lib/ntdb/hash.c

   1  /*
   2    Trivial Database 2: hash 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/hash/hash.h>
  20
  21 /* Default hash function. */
  22 uint32_t ntdb_jenkins_hash(const void *key, size_t length, uint32_t seed,
  23                           void *unused)
  24 {
  25         return hash_stable((const unsigned char *)key, length, seed);
  26 }
  27
  28 uint32_t ntdb_hash(struct ntdb_context *ntdb, const void *ptr, size_t len)
  29 {
  30         return ntdb->hash_fn(ptr, len, ntdb->hash_seed, ntdb->hash_data);
  31 }
  32
  33 static ntdb_bool_err key_matches(struct ntdb_context *ntdb,
  34                                  const struct ntdb_used_record *rec,
  35                                  ntdb_off_t off,
  36                                  const NTDB_DATA *key,
  37                                  const char **rptr)
  38 {
  39         ntdb_bool_err ret = false;
  40         const char *rkey;
  41
  42         if (rec_key_length(rec) != key->dsize) {
  43                 ntdb->stats.compare_wrong_keylen++;
  44                 return ret;
  45         }
  46
  47         rkey = ntdb_access_read(ntdb, off + sizeof(*rec),
  48                                 key->dsize + rec_data_length(rec), false);
  49         if (NTDB_PTR_IS_ERR(rkey)) {
  50                 return (ntdb_bool_err)NTDB_PTR_ERR(rkey);
  51         }
  52         if (memcmp(rkey, key->dptr, key->dsize) == 0) {
  53                 if (rptr) {
  54                         *rptr = rkey;
  55                 } else {
  56                         ntdb_access_release(ntdb, rkey);
  57                 }
  58                 return true;
  59         }
  60         ntdb->stats.compare_wrong_keycmp++;
  61         ntdb_access_release(ntdb, rkey);
  62         return ret;
  63 }
  64
  65 /* Does entry match? */
  66 static ntdb_bool_err match(struct ntdb_context *ntdb,
  67                            uint32_t hash,
  68                            const NTDB_DATA *key,
  69                            ntdb_off_t val,
  70                            struct ntdb_used_record *rec,
  71                            const char **rptr,
  72                            const ntdb_off_t **mapped)
  73 {
  74         ntdb_off_t off;
  75         enum NTDB_ERROR ecode;
  76
  77         ntdb->stats.compares++;
  78
  79         /* Top bits of offset == next bits of hash. */
  80         if (bits_from(hash, ntdb->hash_bits, NTDB_OFF_UPPER_STEAL)
  81             != bits_from(val, 64-NTDB_OFF_UPPER_STEAL, NTDB_OFF_UPPER_STEAL)) {
  82                 ntdb->stats.compare_wrong_offsetbits++;
  83                 return false;
  84         }
  85
  86         /* Unmap before we try to read actual record, which may cause expand */
  87         if (mapped) {
  88                 ntdb_access_release(ntdb, *mapped);
  89                 *mapped = NULL;
  90         }
  91
  92         off = val & NTDB_OFF_MASK;
  93         ecode = ntdb_read_convert(ntdb, off, rec, sizeof(*rec));
  94         if (ecode != NTDB_SUCCESS) {
  95                 return (ntdb_bool_err)ecode;
  96         }
  97
  98         return key_matches(ntdb, rec, off, key, rptr);
  99 }
 100
 101 static bool is_chain(ntdb_off_t val)
 102 {
 103         return val & (1ULL << NTDB_OFF_CHAIN_BIT);
 104 }
 105
 106 static ntdb_off_t hbucket_off(ntdb_off_t base, ntdb_len_t idx)
 107 {
 108         return base + sizeof(struct ntdb_used_record)
 109                 + idx * sizeof(ntdb_off_t);
 110 }
 111
 112 /* This is the core routine which searches the hashtable for an entry.
 113  * On error, no locks are held and -ve is returned.
 114  * Otherwise, hinfo is filled in.
 115  * If not found, the return value is 0.
 116  * If found, the return value is the offset, and *rec is the record. */
 117 ntdb_off_t find_and_lock(struct ntdb_context *ntdb,
 118                          NTDB_DATA key,
 119                          int ltype,
 120                          struct hash_info *h,
 121                          struct ntdb_used_record *rec,
 122                          const char **rptr)
 123 {
 124         ntdb_off_t off, val;
 125         const ntdb_off_t *arr = NULL;
 126         ntdb_len_t i;
 127         bool found_empty;
 128         enum NTDB_ERROR ecode;
 129         struct ntdb_used_record chdr;
 130         ntdb_bool_err berr;
 131
 132         h->h = ntdb_hash(ntdb, key.dptr, key.dsize);
 133
 134         h->table = NTDB_HASH_OFFSET;
 135         h->table_size = 1 << ntdb->hash_bits;
 136         h->bucket = bits_from(h->h, 0, ntdb->hash_bits);
 137         h->old_val = 0;
 138
 139         ecode = ntdb_lock_hash(ntdb, h->bucket, ltype);
 140         if (ecode != NTDB_SUCCESS) {
 141                 return NTDB_ERR_TO_OFF(ecode);
 142         }
 143
 144         off = hbucket_off(h->table, h->bucket);
 145         val = ntdb_read_off(ntdb, off);
 146         if (NTDB_OFF_IS_ERR(val)) {
 147                 ecode = NTDB_OFF_TO_ERR(val);
 148                 goto fail;
 149         }
 150
 151         /* Directly in hash table? */
 152         if (!likely(is_chain(val))) {
 153                 if (val) {
 154                         berr = match(ntdb, h->h, &key, val, rec, rptr, NULL);
 155                         if (berr < 0) {
 156                                 ecode = NTDB_OFF_TO_ERR(berr);
 157                                 goto fail;
 158                         }
 159                         if (berr) {
 160                                 return val & NTDB_OFF_MASK;
 161                         }
 162                         /* If you want to insert here, make a chain. */
 163                         h->old_val = val;
 164                 }
 165                 return 0;
 166         }
 167
 168         /* Nope?  Iterate through chain. */
 169         h->table = val & NTDB_OFF_MASK;
 170
 171         ecode = ntdb_read_convert(ntdb, h->table, &chdr, sizeof(chdr));
 172         if (ecode != NTDB_SUCCESS) {
 173                 goto fail;
 174         }
 175
 176         if (rec_magic(&chdr) != NTDB_CHAIN_MAGIC) {
 177                 ecode = ntdb_logerr(ntdb, NTDB_ERR_CORRUPT,
 178                                     NTDB_LOG_ERROR,
 179                                     "find_and_lock:"
 180                                     " corrupt record %#x at %llu",
 181                                     rec_magic(&chdr), (long long)off);
 182                 goto fail;
 183         }
 184
 185         h->table_size = rec_data_length(&chdr) / sizeof(ntdb_off_t);
 186
 187         found_empty = false;
 188         for (i = 0; i < h->table_size; i++) {
 189                 /* Careful!  match has to unmap this if we access a
 190                  * record (may cause mmap of database to move. */
 191                 if (!arr) {
 192                         arr = ntdb_access_read(ntdb, hbucket_off(h->table, 0),
 193                                                rec_data_length(&chdr), true);
 194                         if (NTDB_PTR_IS_ERR(arr)) {
 195                                 ecode = NTDB_PTR_ERR(arr);
 196                                 goto fail;
 197                         }
 198                 }
 199
 200                 val = arr[i];
 201                 if (val == 0) {
 202                         if (!found_empty) {
 203                                 h->bucket = i;
 204                                 found_empty = true;
 205                         }
 206                 } else {
 207                         berr = match(ntdb, h->h, &key, val, rec, rptr, &arr);
 208                         if (berr < 0) {
 209                                 ecode = NTDB_OFF_TO_ERR(berr);
 210                                 if (arr) {
 211                                         ntdb_access_release(ntdb, arr);
 212                                 }
 213                                 goto fail;
 214                         }
 215                         if (berr) {
 216                                 /* We found it! */
 217                                 h->bucket = i;
 218                                 off = val & NTDB_OFF_MASK;
 219                                 if (arr) {
 220                                         ntdb_access_release(ntdb, arr);
 221                                 }
 222                                 return off;
 223                         }
 224                 }
 225         }
 226         if (!found_empty) {
 227                 /* Set to any non-zero value */
 228                 h->old_val = 1;
 229                 h->bucket = i;
 230         }
 231
 232         if (arr) {
 233                 ntdb_access_release(ntdb, arr);
 234         }
 235         return 0;
 236
 237 fail:
 238         ntdb_unlock_hash(ntdb, h->bucket, ltype);
 239         return NTDB_ERR_TO_OFF(ecode);
 240 }
 241
 242 static ntdb_off_t encode_offset(const struct ntdb_context *ntdb,
 243                                 ntdb_off_t new_off, uint32_t hash)
 244 {
 245         ntdb_off_t extra;
 246
 247         assert((new_off & (1ULL << NTDB_OFF_CHAIN_BIT)) == 0);
 248         assert((new_off >> (64 - NTDB_OFF_UPPER_STEAL)) == 0);
 249         /* We pack extra hash bits into the upper bits of the offset. */
 250         extra = bits_from(hash, ntdb->hash_bits, NTDB_OFF_UPPER_STEAL);
 251         extra <<= (64 - NTDB_OFF_UPPER_STEAL);
 252
 253         return new_off | extra;
 254 }
 255
 256 /* Simply overwrite the hash entry we found before. */
 257 enum NTDB_ERROR replace_in_hash(struct ntdb_context *ntdb,
 258                                 const struct hash_info *h,
 259                                 ntdb_off_t new_off)
 260 {
 261         return ntdb_write_off(ntdb, hbucket_off(h->table, h->bucket),
 262                               encode_offset(ntdb, new_off, h->h));
 263 }
 264
 265 enum NTDB_ERROR delete_from_hash(struct ntdb_context *ntdb,
 266                                  const struct hash_info *h)
 267 {
 268         return ntdb_write_off(ntdb, hbucket_off(h->table, h->bucket), 0);
 269 }
 270
 271
 272 enum NTDB_ERROR add_to_hash(struct ntdb_context *ntdb,
 273                             const struct hash_info *h,
 274                             ntdb_off_t new_off)
 275 {
 276         enum NTDB_ERROR ecode;
 277         ntdb_off_t chain;
 278         struct ntdb_used_record chdr;
 279         const ntdb_off_t *old;
 280         ntdb_off_t *new;
 281
 282         /* We hit an empty bucket during search?  That's where it goes. */
 283         if (!h->old_val) {
 284                 return replace_in_hash(ntdb, h, new_off);
 285         }
 286
 287         /* Full at top-level?  Create a 2-element chain. */
 288         if (h->table == NTDB_HASH_OFFSET) {
 289                 ntdb_off_t pair[2];
 290
 291                 /* One element is old value, the other is the new value. */
 292                 pair[0] = h->old_val;
 293                 pair[1] = encode_offset(ntdb, new_off, h->h);
 294
 295                 chain = alloc(ntdb, 0, sizeof(pair), NTDB_CHAIN_MAGIC, true);
 296                 if (NTDB_OFF_IS_ERR(chain)) {
 297                         return NTDB_OFF_TO_ERR(chain);
 298                 }
 299                 ecode = ntdb_write_convert(ntdb,
 300                                            chain
 301                                            + sizeof(struct ntdb_used_record),
 302                                            pair, sizeof(pair));
 303                 if (ecode == NTDB_SUCCESS) {
 304                         ecode = ntdb_write_off(ntdb,
 305                                                hbucket_off(h->table, h->bucket),
 306                                                chain
 307                                                | (1ULL << NTDB_OFF_CHAIN_BIT));
 308                 }
 309                 return ecode;
 310         }
 311
 312         /* Full bucket.  Expand. */
 313         ecode = ntdb_read_convert(ntdb, h->table, &chdr, sizeof(chdr));
 314         if (ecode != NTDB_SUCCESS) {
 315                 return ecode;
 316         }
 317
 318         if (rec_extra_padding(&chdr) >= sizeof(new_off)) {
 319                 /* Expand in place. */
 320                 uint64_t dlen = rec_data_length(&chdr);
 321
 322                 ecode = set_header(ntdb, &chdr, NTDB_CHAIN_MAGIC, 0,
 323                                    dlen + sizeof(new_off),
 324                                    dlen + rec_extra_padding(&chdr));
 325
 326                 if (ecode != NTDB_SUCCESS) {
 327                         return ecode;
 328                 }
 329                 /* find_and_lock set up h to point to last bucket. */
 330                 ecode = replace_in_hash(ntdb, h, new_off);
 331                 if (ecode != NTDB_SUCCESS) {
 332                         return ecode;
 333                 }
 334                 ecode = ntdb_write_convert(ntdb, h->table, &chdr, sizeof(chdr));
 335                 if (ecode != NTDB_SUCCESS) {
 336                         return ecode;
 337                 }
 338                 /* For futureproofing, we always make the first byte of padding
 339                  * a zero. */
 340                 if (rec_extra_padding(&chdr)) {
 341                         ecode = ntdb->io->twrite(ntdb, h->table + sizeof(chdr)
 342                                                  + dlen + sizeof(new_off),
 343                                                  "", 1);
 344                 }
 345                 return ecode;
 346         }
 347
 348         /* We need to reallocate the chain. */
 349         chain = alloc(ntdb, 0, (h->table_size + 1) * sizeof(ntdb_off_t),
 350                       NTDB_CHAIN_MAGIC, true);
 351         if (NTDB_OFF_IS_ERR(chain)) {
 352                 return NTDB_OFF_TO_ERR(chain);
 353         }
 354
 355         /* Map both and copy across old buckets. */
 356         old = ntdb_access_read(ntdb, hbucket_off(h->table, 0),
 357                                h->table_size*sizeof(ntdb_off_t), true);
 358         if (NTDB_PTR_IS_ERR(old)) {
 359                 return NTDB_PTR_ERR(old);
 360         }
 361         new = ntdb_access_write(ntdb, hbucket_off(chain, 0),
 362                                 (h->table_size + 1)*sizeof(ntdb_off_t), true);
 363         if (NTDB_PTR_IS_ERR(new)) {
 364                 ntdb_access_release(ntdb, old);
 365                 return NTDB_PTR_ERR(new);
 366         }
 367
 368         memcpy(new, old, h->bucket * sizeof(ntdb_off_t));
 369         new[h->bucket] = encode_offset(ntdb, new_off, h->h);
 370         ntdb_access_release(ntdb, old);
 371
 372         ecode = ntdb_access_commit(ntdb, new);
 373         if (ecode != NTDB_SUCCESS) {
 374                 return ecode;
 375         }
 376
 377         /* Free the old chain. */
 378         ecode = add_free_record(ntdb, h->table,
 379                                 sizeof(struct ntdb_used_record)
 380                                 + rec_data_length(&chdr)
 381                                 + rec_extra_padding(&chdr),
 382                                 NTDB_LOCK_WAIT, true);
 383
 384         /* Replace top-level to point to new chain */
 385         return ntdb_write_off(ntdb,
 386                               hbucket_off(NTDB_HASH_OFFSET,
 387                                           bits_from(h->h, 0, ntdb->hash_bits)),
 388                               chain | (1ULL << NTDB_OFF_CHAIN_BIT));
 389 }
 390
 391 /* Traverse support: returns offset of record, or 0 or -ve error. */
 392 static ntdb_off_t iterate_chain(struct ntdb_context *ntdb,
 393                                 ntdb_off_t val,
 394                                 struct hash_info *h)
 395 {
 396         ntdb_off_t i;
 397         enum NTDB_ERROR ecode;
 398         struct ntdb_used_record chdr;
 399
 400         /* First load up chain header. */
 401         h->table = val & NTDB_OFF_MASK;
 402         ecode = ntdb_read_convert(ntdb, h->table, &chdr, sizeof(chdr));
 403         if (ecode != NTDB_SUCCESS) {
 404                 return ecode;
 405         }
 406
 407         if (rec_magic(&chdr) != NTDB_CHAIN_MAGIC) {
 408                 return ntdb_logerr(ntdb, NTDB_ERR_CORRUPT,
 409                                    NTDB_LOG_ERROR,
 410                                    "get_table:"
 411                                    " corrupt record %#x at %llu",
 412                                    rec_magic(&chdr),
 413                                    (long long)h->table);
 414         }
 415
 416         /* Chain length is implied by data length. */
 417         h->table_size = rec_data_length(&chdr) / sizeof(ntdb_off_t);
 418
 419         i = ntdb_find_nonzero_off(ntdb, hbucket_off(h->table, 0), h->bucket,
 420                                   h->table_size);
 421         if (NTDB_OFF_IS_ERR(i)) {
 422                 return i;
 423         }
 424
 425         if (i != h->table_size) {
 426                 /* Return to next bucket. */
 427                 h->bucket = i + 1;
 428                 val = ntdb_read_off(ntdb, hbucket_off(h->table, i));
 429                 if (NTDB_OFF_IS_ERR(val)) {
 430                         return val;
 431                 }
 432                 return val & NTDB_OFF_MASK;
 433         }
 434
 435         /* Go back up to hash table. */
 436         h->table = NTDB_HASH_OFFSET;
 437         h->table_size = 1 << ntdb->hash_bits;
 438         h->bucket = bits_from(h->h, 0, ntdb->hash_bits) + 1;
 439         return 0;
 440 }
 441
 442 /* Keeps hash locked unless returns 0 or error. */
 443 static ntdb_off_t lock_and_iterate_hash(struct ntdb_context *ntdb,
 444                                         struct hash_info *h)
 445 {
 446         ntdb_off_t val, i;
 447         enum NTDB_ERROR ecode;
 448
 449         if (h->table != NTDB_HASH_OFFSET) {
 450                 /* We're in a chain. */
 451                 i = bits_from(h->h, 0, ntdb->hash_bits);
 452                 ecode = ntdb_lock_hash(ntdb, i, F_RDLCK);
 453                 if (ecode != NTDB_SUCCESS) {
 454                         return NTDB_ERR_TO_OFF(ecode);
 455                 }
 456
 457                 /* We dropped lock, bucket might have moved! */
 458                 val = ntdb_read_off(ntdb, hbucket_off(NTDB_HASH_OFFSET, i));
 459                 if (NTDB_OFF_IS_ERR(val)) {
 460                         goto unlock;
 461                 }
 462
 463                 /* We don't remove chains: there should still be one there! */
 464                 if (!val || !is_chain(val)) {
 465                         ecode = ntdb_logerr(ntdb, NTDB_ERR_CORRUPT,
 466                                             NTDB_LOG_ERROR,
 467                                             "iterate_hash:"
 468                                             " vanished hchain %llu at %llu",
 469                                             (long long)val,
 470                                             (long long)i);
 471                         val = NTDB_ERR_TO_OFF(ecode);
 472                         goto unlock;
 473                 }
 474
 475                 /* Find next bucket in the chain. */
 476                 val = iterate_chain(ntdb, val, h);
 477                 if (NTDB_OFF_IS_ERR(val)) {
 478                         goto unlock;
 479                 }
 480                 if (val != 0) {
 481                         return val;
 482                 }
 483                 ntdb_unlock_hash(ntdb, i, F_RDLCK);
 484
 485                 /* OK, we've reset h back to top level. */
 486         }
 487
 488         /* We do this unlocked, then re-check. */
 489         for (i = ntdb_find_nonzero_off(ntdb, hbucket_off(h->table, 0),
 490                                        h->bucket, h->table_size);
 491              i != h->table_size;
 492              i = ntdb_find_nonzero_off(ntdb, hbucket_off(h->table, 0),
 493                                        i+1, h->table_size)) {
 494                 ecode = ntdb_lock_hash(ntdb, i, F_RDLCK);
 495                 if (ecode != NTDB_SUCCESS) {
 496                         return NTDB_ERR_TO_OFF(ecode);
 497                 }
 498
 499                 val = ntdb_read_off(ntdb, hbucket_off(h->table, i));
 500                 if (NTDB_OFF_IS_ERR(val)) {
 501                         goto unlock;
 502                 }
 503
 504                 /* Lost race, and it's empty? */
 505                 if (!val) {
 506                         ntdb->stats.traverse_val_vanished++;
 507                         ntdb_unlock_hash(ntdb, i, F_RDLCK);
 508                         continue;
 509                 }
 510
 511                 if (!is_chain(val)) {
 512                         /* So caller knows what lock to free. */
 513                         h->h = i;
 514                         /* Return to next bucket. */
 515                         h->bucket = i + 1;
 516                         val &= NTDB_OFF_MASK;
 517                         return val;
 518                 }
 519
 520                 /* Start at beginning of chain */
 521                 h->bucket = 0;
 522                 h->h = i;
 523
 524                 val = iterate_chain(ntdb, val, h);
 525                 if (NTDB_OFF_IS_ERR(val)) {
 526                         goto unlock;
 527                 }
 528                 if (val != 0) {
 529                         return val;
 530                 }
 531
 532                 /* Otherwise, bucket has been set to i+1 */
 533                 ntdb_unlock_hash(ntdb, i, F_RDLCK);
 534         }
 535         return 0;
 536
 537 unlock:
 538         ntdb_unlock_hash(ntdb, i, F_RDLCK);
 539         return val;
 540 }
 541
 542 /* Return success if we find something, NTDB_ERR_NOEXIST if none. */
 543 enum NTDB_ERROR next_in_hash(struct ntdb_context *ntdb,
 544                              struct hash_info *h,
 545                              NTDB_DATA *kbuf, size_t *dlen)
 546 {
 547         ntdb_off_t off;
 548         struct ntdb_used_record rec;
 549         enum NTDB_ERROR ecode;
 550
 551         off = lock_and_iterate_hash(ntdb, h);
 552
 553         if (NTDB_OFF_IS_ERR(off)) {
 554                 return NTDB_OFF_TO_ERR(off);
 555         } else if (off == 0) {
 556                 return NTDB_ERR_NOEXIST;
 557         }
 558
 559         /* The hash for this key is still locked. */
 560         ecode = ntdb_read_convert(ntdb, off, &rec, sizeof(rec));
 561         if (ecode != NTDB_SUCCESS) {
 562                 goto unlock;
 563         }
 564         if (rec_magic(&rec) != NTDB_USED_MAGIC) {
 565                 ecode = ntdb_logerr(ntdb, NTDB_ERR_CORRUPT,
 566                                     NTDB_LOG_ERROR,
 567                                     "next_in_hash:"
 568                                     " corrupt record at %llu",
 569                                     (long long)off);
 570                 goto unlock;
 571         }
 572
 573         kbuf->dsize = rec_key_length(&rec);
 574
 575         /* They want data as well? */
 576         if (dlen) {
 577                 *dlen = rec_data_length(&rec);
 578                 kbuf->dptr = ntdb_alloc_read(ntdb, off + sizeof(rec),
 579                                              kbuf->dsize + *dlen);
 580         } else {
 581                 kbuf->dptr = ntdb_alloc_read(ntdb, off + sizeof(rec),
 582                                              kbuf->dsize);
 583         }
 584         if (NTDB_PTR_IS_ERR(kbuf->dptr)) {
 585                 ecode = NTDB_PTR_ERR(kbuf->dptr);
 586                 goto unlock;
 587         }
 588         ecode = NTDB_SUCCESS;
 589
 590 unlock:
 591         ntdb_unlock_hash(ntdb, bits_from(h->h, 0, ntdb->hash_bits), F_RDLCK);
 592         return ecode;
 593
 594 }
 595
 596 enum NTDB_ERROR first_in_hash(struct ntdb_context *ntdb,
 597                              struct hash_info *h,
 598                              NTDB_DATA *kbuf, size_t *dlen)
 599 {
 600         h->table = NTDB_HASH_OFFSET;
 601         h->table_size = 1 << ntdb->hash_bits;
 602         h->bucket = 0;
 603
 604         return next_in_hash(ntdb, h, kbuf, dlen);
 605 }
 606
 607 /* Even if the entry isn't in this hash bucket, you'd have to lock this
 608  * bucket to find it. */
 609 static enum NTDB_ERROR chainlock(struct ntdb_context *ntdb,
 610                                  const NTDB_DATA *key, int ltype)
 611 {
 612         uint32_t h = ntdb_hash(ntdb, key->dptr, key->dsize);
 613
 614         return ntdb_lock_hash(ntdb, bits_from(h, 0, ntdb->hash_bits), ltype);
 615 }
 616
 617 /* lock/unlock one hash chain. This is meant to be used to reduce
 618    contention - it cannot guarantee how many records will be locked */
 619 _PUBLIC_ enum NTDB_ERROR ntdb_chainlock(struct ntdb_context *ntdb, NTDB_DATA key)
 620 {
 621         return chainlock(ntdb, &key, F_WRLCK);
 622 }
 623
 624 _PUBLIC_ void ntdb_chainunlock(struct ntdb_context *ntdb, NTDB_DATA key)
 625 {
 626         uint32_t h = ntdb_hash(ntdb, key.dptr, key.dsize);
 627
 628         ntdb_unlock_hash(ntdb, bits_from(h, 0, ntdb->hash_bits), F_WRLCK);
 629 }
 630
 631 _PUBLIC_ enum NTDB_ERROR ntdb_chainlock_read(struct ntdb_context *ntdb,
 632                                              NTDB_DATA key)
 633 {
 634         return chainlock(ntdb, &key, F_RDLCK);
 635 }
 636
 637 _PUBLIC_ void ntdb_chainunlock_read(struct ntdb_context *ntdb, NTDB_DATA key)
 638 {
 639         uint32_t h = ntdb_hash(ntdb, key.dptr, key.dsize);
 640
 641         ntdb_unlock_hash(ntdb, bits_from(h, 0, ntdb->hash_bits), F_RDLCK);
 642 }