tdb/common/tdb.c

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 /* 
   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)
                return -1;

        /* find previous record in hash chain */
        if (tdb_ofs_read(tdb, TDB_HASH_TOP(rec->full_hash), &i) == -1)
                return -1;
        for (last_ptr = 0; i != rec_ptr; last_ptr = i, i = lastrec.next)
                if (tdb_rec_read(tdb, i, &lastrec) == -1)
                        return -1;

        /* unlink it: next ptr is at start of record. */
        if (last_ptr == 0)
                last_ptr = TDB_HASH_TOP(rec->full_hash);
        if (tdb_ofs_write(tdb, last_ptr, &rec->next) == -1)
                return -1;

        /* recover the space */
        if (tdb_free(tdb, rec_ptr, rec) == -1)
                return -1;
        return 0;
}

static int tdb_count_dead(struct tdb_context *tdb, u32 hash)
{
        int res = 0;
        tdb_off_t rec_ptr;
        struct list_struct rec;
        
        /* read in the hash top */
        if (tdb_ofs_read(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1)
                return 0;

        while (rec_ptr) {
                if (tdb_rec_read(tdb, rec_ptr, &rec) == -1)
                        return 0;

                if (rec.magic == TDB_DEAD_MAGIC) {
                        res += 1;
                }
                rec_ptr = rec.next;
        }
        return res;
}

/*
 * Purge all DEAD records from a hash chain
 */
static int tdb_purge_dead(struct tdb_context *tdb, u32 hash)
{
        int res = -1;
        struct list_struct rec;
        tdb_off_t rec_ptr;

        if (tdb_lock(tdb, -1, F_WRLCK) == -1) {
                return -1;
        }
        
        /* read in the hash top */
        if (tdb_ofs_read(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1)
                goto fail;

        while (rec_ptr) {
                tdb_off_t next;

                if (tdb_rec_read(tdb, rec_ptr, &rec) == -1) {
                        goto fail;
                }

                next = rec.next;

                if (rec.magic == TDB_DEAD_MAGIC
                    && tdb_do_delete(tdb, rec_ptr, &rec) == -1) {
                        goto fail;
                }
                rec_ptr = next;
        }
        res = 0;
 fail:
        tdb_unlock(tdb, -1, F_WRLCK);
        return res;
}

/* delete an entry in the database given a key */
static int tdb_delete_hash(struct tdb_context *tdb, TDB_DATA key, u32 hash)
{
        tdb_off_t rec_ptr;
        struct list_struct rec;
        int ret;

        if (tdb->max_dead_records != 0) {

                /*
                 * Allow for some dead records per hash chain, mainly for
                 * tdb's with a very high create/delete rate like locking.tdb.
                 */

                if (tdb_lock(tdb, BUCKET(hash), F_WRLCK) == -1)
                        return -1;

                if (tdb_count_dead(tdb, hash) >= tdb->max_dead_records) {
                        /*
                         * Don't let the per-chain freelist grow too large,
                         * delete all existing dead records
                         */
                        tdb_purge_dead(tdb, hash);
                }

                if (!(rec_ptr = tdb_find(tdb, key, hash, &rec))) {
                        tdb_unlock(tdb, BUCKET(hash), F_WRLCK);
                        return -1;
                }

                /*
                 * Just mark the record as dead.
                 */
                rec.magic = TDB_DEAD_MAGIC;
                ret = tdb_rec_write(tdb, rec_ptr, &rec);
        }
        else {
                if (!(rec_ptr = tdb_find_lock_hash(tdb, key, hash, F_WRLCK,
                                                   &rec)))
                        return -1;

                ret = tdb_do_delete(tdb, rec_ptr, &rec);
        }

        if (ret == 0) {
                tdb_increment_seqnum(tdb);
        }

        if (tdb_unlock(tdb, BUCKET(rec.full_hash), F_WRLCK) != 0)
                TDB_LOG((tdb, TDB_DEBUG_WARNING, "tdb_delete: WARNING tdb_unlock failed!\n"));
        return ret;
}

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

/*
 * See if we have a dead record around with enough space
 */
static tdb_off_t tdb_find_dead(struct tdb_context *tdb, u32 hash,
                               struct list_struct *r, tdb_len_t length)
{
        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) && r->rec_len >= length) {
                        /*
                         * First fit for simple coding, TODO: change to best
                         * fit
                         */
                        return rec_ptr;
                }
                rec_ptr = r->next;
        }
        return 0;
}

/* store an element in the database, replacing any existing element
   with the same key 

   return 0 on success, -1 on failure
*/
int tdb_store(struct tdb_context *tdb, TDB_DATA key, TDB_DATA dbuf, int flag)
{
        struct list_struct rec;
        u32 hash;
        tdb_off_t rec_ptr;
        char *p = NULL;
        int ret = -1;

        if (tdb->read_only || tdb->traverse_read) {
                tdb->ecode = TDB_ERR_RDONLY;
                return -1;
        }

        /* find which hash bucket it is in */
        hash = tdb->hash_fn(&key);
        if (tdb_lock(tdb, BUCKET(hash), F_WRLCK) == -1)
                return -1;

        /* check for it existing, on insert. */
        if (flag == TDB_INSERT) {
                if (tdb_exists_hash(tdb, key, hash)) {
                        tdb->ecode = TDB_ERR_EXISTS;
                        goto fail;
                }
        } else {
                /* first try in-place update, on modify or replace. */
                if (tdb_update_hash(tdb, key, hash, dbuf) == 0) {
                        goto done;
                }
                if (tdb->ecode == TDB_ERR_NOEXIST &&
                    flag == TDB_MODIFY) {
                        /* if the record doesn't exist and we are in TDB_MODIFY mode then
                         we should fail the store */
                        goto fail;
                }
        }
        /* reset the error code potentially set by the tdb_update() */
        tdb->ecode = TDB_SUCCESS;

        /* delete any existing record - if it doesn't exist we don't
           care.  Doing this first reduces fragmentation, and avoids
           coalescing with `allocated' block before it's updated. */
        if (flag != TDB_INSERT)
                tdb_delete_hash(tdb, key, hash);

        /* Copy key+value *before* allocating free space in case malloc
           fails and we are left with a dead spot in the tdb. */

        if (!(p = (char *)malloc(key.dsize + dbuf.dsize))) {
                tdb->ecode = TDB_ERR_OOM;
                goto fail;
        }

        memcpy(p, key.dptr, key.dsize);
        if (dbuf.dsize)
                memcpy(p+key.dsize, dbuf.dptr, dbuf.dsize);

        if (tdb->max_dead_records != 0) {
                /*
                 * Allow for some dead records per hash chain, look if we can
                 * find one that can hold the new record. We need enough space
                 * for key, data and tailer. If we find one, we don't have to
                 * consult the central freelist.
                 */
                rec_ptr = tdb_find_dead(
                        tdb, hash, &rec,
                        key.dsize + dbuf.dsize + sizeof(tdb_off_t));

                if (rec_ptr != 0) {
                        rec.key_len = key.dsize;
                        rec.data_len = dbuf.dsize;
                        rec.full_hash = hash;
                        rec.magic = TDB_MAGIC;
                        if (tdb_rec_write(tdb, rec_ptr, &rec) == -1
                            || tdb->methods->tdb_write(
                                    tdb, rec_ptr + sizeof(rec),
                                    p, key.dsize + dbuf.dsize) == -1) {
                                goto fail;
                        }
                        goto done;
                }
        }

        /*
         * We have to allocate some space from the freelist, so this means we
         * have to lock it. Use the chance to purge all the DEAD records from
         * the hash chain under the freelist lock.
         */

        if (tdb_lock(tdb, -1, F_WRLCK) == -1) {
                goto fail;
        }

        if ((tdb->max_dead_records != 0)
            && (tdb_purge_dead(tdb, hash) == -1)) {
                tdb_unlock(tdb, -1, F_WRLCK);
                goto fail;
        }

        /* we have to allocate some space */
        rec_ptr = tdb_allocate(tdb, key.dsize + dbuf.dsize, &rec);

        tdb_unlock(tdb, -1, F_WRLCK);

        if (rec_ptr == 0) {
                goto fail;
        }

        /* Read hash top into next ptr */
        if (tdb_ofs_read(tdb, TDB_HASH_TOP(hash), &rec.next) == -1)
                goto fail;

        rec.key_len = key.dsize;
        rec.data_len = dbuf.dsize;
        rec.full_hash = hash;
        rec.magic = TDB_MAGIC;

        /* write out and point the top of the hash chain at it */
        if (tdb_rec_write(tdb, rec_ptr, &rec) == -1
            || tdb->methods->tdb_write(tdb, rec_ptr+sizeof(rec), p, key.dsize+dbuf.dsize)==-1
            || tdb_ofs_write(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1) {
                /* Need to tdb_unallocate() here */
                goto fail;
        }

 done:
        ret = 0;
 fail:
        if (ret == 0) {
                tdb_increment_seqnum(tdb);
        }

        SAFE_FREE(p); 
        tdb_unlock(tdb, BUCKET(hash), F_WRLCK);
        return ret;
}


/* Append to an entry. Create if not exist. */
int tdb_append(struct tdb_context *tdb, TDB_DATA key, TDB_DATA new_dbuf)
{
        u32 hash;
        TDB_DATA dbuf;
        int ret = -1;

        /* find which hash bucket it is in */
        hash = tdb->hash_fn(&key);
        if (tdb_lock(tdb, BUCKET(hash), F_WRLCK) == -1)
                return -1;

        dbuf = tdb_fetch(tdb, key);

        if (dbuf.dptr == NULL) {
                dbuf.dptr = (char *)malloc(new_dbuf.dsize);
        } else {
                char *new_dptr = (char *)realloc(dbuf.dptr,
                                            dbuf.dsize + new_dbuf.dsize);
                if (new_dptr == NULL) {
                        free(dbuf.dptr);
                }
                dbuf.dptr = new_dptr;
        }

        if (dbuf.dptr == NULL) {
                tdb->ecode = TDB_ERR_OOM;
                goto failed;
        }

        memcpy(dbuf.dptr + dbuf.dsize, new_dbuf.dptr, new_dbuf.dsize);
        dbuf.dsize += new_dbuf.dsize;

        ret = tdb_store(tdb, key, dbuf, 0);
        
failed:
        tdb_unlock(tdb, BUCKET(hash), F_WRLCK);
        SAFE_FREE(dbuf.dptr);
        return ret;
}


/*
  return the name of the current tdb file
  useful for external logging functions
*/
const char *tdb_name(struct tdb_context *tdb)
{
        return tdb->name;
}

/*
  return the underlying file descriptor being used by tdb, or -1
  useful for external routines that want to check the device/inode
  of the fd
*/
int tdb_fd(struct tdb_context *tdb)
{
        return tdb->fd;
}

/*
  return the current logging function
  useful for external tdb routines that wish to log tdb errors
*/
tdb_log_func tdb_log_fn(struct tdb_context *tdb)
{
        return tdb->log.log_fn;
}


/*
  get the tdb sequence number. Only makes sense if the writers opened
  with TDB_SEQNUM set. Note that this sequence number will wrap quite
  quickly, so it should only be used for a 'has something changed'
  test, not for code that relies on the count of the number of changes
  made. If you want a counter then use a tdb record.

  The aim of this sequence number is to allow for a very lightweight
  test of a possible tdb change.
*/
int tdb_get_seqnum(struct tdb_context *tdb)
{
        tdb_off_t seqnum=0;

        tdb_ofs_read(tdb, TDB_SEQNUM_OFS, &seqnum);
        return seqnum;
}

int tdb_hash_size(struct tdb_context *tdb)
{
        return tdb->header.hash_size;
}

size_t tdb_map_size(struct tdb_context *tdb)
{
        return tdb->map_size;
}

int tdb_get_flags(struct tdb_context *tdb)
{
        return tdb->flags;
}

---