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                 /* 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         tdb_trace(tdb, "tdb_traverse_read = %i\n", ret);
 218
 219         tdb_transaction_unlock(tdb);
 220
 221         return ret;
 222 }
 223
 224 /*
 225   a write style traverse - needs to get the transaction lock to
 226   prevent deadlocks
 227
 228   WARNING: The data buffer given to the callback fn does NOT meet the
 229   alignment restrictions malloc gives you.
 230 */
 231 int tdb_traverse(struct tdb_context *tdb,
 232                  tdb_traverse_func fn, void *private_data)
 233 {
 234         struct tdb_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
 235         int ret;
 236
 237         if (tdb->read_only || tdb->traverse_read) {
 238                 return tdb_traverse_read(tdb, fn, private_data);
 239         }
 240
 241         if (tdb_transaction_lock(tdb, F_WRLCK)) {
 242                 return -1;
 243         }
 244
 245         tdb->traverse_write++;
 246         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
 247         tdb->traverse_write--;
 248         tdb_trace(tdb, "tdb_traverse = %i\n", ret);
 249
 250         tdb_transaction_unlock(tdb);
 251
 252         return ret;
 253 }
 254
 255
 256 /* find the first entry in the database and return its key */
 257 TDB_DATA tdb_firstkey(struct tdb_context *tdb)
 258 {
 259         TDB_DATA key;
 260         struct list_struct rec;
 261
 262         /* release any old lock */
 263         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
 264                 return tdb_null;
 265         tdb->travlocks.off = tdb->travlocks.hash = 0;
 266         tdb->travlocks.lock_rw = F_RDLCK;
 267
 268         /* Grab first record: locks chain and returned record. */
 269         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) <= 0) {
 270                 tdb_trace(tdb, "tdb_firstkey = ENOENT\n");
 271                 return tdb_null;
 272         }
 273         /* now read the key */
 274         key.dsize = rec.key_len;
 275         key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
 276
 277         tdb_trace(tdb, "tdb_firstkey = ");
 278         tdb_trace_record(tdb, key);
 279         tdb_trace(tdb, "\n");
 280
 281         /* Unlock the hash chain of the record we just read. */
 282         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 283                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
 284         return key;
 285 }
 286
 287 /* find the next entry in the database, returning its key */
 288 TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
 289 {
 290         uint32_t oldhash;
 291         TDB_DATA key = tdb_null;
 292         struct list_struct rec;
 293         unsigned char *k = NULL;
 294
 295         /* Is locked key the old key?  If so, traverse will be reliable. */
 296         if (tdb->travlocks.off) {
 297                 if (tdb_lock(tdb,tdb->travlocks.hash,tdb->travlocks.lock_rw))
 298                         return tdb_null;
 299                 if (tdb_rec_read(tdb, tdb->travlocks.off, &rec) == -1
 300                     || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
 301                                             rec.key_len))
 302                     || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
 303                         /* No, it wasn't: unlock it and start from scratch */
 304                         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0) {
 305                                 tdb_trace(tdb, "tdb_nextkey ");
 306                                 tdb_trace_record(tdb, oldkey);
 307                                 tdb_trace(tdb, "= ENOENT\n");
 308                                 SAFE_FREE(k);
 309                                 return tdb_null;
 310                         }
 311                         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0) {
 312                                 SAFE_FREE(k);
 313                                 return tdb_null;
 314                         }
 315                         tdb->travlocks.off = 0;
 316                 }
 317
 318                 SAFE_FREE(k);
 319         }
 320
 321         if (!tdb->travlocks.off) {
 322                 /* No previous element: do normal find, and lock record */
 323                 tdb->travlocks.off = tdb_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), tdb->travlocks.lock_rw, &rec);
 324                 if (!tdb->travlocks.off) {
 325                         tdb_trace(tdb, "tdb_nextkey ");
 326                         tdb_trace_record(tdb, oldkey);
 327                         tdb_trace(tdb, "= ENOENT\n");
 328                         return tdb_null;
 329                 }
 330                 tdb->travlocks.hash = BUCKET(rec.full_hash);
 331                 if (tdb_lock_record(tdb, tdb->travlocks.off) != 0) {
 332                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
 333                         return tdb_null;
 334                 }
 335         }
 336         oldhash = tdb->travlocks.hash;
 337
 338         /* Grab next record: locks chain and returned record,
 339            unlocks old record */
 340         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) > 0) {
 341                 key.dsize = rec.key_len;
 342                 key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
 343                                           key.dsize);
 344                 /* Unlock the chain of this new record */
 345                 if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 346                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 347         }
 348         /* Unlock the chain of old record */
 349         if (tdb_unlock(tdb, BUCKET(oldhash), tdb->travlocks.lock_rw) != 0)
 350                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 351         tdb_trace(tdb, "tdb_nextkey ");
 352         tdb_trace_record(tdb, oldkey);
 353         tdb_trace(tdb, "= ");
 354         tdb_trace_record(tdb, key);
 355         tdb_trace(tdb, "\n");
 356         return key;
 357 }
 358