lib/tdb/common/transaction.c

   1  /*
   2    Unix SMB/CIFS implementation.
   3
   4    trivial database library
   5
   6    Copyright (C) Andrew Tridgell              2005
   7
   8      ** NOTE! The following LGPL license applies to the tdb
   9      ** library. This does NOT imply that all of Samba is released
  10      ** under the LGPL
  11
  12    This library is free software; you can redistribute it and/or
  13    modify it under the terms of the GNU Lesser General Public
  14    License as published by the Free Software Foundation; either
  15    version 3 of the License, or (at your option) any later version.
  16
  17    This library is distributed in the hope that it will be useful,
  18    but WITHOUT ANY WARRANTY; without even the implied warranty of
  19    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  20    Lesser General Public License for more details.
  21
  22    You should have received a copy of the GNU Lesser General Public
  23    License along with this library; if not, see <http://www.gnu.org/licenses/>.
  24 */
  25
  26 #include "tdb_private.h"
  27
  28 /*
  29   transaction design:
  30
  31   - only allow a single transaction at a time per database. This makes
  32     using the transaction API simpler, as otherwise the caller would
  33     have to cope with temporary failures in transactions that conflict
  34     with other current transactions
  35
  36   - keep the transaction recovery information in the same file as the
  37     database, using a special 'transaction recovery' record pointed at
  38     by the header. This removes the need for extra journal files as
  39     used by some other databases
  40
  41   - dynamically allocated the transaction recover record, re-using it
  42     for subsequent transactions. If a larger record is needed then
  43     tdb_free() the old record to place it on the normal tdb freelist
  44     before allocating the new record
  45
  46   - during transactions, keep a linked list of writes all that have
  47     been performed by intercepting all tdb_write() calls. The hooked
  48     transaction versions of tdb_read() and tdb_write() check this
  49     linked list and try to use the elements of the list in preference
  50     to the real database.
  51
  52   - don't allow any locks to be held when a transaction starts,
  53     otherwise we can end up with deadlock (plus lack of lock nesting
  54     in posix locks would mean the lock is lost)
  55
  56   - if the caller gains a lock during the transaction but doesn't
  57     release it then fail the commit
  58
  59   - allow for nested calls to tdb_transaction_start(), re-using the
  60     existing transaction record. If the inner transaction is cancelled
  61     then a subsequent commit will fail
  62
  63   - keep a mirrored copy of the tdb hash chain heads to allow for the
  64     fast hash heads scan on traverse, updating the mirrored copy in
  65     the transaction version of tdb_write
  66
  67   - allow callers to mix transaction and non-transaction use of tdb,
  68     although once a transaction is started then an exclusive lock is
  69     gained until the transaction is committed or cancelled
  70
  71   - the commit stategy involves first saving away all modified data
  72     into a linearised buffer in the transaction recovery area, then
  73     marking the transaction recovery area with a magic value to
  74     indicate a valid recovery record. In total 4 fsync/msync calls are
  75     needed per commit to prevent race conditions. It might be possible
  76     to reduce this to 3 or even 2 with some more work.
  77
  78   - check for a valid recovery record on open of the tdb, while the
  79     open lock is held. Automatically recover from the transaction
  80     recovery area if needed, then continue with the open as
  81     usual. This allows for smooth crash recovery with no administrator
  82     intervention.
  83
  84   - if TDB_NOSYNC is passed to flags in tdb_open then transactions are
  85     still available, but no transaction recovery area is used and no
  86     fsync/msync calls are made.
  87
  88   - if TDB_ALLOW_NESTING is passed to flags in tdb open, or added using
  89     tdb_add_flags() transaction nesting is enabled.
  90     It resets the TDB_DISALLOW_NESTING flag, as both cannot be used together.
  91     The default is that transaction nesting is allowed.
  92     Note: this default may change in future versions of tdb.
  93
  94     Beware. when transactions are nested a transaction successfully
  95     completed with tdb_transaction_commit() can be silently unrolled later.
  96
  97   - if TDB_DISALLOW_NESTING is passed to flags in tdb open, or added using
  98     tdb_add_flags() transaction nesting is disabled.
  99     It resets the TDB_ALLOW_NESTING flag, as both cannot be used together.
 100     An attempt create a nested transaction will fail with TDB_ERR_NESTING.
 101     The default is that transaction nesting is allowed.
 102     Note: this default may change in future versions of tdb.
 103 */
 104
 105
 106 /*
 107   hold the context of any current transaction
 108 */
 109 struct tdb_transaction {
 110         /* we keep a mirrored copy of the tdb hash heads here so
 111            tdb_next_hash_chain() can operate efficiently */
 112         uint32_t *hash_heads;
 113
 114         /* the original io methods - used to do IOs to the real db */
 115         const struct tdb_methods *io_methods;
 116
 117         /* the list of transaction blocks. When a block is first
 118            written to, it gets created in this list */
 119         uint8_t **blocks;
 120         uint32_t num_blocks;
 121         uint32_t block_size;      /* bytes in each block */
 122         uint32_t last_block_size; /* number of valid bytes in the last block */
 123
 124         /* non-zero when an internal transaction error has
 125            occurred. All write operations will then fail until the
 126            transaction is ended */
 127         int transaction_error;
 128
 129         /* when inside a transaction we need to keep track of any
 130            nested tdb_transaction_start() calls, as these are allowed,
 131            but don't create a new transaction */
 132         int nesting;
 133
 134         /* set when a prepare has already occurred */
 135         bool prepared;
 136         tdb_off_t magic_offset;
 137
 138         /* old file size before transaction */
 139         tdb_len_t old_map_size;
 140
 141         /* we should re-pack on commit */
 142         bool need_repack;
 143 };
 144
 145
 146 /*
 147   read while in a transaction. We need to check first if the data is in our list
 148   of transaction elements, then if not do a real read
 149 */
 150 static int transaction_read(struct tdb_context *tdb, tdb_off_t off, void *buf,
 151                             tdb_len_t len, int cv)
 152 {
 153         uint32_t blk;
 154
 155         /* break it down into block sized ops */
 156         while (len + (off % tdb->transaction->block_size) > tdb->transaction->block_size) {
 157                 tdb_len_t len2 = tdb->transaction->block_size - (off % tdb->transaction->block_size);
 158                 if (transaction_read(tdb, off, buf, len2, cv) != 0) {
 159                         return -1;
 160                 }
 161                 len -= len2;
 162                 off += len2;
 163                 buf = (void *)(len2 + (char *)buf);
 164         }
 165
 166         if (len == 0) {
 167                 return 0;
 168         }
 169
 170         blk = off / tdb->transaction->block_size;
 171
 172         /* see if we have it in the block list */
 173         if (tdb->transaction->num_blocks <= blk ||
 174             tdb->transaction->blocks[blk] == NULL) {
 175                 /* nope, do a real read */
 176                 if (tdb->transaction->io_methods->tdb_read(tdb, off, buf, len, cv) != 0) {
 177                         goto fail;
 178                 }
 179                 return 0;
 180         }
 181
 182         /* it is in the block list. Now check for the last block */
 183         if (blk == tdb->transaction->num_blocks-1) {
 184                 if (len > tdb->transaction->last_block_size) {
 185                         goto fail;
 186                 }
 187         }
 188
 189         /* now copy it out of this block */
 190         memcpy(buf, tdb->transaction->blocks[blk] + (off % tdb->transaction->block_size), len);
 191         if (cv) {
 192                 tdb_convert(buf, len);
 193         }
 194         return 0;
 195
 196 fail:
 197         TDB_LOG((tdb, TDB_DEBUG_FATAL, "transaction_read: failed at off=%d len=%d\n", off, len));
 198         tdb->ecode = TDB_ERR_IO;
 199         tdb->transaction->transaction_error = 1;
 200         return -1;
 201 }
 202
 203
 204 /*
 205   write while in a transaction
 206 */
 207 static int transaction_write(struct tdb_context *tdb, tdb_off_t off,
 208                              const void *buf, tdb_len_t len)
 209 {
 210         uint32_t blk;
 211
 212         /* Only a commit is allowed on a prepared transaction */
 213         if (tdb->transaction->prepared) {
 214                 tdb->ecode = TDB_ERR_EINVAL;
 215                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "transaction_write: transaction already prepared, write not allowed\n"));
 216                 tdb->transaction->transaction_error = 1;
 217                 return -1;
 218         }
 219
 220         /* if the write is to a hash head, then update the transaction
 221            hash heads */
 222         if (len == sizeof(tdb_off_t) && off >= FREELIST_TOP &&
 223             off < FREELIST_TOP+TDB_HASHTABLE_SIZE(tdb)) {
 224                 uint32_t chain = (off-FREELIST_TOP) / sizeof(tdb_off_t);
 225                 memcpy(&tdb->transaction->hash_heads[chain], buf, len);
 226         }
 227
 228         /* break it up into block sized chunks */
 229         while (len + (off % tdb->transaction->block_size) > tdb->transaction->block_size) {
 230                 tdb_len_t len2 = tdb->transaction->block_size - (off % tdb->transaction->block_size);
 231                 if (transaction_write(tdb, off, buf, len2) != 0) {
 232                         return -1;
 233                 }
 234                 len -= len2;
 235                 off += len2;
 236                 if (buf != NULL) {
 237                         buf = (const void *)(len2 + (const char *)buf);
 238                 }
 239         }
 240
 241         if (len == 0) {
 242                 return 0;
 243         }
 244
 245         blk = off / tdb->transaction->block_size;
 246         off = off % tdb->transaction->block_size;
 247
 248         if (tdb->transaction->num_blocks <= blk) {
 249                 uint8_t **new_blocks;
 250                 /* expand the blocks array */
 251                 if (tdb->transaction->blocks == NULL) {
 252                         new_blocks = (uint8_t **)malloc(
 253                                 (blk+1)*sizeof(uint8_t *));
 254                 } else {
 255                         new_blocks = (uint8_t **)realloc(
 256                                 tdb->transaction->blocks,
 257                                 (blk+1)*sizeof(uint8_t *));
 258                 }
 259                 if (new_blocks == NULL) {
 260                         tdb->ecode = TDB_ERR_OOM;
 261                         goto fail;
 262                 }
 263                 memset(&new_blocks[tdb->transaction->num_blocks], 0,
 264                        (1+(blk - tdb->transaction->num_blocks))*sizeof(uint8_t *));
 265                 tdb->transaction->blocks = new_blocks;
 266                 tdb->transaction->num_blocks = blk+1;
 267                 tdb->transaction->last_block_size = 0;
 268         }
 269
 270         /* allocate and fill a block? */
 271         if (tdb->transaction->blocks[blk] == NULL) {
 272                 tdb->transaction->blocks[blk] = (uint8_t *)calloc(tdb->transaction->block_size, 1);
 273                 if (tdb->transaction->blocks[blk] == NULL) {
 274                         tdb->ecode = TDB_ERR_OOM;
 275                         tdb->transaction->transaction_error = 1;
 276                         return -1;
 277                 }
 278                 if (tdb->transaction->old_map_size > blk * tdb->transaction->block_size) {
 279                         tdb_len_t len2 = tdb->transaction->block_size;
 280                         if (len2 + (blk * tdb->transaction->block_size) > tdb->transaction->old_map_size) {
 281                                 len2 = tdb->transaction->old_map_size - (blk * tdb->transaction->block_size);
 282                         }
 283                         if (tdb->transaction->io_methods->tdb_read(tdb, blk * tdb->transaction->block_size,
 284                                                                    tdb->transaction->blocks[blk],
 285                                                                    len2, 0) != 0) {
 286                                 SAFE_FREE(tdb->transaction->blocks[blk]);
 287                                 tdb->ecode = TDB_ERR_IO;
 288                                 goto fail;
 289                         }
 290                         if (blk == tdb->transaction->num_blocks-1) {
 291                                 tdb->transaction->last_block_size = len2;
 292                         }
 293                 }
 294         }
 295
 296         /* overwrite part of an existing block */
 297         if (buf == NULL) {
 298                 memset(tdb->transaction->blocks[blk] + off, 0, len);
 299         } else {
 300                 memcpy(tdb->transaction->blocks[blk] + off, buf, len);
 301         }
 302         if (blk == tdb->transaction->num_blocks-1) {
 303                 if (len + off > tdb->transaction->last_block_size) {
 304                         tdb->transaction->last_block_size = len + off;
 305                 }
 306         }
 307
 308         return 0;
 309
 310 fail:
 311         TDB_LOG((tdb, TDB_DEBUG_FATAL, "transaction_write: failed at off=%d len=%d\n",
 312                  (blk*tdb->transaction->block_size) + off, len));
 313         tdb->transaction->transaction_error = 1;
 314         return -1;
 315 }
 316
 317
 318 /*
 319   write while in a transaction - this varient never expands the transaction blocks, it only
 320   updates existing blocks. This means it cannot change the recovery size
 321 */
 322 static int transaction_write_existing(struct tdb_context *tdb, tdb_off_t off,
 323                                       const void *buf, tdb_len_t len)
 324 {
 325         uint32_t blk;
 326
 327         /* break it up into block sized chunks */
 328         while (len + (off % tdb->transaction->block_size) > tdb->transaction->block_size) {
 329                 tdb_len_t len2 = tdb->transaction->block_size - (off % tdb->transaction->block_size);
 330                 if (transaction_write_existing(tdb, off, buf, len2) != 0) {
 331                         return -1;
 332                 }
 333                 len -= len2;
 334                 off += len2;
 335                 if (buf != NULL) {
 336                         buf = (const void *)(len2 + (const char *)buf);
 337                 }
 338         }
 339
 340         if (len == 0) {
 341                 return 0;
 342         }
 343
 344         blk = off / tdb->transaction->block_size;
 345         off = off % tdb->transaction->block_size;
 346
 347         if (tdb->transaction->num_blocks <= blk ||
 348             tdb->transaction->blocks[blk] == NULL) {
 349                 return 0;
 350         }
 351
 352         if (blk == tdb->transaction->num_blocks-1 &&
 353             off + len > tdb->transaction->last_block_size) {
 354                 if (off >= tdb->transaction->last_block_size) {
 355                         return 0;
 356                 }
 357                 len = tdb->transaction->last_block_size - off;
 358         }
 359
 360         /* overwrite part of an existing block */
 361         memcpy(tdb->transaction->blocks[blk] + off, buf, len);
 362
 363         return 0;
 364 }
 365
 366
 367 /*
 368   accelerated hash chain head search, using the cached hash heads
 369 */
 370 static void transaction_next_hash_chain(struct tdb_context *tdb, uint32_t *chain)
 371 {
 372         uint32_t h = *chain;
 373         for (;h < tdb->header.hash_size;h++) {
 374                 /* the +1 takes account of the freelist */
 375                 if (0 != tdb->transaction->hash_heads[h+1]) {
 376                         break;
 377                 }
 378         }
 379         (*chain) = h;
 380 }
 381
 382 /*
 383   out of bounds check during a transaction
 384 */
 385 static int transaction_oob(struct tdb_context *tdb, tdb_off_t len, int probe)
 386 {
 387         if (len <= tdb->map_size) {
 388                 return 0;
 389         }
 390         tdb->ecode = TDB_ERR_IO;
 391         return -1;
 392 }
 393
 394 /*
 395   transaction version of tdb_expand().
 396 */
 397 static int transaction_expand_file(struct tdb_context *tdb, tdb_off_t size,
 398                                    tdb_off_t addition)
 399 {
 400         /* add a write to the transaction elements, so subsequent
 401            reads see the zero data */
 402         if (transaction_write(tdb, size, NULL, addition) != 0) {
 403                 return -1;
 404         }
 405
 406         tdb->transaction->need_repack = true;
 407
 408         return 0;
 409 }
 410
 411 static const struct tdb_methods transaction_methods = {
 412         transaction_read,
 413         transaction_write,
 414         transaction_next_hash_chain,
 415         transaction_oob,
 416         transaction_expand_file,
 417 };
 418
 419
 420 /*
 421   start a tdb transaction. No token is returned, as only a single
 422   transaction is allowed to be pending per tdb_context
 423 */
 424 static int _tdb_transaction_start(struct tdb_context *tdb,
 425                                   enum tdb_lock_flags lockflags)
 426 {
 427         /* some sanity checks */
 428         if (tdb->read_only || (tdb->flags & TDB_INTERNAL) || tdb->traverse_read) {
 429                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction on a read-only or internal db\n"));
 430                 tdb->ecode = TDB_ERR_EINVAL;
 431                 return -1;
 432         }
 433
 434         /* cope with nested tdb_transaction_start() calls */
 435         if (tdb->transaction != NULL) {
 436                 if (!(tdb->flags & TDB_ALLOW_NESTING)) {
 437                         tdb->ecode = TDB_ERR_NESTING;
 438                         return -1;
 439                 }
 440                 tdb->transaction->nesting++;
 441                 TDB_LOG((tdb, TDB_DEBUG_TRACE, "tdb_transaction_start: nesting %d\n",
 442                          tdb->transaction->nesting));
 443                 return 0;
 444         }
 445
 446         if (tdb_have_extra_locks(tdb)) {
 447                 /* the caller must not have any locks when starting a
 448                    transaction as otherwise we'll be screwed by lack
 449                    of nested locks in posix */
 450                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction with locks held\n"));
 451                 tdb->ecode = TDB_ERR_LOCK;
 452                 return -1;
 453         }
 454
 455         if (tdb->travlocks.next != NULL) {
 456                 /* you cannot use transactions inside a traverse (although you can use
 457                    traverse inside a transaction) as otherwise you can end up with
 458                    deadlock */
 459                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction within a traverse\n"));
 460                 tdb->ecode = TDB_ERR_LOCK;
 461                 return -1;
 462         }
 463
 464         tdb->transaction = (struct tdb_transaction *)
 465                 calloc(sizeof(struct tdb_transaction), 1);
 466         if (tdb->transaction == NULL) {
 467                 tdb->ecode = TDB_ERR_OOM;
 468                 return -1;
 469         }
 470
 471         /* a page at a time seems like a reasonable compromise between compactness and efficiency */
 472         tdb->transaction->block_size = tdb->page_size;
 473
 474         /* get the transaction write lock. This is a blocking lock. As
 475            discussed with Volker, there are a number of ways we could
 476            make this async, which we will probably do in the future */
 477         if (tdb_transaction_lock(tdb, F_WRLCK, lockflags) == -1) {
 478                 SAFE_FREE(tdb->transaction->blocks);
 479                 SAFE_FREE(tdb->transaction);
 480                 if ((lockflags & TDB_LOCK_WAIT) == 0) {
 481                         tdb->ecode = TDB_ERR_NOLOCK;
 482                 }
 483                 return -1;
 484         }
 485
 486         /* get a read lock from the freelist to the end of file. This
 487            is upgraded to a write lock during the commit */
 488         if (tdb_allrecord_lock(tdb, F_RDLCK, TDB_LOCK_WAIT, true) == -1) {
 489                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: failed to get hash locks\n"));
 490                 goto fail_allrecord_lock;
 491         }
 492
 493         /* setup a copy of the hash table heads so the hash scan in
 494            traverse can be fast */
 495         tdb->transaction->hash_heads = (uint32_t *)
 496                 calloc(tdb->header.hash_size+1, sizeof(uint32_t));
 497         if (tdb->transaction->hash_heads == NULL) {
 498                 tdb->ecode = TDB_ERR_OOM;
 499                 goto fail;
 500         }
 501         if (tdb->methods->tdb_read(tdb, FREELIST_TOP, tdb->transaction->hash_heads,
 502                                    TDB_HASHTABLE_SIZE(tdb), 0) != 0) {
 503                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_start: failed to read hash heads\n"));
 504                 tdb->ecode = TDB_ERR_IO;
 505                 goto fail;
 506         }
 507
 508         /* make sure we know about any file expansions already done by
 509            anyone else */
 510         tdb->methods->tdb_oob(tdb, tdb->map_size + 1, 1);
 511         tdb->transaction->old_map_size = tdb->map_size;
 512
 513         /* finally hook the io methods, replacing them with
 514            transaction specific methods */
 515         tdb->transaction->io_methods = tdb->methods;
 516         tdb->methods = &transaction_methods;
 517
 518         /* Trace at the end, so we get sequence number correct. */
 519         tdb_trace(tdb, "tdb_transaction_start");
 520         return 0;
 521
 522 fail:
 523         tdb_allrecord_unlock(tdb, F_RDLCK, false);
 524 fail_allrecord_lock:
 525         tdb_transaction_unlock(tdb, F_WRLCK);
 526         SAFE_FREE(tdb->transaction->blocks);
 527         SAFE_FREE(tdb->transaction->hash_heads);
 528         SAFE_FREE(tdb->transaction);
 529         return -1;
 530 }
 531
 532 int tdb_transaction_start(struct tdb_context *tdb)
 533 {
 534         return _tdb_transaction_start(tdb, TDB_LOCK_WAIT);
 535 }
 536
 537 int tdb_transaction_start_nonblock(struct tdb_context *tdb)
 538 {
 539         return _tdb_transaction_start(tdb, TDB_LOCK_NOWAIT|TDB_LOCK_PROBE);
 540 }
 541
 542 /*
 543   sync to disk
 544 */
 545 static int transaction_sync(struct tdb_context *tdb, tdb_off_t offset, tdb_len_t length)
 546 {
 547         if (tdb->flags & TDB_NOSYNC) {
 548                 return 0;
 549         }
 550
 551 #ifdef HAVE_FDATASYNC
 552         if (fdatasync(tdb->fd) != 0) {
 553 #else
 554         if (fsync(tdb->fd) != 0) {
 555 #endif
 556                 tdb->ecode = TDB_ERR_IO;
 557                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: fsync failed\n"));
 558                 return -1;
 559         }
 560 #ifdef HAVE_MMAP
 561         if (tdb->map_ptr) {
 562                 tdb_off_t moffset = offset & ~(tdb->page_size-1);
 563                 if (msync(moffset + (char *)tdb->map_ptr,
 564                           length + (offset - moffset), MS_SYNC) != 0) {
 565                         tdb->ecode = TDB_ERR_IO;
 566                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: msync failed - %s\n",
 567                                  strerror(errno)));
 568                         return -1;
 569                 }
 570         }
 571 #endif
 572         return 0;
 573 }
 574
 575
 576 static int _tdb_transaction_cancel(struct tdb_context *tdb)
 577 {
 578         int i, ret = 0;
 579
 580         if (tdb->transaction == NULL) {
 581                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_cancel: no transaction\n"));
 582                 return -1;
 583         }
 584
 585         if (tdb->transaction->nesting != 0) {
 586                 tdb->transaction->transaction_error = 1;
 587                 tdb->transaction->nesting--;
 588                 return 0;
 589         }
 590
 591         tdb->map_size = tdb->transaction->old_map_size;
 592
 593         /* free all the transaction blocks */
 594         for (i=0;i<tdb->transaction->num_blocks;i++) {
 595                 if (tdb->transaction->blocks[i] != NULL) {
 596                         free(tdb->transaction->blocks[i]);
 597                 }
 598         }
 599         SAFE_FREE(tdb->transaction->blocks);
 600
 601         if (tdb->transaction->magic_offset) {
 602                 const struct tdb_methods *methods = tdb->transaction->io_methods;
 603                 const uint32_t invalid = TDB_RECOVERY_INVALID_MAGIC;
 604
 605                 /* remove the recovery marker */
 606                 if (methods->tdb_write(tdb, tdb->transaction->magic_offset, &invalid, 4) == -1 ||
 607                 transaction_sync(tdb, tdb->transaction->magic_offset, 4) == -1) {
 608                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_cancel: failed to remove recovery magic\n"));
 609                         ret = -1;
 610                 }
 611         }
 612
 613         /* This also removes the OPEN_LOCK, if we have it. */
 614         tdb_release_transaction_locks(tdb);
 615
 616         /* restore the normal io methods */
 617         tdb->methods = tdb->transaction->io_methods;
 618
 619         SAFE_FREE(tdb->transaction->hash_heads);
 620         SAFE_FREE(tdb->transaction);
 621
 622         return ret;
 623 }
 624
 625 /*
 626   cancel the current transaction
 627 */
 628 int tdb_transaction_cancel(struct tdb_context *tdb)
 629 {
 630         tdb_trace(tdb, "tdb_transaction_cancel");
 631         return _tdb_transaction_cancel(tdb);
 632 }
 633
 634 /*
 635   work out how much space the linearised recovery data will consume
 636 */
 637 static tdb_len_t tdb_recovery_size(struct tdb_context *tdb)
 638 {
 639         tdb_len_t recovery_size = 0;
 640         int i;
 641
 642         recovery_size = sizeof(uint32_t);
 643         for (i=0;i<tdb->transaction->num_blocks;i++) {
 644                 if (i * tdb->transaction->block_size >= tdb->transaction->old_map_size) {
 645                         break;
 646                 }
 647                 if (tdb->transaction->blocks[i] == NULL) {
 648                         continue;
 649                 }
 650                 recovery_size += 2*sizeof(tdb_off_t);
 651                 if (i == tdb->transaction->num_blocks-1) {
 652                         recovery_size += tdb->transaction->last_block_size;
 653                 } else {
 654                         recovery_size += tdb->transaction->block_size;
 655                 }
 656         }
 657
 658         return recovery_size;
 659 }
 660
 661 /*
 662   allocate the recovery area, or use an existing recovery area if it is
 663   large enough
 664 */
 665 static int tdb_recovery_allocate(struct tdb_context *tdb,
 666                                  tdb_len_t *recovery_size,
 667                                  tdb_off_t *recovery_offset,
 668                                  tdb_len_t *recovery_max_size)
 669 {
 670         struct tdb_record rec;
 671         const struct tdb_methods *methods = tdb->transaction->io_methods;
 672         tdb_off_t recovery_head;
 673
 674         if (tdb_ofs_read(tdb, TDB_RECOVERY_HEAD, &recovery_head) == -1) {
 675                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to read recovery head\n"));
 676                 return -1;
 677         }
 678
 679         rec.rec_len = 0;
 680
 681         if (recovery_head != 0) {
 682                 if (methods->tdb_read(tdb, recovery_head, &rec, sizeof(rec), DOCONV()) == -1) {
 683                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to read recovery record\n"));
 684                         return -1;
 685                 }
 686                 /* ignore invalid recovery regions: can happen in crash */
 687                 if (rec.magic != TDB_RECOVERY_MAGIC &&
 688                     rec.magic != TDB_RECOVERY_INVALID_MAGIC) {
 689                         recovery_head = 0;
 690                 }
 691         }
 692
 693         *recovery_size = tdb_recovery_size(tdb);
 694
 695         if (recovery_head != 0 && *recovery_size <= rec.rec_len) {
 696                 /* it fits in the existing area */
 697                 *recovery_max_size = rec.rec_len;
 698                 *recovery_offset = recovery_head;
 699                 return 0;
 700         }
 701
 702         /* we need to free up the old recovery area, then allocate a
 703            new one at the end of the file. Note that we cannot use
 704            tdb_allocate() to allocate the new one as that might return
 705            us an area that is being currently used (as of the start of
 706            the transaction) */
 707         if (recovery_head != 0) {
 708                 if (tdb_free(tdb, recovery_head, &rec) == -1) {
 709                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to free previous recovery area\n"));
 710                         return -1;
 711                 }
 712         }
 713
 714         /* the tdb_free() call might have increased the recovery size */
 715         *recovery_size = tdb_recovery_size(tdb);
 716
 717         /* round up to a multiple of page size */
 718         *recovery_max_size = TDB_ALIGN(sizeof(rec) + *recovery_size, tdb->page_size) - sizeof(rec);
 719         *recovery_offset = tdb->map_size;
 720         recovery_head = *recovery_offset;
 721
 722         if (methods->tdb_expand_file(tdb, tdb->transaction->old_map_size,
 723                                      (tdb->map_size - tdb->transaction->old_map_size) +
 724                                      sizeof(rec) + *recovery_max_size) == -1) {
 725                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to create recovery area\n"));
 726                 return -1;
 727         }
 728
 729         /* remap the file (if using mmap) */
 730         methods->tdb_oob(tdb, tdb->map_size + 1, 1);
 731
 732         /* we have to reset the old map size so that we don't try to expand the file
 733            again in the transaction commit, which would destroy the recovery area */
 734         tdb->transaction->old_map_size = tdb->map_size;
 735
 736         /* write the recovery header offset and sync - we can sync without a race here
 737            as the magic ptr in the recovery record has not been set */
 738         CONVERT(recovery_head);
 739         if (methods->tdb_write(tdb, TDB_RECOVERY_HEAD,
 740                                &recovery_head, sizeof(tdb_off_t)) == -1) {
 741                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to write recovery head\n"));
 742                 return -1;
 743         }
 744         if (transaction_write_existing(tdb, TDB_RECOVERY_HEAD, &recovery_head, sizeof(tdb_off_t)) == -1) {
 745                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to write recovery head\n"));
 746                 return -1;
 747         }
 748
 749         return 0;
 750 }
 751
 752
 753 /*
 754   setup the recovery data that will be used on a crash during commit
 755 */
 756 static int transaction_setup_recovery(struct tdb_context *tdb,
 757                                       tdb_off_t *magic_offset)
 758 {
 759         tdb_len_t recovery_size;
 760         unsigned char *data, *p;
 761         const struct tdb_methods *methods = tdb->transaction->io_methods;
 762         struct tdb_record *rec;
 763         tdb_off_t recovery_offset, recovery_max_size;
 764         tdb_off_t old_map_size = tdb->transaction->old_map_size;
 765         uint32_t magic, tailer;
 766         int i;
 767
 768         /*
 769           check that the recovery area has enough space
 770         */
 771         if (tdb_recovery_allocate(tdb, &recovery_size,
 772                                   &recovery_offset, &recovery_max_size) == -1) {
 773                 return -1;
 774         }
 775
 776         data = (unsigned char *)malloc(recovery_size + sizeof(*rec));
 777         if (data == NULL) {
 778                 tdb->ecode = TDB_ERR_OOM;
 779                 return -1;
 780         }
 781
 782         rec = (struct tdb_record *)data;
 783         memset(rec, 0, sizeof(*rec));
 784
 785         rec->magic    = TDB_RECOVERY_INVALID_MAGIC;
 786         rec->data_len = recovery_size;
 787         rec->rec_len  = recovery_max_size;
 788         rec->key_len  = old_map_size;
 789         CONVERT(rec);
 790
 791         /* build the recovery data into a single blob to allow us to do a single
 792            large write, which should be more efficient */
 793         p = data + sizeof(*rec);
 794         for (i=0;i<tdb->transaction->num_blocks;i++) {
 795                 tdb_off_t offset;
 796                 tdb_len_t length;
 797
 798                 if (tdb->transaction->blocks[i] == NULL) {
 799                         continue;
 800                 }
 801
 802                 offset = i * tdb->transaction->block_size;
 803                 length = tdb->transaction->block_size;
 804                 if (i == tdb->transaction->num_blocks-1) {
 805                         length = tdb->transaction->last_block_size;
 806                 }
 807
 808                 if (offset >= old_map_size) {
 809                         continue;
 810                 }
 811                 if (offset + length > tdb->transaction->old_map_size) {
 812                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: transaction data over new region boundary\n"));
 813                         free(data);
 814                         tdb->ecode = TDB_ERR_CORRUPT;
 815                         return -1;
 816                 }
 817                 memcpy(p, &offset, 4);
 818                 memcpy(p+4, &length, 4);
 819                 if (DOCONV()) {
 820                         tdb_convert(p, 8);
 821                 }
 822                 /* the recovery area contains the old data, not the
 823                    new data, so we have to call the original tdb_read
 824                    method to get it */
 825                 if (methods->tdb_read(tdb, offset, p + 8, length, 0) != 0) {
 826                         free(data);
 827                         tdb->ecode = TDB_ERR_IO;
 828                         return -1;
 829                 }
 830                 p += 8 + length;
 831         }
 832
 833         /* and the tailer */
 834         tailer = sizeof(*rec) + recovery_max_size;
 835         memcpy(p, &tailer, 4);
 836         CONVERT(p);
 837
 838         /* write the recovery data to the recovery area */
 839         if (methods->tdb_write(tdb, recovery_offset, data, sizeof(*rec) + recovery_size) == -1) {
 840                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write recovery data\n"));
 841                 free(data);
 842                 tdb->ecode = TDB_ERR_IO;
 843                 return -1;
 844         }
 845         if (transaction_write_existing(tdb, recovery_offset, data, sizeof(*rec) + recovery_size) == -1) {
 846                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write secondary recovery data\n"));
 847                 free(data);
 848                 tdb->ecode = TDB_ERR_IO;
 849                 return -1;
 850         }
 851
 852         /* as we don't have ordered writes, we have to sync the recovery
 853            data before we update the magic to indicate that the recovery
 854            data is present */
 855         if (transaction_sync(tdb, recovery_offset, sizeof(*rec) + recovery_size) == -1) {
 856                 free(data);
 857                 return -1;
 858         }
 859
 860         free(data);
 861
 862         magic = TDB_RECOVERY_MAGIC;
 863         CONVERT(magic);
 864
 865         *magic_offset = recovery_offset + offsetof(struct tdb_record, magic);
 866
 867         if (methods->tdb_write(tdb, *magic_offset, &magic, sizeof(magic)) == -1) {
 868                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write recovery magic\n"));
 869                 tdb->ecode = TDB_ERR_IO;
 870                 return -1;
 871         }
 872         if (transaction_write_existing(tdb, *magic_offset, &magic, sizeof(magic)) == -1) {
 873                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write secondary recovery magic\n"));
 874                 tdb->ecode = TDB_ERR_IO;
 875                 return -1;
 876         }
 877
 878         /* ensure the recovery magic marker is on disk */
 879         if (transaction_sync(tdb, *magic_offset, sizeof(magic)) == -1) {
 880                 return -1;
 881         }
 882
 883         return 0;
 884 }
 885
 886 static int _tdb_transaction_prepare_commit(struct tdb_context *tdb)
 887 {
 888         const struct tdb_methods *methods;
 889
 890         if (tdb->transaction == NULL) {
 891                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: no transaction\n"));
 892                 return -1;
 893         }
 894
 895         if (tdb->transaction->prepared) {
 896                 tdb->ecode = TDB_ERR_EINVAL;
 897                 _tdb_transaction_cancel(tdb);
 898                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: transaction already prepared\n"));
 899                 return -1;
 900         }
 901
 902         if (tdb->transaction->transaction_error) {
 903                 tdb->ecode = TDB_ERR_IO;
 904                 _tdb_transaction_cancel(tdb);
 905                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: transaction error pending\n"));
 906                 return -1;
 907         }
 908
 909
 910         if (tdb->transaction->nesting != 0) {
 911                 return 0;
 912         }
 913
 914         /* check for a null transaction */
 915         if (tdb->transaction->blocks == NULL) {
 916                 return 0;
 917         }
 918
 919         methods = tdb->transaction->io_methods;
 920
 921         /* if there are any locks pending then the caller has not
 922            nested their locks properly, so fail the transaction */
 923         if (tdb_have_extra_locks(tdb)) {
 924                 tdb->ecode = TDB_ERR_LOCK;
 925                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: locks pending on commit\n"));
 926                 _tdb_transaction_cancel(tdb);
 927                 return -1;
 928         }
 929
 930         /* upgrade the main transaction lock region to a write lock */
 931         if (tdb_allrecord_upgrade(tdb) == -1) {
 932                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: failed to upgrade hash locks\n"));
 933                 _tdb_transaction_cancel(tdb);
 934                 return -1;
 935         }
 936
 937         /* get the open lock - this prevents new users attaching to the database
 938            during the commit */
 939         if (tdb_nest_lock(tdb, OPEN_LOCK, F_WRLCK, TDB_LOCK_WAIT) == -1) {
 940                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: failed to get open lock\n"));
 941                 _tdb_transaction_cancel(tdb);
 942                 return -1;
 943         }
 944
 945         if (!(tdb->flags & TDB_NOSYNC)) {
 946                 /* write the recovery data to the end of the file */
 947                 if (transaction_setup_recovery(tdb, &tdb->transaction->magic_offset) == -1) {
 948                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_prepare_commit: failed to setup recovery data\n"));
 949                         _tdb_transaction_cancel(tdb);
 950                         return -1;
 951                 }
 952         }
 953
 954         tdb->transaction->prepared = true;
 955
 956         /* expand the file to the new size if needed */
 957         if (tdb->map_size != tdb->transaction->old_map_size) {
 958                 if (methods->tdb_expand_file(tdb, tdb->transaction->old_map_size,
 959                                              tdb->map_size -
 960                                              tdb->transaction->old_map_size) == -1) {
 961                         tdb->ecode = TDB_ERR_IO;
 962                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_prepare_commit: expansion failed\n"));
 963                         _tdb_transaction_cancel(tdb);
 964                         return -1;
 965                 }
 966                 tdb->map_size = tdb->transaction->old_map_size;
 967                 methods->tdb_oob(tdb, tdb->map_size + 1, 1);
 968         }
 969
 970         /* Keep the open lock until the actual commit */
 971
 972         return 0;
 973 }
 974
 975 /*
 976    prepare to commit the current transaction
 977 */
 978 int tdb_transaction_prepare_commit(struct tdb_context *tdb)
 979 {
 980         tdb_trace(tdb, "tdb_transaction_prepare_commit");
 981         return _tdb_transaction_prepare_commit(tdb);
 982 }
 983
 984 /*
 985   commit the current transaction
 986 */
 987 int tdb_transaction_commit(struct tdb_context *tdb)
 988 {
 989         const struct tdb_methods *methods;
 990         int i;
 991         bool need_repack;
 992
 993         if (tdb->transaction == NULL) {
 994                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: no transaction\n"));
 995                 return -1;
 996         }
 997
 998         tdb_trace(tdb, "tdb_transaction_commit");
 999
1000         if (tdb->transaction->transaction_error) {
1001                 tdb->ecode = TDB_ERR_IO;
1002                 _tdb_transaction_cancel(tdb);
1003                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: transaction error pending\n"));
1004                 return -1;
1005         }
1006
1007
1008         if (tdb->transaction->nesting != 0) {
1009                 tdb->transaction->nesting--;
1010                 return 0;
1011         }
1012
1013         /* check for a null transaction */
1014         if (tdb->transaction->blocks == NULL) {
1015                 _tdb_transaction_cancel(tdb);
1016                 return 0;
1017         }
1018
1019         if (!tdb->transaction->prepared) {
1020                 int ret = _tdb_transaction_prepare_commit(tdb);
1021                 if (ret)
1022                         return ret;
1023         }
1024
1025         methods = tdb->transaction->io_methods;
1026
1027         /* perform all the writes */
1028         for (i=0;i<tdb->transaction->num_blocks;i++) {
1029                 tdb_off_t offset;
1030                 tdb_len_t length;
1031
1032                 if (tdb->transaction->blocks[i] == NULL) {
1033                         continue;
1034                 }
1035
1036                 offset = i * tdb->transaction->block_size;
1037                 length = tdb->transaction->block_size;
1038                 if (i == tdb->transaction->num_blocks-1) {
1039                         length = tdb->transaction->last_block_size;
1040                 }
1041
1042                 if (methods->tdb_write(tdb, offset, tdb->transaction->blocks[i], length) == -1) {
1043                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: write failed during commit\n"));
1044
1045                         /* we've overwritten part of the data and
1046                            possibly expanded the file, so we need to
1047                            run the crash recovery code */
1048                         tdb->methods = methods;
1049                         tdb_transaction_recover(tdb);
1050
1051                         _tdb_transaction_cancel(tdb);
1052
1053                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: write failed\n"));
1054                         return -1;
1055                 }
1056                 SAFE_FREE(tdb->transaction->blocks[i]);
1057         }
1058
1059         SAFE_FREE(tdb->transaction->blocks);
1060         tdb->transaction->num_blocks = 0;
1061
1062         /* ensure the new data is on disk */
1063         if (transaction_sync(tdb, 0, tdb->map_size) == -1) {
1064                 return -1;
1065         }
1066
1067         /*
1068           TODO: maybe write to some dummy hdr field, or write to magic
1069           offset without mmap, before the last sync, instead of the
1070           utime() call
1071         */
1072
1073         /* on some systems (like Linux 2.6.x) changes via mmap/msync
1074            don't change the mtime of the file, this means the file may
1075            not be backed up (as tdb rounding to block sizes means that
1076            file size changes are quite rare too). The following forces
1077            mtime changes when a transaction completes */
1078 #ifdef HAVE_UTIME
1079         utime(tdb->name, NULL);
1080 #endif
1081
1082         need_repack = tdb->transaction->need_repack;
1083
1084         /* use a transaction cancel to free memory and remove the
1085            transaction locks */
1086         _tdb_transaction_cancel(tdb);
1087
1088         if (need_repack) {
1089                 return tdb_repack(tdb);
1090         }
1091
1092         return 0;
1093 }
1094
1095
1096 /*
1097   recover from an aborted transaction. Must be called with exclusive
1098   database write access already established (including the open
1099   lock to prevent new processes attaching)
1100 */
1101 int tdb_transaction_recover(struct tdb_context *tdb)
1102 {
1103         tdb_off_t recovery_head, recovery_eof;
1104         unsigned char *data, *p;
1105         uint32_t zero = 0;
1106         struct tdb_record rec;
1107
1108         /* find the recovery area */
1109         if (tdb_ofs_read(tdb, TDB_RECOVERY_HEAD, &recovery_head) == -1) {
1110                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery head\n"));
1111                 tdb->ecode = TDB_ERR_IO;
1112                 return -1;
1113         }
1114
1115         if (recovery_head == 0) {
1116                 /* we have never allocated a recovery record */
1117                 return 0;
1118         }
1119
1120         /* read the recovery record */
1121         if (tdb->methods->tdb_read(tdb, recovery_head, &rec,
1122                                    sizeof(rec), DOCONV()) == -1) {
1123                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery record\n"));
1124                 tdb->ecode = TDB_ERR_IO;
1125                 return -1;
1126         }
1127
1128         if (rec.magic != TDB_RECOVERY_MAGIC) {
1129                 /* there is no valid recovery data */
1130                 return 0;
1131         }
1132
1133         if (tdb->read_only) {
1134                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: attempt to recover read only database\n"));
1135                 tdb->ecode = TDB_ERR_CORRUPT;
1136                 return -1;
1137         }
1138
1139         recovery_eof = rec.key_len;
1140
1141         data = (unsigned char *)malloc(rec.data_len);
1142         if (data == NULL) {
1143                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to allocate recovery data\n"));
1144                 tdb->ecode = TDB_ERR_OOM;
1145                 return -1;
1146         }
1147
1148         /* read the full recovery data */
1149         if (tdb->methods->tdb_read(tdb, recovery_head + sizeof(rec), data,
1150                                    rec.data_len, 0) == -1) {
1151                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery data\n"));
1152                 tdb->ecode = TDB_ERR_IO;
1153                 return -1;
1154         }
1155
1156         /* recover the file data */
1157         p = data;
1158         while (p+8 < data + rec.data_len) {
1159                 uint32_t ofs, len;
1160                 if (DOCONV()) {
1161                         tdb_convert(p, 8);
1162                 }
1163                 memcpy(&ofs, p, 4);
1164                 memcpy(&len, p+4, 4);
1165
1166                 if (tdb->methods->tdb_write(tdb, ofs, p+8, len) == -1) {
1167                         free(data);
1168                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to recover %d bytes at offset %d\n", len, ofs));
1169                         tdb->ecode = TDB_ERR_IO;
1170                         return -1;
1171                 }
1172                 p += 8 + len;
1173         }
1174
1175         free(data);
1176
1177         if (transaction_sync(tdb, 0, tdb->map_size) == -1) {
1178                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to sync recovery\n"));
1179                 tdb->ecode = TDB_ERR_IO;
1180                 return -1;
1181         }
1182
1183         /* if the recovery area is after the recovered eof then remove it */
1184         if (recovery_eof <= recovery_head) {
1185                 if (tdb_ofs_write(tdb, TDB_RECOVERY_HEAD, &zero) == -1) {
1186                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to remove recovery head\n"));
1187                         tdb->ecode = TDB_ERR_IO;
1188                         return -1;
1189                 }
1190         }
1191
1192         /* remove the recovery magic */
1193         if (tdb_ofs_write(tdb, recovery_head + offsetof(struct tdb_record, magic),
1194                           &zero) == -1) {
1195                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to remove recovery magic\n"));
1196                 tdb->ecode = TDB_ERR_IO;
1197                 return -1;
1198         }
1199
1200         if (transaction_sync(tdb, 0, recovery_eof) == -1) {
1201                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to sync2 recovery\n"));
1202                 tdb->ecode = TDB_ERR_IO;
1203                 return -1;
1204         }
1205
1206         TDB_LOG((tdb, TDB_DEBUG_TRACE, "tdb_transaction_recover: recovered %d byte database\n",
1207                  recovery_eof));
1208
1209         /* all done */
1210         return 0;
1211 }
1212
1213 /* Any I/O failures we say "needs recovery". */
1214 bool tdb_needs_recovery(struct tdb_context *tdb)
1215 {
1216         tdb_off_t recovery_head;
1217         struct tdb_record rec;
1218
1219         /* find the recovery area */
1220         if (tdb_ofs_read(tdb, TDB_RECOVERY_HEAD, &recovery_head) == -1) {
1221                 return true;
1222         }
1223
1224         if (recovery_head == 0) {
1225                 /* we have never allocated a recovery record */
1226                 return false;
1227         }
1228
1229         /* read the recovery record */
1230         if (tdb->methods->tdb_read(tdb, recovery_head, &rec,
1231                                    sizeof(rec), DOCONV()) == -1) {
1232                 return true;
1233         }
1234
1235         return (rec.magic == TDB_RECOVERY_MAGIC);
1236 }