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