source: branches/samba-3.5.x/lib/tdb/common/traverse.c

Last change on this file was 647, checked in by Silvan Scherrer, 14 years ago

Samba Server 3.5: prevent internal locks, fixes ticket:173 and ticket:140
File size: 11.0 KB
Line 
1 /*
2 Unix SMB/CIFS implementation.
3
4 trivial database library
5
6 Copyright (C) Andrew Tridgell 1999-2005
7 Copyright (C) Paul `Rusty' Russell 2000
8 Copyright (C) Jeremy Allison 2000-2003
9
10 ** NOTE! The following LGPL license applies to the tdb
11 ** library. This does NOT imply that all of Samba is released
12 ** under the LGPL
13
14 This library is free software; you can redistribute it and/or
15 modify it under the terms of the GNU Lesser General Public
16 License as published by the Free Software Foundation; either
17 version 3 of the License, or (at your option) any later version.
18
19 This library is distributed in the hope that it will be useful,
20 but WITHOUT ANY WARRANTY; without even the implied warranty of
21 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
22 Lesser General Public License for more details.
23
24 You should have received a copy of the GNU Lesser General Public
25 License along with this library; if not, see <http://www.gnu.org/licenses/>.
26*/
27
28#include "tdb_private.h"
29
30#define TDB_NEXT_LOCK_ERR ((tdb_off_t)-1)
31
32/* Uses traverse lock: 0 = finish, TDB_NEXT_LOCK_ERR = error,
33 other = record offset */
34static tdb_off_t tdb_next_lock(struct tdb_context *tdb, struct tdb_traverse_lock *tlock,
35 struct tdb_record *rec)
36{
37 int want_next = (tlock->off != 0);
38
39 /* Lock each chain from the start one. */
40 for (; tlock->hash < tdb->header.hash_size; tlock->hash++) {
41 if (!tlock->off && tlock->hash != 0) {
42 /* this is an optimisation for the common case where
43 the hash chain is empty, which is particularly
44 common for the use of tdb with ldb, where large
45 hashes are used. In that case we spend most of our
46 time in tdb_brlock(), locking empty hash chains.
47
48 To avoid this, we do an unlocked pre-check to see
49 if the hash chain is empty before starting to look
50 inside it. If it is empty then we can avoid that
51 hash chain. If it isn't empty then we can't believe
52 the value we get back, as we read it without a
53 lock, so instead we get the lock and re-fetch the
54 value below.
55
56 Notice that not doing this optimisation on the
57 first hash chain is critical. We must guarantee
58 that we have done at least one fcntl lock at the
59 start of a search to guarantee that memory is
60 coherent on SMP systems. If records are added by
61 others during the search then thats OK, and we
62 could possibly miss those with this trick, but we
63 could miss them anyway without this trick, so the
64 semantics don't change.
65
66 With a non-indexed ldb search this trick gains us a
67 factor of around 80 in speed on a linux 2.6.x
68 system (testing using ldbtest).
69 */
70 tdb->methods->next_hash_chain(tdb, &tlock->hash);
71 if (tlock->hash == tdb->header.hash_size) {
72 continue;
73 }
74 }
75
76 if (tdb_lock(tdb, tlock->hash, tlock->lock_rw) == -1)
77 return TDB_NEXT_LOCK_ERR;
78
79 /* No previous record? Start at top of chain. */
80 if (!tlock->off) {
81 if (tdb_ofs_read(tdb, TDB_HASH_TOP(tlock->hash),
82 &tlock->off) == -1)
83 goto fail;
84 } else {
85 /* Otherwise unlock the previous record. */
86 if (tdb_unlock_record(tdb, tlock->off) != 0)
87 goto fail;
88 }
89
90 if (want_next) {
91 /* We have offset of old record: grab next */
92 if (tdb_rec_read(tdb, tlock->off, rec) == -1)
93 goto fail;
94 tlock->off = rec->next;
95 }
96
97 /* Iterate through chain */
98 while( tlock->off) {
99 tdb_off_t current;
100 if (tdb_rec_read(tdb, tlock->off, rec) == -1)
101 goto fail;
102
103 /* Detect infinite loops. From "Shlomi Yaakobovich" <Shlomi@exanet.com>. */
104 if (tlock->off == rec->next) {
105 tdb->ecode = TDB_ERR_CORRUPT;
106 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_next_lock: loop detected.\n"));
107 goto fail;
108 }
109
110 if (!TDB_DEAD(rec)) {
111 /* Woohoo: we found one! */
112 if (tdb_lock_record(tdb, tlock->off) != 0)
113 goto fail;
114 return tlock->off;
115 }
116
117 /* Try to clean dead ones from old traverses */
118 current = tlock->off;
119 tlock->off = rec->next;
120 if (!(tdb->read_only || tdb->traverse_read) &&
121 tdb_do_delete(tdb, current, rec) != 0)
122 goto fail;
123 }
124 tdb_unlock(tdb, tlock->hash, tlock->lock_rw);
125 want_next = 0;
126 }
127 /* We finished iteration without finding anything */
128 tdb->ecode = TDB_SUCCESS;
129 return 0;
130
131 fail:
132 tlock->off = 0;
133 if (tdb_unlock(tdb, tlock->hash, tlock->lock_rw) != 0)
134 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_next_lock: On error unlock failed!\n"));
135 return TDB_NEXT_LOCK_ERR;
136}
137
138/* traverse the entire database - calling fn(tdb, key, data) on each element.
139 return -1 on error or the record count traversed
140 if fn is NULL then it is not called
141 a non-zero return value from fn() indicates that the traversal should stop
142 */
143static int tdb_traverse_internal(struct tdb_context *tdb,
144 tdb_traverse_func fn, void *private_data,
145 struct tdb_traverse_lock *tl)
146{
147 TDB_DATA key, dbuf;
148 struct tdb_record rec;
149 int ret = 0, count = 0;
150 tdb_off_t off;
151
152 /* This was in the initializaton, above, but the IRIX compiler
153 * did not like it. crh
154 */
155 tl->next = tdb->travlocks.next;
156
157 /* fcntl locks don't stack: beware traverse inside traverse */
158 tdb->travlocks.next = tl;
159
160 /* tdb_next_lock places locks on the record returned, and its chain */
161 while ((off = tdb_next_lock(tdb, tl, &rec)) != 0) {
162 if (off == TDB_NEXT_LOCK_ERR) {
163 ret = -1;
164 goto out;
165 }
166 count++;
167 /* now read the full record */
168 key.dptr = tdb_alloc_read(tdb, tl->off + sizeof(rec),
169 rec.key_len + rec.data_len);
170 if (!key.dptr) {
171 ret = -1;
172 if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0)
173 goto out;
174 if (tdb_unlock_record(tdb, tl->off) != 0)
175 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: key.dptr == NULL and unlock_record failed!\n"));
176 goto out;
177 }
178 key.dsize = rec.key_len;
179 dbuf.dptr = key.dptr + rec.key_len;
180 dbuf.dsize = rec.data_len;
181
182 tdb_trace_1rec_retrec(tdb, "traverse", key, dbuf);
183
184 /* Drop chain lock, call out */
185 if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0) {
186 ret = -1;
187 SAFE_FREE(key.dptr);
188 goto out;
189 }
190 if (fn && fn(tdb, key, dbuf, private_data)) {
191 /* They want us to terminate traversal */
192 tdb_trace_ret(tdb, "tdb_traverse_end", count);
193 if (tdb_unlock_record(tdb, tl->off) != 0) {
194 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: unlock_record failed!\n"));;
195 ret = -1;
196 }
197 SAFE_FREE(key.dptr);
198 goto out;
199 }
200 SAFE_FREE(key.dptr);
201 }
202 tdb_trace(tdb, "tdb_traverse_end");
203out:
204 tdb->travlocks.next = tl->next;
205 if (ret < 0)
206 return -1;
207 else
208 return count;
209}
210
211
212/*
213 a write style traverse - temporarily marks the db read only
214*/
215int tdb_traverse_read(struct tdb_context *tdb,
216 tdb_traverse_func fn, void *private_data)
217{
218
219 struct tdb_traverse_lock tl = { NULL, 0, 0, F_RDLCK };
220 int ret;
221
222 /* we need to get a read lock on the transaction lock here to
223 cope with the lock ordering semantics of solaris10 */
224 if (tdb_transaction_lock(tdb, F_RDLCK)) {
225 return -1;
226 }
227
228 tdb->traverse_read++;
229 tdb_trace(tdb, "tdb_traverse_read_start");
230 ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
231 tdb->traverse_read--;
232
233 tdb_transaction_unlock(tdb);
234
235 return ret;
236}
237
238/*
239 a write style traverse - needs to get the transaction lock to
240 prevent deadlocks
241
242 WARNING: The data buffer given to the callback fn does NOT meet the
243 alignment restrictions malloc gives you.
244*/
245int tdb_traverse(struct tdb_context *tdb,
246 tdb_traverse_func fn, void *private_data)
247{
248 struct tdb_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
249 int ret;
250
251 if (tdb->read_only || tdb->traverse_read) {
252 return tdb_traverse_read(tdb, fn, private_data);
253 }
254
255 if (tdb_transaction_lock(tdb, F_WRLCK)) {
256 return -1;
257 }
258
259 tdb->traverse_write++;
260 tdb_trace(tdb, "tdb_traverse_start");
261 ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
262 tdb->traverse_write--;
263
264 tdb_transaction_unlock(tdb);
265
266 return ret;
267}
268
269
270/* find the first entry in the database and return its key */
271TDB_DATA tdb_firstkey(struct tdb_context *tdb)
272{
273 TDB_DATA key;
274 struct tdb_record rec;
275 tdb_off_t off;
276
277 /* release any old lock */
278 if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
279 return tdb_null;
280 tdb->travlocks.off = tdb->travlocks.hash = 0;
281 tdb->travlocks.lock_rw = F_RDLCK;
282
283 /* Grab first record: locks chain and returned record. */
284 off = tdb_next_lock(tdb, &tdb->travlocks, &rec);
285 if (off == 0 || off == TDB_NEXT_LOCK_ERR) {
286 tdb_trace_retrec(tdb, "tdb_firstkey", tdb_null);
287 return tdb_null;
288 }
289 /* now read the key */
290 key.dsize = rec.key_len;
291 key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
292
293 tdb_trace_retrec(tdb, "tdb_firstkey", key);
294
295 /* Unlock the hash chain of the record we just read. */
296 if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
297 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
298 return key;
299}
300
301/* find the next entry in the database, returning its key */
302TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
303{
304 uint32_t oldhash;
305 TDB_DATA key = tdb_null;
306 struct tdb_record rec;
307 unsigned char *k = NULL;
308 tdb_off_t off;
309
310 /* Is locked key the old key? If so, traverse will be reliable. */
311 if (tdb->travlocks.off) {
312 if (tdb_lock(tdb,tdb->travlocks.hash,tdb->travlocks.lock_rw))
313 return tdb_null;
314 if (tdb_rec_read(tdb, tdb->travlocks.off, &rec) == -1
315 || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
316 rec.key_len))
317 || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
318 /* No, it wasn't: unlock it and start from scratch */
319 if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0) {
320 tdb_trace_1rec_retrec(tdb, "tdb_nextkey",
321 oldkey, tdb_null);
322 SAFE_FREE(k);
323 return tdb_null;
324 }
325 if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0) {
326 SAFE_FREE(k);
327 return tdb_null;
328 }
329 tdb->travlocks.off = 0;
330 }
331
332 SAFE_FREE(k);
333 }
334
335 if (!tdb->travlocks.off) {
336 /* No previous element: do normal find, and lock record */
337 tdb->travlocks.off = tdb_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), tdb->travlocks.lock_rw, &rec);
338 if (!tdb->travlocks.off) {
339 tdb_trace_1rec_retrec(tdb, "tdb_nextkey", oldkey, tdb_null);
340 return tdb_null;
341 }
342 tdb->travlocks.hash = BUCKET(rec.full_hash);
343 if (tdb_lock_record(tdb, tdb->travlocks.off) != 0) {
344 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
345 return tdb_null;
346 }
347 }
348 oldhash = tdb->travlocks.hash;
349
350 /* Grab next record: locks chain and returned record,
351 unlocks old record */
352 off = tdb_next_lock(tdb, &tdb->travlocks, &rec);
353 if (off != TDB_NEXT_LOCK_ERR && off != 0) {
354 key.dsize = rec.key_len;
355 key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
356 key.dsize);
357 /* Unlock the chain of this new record */
358 if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
359 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
360 }
361 /* Unlock the chain of old record */
362 if (tdb_unlock(tdb, BUCKET(oldhash), tdb->travlocks.lock_rw) != 0)
363 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
364 tdb_trace_1rec_retrec(tdb, "tdb_nextkey", oldkey, key);
365 return key;
366}
367
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