tdb: cleanup: rename global_lock to allrecord_lock.
[samba.git] / 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         /* set when the OPEN_LOCK has been taken */
139         bool open_lock_taken;
140
141         /* old file size before transaction */
142         tdb_len_t old_map_size;
143
144         /* we should re-pack on commit */
145         bool need_repack;
146 };
147
148
149 /*
150   read while in a transaction. We need to check first if the data is in our list
151   of transaction elements, then if not do a real read
152 */
153 static int transaction_read(struct tdb_context *tdb, tdb_off_t off, void *buf, 
154                             tdb_len_t len, int cv)
155 {
156         uint32_t blk;
157
158         /* break it down into block sized ops */
159         while (len + (off % tdb->transaction->block_size) > tdb->transaction->block_size) {
160                 tdb_len_t len2 = tdb->transaction->block_size - (off % tdb->transaction->block_size);
161                 if (transaction_read(tdb, off, buf, len2, cv) != 0) {
162                         return -1;
163                 }
164                 len -= len2;
165                 off += len2;
166                 buf = (void *)(len2 + (char *)buf);
167         }
168
169         if (len == 0) {
170                 return 0;
171         }
172
173         blk = off / tdb->transaction->block_size;
174
175         /* see if we have it in the block list */
176         if (tdb->transaction->num_blocks <= blk ||
177             tdb->transaction->blocks[blk] == NULL) {
178                 /* nope, do a real read */
179                 if (tdb->transaction->io_methods->tdb_read(tdb, off, buf, len, cv) != 0) {
180                         goto fail;
181                 }
182                 return 0;
183         }
184
185         /* it is in the block list. Now check for the last block */
186         if (blk == tdb->transaction->num_blocks-1) {
187                 if (len > tdb->transaction->last_block_size) {
188                         goto fail;
189                 }
190         }
191         
192         /* now copy it out of this block */
193         memcpy(buf, tdb->transaction->blocks[blk] + (off % tdb->transaction->block_size), len);
194         if (cv) {
195                 tdb_convert(buf, len);
196         }
197         return 0;
198
199 fail:
200         TDB_LOG((tdb, TDB_DEBUG_FATAL, "transaction_read: failed at off=%d len=%d\n", off, len));
201         tdb->ecode = TDB_ERR_IO;
202         tdb->transaction->transaction_error = 1;
203         return -1;
204 }
205
206
207 /*
208   write while in a transaction
209 */
210 static int transaction_write(struct tdb_context *tdb, tdb_off_t off, 
211                              const void *buf, tdb_len_t len)
212 {
213         uint32_t blk;
214
215         /* Only a commit is allowed on a prepared transaction */
216         if (tdb->transaction->prepared) {
217                 tdb->ecode = TDB_ERR_EINVAL;
218                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "transaction_write: transaction already prepared, write not allowed\n"));
219                 tdb->transaction->transaction_error = 1;
220                 return -1;
221         }
222
223         /* if the write is to a hash head, then update the transaction
224            hash heads */
225         if (len == sizeof(tdb_off_t) && off >= FREELIST_TOP &&
226             off < FREELIST_TOP+TDB_HASHTABLE_SIZE(tdb)) {
227                 uint32_t chain = (off-FREELIST_TOP) / sizeof(tdb_off_t);
228                 memcpy(&tdb->transaction->hash_heads[chain], buf, len);
229         }
230
231         /* break it up into block sized chunks */
232         while (len + (off % tdb->transaction->block_size) > tdb->transaction->block_size) {
233                 tdb_len_t len2 = tdb->transaction->block_size - (off % tdb->transaction->block_size);
234                 if (transaction_write(tdb, off, buf, len2) != 0) {
235                         return -1;
236                 }
237                 len -= len2;
238                 off += len2;
239                 if (buf != NULL) {
240                         buf = (const void *)(len2 + (const char *)buf);
241                 }
242         }
243
244         if (len == 0) {
245                 return 0;
246         }
247
248         blk = off / tdb->transaction->block_size;
249         off = off % tdb->transaction->block_size;
250
251         if (tdb->transaction->num_blocks <= blk) {
252                 uint8_t **new_blocks;
253                 /* expand the blocks array */
254                 if (tdb->transaction->blocks == NULL) {
255                         new_blocks = (uint8_t **)malloc(
256                                 (blk+1)*sizeof(uint8_t *));
257                 } else {
258                         new_blocks = (uint8_t **)realloc(
259                                 tdb->transaction->blocks,
260                                 (blk+1)*sizeof(uint8_t *));
261                 }
262                 if (new_blocks == NULL) {
263                         tdb->ecode = TDB_ERR_OOM;
264                         goto fail;
265                 }
266                 memset(&new_blocks[tdb->transaction->num_blocks], 0, 
267                        (1+(blk - tdb->transaction->num_blocks))*sizeof(uint8_t *));
268                 tdb->transaction->blocks = new_blocks;
269                 tdb->transaction->num_blocks = blk+1;
270                 tdb->transaction->last_block_size = 0;
271         }
272
273         /* allocate and fill a block? */
274         if (tdb->transaction->blocks[blk] == NULL) {
275                 tdb->transaction->blocks[blk] = (uint8_t *)calloc(tdb->transaction->block_size, 1);
276                 if (tdb->transaction->blocks[blk] == NULL) {
277                         tdb->ecode = TDB_ERR_OOM;
278                         tdb->transaction->transaction_error = 1;
279                         return -1;                      
280                 }
281                 if (tdb->transaction->old_map_size > blk * tdb->transaction->block_size) {
282                         tdb_len_t len2 = tdb->transaction->block_size;
283                         if (len2 + (blk * tdb->transaction->block_size) > tdb->transaction->old_map_size) {
284                                 len2 = tdb->transaction->old_map_size - (blk * tdb->transaction->block_size);
285                         }
286                         if (tdb->transaction->io_methods->tdb_read(tdb, blk * tdb->transaction->block_size, 
287                                                                    tdb->transaction->blocks[blk], 
288                                                                    len2, 0) != 0) {
289                                 SAFE_FREE(tdb->transaction->blocks[blk]);                               
290                                 tdb->ecode = TDB_ERR_IO;
291                                 goto fail;
292                         }
293                         if (blk == tdb->transaction->num_blocks-1) {
294                                 tdb->transaction->last_block_size = len2;
295                         }                       
296                 }
297         }
298         
299         /* overwrite part of an existing block */
300         if (buf == NULL) {
301                 memset(tdb->transaction->blocks[blk] + off, 0, len);
302         } else {
303                 memcpy(tdb->transaction->blocks[blk] + off, buf, len);
304         }
305         if (blk == tdb->transaction->num_blocks-1) {
306                 if (len + off > tdb->transaction->last_block_size) {
307                         tdb->transaction->last_block_size = len + off;
308                 }
309         }
310
311         return 0;
312
313 fail:
314         TDB_LOG((tdb, TDB_DEBUG_FATAL, "transaction_write: failed at off=%d len=%d\n", 
315                  (blk*tdb->transaction->block_size) + off, len));
316         tdb->transaction->transaction_error = 1;
317         return -1;
318 }
319
320
321 /*
322   write while in a transaction - this varient never expands the transaction blocks, it only
323   updates existing blocks. This means it cannot change the recovery size
324 */
325 static int transaction_write_existing(struct tdb_context *tdb, tdb_off_t off, 
326                                       const void *buf, tdb_len_t len)
327 {
328         uint32_t blk;
329
330         /* break it up into block sized chunks */
331         while (len + (off % tdb->transaction->block_size) > tdb->transaction->block_size) {
332                 tdb_len_t len2 = tdb->transaction->block_size - (off % tdb->transaction->block_size);
333                 if (transaction_write_existing(tdb, off, buf, len2) != 0) {
334                         return -1;
335                 }
336                 len -= len2;
337                 off += len2;
338                 if (buf != NULL) {
339                         buf = (const void *)(len2 + (const char *)buf);
340                 }
341         }
342
343         if (len == 0) {
344                 return 0;
345         }
346
347         blk = off / tdb->transaction->block_size;
348         off = off % tdb->transaction->block_size;
349
350         if (tdb->transaction->num_blocks <= blk ||
351             tdb->transaction->blocks[blk] == NULL) {
352                 return 0;
353         }
354
355         if (blk == tdb->transaction->num_blocks-1 &&
356             off + len > tdb->transaction->last_block_size) {
357                 if (off >= tdb->transaction->last_block_size) {
358                         return 0;
359                 }
360                 len = tdb->transaction->last_block_size - off;
361         }
362
363         /* overwrite part of an existing block */
364         memcpy(tdb->transaction->blocks[blk] + off, buf, len);
365
366         return 0;
367 }
368
369
370 /*
371   accelerated hash chain head search, using the cached hash heads
372 */
373 static void transaction_next_hash_chain(struct tdb_context *tdb, uint32_t *chain)
374 {
375         uint32_t h = *chain;
376         for (;h < tdb->header.hash_size;h++) {
377                 /* the +1 takes account of the freelist */
378                 if (0 != tdb->transaction->hash_heads[h+1]) {
379                         break;
380                 }
381         }
382         (*chain) = h;
383 }
384
385 /*
386   out of bounds check during a transaction
387 */
388 static int transaction_oob(struct tdb_context *tdb, tdb_off_t len, int probe)
389 {
390         if (len <= tdb->map_size) {
391                 return 0;
392         }
393         tdb->ecode = TDB_ERR_IO;
394         return -1;
395 }
396
397 /*
398   transaction version of tdb_expand().
399 */
400 static int transaction_expand_file(struct tdb_context *tdb, tdb_off_t size, 
401                                    tdb_off_t addition)
402 {
403         /* add a write to the transaction elements, so subsequent
404            reads see the zero data */
405         if (transaction_write(tdb, size, NULL, addition) != 0) {
406                 return -1;
407         }
408
409         tdb->transaction->need_repack = true;
410
411         return 0;
412 }
413
414 /*
415   brlock during a transaction - ignore them
416 */
417 static int transaction_brlock(struct tdb_context *tdb,
418                               int rw_type, tdb_off_t offset, size_t len,
419                               enum tdb_lock_flags flags)
420 {
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 /*
442   start a tdb transaction. No token is returned, as only a single
443   transaction is allowed to be pending per tdb_context
444 */
445 int tdb_transaction_start(struct tdb_context *tdb)
446 {
447         /* some sanity checks */
448         if (tdb->read_only || (tdb->flags & TDB_INTERNAL) || tdb->traverse_read) {
449                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction on a read-only or internal db\n"));
450                 tdb->ecode = TDB_ERR_EINVAL;
451                 return -1;
452         }
453
454         /* cope with nested tdb_transaction_start() calls */
455         if (tdb->transaction != NULL) {
456                 if (!(tdb->flags & TDB_ALLOW_NESTING)) {
457                         tdb->ecode = TDB_ERR_NESTING;
458                         return -1;
459                 }
460                 tdb->transaction->nesting++;
461                 TDB_LOG((tdb, TDB_DEBUG_TRACE, "tdb_transaction_start: nesting %d\n", 
462                          tdb->transaction->nesting));
463                 return 0;
464         }
465
466         if (tdb->num_locks != 0 || tdb->allrecord_lock.count) {
467                 /* the caller must not have any locks when starting a
468                    transaction as otherwise we'll be screwed by lack
469                    of nested locks in posix */
470                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction with locks held\n"));
471                 tdb->ecode = TDB_ERR_LOCK;
472                 return -1;
473         }
474
475         if (tdb->travlocks.next != NULL) {
476                 /* you cannot use transactions inside a traverse (although you can use
477                    traverse inside a transaction) as otherwise you can end up with
478                    deadlock */
479                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction within a traverse\n"));
480                 tdb->ecode = TDB_ERR_LOCK;
481                 return -1;
482         }
483
484         tdb->transaction = (struct tdb_transaction *)
485                 calloc(sizeof(struct tdb_transaction), 1);
486         if (tdb->transaction == NULL) {
487                 tdb->ecode = TDB_ERR_OOM;
488                 return -1;
489         }
490
491         /* a page at a time seems like a reasonable compromise between compactness and efficiency */
492         tdb->transaction->block_size = tdb->page_size;
493
494         /* get the transaction write lock. This is a blocking lock. As
495            discussed with Volker, there are a number of ways we could
496            make this async, which we will probably do in the future */
497         if (tdb_transaction_lock(tdb, F_WRLCK) == -1) {
498                 SAFE_FREE(tdb->transaction->blocks);
499                 SAFE_FREE(tdb->transaction);
500                 return -1;
501         }
502         
503         /* get a read lock from the freelist to the end of file. This
504            is upgraded to a write lock during the commit */
505         if (tdb_brlock(tdb, F_RDLCK, FREELIST_TOP, 0, TDB_LOCK_WAIT) == -1) {
506                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: failed to get hash locks\n"));
507                 tdb->ecode = TDB_ERR_LOCK;
508                 goto fail;
509         }
510
511         /* setup a copy of the hash table heads so the hash scan in
512            traverse can be fast */
513         tdb->transaction->hash_heads = (uint32_t *)
514                 calloc(tdb->header.hash_size+1, sizeof(uint32_t));
515         if (tdb->transaction->hash_heads == NULL) {
516                 tdb->ecode = TDB_ERR_OOM;
517                 goto fail;
518         }
519         if (tdb->methods->tdb_read(tdb, FREELIST_TOP, tdb->transaction->hash_heads,
520                                    TDB_HASHTABLE_SIZE(tdb), 0) != 0) {
521                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_start: failed to read hash heads\n"));
522                 tdb->ecode = TDB_ERR_IO;
523                 goto fail;
524         }
525
526         /* make sure we know about any file expansions already done by
527            anyone else */
528         tdb->methods->tdb_oob(tdb, tdb->map_size + 1, 1);
529         tdb->transaction->old_map_size = tdb->map_size;
530
531         /* finally hook the io methods, replacing them with
532            transaction specific methods */
533         tdb->transaction->io_methods = tdb->methods;
534         tdb->methods = &transaction_methods;
535
536         /* Trace at the end, so we get sequence number correct. */
537         tdb_trace(tdb, "tdb_transaction_start");
538         return 0;
539         
540 fail:
541         tdb_brunlock(tdb, F_RDLCK, FREELIST_TOP, 0);
542         tdb_transaction_unlock(tdb, F_WRLCK);
543         SAFE_FREE(tdb->transaction->blocks);
544         SAFE_FREE(tdb->transaction->hash_heads);
545         SAFE_FREE(tdb->transaction);
546         return -1;
547 }
548
549
550 /*
551   sync to disk
552 */
553 static int transaction_sync(struct tdb_context *tdb, tdb_off_t offset, tdb_len_t length)
554 {       
555         if (tdb->flags & TDB_NOSYNC) {
556                 return 0;
557         }
558
559         if (fdatasync(tdb->fd) != 0) {
560                 tdb->ecode = TDB_ERR_IO;
561                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: fsync failed\n"));
562                 return -1;
563         }
564 #ifdef HAVE_MMAP
565         if (tdb->map_ptr) {
566                 tdb_off_t moffset = offset & ~(tdb->page_size-1);
567                 if (msync(moffset + (char *)tdb->map_ptr, 
568                           length + (offset - moffset), MS_SYNC) != 0) {
569                         tdb->ecode = TDB_ERR_IO;
570                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: msync failed - %s\n",
571                                  strerror(errno)));
572                         return -1;
573                 }
574         }
575 #endif
576         return 0;
577 }
578
579
580 /* ltype is F_WRLCK after prepare. */
581 static int _tdb_transaction_cancel(struct tdb_context *tdb, int ltype)
582 {       
583         int i, ret = 0;
584
585         if (tdb->transaction == NULL) {
586                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_cancel: no transaction\n"));
587                 return -1;
588         }
589
590         if (tdb->transaction->nesting != 0) {
591                 tdb->transaction->transaction_error = 1;
592                 tdb->transaction->nesting--;
593                 return 0;
594         }               
595
596         tdb->map_size = tdb->transaction->old_map_size;
597
598         /* free all the transaction blocks */
599         for (i=0;i<tdb->transaction->num_blocks;i++) {
600                 if (tdb->transaction->blocks[i] != NULL) {
601                         free(tdb->transaction->blocks[i]);
602                 }
603         }
604         SAFE_FREE(tdb->transaction->blocks);
605
606         if (tdb->transaction->magic_offset) {
607                 const struct tdb_methods *methods = tdb->transaction->io_methods;
608                 const uint32_t invalid = TDB_RECOVERY_INVALID_MAGIC;
609
610                 /* remove the recovery marker */
611                 if (methods->tdb_write(tdb, tdb->transaction->magic_offset, &invalid, 4) == -1 ||
612                 transaction_sync(tdb, tdb->transaction->magic_offset, 4) == -1) {
613                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_cancel: failed to remove recovery magic\n"));
614                         ret = -1;
615                 }
616         }
617
618         if (tdb->transaction->open_lock_taken) {
619                 tdb_brunlock(tdb, F_WRLCK, OPEN_LOCK, 1);
620                 tdb->transaction->open_lock_taken = false;
621         }
622
623         /* remove any global lock created during the transaction */
624         if (tdb->allrecord_lock.count != 0) {
625                 tdb_brunlock(tdb, tdb->allrecord_lock.ltype,
626                              FREELIST_TOP, 4*tdb->header.hash_size);
627                 tdb->allrecord_lock.count = 0;
628         }
629
630         /* remove any locks created during the transaction */
631         if (tdb->num_locks != 0) {
632                 for (i=0;i<tdb->num_lockrecs;i++) {
633                         tdb_brunlock(tdb, tdb->lockrecs[i].ltype,
634                                      FREELIST_TOP+4*tdb->lockrecs[i].list, 1);
635                 }
636                 tdb->num_locks = 0;
637                 tdb->num_lockrecs = 0;
638                 SAFE_FREE(tdb->lockrecs);
639         }
640
641         /* restore the normal io methods */
642         tdb->methods = tdb->transaction->io_methods;
643
644         tdb_brunlock(tdb, ltype, FREELIST_TOP, 0);
645         tdb_transaction_unlock(tdb, F_WRLCK);
646         SAFE_FREE(tdb->transaction->hash_heads);
647         SAFE_FREE(tdb->transaction);
648         
649         return ret;
650 }
651
652 /*
653   cancel the current transaction
654 */
655 int tdb_transaction_cancel(struct tdb_context *tdb)
656 {
657         int ltype = F_RDLCK;
658         tdb_trace(tdb, "tdb_transaction_cancel");
659         if (tdb->transaction && tdb->transaction->prepared)
660                 ltype = F_WRLCK;
661         return _tdb_transaction_cancel(tdb, ltype);
662 }
663
664 /*
665   work out how much space the linearised recovery data will consume
666 */
667 static tdb_len_t tdb_recovery_size(struct tdb_context *tdb)
668 {
669         tdb_len_t recovery_size = 0;
670         int i;
671
672         recovery_size = sizeof(uint32_t);
673         for (i=0;i<tdb->transaction->num_blocks;i++) {
674                 if (i * tdb->transaction->block_size >= tdb->transaction->old_map_size) {
675                         break;
676                 }
677                 if (tdb->transaction->blocks[i] == NULL) {
678                         continue;
679                 }
680                 recovery_size += 2*sizeof(tdb_off_t);
681                 if (i == tdb->transaction->num_blocks-1) {
682                         recovery_size += tdb->transaction->last_block_size;
683                 } else {
684                         recovery_size += tdb->transaction->block_size;
685                 }
686         }       
687
688         return recovery_size;
689 }
690
691 /*
692   allocate the recovery area, or use an existing recovery area if it is
693   large enough
694 */
695 static int tdb_recovery_allocate(struct tdb_context *tdb, 
696                                  tdb_len_t *recovery_size,
697                                  tdb_off_t *recovery_offset,
698                                  tdb_len_t *recovery_max_size)
699 {
700         struct tdb_record rec;
701         const struct tdb_methods *methods = tdb->transaction->io_methods;
702         tdb_off_t recovery_head;
703
704         if (tdb_ofs_read(tdb, TDB_RECOVERY_HEAD, &recovery_head) == -1) {
705                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to read recovery head\n"));
706                 return -1;
707         }
708
709         rec.rec_len = 0;
710
711         if (recovery_head != 0) {
712                 if (methods->tdb_read(tdb, recovery_head, &rec, sizeof(rec), DOCONV()) == -1) {
713                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to read recovery record\n"));
714                         return -1;
715                 }
716                 /* ignore invalid recovery regions: can happen in crash */
717                 if (rec.magic != TDB_RECOVERY_MAGIC &&
718                     rec.magic != TDB_RECOVERY_INVALID_MAGIC) {
719                         recovery_head = 0;
720                 }
721         }
722
723         *recovery_size = tdb_recovery_size(tdb);
724
725         if (recovery_head != 0 && *recovery_size <= rec.rec_len) {
726                 /* it fits in the existing area */
727                 *recovery_max_size = rec.rec_len;
728                 *recovery_offset = recovery_head;
729                 return 0;
730         }
731
732         /* we need to free up the old recovery area, then allocate a
733            new one at the end of the file. Note that we cannot use
734            tdb_allocate() to allocate the new one as that might return
735            us an area that is being currently used (as of the start of
736            the transaction) */
737         if (recovery_head != 0) {
738                 if (tdb_free(tdb, recovery_head, &rec) == -1) {
739                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to free previous recovery area\n"));
740                         return -1;
741                 }
742         }
743
744         /* the tdb_free() call might have increased the recovery size */
745         *recovery_size = tdb_recovery_size(tdb);
746
747         /* round up to a multiple of page size */
748         *recovery_max_size = TDB_ALIGN(sizeof(rec) + *recovery_size, tdb->page_size) - sizeof(rec);
749         *recovery_offset = tdb->map_size;
750         recovery_head = *recovery_offset;
751
752         if (methods->tdb_expand_file(tdb, tdb->transaction->old_map_size, 
753                                      (tdb->map_size - tdb->transaction->old_map_size) +
754                                      sizeof(rec) + *recovery_max_size) == -1) {
755                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to create recovery area\n"));
756                 return -1;
757         }
758
759         /* remap the file (if using mmap) */
760         methods->tdb_oob(tdb, tdb->map_size + 1, 1);
761
762         /* we have to reset the old map size so that we don't try to expand the file
763            again in the transaction commit, which would destroy the recovery area */
764         tdb->transaction->old_map_size = tdb->map_size;
765
766         /* write the recovery header offset and sync - we can sync without a race here
767            as the magic ptr in the recovery record has not been set */
768         CONVERT(recovery_head);
769         if (methods->tdb_write(tdb, TDB_RECOVERY_HEAD, 
770                                &recovery_head, sizeof(tdb_off_t)) == -1) {
771                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to write recovery head\n"));
772                 return -1;
773         }
774         if (transaction_write_existing(tdb, TDB_RECOVERY_HEAD, &recovery_head, sizeof(tdb_off_t)) == -1) {
775                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to write recovery head\n"));
776                 return -1;
777         }
778
779         return 0;
780 }
781
782
783 /*
784   setup the recovery data that will be used on a crash during commit
785 */
786 static int transaction_setup_recovery(struct tdb_context *tdb, 
787                                       tdb_off_t *magic_offset)
788 {
789         tdb_len_t recovery_size;
790         unsigned char *data, *p;
791         const struct tdb_methods *methods = tdb->transaction->io_methods;
792         struct tdb_record *rec;
793         tdb_off_t recovery_offset, recovery_max_size;
794         tdb_off_t old_map_size = tdb->transaction->old_map_size;
795         uint32_t magic, tailer;
796         int i;
797
798         /*
799           check that the recovery area has enough space
800         */
801         if (tdb_recovery_allocate(tdb, &recovery_size, 
802                                   &recovery_offset, &recovery_max_size) == -1) {
803                 return -1;
804         }
805
806         data = (unsigned char *)malloc(recovery_size + sizeof(*rec));
807         if (data == NULL) {
808                 tdb->ecode = TDB_ERR_OOM;
809                 return -1;
810         }
811
812         rec = (struct tdb_record *)data;
813         memset(rec, 0, sizeof(*rec));
814
815         rec->magic    = TDB_RECOVERY_INVALID_MAGIC;
816         rec->data_len = recovery_size;
817         rec->rec_len  = recovery_max_size;
818         rec->key_len  = old_map_size;
819         CONVERT(rec);
820
821         /* build the recovery data into a single blob to allow us to do a single
822            large write, which should be more efficient */
823         p = data + sizeof(*rec);
824         for (i=0;i<tdb->transaction->num_blocks;i++) {
825                 tdb_off_t offset;
826                 tdb_len_t length;
827
828                 if (tdb->transaction->blocks[i] == NULL) {
829                         continue;
830                 }
831
832                 offset = i * tdb->transaction->block_size;
833                 length = tdb->transaction->block_size;
834                 if (i == tdb->transaction->num_blocks-1) {
835                         length = tdb->transaction->last_block_size;
836                 }
837                 
838                 if (offset >= old_map_size) {
839                         continue;
840                 }
841                 if (offset + length > tdb->transaction->old_map_size) {
842                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: transaction data over new region boundary\n"));
843                         free(data);
844                         tdb->ecode = TDB_ERR_CORRUPT;
845                         return -1;
846                 }
847                 memcpy(p, &offset, 4);
848                 memcpy(p+4, &length, 4);
849                 if (DOCONV()) {
850                         tdb_convert(p, 8);
851                 }
852                 /* the recovery area contains the old data, not the
853                    new data, so we have to call the original tdb_read
854                    method to get it */
855                 if (methods->tdb_read(tdb, offset, p + 8, length, 0) != 0) {
856                         free(data);
857                         tdb->ecode = TDB_ERR_IO;
858                         return -1;
859                 }
860                 p += 8 + length;
861         }
862
863         /* and the tailer */
864         tailer = sizeof(*rec) + recovery_max_size;
865         memcpy(p, &tailer, 4);
866         CONVERT(p);
867
868         /* write the recovery data to the recovery area */
869         if (methods->tdb_write(tdb, recovery_offset, data, sizeof(*rec) + recovery_size) == -1) {
870                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write recovery data\n"));
871                 free(data);
872                 tdb->ecode = TDB_ERR_IO;
873                 return -1;
874         }
875         if (transaction_write_existing(tdb, recovery_offset, data, sizeof(*rec) + recovery_size) == -1) {
876                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write secondary recovery data\n"));
877                 free(data);
878                 tdb->ecode = TDB_ERR_IO;
879                 return -1;
880         }
881
882         /* as we don't have ordered writes, we have to sync the recovery
883            data before we update the magic to indicate that the recovery
884            data is present */
885         if (transaction_sync(tdb, recovery_offset, sizeof(*rec) + recovery_size) == -1) {
886                 free(data);
887                 return -1;
888         }
889
890         free(data);
891
892         magic = TDB_RECOVERY_MAGIC;
893         CONVERT(magic);
894
895         *magic_offset = recovery_offset + offsetof(struct tdb_record, magic);
896
897         if (methods->tdb_write(tdb, *magic_offset, &magic, sizeof(magic)) == -1) {
898                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write recovery magic\n"));
899                 tdb->ecode = TDB_ERR_IO;
900                 return -1;
901         }
902         if (transaction_write_existing(tdb, *magic_offset, &magic, sizeof(magic)) == -1) {
903                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write secondary recovery magic\n"));
904                 tdb->ecode = TDB_ERR_IO;
905                 return -1;
906         }
907
908         /* ensure the recovery magic marker is on disk */
909         if (transaction_sync(tdb, *magic_offset, sizeof(magic)) == -1) {
910                 return -1;
911         }
912
913         return 0;
914 }
915
916 static int _tdb_transaction_prepare_commit(struct tdb_context *tdb)
917 {       
918         const struct tdb_methods *methods;
919
920         if (tdb->transaction == NULL) {
921                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: no transaction\n"));
922                 return -1;
923         }
924
925         if (tdb->transaction->prepared) {
926                 tdb->ecode = TDB_ERR_EINVAL;
927                 _tdb_transaction_cancel(tdb, F_WRLCK);
928                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: transaction already prepared\n"));
929                 return -1;
930         }
931
932         if (tdb->transaction->transaction_error) {
933                 tdb->ecode = TDB_ERR_IO;
934                 _tdb_transaction_cancel(tdb, F_RDLCK);
935                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: transaction error pending\n"));
936                 return -1;
937         }
938
939
940         if (tdb->transaction->nesting != 0) {
941                 return 0;
942         }               
943
944         /* check for a null transaction */
945         if (tdb->transaction->blocks == NULL) {
946                 return 0;
947         }
948
949         methods = tdb->transaction->io_methods;
950         
951         /* if there are any locks pending then the caller has not
952            nested their locks properly, so fail the transaction */
953         if (tdb->num_locks || tdb->allrecord_lock.count) {
954                 tdb->ecode = TDB_ERR_LOCK;
955                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: locks pending on commit\n"));
956                 _tdb_transaction_cancel(tdb, F_RDLCK);
957                 return -1;
958         }
959
960         /* upgrade the main transaction lock region to a write lock */
961         if (tdb_brlock_upgrade(tdb, FREELIST_TOP, 0) == -1) {
962                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: failed to upgrade hash locks\n"));
963                 tdb->ecode = TDB_ERR_LOCK;
964                 _tdb_transaction_cancel(tdb, F_RDLCK);
965                 return -1;
966         }
967
968         /* get the open lock - this prevents new users attaching to the database
969            during the commit */
970         if (tdb_brlock(tdb, F_WRLCK, OPEN_LOCK, 1, TDB_LOCK_WAIT) == -1) {
971                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_prepare_commit: failed to get open lock\n"));
972                 tdb->ecode = TDB_ERR_LOCK;
973                 _tdb_transaction_cancel(tdb, F_WRLCK);
974                 return -1;
975         }
976
977         tdb->transaction->open_lock_taken = true;
978
979         if (!(tdb->flags & TDB_NOSYNC)) {
980                 /* write the recovery data to the end of the file */
981                 if (transaction_setup_recovery(tdb, &tdb->transaction->magic_offset) == -1) {
982                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_prepare_commit: failed to setup recovery data\n"));
983                         _tdb_transaction_cancel(tdb, F_WRLCK);
984                         return -1;
985                 }
986         }
987
988         tdb->transaction->prepared = true;
989
990         /* expand the file to the new size if needed */
991         if (tdb->map_size != tdb->transaction->old_map_size) {
992                 if (methods->tdb_expand_file(tdb, tdb->transaction->old_map_size, 
993                                              tdb->map_size - 
994                                              tdb->transaction->old_map_size) == -1) {
995                         tdb->ecode = TDB_ERR_IO;
996                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_prepare_commit: expansion failed\n"));
997                         _tdb_transaction_cancel(tdb, F_WRLCK);
998                         return -1;
999                 }
1000                 tdb->map_size = tdb->transaction->old_map_size;
1001                 methods->tdb_oob(tdb, tdb->map_size + 1, 1);
1002         }
1003
1004         /* Keep the open lock until the actual commit */
1005
1006         return 0;
1007 }
1008
1009 /*
1010    prepare to commit the current transaction
1011 */
1012 int tdb_transaction_prepare_commit(struct tdb_context *tdb)
1013 {       
1014         tdb_trace(tdb, "tdb_transaction_prepare_commit");
1015         return _tdb_transaction_prepare_commit(tdb);
1016 }
1017
1018 /*
1019   commit the current transaction
1020 */
1021 int tdb_transaction_commit(struct tdb_context *tdb)
1022 {       
1023         const struct tdb_methods *methods;
1024         int i;
1025         bool need_repack;
1026
1027         if (tdb->transaction == NULL) {
1028                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: no transaction\n"));
1029                 return -1;
1030         }
1031
1032         tdb_trace(tdb, "tdb_transaction_commit");
1033
1034         if (tdb->transaction->transaction_error) {
1035                 tdb->ecode = TDB_ERR_IO;
1036                 _tdb_transaction_cancel(tdb, F_RDLCK);
1037                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: transaction error pending\n"));
1038                 return -1;
1039         }
1040
1041
1042         if (tdb->transaction->nesting != 0) {
1043                 tdb->transaction->nesting--;
1044                 return 0;
1045         }
1046
1047         /* check for a null transaction */
1048         if (tdb->transaction->blocks == NULL) {
1049                 _tdb_transaction_cancel(tdb, F_RDLCK);
1050                 return 0;
1051         }
1052
1053         if (!tdb->transaction->prepared) {
1054                 int ret = _tdb_transaction_prepare_commit(tdb);
1055                 if (ret)
1056                         return ret;
1057         }
1058
1059         methods = tdb->transaction->io_methods;
1060
1061         /* perform all the writes */
1062         for (i=0;i<tdb->transaction->num_blocks;i++) {
1063                 tdb_off_t offset;
1064                 tdb_len_t length;
1065
1066                 if (tdb->transaction->blocks[i] == NULL) {
1067                         continue;
1068                 }
1069
1070                 offset = i * tdb->transaction->block_size;
1071                 length = tdb->transaction->block_size;
1072                 if (i == tdb->transaction->num_blocks-1) {
1073                         length = tdb->transaction->last_block_size;
1074                 }
1075
1076                 if (methods->tdb_write(tdb, offset, tdb->transaction->blocks[i], length) == -1) {
1077                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: write failed during commit\n"));
1078                         
1079                         /* we've overwritten part of the data and
1080                            possibly expanded the file, so we need to
1081                            run the crash recovery code */
1082                         tdb->methods = methods;
1083                         tdb_transaction_recover(tdb); 
1084
1085                         _tdb_transaction_cancel(tdb, F_WRLCK);
1086
1087                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: write failed\n"));
1088                         return -1;
1089                 }
1090                 SAFE_FREE(tdb->transaction->blocks[i]);
1091         } 
1092
1093         SAFE_FREE(tdb->transaction->blocks);
1094         tdb->transaction->num_blocks = 0;
1095
1096         /* ensure the new data is on disk */
1097         if (transaction_sync(tdb, 0, tdb->map_size) == -1) {
1098                 return -1;
1099         }
1100
1101         /*
1102           TODO: maybe write to some dummy hdr field, or write to magic
1103           offset without mmap, before the last sync, instead of the
1104           utime() call
1105         */
1106
1107         /* on some systems (like Linux 2.6.x) changes via mmap/msync
1108            don't change the mtime of the file, this means the file may
1109            not be backed up (as tdb rounding to block sizes means that
1110            file size changes are quite rare too). The following forces
1111            mtime changes when a transaction completes */
1112 #ifdef HAVE_UTIME
1113         utime(tdb->name, NULL);
1114 #endif
1115
1116         need_repack = tdb->transaction->need_repack;
1117
1118         /* use a transaction cancel to free memory and remove the
1119            transaction locks */
1120         _tdb_transaction_cancel(tdb, F_WRLCK);
1121
1122         if (need_repack) {
1123                 return tdb_repack(tdb);
1124         }
1125
1126         return 0;
1127 }
1128
1129
1130 /*
1131   recover from an aborted transaction. Must be called with exclusive
1132   database write access already established (including the open
1133   lock to prevent new processes attaching)
1134 */
1135 int tdb_transaction_recover(struct tdb_context *tdb)
1136 {
1137         tdb_off_t recovery_head, recovery_eof;
1138         unsigned char *data, *p;
1139         uint32_t zero = 0;
1140         struct tdb_record rec;
1141
1142         /* find the recovery area */
1143         if (tdb_ofs_read(tdb, TDB_RECOVERY_HEAD, &recovery_head) == -1) {
1144                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery head\n"));
1145                 tdb->ecode = TDB_ERR_IO;
1146                 return -1;
1147         }
1148
1149         if (recovery_head == 0) {
1150                 /* we have never allocated a recovery record */
1151                 return 0;
1152         }
1153
1154         /* read the recovery record */
1155         if (tdb->methods->tdb_read(tdb, recovery_head, &rec, 
1156                                    sizeof(rec), DOCONV()) == -1) {
1157                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery record\n"));           
1158                 tdb->ecode = TDB_ERR_IO;
1159                 return -1;
1160         }
1161
1162         if (rec.magic != TDB_RECOVERY_MAGIC) {
1163                 /* there is no valid recovery data */
1164                 return 0;
1165         }
1166
1167         if (tdb->read_only) {
1168                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: attempt to recover read only database\n"));
1169                 tdb->ecode = TDB_ERR_CORRUPT;
1170                 return -1;
1171         }
1172
1173         recovery_eof = rec.key_len;
1174
1175         data = (unsigned char *)malloc(rec.data_len);
1176         if (data == NULL) {
1177                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to allocate recovery data\n"));         
1178                 tdb->ecode = TDB_ERR_OOM;
1179                 return -1;
1180         }
1181
1182         /* read the full recovery data */
1183         if (tdb->methods->tdb_read(tdb, recovery_head + sizeof(rec), data,
1184                                    rec.data_len, 0) == -1) {
1185                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery data\n"));             
1186                 tdb->ecode = TDB_ERR_IO;
1187                 return -1;
1188         }
1189
1190         /* recover the file data */
1191         p = data;
1192         while (p+8 < data + rec.data_len) {
1193                 uint32_t ofs, len;
1194                 if (DOCONV()) {
1195                         tdb_convert(p, 8);
1196                 }
1197                 memcpy(&ofs, p, 4);
1198                 memcpy(&len, p+4, 4);
1199
1200                 if (tdb->methods->tdb_write(tdb, ofs, p+8, len) == -1) {
1201                         free(data);
1202                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to recover %d bytes at offset %d\n", len, ofs));
1203                         tdb->ecode = TDB_ERR_IO;
1204                         return -1;
1205                 }
1206                 p += 8 + len;
1207         }
1208
1209         free(data);
1210
1211         if (transaction_sync(tdb, 0, tdb->map_size) == -1) {
1212                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to sync recovery\n"));
1213                 tdb->ecode = TDB_ERR_IO;
1214                 return -1;
1215         }
1216
1217         /* if the recovery area is after the recovered eof then remove it */
1218         if (recovery_eof <= recovery_head) {
1219                 if (tdb_ofs_write(tdb, TDB_RECOVERY_HEAD, &zero) == -1) {
1220                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to remove recovery head\n"));
1221                         tdb->ecode = TDB_ERR_IO;
1222                         return -1;                      
1223                 }
1224         }
1225
1226         /* remove the recovery magic */
1227         if (tdb_ofs_write(tdb, recovery_head + offsetof(struct tdb_record, magic),
1228                           &zero) == -1) {
1229                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to remove recovery magic\n"));
1230                 tdb->ecode = TDB_ERR_IO;
1231                 return -1;                      
1232         }
1233         
1234         /* reduce the file size to the old size */
1235         tdb_munmap(tdb);
1236         if (ftruncate(tdb->fd, recovery_eof) != 0) {
1237                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to reduce to recovery size\n"));
1238                 tdb->ecode = TDB_ERR_IO;
1239                 return -1;                      
1240         }
1241         tdb->map_size = recovery_eof;
1242         tdb_mmap(tdb);
1243
1244         if (transaction_sync(tdb, 0, recovery_eof) == -1) {
1245                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to sync2 recovery\n"));
1246                 tdb->ecode = TDB_ERR_IO;
1247                 return -1;
1248         }
1249
1250         TDB_LOG((tdb, TDB_DEBUG_TRACE, "tdb_transaction_recover: recovered %d byte database\n", 
1251                  recovery_eof));
1252
1253         /* all done */
1254         return 0;
1255 }