source: trunk-3.0/source/tdb/common/tdb.c@ 102

 /* 
   Unix SMB/CIFS implementation.

   trivial database library

   Copyright (C) Andrew Tridgell              1999-2005
   Copyright (C) Paul `Rusty' Russell              2000
   Copyright (C) Jeremy Allison                    2000-2003
   
     ** NOTE! The following LGPL license applies to the tdb
     ** library. This does NOT imply that all of Samba is released
     ** under the LGPL
   
   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2 of the License, or (at your option) any later version.

   This library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

#include "tdb_private.h"

TDB_DATA tdb_null;

/*
  increment the tdb sequence number if the tdb has been opened using
  the TDB_SEQNUM flag
*/
static void tdb_increment_seqnum(struct tdb_context *tdb)
{
        tdb_off_t seqnum=0;
        
        if (!(tdb->flags & TDB_SEQNUM)) {
                return;
        }

        if (tdb_brlock(tdb, TDB_SEQNUM_OFS, F_WRLCK, F_SETLKW, 1, 1) != 0) {
                return;
        }

        /* we ignore errors from this, as we have no sane way of
           dealing with them.
        */
        tdb_ofs_read(tdb, TDB_SEQNUM_OFS, &seqnum);
        seqnum++;
        tdb_ofs_write(tdb, TDB_SEQNUM_OFS, &seqnum);

        tdb_brlock(tdb, TDB_SEQNUM_OFS, F_UNLCK, F_SETLKW, 1, 1);
}

static int tdb_key_compare(TDB_DATA key, TDB_DATA data, void *private_data)
{
        return memcmp(data.dptr, key.dptr, data.dsize);
}

/* Returns 0 on fail.  On success, return offset of record, and fills
   in rec */
static tdb_off_t tdb_find(struct tdb_context *tdb, TDB_DATA key, u32 hash,
                        struct list_struct *r)
{
        tdb_off_t rec_ptr;
        
        /* read in the hash top */
        if (tdb_ofs_read(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1)
                return 0;

        /* keep looking until we find the right record */
        while (rec_ptr) {
                if (tdb_rec_read(tdb, rec_ptr, r) == -1)
                        return 0;

                if (!TDB_DEAD(r) && hash==r->full_hash
                    && key.dsize==r->key_len
                    && tdb_parse_data(tdb, key, rec_ptr + sizeof(*r),
                                      r->key_len, tdb_key_compare,
                                      NULL) == 0) {
                        return rec_ptr;
                }
                rec_ptr = r->next;
        }
        return TDB_ERRCODE(TDB_ERR_NOEXIST, 0);
}

/* As tdb_find, but if you succeed, keep the lock */
tdb_off_t tdb_find_lock_hash(struct tdb_context *tdb, TDB_DATA key, u32 hash, int locktype,
                           struct list_struct *rec)
{
        u32 rec_ptr;

        if (tdb_lock(tdb, BUCKET(hash), locktype) == -1)
                return 0;
        if (!(rec_ptr = tdb_find(tdb, key, hash, rec)))
                tdb_unlock(tdb, BUCKET(hash), locktype);
        return rec_ptr;
}


/* update an entry in place - this only works if the new data size
   is <= the old data size and the key exists.
   on failure return -1.
*/
static int tdb_update_hash(struct tdb_context *tdb, TDB_DATA key, u32 hash, TDB_DATA dbuf)
{
        struct list_struct rec;
        tdb_off_t rec_ptr;

        /* find entry */
        if (!(rec_ptr = tdb_find(tdb, key, hash, &rec)))
                return -1;

        /* must be long enough key, data and tailer */
        if (rec.rec_len < key.dsize + dbuf.dsize + sizeof(tdb_off_t)) {
                tdb->ecode = TDB_SUCCESS; /* Not really an error */
                return -1;
        }

        if (tdb->methods->tdb_write(tdb, rec_ptr + sizeof(rec) + rec.key_len,
                      dbuf.dptr, dbuf.dsize) == -1)
                return -1;

        if (dbuf.dsize != rec.data_len) {
                /* update size */
                rec.data_len = dbuf.dsize;
                return tdb_rec_write(tdb, rec_ptr, &rec);
        }
 
        return 0;
}

/* find an entry in the database given a key */
/* If an entry doesn't exist tdb_err will be set to
 * TDB_ERR_NOEXIST. If a key has no data attached
 * then the TDB_DATA will have zero length but
 * a non-zero pointer
 */
TDB_DATA tdb_fetch(struct tdb_context *tdb, TDB_DATA key)
{
        tdb_off_t rec_ptr;
        struct list_struct rec;
        TDB_DATA ret;
        u32 hash;

        /* find which hash bucket it is in */
        hash = tdb->hash_fn(&key);
        if (!(rec_ptr = tdb_find_lock_hash(tdb,key,hash,F_RDLCK,&rec)))
                return tdb_null;

        ret.dptr = tdb_alloc_read(tdb, rec_ptr + sizeof(rec) + rec.key_len,
                                  rec.data_len);
        ret.dsize = rec.data_len;
        tdb_unlock(tdb, BUCKET(rec.full_hash), F_RDLCK);
        return ret;
}

/*
 * Find an entry in the database and hand the record's data to a parsing
 * function. The parsing function is executed under the chain read lock, so it
 * should be fast and should not block on other syscalls.
 *
 * DONT CALL OTHER TDB CALLS FROM THE PARSER, THIS MIGHT LEAD TO SEGFAULTS.
 *
 * For mmapped tdb's that do not have a transaction open it points the parsing
 * function directly at the mmap area, it avoids the malloc/memcpy in this
 * case. If a transaction is open or no mmap is available, it has to do
 * malloc/read/parse/free.
 *
 * This is interesting for all readers of potentially large data structures in
 * the tdb records, ldb indexes being one example.
 */

int tdb_parse_record(struct tdb_context *tdb, TDB_DATA key,
                     int (*parser)(TDB_DATA key, TDB_DATA data,
                                   void *private_data),
                     void *private_data)
{
        tdb_off_t rec_ptr;
        struct list_struct rec;
        int ret;
        u32 hash;

        /* find which hash bucket it is in */
        hash = tdb->hash_fn(&key);

        if (!(rec_ptr = tdb_find_lock_hash(tdb,key,hash,F_RDLCK,&rec))) {
                return TDB_ERRCODE(TDB_ERR_NOEXIST, 0);
        }

        ret = tdb_parse_data(tdb, key, rec_ptr + sizeof(rec) + rec.key_len,
                             rec.data_len, parser, private_data);

        tdb_unlock(tdb, BUCKET(rec.full_hash), F_RDLCK);

        return ret;
}

/* check if an entry in the database exists 

   note that 1 is returned if the key is found and 0 is returned if not found
   this doesn't match the conventions in the rest of this module, but is
   compatible with gdbm
*/
static int tdb_exists_hash(struct tdb_context *tdb, TDB_DATA key, u32 hash)
{
        struct list_struct rec;
        
        if (tdb_find_lock_hash(tdb, key, hash, F_RDLCK, &rec) == 0)
                return 0;
        tdb_unlock(tdb, BUCKET(rec.full_hash), F_RDLCK);
        return 1;
}

int tdb_exists(struct tdb_context *tdb, TDB_DATA key)
{
        u32 hash = tdb->hash_fn(&key);
        return tdb_exists_hash(tdb, key, hash);
}

/* actually delete an entry in the database given the offset */
int tdb_do_delete(struct tdb_context *tdb, tdb_off_t rec_ptr, struct list_struct*rec)
{
        tdb_off_t last_ptr, i;
        struct list_struct lastrec;

        if (tdb->read_only || tdb->traverse_read) return -1;

        if (tdb_write_lock_record(tdb, rec_ptr) == -1) {
                /* Someone traversing here: mark it as dead */
                rec->magic = TDB_DEAD_MAGIC;
                return tdb_rec_write(tdb, rec_ptr, rec);
        }
        if (tdb_write_unlock_record(tdb, rec_ptr) != 0)