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tdb.c

/*
URL: svn://svnanon.samba.org/samba/branches/SAMBA_4_0/source/lib/tdb/common
Rev: 23590
Last Changed Date: 2007-06-22 13:36:10 -0400 (Fri, 22 Jun 2007)
*/
 /* 
   trivial database library - standalone version

   Copyright (C) Andrew Tridgell              1999-2005
   Copyright (C) Jeremy Allison               2000-2006
   Copyright (C) Paul `Rusty' Russell         2000
   
     ** 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
*/

#ifdef CONFIG_STAND_ALONE
#define HAVE_MMAP
#define HAVE_STRDUP
#define HAVE_SYS_MMAN_H
#define HAVE_UTIME_H
#define HAVE_UTIME
#endif
#define _XOPEN_SOURCE 500

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <stddef.h>
#include <errno.h>
#include <string.h>
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif
#include <sys/time.h>
#include <sys/types.h>
#include <time.h>
#ifdef HAVE_UTIME_H
#include <utime.h>
#endif
#include <sys/stat.h>
#include <sys/file.h>
#include <fcntl.h>

#ifdef HAVE_SYS_MMAN_H
#include <sys/mman.h>
#endif

#ifndef MAP_FILE
#define MAP_FILE 0
#endif

#ifndef MAP_FAILED
#define MAP_FAILED ((void *)-1)
#endif

#ifndef HAVE_STRDUP
#define strdup rep_strdup
static char *rep_strdup(const char *s)
{
      char *ret;
      int length;
      if (!s)
            return NULL;

      if (!length)
            length = strlen(s);

      ret = malloc(length + 1);
      if (ret) {
            strncpy(ret, s, length);
            ret[length] = '\0';
      }
      return ret;
}
#endif

#ifndef PRINTF_ATTRIBUTE
#if (__GNUC__ >= 3) && (__GNUC_MINOR__ >= 1 )
/** Use gcc attribute to check printf fns.  a1 is the 1-based index of
 * the parameter containing the format, and a2 the index of the first
 * argument. Note that some gcc 2.x versions don't handle this
 * properly **/
#define PRINTF_ATTRIBUTE(a1, a2) __attribute__ ((format (__printf__, a1, a2)))
#else
#define PRINTF_ATTRIBUTE(a1, a2)
#endif
#endif

typedef int bool;

#include "tdb.h"

#ifndef u32
#define u32 unsigned
#endif

#ifndef HAVE_GETPAGESIZE
#define getpagesize() 0x2000
#endif

typedef u32 tdb_len_t;
typedef u32 tdb_off_t;

#ifndef offsetof
#define offsetof(t,f) ((unsigned int)&((t *)0)->f)
#endif

#define TDB_MAGIC_FOOD "TDB file\n"
#define TDB_VERSION (0x26011967 + 6)
#define TDB_MAGIC (0x26011999U)
#define TDB_FREE_MAGIC (~TDB_MAGIC)
#define TDB_DEAD_MAGIC (0xFEE1DEAD)
#define TDB_RECOVERY_MAGIC (0xf53bc0e7U)
#define TDB_ALIGNMENT 4
#define MIN_REC_SIZE (2*sizeof(struct list_struct) + TDB_ALIGNMENT)
#define DEFAULT_HASH_SIZE 131
#define FREELIST_TOP (sizeof(struct tdb_header))
#define TDB_ALIGN(x,a) (((x) + (a)-1) & ~((a)-1))
#define TDB_BYTEREV(x) (((((x)&0xff)<<24)|((x)&0xFF00)<<8)|(((x)>>8)&0xFF00)|((x)>>24))
#define TDB_DEAD(r) ((r)->magic == TDB_DEAD_MAGIC)
#define TDB_BAD_MAGIC(r) ((r)->magic != TDB_MAGIC && !TDB_DEAD(r))
#define TDB_HASH_TOP(hash) (FREELIST_TOP + (BUCKET(hash)+1)*sizeof(tdb_off_t))
#define TDB_HASHTABLE_SIZE(tdb) ((tdb->header.hash_size+1)*sizeof(tdb_off_t))
#define TDB_DATA_START(hash_size) TDB_HASH_TOP(hash_size-1)
#define TDB_RECOVERY_HEAD offsetof(struct tdb_header, recovery_start)
#define TDB_SEQNUM_OFS    offsetof(struct tdb_header, sequence_number)
#define TDB_PAD_BYTE 0x42
#define TDB_PAD_U32  0x42424242

/* NB assumes there is a local variable called "tdb" that is the
 * current context, also takes doubly-parenthesized print-style
 * argument. */
#define TDB_LOG(x) tdb->log.log_fn x

/* lock offsets */
#define GLOBAL_LOCK      0
#define ACTIVE_LOCK      4
#define TRANSACTION_LOCK 8

/* free memory if the pointer is valid and zero the pointer */
#ifndef SAFE_FREE
#define SAFE_FREE(x) do { if ((x) != NULL) {free(x); (x)=NULL;} } while(0)
#endif

#define BUCKET(hash) ((hash) % tdb->header.hash_size)

#define DOCONV() (tdb->flags & TDB_CONVERT)
#define CONVERT(x) (DOCONV() ? tdb_convert(&x, sizeof(x)) : &x)


/* the body of the database is made of one list_struct for the free space
   plus a separate data list for each hash value */
struct list_struct {
      tdb_off_t next; /* offset of the next record in the list */
      tdb_len_t rec_len; /* total byte length of record */
      tdb_len_t key_len; /* byte length of key */
      tdb_len_t data_len; /* byte length of data */
      u32 full_hash; /* the full 32 bit hash of the key */
      u32 magic;   /* try to catch errors */
      /* the following union is implied:
            union {
                  char record[rec_len];
                  struct {
                        char key[key_len];
                        char data[data_len];
                  }
                  u32 totalsize; (tailer)
            }
      */
};


/* this is stored at the front of every database */
struct tdb_header {
      char magic_food[32]; /* for /etc/magic */
      u32 version; /* version of the code */
      u32 hash_size; /* number of hash entries */
      tdb_off_t rwlocks; /* obsolete - kept to detect old formats */
      tdb_off_t recovery_start; /* offset of transaction recovery region */
      tdb_off_t sequence_number; /* used when TDB_SEQNUM is set */
      tdb_off_t reserved[29];
};

struct tdb_lock_type {
      int list;
      u32 count;
      u32 ltype;
};

struct tdb_traverse_lock {
      struct tdb_traverse_lock *next;
      u32 off;
      u32 hash;
      int lock_rw;
};


struct tdb_methods {
      int (*tdb_read)(struct tdb_context *, tdb_off_t , void *, tdb_len_t , int );
      int (*tdb_write)(struct tdb_context *, tdb_off_t, const void *, tdb_len_t);
      void (*next_hash_chain)(struct tdb_context *, u32 *);
      int (*tdb_oob)(struct tdb_context *, tdb_off_t , int );
      int (*tdb_expand_file)(struct tdb_context *, tdb_off_t , tdb_off_t );
      int (*tdb_brlock)(struct tdb_context *, tdb_off_t , int, int, int, size_t);
};

struct tdb_context {
      char *name; /* the name of the database */
      void *map_ptr; /* where it is currently mapped */
      int fd; /* open file descriptor for the database */
      tdb_len_t map_size; /* how much space has been mapped */
      int read_only; /* opened read-only */
      int traverse_read; /* read-only traversal */
      struct tdb_lock_type global_lock;
      int num_lockrecs;
      struct tdb_lock_type *lockrecs; /* only real locks, all with count>0 */
      enum TDB_ERROR ecode; /* error code for last tdb error */
      struct tdb_header header; /* a cached copy of the header */
      u32 flags; /* the flags passed to tdb_open */
      struct tdb_traverse_lock travlocks; /* current traversal locks */
      struct tdb_context *next; /* all tdbs to avoid multiple opens */
      dev_t device;     /* uniquely identifies this tdb */
      ino_t inode;      /* uniquely identifies this tdb */
      struct tdb_logging_context log;
      unsigned int (*hash_fn)(TDB_DATA *key);
      int open_flags; /* flags used in the open - needed by reopen */
      unsigned int num_locks; /* number of chain locks held */
      const struct tdb_methods *methods;
      struct tdb_transaction *transaction;
      int page_size;
      int max_dead_records;
      bool have_transaction_lock;
};


/*
  internal prototypes
*/
static int tdb_munmap(struct tdb_context *tdb);
static void tdb_mmap(struct tdb_context *tdb);
static int tdb_lock(struct tdb_context *tdb, int list, int ltype);
static int tdb_unlock(struct tdb_context *tdb, int list, int ltype);
static int tdb_brlock(struct tdb_context *tdb, tdb_off_t offset, int rw_type, int lck_type, int probe, size_t len);
static int tdb_transaction_lock(struct tdb_context *tdb, int ltype);
static int tdb_transaction_unlock(struct tdb_context *tdb);
static int tdb_brlock_upgrade(struct tdb_context *tdb, tdb_off_t offset, size_t len);
static int tdb_write_lock_record(struct tdb_context *tdb, tdb_off_t off);
static int tdb_write_unlock_record(struct tdb_context *tdb, tdb_off_t off);
static int tdb_ofs_read(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d);
static int tdb_ofs_write(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d);
static void *tdb_convert(void *buf, u32 size);
static int tdb_free(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec);
static tdb_off_t tdb_allocate(struct tdb_context *tdb, tdb_len_t length, struct list_struct *rec);
static int tdb_ofs_read(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d);
static int tdb_ofs_write(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d);
static int tdb_lock_record(struct tdb_context *tdb, tdb_off_t off);
static int tdb_unlock_record(struct tdb_context *tdb, tdb_off_t off);
static int tdb_rec_read(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec);
static int tdb_rec_write(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec);
static int tdb_do_delete(struct tdb_context *tdb, tdb_off_t rec_ptr, struct list_struct *rec);
static unsigned char *tdb_alloc_read(struct tdb_context *tdb, tdb_off_t offset, tdb_len_t len);
static int tdb_parse_data(struct tdb_context *tdb, TDB_DATA key,
               tdb_off_t offset, tdb_len_t len,
               int (*parser)(TDB_DATA key, TDB_DATA data,
                         void *private_data),
               void *private_data);
static tdb_off_t tdb_find_lock_hash(struct tdb_context *tdb, TDB_DATA key, u32 hash, int locktype,
                     struct list_struct *rec);
static void tdb_io_init(struct tdb_context *tdb);
static int tdb_expand(struct tdb_context *tdb, tdb_off_t size);
static int tdb_rec_free_read(struct tdb_context *tdb, tdb_off_t off,
                  struct list_struct *rec);


/* file: error.c */

enum TDB_ERROR tdb_error(struct tdb_context *tdb)
{
      return tdb->ecode;
}

static struct tdb_errname {
      enum TDB_ERROR ecode; const char *estring;
} emap[] = { {TDB_SUCCESS, "Success"},
           {TDB_ERR_CORRUPT, "Corrupt database"},
           {TDB_ERR_IO, "IO Error"},
           {TDB_ERR_LOCK, "Locking error"},
           {TDB_ERR_OOM, "Out of memory"},
           {TDB_ERR_EXISTS, "Record exists"},
           {TDB_ERR_NOLOCK, "Lock exists on other keys"},
           {TDB_ERR_EINVAL, "Invalid parameter"},
           {TDB_ERR_NOEXIST, "Record does not exist"},
           {TDB_ERR_RDONLY, "write not permitted"} };

/* Error string for the last tdb error */
const char *tdb_errorstr(struct tdb_context *tdb)
{
      u32 i;
      for (i = 0; i < sizeof(emap) / sizeof(struct tdb_errname); i++)
            if (tdb->ecode == emap[i].ecode)
                  return emap[i].estring;
      return "Invalid error code";
}

/* file: lock.c */

#define TDB_MARK_LOCK 0x80000000

/* a byte range locking function - return 0 on success
   this functions locks/unlocks 1 byte at the specified offset.

   On error, errno is also set so that errors are passed back properly
   through tdb_open(). 

   note that a len of zero means lock to end of file
*/
int tdb_brlock(struct tdb_context *tdb, tdb_off_t offset, 
             int rw_type, int lck_type, int probe, size_t len)
{
      struct flock fl;
      int ret;

      if (tdb->flags & TDB_NOLOCK) {
            return 0;
      }

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

      fl.l_type = rw_type;
      fl.l_whence = SEEK_SET;
      fl.l_start = offset;
      fl.l_len = len;
      fl.l_pid = 0;

      do {
            ret = fcntl(tdb->fd,lck_type,&fl);
      } while (ret == -1 && errno == EINTR);

      if (ret == -1) {
            /* Generic lock error. errno set by fcntl.
             * EAGAIN is an expected return from non-blocking
             * locks. */
            if (!probe && lck_type != F_SETLK) {
                  /* Ensure error code is set for log fun to examine. */
                  tdb->ecode = TDB_ERR_LOCK;
                  TDB_LOG((tdb, TDB_DEBUG_TRACE,"tdb_brlock failed (fd=%d) at offset %d rw_type=%d lck_type=%d len=%d\n", 
                         tdb->fd, offset, rw_type, lck_type, (int)len));
            }
            return TDB_ERRCODE(TDB_ERR_LOCK, -1);
      }
      return 0;
}


/*
  upgrade a read lock to a write lock. This needs to be handled in a
  special way as some OSes (such as solaris) have too conservative
  deadlock detection and claim a deadlock when progress can be
  made. For those OSes we may loop for a while.  
*/
int tdb_brlock_upgrade(struct tdb_context *tdb, tdb_off_t offset, size_t len)
{
      int count = 1000;
      while (count--) {
            struct timeval tv;
            if (tdb_brlock(tdb, offset, F_WRLCK, F_SETLKW, 1, len) == 0) {
                  return 0;
            }
            if (errno != EDEADLK) {
                  break;
            }
            /* sleep for as short a time as we can - more portable than usleep() */
            tv.tv_sec = 0;
            tv.tv_usec = 1;
            select(0, NULL, NULL, NULL, &tv);
      }
      TDB_LOG((tdb, TDB_DEBUG_TRACE,"tdb_brlock_upgrade failed at offset %d\n", offset));
      return -1;
}


/* lock a list in the database. list -1 is the alloc list */
static int _tdb_lock(struct tdb_context *tdb, int list, int ltype, int op)
{
      struct tdb_lock_type *new_lck;
      int i;
      bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);

      ltype &= ~TDB_MARK_LOCK;

      /* a global lock allows us to avoid per chain locks */
      if (tdb->global_lock.count && 
          (ltype == tdb->global_lock.ltype || ltype == F_RDLCK)) {
            return 0;
      }

      if (tdb->global_lock.count) {
            return TDB_ERRCODE(TDB_ERR_LOCK, -1);
      }

      if (list < -1 || list >= (int)tdb->header.hash_size) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR,"tdb_lock: invalid list %d for ltype=%d\n", 
                     list, ltype));
            return -1;
      }
      if (tdb->flags & TDB_NOLOCK)
            return 0;

      for (i=0; i<tdb->num_lockrecs; i++) {
            if (tdb->lockrecs[i].list == list) {
                  if (tdb->lockrecs[i].count == 0) {
                        /*
                         * Can't happen, see tdb_unlock(). It should
                         * be an assert.
                         */
                        TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_lock: "
                               "lck->count == 0 for list %d", list));
                  }
                  /*
                   * Just increment the in-memory struct, posix locks
                   * don't stack.
                   */
                  tdb->lockrecs[i].count++;
                  return 0;
            }
      }

      new_lck = (struct tdb_lock_type *)realloc(
            tdb->lockrecs,
            sizeof(*tdb->lockrecs) * (tdb->num_lockrecs+1));
      if (new_lck == NULL) {
            errno = ENOMEM;
            return -1;
      }
      tdb->lockrecs = new_lck;

      /* Since fcntl locks don't nest, we do a lock for the first one,
         and simply bump the count for future ones */
      if (!mark_lock &&
          tdb->methods->tdb_brlock(tdb,FREELIST_TOP+4*list, ltype, op,
                             0, 1)) {
            return -1;
      }

      tdb->num_locks++;

      tdb->lockrecs[tdb->num_lockrecs].list = list;
      tdb->lockrecs[tdb->num_lockrecs].count = 1;
      tdb->lockrecs[tdb->num_lockrecs].ltype = ltype;
      tdb->num_lockrecs += 1;

      return 0;
}

/* lock a list in the database. list -1 is the alloc list */
int tdb_lock(struct tdb_context *tdb, int list, int ltype)
{
      int ret;
      ret = _tdb_lock(tdb, list, ltype, F_SETLKW);
      if (ret) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_lock failed on list %d "
                   "ltype=%d (%s)\n",  list, ltype, strerror(errno)));
      }
      return ret;
}

/* lock a list in the database. list -1 is the alloc list. non-blocking lock */
int tdb_lock_nonblock(struct tdb_context *tdb, int list, int ltype)
{
      return _tdb_lock(tdb, list, ltype, F_SETLK);
}


/* unlock the database: returns void because it's too late for errors. */
      /* changed to return int it may be interesting to know there
         has been an error  --simo */
int tdb_unlock(struct tdb_context *tdb, int list, int ltype)
{
      int ret = -1;
      int i;
      struct tdb_lock_type *lck = NULL;
      bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);

      ltype &= ~TDB_MARK_LOCK;

      /* a global lock allows us to avoid per chain locks */
      if (tdb->global_lock.count && 
          (ltype == tdb->global_lock.ltype || ltype == F_RDLCK)) {
            return 0;
      }

      if (tdb->global_lock.count) {
            return TDB_ERRCODE(TDB_ERR_LOCK, -1);
      }

      if (tdb->flags & TDB_NOLOCK)
            return 0;

      /* Sanity checks */
      if (list < -1 || list >= (int)tdb->header.hash_size) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_unlock: list %d invalid (%d)\n", list, tdb->header.hash_size));
            return ret;
      }

      for (i=0; i<tdb->num_lockrecs; i++) {
            if (tdb->lockrecs[i].list == list) {
                  lck = &tdb->lockrecs[i];
                  break;
            }
      }

      if ((lck == NULL) || (lck->count == 0)) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_unlock: count is 0\n"));
            return -1;
      }

      if (lck->count > 1) {
            lck->count--;
            return 0;
      }

      /*
       * This lock has count==1 left, so we need to unlock it in the
       * kernel. We don't bother with decrementing the in-memory array
       * element, we're about to overwrite it with the last array element
       * anyway.
       */

      if (mark_lock) {
            ret = 0;
      } else {
            ret = tdb->methods->tdb_brlock(tdb, FREELIST_TOP+4*list, F_UNLCK,
                                     F_SETLKW, 0, 1);
      }
      tdb->num_locks--;

      /*
       * Shrink the array by overwriting the element just unlocked with the
       * last array element.
       */

      if (tdb->num_lockrecs > 1) {
            *lck = tdb->lockrecs[tdb->num_lockrecs-1];
      }
      tdb->num_lockrecs -= 1;

      /*
       * We don't bother with realloc when the array shrinks, but if we have
       * a completely idle tdb we should get rid of the locked array.
       */

      if (tdb->num_lockrecs == 0) {
            SAFE_FREE(tdb->lockrecs);
      }

      if (ret)
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_unlock: An error occurred unlocking!\n")); 
      return ret;
}

/*
  get the transaction lock
 */
int tdb_transaction_lock(struct tdb_context *tdb, int ltype)
{
      if (tdb->have_transaction_lock || tdb->global_lock.count) {
            return 0;
      }
      if (tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, ltype, 
                             F_SETLKW, 0, 1) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_lock: failed to get transaction lock\n"));
            tdb->ecode = TDB_ERR_LOCK;
            return -1;
      }
      tdb->have_transaction_lock = 1;
      return 0;
}

/*
  release the transaction lock
 */
int tdb_transaction_unlock(struct tdb_context *tdb)
{
      int ret;
      if (!tdb->have_transaction_lock) {
            return 0;
      }
      ret = tdb->methods->tdb_brlock(tdb, TRANSACTION_LOCK, F_UNLCK, F_SETLKW, 0, 1);
      if (ret == 0) {
            tdb->have_transaction_lock = 0;
      }
      return ret;
}




/* lock/unlock entire database */
static int _tdb_lockall(struct tdb_context *tdb, int ltype, int op)
{
      bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);

      ltype &= ~TDB_MARK_LOCK;

      /* There are no locks on read-only dbs */
      if (tdb->read_only || tdb->traverse_read)
            return TDB_ERRCODE(TDB_ERR_LOCK, -1);

      if (tdb->global_lock.count && tdb->global_lock.ltype == ltype) {
            tdb->global_lock.count++;
            return 0;
      }

      if (tdb->global_lock.count) {
            /* a global lock of a different type exists */
            return TDB_ERRCODE(TDB_ERR_LOCK, -1);
      }
      
      if (tdb->num_locks != 0) {
            /* can't combine global and chain locks */
            return TDB_ERRCODE(TDB_ERR_LOCK, -1);
      }

      if (!mark_lock &&
          tdb->methods->tdb_brlock(tdb, FREELIST_TOP, ltype, op,
                             0, 4*tdb->header.hash_size)) {
            if (op == F_SETLKW) {
                  TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_lockall failed (%s)\n", strerror(errno)));
            }
            return -1;
      }

      tdb->global_lock.count = 1;
      tdb->global_lock.ltype = ltype;

      return 0;
}



/* unlock entire db */
static int _tdb_unlockall(struct tdb_context *tdb, int ltype)
{
      bool mark_lock = ((ltype & TDB_MARK_LOCK) == TDB_MARK_LOCK);

      ltype &= ~TDB_MARK_LOCK;

      /* There are no locks on read-only dbs */
      if (tdb->read_only || tdb->traverse_read) {
            return TDB_ERRCODE(TDB_ERR_LOCK, -1);
      }

      if (tdb->global_lock.ltype != ltype || tdb->global_lock.count == 0) {
            return TDB_ERRCODE(TDB_ERR_LOCK, -1);
      }

      if (tdb->global_lock.count > 1) {
            tdb->global_lock.count--;
            return 0;
      }

      if (!mark_lock &&
          tdb->methods->tdb_brlock(tdb, FREELIST_TOP, F_UNLCK, F_SETLKW, 
                             0, 4*tdb->header.hash_size)) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_unlockall failed (%s)\n", strerror(errno)));
            return -1;
      }

      tdb->global_lock.count = 0;
      tdb->global_lock.ltype = 0;

      return 0;
}

/* lock entire database with write lock */
int tdb_lockall(struct tdb_context *tdb)
{
      return _tdb_lockall(tdb, F_WRLCK, F_SETLKW);
}

/* lock entire database with write lock - mark only */
int tdb_lockall_mark(struct tdb_context *tdb)
{
      return _tdb_lockall(tdb, F_WRLCK | TDB_MARK_LOCK, F_SETLKW);
}

/* unlock entire database with write lock - unmark only */
int tdb_lockall_unmark(struct tdb_context *tdb)
{
      return _tdb_unlockall(tdb, F_WRLCK | TDB_MARK_LOCK);
}

/* lock entire database with write lock - nonblocking varient */
int tdb_lockall_nonblock(struct tdb_context *tdb)
{
      return _tdb_lockall(tdb, F_WRLCK, F_SETLK);
}

/* unlock entire database with write lock */
int tdb_unlockall(struct tdb_context *tdb)
{
      return _tdb_unlockall(tdb, F_WRLCK);
}

/* lock entire database with read lock */
int tdb_lockall_read(struct tdb_context *tdb)
{
      return _tdb_lockall(tdb, F_RDLCK, F_SETLKW);
}

/* lock entire database with read lock - nonblock varient */
int tdb_lockall_read_nonblock(struct tdb_context *tdb)
{
      return _tdb_lockall(tdb, F_RDLCK, F_SETLK);
}

/* unlock entire database with read lock */
int tdb_unlockall_read(struct tdb_context *tdb)
{
      return _tdb_unlockall(tdb, F_RDLCK);
}

/* lock/unlock one hash chain. This is meant to be used to reduce
   contention - it cannot guarantee how many records will be locked */
int tdb_chainlock(struct tdb_context *tdb, TDB_DATA key)
{
      return tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK);
}

/* lock/unlock one hash chain, non-blocking. This is meant to be used
   to reduce contention - it cannot guarantee how many records will be
   locked */
int tdb_chainlock_nonblock(struct tdb_context *tdb, TDB_DATA key)
{
      return tdb_lock_nonblock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK);
}

/* mark a chain as locked without actually locking it. Warning! use with great caution! */
int tdb_chainlock_mark(struct tdb_context *tdb, TDB_DATA key)
{
      return tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK | TDB_MARK_LOCK);
}

/* unmark a chain as locked without actually locking it. Warning! use with great caution! */
int tdb_chainlock_unmark(struct tdb_context *tdb, TDB_DATA key)
{
      return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK | TDB_MARK_LOCK);
}

int tdb_chainunlock(struct tdb_context *tdb, TDB_DATA key)
{
      return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK);
}

int tdb_chainlock_read(struct tdb_context *tdb, TDB_DATA key)
{
      return tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_RDLCK);
}

int tdb_chainunlock_read(struct tdb_context *tdb, TDB_DATA key)
{
      return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_RDLCK);
}



/* record lock stops delete underneath */
int tdb_lock_record(struct tdb_context *tdb, tdb_off_t off)
{
      return off ? tdb->methods->tdb_brlock(tdb, off, F_RDLCK, F_SETLKW, 0, 1) : 0;
}

/*
  Write locks override our own fcntl readlocks, so check it here.
  Note this is meant to be F_SETLK, *not* F_SETLKW, as it's not
  an error to fail to get the lock here.
*/
int tdb_write_lock_record(struct tdb_context *tdb, tdb_off_t off)
{
      struct tdb_traverse_lock *i;
      for (i = &tdb->travlocks; i; i = i->next)
            if (i->off == off)
                  return -1;
      return tdb->methods->tdb_brlock(tdb, off, F_WRLCK, F_SETLK, 1, 1);
}

/*
  Note this is meant to be F_SETLK, *not* F_SETLKW, as it's not
  an error to fail to get the lock here.
*/
int tdb_write_unlock_record(struct tdb_context *tdb, tdb_off_t off)
{
      return tdb->methods->tdb_brlock(tdb, off, F_UNLCK, F_SETLK, 0, 1);
}

/* fcntl locks don't stack: avoid unlocking someone else's */
int tdb_unlock_record(struct tdb_context *tdb, tdb_off_t off)
{
      struct tdb_traverse_lock *i;
      u32 count = 0;

      if (off == 0)
            return 0;
      for (i = &tdb->travlocks; i; i = i->next)
            if (i->off == off)
                  count++;
      return (count == 1 ? tdb->methods->tdb_brlock(tdb, off, F_UNLCK, F_SETLKW, 0, 1) : 0);
}

/* file: io.c */

/* check for an out of bounds access - if it is out of bounds then
   see if the database has been expanded by someone else and expand
   if necessary 
   note that "len" is the minimum length needed for the db
*/
static int tdb_oob(struct tdb_context *tdb, tdb_off_t len, int probe)
{
      struct stat st;
      if (len <= tdb->map_size)
            return 0;
      if (tdb->flags & TDB_INTERNAL) {
            if (!probe) {
                  /* Ensure ecode is set for log fn. */
                  tdb->ecode = TDB_ERR_IO;
                  TDB_LOG((tdb, TDB_DEBUG_FATAL,"tdb_oob len %d beyond internal malloc size %d\n",
                         (int)len, (int)tdb->map_size));
            }
            return TDB_ERRCODE(TDB_ERR_IO, -1);
      }

      if (fstat(tdb->fd, &st) == -1) {
            return TDB_ERRCODE(TDB_ERR_IO, -1);
      }

      if (st.st_size < (size_t)len) {
            if (!probe) {
                  /* Ensure ecode is set for log fn. */
                  tdb->ecode = TDB_ERR_IO;
                  TDB_LOG((tdb, TDB_DEBUG_FATAL,"tdb_oob len %d beyond eof at %d\n",
                         (int)len, (int)st.st_size));
            }
            return TDB_ERRCODE(TDB_ERR_IO, -1);
      }

      /* Unmap, update size, remap */
      if (tdb_munmap(tdb) == -1)
            return TDB_ERRCODE(TDB_ERR_IO, -1);
      tdb->map_size = st.st_size;
      tdb_mmap(tdb);
      return 0;
}

/* write a lump of data at a specified offset */
static int tdb_write(struct tdb_context *tdb, tdb_off_t off, 
                 const void *buf, tdb_len_t len)
{
      if (len == 0) {
            return 0;
      }

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

      if (tdb->methods->tdb_oob(tdb, off + len, 0) != 0)
            return -1;

      if (tdb->map_ptr) {
            memcpy(off + (char *)tdb->map_ptr, buf, len);
      } else if (pwrite(tdb->fd, buf, len, off) != (ssize_t)len) {
            /* Ensure ecode is set for log fn. */
            tdb->ecode = TDB_ERR_IO;
            TDB_LOG((tdb, TDB_DEBUG_FATAL,"tdb_write failed at %d len=%d (%s)\n",
                     off, len, strerror(errno)));
            return TDB_ERRCODE(TDB_ERR_IO, -1);
      }
      return 0;
}

/* Endian conversion: we only ever deal with 4 byte quantities */
void *tdb_convert(void *buf, u32 size)
{
      u32 i, *p = (u32 *)buf;
      for (i = 0; i < size / 4; i++)
            p[i] = TDB_BYTEREV(p[i]);
      return buf;
}


/* read a lump of data at a specified offset, maybe convert */
static int tdb_read(struct tdb_context *tdb, tdb_off_t off, void *buf, 
                tdb_len_t len, int cv)
{
      if (tdb->methods->tdb_oob(tdb, off + len, 0) != 0) {
            return -1;
      }

      if (tdb->map_ptr) {
            memcpy(buf, off + (char *)tdb->map_ptr, len);
      } else {
            ssize_t ret = pread(tdb->fd, buf, len, off);
            if (ret != (ssize_t)len) {
                  /* Ensure ecode is set for log fn. */
                  tdb->ecode = TDB_ERR_IO;
                  TDB_LOG((tdb, TDB_DEBUG_FATAL,"tdb_read failed at %d "
                         "len=%d ret=%d (%s) map_size=%d\n",
                         (int)off, (int)len, (int)ret, strerror(errno),
                         (int)tdb->map_size));
                  return TDB_ERRCODE(TDB_ERR_IO, -1);
            }
      }
      if (cv) {
            tdb_convert(buf, len);
      }
      return 0;
}



/*
  do an unlocked scan of the hash table heads to find the next non-zero head. The value
  will then be confirmed with the lock held
*/          
static void tdb_next_hash_chain(struct tdb_context *tdb, u32 *chain)
{
      u32 h = *chain;
      if (tdb->map_ptr) {
            for (;h < tdb->header.hash_size;h++) {
                  if (0 != *(u32 *)(TDB_HASH_TOP(h) + (unsigned char *)tdb->map_ptr)) {
                        break;
                  }
            }
      } else {
            u32 off=0;
            for (;h < tdb->header.hash_size;h++) {
                  if (tdb_ofs_read(tdb, TDB_HASH_TOP(h), &off) != 0 || off != 0) {
                        break;
                  }
            }
      }
      (*chain) = h;
}


int tdb_munmap(struct tdb_context *tdb)
{
      if (tdb->flags & TDB_INTERNAL)
            return 0;

#ifdef HAVE_MMAP
      if (tdb->map_ptr) {
            int ret = munmap(tdb->map_ptr, tdb->map_size);
            if (ret != 0)
                  return ret;
      }
#endif
      tdb->map_ptr = NULL;
      return 0;
}

void tdb_mmap(struct tdb_context *tdb)
{
      if (tdb->flags & TDB_INTERNAL)
            return;

#ifdef HAVE_MMAP
      if (!(tdb->flags & TDB_NOMMAP)) {
            tdb->map_ptr = mmap(NULL, tdb->map_size, 
                            PROT_READ|(tdb->read_only? 0:PROT_WRITE), 
                            MAP_SHARED|MAP_FILE, tdb->fd, 0);

            /*
             * NB. When mmap fails it returns MAP_FAILED *NOT* NULL !!!!
             */

            if (tdb->map_ptr == MAP_FAILED) {
                  tdb->map_ptr = NULL;
                  TDB_LOG((tdb, TDB_DEBUG_WARNING, "tdb_mmap failed for size %d (%s)\n", 
                         tdb->map_size, strerror(errno)));
            }
      } else {
            tdb->map_ptr = NULL;
      }
#else
      tdb->map_ptr = NULL;
#endif
}

/* expand a file.  we prefer to use ftruncate, as that is what posix
  says to use for mmap expansion */
static int tdb_expand_file(struct tdb_context *tdb, tdb_off_t size, tdb_off_t addition)
{
      char buf[1024];

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

      if (ftruncate(tdb->fd, size+addition) == -1) {
            char b = 0;
            if (pwrite(tdb->fd,  &b, 1, (size+addition) - 1) != 1) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "expand_file to %d failed (%s)\n", 
                         size+addition, strerror(errno)));
                  return -1;
            }
      }

      /* now fill the file with something. This ensures that the
         file isn't sparse, which would be very bad if we ran out of
         disk. This must be done with write, not via mmap */
      memset(buf, TDB_PAD_BYTE, sizeof(buf));
      while (addition) {
            int n = addition>sizeof(buf)?sizeof(buf):addition;
            int ret = pwrite(tdb->fd, buf, n, size);
            if (ret != n) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "expand_file write of %d failed (%s)\n", 
                           n, strerror(errno)));
                  return -1;
            }
            addition -= n;
            size += n;
      }
      return 0;
}


/* expand the database at least size bytes by expanding the underlying
   file and doing the mmap again if necessary */
int tdb_expand(struct tdb_context *tdb, tdb_off_t size)
{
      struct list_struct rec;
      tdb_off_t offset;

      if (tdb_lock(tdb, -1, F_WRLCK) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "lock failed in tdb_expand\n"));
            return -1;
      }

      /* must know about any previous expansions by another process */
      tdb->methods->tdb_oob(tdb, tdb->map_size + 1, 1);

      /* always make room for at least 10 more records, and round
           the database up to a multiple of the page size */
      size = TDB_ALIGN(tdb->map_size + size*10, tdb->page_size) - tdb->map_size;

      if (!(tdb->flags & TDB_INTERNAL))
            tdb_munmap(tdb);

      /*
       * We must ensure the file is unmapped before doing this
       * to ensure consistency with systems like OpenBSD where
       * writes and mmaps are not consistent.
       */

      /* expand the file itself */
      if (!(tdb->flags & TDB_INTERNAL)) {
            if (tdb->methods->tdb_expand_file(tdb, tdb->map_size, size) != 0)
                  goto fail;
      }

      tdb->map_size += size;

      if (tdb->flags & TDB_INTERNAL) {
            char *new_map_ptr = (char *)realloc(tdb->map_ptr,
                                        tdb->map_size);
            if (!new_map_ptr) {
                  tdb->map_size -= size;
                  goto fail;
            }
            tdb->map_ptr = new_map_ptr;
      } else {
            /*
             * We must ensure the file is remapped before adding the space
             * to ensure consistency with systems like OpenBSD where
             * writes and mmaps are not consistent.
             */

            /* We're ok if the mmap fails as we'll fallback to read/write */
            tdb_mmap(tdb);
      }

      /* form a new freelist record */
      memset(&rec,'\0',sizeof(rec));
      rec.rec_len = size - sizeof(rec);

      /* link it into the free list */
      offset = tdb->map_size - size;
      if (tdb_free(tdb, offset, &rec) == -1)
            goto fail;

      tdb_unlock(tdb, -1, F_WRLCK);
      return 0;
 fail:
      tdb_unlock(tdb, -1, F_WRLCK);
      return -1;
}

/* read/write a tdb_off_t */
int tdb_ofs_read(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d)
{
      return tdb->methods->tdb_read(tdb, offset, (char*)d, sizeof(*d), DOCONV());
}

int tdb_ofs_write(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d)
{
      tdb_off_t off = *d;
      return tdb->methods->tdb_write(tdb, offset, CONVERT(off), sizeof(*d));
}


/* read a lump of data, allocating the space for it */
unsigned char *tdb_alloc_read(struct tdb_context *tdb, tdb_off_t offset, tdb_len_t len)
{
      unsigned char *buf;

      /* some systems don't like zero length malloc */
      if (len == 0) {
            len = 1;
      }

      if (!(buf = (unsigned char *)malloc(len))) {
            /* Ensure ecode is set for log fn. */
            tdb->ecode = TDB_ERR_OOM;
            TDB_LOG((tdb, TDB_DEBUG_ERROR,"tdb_alloc_read malloc failed len=%d (%s)\n",
                     len, strerror(errno)));
            return TDB_ERRCODE(TDB_ERR_OOM, buf);
      }
      if (tdb->methods->tdb_read(tdb, offset, buf, len, 0) == -1) {
            SAFE_FREE(buf);
            return NULL;
      }
      return buf;
}

/* Give a piece of tdb data to a parser */

int tdb_parse_data(struct tdb_context *tdb, TDB_DATA key,
               tdb_off_t offset, tdb_len_t len,
               int (*parser)(TDB_DATA key, TDB_DATA data,
                         void *private_data),
               void *private_data)
{
      TDB_DATA data;
      int result;

      data.dsize = len;

      if ((tdb->transaction == NULL) && (tdb->map_ptr != NULL)) {
            /*
             * Optimize by avoiding the malloc/memcpy/free, point the
             * parser directly at the mmap area.
             */
            if (tdb->methods->tdb_oob(tdb, offset+len, 0) != 0) {
                  return -1;
            }
            data.dptr = offset + (unsigned char *)tdb->map_ptr;
            return parser(key, data, private_data);
      }

      if (!(data.dptr = tdb_alloc_read(tdb, offset, len))) {
            return -1;
      }

      result = parser(key, data, private_data);
      free(data.dptr);
      return result;
}

/* read/write a record */
int tdb_rec_read(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec)
{
      if (tdb->methods->tdb_read(tdb, offset, rec, sizeof(*rec),DOCONV()) == -1)
            return -1;
      if (TDB_BAD_MAGIC(rec)) {
            /* Ensure ecode is set for log fn. */
            tdb->ecode = TDB_ERR_CORRUPT;
            TDB_LOG((tdb, TDB_DEBUG_FATAL,"tdb_rec_read bad magic 0x%x at offset=%d\n", rec->magic, offset));
            return TDB_ERRCODE(TDB_ERR_CORRUPT, -1);
      }
      return tdb->methods->tdb_oob(tdb, rec->next+sizeof(*rec), 0);
}

int tdb_rec_write(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec)
{
      struct list_struct r = *rec;
      return tdb->methods->tdb_write(tdb, offset, CONVERT(r), sizeof(r));
}

static const struct tdb_methods io_methods = {
      tdb_read,
      tdb_write,
      tdb_next_hash_chain,
      tdb_oob,
      tdb_expand_file,
      tdb_brlock
};

/*
  initialise the default methods table
*/
void tdb_io_init(struct tdb_context *tdb)
{
      tdb->methods = &io_methods;
}

/* file: transaction.c */

/*
  transaction design:

  - only allow a single transaction at a time per database. This makes
    using the transaction API simpler, as otherwise the caller would
    have to cope with temporary failures in transactions that conflict
    with other current transactions

  - keep the transaction recovery information in the same file as the
    database, using a special 'transaction recovery' record pointed at
    by the header. This removes the need for extra journal files as
    used by some other databases

  - dynamically allocated the transaction recover record, re-using it
    for subsequent transactions. If a larger record is needed then
    tdb_free() the old record to place it on the normal tdb freelist
    before allocating the new record

  - during transactions, keep a linked list of writes all that have
    been performed by intercepting all tdb_write() calls. The hooked
    transaction versions of tdb_read() and tdb_write() check this
    linked list and try to use the elements of the list in preference
    to the real database.

  - don't allow any locks to be held when a transaction starts,
    otherwise we can end up with deadlock (plus lack of lock nesting
    in posix locks would mean the lock is lost)

  - if the caller gains a lock during the transaction but doesn't
    release it then fail the commit

  - allow for nested calls to tdb_transaction_start(), re-using the
    existing transaction record. If the inner transaction is cancelled
    then a subsequent commit will fail
 
  - keep a mirrored copy of the tdb hash chain heads to allow for the
    fast hash heads scan on traverse, updating the mirrored copy in
    the transaction version of tdb_write

  - allow callers to mix transaction and non-transaction use of tdb,
    although once a transaction is started then an exclusive lock is
    gained until the transaction is committed or cancelled

  - the commit stategy involves first saving away all modified data
    into a linearised buffer in the transaction recovery area, then
    marking the transaction recovery area with a magic value to
    indicate a valid recovery record. In total 4 fsync/msync calls are
    needed per commit to prevent race conditions. It might be possible
    to reduce this to 3 or even 2 with some more work.

  - check for a valid recovery record on open of the tdb, while the
    global lock is held. Automatically recover from the transaction
    recovery area if needed, then continue with the open as
    usual. This allows for smooth crash recovery with no administrator
    intervention.

  - if TDB_NOSYNC is passed to flags in tdb_open then transactions are
    still available, but no transaction recovery area is used and no
    fsync/msync calls are made.

*/

struct tdb_transaction_el {
      struct tdb_transaction_el *next, *prev;
      tdb_off_t offset;
      tdb_len_t length;
      unsigned char *data;
};

/*
  hold the context of any current transaction
*/
struct tdb_transaction {
      /* we keep a mirrored copy of the tdb hash heads here so
         tdb_next_hash_chain() can operate efficiently */
      u32 *hash_heads;

      /* the original io methods - used to do IOs to the real db */
      const struct tdb_methods *io_methods;

      /* the list of transaction elements. We use a doubly linked
         list with a last pointer to allow us to keep the list
         ordered, with first element at the front of the list. It
         needs to be doubly linked as the read/write traversals need
         to be backwards, while the commit needs to be forwards */
      struct tdb_transaction_el *elements, *elements_last;

      /* non-zero when an internal transaction error has
         occurred. All write operations will then fail until the
         transaction is ended */
      int transaction_error;

      /* when inside a transaction we need to keep track of any
         nested tdb_transaction_start() calls, as these are allowed,
         but don't create a new transaction */
      int nesting;

      /* old file size before transaction */
      tdb_len_t old_map_size;
};


/*
  read while in a transaction. We need to check first if the data is in our list
  of transaction elements, then if not do a real read
*/
static int transaction_read(struct tdb_context *tdb, tdb_off_t off, void *buf, 
                      tdb_len_t len, int cv)
{
      struct tdb_transaction_el *el;

      /* we need to walk the list backwards to get the most recent data */
      for (el=tdb->transaction->elements_last;el;el=el->prev) {
            tdb_len_t partial;

            if (off+len <= el->offset) {
                  continue;
            }
            if (off >= el->offset + el->length) {
                  continue;
            }

            /* an overlapping read - needs to be split into up to
               2 reads and a memcpy */
            if (off < el->offset) {
                  partial = el->offset - off;
                  if (transaction_read(tdb, off, buf, partial, cv) != 0) {
                        goto fail;
                  }
                  len -= partial;
                  off += partial;
                  buf = (void *)(partial + (char *)buf);
            }
            if (off + len <= el->offset + el->length) {
                  partial = len;
            } else {
                  partial = el->offset + el->length - off;
            }
            memcpy(buf, el->data + (off - el->offset), partial);
            if (cv) {
                  tdb_convert(buf, len);
            }
            len -= partial;
            off += partial;
            buf = (void *)(partial + (char *)buf);
            
            if (len != 0 && transaction_read(tdb, off, buf, len, cv) != 0) {
                  goto fail;
            }

            return 0;
      }

      /* its not in the transaction elements - do a real read */
      return tdb->transaction->io_methods->tdb_read(tdb, off, buf, len, cv);

fail:
      TDB_LOG((tdb, TDB_DEBUG_FATAL, "transaction_read: failed at off=%d len=%d\n", off, len));
      tdb->ecode = TDB_ERR_IO;
      tdb->transaction->transaction_error = 1;
      return -1;
}


/*
  write while in a transaction
*/
static int transaction_write(struct tdb_context *tdb, tdb_off_t off, 
                       const void *buf, tdb_len_t len)
{
      struct tdb_transaction_el *el, *best_el=NULL;

      if (len == 0) {
            return 0;
      }
      
      /* if the write is to a hash head, then update the transaction
         hash heads */
      if (len == sizeof(tdb_off_t) && off >= FREELIST_TOP &&
          off < FREELIST_TOP+TDB_HASHTABLE_SIZE(tdb)) {
            u32 chain = (off-FREELIST_TOP) / sizeof(tdb_off_t);
            memcpy(&tdb->transaction->hash_heads[chain], buf, len);
      }

      /* first see if we can replace an existing entry */
      for (el=tdb->transaction->elements_last;el;el=el->prev) {
            tdb_len_t partial;

            if (best_el == NULL && off == el->offset+el->length) {
                  best_el = el;
            }

            if (off+len <= el->offset) {
                  continue;
            }
            if (off >= el->offset + el->length) {
                  continue;
            }

            /* an overlapping write - needs to be split into up to
               2 writes and a memcpy */
            if (off < el->offset) {
                  partial = el->offset - off;
                  if (transaction_write(tdb, off, buf, partial) != 0) {
                        goto fail;
                  }
                  len -= partial;
                  off += partial;
                  buf = (const void *)(partial + (const char *)buf);
            }
            if (off + len <= el->offset + el->length) {
                  partial = len;
            } else {
                  partial = el->offset + el->length - off;
            }
            memcpy(el->data + (off - el->offset), buf, partial);
            len -= partial;
            off += partial;
            buf = (const void *)(partial + (const char *)buf);
            
            if (len != 0 && transaction_write(tdb, off, buf, len) != 0) {
                  goto fail;
            }

            return 0;
      }

      /* see if we can append the new entry to an existing entry */
      if (best_el && best_el->offset + best_el->length == off && 
          (off+len < tdb->transaction->old_map_size ||
           off > tdb->transaction->old_map_size)) {
            unsigned char *data = best_el->data;
            el = best_el;
            el->data = (unsigned char *)realloc(el->data,
                                        el->length + len);
            if (el->data == NULL) {
                  tdb->ecode = TDB_ERR_OOM;
                  tdb->transaction->transaction_error = 1;
                  el->data = data;
                  return -1;
            }
            if (buf) {
                  memcpy(el->data + el->length, buf, len);
            } else {
                  memset(el->data + el->length, TDB_PAD_BYTE, len);
            }
            el->length += len;
            return 0;
      }

      /* add a new entry at the end of the list */
      el = (struct tdb_transaction_el *)malloc(sizeof(*el));
      if (el == NULL) {
            tdb->ecode = TDB_ERR_OOM;
            tdb->transaction->transaction_error = 1;        
            return -1;
      }
      el->next = NULL;
      el->prev = tdb->transaction->elements_last;
      el->offset = off;
      el->length = len;
      el->data = (unsigned char *)malloc(len);
      if (el->data == NULL) {
            free(el);
            tdb->ecode = TDB_ERR_OOM;
            tdb->transaction->transaction_error = 1;        
            return -1;
      }
      if (buf) {
            memcpy(el->data, buf, len);
      } else {
            memset(el->data, TDB_PAD_BYTE, len);
      }
      if (el->prev) {
            el->prev->next = el;
      } else {
            tdb->transaction->elements = el;
      }
      tdb->transaction->elements_last = el;
      return 0;

fail:
      TDB_LOG((tdb, TDB_DEBUG_FATAL, "transaction_write: failed at off=%d len=%d\n", off, len));
      tdb->ecode = TDB_ERR_IO;
      tdb->transaction->transaction_error = 1;
      return -1;
}

/*
  accelerated hash chain head search, using the cached hash heads
*/
static void transaction_next_hash_chain(struct tdb_context *tdb, u32 *chain)
{
      u32 h = *chain;
      for (;h < tdb->header.hash_size;h++) {
            /* the +1 takes account of the freelist */
            if (0 != tdb->transaction->hash_heads[h+1]) {
                  break;
            }
      }
      (*chain) = h;
}

/*
  out of bounds check during a transaction
*/
static int transaction_oob(struct tdb_context *tdb, tdb_off_t len, int probe)
{
      if (len <= tdb->map_size) {
            return 0;
      }
      return TDB_ERRCODE(TDB_ERR_IO, -1);
}

/*
  transaction version of tdb_expand().
*/
static int transaction_expand_file(struct tdb_context *tdb, tdb_off_t size, 
                           tdb_off_t addition)
{
      /* add a write to the transaction elements, so subsequent
         reads see the zero data */
      if (transaction_write(tdb, size, NULL, addition) != 0) {
            return -1;
      }

      return 0;
}

/*
  brlock during a transaction - ignore them
*/
static int transaction_brlock(struct tdb_context *tdb, tdb_off_t offset, 
                        int rw_type, int lck_type, int probe, size_t len)
{
      return 0;
}

static const struct tdb_methods transaction_methods = {
      transaction_read,
      transaction_write,
      transaction_next_hash_chain,
      transaction_oob,
      transaction_expand_file,
      transaction_brlock
};


/*
  start a tdb transaction. No token is returned, as only a single
  transaction is allowed to be pending per tdb_context
*/
int tdb_transaction_start(struct tdb_context *tdb)
{
      /* some sanity checks */
      if (tdb->read_only || (tdb->flags & TDB_INTERNAL) || tdb->traverse_read) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction on a read-only or internal db\n"));
            tdb->ecode = TDB_ERR_EINVAL;
            return -1;
      }

      /* cope with nested tdb_transaction_start() calls */
      if (tdb->transaction != NULL) {
            tdb->transaction->nesting++;
            TDB_LOG((tdb, TDB_DEBUG_TRACE, "tdb_transaction_start: nesting %d\n", 
                   tdb->transaction->nesting));
            return 0;
      }

      if (tdb->num_locks != 0 || tdb->global_lock.count) {
            /* the caller must not have any locks when starting a
               transaction as otherwise we'll be screwed by lack
               of nested locks in posix */
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction with locks held\n"));
            tdb->ecode = TDB_ERR_LOCK;
            return -1;
      }

      if (tdb->travlocks.next != NULL) {
            /* you cannot use transactions inside a traverse (although you can use
               traverse inside a transaction) as otherwise you can end up with
               deadlock */
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: cannot start a transaction within a traverse\n"));
            tdb->ecode = TDB_ERR_LOCK;
            return -1;
      }

      tdb->transaction = (struct tdb_transaction *)
            calloc(sizeof(struct tdb_transaction), 1);
      if (tdb->transaction == NULL) {
            tdb->ecode = TDB_ERR_OOM;
            return -1;
      }

      /* get the transaction write lock. This is a blocking lock. As
         discussed with Volker, there are a number of ways we could
         make this async, which we will probably do in the future */
      if (tdb_transaction_lock(tdb, F_WRLCK) == -1) {
            SAFE_FREE(tdb->transaction);
            return -1;
      }
      
      /* get a read lock from the freelist to the end of file. This
         is upgraded to a write lock during the commit */
      if (tdb_brlock(tdb, FREELIST_TOP, F_RDLCK, F_SETLKW, 0, 0) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: failed to get hash locks\n"));
            tdb->ecode = TDB_ERR_LOCK;
            goto fail;
      }

      /* setup a copy of the hash table heads so the hash scan in
         traverse can be fast */
      tdb->transaction->hash_heads = (u32 *)
            calloc(tdb->header.hash_size+1, sizeof(u32));
      if (tdb->transaction->hash_heads == NULL) {
            tdb->ecode = TDB_ERR_OOM;
            goto fail;
      }
      if (tdb->methods->tdb_read(tdb, FREELIST_TOP, tdb->transaction->hash_heads,
                           TDB_HASHTABLE_SIZE(tdb), 0) != 0) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_start: failed to read hash heads\n"));
            tdb->ecode = TDB_ERR_IO;
            goto fail;
      }

      /* make sure we know about any file expansions already done by
         anyone else */
      tdb->methods->tdb_oob(tdb, tdb->map_size + 1, 1);
      tdb->transaction->old_map_size = tdb->map_size;

      /* finally hook the io methods, replacing them with
         transaction specific methods */
      tdb->transaction->io_methods = tdb->methods;
      tdb->methods = &transaction_methods;

      /* by calling this transaction write here, we ensure that we don't grow the
         transaction linked list due to hash table updates */
      if (transaction_write(tdb, FREELIST_TOP, tdb->transaction->hash_heads, 
                        TDB_HASHTABLE_SIZE(tdb)) != 0) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_start: failed to prime hash table\n"));
            tdb->ecode = TDB_ERR_IO;
            tdb->methods = tdb->transaction->io_methods;
            goto fail;
      }

      return 0;
      
fail:
      tdb_brlock(tdb, FREELIST_TOP, F_UNLCK, F_SETLKW, 0, 0);
      tdb_transaction_unlock(tdb);
      SAFE_FREE(tdb->transaction->hash_heads);
      SAFE_FREE(tdb->transaction);
      return -1;
}


/*
  cancel the current transaction
*/
int tdb_transaction_cancel(struct tdb_context *tdb)
{     
      if (tdb->transaction == NULL) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_cancel: no transaction\n"));
            return -1;
      }

      if (tdb->transaction->nesting != 0) {
            tdb->transaction->transaction_error = 1;
            tdb->transaction->nesting--;
            return 0;
      }           

      tdb->map_size = tdb->transaction->old_map_size;

      /* free all the transaction elements */
      while (tdb->transaction->elements) {
            struct tdb_transaction_el *el = tdb->transaction->elements;
            tdb->transaction->elements = el->next;
            free(el->data);
            free(el);
      }

      /* remove any global lock created during the transaction */
      if (tdb->global_lock.count != 0) {
            tdb_brlock(tdb, FREELIST_TOP, F_UNLCK, F_SETLKW, 0, 4*tdb->header.hash_size);
            tdb->global_lock.count = 0;
      }

      /* remove any locks created during the transaction */
      if (tdb->num_locks != 0) {
            int i;
            for (i=0;i<tdb->num_lockrecs;i++) {
                  tdb_brlock(tdb,FREELIST_TOP+4*tdb->lockrecs[i].list,
                           F_UNLCK,F_SETLKW, 0, 1);
            }
            tdb->num_locks = 0;
            tdb->num_lockrecs = 0;
            SAFE_FREE(tdb->lockrecs);
      }

      /* restore the normal io methods */
      tdb->methods = tdb->transaction->io_methods;

      tdb_brlock(tdb, FREELIST_TOP, F_UNLCK, F_SETLKW, 0, 0);
      tdb_transaction_unlock(tdb);
      SAFE_FREE(tdb->transaction->hash_heads);
      SAFE_FREE(tdb->transaction);
      
      return 0;
}

/*
  sync to disk
*/
static int transaction_sync(struct tdb_context *tdb, tdb_off_t offset, tdb_len_t length)
{     
      if (fsync(tdb->fd) != 0) {
            tdb->ecode = TDB_ERR_IO;
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: fsync failed\n"));
            return -1;
      }
#ifdef MS_SYNC
      if (tdb->map_ptr) {
            tdb_off_t moffset = offset & ~(tdb->page_size-1);
            if (msync(moffset + (char *)tdb->map_ptr, 
                    length + (offset - moffset), MS_SYNC) != 0) {
                  tdb->ecode = TDB_ERR_IO;
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction: msync failed - %s\n",
                         strerror(errno)));
                  return -1;
            }
      }
#endif
      return 0;
}


/*
  work out how much space the linearised recovery data will consume
*/
static tdb_len_t tdb_recovery_size(struct tdb_context *tdb)
{
      struct tdb_transaction_el *el;
      tdb_len_t recovery_size = 0;

      recovery_size = sizeof(u32);
      for (el=tdb->transaction->elements;el;el=el->next) {
            if (el->offset >= tdb->transaction->old_map_size) {
                  continue;
            }
            recovery_size += 2*sizeof(tdb_off_t) + el->length;
      }

      return recovery_size;
}

/*
  allocate the recovery area, or use an existing recovery area if it is
  large enough
*/
static int tdb_recovery_allocate(struct tdb_context *tdb, 
                         tdb_len_t *recovery_size,
                         tdb_off_t *recovery_offset,
                         tdb_len_t *recovery_max_size)
{
      struct list_struct rec;
      const struct tdb_methods *methods = tdb->transaction->io_methods;
      tdb_off_t recovery_head;

      if (tdb_ofs_read(tdb, TDB_RECOVERY_HEAD, &recovery_head) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to read recovery head\n"));
            return -1;
      }

      rec.rec_len = 0;

      if (recovery_head != 0 && 
          methods->tdb_read(tdb, recovery_head, &rec, sizeof(rec), DOCONV()) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to read recovery record\n"));
            return -1;
      }

      *recovery_size = tdb_recovery_size(tdb);

      if (recovery_head != 0 && *recovery_size <= rec.rec_len) {
            /* it fits in the existing area */
            *recovery_max_size = rec.rec_len;
            *recovery_offset = recovery_head;
            return 0;
      }

      /* we need to free up the old recovery area, then allocate a
         new one at the end of the file. Note that we cannot use
         tdb_allocate() to allocate the new one as that might return
         us an area that is being currently used (as of the start of
         the transaction) */
      if (recovery_head != 0) {
            if (tdb_free(tdb, recovery_head, &rec) == -1) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to free previous recovery area\n"));
                  return -1;
            }
      }

      /* the tdb_free() call might have increased the recovery size */
      *recovery_size = tdb_recovery_size(tdb);

      /* round up to a multiple of page size */
      *recovery_max_size = TDB_ALIGN(sizeof(rec) + *recovery_size, tdb->page_size) - sizeof(rec);
      *recovery_offset = tdb->map_size;
      recovery_head = *recovery_offset;

      if (methods->tdb_expand_file(tdb, tdb->transaction->old_map_size, 
                             (tdb->map_size - tdb->transaction->old_map_size) +
                             sizeof(rec) + *recovery_max_size) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to create recovery area\n"));
            return -1;
      }

      /* remap the file (if using mmap) */
      methods->tdb_oob(tdb, tdb->map_size + 1, 1);

      /* we have to reset the old map size so that we don't try to expand the file
         again in the transaction commit, which would destroy the recovery area */
      tdb->transaction->old_map_size = tdb->map_size;

      /* write the recovery header offset and sync - we can sync without a race here
         as the magic ptr in the recovery record has not been set */
      CONVERT(recovery_head);
      if (methods->tdb_write(tdb, TDB_RECOVERY_HEAD, 
                         &recovery_head, sizeof(tdb_off_t)) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_recovery_allocate: failed to write recovery head\n"));
            return -1;
      }

      return 0;
}


/*
  setup the recovery data that will be used on a crash during commit
*/
static int transaction_setup_recovery(struct tdb_context *tdb, 
                              tdb_off_t *magic_offset)
{
      struct tdb_transaction_el *el;
      tdb_len_t recovery_size;
      unsigned char *data, *p;
      const struct tdb_methods *methods = tdb->transaction->io_methods;
      struct list_struct *rec;
      tdb_off_t recovery_offset, recovery_max_size;
      tdb_off_t old_map_size = tdb->transaction->old_map_size;
      u32 magic, tailer;

      /*
        check that the recovery area has enough space
      */
      if (tdb_recovery_allocate(tdb, &recovery_size, 
                          &recovery_offset, &recovery_max_size) == -1) {
            return -1;
      }

      data = (unsigned char *)malloc(recovery_size + sizeof(*rec));
      if (data == NULL) {
            tdb->ecode = TDB_ERR_OOM;
            return -1;
      }

      rec = (struct list_struct *)data;
      memset(rec, 0, sizeof(*rec));

      rec->magic    = 0;
      rec->data_len = recovery_size;
      rec->rec_len  = recovery_max_size;
      rec->key_len  = old_map_size;
      CONVERT(rec);

      /* build the recovery data into a single blob to allow us to do a single
         large write, which should be more efficient */
      p = data + sizeof(*rec);
      for (el=tdb->transaction->elements;el;el=el->next) {
            if (el->offset >= old_map_size) {
                  continue;
            }
            if (el->offset + el->length > tdb->transaction->old_map_size) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: transaction data over new region boundary\n"));
                  free(data);
                  tdb->ecode = TDB_ERR_CORRUPT;
                  return -1;
            }
            memcpy(p, &el->offset, 4);
            memcpy(p+4, &el->length, 4);
            if (DOCONV()) {
                  tdb_convert(p, 8);
            }
            /* the recovery area contains the old data, not the
               new data, so we have to call the original tdb_read
               method to get it */
            if (methods->tdb_read(tdb, el->offset, p + 8, el->length, 0) != 0) {
                  free(data);
                  tdb->ecode = TDB_ERR_IO;
                  return -1;
            }
            p += 8 + el->length;
      }

      /* and the tailer */
      tailer = sizeof(*rec) + recovery_max_size;
      memcpy(p, &tailer, 4);
      CONVERT(p);

      /* write the recovery data to the recovery area */
      if (methods->tdb_write(tdb, recovery_offset, data, sizeof(*rec) + recovery_size) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write recovery data\n"));
            free(data);
            tdb->ecode = TDB_ERR_IO;
            return -1;
      }

      /* as we don't have ordered writes, we have to sync the recovery
         data before we update the magic to indicate that the recovery
         data is present */
      if (transaction_sync(tdb, recovery_offset, sizeof(*rec) + recovery_size) == -1) {
            free(data);
            return -1;
      }

      free(data);

      magic = TDB_RECOVERY_MAGIC;
      CONVERT(magic);

      *magic_offset = recovery_offset + offsetof(struct list_struct, magic);

      if (methods->tdb_write(tdb, *magic_offset, &magic, sizeof(magic)) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_setup_recovery: failed to write recovery magic\n"));
            tdb->ecode = TDB_ERR_IO;
            return -1;
      }

      /* ensure the recovery magic marker is on disk */
      if (transaction_sync(tdb, *magic_offset, sizeof(magic)) == -1) {
            return -1;
      }

      return 0;
}

/*
  commit the current transaction
*/
int tdb_transaction_commit(struct tdb_context *tdb)
{     
      const struct tdb_methods *methods;
      tdb_off_t magic_offset = 0;
      u32 zero = 0;

      if (tdb->transaction == NULL) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: no transaction\n"));
            return -1;
      }

      if (tdb->transaction->transaction_error) {
            tdb->ecode = TDB_ERR_IO;
            tdb_transaction_cancel(tdb);
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: transaction error pending\n"));
            return -1;
      }

      if (tdb->transaction->nesting != 0) {
            tdb->transaction->nesting--;
            return 0;
      }           

      /* check for a null transaction */
      if (tdb->transaction->elements == NULL) {
            tdb_transaction_cancel(tdb);
            return 0;
      }

      methods = tdb->transaction->io_methods;
      
      /* if there are any locks pending then the caller has not
         nested their locks properly, so fail the transaction */
      if (tdb->num_locks || tdb->global_lock.count) {
            tdb->ecode = TDB_ERR_LOCK;
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: locks pending on commit\n"));
            tdb_transaction_cancel(tdb);
            return -1;
      }

      /* upgrade the main transaction lock region to a write lock */
      if (tdb_brlock_upgrade(tdb, FREELIST_TOP, 0) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_start: failed to upgrade hash locks\n"));
            tdb->ecode = TDB_ERR_LOCK;
            tdb_transaction_cancel(tdb);
            return -1;
      }

      /* get the global lock - this prevents new users attaching to the database
         during the commit */
      if (tdb_brlock(tdb, GLOBAL_LOCK, F_WRLCK, F_SETLKW, 0, 1) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_transaction_commit: failed to get global lock\n"));
            tdb->ecode = TDB_ERR_LOCK;
            tdb_transaction_cancel(tdb);
            return -1;
      }

      if (!(tdb->flags & TDB_NOSYNC)) {
            /* write the recovery data to the end of the file */
            if (transaction_setup_recovery(tdb, &magic_offset) == -1) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: failed to setup recovery data\n"));
                  tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);
                  tdb_transaction_cancel(tdb);
                  return -1;
            }
      }

      /* expand the file to the new size if needed */
      if (tdb->map_size != tdb->transaction->old_map_size) {
            if (methods->tdb_expand_file(tdb, tdb->transaction->old_map_size, 
                                   tdb->map_size - 
                                   tdb->transaction->old_map_size) == -1) {
                  tdb->ecode = TDB_ERR_IO;
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: expansion failed\n"));
                  tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);
                  tdb_transaction_cancel(tdb);
                  return -1;
            }
            tdb->map_size = tdb->transaction->old_map_size;
            methods->tdb_oob(tdb, tdb->map_size + 1, 1);
      }

      /* perform all the writes */
      while (tdb->transaction->elements) {
            struct tdb_transaction_el *el = tdb->transaction->elements;

            if (methods->tdb_write(tdb, el->offset, el->data, el->length) == -1) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: write failed during commit\n"));
                  
                  /* we've overwritten part of the data and
                     possibly expanded the file, so we need to
                     run the crash recovery code */
                  tdb->methods = methods;
                  tdb_transaction_recover(tdb); 

                  tdb_transaction_cancel(tdb);
                  tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);

                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: write failed\n"));
                  return -1;
            }
            tdb->transaction->elements = el->next;
            free(el->data); 
            free(el);
      } 

      if (!(tdb->flags & TDB_NOSYNC)) {
            /* ensure the new data is on disk */
            if (transaction_sync(tdb, 0, tdb->map_size) == -1) {
                  return -1;
            }

            /* remove the recovery marker */
            if (methods->tdb_write(tdb, magic_offset, &zero, 4) == -1) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_commit: failed to remove recovery magic\n"));
                  return -1;
            }

            /* ensure the recovery marker has been removed on disk */
            if (transaction_sync(tdb, magic_offset, 4) == -1) {
                  return -1;
            }
      }

      tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1);

      /*
        TODO: maybe write to some dummy hdr field, or write to magic
        offset without mmap, before the last sync, instead of the
        utime() call
      */

      /* on some systems (like Linux 2.6.x) changes via mmap/msync
         don't change the mtime of the file, this means the file may
         not be backed up (as tdb rounding to block sizes means that
         file size changes are quite rare too). The following forces
         mtime changes when a transaction completes */
#ifdef HAVE_UTIME
      utime(tdb->name, NULL);
#endif

      /* use a transaction cancel to free memory and remove the
         transaction locks */
      tdb_transaction_cancel(tdb);
      return 0;
}


/*
  recover from an aborted transaction. Must be called with exclusive
  database write access already established (including the global
  lock to prevent new processes attaching)
*/
int tdb_transaction_recover(struct tdb_context *tdb)
{
      tdb_off_t recovery_head, recovery_eof;
      unsigned char *data, *p;
      u32 zero = 0;
      struct list_struct rec;

      /* find the recovery area */
      if (tdb_ofs_read(tdb, TDB_RECOVERY_HEAD, &recovery_head) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery head\n"));
            tdb->ecode = TDB_ERR_IO;
            return -1;
      }

      if (recovery_head == 0) {
            /* we have never allocated a recovery record */
            return 0;
      }

      /* read the recovery record */
      if (tdb->methods->tdb_read(tdb, recovery_head, &rec, 
                           sizeof(rec), DOCONV()) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery record\n"));         
            tdb->ecode = TDB_ERR_IO;
            return -1;
      }

      if (rec.magic != TDB_RECOVERY_MAGIC) {
            /* there is no valid recovery data */
            return 0;
      }

      if (tdb->read_only) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: attempt to recover read only database\n"));
            tdb->ecode = TDB_ERR_CORRUPT;
            return -1;
      }

      recovery_eof = rec.key_len;

      data = (unsigned char *)malloc(rec.data_len);
      if (data == NULL) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to allocate recovery data\n"));       
            tdb->ecode = TDB_ERR_OOM;
            return -1;
      }

      /* read the full recovery data */
      if (tdb->methods->tdb_read(tdb, recovery_head + sizeof(rec), data,
                           rec.data_len, 0) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to read recovery data\n"));           
            tdb->ecode = TDB_ERR_IO;
            return -1;
      }

      /* recover the file data */
      p = data;
      while (p+8 < data + rec.data_len) {
            u32 ofs, len;
            if (DOCONV()) {
                  tdb_convert(p, 8);
            }
            memcpy(&ofs, p, 4);
            memcpy(&len, p+4, 4);

            if (tdb->methods->tdb_write(tdb, ofs, p+8, len) == -1) {
                  free(data);
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to recover %d bytes at offset %d\n", len, ofs));
                  tdb->ecode = TDB_ERR_IO;
                  return -1;
            }
            p += 8 + len;
      }

      free(data);

      if (transaction_sync(tdb, 0, tdb->map_size) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to sync recovery\n"));
            tdb->ecode = TDB_ERR_IO;
            return -1;
      }

      /* if the recovery area is after the recovered eof then remove it */
      if (recovery_eof <= recovery_head) {
            if (tdb_ofs_write(tdb, TDB_RECOVERY_HEAD, &zero) == -1) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to remove recovery head\n"));
                  tdb->ecode = TDB_ERR_IO;
                  return -1;              
            }
      }

      /* remove the recovery magic */
      if (tdb_ofs_write(tdb, recovery_head + offsetof(struct list_struct, magic), 
                    &zero) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to remove recovery magic\n"));
            tdb->ecode = TDB_ERR_IO;
            return -1;              
      }
      
      /* reduce the file size to the old size */
      tdb_munmap(tdb);
      if (ftruncate(tdb->fd, recovery_eof) != 0) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to reduce to recovery size\n"));
            tdb->ecode = TDB_ERR_IO;
            return -1;              
      }
      tdb->map_size = recovery_eof;
      tdb_mmap(tdb);

      if (transaction_sync(tdb, 0, recovery_eof) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_transaction_recover: failed to sync2 recovery\n"));
            tdb->ecode = TDB_ERR_IO;
            return -1;
      }

      TDB_LOG((tdb, TDB_DEBUG_TRACE, "tdb_transaction_recover: recovered %d byte database\n", 
             recovery_eof));

      /* all done */
      return 0;
}

/* file: freelist.c */

/* read a freelist record and check for simple errors */
static int tdb_rec_free_read(struct tdb_context *tdb, tdb_off_t off, struct list_struct *rec)
{
      if (tdb->methods->tdb_read(tdb, off, rec, sizeof(*rec),DOCONV()) == -1)
            return -1;

      if (rec->magic == TDB_MAGIC) {
            /* this happens when a app is showdown while deleting a record - we should
               not completely fail when this happens */
            TDB_LOG((tdb, TDB_DEBUG_WARNING, "tdb_rec_free_read non-free magic 0x%x at offset=%d - fixing\n", 
                   rec->magic, off));
            rec->magic = TDB_FREE_MAGIC;
            if (tdb->methods->tdb_write(tdb, off, rec, sizeof(*rec)) == -1)
                  return -1;
      }

      if (rec->magic != TDB_FREE_MAGIC) {
            /* Ensure ecode is set for log fn. */
            tdb->ecode = TDB_ERR_CORRUPT;
            TDB_LOG((tdb, TDB_DEBUG_WARNING, "tdb_rec_free_read bad magic 0x%x at offset=%d\n", 
                     rec->magic, off));
            return TDB_ERRCODE(TDB_ERR_CORRUPT, -1);
      }
      if (tdb->methods->tdb_oob(tdb, rec->next+sizeof(*rec), 0) != 0)
            return -1;
      return 0;
}



/* Remove an element from the freelist.  Must have alloc lock. */
static int remove_from_freelist(struct tdb_context *tdb, tdb_off_t off, tdb_off_t next)
{
      tdb_off_t last_ptr, i;

      /* read in the freelist top */
      last_ptr = FREELIST_TOP;
      while (tdb_ofs_read(tdb, last_ptr, &i) != -1 && i != 0) {
            if (i == off) {
                  /* We've found it! */
                  return tdb_ofs_write(tdb, last_ptr, &next);
            }
            /* Follow chain (next offset is at start of record) */
            last_ptr = i;
      }
      TDB_LOG((tdb, TDB_DEBUG_FATAL,"remove_from_freelist: not on list at off=%d\n", off));
      return TDB_ERRCODE(TDB_ERR_CORRUPT, -1);
}


/* update a record tailer (must hold allocation lock) */
static int update_tailer(struct tdb_context *tdb, tdb_off_t offset,
                   const struct list_struct *rec)
{
      tdb_off_t totalsize;

      /* Offset of tailer from record header */
      totalsize = sizeof(*rec) + rec->rec_len;
      return tdb_ofs_write(tdb, offset + totalsize - sizeof(tdb_off_t),
                   &totalsize);
}

/* Add an element into the freelist. Merge adjacent records if
   neccessary. */
int tdb_free(struct tdb_context *tdb, tdb_off_t offset, struct list_struct *rec)
{
      tdb_off_t right, left;

      /* Allocation and tailer lock */
      if (tdb_lock(tdb, -1, F_WRLCK) != 0)
            return -1;

      /* set an initial tailer, so if we fail we don't leave a bogus record */
      if (update_tailer(tdb, offset, rec) != 0) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: update_tailer failed!\n"));
            goto fail;
      }

      /* Look right first (I'm an Australian, dammit) */
      right = offset + sizeof(*rec) + rec->rec_len;
      if (right + sizeof(*rec) <= tdb->map_size) {
            struct list_struct r;

            if (tdb->methods->tdb_read(tdb, right, &r, sizeof(r), DOCONV()) == -1) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: right read failed at %u\n", right));
                  goto left;
            }

            /* If it's free, expand to include it. */
            if (r.magic == TDB_FREE_MAGIC) {
                  if (remove_from_freelist(tdb, right, r.next) == -1) {
                        TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: right free failed at %u\n", right));
                        goto left;
                  }
                  rec->rec_len += sizeof(r) + r.rec_len;
            }
      }

left:
      /* Look left */
      left = offset - sizeof(tdb_off_t);
      if (left > TDB_DATA_START(tdb->header.hash_size)) {
            struct list_struct l;
            tdb_off_t leftsize;
            
            /* Read in tailer and jump back to header */
            if (tdb_ofs_read(tdb, left, &leftsize) == -1) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: left offset read failed at %u\n", left));
                  goto update;
            }

            /* it could be uninitialised data */
            if (leftsize == 0 || leftsize == TDB_PAD_U32) {
                  goto update;
            }

            left = offset - leftsize;

            /* Now read in record */
            if (tdb->methods->tdb_read(tdb, left, &l, sizeof(l), DOCONV()) == -1) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: left read failed at %u (%u)\n", left, leftsize));
                  goto update;
            }

            /* If it's free, expand to include it. */
            if (l.magic == TDB_FREE_MAGIC) {
                  if (remove_from_freelist(tdb, left, l.next) == -1) {
                        TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: left free failed at %u\n", left));
                        goto update;
                  } else {
                        offset = left;
                        rec->rec_len += leftsize;
                  }
            }
      }

update:
      if (update_tailer(tdb, offset, rec) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free: update_tailer failed at %u\n", offset));
            goto fail;
      }

      /* Now, prepend to free list */
      rec->magic = TDB_FREE_MAGIC;

      if (tdb_ofs_read(tdb, FREELIST_TOP, &rec->next) == -1 ||
          tdb_rec_write(tdb, offset, rec) == -1 ||
          tdb_ofs_write(tdb, FREELIST_TOP, &offset) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_free record write failed at offset=%d\n", offset));
            goto fail;
      }

      /* And we're done. */
      tdb_unlock(tdb, -1, F_WRLCK);
      return 0;

 fail:
      tdb_unlock(tdb, -1, F_WRLCK);
      return -1;
}


/* 
   the core of tdb_allocate - called when we have decided which
   free list entry to use
 */
static tdb_off_t tdb_allocate_ofs(struct tdb_context *tdb, tdb_len_t length, tdb_off_t rec_ptr,
                        struct list_struct *rec, tdb_off_t last_ptr)
{
      struct list_struct newrec;
      tdb_off_t newrec_ptr;

      memset(&newrec, '\0', sizeof(newrec));

      /* found it - now possibly split it up  */
      if (rec->rec_len > length + MIN_REC_SIZE) {
            /* Length of left piece */
            length = TDB_ALIGN(length, TDB_ALIGNMENT);
            
            /* Right piece to go on free list */
            newrec.rec_len = rec->rec_len - (sizeof(*rec) + length);
            newrec_ptr = rec_ptr + sizeof(*rec) + length;
            
            /* And left record is shortened */
            rec->rec_len = length;
      } else {
            newrec_ptr = 0;
      }
      
      /* Remove allocated record from the free list */
      if (tdb_ofs_write(tdb, last_ptr, &rec->next) == -1) {
            return 0;
      }
      
      /* Update header: do this before we drop alloc
         lock, otherwise tdb_free() might try to
         merge with us, thinking we're free.
         (Thanks Jeremy Allison). */
      rec->magic = TDB_MAGIC;
      if (tdb_rec_write(tdb, rec_ptr, rec) == -1) {
            return 0;
      }
      
      /* Did we create new block? */
      if (newrec_ptr) {
            /* Update allocated record tailer (we
               shortened it). */
            if (update_tailer(tdb, rec_ptr, rec) == -1) {
                  return 0;
            }
            
            /* Free new record */
            if (tdb_free(tdb, newrec_ptr, &newrec) == -1) {
                  return 0;
            }
      }
      
      /* all done - return the new record offset */
      return rec_ptr;
}

/* allocate some space from the free list. The offset returned points
   to a unconnected list_struct within the database with room for at
   least length bytes of total data

   0 is returned if the space could not be allocated
 */
tdb_off_t tdb_allocate(struct tdb_context *tdb, tdb_len_t length, struct list_struct *rec)
{
      tdb_off_t rec_ptr, last_ptr, newrec_ptr;
      struct {
            tdb_off_t rec_ptr, last_ptr;
            tdb_len_t rec_len;
      } bestfit;

      if (tdb_lock(tdb, -1, F_WRLCK) == -1)
            return 0;

      /* Extra bytes required for tailer */
      length += sizeof(tdb_off_t);

 again:
      last_ptr = FREELIST_TOP;

      /* read in the freelist top */
      if (tdb_ofs_read(tdb, FREELIST_TOP, &rec_ptr) == -1)
            goto fail;

      bestfit.rec_ptr = 0;
      bestfit.last_ptr = 0;
      bestfit.rec_len = 0;

      /* 
         this is a best fit allocation strategy. Originally we used
         a first fit strategy, but it suffered from massive fragmentation
         issues when faced with a slowly increasing record size.
       */
      while (rec_ptr) {
            if (tdb_rec_free_read(tdb, rec_ptr, rec) == -1) {
                  goto fail;
            }

            if (rec->rec_len >= length) {
                  if (bestfit.rec_ptr == 0 ||
                      rec->rec_len < bestfit.rec_len) {
                        bestfit.rec_len = rec->rec_len;
                        bestfit.rec_ptr = rec_ptr;
                        bestfit.last_ptr = last_ptr;
                        /* consider a fit to be good enough if
                           we aren't wasting more than half
                           the space */
                        if (bestfit.rec_len < 2*length) {
                              break;
                        }
                  }
            }

            /* move to the next record */
            last_ptr = rec_ptr;
            rec_ptr = rec->next;
      }

      if (bestfit.rec_ptr != 0) {
            if (tdb_rec_free_read(tdb, bestfit.rec_ptr, rec) == -1) {
                  goto fail;
            }

            newrec_ptr = tdb_allocate_ofs(tdb, length, bestfit.rec_ptr, rec, bestfit.last_ptr);
            tdb_unlock(tdb, -1, F_WRLCK);
            return newrec_ptr;
      }

      /* we didn't find enough space. See if we can expand the
         database and if we can then try again */
      if (tdb_expand(tdb, length + sizeof(*rec)) == 0)
            goto again;
 fail:
      tdb_unlock(tdb, -1, F_WRLCK);
      return 0;
}

/* file: freelistcheck.c */

/* Check the freelist is good and contains no loops.
   Very memory intensive - only do this as a consistency
   checker. Heh heh - uses an in memory tdb as the storage
   for the "seen" record list. For some reason this strikes
   me as extremely clever as I don't have to write another tree
   data structure implementation :-).
 */

static int seen_insert(struct tdb_context *mem_tdb, tdb_off_t rec_ptr)
{
      TDB_DATA key, data;

      memset(&data, '\0', sizeof(data));
      key.dptr = (unsigned char *)&rec_ptr;
      key.dsize = sizeof(rec_ptr);
      return tdb_store(mem_tdb, key, data, TDB_INSERT);
}

int tdb_validate_freelist(struct tdb_context *tdb, int *pnum_entries)
{
      struct tdb_context *mem_tdb = NULL;
      struct list_struct rec;
      tdb_off_t rec_ptr, last_ptr;
      int ret = -1;

      *pnum_entries = 0;

      mem_tdb = tdb_open("flval", tdb->header.hash_size,
                        TDB_INTERNAL, O_RDWR, 0600);
      if (!mem_tdb) {
            return -1;
      }

      if (tdb_lock(tdb, -1, F_WRLCK) == -1) {
            tdb_close(mem_tdb);
            return 0;
      }

      last_ptr = FREELIST_TOP;

      /* Store the FREELIST_TOP record. */
      if (seen_insert(mem_tdb, last_ptr) == -1) {
            ret = TDB_ERRCODE(TDB_ERR_CORRUPT, -1);
            goto fail;
      }

      /* read in the freelist top */
      if (tdb_ofs_read(tdb, FREELIST_TOP, &rec_ptr) == -1) {
            goto fail;
      }

      while (rec_ptr) {

            /* If we can't store this record (we've seen it
               before) then the free list has a loop and must
               be corrupt. */

            if (seen_insert(mem_tdb, rec_ptr)) {
                  ret = TDB_ERRCODE(TDB_ERR_CORRUPT, -1);
                  goto fail;
            }

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

            /* move to the next record */
            last_ptr = rec_ptr;
            rec_ptr = rec.next;
            *pnum_entries += 1;
      }

      ret = 0;

  fail:

      tdb_close(mem_tdb);
      tdb_unlock(tdb, -1, F_WRLCK);
      return ret;
}

/* file: traverse.c */

/* Uses traverse lock: 0 = finish, -1 = error, other = record offset */
static int tdb_next_lock(struct tdb_context *tdb, struct tdb_traverse_lock *tlock,
                   struct list_struct *rec)
{
      int want_next = (tlock->off != 0);

      /* Lock each chain from the start one. */
      for (; tlock->hash < tdb->header.hash_size; tlock->hash++) {
            if (!tlock->off && tlock->hash != 0) {
                  /* this is an optimisation for the common case where
                     the hash chain is empty, which is particularly
                     common for the use of tdb with ldb, where large
                     hashes are used. In that case we spend most of our
                     time in tdb_brlock(), locking empty hash chains.
                     
                     To avoid this, we do an unlocked pre-check to see
                     if the hash chain is empty before starting to look
                     inside it. If it is empty then we can avoid that
                     hash chain. If it isn't empty then we can't believe
                     the value we get back, as we read it without a
                     lock, so instead we get the lock and re-fetch the
                     value below.
                     
                     Notice that not doing this optimisation on the
                     first hash chain is critical. We must guarantee
                     that we have done at least one fcntl lock at the
                     start of a search to guarantee that memory is
                     coherent on SMP systems. If records are added by
                     others during the search then thats OK, and we
                     could possibly miss those with this trick, but we
                     could miss them anyway without this trick, so the
                     semantics don't change.
                     
                     With a non-indexed ldb search this trick gains us a
                     factor of around 80 in speed on a linux 2.6.x
                     system (testing using ldbtest).
                  */
                  tdb->methods->next_hash_chain(tdb, &tlock->hash);
                  if (tlock->hash == tdb->header.hash_size) {
                        continue;
                  }
            }

            if (tdb_lock(tdb, tlock->hash, tlock->lock_rw) == -1)
                  return -1;

            /* No previous record?  Start at top of chain. */
            if (!tlock->off) {
                  if (tdb_ofs_read(tdb, TDB_HASH_TOP(tlock->hash),
                             &tlock->off) == -1)
                        goto fail;
            } else {
                  /* Otherwise unlock the previous record. */
                  if (tdb_unlock_record(tdb, tlock->off) != 0)
                        goto fail;
            }

            if (want_next) {
                  /* We have offset of old record: grab next */
                  if (tdb_rec_read(tdb, tlock->off, rec) == -1)
                        goto fail;
                  tlock->off = rec->next;
            }

            /* Iterate through chain */
            while( tlock->off) {
                  tdb_off_t current;
                  if (tdb_rec_read(tdb, tlock->off, rec) == -1)
                        goto fail;

                  /* Detect infinite loops. From "Shlomi Yaakobovich" <Shlomi@exanet.com>. */
                  if (tlock->off == rec->next) {
                        TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_next_lock: loop detected.\n"));
                        goto fail;
                  }

                  if (!TDB_DEAD(rec)) {
                        /* Woohoo: we found one! */
                        if (tdb_lock_record(tdb, tlock->off) != 0)
                              goto fail;
                        return tlock->off;
                  }

                  /* Try to clean dead ones from old traverses */
                  current = tlock->off;
                  tlock->off = rec->next;
                  if (!(tdb->read_only || tdb->traverse_read) && 
                      tdb_do_delete(tdb, current, rec) != 0)
                        goto fail;
            }
            tdb_unlock(tdb, tlock->hash, tlock->lock_rw);
            want_next = 0;
      }
      /* We finished iteration without finding anything */
      return TDB_ERRCODE(TDB_SUCCESS, 0);

 fail:
      tlock->off = 0;
      if (tdb_unlock(tdb, tlock->hash, tlock->lock_rw) != 0)
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_next_lock: On error unlock failed!\n"));
      return -1;
}

/* traverse the entire database - calling fn(tdb, key, data) on each element.
   return -1 on error or the record count traversed
   if fn is NULL then it is not called
   a non-zero return value from fn() indicates that the traversal should stop
  */
static int tdb_traverse_internal(struct tdb_context *tdb, 
                         tdb_traverse_func fn, void *private_data,
                         struct tdb_traverse_lock *tl)
{
      TDB_DATA key, dbuf;
      struct list_struct rec;
      int ret, count = 0;

      /* This was in the initializaton, above, but the IRIX compiler
       * did not like it.  crh
       */
      tl->next = tdb->travlocks.next;

      /* fcntl locks don't stack: beware traverse inside traverse */
      tdb->travlocks.next = tl;

      /* tdb_next_lock places locks on the record returned, and its chain */
      while ((ret = tdb_next_lock(tdb, tl, &rec)) > 0) {
            count++;
            /* now read the full record */
            key.dptr = tdb_alloc_read(tdb, tl->off + sizeof(rec), 
                                rec.key_len + rec.data_len);
            if (!key.dptr) {
                  ret = -1;
                  if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0)
                        goto out;
                  if (tdb_unlock_record(tdb, tl->off) != 0)
                        TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: key.dptr == NULL and unlock_record failed!\n"));
                  goto out;
            }
            key.dsize = rec.key_len;
            dbuf.dptr = key.dptr + rec.key_len;
            dbuf.dsize = rec.data_len;

            /* Drop chain lock, call out */
            if (tdb_unlock(tdb, tl->hash, tl->lock_rw) != 0) {
                  ret = -1;
                  SAFE_FREE(key.dptr);
                  goto out;
            }
            if (fn && fn(tdb, key, dbuf, private_data)) {
                  /* They want us to terminate traversal */
                  ret = count;
                  if (tdb_unlock_record(tdb, tl->off) != 0) {
                        TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_traverse: unlock_record failed!\n"));;
                        ret = -1;
                  }
                  SAFE_FREE(key.dptr);
                  goto out;
            }
            SAFE_FREE(key.dptr);
      }
out:
      tdb->travlocks.next = tl->next;
      if (ret < 0)
            return -1;
      else
            return count;
}


/*
  a write style traverse - temporarily marks the db read only
*/
int tdb_traverse_read(struct tdb_context *tdb, 
                  tdb_traverse_func fn, void *private_data)
{
      struct tdb_traverse_lock tl = { NULL, 0, 0, F_RDLCK };
      int ret;

      /* we need to get a read lock on the transaction lock here to
         cope with the lock ordering semantics of solaris10 */
      if (tdb_transaction_lock(tdb, F_RDLCK)) {
            return -1;
      }

      tdb->traverse_read++;
      ret = tdb_traverse_internal(tdb, fn, private_data, &tl);
      tdb->traverse_read--;

      tdb_transaction_unlock(tdb);

      return ret;
}

/*
  a write style traverse - needs to get the transaction lock to
  prevent deadlocks
*/
int tdb_traverse(struct tdb_context *tdb, 
             tdb_traverse_func fn, void *private_data)
{
      struct tdb_traverse_lock tl = { NULL, 0, 0, F_WRLCK };
      int ret;

      if (tdb->read_only || tdb->traverse_read) {
            return tdb_traverse_read(tdb, fn, private_data);
      }
      
      if (tdb_transaction_lock(tdb, F_WRLCK)) {
            return -1;
      }

      ret = tdb_traverse_internal(tdb, fn, private_data, &tl);

      tdb_transaction_unlock(tdb);

      return ret;
}


/* find the first entry in the database and return its key */
TDB_DATA tdb_firstkey(struct tdb_context *tdb)
{
      TDB_DATA key;
      struct list_struct rec;

      /* release any old lock */
      if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0)
            return tdb_null;
      tdb->travlocks.off = tdb->travlocks.hash = 0;
      tdb->travlocks.lock_rw = F_RDLCK;

      /* Grab first record: locks chain and returned record. */
      if (tdb_next_lock(tdb, &tdb->travlocks, &rec) <= 0)
            return tdb_null;
      /* now read the key */
      key.dsize = rec.key_len;
      key.dptr =tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),key.dsize);

      /* Unlock the hash chain of the record we just read. */
      if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
      return key;
}

/* find the next entry in the database, returning its key */
TDB_DATA tdb_nextkey(struct tdb_context *tdb, TDB_DATA oldkey)
{
      u32 oldhash;
      TDB_DATA key = tdb_null;
      struct list_struct rec;
      unsigned char *k = NULL;

      /* Is locked key the old key?  If so, traverse will be reliable. */
      if (tdb->travlocks.off) {
            if (tdb_lock(tdb,tdb->travlocks.hash,tdb->travlocks.lock_rw))
                  return tdb_null;
            if (tdb_rec_read(tdb, tdb->travlocks.off, &rec) == -1
                || !(k = tdb_alloc_read(tdb,tdb->travlocks.off+sizeof(rec),
                                  rec.key_len))
                || memcmp(k, oldkey.dptr, oldkey.dsize) != 0) {
                  /* No, it wasn't: unlock it and start from scratch */
                  if (tdb_unlock_record(tdb, tdb->travlocks.off) != 0) {
                        SAFE_FREE(k);
                        return tdb_null;
                  }
                  if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0) {
                        SAFE_FREE(k);
                        return tdb_null;
                  }
                  tdb->travlocks.off = 0;
            }

            SAFE_FREE(k);
      }

      if (!tdb->travlocks.off) {
            /* No previous element: do normal find, and lock record */
            tdb->travlocks.off = tdb_find_lock_hash(tdb, oldkey, tdb->hash_fn(&oldkey), tdb->travlocks.lock_rw, &rec);
            if (!tdb->travlocks.off)
                  return tdb_null;
            tdb->travlocks.hash = BUCKET(rec.full_hash);
            if (tdb_lock_record(tdb, tdb->travlocks.off) != 0) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: lock_record failed (%s)!\n", strerror(errno)));
                  return tdb_null;
            }
      }
      oldhash = tdb->travlocks.hash;

      /* Grab next record: locks chain and returned record,
         unlocks old record */
      if (tdb_next_lock(tdb, &tdb->travlocks, &rec) > 0) {
            key.dsize = rec.key_len;
            key.dptr = tdb_alloc_read(tdb, tdb->travlocks.off+sizeof(rec),
                                key.dsize);
            /* Unlock the chain of this new record */
            if (tdb_unlock(tdb, tdb->travlocks.hash, tdb->travlocks.lock_rw) != 0)
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
      }
      /* Unlock the chain of old record */
      if (tdb_unlock(tdb, BUCKET(oldhash), tdb->travlocks.lock_rw) != 0)
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
      return key;
}

/* file: dump.c */

static tdb_off_t tdb_dump_record(struct tdb_context *tdb, int hash,
                         tdb_off_t offset)
{
      struct list_struct rec;
      tdb_off_t tailer_ofs, tailer;

      if (tdb->methods->tdb_read(tdb, offset, (char *)&rec, 
                           sizeof(rec), DOCONV()) == -1) {
            printf("ERROR: failed to read record at %u\n", offset);
            return 0;
      }

      printf(" rec: hash=%d offset=0x%08x next=0x%08x rec_len=%d "
             "key_len=%d data_len=%d full_hash=0x%x magic=0x%x\n",
             hash, offset, rec.next, rec.rec_len, rec.key_len, rec.data_len,
             rec.full_hash, rec.magic);

      tailer_ofs = offset + sizeof(rec) + rec.rec_len - sizeof(tdb_off_t);

      if (tdb_ofs_read(tdb, tailer_ofs, &tailer) == -1) {
            printf("ERROR: failed to read tailer at %u\n", tailer_ofs);
            return rec.next;
      }

      if (tailer != rec.rec_len + sizeof(rec)) {
            printf("ERROR: tailer does not match record! tailer=%u totalsize=%u\n",
                        (unsigned int)tailer, (unsigned int)(rec.rec_len + sizeof(rec)));
      }
      return rec.next;
}

static int tdb_dump_chain(struct tdb_context *tdb, int i)
{
      tdb_off_t rec_ptr, top;

      top = TDB_HASH_TOP(i);

      if (tdb_lock(tdb, i, F_WRLCK) != 0)
            return -1;

      if (tdb_ofs_read(tdb, top, &rec_ptr) == -1)
            return tdb_unlock(tdb, i, F_WRLCK);

      if (rec_ptr)
            printf("hash=%d\n", i);

      while (rec_ptr) {
            rec_ptr = tdb_dump_record(tdb, i, rec_ptr);
      }

      return tdb_unlock(tdb, i, F_WRLCK);
}

void tdb_dump_all(struct tdb_context *tdb)
{
      int i;
      for (i=0;i<tdb->header.hash_size;i++) {
            tdb_dump_chain(tdb, i);
      }
      printf("freelist:\n");
      tdb_dump_chain(tdb, -1);
}

int tdb_printfreelist(struct tdb_context *tdb)
{
      int ret;
      long total_free = 0;
      tdb_off_t offset, rec_ptr;
      struct list_struct rec;

      if ((ret = tdb_lock(tdb, -1, F_WRLCK)) != 0)
            return ret;

      offset = FREELIST_TOP;

      /* read in the freelist top */
      if (tdb_ofs_read(tdb, offset, &rec_ptr) == -1) {
            tdb_unlock(tdb, -1, F_WRLCK);
            return 0;
      }

      printf("freelist top=[0x%08x]\n", rec_ptr );
      while (rec_ptr) {
            if (tdb->methods->tdb_read(tdb, rec_ptr, (char *)&rec, 
                                 sizeof(rec), DOCONV()) == -1) {
                  tdb_unlock(tdb, -1, F_WRLCK);
                  return -1;
            }

            if (rec.magic != TDB_FREE_MAGIC) {
                  printf("bad magic 0x%08x in free list\n", rec.magic);
                  tdb_unlock(tdb, -1, F_WRLCK);
                  return -1;
            }

            printf("entry offset=[0x%08x], rec.rec_len = [0x%08x (%d)] (end = 0x%08x)\n", 
                   rec_ptr, rec.rec_len, rec.rec_len, rec_ptr + rec.rec_len);
            total_free += rec.rec_len;

            /* move to the next record */
            rec_ptr = rec.next;
      }
      printf("total rec_len = [0x%08x (%d)]\n", (int)total_free, 
               (int)total_free);

      return tdb_unlock(tdb, -1, F_WRLCK);
}

/* file: tdb.c */

TDB_DATA tdb_null;

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

/*
  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)
{
      if (!(tdb->flags & TDB_SEQNUM)) {
            return;
      }

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

      tdb_increment_seqnum_nonblock(tdb);

      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 = (unsigned char *)malloc(new_dbuf.dsize);
      } else {
            unsigned char *new_dptr = (unsigned 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;
}


/*
  enable sequence number handling on an open tdb
*/
void tdb_enable_seqnum(struct tdb_context *tdb)
{
      tdb->flags |= TDB_SEQNUM;
}

/* file: open.c */

/* all contexts, to ensure no double-opens (fcntl locks don't nest!) */
static struct tdb_context *tdbs = NULL;


/* This is based on the hash algorithm from gdbm */
static unsigned int default_tdb_hash(TDB_DATA *key)
{
      u32 value;  /* Used to compute the hash value.  */
      u32   i;    /* Used to cycle through random values. */

      /* Set the initial value from the key size. */
      for (value = 0x238F13AF * key->dsize, i=0; i < key->dsize; i++)
            value = (value + (key->dptr[i] << (i*5 % 24)));

      return (1103515243 * value + 12345);  
}


/* initialise a new database with a specified hash size */
static int tdb_new_database(struct tdb_context *tdb, int hash_size)
{
      struct tdb_header *newdb;
      int size, ret = -1;

      /* We make it up in memory, then write it out if not internal */
      size = sizeof(struct tdb_header) + (hash_size+1)*sizeof(tdb_off_t);
      if (!(newdb = (struct tdb_header *)calloc(size, 1)))
            return TDB_ERRCODE(TDB_ERR_OOM, -1);

      /* Fill in the header */
      newdb->version = TDB_VERSION;
      newdb->hash_size = hash_size;
      if (tdb->flags & TDB_INTERNAL) {
            tdb->map_size = size;
            tdb->map_ptr = (char *)newdb;
            memcpy(&tdb->header, newdb, sizeof(tdb->header));
            /* Convert the `ondisk' version if asked. */
            CONVERT(*newdb);
            return 0;
      }
      if (lseek(tdb->fd, 0, SEEK_SET) == -1)
            goto fail;

      if (ftruncate(tdb->fd, 0) == -1)
            goto fail;

      /* This creates an endian-converted header, as if read from disk */
      CONVERT(*newdb);
      memcpy(&tdb->header, newdb, sizeof(tdb->header));
      /* Don't endian-convert the magic food! */
      memcpy(newdb->magic_food, TDB_MAGIC_FOOD, strlen(TDB_MAGIC_FOOD)+1);
      if (write(tdb->fd, newdb, size) != size) {
            ret = -1;
      } else {
            ret = 0;
      }

  fail:
      SAFE_FREE(newdb);
      return ret;
}



static int tdb_already_open(dev_t device,
                      ino_t ino)
{
      struct tdb_context *i;
      
      for (i = tdbs; i; i = i->next) {
            if (i->device == device && i->inode == ino) {
                  return 1;
            }
      }

      return 0;
}

/* open the database, creating it if necessary 

   The open_flags and mode are passed straight to the open call on the
   database file. A flags value of O_WRONLY is invalid. The hash size
   is advisory, use zero for a default value.

   Return is NULL on error, in which case errno is also set.  Don't 
   try to call tdb_error or tdb_errname, just do strerror(errno).

   @param name may be NULL for internal databases. */
struct tdb_context *tdb_open(const char *name, int hash_size, int tdb_flags,
                  int open_flags, mode_t mode)
{
      return tdb_open_ex(name, hash_size, tdb_flags, open_flags, mode, NULL, NULL);
}

/* a default logging function */
static void null_log_fn(struct tdb_context *tdb, enum tdb_debug_level level, const char *fmt, ...) PRINTF_ATTRIBUTE(3, 4);
static void null_log_fn(struct tdb_context *tdb, enum tdb_debug_level level, const char *fmt, ...)
{
}


struct tdb_context *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
                        int open_flags, mode_t mode,
                        const struct tdb_logging_context *log_ctx,
                        tdb_hash_func hash_fn)
{
      struct tdb_context *tdb;
      struct stat st;
      int rev = 0, locked = 0;
      unsigned char *vp;
      u32 vertest;

      if (!(tdb = (struct tdb_context *)calloc(1, sizeof *tdb))) {
            /* Can't log this */
            errno = ENOMEM;
            goto fail;
      }
      tdb_io_init(tdb);
      tdb->fd = -1;
      tdb->name = NULL;
      tdb->map_ptr = NULL;
      tdb->flags = tdb_flags;
      tdb->open_flags = open_flags;
      if (log_ctx) {
            tdb->log = *log_ctx;
      } else {
            tdb->log.log_fn = null_log_fn;
            tdb->log.log_private = NULL;
      }
      tdb->hash_fn = hash_fn ? hash_fn : default_tdb_hash;

      /* cache the page size */
      tdb->page_size = getpagesize();
      if (tdb->page_size <= 0) {
            tdb->page_size = 0x2000;
      }

      if ((open_flags & O_ACCMODE) == O_WRONLY) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: can't open tdb %s write-only\n",
                   name));
            errno = EINVAL;
            goto fail;
      }
      
      if (hash_size == 0)
            hash_size = DEFAULT_HASH_SIZE;
      if ((open_flags & O_ACCMODE) == O_RDONLY) {
            tdb->read_only = 1;
            /* read only databases don't do locking or clear if first */
            tdb->flags |= TDB_NOLOCK;
            tdb->flags &= ~TDB_CLEAR_IF_FIRST;
      }

      /* internal databases don't mmap or lock, and start off cleared */
      if (tdb->flags & TDB_INTERNAL) {
            tdb->flags |= (TDB_NOLOCK | TDB_NOMMAP);
            tdb->flags &= ~TDB_CLEAR_IF_FIRST;
            if (tdb_new_database(tdb, hash_size) != 0) {
                  TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: tdb_new_database failed!"));
                  goto fail;
            }
            goto internal;
      }

      if ((tdb->fd = open(name, open_flags, mode)) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_WARNING, "tdb_open_ex: could not open file %s: %s\n",
                   name, strerror(errno)));
            goto fail;  /* errno set by open(2) */
      }

      /* ensure there is only one process initialising at once */
      if (tdb->methods->tdb_brlock(tdb, GLOBAL_LOCK, F_WRLCK, F_SETLKW, 0, 1) == -1) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: failed to get global lock on %s: %s\n",
                   name, strerror(errno)));
            goto fail;  /* errno set by tdb_brlock */
      }

      /* we need to zero database if we are the only one with it open */
      if ((tdb_flags & TDB_CLEAR_IF_FIRST) &&
          (locked = (tdb->methods->tdb_brlock(tdb, ACTIVE_LOCK, F_WRLCK, F_SETLK, 0, 1) == 0))) {
            open_flags |= O_CREAT;
            if (ftruncate(tdb->fd, 0) == -1) {
                  TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_open_ex: "
                         "failed to truncate %s: %s\n",
                         name, strerror(errno)));
                  goto fail; /* errno set by ftruncate */
            }
      }

      if (read(tdb->fd, &tdb->header, sizeof(tdb->header)) != sizeof(tdb->header)
          || strcmp(tdb->header.magic_food, TDB_MAGIC_FOOD) != 0
          || (tdb->header.version != TDB_VERSION
            && !(rev = (tdb->header.version==TDB_BYTEREV(TDB_VERSION))))) {
            /* its not a valid database - possibly initialise it */
            if (!(open_flags & O_CREAT) || tdb_new_database(tdb, hash_size) == -1) {
                  errno = EIO; /* ie bad format or something */
                  goto fail;
            }
            rev = (tdb->flags & TDB_CONVERT);
      }
      vp = (unsigned char *)&tdb->header.version;
      vertest = (((u32)vp[0]) << 24) | (((u32)vp[1]) << 16) |
              (((u32)vp[2]) << 8) | (u32)vp[3];
      tdb->flags |= (vertest==TDB_VERSION) ? TDB_BIGENDIAN : 0;
      if (!rev)
            tdb->flags &= ~TDB_CONVERT;
      else {
            tdb->flags |= TDB_CONVERT;
            tdb_convert(&tdb->header, sizeof(tdb->header));
      }
      if (fstat(tdb->fd, &st) == -1)
            goto fail;

      if (tdb->header.rwlocks != 0) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: spinlocks no longer supported\n"));
            goto fail;
      }

      /* Is it already in the open list?  If so, fail. */
      if (tdb_already_open(st.st_dev, st.st_ino)) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: "
                   "%s (%d,%d) is already open in this process\n",
                   name, (int)st.st_dev, (int)st.st_ino));
            errno = EBUSY;
            goto fail;
      }

      if (!(tdb->name = (char *)strdup(name))) {
            errno = ENOMEM;
            goto fail;
      }

      tdb->map_size = st.st_size;
      tdb->device = st.st_dev;
      tdb->inode = st.st_ino;
      tdb->max_dead_records = 0;
      tdb_mmap(tdb);
      if (locked) {
            if (tdb->methods->tdb_brlock(tdb, ACTIVE_LOCK, F_UNLCK, F_SETLK, 0, 1) == -1) {
                  TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: "
                         "failed to take ACTIVE_LOCK on %s: %s\n",
                         name, strerror(errno)));
                  goto fail;
            }

      }

      /* We always need to do this if the CLEAR_IF_FIRST flag is set, even if
         we didn't get the initial exclusive lock as we need to let all other
         users know we're using it. */

      if (tdb_flags & TDB_CLEAR_IF_FIRST) {
            /* leave this lock in place to indicate it's in use */
            if (tdb->methods->tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0, 1) == -1)
                  goto fail;
      }

      /* if needed, run recovery */
      if (tdb_transaction_recover(tdb) == -1) {
            goto fail;
      }

 internal:
      /* Internal (memory-only) databases skip all the code above to
       * do with disk files, and resume here by releasing their
       * global lock and hooking into the active list. */
      if (tdb->methods->tdb_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0, 1) == -1)
            goto fail;
      tdb->next = tdbs;
      tdbs = tdb;
      return tdb;

 fail:
      { int save_errno = errno;

      if (!tdb)
            return NULL;
      
      if (tdb->map_ptr) {
            if (tdb->flags & TDB_INTERNAL)
                  SAFE_FREE(tdb->map_ptr);
            else
                  tdb_munmap(tdb);
      }
      SAFE_FREE(tdb->name);
      if (tdb->fd != -1)
            if (close(tdb->fd) != 0)
                  TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_open_ex: failed to close tdb->fd on error!\n"));
      SAFE_FREE(tdb);
      errno = save_errno;
      return NULL;
      }
}

/*
 * Set the maximum number of dead records per hash chain
 */

void tdb_set_max_dead(struct tdb_context *tdb, int max_dead)
{
      tdb->max_dead_records = max_dead;
}

/**
 * Close a database.
 *
 * @returns -1 for error; 0 for success.
 **/
int tdb_close(struct tdb_context *tdb)
{
      struct tdb_context **i;
      int ret = 0;

      if (tdb->transaction) {
            tdb_transaction_cancel(tdb);
      }

      if (tdb->map_ptr) {
            if (tdb->flags & TDB_INTERNAL)
                  SAFE_FREE(tdb->map_ptr);
            else
                  tdb_munmap(tdb);
      }
      SAFE_FREE(tdb->name);
      if (tdb->fd != -1)
            ret = close(tdb->fd);
      SAFE_FREE(tdb->lockrecs);

      /* Remove from contexts list */
      for (i = &tdbs; *i; i = &(*i)->next) {
            if (*i == tdb) {
                  *i = tdb->next;
                  break;
            }
      }

      memset(tdb, 0, sizeof(*tdb));
      SAFE_FREE(tdb);

      return ret;
}

/* register a loging function */
void tdb_set_logging_function(struct tdb_context *tdb,
                              const struct tdb_logging_context *log_ctx)
{
        tdb->log = *log_ctx;
}

void *tdb_get_logging_private(struct tdb_context *tdb)
{
      return tdb->log.log_private;
}

/* reopen a tdb - this can be used after a fork to ensure that we have an independent
   seek pointer from our parent and to re-establish locks */
int tdb_reopen(struct tdb_context *tdb)
{
      struct stat st;

      if (tdb->flags & TDB_INTERNAL) {
            return 0; /* Nothing to do. */
      }

      if (tdb->num_locks != 0 || tdb->global_lock.count) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_reopen: reopen not allowed with locks held\n"));
            goto fail;
      }

      if (tdb->transaction != 0) {
            TDB_LOG((tdb, TDB_DEBUG_ERROR, "tdb_reopen: reopen not allowed inside a transaction\n"));
            goto fail;
      }

      if (tdb_munmap(tdb) != 0) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: munmap failed (%s)\n", strerror(errno)));
            goto fail;
      }
      if (close(tdb->fd) != 0)
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: WARNING closing tdb->fd failed!\n"));
      tdb->fd = open(tdb->name, tdb->open_flags & ~(O_CREAT|O_TRUNC), 0);
      if (tdb->fd == -1) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: open failed (%s)\n", strerror(errno)));
            goto fail;
      }
      if ((tdb->flags & TDB_CLEAR_IF_FIRST) && 
          (tdb->methods->tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0, 1) == -1)) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: failed to obtain active lock\n"));
            goto fail;
      }
      if (fstat(tdb->fd, &st) != 0) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: fstat failed (%s)\n", strerror(errno)));
            goto fail;
      }
      if (st.st_ino != tdb->inode || st.st_dev != tdb->device) {
            TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_reopen: file dev/inode has changed!\n"));
            goto fail;
      }
      tdb_mmap(tdb);

      return 0;

fail:
      tdb_close(tdb);
      return -1;
}

/* reopen all tdb's */
int tdb_reopen_all(int parent_longlived)
{
      struct tdb_context *tdb;

      for (tdb=tdbs; tdb; tdb = tdb->next) {
            /*
             * If the parent is longlived (ie. a
             * parent daemon architecture), we know
             * it will keep it's active lock on a
             * tdb opened with CLEAR_IF_FIRST. Thus
             * for child processes we don't have to
             * add an active lock. This is essential
             * to improve performance on systems that
             * keep POSIX locks as a non-scalable data
             * structure in the kernel.
             */
            if (parent_longlived) {
                  /* Ensure no clear-if-first. */
                  tdb->flags &= ~TDB_CLEAR_IF_FIRST;
            }

            if (tdb_reopen(tdb) != 0)
                  return -1;
      }

      return 0;
}

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