git.ozlabs.org Git - ccan/blob - ccan/tdb2/tdb1_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 "tdb1_private.h"
  29
  30 #define TDB1_NEXT_LOCK_ERR ((tdb1_off_t)-1)
  31
  32 /* Uses traverse lock: 0 = finish, TDB1_NEXT_LOCK_ERR = error,
  33    other = record offset */
  34 static tdb1_off_t tdb1_next_lock(struct tdb1_context *tdb, struct tdb1_traverse_lock *tlock,
  35                          struct tdb1_record *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 tdb1_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 (tdb1_lock(tdb, tlock->hash, tlock->lock_rw) == -1)
  77                         return TDB1_NEXT_LOCK_ERR;
  78
  79                 /* No previous record?  Start at top of chain. */
  80                 if (!tlock->off) {
  81                         if (tdb1_ofs_read(tdb, TDB1_HASH_TOP(tlock->hash),
  82                                      &tlock->off) == -1)
  83                                 goto fail;
  84                 } else {
  85                         /* Otherwise unlock the previous record. */
  86                         if (tdb1_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 (tdb1_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                         tdb1_off_t current;
 100                         if (tdb1_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 = TDB1_ERR_CORRUPT;
 106                                 TDB1_LOG((tdb, TDB1_DEBUG_FATAL, "tdb1_next_lock: loop detected.\n"));
 107                                 goto fail;
 108                         }
 109
 110                         if (!TDB1_DEAD(rec)) {
 111                                 /* Woohoo: we found one! */
 112                                 if (tdb1_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                             tdb1_do_delete(tdb, current, rec) != 0)
 122                                 goto fail;
 123                 }
 124                 tdb1_unlock(tdb, tlock->hash, tlock->lock_rw);
 125                 want_next = 0;
 126         }
 127         /* We finished iteration without finding anything */
 128         tdb->ecode = TDB1_SUCCESS;
 129         return 0;
 130
 131  fail:
 132         tlock->off = 0;
 133         if (tdb1_unlock(tdb, tlock->hash, tlock->lock_rw) != 0)
 134                 TDB1_LOG((tdb, TDB1_DEBUG_FATAL, "tdb1_next_lock: On error unlock failed!\n"));
 135         return TDB1_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 tdb1_traverse_internal(struct tdb1_context *tdb,
 144                                  tdb1_traverse_func fn, void *private_data,
 145                                  struct tdb1_traverse_lock *tl)
 146 {
 147         TDB1_DATA key, dbuf;
 148         struct tdb1_record rec;
 149         int ret = 0, count = 0;
 150         tdb1_off_t off;
 151
 152         /* This was in the initializaton, above, but the IRIX compiler
 153          * did not like it.  crh
 154          */
 155         tl->next = tdb->travlocks.next;
 156
 157         /* fcntl locks don't stack: beware traverse inside traverse */
 158         tdb->travlocks.next = tl;
 159
 160         /* tdb1_next_lock places locks on the record returned, and its chain */
 161         while ((off = tdb1_next_lock(tdb, tl, &rec)) != 0) {
 162                 if (off == TDB1_NEXT_LOCK_ERR) {
 163                         ret = -1;
 164                         goto out;
 165                 }
 166                 count++;
 167                 /* now read the full record */
 168                 key.dptr = tdb1_alloc_read(tdb, tl->off + sizeof(rec),
 169                                           rec.key_len + rec.data_len);
 170                 if (!key.dptr) {
 171                         ret = -1;
 172                         if (tdb1_unlock(tdb, tl->hash, tl->lock_rw) != 0)
 173                                 goto out;
 174                         if (tdb1_unlock_record(tdb, tl->off) != 0)
 175                                 TDB1_LOG((tdb, TDB1_DEBUG_FATAL, "tdb1_traverse: key.dptr == NULL and unlock_record failed!\n"));
 176                         goto out;
 177                 }
 178                 key.dsize = rec.key_len;
 179                 dbuf.dptr = key.dptr + rec.key_len;
 180                 dbuf.dsize = rec.data_len;
 181
 182                 /* Drop chain lock, call out */
 183                 if (tdb1_unlock(tdb, tl->hash, tl->lock_rw) != 0) {
 184                         ret = -1;
 185                         SAFE_FREE(key.dptr);
 186                         goto out;
 187                 }
 188                 if (fn && fn(tdb, key, dbuf, private_data)) {
 189                         /* They want us to terminate traversal */
 190                         if (tdb1_unlock_record(tdb, tl->off) != 0) {
 191                                 TDB1_LOG((tdb, TDB1_DEBUG_FATAL, "tdb1_traverse: unlock_record failed!\n"));;
 192                                 ret = -1;
 193                         }
 194                         SAFE_FREE(key.dptr);
 195                         goto out;
 196                 }
 197                 SAFE_FREE(key.dptr);
 198         }
 199 out:
 200         tdb->travlocks.next = tl->next;
 201         if (ret < 0)
 202                 return -1;
 203         else
 204                 return count;
 205 }
 206
 207
 208 /*
 209   a write style traverse - temporarily marks the db read only
 210 */
 211 _PUBLIC_ int tdb1_traverse_read(struct tdb1_context *tdb,
 212                       tdb1_traverse_func fn, void *private_data)
 213 {
 214         struct tdb1_traverse_lock tl = { NULL, 0, 0, F_RDLCK };
 215         int ret;
 216
 217         /* we need to get a read lock on the transaction lock here to
 218            cope with the lock ordering semantics of solaris10 */
 219         if (tdb1_transaction_lock(tdb, F_RDLCK, TDB1_LOCK_WAIT)) {
 220                 return -1;
 221         }
 222
 223         tdb->traverse_read++;
 224         ret = tdb1_traverse_internal(tdb, fn, private_data, &tl);
 225         tdb->traverse_read--;
 226
 227         tdb1_transaction_unlock(tdb, F_RDLCK);
 228
 229         return ret;
 230 }
 231
 232 /*
 233   a write style traverse - needs to get the transaction lock to
 234   prevent deadlocks
 235
 236   WARNING: The data buffer given to the callback fn does NOT meet the
 237   alignment restrictions malloc gives you.
 238 */
 239 _PUBLIC_ int tdb1_traverse(struct tdb1_context *tdb,
 240                  tdb1_traverse_func fn, void *private_data)
 241 {
 242         struct tdb1_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
 243         int ret;
 244
 245         if (tdb->read_only || tdb->traverse_read) {
 246                 return tdb1_traverse_read(tdb, fn, private_data);
 247         }
 248
 249         if (tdb1_transaction_lock(tdb, F_WRLCK, TDB1_LOCK_WAIT)) {
 250                 return -1;
 251         }
 252
 253         tdb->traverse_write++;
 254         ret = tdb1_traverse_internal(tdb, fn, private_data, &tl);
 255         tdb->traverse_write--;
 256
 257         tdb1_transaction_unlock(tdb, F_WRLCK);
 258
 259         return ret;
 260 }
 261
 262
 263 /* find the first entry in the database and return its key */
 264 _PUBLIC_ TDB1_DATA tdb1_firstkey(struct tdb1_context *tdb)
 265 {
 266         TDB1_DATA key;
 267         struct tdb1_record rec;
 268         tdb1_off_t off;
 269
 270         /* release any old lock */
 271         if (tdb1_unlock_record(tdb, tdb->travlocks.off) != 0)
 272                 return tdb1_null;
 273         tdb->travlocks.off = tdb->travlocks.hash = 0;
 274         tdb->travlocks.lock_rw = F_RDLCK;
 275
 276         /* Grab first record: locks chain and returned record. */
 277         off = tdb1_next_lock(tdb, &tdb->travlocks, &rec);
 278         if (off == 0 || off == TDB1_NEXT_LOCK_ERR) {
 279                 return tdb1_null;
 280         }
 281         /* now read the key */
 282         key.dsize = rec.key_len;
 283         key.dptr =tdb1_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
 284
 285         /* Unlock the hash chain of the record we just read. */
 286         if (tdb1_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 287                 TDB1_LOG((tdb, TDB1_DEBUG_FATAL, "tdb1_firstkey: error occurred while tdb1_unlocking!\n"));
 288         return key;
 289 }
 290
 291 /* find the next entry in the database, returning its key */
 292 _PUBLIC_ TDB1_DATA tdb1_nextkey(struct tdb1_context *tdb, TDB1_DATA oldkey)
 293 {
 294         uint32_t oldhash;
 295         TDB1_DATA key = tdb1_null;
 296         struct tdb1_record rec;
 297         unsigned char *k = NULL;
 298         tdb1_off_t off;
 299
 300         /* Is locked key the old key?  If so, traverse will be reliable. */
 301         if (tdb->travlocks.off) {
 302                 if (tdb1_lock(tdb,tdb->travlocks.hash,tdb->travlocks.lock_rw))
 303                         return tdb1_null;
 304                 if (tdb1_rec_read(tdb, tdb->travlocks.off, &rec) == -1
 305                     || !(k = tdb1_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
 306                                             rec.key_len))
 307                     || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
 308                         /* No, it wasn't: unlock it and start from scratch */
 309                         if (tdb1_unlock_record(tdb, tdb->travlocks.off) != 0) {
 310                                 SAFE_FREE(k);
 311                                 return tdb1_null;
 312                         }
 313                         if (tdb1_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0) {
 314                                 SAFE_FREE(k);
 315                                 return tdb1_null;
 316                         }
 317                         tdb->travlocks.off = 0;
 318                 }
 319
 320                 SAFE_FREE(k);
 321         }
 322
 323         if (!tdb->travlocks.off) {
 324                 /* No previous element: do normal find, and lock record */
 325                 tdb->travlocks.off = tdb1_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), tdb->travlocks.lock_rw, &rec);
 326                 if (!tdb->travlocks.off) {
 327                         return tdb1_null;
 328                 }
 329                 tdb->travlocks.hash = TDB1_BUCKET(rec.full_hash);
 330                 if (tdb1_lock_record(tdb, tdb->travlocks.off) != 0) {
 331                         TDB1_LOG((tdb, TDB1_DEBUG_FATAL, "tdb1_nextkey: lock_record failed (%s)!\n", strerror(errno)));
 332                         return tdb1_null;
 333                 }
 334         }
 335         oldhash = tdb->travlocks.hash;
 336
 337         /* Grab next record: locks chain and returned record,
 338            unlocks old record */
 339         off = tdb1_next_lock(tdb, &tdb->travlocks, &rec);
 340         if (off != TDB1_NEXT_LOCK_ERR && off != 0) {
 341                 key.dsize = rec.key_len;
 342                 key.dptr = tdb1_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
 343                                           key.dsize);
 344                 /* Unlock the chain of this new record */
 345                 if (tdb1_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 346                         TDB1_LOG((tdb, TDB1_DEBUG_FATAL, "tdb1_nextkey: WARNING tdb1_unlock failed!\n"));
 347         }
 348         /* Unlock the chain of old record */
 349         if (tdb1_unlock(tdb, TDB1_BUCKET(oldhash), tdb->travlocks.lock_rw) != 0)
 350                 TDB1_LOG((tdb, TDB1_DEBUG_FATAL, "tdb1_nextkey: WARNING tdb1_unlock failed!\n"));
 351         return key;
 352 }