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 #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 */
  34 static 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->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->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   */
 143 static 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         size_t recbuf_len;
 152
 153         recbuf_len = 4096;
 154         key.dptr = malloc(recbuf_len);
 155         if (key.dptr == NULL) {
 156                 return -1;
 157         }
 158
 159         /* This was in the initialization, above, but the IRIX compiler
 160          * did not like it.  crh
 161          */
 162         tl->next = tdb->travlocks.next;
 163
 164         /* fcntl locks don't stack: beware traverse inside traverse */
 165         tdb->travlocks.next = tl;
 166
 167         /* tdb_next_lock places locks on the record returned, and its chain */
 168         while ((off = tdb_next_lock(tdb, tl, &rec)) != 0) {
 169                 tdb_len_t full_len = rec.key_len + rec.data_len;
 170                 int nread;
 171
 172                 if (full_len > recbuf_len) {
 173                         recbuf_len = full_len;
 174
 175                         /*
 176                          * No realloc, we don't need the old data and thus can
 177                          * do without the memcpy
 178                          */
 179                         free(key.dptr);
 180                         key.dptr = malloc(recbuf_len);
 181
 182                         if (key.dptr == NULL) {
 183                                 ret = -1;
 184                                 if (tdb_unlock(tdb, tl->hash, tl->lock_rw)
 185                                     != 0) {
 186                                         goto out;
 187                                 }
 188                                 if (tdb_unlock_record(tdb, tl->off) != 0) {
 189                                         TDB_LOG((tdb, TDB_DEBUG_FATAL,
 190                                                  "tdb_traverse: malloc "
 191                                                  "failed and unlock_record "
 192                                                  "failed!\n"));
 193                                 }
 194                                 goto out;
 195                         }
 196                 }
 197
 198                 if (off == TDB_NEXT_LOCK_ERR) {
 199                         ret = -1;
 200                         goto out;
 201                 }
 202                 count++;
 203                 /* now read the full record */
 204                 nread = tdb->methods->tdb_read(tdb, tl->off + sizeof(rec),
 205                                                key.dptr, full_len, 0);
 206                 if (nread == -1) {
 207                         ret = -1;
 208                         if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0)
 209                                 goto out;
 210                         if (tdb_unlock_record(tdb, tl->off) != 0)
 211                                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: key.dptr == NULL and unlock_record failed!\n"));
 212                         goto out;
 213                 }
 214                 key.dsize = rec.key_len;
 215                 dbuf.dptr = key.dptr + rec.key_len;
 216                 dbuf.dsize = rec.data_len;
 217
 218                 tdb_trace_1rec_retrec(tdb, "traverse", key, dbuf);
 219
 220                 /* Drop chain lock, call out */
 221                 if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0) {
 222                         ret = -1;
 223                         goto out;
 224                 }
 225                 if (fn && fn(tdb, key, dbuf, private_data)) {
 226                         /* They want us to terminate traversal */
 227                         tdb_trace_ret(tdb, "tdb_traverse_end", count);
 228                         if (tdb_unlock_record(tdb, tl->off) != 0) {
 229                                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: unlock_record failed!\n"));;
 230                                 ret = -1;
 231                         }
 232                         goto out;
 233                 }
 234         }
 235         tdb_trace(tdb, "tdb_traverse_end");
 236 out:
 237         SAFE_FREE(key.dptr);
 238         tdb->travlocks.next = tl->next;
 239         if (ret < 0)
 240                 return -1;
 241         else
 242                 return count;
 243 }
 244
 245
 246 /*
 247   a read style traverse - temporarily marks each record read only
 248 */
 249 _PUBLIC_ int tdb_traverse_read(struct tdb_context *tdb,
 250                       tdb_traverse_func fn, void *private_data)
 251 {
 252         struct tdb_traverse_lock tl = { NULL, 0, 0, F_RDLCK };
 253         int ret;
 254
 255         tdb->traverse_read++;
 256         tdb_trace(tdb, "tdb_traverse_read_start");
 257         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
 258         tdb->traverse_read--;
 259
 260         return ret;
 261 }
 262
 263 /*
 264   a write style traverse - needs to get the transaction lock to
 265   prevent deadlocks
 266
 267   WARNING: The data buffer given to the callback fn does NOT meet the
 268   alignment guarantees malloc gives you.
 269 */
 270 _PUBLIC_ int tdb_traverse(struct tdb_context *tdb,
 271                  tdb_traverse_func fn, void *private_data)
 272 {
 273         struct tdb_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
 274         enum tdb_lock_flags lock_flags;
 275         int ret;
 276
 277         if (tdb->read_only || tdb->traverse_read) {
 278                 return tdb_traverse_read(tdb, fn, private_data);
 279         }
 280
 281         lock_flags = TDB_LOCK_WAIT;
 282
 283         if (tdb->allrecord_lock.count != 0) {
 284                 /*
 285                  * This avoids a deadlock between tdb_lockall() and
 286                  * tdb_traverse(). See
 287                  * https://bugzilla.samba.org/show_bug.cgi?id=11381
 288                  */
 289                 lock_flags = TDB_LOCK_NOWAIT;
 290         }
 291
 292         if (tdb_transaction_lock(tdb, F_WRLCK, lock_flags)) {
 293                 return -1;
 294         }
 295
 296         tdb->traverse_write++;
 297         tdb_trace(tdb, "tdb_traverse_start");
 298         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
 299         tdb->traverse_write--;
 300
 301         tdb_transaction_unlock(tdb, F_WRLCK);
 302
 303         return ret;
 304 }
 305
 306
 307 /* find the first entry in the database and return its key */
 308 _PUBLIC_ TDB_DATA tdb_firstkey(struct tdb_context *tdb)
 309 {
 310         TDB_DATA key;
 311         struct tdb_record rec;
 312         tdb_off_t off;
 313
 314         /* release any old lock */
 315         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
 316                 return tdb_null;
 317         tdb->travlocks.off = tdb->travlocks.hash = 0;
 318         tdb->travlocks.lock_rw = F_RDLCK;
 319
 320         /* Grab first record: locks chain and returned record. */
 321         off = tdb_next_lock(tdb, &tdb->travlocks, &rec);
 322         if (off == 0 || off == TDB_NEXT_LOCK_ERR) {
 323                 tdb_trace_retrec(tdb, "tdb_firstkey", tdb_null);
 324                 return tdb_null;
 325         }
 326         /* now read the key */
 327         key.dsize = rec.key_len;
 328         key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
 329
 330         tdb_trace_retrec(tdb, "tdb_firstkey", key);
 331
 332         /* Unlock the hash chain of the record we just read. */
 333         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 334                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
 335         return key;
 336 }
 337
 338 /* find the next entry in the database, returning its key */
 339 _PUBLIC_ TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
 340 {
 341         uint32_t oldhash;
 342         TDB_DATA key = tdb_null;
 343         struct tdb_record rec;
 344         unsigned char *k = NULL;
 345         tdb_off_t off;
 346
 347         /* Is locked key the old key?  If so, traverse will be reliable. */
 348         if (tdb->travlocks.off) {
 349                 if (tdb_lock(tdb,tdb->travlocks.hash,tdb->travlocks.lock_rw))
 350                         return tdb_null;
 351                 if (tdb_rec_read(tdb, tdb->travlocks.off, &rec) == -1
 352                     || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
 353                                             rec.key_len))
 354                     || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
 355                         /* No, it wasn't: unlock it and start from scratch */
 356                         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0) {
 357                                 tdb_trace_1rec_retrec(tdb, "tdb_nextkey",
 358                                                       oldkey, tdb_null);
 359                                 SAFE_FREE(k);
 360                                 return tdb_null;
 361                         }
 362                         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0) {
 363                                 SAFE_FREE(k);
 364                                 return tdb_null;
 365                         }
 366                         tdb->travlocks.off = 0;
 367                 }
 368
 369                 SAFE_FREE(k);
 370         }
 371
 372         if (!tdb->travlocks.off) {
 373                 /* No previous element: do normal find, and lock record */
 374                 tdb->travlocks.off = tdb_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), tdb->travlocks.lock_rw, &rec);
 375                 if (!tdb->travlocks.off) {
 376                         tdb_trace_1rec_retrec(tdb, "tdb_nextkey", oldkey, tdb_null);
 377                         return tdb_null;
 378                 }
 379                 tdb->travlocks.hash = BUCKET(rec.full_hash);
 380                 if (tdb_lock_record(tdb, tdb->travlocks.off) != 0) {
 381                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
 382                         return tdb_null;
 383                 }
 384         }
 385         oldhash = tdb->travlocks.hash;
 386
 387         /* Grab next record: locks chain and returned record,
 388            unlocks old record */
 389         off = tdb_next_lock(tdb, &tdb->travlocks, &rec);
 390         if (off != TDB_NEXT_LOCK_ERR && off != 0) {
 391                 key.dsize = rec.key_len;
 392                 key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
 393                                           key.dsize);
 394                 /* Unlock the chain of this new record */
 395                 if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 396                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 397         }
 398         /* Unlock the chain of old record */
 399         if (tdb_unlock(tdb, BUCKET(oldhash), tdb->travlocks.lock_rw) != 0)
 400                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 401         tdb_trace_1rec_retrec(tdb, "tdb_nextkey", oldkey, key);
 402         return key;
 403 }
 404