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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 enum TDB_ERROR 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 (TDB_OFF_IS_ERR(off)) {
  73                         return off;
  74                 }
  75
  76                 rnd = random();
  77                 if (rnd >= max) {
  78                         tdb->ftable_off = off;
  79                         tdb->ftable = count;
  80                         max = rnd;
  81                 }
  82
  83                 off = next_ftable(tdb, off);
  84                 count++;
  85         }
  86         return TDB_SUCCESS;
  87 }
  88
  89 /* Offset of a given bucket. */
  90 tdb_off_t bucket_off(tdb_off_t ftable_off, unsigned bucket)
  91 {
  92         return ftable_off + offsetof(struct tdb_freetable, buckets)
  93                 + bucket * sizeof(tdb_off_t);
  94 }
  95
  96 /* Returns free_buckets + 1, or list number to search, or -ve error. */
  97 static tdb_off_t find_free_head(struct tdb_context *tdb,
  98                                 tdb_off_t ftable_off,
  99                                 tdb_off_t bucket)
 100 {
 101         /* Speculatively search for a non-zero bucket. */
 102         return tdb_find_nonzero_off(tdb, bucket_off(ftable_off, 0),
 103                                     bucket, TDB_FREE_BUCKETS);
 104 }
 105
 106 static void check_list(struct tdb_context *tdb, tdb_off_t b_off)
 107 {
 108 #ifdef CCAN_TDB2_DEBUG
 109         tdb_off_t off, prev = 0, first;
 110         struct tdb_free_record r;
 111
 112         first = off = tdb_read_off(tdb, b_off);
 113         while (off != 0) {
 114                 tdb_read_convert(tdb, off, &r, sizeof(r));
 115                 if (frec_magic(&r) != TDB_FREE_MAGIC)
 116                         abort();
 117                 if (prev && frec_prev(&r) != prev)
 118                         abort();
 119                 prev = off;
 120                 off = r.next;
 121         }
 122
 123         if (first) {
 124                 tdb_read_convert(tdb, first, &r, sizeof(r));
 125                 if (frec_prev(&r) != prev)
 126                         abort();
 127         }
 128 #endif
 129 }
 130
 131 /* Remove from free bucket. */
 132 static enum TDB_ERROR remove_from_list(struct tdb_context *tdb,
 133                                        tdb_off_t b_off, tdb_off_t r_off,
 134                                        const struct tdb_free_record *r)
 135 {
 136         tdb_off_t off, prev_next, head;
 137         enum TDB_ERROR ecode;
 138
 139         /* Is this only element in list?  Zero out bucket, and we're done. */
 140         if (frec_prev(r) == r_off)
 141                 return tdb_write_off(tdb, b_off, 0);
 142
 143         /* off = &r->prev->next */
 144         off = frec_prev(r) + offsetof(struct tdb_free_record, next);
 145
 146         /* Get prev->next */
 147         prev_next = tdb_read_off(tdb, off);
 148         if (TDB_OFF_IS_ERR(prev_next))
 149                 return prev_next;
 150
 151         /* If prev->next == 0, we were head: update bucket to point to next. */
 152         if (prev_next == 0) {
 153 #ifdef CCAN_TDB2_DEBUG
 154                 if (tdb_read_off(tdb, b_off) != r_off) {
 155                         return tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 156                                           "remove_from_list:"
 157                                           " %llu head %llu on list %llu",
 158                                           (long long)r_off,
 159                                           (long long)tdb_read_off(tdb, b_off),
 160                                           (long long)b_off);
 161                 }
 162 #endif
 163                 ecode = tdb_write_off(tdb, b_off, r->next);
 164                 if (ecode != TDB_SUCCESS)
 165                         return ecode;
 166         } else {
 167                 /* r->prev->next = r->next */
 168                 ecode = tdb_write_off(tdb, off, r->next);
 169                 if (ecode != TDB_SUCCESS)
 170                         return ecode;
 171         }
 172
 173         /* If we were the tail, off = &head->prev. */
 174         if (r->next == 0) {
 175                 head = tdb_read_off(tdb, b_off);
 176                 if (TDB_OFF_IS_ERR(head))
 177                         return head;
 178                 off = head + offsetof(struct tdb_free_record, magic_and_prev);
 179         } else {
 180                 /* off = &r->next->prev */
 181                 off = r->next + offsetof(struct tdb_free_record,
 182                                          magic_and_prev);
 183         }
 184
 185 #ifdef CCAN_TDB2_DEBUG
 186         /* *off == r */
 187         if ((tdb_read_off(tdb, off) & TDB_OFF_MASK) != r_off) {
 188                 return tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 189                                   "remove_from_list:"
 190                                   " %llu bad prev in list %llu",
 191                                   (long long)r_off, (long long)b_off);
 192         }
 193 #endif
 194         /* r->next->prev = r->prev */
 195         return tdb_write_off(tdb, off, r->magic_and_prev);
 196 }
 197
 198 /* Enqueue in this free bucket. */
 199 static enum TDB_ERROR enqueue_in_free(struct tdb_context *tdb,
 200                                       tdb_off_t b_off,
 201                                       tdb_off_t off,
 202                                       tdb_len_t len)
 203 {
 204         struct tdb_free_record new;
 205         enum TDB_ERROR ecode;
 206         tdb_off_t prev;
 207         uint64_t magic = (TDB_FREE_MAGIC << (64 - TDB_OFF_UPPER_STEAL));
 208
 209         /* We only need to set ftable_and_len; rest is set in enqueue_in_free */
 210         new.ftable_and_len = ((uint64_t)tdb->ftable << (64 - TDB_OFF_UPPER_STEAL))
 211                 | len;
 212
 213         /* new->next = head. */
 214         new.next = tdb_read_off(tdb, b_off);
 215         if (TDB_OFF_IS_ERR(new.next)) {
 216                 return new.next;
 217         }
 218
 219         /* First element?  Prev points to ourselves. */
 220         if (!new.next) {
 221                 new.magic_and_prev = (magic | off);
 222         } else {
 223                 /* new->prev = next->prev */
 224                 prev = tdb_read_off(tdb,
 225                                     new.next + offsetof(struct tdb_free_record,
 226                                                         magic_and_prev));
 227                 new.magic_and_prev = prev;
 228                 if (frec_magic(&new) != TDB_FREE_MAGIC) {
 229                         return tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 230                                           "enqueue_in_free: %llu bad head"
 231                                           " prev %llu",
 232                                           (long long)new.next,
 233                                           (long long)prev);
 234                 }
 235                 /* next->prev = new. */
 236                 ecode = tdb_write_off(tdb, new.next
 237                                       + offsetof(struct tdb_free_record,
 238                                                  magic_and_prev),
 239                                       off | magic);
 240                 if (ecode != TDB_SUCCESS) {
 241                         return ecode;
 242                 }
 243
 244 #ifdef CCAN_TDB2_DEBUG
 245                 prev = tdb_read_off(tdb, frec_prev(&new)
 246                                     + offsetof(struct tdb_free_record, next));
 247                 if (prev != 0) {
 248                         return tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 249                                           "enqueue_in_free:"
 250                                           " %llu bad tail next ptr %llu",
 251                                           (long long)frec_prev(&new)
 252                                           + offsetof(struct tdb_free_record,
 253                                                      next),
 254                                           (long long)prev);
 255                 }
 256 #endif
 257         }
 258         /* head = new */
 259         ecode = tdb_write_off(tdb, b_off, off);
 260         if (ecode != TDB_SUCCESS) {
 261                 return ecode;
 262         }
 263
 264         return tdb_write_convert(tdb, off, &new, sizeof(new));
 265 }
 266
 267 /* List need not be locked. */
 268 enum TDB_ERROR add_free_record(struct tdb_context *tdb,
 269                                tdb_off_t off, tdb_len_t len_with_header)
 270 {
 271         tdb_off_t b_off;
 272         tdb_len_t len;
 273         enum TDB_ERROR ecode;
 274
 275         assert(len_with_header >= sizeof(struct tdb_free_record));
 276
 277         len = len_with_header - sizeof(struct tdb_used_record);
 278
 279         b_off = bucket_off(tdb->ftable_off, size_to_bucket(len));
 280         ecode = tdb_lock_free_bucket(tdb, b_off, TDB_LOCK_WAIT);
 281         if (ecode != TDB_SUCCESS) {
 282                 return ecode;
 283         }
 284
 285         ecode = enqueue_in_free(tdb, b_off, off, len);
 286         check_list(tdb, b_off);
 287         tdb_unlock_free_bucket(tdb, b_off);
 288         return ecode;
 289 }
 290
 291 static size_t adjust_size(size_t keylen, size_t datalen)
 292 {
 293         size_t size = keylen + datalen;
 294
 295         if (size < TDB_MIN_DATA_LEN)
 296                 size = TDB_MIN_DATA_LEN;
 297
 298         /* Round to next uint64_t boundary. */
 299         return (size + (sizeof(uint64_t) - 1ULL)) & ~(sizeof(uint64_t) - 1ULL);
 300 }
 301
 302 /* If we have enough left over to be useful, split that off. */
 303 static size_t record_leftover(size_t keylen, size_t datalen,
 304                               bool want_extra, size_t total_len)
 305 {
 306         ssize_t leftover;
 307
 308         if (want_extra)
 309                 datalen += datalen / 2;
 310         leftover = total_len - adjust_size(keylen, datalen);
 311
 312         if (leftover < (ssize_t)sizeof(struct tdb_free_record))
 313                 return 0;
 314
 315         return leftover;
 316 }
 317
 318 static tdb_off_t ftable_offset(struct tdb_context *tdb, unsigned int ftable)
 319 {
 320         tdb_off_t off;
 321         unsigned int i;
 322
 323         if (likely(tdb->ftable == ftable))
 324                 return tdb->ftable_off;
 325
 326         off = first_ftable(tdb);
 327         for (i = 0; i < ftable; i++) {
 328                 if (TDB_OFF_IS_ERR(off)) {
 329                         break;
 330                 }
 331                 off = next_ftable(tdb, off);
 332         }
 333         return off;
 334 }
 335
 336 /* Note: we unlock the current bucket if we coalesce or fail. */
 337 static tdb_bool_err coalesce(struct tdb_context *tdb,
 338                              tdb_off_t off, tdb_off_t b_off,
 339                              tdb_len_t data_len)
 340 {
 341         tdb_off_t end;
 342         struct tdb_free_record rec;
 343         enum TDB_ERROR ecode;
 344
 345         add_stat(tdb, alloc_coalesce_tried, 1);
 346         end = off + sizeof(struct tdb_used_record) + data_len;
 347
 348         while (end < tdb->file->map_size) {
 349                 const struct tdb_free_record *r;
 350                 tdb_off_t nb_off;
 351                 unsigned ftable, bucket;
 352
 353                 r = tdb_access_read(tdb, end, sizeof(*r), true);
 354                 if (TDB_PTR_IS_ERR(r)) {
 355                         ecode = TDB_PTR_ERR(r);
 356                         goto err;
 357                 }
 358
 359                 if (frec_magic(r) != TDB_FREE_MAGIC
 360                     || frec_ftable(r) == TDB_FTABLE_NONE) {
 361                         tdb_access_release(tdb, r);
 362                         break;
 363                 }
 364
 365                 ftable = frec_ftable(r);
 366                 bucket = size_to_bucket(frec_len(r));
 367                 nb_off = ftable_offset(tdb, ftable);
 368                 if (TDB_OFF_IS_ERR(nb_off)) {
 369                         tdb_access_release(tdb, r);
 370                         ecode = nb_off;
 371                         goto err;
 372                 }
 373                 nb_off = bucket_off(nb_off, bucket);
 374                 tdb_access_release(tdb, r);
 375
 376                 /* We may be violating lock order here, so best effort. */
 377                 if (tdb_lock_free_bucket(tdb, nb_off, TDB_LOCK_NOWAIT)
 378                     != TDB_SUCCESS) {
 379                         add_stat(tdb, alloc_coalesce_lockfail, 1);
 380                         break;
 381                 }
 382
 383                 /* Now we have lock, re-check. */
 384                 ecode = tdb_read_convert(tdb, end, &rec, sizeof(rec));
 385                 if (ecode != TDB_SUCCESS) {
 386                         tdb_unlock_free_bucket(tdb, nb_off);
 387                         goto err;
 388                 }
 389
 390                 if (unlikely(frec_magic(&rec) != TDB_FREE_MAGIC)) {
 391                         add_stat(tdb, alloc_coalesce_race, 1);
 392                         tdb_unlock_free_bucket(tdb, nb_off);
 393                         break;
 394                 }
 395
 396                 if (unlikely(frec_ftable(&rec) != ftable)
 397                     || unlikely(size_to_bucket(frec_len(&rec)) != bucket)) {
 398                         add_stat(tdb, alloc_coalesce_race, 1);
 399                         tdb_unlock_free_bucket(tdb, nb_off);
 400                         break;
 401                 }
 402
 403                 ecode = remove_from_list(tdb, nb_off, end, &rec);
 404                 check_list(tdb, nb_off);
 405                 if (ecode != TDB_SUCCESS) {
 406                         tdb_unlock_free_bucket(tdb, nb_off);
 407                         goto err;
 408                 }
 409
 410                 end += sizeof(struct tdb_used_record) + frec_len(&rec);
 411                 tdb_unlock_free_bucket(tdb, nb_off);
 412                 add_stat(tdb, alloc_coalesce_num_merged, 1);
 413         }
 414
 415         /* Didn't find any adjacent free? */
 416         if (end == off + sizeof(struct tdb_used_record) + data_len)
 417                 return false;
 418
 419         /* OK, expand initial record */
 420         ecode = tdb_read_convert(tdb, off, &rec, sizeof(rec));
 421         if (ecode != TDB_SUCCESS) {
 422                 goto err;
 423         }
 424
 425         if (frec_len(&rec) != data_len) {
 426                 ecode = tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 427                                    "coalesce: expected data len %zu not %zu",
 428                                    (size_t)data_len, (size_t)frec_len(&rec));
 429                 goto err;
 430         }
 431
 432         ecode = remove_from_list(tdb, b_off, off, &rec);
 433         check_list(tdb, b_off);
 434         if (ecode != TDB_SUCCESS) {
 435                 goto err;
 436         }
 437
 438         /* We have to drop this to avoid deadlocks, so make sure record
 439          * doesn't get coalesced by someone else! */
 440         rec.ftable_and_len = (TDB_FTABLE_NONE << (64 - TDB_OFF_UPPER_STEAL))
 441                 | (end - off - sizeof(struct tdb_used_record));
 442         ecode = tdb_write_off(tdb, off + offsetof(struct tdb_free_record,
 443                                                   ftable_and_len),
 444                               rec.ftable_and_len);
 445         if (ecode != TDB_SUCCESS) {
 446                 goto err;
 447         }
 448
 449         add_stat(tdb, alloc_coalesce_succeeded, 1);
 450         tdb_unlock_free_bucket(tdb, b_off);
 451
 452         ecode = add_free_record(tdb, off, end - off);
 453         if (ecode != TDB_SUCCESS) {
 454                 return ecode;
 455         }
 456         return true;
 457
 458 err:
 459         /* To unify error paths, we *always* unlock bucket on error. */
 460         tdb_unlock_free_bucket(tdb, b_off);
 461         return ecode;
 462 }
 463
 464 /* We need size bytes to put our key and data in. */
 465 static tdb_off_t lock_and_alloc(struct tdb_context *tdb,
 466                                 tdb_off_t ftable_off,
 467                                 tdb_off_t bucket,
 468                                 size_t keylen, size_t datalen,
 469                                 bool want_extra,
 470                                 unsigned magic,
 471                                 unsigned hashlow)
 472 {
 473         tdb_off_t off, b_off,best_off;
 474         struct tdb_free_record best = { 0 };
 475         double multiplier;
 476         size_t size = adjust_size(keylen, datalen);
 477         enum TDB_ERROR ecode;
 478
 479         add_stat(tdb, allocs, 1);
 480 again:
 481         b_off = bucket_off(ftable_off, bucket);
 482
 483         /* FIXME: Try non-blocking wait first, to measure contention. */
 484         /* Lock this bucket. */
 485         ecode = tdb_lock_free_bucket(tdb, b_off, TDB_LOCK_WAIT);
 486         if (ecode != TDB_SUCCESS) {
 487                 return ecode;
 488         }
 489
 490         best.ftable_and_len = -1ULL;
 491         best_off = 0;
 492
 493         /* Get slack if we're after extra. */
 494         if (want_extra)
 495                 multiplier = 1.5;
 496         else
 497                 multiplier = 1.0;
 498
 499         /* Walk the list to see if any are large enough, getting less fussy
 500          * as we go. */
 501         off = tdb_read_off(tdb, b_off);
 502         if (TDB_OFF_IS_ERR(off)) {
 503                 ecode = off;
 504                 goto unlock_err;
 505         }
 506
 507         while (off) {
 508                 const struct tdb_free_record *r;
 509                 tdb_len_t len;
 510                 tdb_off_t next;
 511                 int coal;
 512
 513                 r = tdb_access_read(tdb, off, sizeof(*r), true);
 514                 if (TDB_PTR_IS_ERR(r)) {
 515                         ecode = TDB_PTR_ERR(r);
 516                         goto unlock_err;
 517                 }
 518
 519                 if (frec_magic(r) != TDB_FREE_MAGIC) {
 520                         ecode = tdb_logerr(tdb, TDB_ERR_CORRUPT, TDB_LOG_ERROR,
 521                                            "lock_and_alloc:"
 522                                            " %llu non-free 0x%llx",
 523                                            (long long)off,
 524                                            (long long)r->magic_and_prev);
 525                         tdb_access_release(tdb, r);
 526                         goto unlock_err;
 527                 }
 528
 529                 if (frec_len(r) >= size && frec_len(r) < frec_len(&best)) {
 530                         best_off = off;
 531                         best = *r;
 532                 }
 533
 534                 if (frec_len(&best) <= size * multiplier && best_off) {
 535                         tdb_access_release(tdb, r);
 536                         break;
 537                 }
 538
 539                 multiplier *= 1.01;
 540
 541                 next = r->next;
 542                 len = frec_len(r);
 543                 tdb_access_release(tdb, r);
 544
 545                 /* Since we're going slow anyway, try coalescing here. */
 546                 coal = coalesce(tdb, off, b_off, len);
 547                 if (coal == 1) {
 548                         /* This has unlocked list, restart. */
 549                         goto again;
 550                 }
 551                 if (coal < 0) {
 552                         /* This has already unlocked on error. */
 553                         return coal;
 554                 }
 555                 off = next;
 556         }
 557
 558         /* If we found anything at all, use it. */
 559         if (best_off) {
 560                 struct tdb_used_record rec;
 561                 size_t leftover;
 562
 563                 /* We're happy with this size: take it. */
 564                 ecode = remove_from_list(tdb, b_off, best_off, &best);
 565                 check_list(tdb, b_off);
 566                 if (ecode != TDB_SUCCESS) {
 567                         goto unlock_err;
 568                 }
 569
 570                 leftover = record_leftover(keylen, datalen, want_extra,
 571                                            frec_len(&best));
 572
 573                 assert(keylen + datalen + leftover <= frec_len(&best));
 574                 /* We need to mark non-free before we drop lock, otherwise
 575                  * coalesce() could try to merge it! */
 576                 ecode = set_header(tdb, &rec, magic, keylen, datalen,
 577                                    frec_len(&best) - leftover, hashlow);
 578                 if (ecode != TDB_SUCCESS) {
 579                         goto unlock_err;
 580                 }
 581
 582                 ecode = tdb_write_convert(tdb, best_off, &rec, sizeof(rec));
 583                 if (ecode != TDB_SUCCESS) {
 584                         goto unlock_err;
 585                 }
 586
 587                 /* For futureproofing, we put a 0 in any unused space. */
 588                 if (rec_extra_padding(&rec)) {
 589                         ecode = tdb->methods->twrite(tdb, best_off + sizeof(rec)
 590                                                      + keylen + datalen, "", 1);
 591                         if (ecode != TDB_SUCCESS) {
 592                                 goto unlock_err;
 593                         }
 594                 }
 595
 596                 /* Bucket of leftover will be <= current bucket, so nested
 597                  * locking is allowed. */
 598                 if (leftover) {
 599                         add_stat(tdb, alloc_leftover, 1);
 600                         ecode = add_free_record(tdb,
 601                                                 best_off + sizeof(rec)
 602                                                 + frec_len(&best) - leftover,
 603                                                 leftover);
 604                         if (ecode != TDB_SUCCESS) {
 605                                 best_off = ecode;
 606                         }
 607                 }
 608                 tdb_unlock_free_bucket(tdb, b_off);
 609
 610                 return best_off;
 611         }
 612
 613         tdb_unlock_free_bucket(tdb, b_off);
 614         return 0;
 615
 616 unlock_err:
 617         tdb_unlock_free_bucket(tdb, b_off);
 618         return ecode;
 619 }
 620
 621 /* Get a free block from current free list, or 0 if none, -ve on error. */
 622 static tdb_off_t get_free(struct tdb_context *tdb,
 623                           size_t keylen, size_t datalen, bool want_extra,
 624                           unsigned magic, unsigned hashlow)
 625 {
 626         tdb_off_t off, ftable_off;
 627         tdb_off_t start_b, b, ftable;
 628         bool wrapped = false;
 629
 630         /* If they are growing, add 50% to get to higher bucket. */
 631         if (want_extra)
 632                 start_b = size_to_bucket(adjust_size(keylen,
 633                                                      datalen + datalen / 2));
 634         else
 635                 start_b = size_to_bucket(adjust_size(keylen, datalen));
 636
 637         ftable_off = tdb->ftable_off;
 638         ftable = tdb->ftable;
 639         while (!wrapped || ftable_off != tdb->ftable_off) {
 640                 /* Start at exact size bucket, and search up... */
 641                 for (b = find_free_head(tdb, ftable_off, start_b);
 642                      b < TDB_FREE_BUCKETS;
 643                      b = find_free_head(tdb, ftable_off, b + 1)) {
 644                         /* Try getting one from list. */
 645                         off = lock_and_alloc(tdb, ftable_off,
 646                                              b, keylen, datalen, want_extra,
 647                                              magic, hashlow);
 648                         if (TDB_OFF_IS_ERR(off))
 649                                 return off;
 650                         if (off != 0) {
 651                                 if (b == start_b)
 652                                         add_stat(tdb, alloc_bucket_exact, 1);
 653                                 if (b == TDB_FREE_BUCKETS - 1)
 654                                         add_stat(tdb, alloc_bucket_max, 1);
 655                                 /* Worked?  Stay using this list. */
 656                                 tdb->ftable_off = ftable_off;
 657                                 tdb->ftable = ftable;
 658                                 return off;
 659                         }
 660                         /* Didn't work.  Try next bucket. */
 661                 }
 662
 663                 if (TDB_OFF_IS_ERR(b)) {
 664                         return b;
 665                 }
 666
 667                 /* Hmm, try next table. */
 668                 ftable_off = next_ftable(tdb, ftable_off);
 669                 if (TDB_OFF_IS_ERR(ftable_off)) {
 670                         return ftable_off;
 671                 }
 672                 ftable++;
 673
 674                 if (ftable_off == 0) {
 675                         wrapped = true;
 676                         ftable_off = first_ftable(tdb);
 677                         if (TDB_OFF_IS_ERR(ftable_off)) {
 678                                 return ftable_off;
 679                         }
 680                         ftable = 0;
 681                 }
 682         }
 683
 684         return 0;
 685 }
 686
 687 enum TDB_ERROR set_header(struct tdb_context *tdb,
 688                           struct tdb_used_record *rec,
 689                           unsigned magic, uint64_t keylen, uint64_t datalen,
 690                           uint64_t actuallen, unsigned hashlow)
 691 {
 692         uint64_t keybits = (fls64(keylen) + 1) / 2;
 693
 694         /* Use bottom bits of hash, so it's independent of hash table size. */
 695         rec->magic_and_meta = (hashlow & ((1 << 11)-1))
 696                 | ((actuallen - (keylen + datalen)) << 11)
 697                 | (keybits << 43)
 698                 | ((uint64_t)magic << 48);
 699         rec->key_and_data_len = (keylen | (datalen << (keybits*2)));
 700
 701         /* Encoding can fail on big values. */
 702         if (rec_key_length(rec) != keylen
 703             || rec_data_length(rec) != datalen
 704             || rec_extra_padding(rec) != actuallen - (keylen + datalen)) {
 705                 return tdb_logerr(tdb, TDB_ERR_IO, TDB_LOG_ERROR,
 706                                   "Could not encode k=%llu,d=%llu,a=%llu",
 707                                   (long long)keylen, (long long)datalen,
 708                                   (long long)actuallen);
 709         }
 710         return TDB_SUCCESS;
 711 }
 712
 713 /* Expand the database. */
 714 static enum TDB_ERROR tdb_expand(struct tdb_context *tdb, tdb_len_t size)
 715 {
 716         uint64_t old_size;
 717         tdb_len_t wanted;
 718         enum TDB_ERROR ecode;
 719
 720         /* We need room for the record header too. */
 721         wanted = sizeof(struct tdb_used_record) + size;
 722
 723         /* Need to hold a hash lock to expand DB: transactions rely on it. */
 724         if (!(tdb->flags & TDB_NOLOCK)
 725             && !tdb->file->allrecord_lock.count && !tdb_has_hash_locks(tdb)) {
 726                 return tdb_logerr(tdb, TDB_ERR_LOCK, TDB_LOG_ERROR,
 727                                   "tdb_expand: must hold lock during expand");
 728         }
 729
 730         /* always make room for at least 100 more records, and at
 731            least 25% more space. */
 732         if (size * TDB_EXTENSION_FACTOR > tdb->file->map_size / 4)
 733                 wanted = size * TDB_EXTENSION_FACTOR;
 734         else
 735                 wanted = tdb->file->map_size / 4;
 736         wanted = adjust_size(0, wanted);
 737
 738         /* Only one person can expand file at a time. */
 739         ecode = tdb_lock_expand(tdb, F_WRLCK);
 740         if (ecode != TDB_SUCCESS) {
 741                 return ecode;
 742         }
 743
 744         /* Someone else may have expanded the file, so retry. */
 745         old_size = tdb->file->map_size;
 746         tdb->methods->oob(tdb, tdb->file->map_size + 1, true);
 747         if (tdb->file->map_size != old_size) {
 748                 tdb_unlock_expand(tdb, F_WRLCK);
 749                 return TDB_SUCCESS;
 750         }
 751
 752         ecode = tdb->methods->expand_file(tdb, wanted);
 753         if (ecode != TDB_SUCCESS) {
 754                 tdb_unlock_expand(tdb, F_WRLCK);
 755                 return ecode;
 756         }
 757
 758         /* We need to drop this lock before adding free record. */
 759         tdb_unlock_expand(tdb, F_WRLCK);
 760
 761         add_stat(tdb, expands, 1);
 762         return add_free_record(tdb, old_size, wanted);
 763 }
 764
 765 /* This won't fail: it will expand the database if it has to. */
 766 tdb_off_t alloc(struct tdb_context *tdb, size_t keylen, size_t datalen,
 767                 uint64_t hash, unsigned magic, bool growing)
 768 {
 769         tdb_off_t off;
 770
 771         /* We can't hold pointers during this: we could unmap! */
 772         assert(!tdb->direct_access);
 773
 774         for (;;) {
 775                 enum TDB_ERROR ecode;
 776                 off = get_free(tdb, keylen, datalen, growing, magic, hash);
 777                 if (likely(off != 0))
 778                         break;
 779
 780                 ecode = tdb_expand(tdb, adjust_size(keylen, datalen));
 781                 if (ecode != TDB_SUCCESS) {
 782                         return ecode;
 783                 }
 784         }
 785
 786         return off;
 787 }