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
 218         tdb_transaction_unlock(tdb);
 219
 220         return ret;
 221 }
 222
 223 /*
 224   a write style traverse - needs to get the transaction lock to
 225   prevent deadlocks
 226
 227   WARNING: The data buffer given to the callback fn does NOT meet the
 228   alignment restrictions malloc gives you.
 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_transaction_lock(tdb, F_WRLCK)) {
 241                 return -1;
 242         }
 243
 244         tdb->traverse_write++;
 245         ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
 246         tdb->traverse_write--;
 247
 248         tdb_transaction_unlock(tdb);
 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         /* Grab first record: locks chain and returned record. */
 267         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) <= 0)
 268                 return tdb_null;
 269         /* now read the key */
 270         key.dsize = rec.key_len;
 271         key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
 272
 273         /* Unlock the hash chain of the record we just read. */
 274         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 275                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
 276         return key;
 277 }
 278
 279 /* find the next entry in the database, returning its key */
 280 TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
 281 {
 282         uint32_t oldhash;
 283         TDB_DATA key = tdb_null;
 284         struct list_struct rec;
 285         unsigned char *k = NULL;
 286
 287         /* Is locked key the old key?  If so, traverse will be reliable. */
 288         if (tdb->travlocks.off) {
 289                 if (tdb_lock(tdb,tdb->travlocks.hash,tdb->travlocks.lock_rw))
 290                         return tdb_null;
 291                 if (tdb_rec_read(tdb, tdb->travlocks.off, &rec) == -1
 292                     || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
 293                                             rec.key_len))
 294                     || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
 295                         /* No, it wasn't: unlock it and start from scratch */
 296                         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0) {
 297                                 SAFE_FREE(k);
 298                                 return tdb_null;
 299                         }
 300                         if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0) {
 301                                 SAFE_FREE(k);
 302                                 return tdb_null;
 303                         }
 304                         tdb->travlocks.off = 0;
 305                 }
 306
 307                 SAFE_FREE(k);
 308         }
 309
 310         if (!tdb->travlocks.off) {
 311                 /* No previous element: do normal find, and lock record */
 312                 tdb->travlocks.off = tdb_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), tdb->travlocks.lock_rw, &rec);
 313                 if (!tdb->travlocks.off)
 314                         return tdb_null;
 315                 tdb->travlocks.hash = BUCKET(rec.full_hash);
 316                 if (tdb_lock_record(tdb, tdb->travlocks.off) != 0) {
 317                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
 318                         return tdb_null;
 319                 }
 320         }
 321         oldhash = tdb->travlocks.hash;
 322
 323         /* Grab next record: locks chain and returned record,
 324            unlocks old record */
 325         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) > 0) {
 326                 key.dsize = rec.key_len;
 327                 key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
 328                                           key.dsize);
 329                 /* Unlock the chain of this new record */
 330                 if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
 331                         TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 332         }
 333         /* Unlock the chain of old record */
 334         if (tdb_unlock(tdb, BUCKET(oldhash), tdb->travlocks.lock_rw) != 0)
 335                 TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 336         return key;
 337 }
 338