r10421: following on discussions with simo, I have worked out a way of
[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 2 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, write to the Free Software
26    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
27 */
28
29 #include "tdb_private.h"
30
31 /* Uses traverse lock: 0 = finish, -1 = error, other = record offset */
32 static int tdb_next_lock(struct tdb_context *tdb, struct tdb_traverse_lock *tlock,
33                          struct list_struct *rec)
34 {
35         int want_next = (tlock->off != 0);
36
37         /* Lock each chain from the start one. */
38         for (; tlock->hash < tdb->header.hash_size; tlock->hash++) {
39                 if (!tlock->off && tlock->hash != 0) {
40                         /* this is an optimisation for the common case where
41                            the hash chain is empty, which is particularly
42                            common for the use of tdb with ldb, where large
43                            hashes are used. In that case we spend most of our
44                            time in tdb_brlock(), locking empty hash chains.
45                            
46                            To avoid this, we do an unlocked pre-check to see
47                            if the hash chain is empty before starting to look
48                            inside it. If it is empty then we can avoid that
49                            hash chain. If it isn't empty then we can't believe
50                            the value we get back, as we read it without a
51                            lock, so instead we get the lock and re-fetch the
52                            value below.
53                            
54                            Notice that not doing this optimisation on the
55                            first hash chain is critical. We must guarantee
56                            that we have done at least one fcntl lock at the
57                            start of a search to guarantee that memory is
58                            coherent on SMP systems. If records are added by
59                            others during the search then thats OK, and we
60                            could possibly miss those with this trick, but we
61                            could miss them anyway without this trick, so the
62                            semantics don't change.
63                            
64                            With a non-indexed ldb search this trick gains us a
65                            factor of around 80 in speed on a linux 2.6.x
66                            system (testing using ldbtest).
67                         */
68                         tdb->methods->next_hash_chain(tdb, &tlock->hash);
69                         if (tlock->hash == tdb->header.hash_size) {
70                                 continue;
71                         }
72                 }
73
74                 if (tdb_lock(tdb, tlock->hash, tlock->lock_rw) == -1)
75                         return -1;
76
77                 /* No previous record?  Start at top of chain. */
78                 if (!tlock->off) {
79                         if (tdb_ofs_read(tdb, TDB_HASH_TOP(tlock->hash),
80                                      &tlock->off) == -1)
81                                 goto fail;
82                 } else {
83                         /* Otherwise unlock the previous record. */
84                         if (tdb_unlock_record(tdb, tlock->off) != 0)
85                                 goto fail;
86                 }
87
88                 if (want_next) {
89                         /* We have offset of old record: grab next */
90                         if (tdb_rec_read(tdb, tlock->off, rec) == -1)
91                                 goto fail;
92                         tlock->off = rec->next;
93                 }
94
95                 /* Iterate through chain */
96                 while( tlock->off) {
97                         tdb_off_t current;
98                         if (tdb_rec_read(tdb, tlock->off, rec) == -1)
99                                 goto fail;
100
101                         /* Detect infinite loops. From "Shlomi Yaakobovich" <Shlomi@exanet.com>. */
102                         if (tlock->off == rec->next) {
103                                 TDB_LOG((tdb, 0, "tdb_next_lock: loop detected.\n"));
104                                 goto fail;
105                         }
106
107                         if (!TDB_DEAD(rec)) {
108                                 /* Woohoo: we found one! */
109                                 if (tdb_lock_record(tdb, tlock->off) != 0)
110                                         goto fail;
111                                 return tlock->off;
112                         }
113
114                         /* Try to clean dead ones from old traverses */
115                         current = tlock->off;
116                         tlock->off = rec->next;
117                         if (!tdb->read_only && 
118                             tdb_do_delete(tdb, current, rec) != 0)
119                                 goto fail;
120                 }
121                 tdb_unlock(tdb, tlock->hash, tlock->lock_rw);
122                 want_next = 0;
123         }
124         /* We finished iteration without finding anything */
125         return TDB_ERRCODE(TDB_SUCCESS, 0);
126
127  fail:
128         tlock->off = 0;
129         if (tdb_unlock(tdb, tlock->hash, tlock->lock_rw) != 0)
130                 TDB_LOG((tdb, 0, "tdb_next_lock: On error unlock failed!\n"));
131         return -1;
132 }
133
134 /* traverse the entire database - calling fn(tdb, key, data) on each element.
135    return -1 on error or the record count traversed
136    if fn is NULL then it is not called
137    a non-zero return value from fn() indicates that the traversal should stop
138   */
139 static int tdb_traverse_internal(struct tdb_context *tdb, 
140                                  tdb_traverse_func fn, void *private,
141                                  struct tdb_traverse_lock *tl)
142 {
143         TDB_DATA key, dbuf;
144         struct list_struct rec;
145         int ret, count = 0;
146
147         /* This was in the initializaton, above, but the IRIX compiler
148          * did not like it.  crh
149          */
150         tl->next = tdb->travlocks.next;
151
152         /* fcntl locks don't stack: beware traverse inside traverse */
153         tdb->travlocks.next = tl;
154
155         /* tdb_next_lock places locks on the record returned, and its chain */
156         while ((ret = tdb_next_lock(tdb, tl, &rec)) > 0) {
157                 count++;
158                 /* now read the full record */
159                 key.dptr = tdb_alloc_read(tdb, tl->off + sizeof(rec), 
160                                           rec.key_len + rec.data_len);
161                 if (!key.dptr) {
162                         ret = -1;
163                         if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0)
164                                 goto out;
165                         if (tdb_unlock_record(tdb, tl->off) != 0)
166                                 TDB_LOG((tdb, 0, "tdb_traverse: key.dptr == NULL and unlock_record failed!\n"));
167                         goto out;
168                 }
169                 key.dsize = rec.key_len;
170                 dbuf.dptr = key.dptr + rec.key_len;
171                 dbuf.dsize = rec.data_len;
172
173                 /* Drop chain lock, call out */
174                 if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0) {
175                         ret = -1;
176                         goto out;
177                 }
178                 if (fn && fn(tdb, key, dbuf, private)) {
179                         /* They want us to terminate traversal */
180                         ret = count;
181                         if (tdb_unlock_record(tdb, tl->off) != 0) {
182                                 TDB_LOG((tdb, 0, "tdb_traverse: unlock_record failed!\n"));;
183                                 ret = -1;
184                         }
185                         tdb->travlocks.next = tl->next;
186                         SAFE_FREE(key.dptr);
187                         return count;
188                 }
189                 SAFE_FREE(key.dptr);
190         }
191 out:
192         tdb->travlocks.next = tl->next;
193         if (ret < 0)
194                 return -1;
195         else
196                 return count;
197 }
198
199
200 /*
201   a write style traverse - temporarily marks the db read only
202 */
203 int tdb_traverse_read(struct tdb_context *tdb, 
204                       tdb_traverse_func fn, void *private)
205 {
206         struct tdb_traverse_lock tl = { NULL, 0, 0, F_RDLCK };
207         int ret, read_only = tdb->read_only;
208         tdb->read_only = 1;
209         ret = tdb_traverse_internal(tdb, fn, private, &tl);
210         tdb->read_only = read_only;
211         return ret;
212 }
213
214 /*
215   a write style traverse - needs to get the transaction lock to
216   prevent deadlocks
217 */
218 int tdb_traverse(struct tdb_context *tdb, 
219                  tdb_traverse_func fn, void *private)
220 {
221         struct tdb_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
222         int ret;
223         
224         if (tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, F_WRLCK, F_SETLKW, 0) == -1) {
225                 TDB_LOG((tdb, 0, "tdb_traverse: failed to get transaction lock\n"));
226                 tdb->ecode = TDB_ERR_LOCK;
227                 return -1;
228         }
229
230         ret = tdb_traverse_internal(tdb, fn, private, &tl);
231
232         tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, F_UNLCK, F_SETLKW, 0);
233
234         return ret;
235 }
236
237
238 /* find the first entry in the database and return its key */
239 TDB_DATA tdb_firstkey(struct tdb_context *tdb)
240 {
241         TDB_DATA key;
242         struct list_struct rec;
243
244         /* release any old lock */
245         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
246                 return tdb_null;
247         tdb->travlocks.off = tdb->travlocks.hash = 0;
248
249         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) <= 0)
250                 return tdb_null;
251         /* now read the key */
252         key.dsize = rec.key_len;
253         key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
254         if (tdb_unlock(tdb, BUCKET(tdb->travlocks.hash), F_WRLCK) != 0)
255                 TDB_LOG((tdb, 0, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
256         return key;
257 }
258
259 /* find the next entry in the database, returning its key */
260 TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
261 {
262         u32 oldhash;
263         TDB_DATA key = tdb_null;
264         struct list_struct rec;
265         unsigned char *k = NULL;
266
267         /* Is locked key the old key?  If so, traverse will be reliable. */
268         if (tdb->travlocks.off) {
269                 if (tdb_lock(tdb,tdb->travlocks.hash,F_WRLCK))
270                         return tdb_null;
271                 if (tdb_rec_read(tdb, tdb->travlocks.off, &rec) == -1
272                     || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
273                                             rec.key_len))
274                     || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
275                         /* No, it wasn't: unlock it and start from scratch */
276                         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
277                                 return tdb_null;
278                         if (tdb_unlock(tdb, tdb->travlocks.hash, F_WRLCK) != 0)
279                                 return tdb_null;
280                         tdb->travlocks.off = 0;
281                 }
282
283                 SAFE_FREE(k);
284         }
285
286         if (!tdb->travlocks.off) {
287                 /* No previous element: do normal find, and lock record */
288                 tdb->travlocks.off = tdb_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), F_WRLCK, &rec);
289                 if (!tdb->travlocks.off)
290                         return tdb_null;
291                 tdb->travlocks.hash = BUCKET(rec.full_hash);
292                 if (tdb_lock_record(tdb, tdb->travlocks.off) != 0) {
293                         TDB_LOG((tdb, 0, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
294                         return tdb_null;
295                 }
296         }
297         oldhash = tdb->travlocks.hash;
298
299         /* Grab next record: locks chain and returned record,
300            unlocks old record */
301         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) > 0) {
302                 key.dsize = rec.key_len;
303                 key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
304                                           key.dsize);
305                 /* Unlock the chain of this new record */
306                 if (tdb_unlock(tdb, tdb->travlocks.hash, F_WRLCK) != 0)
307                         TDB_LOG((tdb, 0, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
308         }
309         /* Unlock the chain of old record */
310         if (tdb_unlock(tdb, BUCKET(oldhash), F_WRLCK) != 0)
311                 TDB_LOG((tdb, 0, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
312         return key;
313 }
314