source4/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, F_WRLCK) == -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, 0, "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 &&
 118                             tdb_do_delete(tdb, current, rec) != 0)
 119                                 goto fail;
 120                 }
 121                 tdb_unlock(tdb, tlock->hash, F_WRLCK);
 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, F_WRLCK) != 0)
 130                 TDB_LOG((tdb, 0, "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 int tdb_traverse(struct tdb_context *tdb, tdb_traverse_func fn, void *private)
 140 {
 141         TDB_DATA key, dbuf;
 142         struct list_struct rec;
 143         struct tdb_traverse_lock tl = { NULL, 0, 0 };
 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, F_WRLCK) != 0)
 163                                 goto out;
 164                         if (tdb_unlock_record(tdb, tl.off) != 0)
 165                                 TDB_LOG((tdb, 0, "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, F_WRLCK) != 0) {
 174                         ret = -1;
 175                         goto out;
 176                 }
 177                 if (fn && fn(tdb, key, dbuf, private)) {
 178                         /* They want us to terminate traversal */
 179                         ret = count;
 180                         if (tdb_unlock_record(tdb, tl.off) != 0) {
 181                                 TDB_LOG((tdb, 0, "tdb_traverse: unlock_record failed!\n"));;
 182                                 ret = -1;
 183                         }
 184                         tdb->travlocks.next = tl.next;
 185                         SAFE_FREE(key.dptr);
 186                         return count;
 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 /* find the first entry in the database and return its key */
 199 TDB_DATA tdb_firstkey(struct tdb_context *tdb)
 200 {
 201         TDB_DATA key;
 202         struct list_struct rec;
 203
 204         /* release any old lock */
 205         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
 206                 return tdb_null;
 207         tdb->travlocks.off = tdb->travlocks.hash = 0;
 208
 209         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) <= 0)
 210                 return tdb_null;
 211         /* now read the key */
 212         key.dsize = rec.key_len;
 213         key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);
 214         if (tdb_unlock(tdb, BUCKET(tdb->travlocks.hash), F_WRLCK) != 0)
 215                 TDB_LOG((tdb, 0, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
 216         return key;
 217 }
 218
 219 /* find the next entry in the database, returning its key */
 220 TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
 221 {
 222         u32 oldhash;
 223         TDB_DATA key = tdb_null;
 224         struct list_struct rec;
 225         unsigned char *k = NULL;
 226
 227         /* Is locked key the old key?  If so, traverse will be reliable. */
 228         if (tdb->travlocks.off) {
 229                 if (tdb_lock(tdb,tdb->travlocks.hash,F_WRLCK))
 230                         return tdb_null;
 231                 if (tdb_rec_read(tdb, tdb->travlocks.off, &rec) == -1
 232                     || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
 233                                             rec.key_len))
 234                     || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
 235                         /* No, it wasn't: unlock it and start from scratch */
 236                         if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
 237                                 return tdb_null;
 238                         if (tdb_unlock(tdb, tdb->travlocks.hash, F_WRLCK) != 0)
 239                                 return tdb_null;
 240                         tdb->travlocks.off = 0;
 241                 }
 242
 243                 SAFE_FREE(k);
 244         }
 245
 246         if (!tdb->travlocks.off) {
 247                 /* No previous element: do normal find, and lock record */
 248                 tdb->travlocks.off = tdb_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), F_WRLCK, &rec);
 249                 if (!tdb->travlocks.off)
 250                         return tdb_null;
 251                 tdb->travlocks.hash = BUCKET(rec.full_hash);
 252                 if (tdb_lock_record(tdb, tdb->travlocks.off) != 0) {
 253                         TDB_LOG((tdb, 0, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
 254                         return tdb_null;
 255                 }
 256         }
 257         oldhash = tdb->travlocks.hash;
 258
 259         /* Grab next record: locks chain and returned record,
 260            unlocks old record */
 261         if (tdb_next_lock(tdb, &tdb->travlocks, &rec) > 0) {
 262                 key.dsize = rec.key_len;
 263                 key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
 264                                           key.dsize);
 265                 /* Unlock the chain of this new record */
 266                 if (tdb_unlock(tdb, tdb->travlocks.hash, F_WRLCK) != 0)
 267                         TDB_LOG((tdb, 0, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 268         }
 269         /* Unlock the chain of old record */
 270         if (tdb_unlock(tdb, BUCKET(oldhash), F_WRLCK) != 0)
 271                 TDB_LOG((tdb, 0, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
 272         return key;
 273 }
 274