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, TDB_DEBUG_FATAL, "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 || tdb->traverse_read) &&
 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, TDB_DEBUG_FATAL, "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_data,
 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, TDB_DEBUG_FATAL, "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                         SAFE_FREE(key.dptr);
 177                         goto out;
 178                 }
 179                 if (fn && fn(tdb, key, dbuf, private_data)) {
 180                         /* They want us to terminate traversal */
 181                         ret = count;
 182                         if (tdb_unlock_record(tdb, tl->off) != 0) {
 183                                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: unlock_record failed!\n"));;
 184                                 ret = -1;
 185                         }
 186                         SAFE_FREE(key.dptr);
 187                         goto out;
 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_data)
 205 {
 206         struct tdb_traverse_lock tl = { NULL, 0, 0, F_RDLCK };
 207         int ret;
 208
 209         /* we need to get a read lock on the transaction lock here to
 210            cope with the lock ordering semantics of solaris10 */
 211         if (tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, F_RDLCK, F_SETLKW, 0, 1) == -1) {
 212                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_traverse_read: failed to get transaction lock\n"));
 213                 tdb->ecode = TDB_ERR_LOCK;
 214                 return -1;
 215         }
 216
 217         tdb->traverse_read++;
 218         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
 219         tdb->traverse_read--;
 220
 221         tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, F_UNLCK, F_SETLKW, 0, 1);
 222
 223         return ret;
 224 }
 225
 226 /*
 227   a write style traverse - needs to get the transaction lock to
 228   prevent deadlocks
 229 */
 230 int tdb_traverse(struct tdb_context *tdb,
 231                  tdb_traverse_func fn, void *private_data)
 232 {
 233         struct tdb_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
 234         int ret;
 235
 236         if (tdb->read_only || tdb->traverse_read) {
 237                 return tdb_traverse_read(tdb, fn, private_data);
 238         }
 239
 240         if (tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, F_WRLCK, F_SETLKW, 0, 1) == -1) {
 241                 TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_traverse: failed to get transaction lock\n"));
 242                 tdb->ecode = TDB_ERR_LOCK;
 243                 return -1;
 244         }
 245
 246         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
 247
 248         tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, F_UNLCK, F_SETLKW, 0, 1);
 249
 250         return ret;
 251 }
 252
 253
 254 /* find the first entry in the database and return its key */
 255 TDB_DATA tdb_firstkey(struct tdb_context *tdb)
 256 {
 257         TDB_DATA key;
 258         struct list_struct rec;
 259
 260         /* release any old lock */
 261         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
 262                 return tdb_null;
 263         tdb->travlocks.off = tdb->travlocks.hash = 0;
 264         tdb->travlocks.lock_rw = F_RDLCK;
 265
 266         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) <= 0)
 267                 return tdb_null;
 268         /* now read the key */
 269         key.dsize = rec.key_len;
 270         key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
 271         if (tdb_unlock(tdb, BUCKET(tdb->travlocks.hash), F_WRLCK) != 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         u32 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,F_WRLCK))
 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, F_WRLCK) != 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), F_WRLCK, &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, F_WRLCK) != 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), F_WRLCK) != 0)
 332                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 333         return key;
 334 }
 335