tdb: more testcase fixup.
[ccan] / ccan / tdb / 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 /*
412   brlock during a transaction - ignore them
413 */
414 static int transaction_brlock(struct tdb_context *tdb,
415                               int rw_type, tdb_off_t offset, size_t len,
416                               enum tdb_lock_flags flags)
417 {
418         /* FIXME: We actually grab the open lock during a transaction. */
419         if (offset == OPEN_LOCK)
420                 return tdb_brlock(tdb, rw_type, offset, len, flags);
421         return 0;
422 }
423
424 static int transaction_brunlock(struct tdb_context *tdb,
425                                 int rw_type, tdb_off_t offset, size_t len)
426 {
427         return 0;
428 }
429
430 static const struct tdb_methods transaction_methods = {
431         transaction_read,
432         transaction_write,
433         transaction_next_hash_chain,
434         transaction_oob,
435         transaction_expand_file,
436         transaction_brlock,
437         transaction_brunlock
438 };
439
440 /*
441   sync to disk
442 */
443 static int transaction_sync(struct tdb_context *tdb, tdb_off_t offset, tdb_len_t length)
444 {       
445         if (tdb->flags & TDB_NOSYNC) {
446                 return 0;
447         }
448
449         if (fsync(tdb->fd) != 0) {
450                 tdb->ecode = TDB_ERR_IO;
451                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: fsync failed\n"));
452                 return -1;
453         }
454 #ifdef MS_SYNC
455         if (tdb->map_ptr) {
456                 tdb_off_t moffset = offset & ~(tdb->page_size-1);
457                 if (msync(moffset + (char *)tdb->map_ptr, 
458                           length + (offset - moffset), MS_SYNC) != 0) {
459                         tdb->ecode = TDB_ERR_IO;
460                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: msync failed - %s\n",
461                                  strerror(errno)));
462                         return -1;
463                 }
464         }
465 #endif
466         return 0;
467 }
468
469
470 static int _tdb_transaction_cancel(struct tdb_context *tdb)
471 {
472         int i, ret = 0;
473
474         if (tdb->transaction == NULL) {
475                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_cancel: no transaction\n"));
476                 return -1;
477         }
478
479         if (tdb->transaction->nesting != 0) {
480                 tdb->transaction->transaction_error = 1;
481                 tdb->transaction->nesting--;
482                 return 0;
483         }               
484
485         tdb->map_size = tdb->transaction->old_map_size;
486
487         /* free all the transaction blocks */
488         for (i=0;i<tdb->transaction->num_blocks;i++) {
489                 if (tdb->transaction->blocks[i] != NULL) {
490                         free(tdb->transaction->blocks[i]);
491                 }
492         }
493         SAFE_FREE(tdb->transaction->blocks);
494
495         if (tdb->transaction->magic_offset) {
496                 const struct tdb_methods *methods = tdb->transaction->io_methods;
497                 uint32_t invalid = TDB_RECOVERY_INVALID_MAGIC;
498
499                 /* remove the recovery marker */
500                 if (methods->tdb_write(tdb, tdb->transaction->magic_offset, &invalid, 4) == -1 ||
501                 transaction_sync(tdb, tdb->transaction->magic_offset, 4) == -1) {
502                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_cancel: failed to remove recovery magic\n"));
503                         ret = -1;
504                 }
505         }
506
507         /* This also removes the OPEN_LOCK, if we have it. */
508         tdb_release_extra_locks(tdb);
509
510         /* restore the normal io methods */
511         tdb->methods = tdb->transaction->io_methods;
512
513         tdb_transaction_unlock(tdb, F_WRLCK);
514         SAFE_FREE(tdb->transaction->hash_heads);
515         SAFE_FREE(tdb->transaction);
516         
517         return ret;
518 }
519
520 /*
521   start a tdb transaction. No token is returned, as only a single
522   transaction is allowed to be pending per tdb_context
523 */
524 int tdb_transaction_start(struct tdb_context *tdb)
525 {
526         /* some sanity checks */
527         if (tdb->read_only || (tdb->flags & TDB_INTERNAL) || tdb->traverse_read) {
528                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction on a read-only or internal db\n"));
529                 tdb->ecode = TDB_ERR_EINVAL;
530                 return -1;
531         }
532
533         /* cope with nested tdb_transaction_start() calls */
534         if (tdb->transaction != NULL) {
535                 if (!(tdb->flags & TDB_ALLOW_NESTING)) {
536                         tdb->ecode = TDB_ERR_NESTING;
537                         return -1;
538                 }
539                 tdb_trace(tdb, "tdb_transaction_start");
540                 tdb->transaction->nesting++;
541                 TDB_LOG((tdb, TDB_DEBUG_TRACE, "tdb_transaction_start: nesting %d\n", 
542                          tdb->transaction->nesting));
543                 return 0;
544         }
545
546         if (tdb_have_extra_locks(tdb)) {
547                 /* the caller must not have any locks when starting a
548                    transaction as otherwise we'll be screwed by lack
549                    of nested locks in posix */
550                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction with locks held\n"));
551                 tdb->ecode = TDB_ERR_LOCK;
552                 return -1;
553         }
554
555         if (tdb->travlocks.next != NULL) {
556                 /* you cannot use transactions inside a traverse (although you can use
557                    traverse inside a transaction) as otherwise you can end up with
558                    deadlock */
559                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction within a traverse\n"));
560                 tdb->ecode = TDB_ERR_LOCK;
561                 return -1;
562         }
563
564         tdb->transaction = (struct tdb_transaction *)
565                 calloc(sizeof(struct tdb_transaction), 1);
566         if (tdb->transaction == NULL) {
567                 tdb->ecode = TDB_ERR_OOM;
568                 return -1;
569         }
570
571         /* a page at a time seems like a reasonable compromise between compactness and efficiency */
572         tdb->transaction->block_size = tdb->page_size;
573
574         /* get the transaction write lock. This is a blocking lock. As
575            discussed with Volker, there are a number of ways we could
576            make this async, which we will probably do in the future */
577         if (tdb_transaction_lock(tdb, F_WRLCK) == -1) {
578                 SAFE_FREE(tdb->transaction->blocks);
579                 SAFE_FREE(tdb->transaction);
580                 return -1;
581         }
582         
583         /* get a read lock from the freelist to the end of file. This
584            is upgraded to a write lock during the commit */
585         if (tdb_allrecord_lock(tdb, F_RDLCK, TDB_LOCK_WAIT, true) == -1) {
586                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: failed to get hash locks\n"));
587                 goto fail_allrecord_lock;
588         }
589
590         /* setup a copy of the hash table heads so the hash scan in
591            traverse can be fast */
592         tdb->transaction->hash_heads = (uint32_t *)
593                 calloc(tdb->header.hash_size+1, sizeof(uint32_t));
594         if (tdb->transaction->hash_heads == NULL) {
595                 tdb->ecode = TDB_ERR_OOM;
596                 goto fail;
597         }
598         if (tdb->methods->tdb_read(tdb, FREELIST_TOP, tdb->transaction->hash_heads,
599                                    TDB_HASHTABLE_SIZE(tdb), 0) != 0) {
600                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_start: failed to read hash heads\n"));
601                 tdb->ecode = TDB_ERR_IO;
602                 goto fail;
603         }
604
605         /* make sure we know about any file expansions already done by
606            anyone else */
607         tdb->methods->tdb_oob(tdb, tdb->map_size + 1, 1);
608         tdb->transaction->old_map_size = tdb->map_size;
609
610         /* finally hook the io methods, replacing them with
611            transaction specific methods */
612         tdb->transaction->io_methods = tdb->methods;
613         tdb->methods = &transaction_methods;
614
615         /* Trace at the end, so we get sequence number correct. */
616         tdb_trace(tdb, "tdb_transaction_start");
617         return 0;
618         
619 fail:
620         tdb_allrecord_unlock(tdb, F_RDLCK, false);
621 fail_allrecord_lock:
622         tdb_transaction_unlock(tdb, F_WRLCK);
623         SAFE_FREE(tdb->transaction->blocks);
624         SAFE_FREE(tdb->transaction->hash_heads);
625         SAFE_FREE(tdb->transaction);
626         return -1;
627 }
628
629
630 /*
631   cancel the current transaction
632 */
633 int tdb_transaction_cancel(struct tdb_context *tdb)
634 {
635         tdb_trace(tdb, "tdb_transaction_cancel");
636         return _tdb_transaction_cancel(tdb);
637 }
638
639 /*
640   work out how much space the linearised recovery data will consume
641 */
642 static tdb_len_t tdb_recovery_size(struct tdb_context *tdb)
643 {
644         tdb_len_t recovery_size = 0;
645         int i;
646
647         recovery_size = sizeof(uint32_t);
648         for (i=0;i<tdb->transaction->num_blocks;i++) {
649                 if (i * tdb->transaction->block_size >= tdb->transaction->old_map_size) {
650                         break;
651                 }
652                 if (tdb->transaction->blocks[i] == NULL) {
653                         continue;
654                 }
655                 recovery_size += 2*sizeof(tdb_off_t);
656                 if (i == tdb->transaction->num_blocks-1) {
657                         recovery_size += tdb->transaction->last_block_size;
658                 } else {
659                         recovery_size += tdb->transaction->block_size;
660                 }
661         }       
662
663         return recovery_size;
664 }
665
666 /*
667   allocate the recovery area, or use an existing recovery area if it is
668   large enough
669 */
670 static int tdb_recovery_allocate(struct tdb_context *tdb, 
671                                  tdb_len_t *recovery_size,
672                                  tdb_off_t *recovery_offset,
673                                  tdb_len_t *recovery_max_size)
674 {
675         struct tdb_record rec;
676         const struct tdb_methods *methods = tdb->transaction->io_methods;
677         tdb_off_t recovery_head;
678
679         if (tdb_ofs_read(tdb, TDB_RECOVERY_HEAD, &recovery_head) == -1) {
680                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to read recovery head\n"));
681                 return -1;
682         }
683
684         rec.rec_len = 0;
685
686         if (recovery_head != 0) {
687                 if (methods->tdb_read(tdb, recovery_head, &rec, sizeof(rec), DOCONV()) == -1) {
688                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to read recovery record\n"));
689                         return -1;
690                 }
691                 /* ignore invalid recovery regions: can happen in crash */
692                 if (rec.magic != TDB_RECOVERY_MAGIC &&
693                     rec.magic != TDB_RECOVERY_INVALID_MAGIC) {
694                         recovery_head = 0;
695                 }
696         }
697
698         *recovery_size = tdb_recovery_size(tdb);
699
700         if (recovery_head != 0 && *recovery_size <= rec.rec_len) {
701                 /* it fits in the existing area */
702                 *recovery_max_size = rec.rec_len;
703                 *recovery_offset = recovery_head;
704                 return 0;
705         }
706
707         /* we need to free up the old recovery area, then allocate a
708            new one at the end of the file. Note that we cannot use
709            tdb_allocate() to allocate the new one as that might return
710            us an area that is being currently used (as of the start of
711            the transaction) */
712         if (recovery_head != 0) {
713                 if (tdb_free(tdb, recovery_head, &rec) == -1) {
714                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to free previous recovery area\n"));
715                         return -1;
716                 }
717         }
718
719         /* the tdb_free() call might have increased the recovery size */
720         *recovery_size = tdb_recovery_size(tdb);
721
722         /* round up to a multiple of page size */
723         *recovery_max_size = TDB_ALIGN(sizeof(rec) + *recovery_size, tdb->page_size) - sizeof(rec);
724         *recovery_offset = tdb->map_size;
725         recovery_head = *recovery_offset;
726
727         if (methods->tdb_expand_file(tdb, tdb->transaction->old_map_size, 
728                                      (tdb->map_size - tdb->transaction->old_map_size) +
729                                      sizeof(rec) + *recovery_max_size) == -1) {
730                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to create recovery area\n"));
731                 return -1;
732         }
733
734         /* remap the file (if using mmap) */
735         methods->tdb_oob(tdb, tdb->map_size + 1, 1);
736
737         /* we have to reset the old map size so that we don't try to expand the file
738            again in the transaction commit, which would destroy the recovery area */
739         tdb->transaction->old_map_size = tdb->map_size;
740
741         /* write the recovery header offset and sync - we can sync without a race here
742            as the magic ptr in the recovery record has not been set */
743         CONVERT(recovery_head);
744         if (methods->tdb_write(tdb, TDB_RECOVERY_HEAD, 
745                                &recovery_head, sizeof(tdb_off_t)) == -1) {
746                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to write recovery head\n"));
747                 return -1;
748         }
749         if (transaction_write_existing(tdb, TDB_RECOVERY_HEAD, &recovery_head, sizeof(tdb_off_t)) == -1) {
750                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to write recovery head\n"));
751                 return -1;
752         }
753
754         return 0;
755 }
756
757
758 /*
759   setup the recovery data that will be used on a crash during commit
760 */
761 static int transaction_setup_recovery(struct tdb_context *tdb, 
762                                       tdb_off_t *magic_offset)
763 {
764         tdb_len_t recovery_size;
765         unsigned char *data, *p;
766         const struct tdb_methods *methods = tdb->transaction->io_methods;
767         struct tdb_record *rec;
768         tdb_off_t recovery_offset, recovery_max_size;
769         tdb_off_t old_map_size = tdb->transaction->old_map_size;
770         uint32_t magic, tailer;
771         int i;
772
773         /*
774           check that the recovery area has enough space
775         */
776         if (tdb_recovery_allocate(tdb, &recovery_size, 
777                                   &recovery_offset, &recovery_max_size) == -1) {
778                 return -1;
779         }
780
781         data = (unsigned char *)malloc(recovery_size + sizeof(*rec));
782         if (data == NULL) {
783                 tdb->ecode = TDB_ERR_OOM;
784                 return -1;
785         }
786
787         rec = (struct tdb_record *)data;
788         memset(rec, 0, sizeof(*rec));
789
790         rec->magic    = TDB_RECOVERY_INVALID_MAGIC;
791         rec->data_len = recovery_size;
792         rec->rec_len  = recovery_max_size;
793         rec->key_len  = old_map_size;
794         CONVERT(rec);
795
796         /* build the recovery data into a single blob to allow us to do a single
797            large write, which should be more efficient */
798         p = data + sizeof(*rec);
799         for (i=0;i<tdb->transaction->num_blocks;i++) {
800                 tdb_off_t offset;
801                 tdb_len_t length;
802
803                 if (tdb->transaction->blocks[i] == NULL) {
804                         continue;
805                 }
806
807                 offset = i * tdb->transaction->block_size;
808                 length = tdb->transaction->block_size;
809                 if (i == tdb->transaction->num_blocks-1) {
810                         length = tdb->transaction->last_block_size;
811                 }
812                 
813                 if (offset >= old_map_size) {
814                         continue;
815                 }
816                 if (offset + length > tdb->transaction->old_map_size) {
817                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: transaction data over new region boundary\n"));
818                         free(data);
819                         tdb->ecode = TDB_ERR_CORRUPT;
820                         return -1;
821                 }
822                 memcpy(p, &offset, 4);
823                 memcpy(p+4, &length, 4);
824                 if (DOCONV()) {
825                         tdb_convert(p, 8);
826                 }
827                 /* the recovery area contains the old data, not the
828                    new data, so we have to call the original tdb_read
829                    method to get it */
830                 if (methods->tdb_read(tdb, offset, p + 8, length, 0) != 0) {
831                         free(data);
832                         tdb->ecode = TDB_ERR_IO;
833                         return -1;
834                 }
835                 p += 8 + length;
836         }
837
838         /* and the tailer */
839         tailer = sizeof(*rec) + recovery_max_size;
840         memcpy(p, &tailer, 4);
841         CONVERT(p);
842
843         /* write the recovery data to the recovery area */
844         if (methods->tdb_write(tdb, recovery_offset, data, sizeof(*rec) + recovery_size) == -1) {
845                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write recovery data\n"));
846                 free(data);
847                 tdb->ecode = TDB_ERR_IO;
848                 return -1;
849         }
850         if (transaction_write_existing(tdb, recovery_offset, data, sizeof(*rec) + recovery_size) == -1) {
851                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write secondary recovery data\n"));
852                 free(data);
853                 tdb->ecode = TDB_ERR_IO;
854                 return -1;
855         }
856
857         /* as we don't have ordered writes, we have to sync the recovery
858            data before we update the magic to indicate that the recovery
859            data is present */
860         if (transaction_sync(tdb, recovery_offset, sizeof(*rec) + recovery_size) == -1) {
861                 free(data);
862                 return -1;
863         }
864
865         free(data);
866
867         magic = TDB_RECOVERY_MAGIC;
868         CONVERT(magic);
869
870         *magic_offset = recovery_offset + offsetof(struct tdb_record, magic);
871
872         if (methods->tdb_write(tdb, *magic_offset, &magic, sizeof(magic)) == -1) {
873                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write recovery magic\n"));
874                 tdb->ecode = TDB_ERR_IO;
875                 return -1;
876         }
877         if (transaction_write_existing(tdb, *magic_offset, &magic, sizeof(magic)) == -1) {
878                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write secondary recovery magic\n"));
879                 tdb->ecode = TDB_ERR_IO;
880                 return -1;
881         }
882
883         /* ensure the recovery magic marker is on disk */
884         if (transaction_sync(tdb, *magic_offset, sizeof(magic)) == -1) {
885                 return -1;
886         }
887
888         return 0;
889 }
890
891 static int _tdb_transaction_prepare_commit(struct tdb_context *tdb)
892 {       
893         const struct tdb_methods *methods;
894
895         if (tdb->transaction == NULL) {
896                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: no transaction\n"));
897                 return -1;
898         }
899
900         if (tdb->transaction->prepared) {
901                 tdb->ecode = TDB_ERR_EINVAL;
902                 _tdb_transaction_cancel(tdb);
903                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: transaction already prepared\n"));
904                 return -1;
905         }
906
907         if (tdb->transaction->transaction_error) {
908                 tdb->ecode = TDB_ERR_IO;
909                 _tdb_transaction_cancel(tdb);
910                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: transaction error pending\n"));
911                 return -1;
912         }
913
914
915         if (tdb->transaction->nesting != 0) {
916                 tdb->transaction->nesting--;
917                 return 0;
918         }               
919
920         /* check for a null transaction */
921         if (tdb->transaction->blocks == NULL) {
922                 return 0;
923         }
924
925         methods = tdb->transaction->io_methods;
926         
927         /* if there are any locks pending then the caller has not
928            nested their locks properly, so fail the transaction */
929         if (tdb_have_extra_locks(tdb)) {
930                 tdb->ecode = TDB_ERR_LOCK;
931                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: locks pending on commit\n"));
932                 _tdb_transaction_cancel(tdb);
933                 return -1;
934         }
935
936         /* upgrade the main transaction lock region to a write lock */
937         if (tdb_allrecord_upgrade(tdb) == -1) {
938                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: failed to upgrade hash locks\n"));
939                 _tdb_transaction_cancel(tdb);
940                 return -1;
941         }
942
943         /* get the open lock - this prevents new users attaching to the database
944            during the commit */
945         if (tdb_nest_lock(tdb, OPEN_LOCK, F_WRLCK, TDB_LOCK_WAIT) == -1) {
946                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: failed to get open lock\n"));
947                 _tdb_transaction_cancel(tdb);
948                 return -1;
949         }
950
951         if (!(tdb->flags & TDB_NOSYNC)) {
952                 /* write the recovery data to the end of the file */
953                 if (transaction_setup_recovery(tdb, &tdb->transaction->magic_offset) == -1) {
954                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_prepare_commit: failed to setup recovery data\n"));
955                         _tdb_transaction_cancel(tdb);
956                         return -1;
957                 }
958         }
959
960         tdb->transaction->prepared = true;
961
962         /* expand the file to the new size if needed */
963         if (tdb->map_size != tdb->transaction->old_map_size) {
964                 if (methods->tdb_expand_file(tdb, tdb->transaction->old_map_size, 
965                                              tdb->map_size - 
966                                              tdb->transaction->old_map_size) == -1) {
967                         tdb->ecode = TDB_ERR_IO;
968                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_prepare_commit: expansion failed\n"));
969                         _tdb_transaction_cancel(tdb);
970                         return -1;
971                 }
972                 tdb->map_size = tdb->transaction->old_map_size;
973                 methods->tdb_oob(tdb, tdb->map_size + 1, 1);
974         }
975
976         /* Keep the open lock until the actual commit */
977
978         return 0;
979 }
980
981 /*
982    prepare to commit the current transaction
983 */
984 int tdb_transaction_prepare_commit(struct tdb_context *tdb)
985 {       
986         tdb_trace(tdb, "tdb_transaction_prepare_commit");
987         return _tdb_transaction_prepare_commit(tdb);
988 }
989
990 /*
991   commit the current transaction
992 */
993 int tdb_transaction_commit(struct tdb_context *tdb)
994 {       
995         const struct tdb_methods *methods;
996         int i;
997         bool need_repack;
998
999         if (tdb->transaction == NULL) {
1000                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: no transaction\n"));
1001                 return -1;
1002         }
1003
1004         tdb_trace(tdb, "tdb_transaction_commit");
1005
1006         if (tdb->transaction->transaction_error) {
1007                 tdb->ecode = TDB_ERR_IO;
1008                 tdb_transaction_cancel(tdb);
1009                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: transaction error pending\n"));
1010                 return -1;
1011         }
1012
1013
1014         if (tdb->transaction->nesting != 0) {
1015                 tdb->transaction->nesting--;
1016                 return 0;
1017         }
1018
1019         /* check for a null transaction */
1020         if (tdb->transaction->blocks == NULL) {
1021                 _tdb_transaction_cancel(tdb);
1022                 return 0;
1023         }
1024
1025         if (!tdb->transaction->prepared) {
1026                 int ret = _tdb_transaction_prepare_commit(tdb);
1027                 if (ret)
1028                         return ret;
1029         }
1030
1031         methods = tdb->transaction->io_methods;
1032
1033         /* perform all the writes */
1034         for (i=0;i<tdb->transaction->num_blocks;i++) {
1035                 tdb_off_t offset;
1036                 tdb_len_t length;
1037
1038                 if (tdb->transaction->blocks[i] == NULL) {
1039                         continue;
1040                 }
1041
1042                 offset = i * tdb->transaction->block_size;
1043                 length = tdb->transaction->block_size;
1044                 if (i == tdb->transaction->num_blocks-1) {
1045                         length = tdb->transaction->last_block_size;
1046                 }
1047
1048                 if (methods->tdb_write(tdb, offset, tdb->transaction->blocks[i], length) == -1) {
1049                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: write failed during commit\n"));
1050                         
1051                         /* we've overwritten part of the data and
1052                            possibly expanded the file, so we need to
1053                            run the crash recovery code */
1054                         tdb->methods = methods;
1055                         tdb_transaction_recover(tdb); 
1056
1057                         _tdb_transaction_cancel(tdb);
1058
1059                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: write failed\n"));
1060                         return -1;
1061                 }
1062                 SAFE_FREE(tdb->transaction->blocks[i]);
1063         } 
1064
1065         SAFE_FREE(tdb->transaction->blocks);
1066         tdb->transaction->num_blocks = 0;
1067
1068         /* ensure the new data is on disk */
1069         if (transaction_sync(tdb, 0, tdb->map_size) == -1) {
1070                 return -1;
1071         }
1072
1073         /*
1074           TODO: maybe write to some dummy hdr field, or write to magic
1075           offset without mmap, before the last sync, instead of the
1076           utime() call
1077         */
1078
1079         /* on some systems (like Linux 2.6.x) changes via mmap/msync
1080            don't change the mtime of the file, this means the file may
1081            not be backed up (as tdb rounding to block sizes means that
1082            file size changes are quite rare too). The following forces
1083            mtime changes when a transaction completes */
1084 #if HAVE_UTIME
1085         utime(tdb->name, NULL);
1086 #endif
1087
1088         need_repack = tdb->transaction->need_repack;
1089
1090         /* use a transaction cancel to free memory and remove the
1091            transaction locks */
1092         _tdb_transaction_cancel(tdb);
1093
1094         if (need_repack) {
1095                 return tdb_repack(tdb);
1096         }
1097
1098         return 0;
1099 }
1100
1101
1102 /*
1103   recover from an aborted transaction. Must be called with exclusive
1104   database write access already established (including the open
1105   lock to prevent new processes attaching)
1106 */
1107 int tdb_transaction_recover(struct tdb_context *tdb)
1108 {
1109         tdb_off_t recovery_head, recovery_eof;
1110         unsigned char *data, *p;
1111         uint32_t zero = 0;
1112         struct tdb_record rec;
1113
1114         /* find the recovery area */
1115         if (tdb_ofs_read(tdb, TDB_RECOVERY_HEAD, &recovery_head) == -1) {
1116                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery head\n"));
1117                 tdb->ecode = TDB_ERR_IO;
1118                 return -1;
1119         }
1120
1121         if (recovery_head == 0) {
1122                 /* we have never allocated a recovery record */
1123                 return 0;
1124         }
1125
1126         /* read the recovery record */
1127         if (tdb->methods->tdb_read(tdb, recovery_head, &rec, 
1128                                    sizeof(rec), DOCONV()) == -1) {
1129                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery record\n"));           
1130                 tdb->ecode = TDB_ERR_IO;
1131                 return -1;
1132         }
1133
1134         if (rec.magic != TDB_RECOVERY_MAGIC) {
1135                 /* there is no valid recovery data */
1136                 return 0;
1137         }
1138
1139         if (tdb->read_only) {
1140                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: attempt to recover read only database\n"));
1141                 tdb->ecode = TDB_ERR_CORRUPT;
1142                 return -1;
1143         }
1144
1145         recovery_eof = rec.key_len;
1146
1147         data = (unsigned char *)malloc(rec.data_len);
1148         if (data == NULL) {
1149                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to allocate recovery data\n"));         
1150                 tdb->ecode = TDB_ERR_OOM;
1151                 return -1;
1152         }
1153
1154         /* read the full recovery data */
1155         if (tdb->methods->tdb_read(tdb, recovery_head + sizeof(rec), data,
1156                                    rec.data_len, 0) == -1) {
1157                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery data\n"));             
1158                 tdb->ecode = TDB_ERR_IO;
1159                 return -1;
1160         }
1161
1162         /* recover the file data */
1163         p = data;
1164         while (p+8 < data + rec.data_len) {
1165                 uint32_t ofs, len;
1166                 if (DOCONV()) {
1167                         tdb_convert(p, 8);
1168                 }
1169                 memcpy(&ofs, p, 4);
1170                 memcpy(&len, p+4, 4);
1171
1172                 if (tdb->methods->tdb_write(tdb, ofs, p+8, len) == -1) {
1173                         free(data);
1174                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to recover %d bytes at offset %d\n", len, ofs));
1175                         tdb->ecode = TDB_ERR_IO;
1176                         return -1;
1177                 }
1178                 p += 8 + len;
1179         }
1180
1181         free(data);
1182
1183         if (transaction_sync(tdb, 0, tdb->map_size) == -1) {
1184                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to sync recovery\n"));
1185                 tdb->ecode = TDB_ERR_IO;
1186                 return -1;
1187         }
1188
1189         /* if the recovery area is after the recovered eof then remove it */
1190         if (recovery_eof <= recovery_head) {
1191                 if (tdb_ofs_write(tdb, TDB_RECOVERY_HEAD, &zero) == -1) {
1192                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to remove recovery head\n"));
1193                         tdb->ecode = TDB_ERR_IO;
1194                         return -1;                      
1195                 }
1196         }
1197
1198         /* remove the recovery magic */
1199         if (tdb_ofs_write(tdb, recovery_head + offsetof(struct tdb_record, magic),
1200                           &zero) == -1) {
1201                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to remove recovery magic\n"));
1202                 tdb->ecode = TDB_ERR_IO;
1203                 return -1;                      
1204         }
1205         
1206         if (transaction_sync(tdb, 0, recovery_eof) == -1) {
1207                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to sync2 recovery\n"));
1208                 tdb->ecode = TDB_ERR_IO;
1209                 return -1;
1210         }
1211
1212         TDB_LOG((tdb, TDB_DEBUG_TRACE, "tdb_transaction_recover: recovered %d byte database\n", 
1213                  recovery_eof));
1214
1215         /* all done */
1216         return 0;
1217 }