git.ozlabs.org Git - ccan/blob - ccan/tdb2/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 <assert.h>
  20 #include <ccan/hash/hash.h>
  21
  22 static uint64_t jenkins_hash(const void *key, size_t length, uint64_t seed,
  23                              void *arg)
  24 {
  25         uint64_t ret;
  26         /* hash64_stable assumes lower bits are more important; they are a
  27          * slightly better hash.  We use the upper bits first, so swap them. */
  28         ret = hash64_stable((const unsigned char *)key, length, seed);
  29         return (ret >> 32) | (ret << 32);
  30 }
  31
  32 void tdb_hash_init(struct tdb_context *tdb)
  33 {
  34         tdb->khash = jenkins_hash;
  35         tdb->hash_priv = NULL;
  36 }
  37
  38 uint64_t tdb_hash(struct tdb_context *tdb, const void *ptr, size_t len)
  39 {
  40         return tdb->khash(ptr, len, tdb->hash_seed, tdb->hash_priv);
  41 }
  42
  43 uint64_t hash_record(struct tdb_context *tdb, tdb_off_t off)
  44 {
  45         const struct tdb_used_record *r;
  46         const void *key;
  47         uint64_t klen, hash;
  48
  49         r = tdb_access_read(tdb, off, sizeof(*r), true);
  50         if (!r)
  51                 /* FIXME */
  52                 return 0;
  53
  54         klen = rec_key_length(r);
  55         tdb_access_release(tdb, r);
  56
  57         key = tdb_access_read(tdb, off + sizeof(*r), klen, false);
  58         if (!key)
  59                 return 0;
  60
  61         hash = tdb_hash(tdb, key, klen);
  62         tdb_access_release(tdb, key);
  63         return hash;
  64 }
  65
  66 /* Get bits from a value. */
  67 static uint32_t bits(uint64_t val, unsigned start, unsigned num)
  68 {
  69         assert(num <= 32);
  70         return (val >> start) & ((1U << num) - 1);
  71 }
  72
  73 /* We take bits from the top: that way we can lock whole sections of the hash
  74  * by using lock ranges. */
  75 static uint32_t use_bits(struct hash_info *h, unsigned num)
  76 {
  77         h->hash_used += num;
  78         return bits(h->h, 64 - h->hash_used, num);
  79 }
  80
  81 static bool key_matches(struct tdb_context *tdb,
  82                         const struct tdb_used_record *rec,
  83                         tdb_off_t off,
  84                         const struct tdb_data *key)
  85 {
  86         bool ret = false;
  87         const char *rkey;
  88
  89         if (rec_key_length(rec) != key->dsize) {
  90                 add_stat(tdb, compare_wrong_keylen, 1);
  91                 return ret;
  92         }
  93
  94         rkey = tdb_access_read(tdb, off + sizeof(*rec), key->dsize, false);
  95         if (!rkey)
  96                 return ret;
  97         if (memcmp(rkey, key->dptr, key->dsize) == 0)
  98                 ret = true;
  99         else
 100                 add_stat(tdb, compare_wrong_keycmp, 1);
 101         tdb_access_release(tdb, rkey);
 102         return ret;
 103 }
 104
 105 /* Does entry match? */
 106 static bool match(struct tdb_context *tdb,
 107                   struct hash_info *h,
 108                   const struct tdb_data *key,
 109                   tdb_off_t val,
 110                   struct tdb_used_record *rec)
 111 {
 112         tdb_off_t off;
 113
 114         add_stat(tdb, compares, 1);
 115         /* Desired bucket must match. */
 116         if (h->home_bucket != (val & TDB_OFF_HASH_GROUP_MASK)) {
 117                 add_stat(tdb, compare_wrong_bucket, 1);
 118                 return false;
 119         }
 120
 121         /* Top bits of offset == next bits of hash. */
 122         if (bits(val, TDB_OFF_HASH_EXTRA_BIT, TDB_OFF_UPPER_STEAL_EXTRA)
 123             != bits(h->h, 64 - h->hash_used - TDB_OFF_UPPER_STEAL_EXTRA,
 124                     TDB_OFF_UPPER_STEAL_EXTRA)) {
 125                 add_stat(tdb, compare_wrong_offsetbits, 1);
 126                 return false;
 127         }
 128
 129         off = val & TDB_OFF_MASK;
 130         if (tdb_read_convert(tdb, off, rec, sizeof(*rec)) == -1)
 131                 return false;
 132
 133         if ((h->h & ((1 << 11)-1)) != rec_hash(rec)) {
 134                 add_stat(tdb, compare_wrong_rechash, 1);
 135                 return false;
 136         }
 137
 138         return key_matches(tdb, rec, off, key);
 139 }
 140
 141 static tdb_off_t hbucket_off(tdb_off_t group_start, unsigned bucket)
 142 {
 143         return group_start
 144                 + (bucket % (1 << TDB_HASH_GROUP_BITS)) * sizeof(tdb_off_t);
 145 }
 146
 147 bool is_subhash(tdb_off_t val)
 148 {
 149         return (val >> TDB_OFF_UPPER_STEAL_SUBHASH_BIT) & 1;
 150 }
 151
 152 /* FIXME: Guess the depth, don't over-lock! */
 153 static tdb_off_t hlock_range(tdb_off_t group, tdb_off_t *size)
 154 {
 155         *size = 1ULL << (64 - (TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS));
 156         return group << (64 - (TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS));
 157 }
 158
 159 static tdb_off_t COLD find_in_chain(struct tdb_context *tdb,
 160                                     struct tdb_data key,
 161                                     tdb_off_t chain,
 162                                     struct hash_info *h,
 163                                     struct tdb_used_record *rec,
 164                                     struct traverse_info *tinfo)
 165 {
 166         tdb_off_t off, next;
 167
 168         /* In case nothing is free, we set these to zero. */
 169         h->home_bucket = h->found_bucket = 0;
 170
 171         for (off = chain; off; off = next) {
 172                 unsigned int i;
 173
 174                 h->group_start = off;
 175                 if (tdb_read_convert(tdb, off, h->group, sizeof(h->group)))
 176                         return TDB_OFF_ERR;
 177
 178                 for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
 179                         tdb_off_t recoff;
 180                         if (!h->group[i]) {
 181                                 /* Remember this empty bucket. */
 182                                 h->home_bucket = h->found_bucket = i;
 183                                 continue;
 184                         }
 185
 186                         /* We can insert extra bits via add_to_hash
 187                          * empty bucket logic. */
 188                         recoff = h->group[i] & TDB_OFF_MASK;
 189                         if (tdb_read_convert(tdb, recoff, rec, sizeof(*rec)))
 190                                 return TDB_OFF_ERR;
 191
 192                         if (key_matches(tdb, rec, recoff, &key)) {
 193                                 h->home_bucket = h->found_bucket = i;
 194
 195                                 if (tinfo) {
 196                                         tinfo->levels[tinfo->num_levels]
 197                                                 .hashtable = off;
 198                                         tinfo->levels[tinfo->num_levels]
 199                                                 .total_buckets
 200                                                 = 1 << TDB_HASH_GROUP_BITS;
 201                                         tinfo->levels[tinfo->num_levels].entry
 202                                                 = i;
 203                                         tinfo->num_levels++;
 204                                 }
 205                                 return recoff;
 206                         }
 207                 }
 208                 next = tdb_read_off(tdb, off
 209                                     + offsetof(struct tdb_chain, next));
 210                 if (next == TDB_OFF_ERR)
 211                         return TDB_OFF_ERR;
 212                 if (next)
 213                         next += sizeof(struct tdb_used_record);
 214         }
 215         return 0;
 216 }
 217
 218 /* This is the core routine which searches the hashtable for an entry.
 219  * On error, no locks are held and TDB_OFF_ERR is returned.
 220  * Otherwise, hinfo is filled in (and the optional tinfo).
 221  * If not found, the return value is 0.
 222  * If found, the return value is the offset, and *rec is the record. */
 223 tdb_off_t find_and_lock(struct tdb_context *tdb,
 224                         struct tdb_data key,
 225                         int ltype,
 226                         struct hash_info *h,
 227                         struct tdb_used_record *rec,
 228                         struct traverse_info *tinfo)
 229 {
 230         uint32_t i, group;
 231         tdb_off_t hashtable;
 232
 233         h->h = tdb_hash(tdb, key.dptr, key.dsize);
 234         h->hash_used = 0;
 235         group = use_bits(h, TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS);
 236         h->home_bucket = use_bits(h, TDB_HASH_GROUP_BITS);
 237
 238         h->hlock_start = hlock_range(group, &h->hlock_range);
 239         if (tdb_lock_hashes(tdb, h->hlock_start, h->hlock_range, ltype,
 240                             TDB_LOCK_WAIT))
 241                 return TDB_OFF_ERR;
 242
 243         hashtable = offsetof(struct tdb_header, hashtable);
 244         if (tinfo) {
 245                 tinfo->toplevel_group = group;
 246                 tinfo->num_levels = 1;
 247                 tinfo->levels[0].entry = 0;
 248                 tinfo->levels[0].hashtable = hashtable
 249                         + (group << TDB_HASH_GROUP_BITS) * sizeof(tdb_off_t);
 250                 tinfo->levels[0].total_buckets = 1 << TDB_HASH_GROUP_BITS;
 251         }
 252
 253         while (h->hash_used <= 64) {
 254                 /* Read in the hash group. */
 255                 h->group_start = hashtable
 256                         + group * (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
 257
 258                 if (tdb_read_convert(tdb, h->group_start, &h->group,
 259                                      sizeof(h->group)) == -1)
 260                         goto fail;
 261
 262                 /* Pointer to another hash table?  Go down... */
 263                 if (is_subhash(h->group[h->home_bucket])) {
 264                         hashtable = (h->group[h->home_bucket] & TDB_OFF_MASK)
 265                                 + sizeof(struct tdb_used_record);
 266                         if (tinfo) {
 267                                 /* When we come back, use *next* bucket */
 268                                 tinfo->levels[tinfo->num_levels-1].entry
 269                                         += h->home_bucket + 1;
 270                         }
 271                         group = use_bits(h, TDB_SUBLEVEL_HASH_BITS
 272                                          - TDB_HASH_GROUP_BITS);
 273                         h->home_bucket = use_bits(h, TDB_HASH_GROUP_BITS);
 274                         if (tinfo) {
 275                                 tinfo->levels[tinfo->num_levels].hashtable
 276                                         = hashtable;
 277                                 tinfo->levels[tinfo->num_levels].total_buckets
 278                                         = 1 << TDB_SUBLEVEL_HASH_BITS;
 279                                 tinfo->levels[tinfo->num_levels].entry
 280                                         = group << TDB_HASH_GROUP_BITS;
 281                                 tinfo->num_levels++;
 282                         }
 283                         continue;
 284                 }
 285
 286                 /* It's in this group: search (until 0 or all searched) */
 287                 for (i = 0, h->found_bucket = h->home_bucket;
 288                      i < (1 << TDB_HASH_GROUP_BITS);
 289                      i++, h->found_bucket = ((h->found_bucket+1)
 290                                              % (1 << TDB_HASH_GROUP_BITS))) {
 291                         if (is_subhash(h->group[h->found_bucket]))
 292                                 continue;
 293
 294                         if (!h->group[h->found_bucket])
 295                                 break;
 296
 297                         if (match(tdb, h, &key, h->group[h->found_bucket],
 298                                   rec)) {
 299                                 if (tinfo) {
 300                                         tinfo->levels[tinfo->num_levels-1].entry
 301                                                 += h->found_bucket;
 302                                 }
 303                                 return h->group[h->found_bucket] & TDB_OFF_MASK;
 304                         }
 305                 }
 306                 /* Didn't find it: h indicates where it would go. */
 307                 return 0;
 308         }
 309
 310         return find_in_chain(tdb, key, hashtable, h, rec, tinfo);
 311
 312 fail:
 313         tdb_unlock_hashes(tdb, h->hlock_start, h->hlock_range, ltype);
 314         return TDB_OFF_ERR;
 315 }
 316
 317 /* I wrote a simple test, expanding a hash to 2GB, for the following
 318  * cases:
 319  * 1) Expanding all the buckets at once,
 320  * 2) Expanding the bucket we wanted to place the new entry into.
 321  * 3) Expanding the most-populated bucket,
 322  *
 323  * I measured the worst/average/best density during this process.
 324  * 1) 3%/16%/30%
 325  * 2) 4%/20%/38%
 326  * 3) 6%/22%/41%
 327  *
 328  * So we figure out the busiest bucket for the moment.
 329  */
 330 static unsigned fullest_bucket(struct tdb_context *tdb,
 331                                const tdb_off_t *group,
 332                                unsigned new_bucket)
 333 {
 334         unsigned counts[1 << TDB_HASH_GROUP_BITS] = { 0 };
 335         unsigned int i, best_bucket;
 336
 337         /* Count the new entry. */
 338         counts[new_bucket]++;
 339         best_bucket = new_bucket;
 340
 341         for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
 342                 unsigned this_bucket;
 343
 344                 if (is_subhash(group[i]))
 345                         continue;
 346                 this_bucket = group[i] & TDB_OFF_HASH_GROUP_MASK;
 347                 if (++counts[this_bucket] > counts[best_bucket])
 348                         best_bucket = this_bucket;
 349         }
 350
 351         return best_bucket;
 352 }
 353
 354 static bool put_into_group(tdb_off_t *group,
 355                            unsigned bucket, tdb_off_t encoded)
 356 {
 357         unsigned int i;
 358
 359         for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
 360                 unsigned b = (bucket + i) % (1 << TDB_HASH_GROUP_BITS);
 361
 362                 if (group[b] == 0) {
 363                         group[b] = encoded;
 364                         return true;
 365                 }
 366         }
 367         return false;
 368 }
 369
 370 static void force_into_group(tdb_off_t *group,
 371                              unsigned bucket, tdb_off_t encoded)
 372 {
 373         if (!put_into_group(group, bucket, encoded))
 374                 abort();
 375 }
 376
 377 static tdb_off_t encode_offset(tdb_off_t new_off, struct hash_info *h)
 378 {
 379         return h->home_bucket
 380                 | new_off
 381                 | ((uint64_t)bits(h->h,
 382                                   64 - h->hash_used - TDB_OFF_UPPER_STEAL_EXTRA,
 383                                   TDB_OFF_UPPER_STEAL_EXTRA)
 384                    << TDB_OFF_HASH_EXTRA_BIT);
 385 }
 386
 387 /* Simply overwrite the hash entry we found before. */
 388 int replace_in_hash(struct tdb_context *tdb,
 389                     struct hash_info *h,
 390                     tdb_off_t new_off)
 391 {
 392         return tdb_write_off(tdb, hbucket_off(h->group_start, h->found_bucket),
 393                              encode_offset(new_off, h));
 394 }
 395
 396 /* We slot in anywhere that's empty in the chain. */
 397 static int COLD add_to_chain(struct tdb_context *tdb,
 398                              tdb_off_t subhash,
 399                              tdb_off_t new_off)
 400 {
 401         size_t entry = tdb_find_zero_off(tdb, subhash, 1<<TDB_HASH_GROUP_BITS);
 402
 403         if (entry == 1 << TDB_HASH_GROUP_BITS) {
 404                 tdb_off_t next;
 405
 406                 next = tdb_read_off(tdb, subhash
 407                                     + offsetof(struct tdb_chain, next));
 408                 if (next == TDB_OFF_ERR)
 409                         return -1;
 410
 411                 if (!next) {
 412                         next = alloc(tdb, 0, sizeof(struct tdb_chain), 2,
 413                                      false);
 414                         if (next == TDB_OFF_ERR)
 415                                 return -1;
 416                         if (zero_out(tdb, next+sizeof(struct tdb_used_record),
 417                                      sizeof(struct tdb_chain)))
 418                                 return -1;
 419                         if (tdb_write_off(tdb, subhash
 420                                           + offsetof(struct tdb_chain, next),
 421                                           next) != 0)
 422                                 return -1;
 423                 }
 424                 return add_to_chain(tdb, next, new_off);
 425         }
 426
 427         return tdb_write_off(tdb, subhash + entry * sizeof(tdb_off_t),
 428                              new_off);
 429 }
 430
 431 /* Add into a newly created subhash. */
 432 static int add_to_subhash(struct tdb_context *tdb, tdb_off_t subhash,
 433                           unsigned hash_used, tdb_off_t val)
 434 {
 435         tdb_off_t off = (val & TDB_OFF_MASK), *group;
 436         struct hash_info h;
 437         unsigned int gnum;
 438
 439         h.hash_used = hash_used;
 440
 441         if (hash_used + TDB_SUBLEVEL_HASH_BITS > 64)
 442                 return add_to_chain(tdb, subhash, off);
 443
 444         h.h = hash_record(tdb, off);
 445         gnum = use_bits(&h, TDB_SUBLEVEL_HASH_BITS-TDB_HASH_GROUP_BITS);
 446         h.group_start = subhash
 447                 + gnum * (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
 448         h.home_bucket = use_bits(&h, TDB_HASH_GROUP_BITS);
 449
 450         group = tdb_access_write(tdb, h.group_start,
 451                                  sizeof(*group) << TDB_HASH_GROUP_BITS, true);
 452         if (!group)
 453                 return -1;
 454         force_into_group(group, h.home_bucket, encode_offset(off, &h));
 455         return tdb_access_commit(tdb, group);
 456 }
 457
 458 static int expand_group(struct tdb_context *tdb, struct hash_info *h)
 459 {
 460         unsigned bucket, num_vals, i, hash;
 461         size_t subsize;
 462         tdb_off_t subhash;
 463         tdb_off_t vals[1 << TDB_HASH_GROUP_BITS];
 464
 465         /* Attach new empty subhash under fullest bucket. */
 466         bucket = fullest_bucket(tdb, h->group, h->home_bucket);
 467
 468         if (h->hash_used == 64) {
 469                 add_stat(tdb, alloc_chain, 1);
 470                 subsize = sizeof(struct tdb_chain);
 471                 hash = 2;
 472         } else {
 473                 add_stat(tdb, alloc_subhash, 1);
 474                 subsize = (sizeof(tdb_off_t) << TDB_SUBLEVEL_HASH_BITS);
 475                 hash = 0;
 476         }
 477
 478         subhash = alloc(tdb, 0, subsize, hash, false);
 479         if (subhash == TDB_OFF_ERR)
 480                 return -1;
 481
 482         if (zero_out(tdb, subhash + sizeof(struct tdb_used_record), subsize))
 483                 return -1;
 484
 485         /* Remove any which are destined for bucket or are in wrong place. */
 486         num_vals = 0;
 487         for (i = 0; i < (1 << TDB_HASH_GROUP_BITS); i++) {
 488                 unsigned home_bucket = h->group[i] & TDB_OFF_HASH_GROUP_MASK;
 489                 if (!h->group[i] || is_subhash(h->group[i]))
 490                         continue;
 491                 if (home_bucket == bucket || home_bucket != i) {
 492                         vals[num_vals++] = h->group[i];
 493                         h->group[i] = 0;
 494                 }
 495         }
 496         /* FIXME: This assert is valid, but we do this during unit test :( */
 497         /* assert(num_vals); */
 498
 499         /* Overwrite expanded bucket with subhash pointer. */
 500         h->group[bucket] = subhash | (1ULL << TDB_OFF_UPPER_STEAL_SUBHASH_BIT);
 501
 502         /* Point to actual contents of record. */
 503         subhash += sizeof(struct tdb_used_record);
 504
 505         /* Put values back. */
 506         for (i = 0; i < num_vals; i++) {
 507                 unsigned this_bucket = vals[i] & TDB_OFF_HASH_GROUP_MASK;
 508
 509                 if (this_bucket == bucket) {
 510                         if (add_to_subhash(tdb, subhash, h->hash_used, vals[i]))
 511                                 return -1;
 512                 } else {
 513                         /* There should be room to put this back. */
 514                         force_into_group(h->group, this_bucket, vals[i]);
 515                 }
 516         }
 517         return 0;
 518 }
 519
 520 int delete_from_hash(struct tdb_context *tdb, struct hash_info *h)
 521 {
 522         unsigned int i, num_movers = 0;
 523         tdb_off_t movers[1 << TDB_HASH_GROUP_BITS];
 524
 525         h->group[h->found_bucket] = 0;
 526         for (i = 1; i < (1 << TDB_HASH_GROUP_BITS); i++) {
 527                 unsigned this_bucket;
 528
 529                 this_bucket = (h->found_bucket+i) % (1 << TDB_HASH_GROUP_BITS);
 530                 /* Empty bucket?  We're done. */
 531                 if (!h->group[this_bucket])
 532                         break;
 533
 534                 /* Ignore subhashes. */
 535                 if (is_subhash(h->group[this_bucket]))
 536                         continue;
 537
 538                 /* If this one is not happy where it is, we'll move it. */
 539                 if ((h->group[this_bucket] & TDB_OFF_HASH_GROUP_MASK)
 540                     != this_bucket) {
 541                         movers[num_movers++] = h->group[this_bucket];
 542                         h->group[this_bucket] = 0;
 543                 }
 544         }
 545
 546         /* Put back the ones we erased. */
 547         for (i = 0; i < num_movers; i++) {
 548                 force_into_group(h->group, movers[i] & TDB_OFF_HASH_GROUP_MASK,
 549                                  movers[i]);
 550         }
 551
 552         /* Now we write back the hash group */
 553         return tdb_write_convert(tdb, h->group_start,
 554                                  h->group, sizeof(h->group));
 555 }
 556
 557 int add_to_hash(struct tdb_context *tdb, struct hash_info *h, tdb_off_t new_off)
 558 {
 559         /* We hit an empty bucket during search?  That's where it goes. */
 560         if (!h->group[h->found_bucket]) {
 561                 h->group[h->found_bucket] = encode_offset(new_off, h);
 562                 /* Write back the modified group. */
 563                 return tdb_write_convert(tdb, h->group_start,
 564                                          h->group, sizeof(h->group));
 565         }
 566
 567         if (h->hash_used > 64)
 568                 return add_to_chain(tdb, h->group_start, new_off);
 569
 570         /* We're full.  Expand. */
 571         if (expand_group(tdb, h) == -1)
 572                 return -1;
 573
 574         if (is_subhash(h->group[h->home_bucket])) {
 575                 /* We were expanded! */
 576                 tdb_off_t hashtable;
 577                 unsigned int gnum;
 578
 579                 /* Write back the modified group. */
 580                 if (tdb_write_convert(tdb, h->group_start, h->group,
 581                                       sizeof(h->group)))
 582                         return -1;
 583
 584                 /* Move hashinfo down a level. */
 585                 hashtable = (h->group[h->home_bucket] & TDB_OFF_MASK)
 586                         + sizeof(struct tdb_used_record);
 587                 gnum = use_bits(h,TDB_SUBLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS);
 588                 h->home_bucket = use_bits(h, TDB_HASH_GROUP_BITS);
 589                 h->group_start = hashtable
 590                         + gnum * (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
 591                 if (tdb_read_convert(tdb, h->group_start, &h->group,
 592                                      sizeof(h->group)) == -1)
 593                         return -1;
 594         }
 595
 596         /* Expanding the group must have made room if it didn't choose this
 597          * bucket. */
 598         if (put_into_group(h->group, h->home_bucket, encode_offset(new_off, h)))
 599                 return tdb_write_convert(tdb, h->group_start,
 600                                          h->group, sizeof(h->group));
 601
 602         /* This can happen if all hashes in group (and us) dropped into same
 603          * group in subhash. */
 604         return add_to_hash(tdb, h, new_off);
 605 }
 606
 607 /* Traverse support: returns offset of record, or 0 or TDB_OFF_ERR. */
 608 static tdb_off_t iterate_hash(struct tdb_context *tdb,
 609                               struct traverse_info *tinfo)
 610 {
 611         tdb_off_t off, val;
 612         unsigned int i;
 613         struct traverse_level *tlevel;
 614
 615         tlevel = &tinfo->levels[tinfo->num_levels-1];
 616
 617 again:
 618         for (i = tdb_find_nonzero_off(tdb, tlevel->hashtable,
 619                                       tlevel->entry, tlevel->total_buckets);
 620              i != tlevel->total_buckets;
 621              i = tdb_find_nonzero_off(tdb, tlevel->hashtable,
 622                                       i+1, tlevel->total_buckets)) {
 623                 val = tdb_read_off(tdb, tlevel->hashtable+sizeof(tdb_off_t)*i);
 624                 if (unlikely(val == TDB_OFF_ERR))
 625                         return TDB_OFF_ERR;
 626
 627                 off = val & TDB_OFF_MASK;
 628
 629                 /* This makes the delete-all-in-traverse case work
 630                  * (and simplifies our logic a little). */
 631                 if (off == tinfo->prev)
 632                         continue;
 633
 634                 tlevel->entry = i;
 635
 636                 if (!is_subhash(val)) {
 637                         /* Found one. */
 638                         tinfo->prev = off;
 639                         return off;
 640                 }
 641
 642                 /* When we come back, we want the next one */
 643                 tlevel->entry++;
 644                 tinfo->num_levels++;
 645                 tlevel++;
 646                 tlevel->hashtable = off + sizeof(struct tdb_used_record);
 647                 tlevel->entry = 0;
 648                 /* Next level is a chain? */
 649                 if (unlikely(tinfo->num_levels == TDB_MAX_LEVELS + 1))
 650                         tlevel->total_buckets = (1 << TDB_HASH_GROUP_BITS);
 651                 else
 652                         tlevel->total_buckets = (1 << TDB_SUBLEVEL_HASH_BITS);
 653                 goto again;
 654         }
 655
 656         /* Nothing there? */
 657         if (tinfo->num_levels == 1)
 658                 return 0;
 659
 660         /* Handle chained entries. */
 661         if (unlikely(tinfo->num_levels == TDB_MAX_LEVELS + 1)) {
 662                 tlevel->hashtable = tdb_read_off(tdb, tlevel->hashtable
 663                                                  + offsetof(struct tdb_chain,
 664                                                             next));
 665                 if (tlevel->hashtable == TDB_OFF_ERR)
 666                         return TDB_OFF_ERR;
 667                 if (tlevel->hashtable) {
 668                         tlevel->hashtable += sizeof(struct tdb_used_record);
 669                         tlevel->entry = 0;
 670                         goto again;
 671                 }
 672         }
 673
 674         /* Go back up and keep searching. */
 675         tinfo->num_levels--;
 676         tlevel--;
 677         goto again;
 678 }
 679
 680 /* Return 1 if we find something, 0 if not, -1 on error. */
 681 int next_in_hash(struct tdb_context *tdb, int ltype,
 682                  struct traverse_info *tinfo,
 683                  TDB_DATA *kbuf, size_t *dlen)
 684 {
 685         const unsigned group_bits = TDB_TOPLEVEL_HASH_BITS-TDB_HASH_GROUP_BITS;
 686         tdb_off_t hlock_start, hlock_range, off;
 687
 688         while (tinfo->toplevel_group < (1 << group_bits)) {
 689                 hlock_start = (tdb_off_t)tinfo->toplevel_group
 690                         << (64 - group_bits);
 691                 hlock_range = 1ULL << group_bits;
 692                 if (tdb_lock_hashes(tdb, hlock_start, hlock_range, ltype,
 693                                     TDB_LOCK_WAIT) != 0)
 694                         return -1;
 695
 696                 off = iterate_hash(tdb, tinfo);
 697                 if (off) {
 698                         struct tdb_used_record rec;
 699
 700                         if (tdb_read_convert(tdb, off, &rec, sizeof(rec))) {
 701                                 tdb_unlock_hashes(tdb,
 702                                                   hlock_start, hlock_range,
 703                                                   ltype);
 704                                 return -1;
 705                         }
 706                         if (rec_magic(&rec) != TDB_MAGIC) {
 707                                 tdb_logerr(tdb, TDB_ERR_CORRUPT,
 708                                            TDB_DEBUG_FATAL,
 709                                            "next_in_hash:"
 710                                            " corrupt record at %llu",
 711                                            (long long)off);
 712                                 return -1;
 713                         }
 714
 715                         kbuf->dsize = rec_key_length(&rec);
 716
 717                         /* They want data as well? */
 718                         if (dlen) {
 719                                 *dlen = rec_data_length(&rec);
 720                                 kbuf->dptr = tdb_alloc_read(tdb,
 721                                                             off + sizeof(rec),
 722                                                             kbuf->dsize
 723                                                             + *dlen);
 724                         } else {
 725                                 kbuf->dptr = tdb_alloc_read(tdb,
 726                                                             off + sizeof(rec),
 727                                                             kbuf->dsize);
 728                         }
 729                         tdb_unlock_hashes(tdb, hlock_start, hlock_range, ltype);
 730                         return kbuf->dptr ? 1 : -1;
 731                 }
 732
 733                 tdb_unlock_hashes(tdb, hlock_start, hlock_range, ltype);
 734
 735                 tinfo->toplevel_group++;
 736                 tinfo->levels[0].hashtable
 737                         += (sizeof(tdb_off_t) << TDB_HASH_GROUP_BITS);
 738                 tinfo->levels[0].entry = 0;
 739         }
 740         return 0;
 741 }
 742
 743 /* Return 1 if we find something, 0 if not, -1 on error. */
 744 int first_in_hash(struct tdb_context *tdb, int ltype,
 745                   struct traverse_info *tinfo,
 746                   TDB_DATA *kbuf, size_t *dlen)
 747 {
 748         tinfo->prev = 0;
 749         tinfo->toplevel_group = 0;
 750         tinfo->num_levels = 1;
 751         tinfo->levels[0].hashtable = offsetof(struct tdb_header, hashtable);
 752         tinfo->levels[0].entry = 0;
 753         tinfo->levels[0].total_buckets = (1 << TDB_HASH_GROUP_BITS);
 754
 755         return next_in_hash(tdb, ltype, tinfo, kbuf, dlen);
 756 }
 757
 758 /* Even if the entry isn't in this hash bucket, you'd have to lock this
 759  * bucket to find it. */
 760 static int chainlock(struct tdb_context *tdb, const TDB_DATA *key,
 761                      int ltype, enum tdb_lock_flags waitflag,
 762                      const char *func)
 763 {
 764         int ret;
 765         uint64_t h = tdb_hash(tdb, key->dptr, key->dsize);
 766         tdb_off_t lockstart, locksize;
 767         unsigned int group, gbits;
 768
 769         gbits = TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS;
 770         group = bits(h, 64 - gbits, gbits);
 771
 772         lockstart = hlock_range(group, &locksize);
 773
 774         ret = tdb_lock_hashes(tdb, lockstart, locksize, ltype, waitflag);
 775         tdb_trace_1rec(tdb, func, *key);
 776         return ret;
 777 }
 778
 779 /* lock/unlock one hash chain. This is meant to be used to reduce
 780    contention - it cannot guarantee how many records will be locked */
 781 int tdb_chainlock(struct tdb_context *tdb, TDB_DATA key)
 782 {
 783         return chainlock(tdb, &key, F_WRLCK, TDB_LOCK_WAIT, "tdb_chainlock");
 784 }
 785
 786 int tdb_chainunlock(struct tdb_context *tdb, TDB_DATA key)
 787 {
 788         uint64_t h = tdb_hash(tdb, key.dptr, key.dsize);
 789         tdb_off_t lockstart, locksize;
 790         unsigned int group, gbits;
 791
 792         gbits = TDB_TOPLEVEL_HASH_BITS - TDB_HASH_GROUP_BITS;
 793         group = bits(h, 64 - gbits, gbits);
 794
 795         lockstart = hlock_range(group, &locksize);
 796
 797         tdb_trace_1rec(tdb, "tdb_chainunlock", key);
 798         return tdb_unlock_hashes(tdb, lockstart, locksize, F_WRLCK);
 799 }