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 list_struct *rec)
  36 {
  37         int want_next = (tlock->off != 0);
  38
  39         /* Lock each chain from the start one. */
  40         for (; tlock->hash < tdb->header.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->header.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         return TDB_ERRCODE(TDB_SUCCESS, 0);
 129
 130  fail:
 131         tlock->off = 0;
 132         if (tdb_unlock(tdb, tlock->hash, tlock->lock_rw) != 0)
 133                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_next_lock: On error unlock failed!\n"));
 134         return TDB_NEXT_LOCK_ERR;
 135 }
 136
 137 /* traverse the entire database - calling fn(tdb, key, data) on each element.
 138    return -1 on error or the record count traversed
 139    if fn is NULL then it is not called
 140    a non-zero return value from fn() indicates that the traversal should stop
 141   */
 142 static int tdb_traverse_internal(struct tdb_context *tdb,
 143                                  tdb_traverse_func fn, void *private_data,
 144                                  struct tdb_traverse_lock *tl)
 145 {
 146         TDB_DATA key, dbuf;
 147         struct list_struct rec;
 148         int ret = 0, count = 0;
 149         tdb_off_t off;
 150
 151         /* This was in the initializaton, above, but the IRIX compiler
 152          * did not like it.  crh
 153          */
 154         tl->next = tdb->travlocks.next;
 155
 156         /* fcntl locks don't stack: beware traverse inside traverse */
 157         tdb->travlocks.next = tl;
 158
 159         /* tdb_next_lock places locks on the record returned, and its chain */
 160         while ((off = tdb_next_lock(tdb, tl, &rec)) != 0) {
 161                 if (off == TDB_NEXT_LOCK_ERR) {
 162                         ret = -1;
 163                         goto out;
 164                 }
 165                 count++;
 166                 /* now read the full record */
 167                 key.dptr = tdb_alloc_read(tdb, tl->off + sizeof(rec),
 168                                           rec.key_len + rec.data_len);
 169                 if (!key.dptr) {
 170                         ret = -1;
 171                         if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0)
 172                                 goto out;
 173                         if (tdb_unlock_record(tdb, tl->off) != 0)
 174                                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: key.dptr == NULL and unlock_record failed!\n"));
 175                         goto out;
 176                 }
 177                 key.dsize = rec.key_len;
 178                 dbuf.dptr = key.dptr + rec.key_len;
 179                 dbuf.dsize = rec.data_len;
 180
 181                 /* Drop chain lock, call out */
 182                 if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0) {
 183                         ret = -1;
 184                         SAFE_FREE(key.dptr);
 185                         goto out;
 186                 }
 187                 if (fn && fn(tdb, key, dbuf, private_data)) {
 188                         /* They want us to terminate traversal */
 189                         if (tdb_unlock_record(tdb, tl->off) != 0) {
 190                                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: unlock_record failed!\n"));;
 191                                 ret = -1;
 192                         }
 193                         SAFE_FREE(key.dptr);
 194                         goto out;
 195                 }
 196                 SAFE_FREE(key.dptr);
 197         }
 198 out:
 199         tdb->travlocks.next = tl->next;
 200         if (ret < 0)
 201                 return -1;
 202         else
 203                 return count;
 204 }
 205
 206
 207 /*
 208   a write style traverse - temporarily marks the db read only
 209 */
 210 int tdb_traverse_read(struct tdb_context *tdb,
 211                       tdb_traverse_func fn, void *private_data)
 212 {
 213         struct tdb_traverse_lock tl = { NULL, 0, 0, F_RDLCK };
 214         int ret;
 215
 216         /* we need to get a read lock on the transaction lock here to
 217            cope with the lock ordering semantics of solaris10 */
 218         if (tdb_transaction_lock(tdb, F_RDLCK)) {
 219                 return -1;
 220         }
 221
 222         tdb->traverse_read++;
 223         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
 224         tdb->traverse_read--;
 225
 226         tdb_transaction_unlock(tdb);
 227
 228         return ret;
 229 }
 230
 231 /*
 232   a write style traverse - needs to get the transaction lock to
 233   prevent deadlocks
 234
 235   WARNING: The data buffer given to the callback fn does NOT meet the
 236   alignment restrictions malloc gives you.
 237 */
 238 int tdb_traverse(struct tdb_context *tdb,
 239                  tdb_traverse_func fn, void *private_data)
 240 {
 241         struct tdb_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
 242         int ret;
 243
 244         if (tdb->read_only || tdb->traverse_read) {
 245                 return tdb_traverse_read(tdb, fn, private_data);
 246         }
 247
 248         if (tdb_transaction_lock(tdb, F_WRLCK)) {
 249                 return -1;
 250         }
 251
 252         tdb->traverse_write++;
 253         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
 254         tdb->traverse_write--;
 255
 256         tdb_transaction_unlock(tdb);
 257
 258         return ret;
 259 }
 260
 261
 262 /* find the first entry in the database and return its key */
 263 TDB_DATA tdb_firstkey(struct tdb_context *tdb)
 264 {
 265         TDB_DATA key;
 266         struct list_struct rec;
 267         tdb_off_t off;
 268
 269         /* release any old lock */
 270         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
 271                 return tdb_null;
 272         tdb->travlocks.off = tdb->travlocks.hash = 0;
 273         tdb->travlocks.lock_rw = F_RDLCK;
 274
 275         /* Grab first record: locks chain and returned record. */
 276         off = tdb_next_lock(tdb, &tdb->travlocks, &rec);
 277         if (off == 0 || off == TDB_NEXT_LOCK_ERR)
 278                 return tdb_null;
 279         /* now read the key */
 280         key.dsize = rec.key_len;
 281         key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
 282
 283         /* Unlock the hash chain of the record we just read. */
 284         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 285                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
 286         return key;
 287 }
 288
 289 /* find the next entry in the database, returning its key */
 290 TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
 291 {
 292         uint32_t oldhash;
 293         TDB_DATA key = tdb_null;
 294         struct list_struct rec;
 295         unsigned char *k = NULL;
 296         tdb_off_t off;
 297
 298         /* Is locked key the old key?  If so, traverse will be reliable. */
 299         if (tdb->travlocks.off) {
 300                 if (tdb_lock(tdb,tdb->travlocks.hash,tdb->travlocks.lock_rw))
 301                         return tdb_null;
 302                 if (tdb_rec_read(tdb, tdb->travlocks.off, &rec) == -1
 303                     || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
 304                                             rec.key_len))
 305                     || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
 306                         /* No, it wasn't: unlock it and start from scratch */
 307                         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0) {
 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                         return tdb_null;
 326                 tdb->travlocks.hash = BUCKET(rec.full_hash);
 327                 if (tdb_lock_record(tdb, tdb->travlocks.off) != 0) {
 328                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
 329                         return tdb_null;
 330                 }
 331         }
 332         oldhash = tdb->travlocks.hash;
 333
 334         /* Grab next record: locks chain and returned record,
 335            unlocks old record */
 336         off = tdb_next_lock(tdb, &tdb->travlocks, &rec);
 337         if (off != TDB_NEXT_LOCK_ERR && off != 0) {
 338                 key.dsize = rec.key_len;
 339                 key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
 340                                           key.dsize);
 341                 /* Unlock the chain of this new record */
 342                 if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 343                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 344         }
 345         /* Unlock the chain of old record */
 346         if (tdb_unlock(tdb, BUCKET(oldhash), tdb->travlocks.lock_rw) != 0)
 347                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 348         return key;
 349 }
 350