 511                         goto unlock_err;
 512                 }
 513
 514                 /* Bucket of leftover will be <= current bucket, so nested
 515                  * locking is allowed. */
 516                 if (leftover) {
 517                         add_stat(tdb, alloc_leftover, 1);
 518                         if (add_free_record(tdb,
 519                                             best_off + sizeof(rec)
 520                                             + frec_len(&best) - leftover,
 521                                             leftover))
 522                                 best_off = TDB_OFF_ERR;
 523                 }
 524                 tdb_unlock_free_bucket(tdb, b_off);
 525
 526                 return best_off;
 527         }
 528
 529         tdb_unlock_free_bucket(tdb, b_off);
 530         return 0;
 531
 532 unlock_err:
 533         tdb_unlock_free_bucket(tdb, b_off);
 534         return TDB_OFF_ERR;
 535 }
 536
 537 /* Get a free block from current free list, or 0 if none. */
 538 static tdb_off_t get_free(struct tdb_context *tdb,
 539                           size_t keylen, size_t datalen, bool want_extra,
 540                           unsigned magic, unsigned hashlow)
 541 {
 542         tdb_off_t off, ftable_off;
 543         unsigned start_b, b, ftable;
 544         bool wrapped = false;
 545
 546         /* If they are growing, add 50% to get to higher bucket. */
 547         if (want_extra)
 548                 start_b = size_to_bucket(adjust_size(keylen,
 549                                                      datalen + datalen / 2));
 550         else
 551                 start_b = size_to_bucket(adjust_size(keylen, datalen));
 552
 553         ftable_off = tdb->ftable_off;
 554         ftable = tdb->ftable;
 555         while (!wrapped || ftable_off != tdb->ftable_off) {
 556                 /* Start at exact size bucket, and search up... */
 557                 for (b = find_free_head(tdb, ftable_off, start_b);
 558                      b < TDB_FREE_BUCKETS;
 559                      b = find_free_head(tdb, ftable_off, b + 1)) {
 560                         /* Try getting one from list. */
 561                         off = lock_and_alloc(tdb, ftable_off,
 562                                              b, keylen, datalen, want_extra,
 563                                              magic, hashlow);
 564                         if (off == TDB_OFF_ERR)
 565                                 return TDB_OFF_ERR;
 566                         if (off != 0) {
 567                                 if (b == start_b)
 568                                         add_stat(tdb, alloc_bucket_exact, 1);
 569                                 if (b == TDB_FREE_BUCKETS - 1)
 570                                         add_stat(tdb, alloc_bucket_max, 1);
 571                                 /* Worked?  Stay using this list. */
 572                                 tdb->ftable_off = ftable_off;
 573                                 tdb->ftable = ftable;
 574                                 return off;
 575                         }
 576                         /* Didn't work.  Try next bucket. */
 577                 }
 578
 579                 /* Hmm, try next table. */
 580                 ftable_off = next_ftable(tdb, ftable_off);
 581                 ftable++;
 582
 583                 if (ftable_off == 0) {
 584                         wrapped = true;
 585                         ftable_off = first_ftable(tdb);
 586                         ftable = 0;
 587                 }
 588         }
 589
 590         return 0;
 591 }
 592
 593 int set_header(struct tdb_context *tdb,
 594                struct tdb_used_record *rec,
 595                unsigned magic, uint64_t keylen, uint64_t datalen,
 596                uint64_t actuallen, unsigned hashlow)
 597 {
 598         uint64_t keybits = (fls64(keylen) + 1) / 2;
 599
 600         /* Use bottom bits of hash, so it's independent of hash table size. */
 601         rec->magic_and_meta = (hashlow & ((1 << 11)-1))
 602                 | ((actuallen - (keylen + datalen)) << 11)
 603                 | (keybits << 43)
 604                 | ((uint64_t)magic << 48);
 605         rec->key_and_data_len = (keylen | (datalen << (keybits*2)));
 606
 607         /* Encoding can fail on big values. */
 608         if (rec_key_length(rec) != keylen
 609             || rec_data_length(rec) != datalen
 610             || rec_extra_padding(rec) != actuallen - (keylen + datalen)) {
 611                 tdb_logerr(tdb, TDB_ERR_IO, TDB_LOG_ERROR,
 612                          "Could not encode k=%llu,d=%llu,a=%llu",
 613                          (long long)keylen, (long long)datalen,
 614                          (long long)actuallen);
 615                 return -1;
 616         }
 617         return 0;
 618 }
 619
 620 /* Expand the database. */
 621 static int tdb_expand(struct tdb_context *tdb, tdb_len_t size)
 622 {
 623         uint64_t old_size;
 624         tdb_len_t wanted;
 625         enum TDB_ERROR ecode;
 626
 627         /* We need room for the record header too. */
 628         wanted = sizeof(struct tdb_used_record) + size;
 629
 630         /* Need to hold a hash lock to expand DB: transactions rely on it. */
 631         if (!(tdb->flags & TDB_NOLOCK)
 632             && !tdb->allrecord_lock.count && !tdb_has_hash_locks(tdb)) {
 633                 tdb_logerr(tdb, TDB_ERR_LOCK, TDB_LOG_ERROR,
 634                            "tdb_expand: must hold lock during expand");
 635                 return -1;
 636         }
 637
 638         /* always make room for at least 100 more records, and at
 639            least 25% more space. */
 640         if (size * TDB_EXTENSION_FACTOR > tdb->map_size / 4)
 641                 wanted = size * TDB_EXTENSION_FACTOR;
 642         else
 643                 wanted = tdb->map_size / 4;
 644         wanted = adjust_size(0, wanted);
 645
 646         /* Only one person can expand file at a time. */
 647         ecode = tdb_lock_expand(tdb, F_WRLCK);
 648         if (ecode != TDB_SUCCESS) {
 649                 tdb->ecode = ecode;
 650                 return -1;
 651         }
 652
 653         /* Someone else may have expanded the file, so retry. */
 654         old_size = tdb->map_size;
 655         tdb->methods->oob(tdb, tdb->map_size + 1, true);
 656         if (tdb->map_size != old_size) {
 657                 tdb_unlock_expand(tdb, F_WRLCK);
 658                 return 0;
 659         }
 660
 661         ecode = tdb->methods->expand_file(tdb, wanted);
 662         if (ecode != TDB_SUCCESS) {
 663                 tdb->ecode = ecode;
 664                 tdb_unlock_expand(tdb, F_WRLCK);
 665                 return -1;
 666         }
 667
 668         /* We need to drop this lock before adding free record. */
 669         tdb_unlock_expand(tdb, F_WRLCK);
 670
 671         add_stat(tdb, expands, 1);
 672         return add_free_record(tdb, old_size, wanted);
 673 }
 674
 675 /* This won't fail: it will expand the database if it has to. */
 676 tdb_off_t alloc(struct tdb_context *tdb, size_t keylen, size_t datalen,
 677                 uint64_t hash, unsigned magic, bool growing)
 678 {
 679         tdb_off_t off;
 680
 681         /* We can't hold pointers during this: we could unmap! */
 682         assert(!tdb->direct_access);
 683
 684         for (;;) {
 685                 off = get_free(tdb, keylen, datalen, growing, magic, hash);
 686                 if (likely(off != 0))
 687                         break;
 688
 689                 if (tdb_expand(tdb, adjust_size(keylen, datalen)))
 690                         return TDB_OFF_ERR;
 691         }
 692
 693         return off;
 694 }