summaryrefslogtreecommitdiff
path: root/lib/tdb/common/lock.c
blob: f156c0fa7b2e548640d47db23df71c9427ec73ce (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
 /* 
   Unix SMB/CIFS implementation.

   trivial database library

   Copyright (C) Andrew Tridgell              1999-2005
   Copyright (C) Paul `Rusty' Russell		   2000
   Copyright (C) Jeremy Allison			   2000-2003
   
     ** NOTE! The following LGPL license applies to the tdb
     ** library. This does NOT imply that all of Samba is released
     ** under the LGPL
   
   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 3 of the License, or (at your option) any later version.

   This library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/

#include "tdb_private.h"

#define TDB_MARK_LOCK 0x80000000

void tdb_setalarm_sigptr(struct tdb_context *tdb, volatile sig_atomic_t *ptr)
{
	tdb->interrupt_sig_ptr = ptr;
}

/* a byte range locking function - return 0 on success
   this functions locks/unlocks 1 byte at the specified offset.

   On error, errno is also set so that errors are passed back properly
   through tdb_open(). 

   note that a len of zero means lock to end of file
*/
int tdb_brlock(struct tdb_context *tdb, tdb_off_t offset, 
	       int rw_type, int lck_type, int probe, size_t len)
{
	struct flock fl;
	int ret;

	if (tdb->flags & TDB_NOLOCK) {
		return 0;
	}

	if ((rw_type == F_WRLCK) && (tdb->read_only || tdb->traverse_read)) {
		tdb->ecode = TDB_ERR_RDONLY;
		return -1;
	}

	fl.l_type = rw_type;
	fl.l_whence = SEEK_SET;
	fl.l_start = offset;
	fl.l_len = len;
	fl.l_pid = 0;

	do {
		ret = fcntl(tdb->fd,lck_type,&fl);

		/* Check for a sigalarm break. */
		if (ret == -1 && errno == EINTR &&
				tdb->interrupt_sig_ptr &&
				*tdb->interrupt_sig_ptr) {
			break;
		}
	} while (ret == -1 && errno == EINTR);

	if (ret == -1) {
		/* Generic lock error. errno set by fcntl.
		 * EAGAIN is an expected return from non-blocking
		 * locks. */
		if (!probe && lck_type != F_SETLK) {
			/* Ensure error code is set for log fun to examine. */
			tdb->ecode = TDB_ERR_LOCK;
			TDB_LOG((tdb, TDB_DEBUG_TRACE,"tdb_brlock failed (fd=%d) at offset %d rw_type=%d lck_type=%d len=%d\n", 
				 tdb->fd, offset, rw_type, lck_type, (int)len));
		}
		return TDB_ERRCODE(TDB_ERR_LOCK, -1);
	}
	return 0;
}


/*
  upgrade a read lock to a write lock. This needs to be handled in a
  special way as some OSes (such as solaris) have too conservative
  deadlock detection and claim a deadlock when progress can be
  made. For those OSes we may loop for a while.  
*/
int tdb_brlock_upgrade(struct tdb_context *tdb, tdb_off_t offset, size_t len)
{
	int count = 1000;
	while (count--) {
		struct timeval tv;
		if (tdb_brlock(tdb, offset, F_WRLCK, F_SETLKW, 1, len) == 0) {
			return 0;
		}
		if (errno != EDEADLK) {
			break;
		}
		/* sleep for as short a time as we can - more portable than usleep() */
		tv.tv_sec = 0;
		tv.tv_usec = 1;
		select(0, NULL, NULL, NULL, &tv);
	}
	TDB_LOG((tdb, TDB_DEBUG_TRACE,"tdb_brlock_upgrade failed at offset %d\n", offset));
	return -1;
}


/* lock a list in the database. list -1 is the alloc list */
static int _tdb_lock(struct tdb_context *tdb, int list, int ltype, int op)
{
	struct tdb_lock_type *new_lck;
	int i;
	bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);

	ltype &= ~TDB_MARK_LOCK;

	/* a global lock allows us to avoid per chain locks */
	if (tdb->global_lock.count && 
	    (ltype == tdb->global_lock.ltype || ltype == F_RDLCK)) {
		return 0;
	}

	if (tdb->global_lock.count) {
		return TDB_ERRCODE(TDB_ERR_LOCK, -1);
	}

	if (list < -1 || list >= (int)tdb->header.hash_size) {
		TDB_LOG((tdb, TDB_DEBUG_ERROR,"tdb_lock: invalid list %d for ltype=%d\n", 
			   list, ltype));
		return -1;
	}
	if (tdb->flags & TDB_NOLOCK)
		return 0;

	for (i=0; i<tdb->num_lockrecs; i++) {
		if (tdb->lockrecs[i].list == list) {
			if (tdb->lockrecs[i].count == 0) {
				/*
				 * Can't happen, see tdb_unlock(). It should
				 * be an assert.
				 */
				TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_lock: "
					 "lck->count == 0 for list %d", list));
			}
			/*
			 * Just increment the in-memory struct, posix locks
			 * don't stack.
			 */
			tdb->lockrecs[i].count++;
			return 0;
		}
	}

	new_lck = (struct tdb_lock_type *)realloc(
		tdb->lockrecs,
		sizeof(*tdb->lockrecs) * (tdb->num_lockrecs+1));
	if (new_lck == NULL) {
		errno = ENOMEM;
		return -1;
	}
	tdb->lockrecs = new_lck;

	/* Since fcntl locks don't nest, we do a lock for the first one,
	   and simply bump the count for future ones */
	if (!mark_lock &&
	    tdb->methods->tdb_brlock(tdb,FREELIST_TOP+4*list, ltype, op,
				     0, 1)) {
		return -1;
	}

	tdb->num_locks++;

	tdb->lockrecs[tdb->num_lockrecs].list = list;
	tdb->lockrecs[tdb->num_lockrecs].count = 1;
	tdb->lockrecs[tdb->num_lockrecs].ltype = ltype;
	tdb->num_lockrecs += 1;

	return 0;
}

/* lock a list in the database. list -1 is the alloc list */
int tdb_lock(struct tdb_context *tdb, int list, int ltype)
{
	int ret;
	ret = _tdb_lock(tdb, list, ltype, F_SETLKW);
	if (ret) {
		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_lock failed on list %d "
			 "ltype=%d (%s)\n",  list, ltype, strerror(errno)));
	}
	return ret;
}

/* lock a list in the database. list -1 is the alloc list. non-blocking lock */
int tdb_lock_nonblock(struct tdb_context *tdb, int list, int ltype)
{
	return _tdb_lock(tdb, list, ltype, F_SETLK);
}


/* unlock the database: returns void because it's too late for errors. */
	/* changed to return int it may be interesting to know there
	   has been an error  --simo */
int tdb_unlock(struct tdb_context *tdb, int list, int ltype)
{
	int ret = -1;
	int i;
	struct tdb_lock_type *lck = NULL;
	bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);

	ltype &= ~TDB_MARK_LOCK;

	/* a global lock allows us to avoid per chain locks */
	if (tdb->global_lock.count && 
	    (ltype == tdb->global_lock.ltype || ltype == F_RDLCK)) {
		return 0;
	}

	if (tdb->global_lock.count) {
		return TDB_ERRCODE(TDB_ERR_LOCK, -1);
	}

	if (tdb->flags & TDB_NOLOCK)
		return 0;

	/* Sanity checks */
	if (list < -1 || list >= (int)tdb->header.hash_size) {
		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_unlock: list %d invalid (%d)\n", list, tdb->header.hash_size));
		return ret;
	}

	for (i=0; i<tdb->num_lockrecs; i++) {
		if (tdb->lockrecs[i].list == list) {
			lck = &tdb->lockrecs[i];
			break;
		}
	}

	if ((lck == NULL) || (lck->count == 0)) {
		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_unlock: count is 0\n"));
		return -1;
	}

	if (lck->count > 1) {
		lck->count--;
		return 0;
	}

	/*
	 * This lock has count==1 left, so we need to unlock it in the
	 * kernel. We don't bother with decrementing the in-memory array
	 * element, we're about to overwrite it with the last array element
	 * anyway.
	 */

	if (mark_lock) {
		ret = 0;
	} else {
		ret = tdb->methods->tdb_brlock(tdb, FREELIST_TOP+4*list, F_UNLCK,
					       F_SETLKW, 0, 1);
	}
	tdb->num_locks--;

	/*
	 * Shrink the array by overwriting the element just unlocked with the
	 * last array element.
	 */

	if (tdb->num_lockrecs > 1) {
		*lck = tdb->lockrecs[tdb->num_lockrecs-1];
	}
	tdb->num_lockrecs -= 1;

	/*
	 * We don't bother with realloc when the array shrinks, but if we have
	 * a completely idle tdb we should get rid of the locked array.
	 */

	if (tdb->num_lockrecs == 0) {
		SAFE_FREE(tdb->lockrecs);
	}

	if (ret)
		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_unlock: An error occurred unlocking!\n")); 
	return ret;
}

/*
  get the transaction lock
 */
int tdb_transaction_lock(struct tdb_context *tdb, int ltype)
{
	if (tdb->have_transaction_lock || tdb->global_lock.count) {
		return 0;
	}
	if (tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, ltype, 
				     F_SETLKW, 0, 1) == -1) {
		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_lock: failed to get transaction lock\n"));
		tdb->ecode = TDB_ERR_LOCK;
		return -1;
	}
	tdb->have_transaction_lock = 1;
	return 0;
}

/*
  release the transaction lock
 */
int tdb_transaction_unlock(struct tdb_context *tdb)
{
	int ret;
	if (!tdb->have_transaction_lock) {
		return 0;
	}
	ret = tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, F_UNLCK, F_SETLKW, 0, 1);
	if (ret == 0) {
		tdb->have_transaction_lock = 0;
	}
	return ret;
}




/* lock/unlock entire database */
static int _tdb_lockall(struct tdb_context *tdb, int ltype, int op)
{
	bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);

	ltype &= ~TDB_MARK_LOCK;

	/* There are no locks on read-only dbs */
	if (tdb->read_only || tdb->traverse_read)
		return TDB_ERRCODE(TDB_ERR_LOCK, -1);

	if (tdb->global_lock.count && tdb->global_lock.ltype == ltype) {
		tdb->global_lock.count++;
		return 0;
	}

	if (tdb->global_lock.count) {
		/* a global lock of a different type exists */
		return TDB_ERRCODE(TDB_ERR_LOCK, -1);
	}
	
	if (tdb->num_locks != 0) {
		/* can't combine global and chain locks */
		return TDB_ERRCODE(TDB_ERR_LOCK, -1);
	}

	if (!mark_lock &&
	    tdb->methods->tdb_brlock(tdb, FREELIST_TOP, ltype, op,
				     0, 4*tdb->header.hash_size)) {
		if (op == F_SETLKW) {
			TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_lockall failed (%s)\n", strerror(errno)));
		}
		return -1;
	}

	tdb->global_lock.count = 1;
	tdb->global_lock.ltype = ltype;

	return 0;
}



/* unlock entire db */
static int _tdb_unlockall(struct tdb_context *tdb, int ltype)
{
	bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);

	ltype &= ~TDB_MARK_LOCK;

	/* There are no locks on read-only dbs */
	if (tdb->read_only || tdb->traverse_read) {
		return TDB_ERRCODE(TDB_ERR_LOCK, -1);
	}

	if (tdb->global_lock.ltype != ltype || tdb->global_lock.count == 0) {
		return TDB_ERRCODE(TDB_ERR_LOCK, -1);
	}

	if (tdb->global_lock.count > 1) {
		tdb->global_lock.count--;
		return 0;
	}

	if (!mark_lock &&
	    tdb->methods->tdb_brlock(tdb, FREELIST_TOP, F_UNLCK, F_SETLKW, 
				     0, 4*tdb->header.hash_size)) {
		TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_unlockall failed (%s)\n", strerror(errno)));
		return -1;
	}

	tdb->global_lock.count = 0;
	tdb->global_lock.ltype = 0;

	return 0;
}

/* lock entire database with write lock */
int tdb_lockall(struct tdb_context *tdb)
{
	return _tdb_lockall(tdb, F_WRLCK, F_SETLKW);
}

/* lock entire database with write lock - mark only */
int tdb_lockall_mark(struct tdb_context *tdb)
{
	return _tdb_lockall(tdb, F_WRLCK | TDB_MARK_LOCK, F_SETLKW);
}

/* unlock entire database with write lock - unmark only */
int tdb_lockall_unmark(struct tdb_context *tdb)
{
	return _tdb_unlockall(tdb, F_WRLCK | TDB_MARK_LOCK);
}

/* lock entire database with write lock - nonblocking varient */
int tdb_lockall_nonblock(struct tdb_context *tdb)
{
	return _tdb_lockall(tdb, F_WRLCK, F_SETLK);
}

/* unlock entire database with write lock */
int tdb_unlockall(struct tdb_context *tdb)
{
	return _tdb_unlockall(tdb, F_WRLCK);
}

/* lock entire database with read lock */
int tdb_lockall_read(struct tdb_context *tdb)
{
	return _tdb_lockall(tdb, F_RDLCK, F_SETLKW);
}

/* lock entire database with read lock - nonblock varient */
int tdb_lockall_read_nonblock(struct tdb_context *tdb)
{
	return _tdb_lockall(tdb, F_RDLCK, F_SETLK);
}

/* unlock entire database with read lock */
int tdb_unlockall_read(struct tdb_context *tdb)
{
	return _tdb_unlockall(tdb, F_RDLCK);
}

/* lock/unlock one hash chain. This is meant to be used to reduce
   contention - it cannot guarantee how many records will be locked */
int tdb_chainlock(struct tdb_context *tdb, TDB_DATA key)
{
	return tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK);
}

/* lock/unlock one hash chain, non-blocking. This is meant to be used
   to reduce contention - it cannot guarantee how many records will be
   locked */
int tdb_chainlock_nonblock(struct tdb_context *tdb, TDB_DATA key)
{
	return tdb_lock_nonblock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK);
}

/* mark a chain as locked without actually locking it. Warning! use with great caution! */
int tdb_chainlock_mark(struct tdb_context *tdb, TDB_DATA key)
{
	return tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK | TDB_MARK_LOCK);
}

/* unmark a chain as locked without actually locking it. Warning! use with great caution! */
int tdb_chainlock_unmark(struct tdb_context *tdb, TDB_DATA key)
{
	return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK | TDB_MARK_LOCK);
}

int tdb_chainunlock(struct tdb_context *tdb, TDB_DATA key)
{
	return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK);
}

int tdb_chainlock_read(struct tdb_context *tdb, TDB_DATA key)
{
	return tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_RDLCK);
}

int tdb_chainunlock_read(struct tdb_context *tdb, TDB_DATA key)
{
	return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_RDLCK);
}



/* record lock stops delete underneath */
int tdb_lock_record(struct tdb_context *tdb, tdb_off_t off)
{
	if (tdb->global_lock.count) {
		return 0;
	}
	return off ? tdb->methods->tdb_brlock(tdb, off, F_RDLCK, F_SETLKW, 0, 1) : 0;
}

/*
  Write locks override our own fcntl readlocks, so check it here.
  Note this is meant to be F_SETLK, *not* F_SETLKW, as it's not
  an error to fail to get the lock here.
*/
int tdb_write_lock_record(struct tdb_context *tdb, tdb_off_t off)
{
	struct tdb_traverse_lock *i;
	for (i = &tdb->travlocks; i; i = i->next)
		if (i->off == off)
			return -1;
	return tdb->methods->tdb_brlock(tdb, off, F_WRLCK, F_SETLK, 1, 1);
}

/*
  Note this is meant to be F_SETLK, *not* F_SETLKW, as it's not
  an error to fail to get the lock here.
*/
int tdb_write_unlock_record(struct tdb_context *tdb, tdb_off_t off)
{
	return tdb->methods->tdb_brlock(tdb, off, F_UNLCK, F_SETLK, 0, 1);
}

/* fcntl locks don't stack: avoid unlocking someone else's */
int tdb_unlock_record(struct tdb_context *tdb, tdb_off_t off)
{
	struct tdb_traverse_lock *i;
	uint32_t count = 0;

	if (tdb->global_lock.count) {
		return 0;
	}

	if (off == 0)
		return 0;
	for (i = &tdb->travlocks; i; i = i->next)
		if (i->off == off)
			count++;
	return (count == 1 ? tdb->methods->tdb_brlock(tdb, off, F_UNLCK, F_SETLKW, 0, 1) : 0);
}