merged tdb from ctdb bzr tree
[ira/wip.git] / source / lib / tdb / common / 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                 /* Drop chain lock, call out */
173                 if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0) {
174                         ret = -1;
175                         SAFE_FREE(key.dptr);
176                         goto out;
177                 }
178                 if (fn && fn(tdb, key, dbuf, private_data)) {
179                         /* They want us to terminate traversal */
180                         ret = count;
181                         if (tdb_unlock_record(tdb, tl->off) != 0) {
182                                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: unlock_record failed!\n"));;
183                                 ret = -1;
184                         }
185                         SAFE_FREE(key.dptr);
186                         goto out;
187                 }
188                 SAFE_FREE(key.dptr);
189         }
190 out:
191         tdb->travlocks.next = tl->next;
192         if (ret < 0)
193                 return -1;
194         else
195                 return count;
196 }
197
198
199 /*
200   a write style traverse - temporarily marks the db read only
201 */
202 int tdb_traverse_read(struct tdb_context *tdb, 
203                       tdb_traverse_func fn, void *private_data)
204 {
205         struct tdb_traverse_lock tl = { NULL, 0, 0, F_RDLCK };
206         int ret;
207
208         /* we need to get a read lock on the transaction lock here to
209            cope with the lock ordering semantics of solaris10 */
210         if (tdb_transaction_lock(tdb, F_RDLCK)) {
211                 return -1;
212         }
213
214         tdb->traverse_read++;
215         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
216         tdb->traverse_read--;
217
218         tdb_transaction_unlock(tdb);
219
220         return ret;
221 }
222
223 /*
224   a write style traverse - needs to get the transaction lock to
225   prevent deadlocks
226 */
227 int tdb_traverse(struct tdb_context *tdb, 
228                  tdb_traverse_func fn, void *private_data)
229 {
230         struct tdb_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
231         int ret;
232
233         if (tdb->read_only || tdb->traverse_read) {
234                 return tdb_traverse_read(tdb, fn, private_data);
235         }
236         
237         if (tdb_transaction_lock(tdb, F_WRLCK)) {
238                 return -1;
239         }
240
241         tdb->traverse_write++;
242         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
243         tdb->traverse_write--;
244
245         tdb_transaction_unlock(tdb);
246
247         return ret;
248 }
249
250
251 /* find the first entry in the database and return its key */
252 TDB_DATA tdb_firstkey(struct tdb_context *tdb)
253 {
254         TDB_DATA key;
255         struct list_struct rec;
256
257         /* release any old lock */
258         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
259                 return tdb_null;
260         tdb->travlocks.off = tdb->travlocks.hash = 0;
261         tdb->travlocks.lock_rw = F_RDLCK;
262
263         /* Grab first record: locks chain and returned record. */
264         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) <= 0)
265                 return tdb_null;
266         /* now read the key */
267         key.dsize = rec.key_len;
268         key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
269
270         /* Unlock the hash chain of the record we just read. */
271         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
272                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
273         return key;
274 }
275
276 /* find the next entry in the database, returning its key */
277 TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
278 {
279         uint32_t oldhash;
280         TDB_DATA key = tdb_null;
281         struct list_struct rec;
282         unsigned char *k = NULL;
283
284         /* Is locked key the old key?  If so, traverse will be reliable. */
285         if (tdb->travlocks.off) {
286                 if (tdb_lock(tdb,tdb->travlocks.hash,tdb->travlocks.lock_rw))
287                         return tdb_null;
288                 if (tdb_rec_read(tdb, tdb->travlocks.off, &rec) == -1
289                     || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
290                                             rec.key_len))
291                     || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
292                         /* No, it wasn't: unlock it and start from scratch */
293                         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0) {
294                                 SAFE_FREE(k);
295                                 return tdb_null;
296                         }
297                         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0) {
298                                 SAFE_FREE(k);
299                                 return tdb_null;
300                         }
301                         tdb->travlocks.off = 0;
302                 }
303
304                 SAFE_FREE(k);
305         }
306
307         if (!tdb->travlocks.off) {
308                 /* No previous element: do normal find, and lock record */
309                 tdb->travlocks.off = tdb_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), tdb->travlocks.lock_rw, &rec);
310                 if (!tdb->travlocks.off)
311                         return tdb_null;
312                 tdb->travlocks.hash = BUCKET(rec.full_hash);
313                 if (tdb_lock_record(tdb, tdb->travlocks.off) != 0) {
314                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
315                         return tdb_null;
316                 }
317         }
318         oldhash = tdb->travlocks.hash;
319
320         /* Grab next record: locks chain and returned record,
321            unlocks old record */
322         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) > 0) {
323                 key.dsize = rec.key_len;
324                 key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
325                                           key.dsize);
326                 /* Unlock the chain of this new record */
327                 if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
328                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
329         }
330         /* Unlock the chain of old record */
331         if (tdb_unlock(tdb, BUCKET(oldhash), tdb->travlocks.lock_rw) != 0)
332                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
333         return key;
334 }
335