git.ozlabs.org Git - ccan/blob - 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->traverse_read == 0 && 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         if (tdb->traverse_read == 0) {
 224                 tdb_transaction_unlock(tdb);
 225         }
 226
 227         return ret;
 228 }
 229
 230 /*
 231   a write style traverse - needs to get the transaction lock to
 232   prevent deadlocks
 233
 234   WARNING: The data buffer given to the callback fn does NOT meet the
 235   alignment restrictions malloc gives you.
 236 */
 237 int tdb_traverse(struct tdb_context *tdb,
 238                  tdb_traverse_func fn, void *private_data)
 239 {
 240         struct tdb_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
 241         int ret;
 242
 243         if (tdb->read_only || tdb->traverse_read) {
 244                 return tdb_traverse_read(tdb, fn, private_data);
 245         }
 246
 247         /* Nested traversals: transaction lock doesn't nest. */
 248         if (tdb->traverse_write == 0 && tdb_transaction_lock(tdb, F_WRLCK)) {
 249                 return -1;
 250         }
 251
 252         tdb->traverse_write++;
 253         tdb_trace(tdb, "tdb_traverse_start");
 254         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
 255         tdb->traverse_write--;
 256
 257         if (tdb->traverse_write == 0) {
 258                 tdb_transaction_unlock(tdb);
 259         }
 260
 261         return ret;
 262 }
 263
 264
 265 /* find the first entry in the database and return its key */
 266 TDB_DATA tdb_firstkey(struct tdb_context *tdb)
 267 {
 268         TDB_DATA key;
 269         struct list_struct rec;
 270
 271         /* release any old lock */
 272         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
 273                 return tdb_null;
 274         tdb->travlocks.off = tdb->travlocks.hash = 0;
 275         tdb->travlocks.lock_rw = F_RDLCK;
 276
 277         /* Grab first record: locks chain and returned record. */
 278         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) <= 0) {
 279                 tdb_trace_retrec(tdb, "tdb_firstkey", tdb_null);
 280                 return tdb_null;
 281         }
 282         /* now read the key */
 283         key.dsize = rec.key_len;
 284         key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
 285
 286         tdb_trace_retrec(tdb, "tdb_firstkey", key);
 287
 288         /* Unlock the hash chain of the record we just read. */
 289         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 290                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
 291         return key;
 292 }
 293
 294 /* find the next entry in the database, returning its key */
 295 TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
 296 {
 297         uint32_t oldhash;
 298         TDB_DATA key = tdb_null;
 299         struct list_struct rec;
 300         unsigned char *k = NULL;
 301
 302         /* Is locked key the old key?  If so, traverse will be reliable. */
 303         if (tdb->travlocks.off) {
 304                 if (tdb_lock(tdb,tdb->travlocks.hash,tdb->travlocks.lock_rw))
 305                         return tdb_null;
 306                 if (tdb_rec_read(tdb, tdb->travlocks.off, &rec) == -1
 307                     || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
 308                                             rec.key_len))
 309                     || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
 310                         /* No, it wasn't: unlock it and start from scratch */
 311                         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0) {
 312                                 tdb_trace_1rec_retrec(tdb, "tdb_nextkey",
 313                                                       oldkey, tdb_null);
 314                                 SAFE_FREE(k);
 315                                 return tdb_null;
 316                         }
 317                         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0) {
 318                                 SAFE_FREE(k);
 319                                 return tdb_null;
 320                         }
 321                         tdb->travlocks.off = 0;
 322                 }
 323
 324                 SAFE_FREE(k);
 325         }
 326
 327         if (!tdb->travlocks.off) {
 328                 /* No previous element: do normal find, and lock record */
 329                 tdb->travlocks.off = tdb_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), tdb->travlocks.lock_rw, &rec);
 330                 if (!tdb->travlocks.off) {
 331                         tdb_trace_1rec_retrec(tdb, "tdb_nextkey", oldkey, tdb_null);
 332                         return tdb_null;
 333                 }
 334                 tdb->travlocks.hash = BUCKET(rec.full_hash);
 335                 if (tdb_lock_record(tdb, tdb->travlocks.off) != 0) {
 336                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
 337                         return tdb_null;
 338                 }
 339         }
 340         oldhash = tdb->travlocks.hash;
 341
 342         /* Grab next record: locks chain and returned record,
 343            unlocks old record */
 344         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) > 0) {
 345                 key.dsize = rec.key_len;
 346                 key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
 347                                           key.dsize);
 348                 /* Unlock the chain of this new record */
 349                 if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 350                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 351         }
 352         /* Unlock the chain of old record */
 353         if (tdb_unlock(tdb, BUCKET(oldhash), tdb->travlocks.lock_rw) != 0)
 354                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 355         tdb_trace_1rec_retrec(tdb, "tdb_nextkey", oldkey, key);
 356         return key;
 357 }
 358