Make xenstored use tdb, transactions can soft-fail (EAGAIN)

Transactions no longer take root dir, no longer lock & block: commit can fail spuriously with EAGAIN, not ETIMEDOUT.
Speeds up transactions by over 1000 times, should be NFS safe.
New program: xs_tdb_dump to dump raw TDB contents.
Don't do failure testing: we are no longer robust against all ENOMEM 8(
Introduce "struct node" which contains perms, children and data.
Make struct xs_permissions unpadded, so we can write to tdb w/o valgrind complaints.
Gently modify TDB to use talloc, not do alloc on tdb_delete.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 2151 insertions, 0 deletions

diff --git a/tools/xenstore/tdb.c b/tools/xenstore/tdb.c
new file mode 100644
index 0000000000..558d5fd16d
--- /dev/null
+++ b/tools/xenstore/tdb.c
@@ -0,0 +1,2151 @@
+ /* 
+   Unix SMB/CIFS implementation.
+
+   trivial database library
+
+   Copyright (C) Andrew Tridgell              1999-2004
+   Copyright (C) Paul `Rusty' Russell		   2000
+   Copyright (C) Jeremy Allison			   2000-2003
+   
+     ** NOTE! The following LGPL license applies to the tdb
+     ** library. This does NOT imply that all of Samba is released
+     ** under the LGPL
+   
+   This library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2 of the License, or (at your option) any later version.
+
+   This library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with this library; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+*/
+
+
+#ifndef _SAMBA_BUILD_
+#if HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include "tdb.h"
+#include <stdarg.h>
+#include "talloc.h"
+#define HAVE_MMAP
+#else
+#include "includes.h"
+#include "lib/tdb/include/tdb.h"
+#include "system/time.h"
+#include "system/shmem.h"
+#include "system/filesys.h"
+#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_ALIGNMENT 4
+#define MIN_REC_SIZE (2*sizeof(struct list_struct) + TDB_ALIGNMENT)
+#define DEFAULT_HASH_SIZE 131
+#define TDB_PAGE_SIZE 0x2000
+#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))
+#define TDB_DATA_START(hash_size) (TDB_HASH_TOP(hash_size-1))
+
+
+/* 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_fn x
+
+/* lock offsets */
+#define GLOBAL_LOCK 0
+#define ACTIVE_LOCK 4
+
+#ifndef MAP_FILE
+#define MAP_FILE 0
+#endif
+
+#ifndef MAP_FAILED
+#define MAP_FAILED ((void *)-1)
+#endif
+
+#ifndef discard_const_p
+# if defined(__intptr_t_defined) || defined(HAVE_INTPTR_T)
+#  define discard_const(ptr) ((void *)((intptr_t)(ptr)))
+# else
+#  define discard_const(ptr) ((void *)(ptr))
+# endif
+# define discard_const_p(type, ptr) ((type *)discard_const(ptr))
+#endif
+
+/* free memory if the pointer is valid and zero the pointer */
+#ifndef SAFE_FREE
+#define SAFE_FREE(x) do { if ((x) != NULL) {talloc_free(discard_const_p(void *, (x))); (x)=NULL;} } while(0)
+#endif
+
+#define BUCKET(hash) ((hash) % tdb->header.hash_size)
+TDB_DATA tdb_null;
+
+/* all contexts, to ensure no double-opens (fcntl locks don't nest!) */
+static TDB_CONTEXT *tdbs = NULL;
+
+static int tdb_munmap(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;
+}
+
+static void tdb_mmap(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, 2, "tdb_mmap failed for size %d (%s)\n", 
+				 tdb->map_size, strerror(errno)));
+		}
+	} else {
+		tdb->map_ptr = NULL;
+	}
+#else
+	tdb->map_ptr = NULL;
+#endif
+}
+
+/* Endian conversion: we only ever deal with 4 byte quantities */
+static void *convert(void *buf, u32 size)
+{
+	u32 i, *p = buf;
+	for (i = 0; i < size / 4; i++)
+		p[i] = TDB_BYTEREV(p[i]);
+	return buf;
+}
+#define DOCONV() (tdb->flags & TDB_CONVERT)
+#define CONVERT(x) (DOCONV() ? 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 next; /* offset of the next record in the list */
+	tdb_len rec_len; /* total byte length of record */
+	tdb_len key_len; /* byte length of key */
+	tdb_len 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)
+		}
+	*/
+};
+
+/* 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(). */
+static int tdb_brlock(TDB_CONTEXT *tdb, tdb_off offset, 
+		      int rw_type, int lck_type, int probe)
+{
+	struct flock fl;
+	int ret;
+
+	if (tdb->flags & TDB_NOLOCK)
+		return 0;
+	if ((rw_type == F_WRLCK) && (tdb->read_only)) {
+		errno = EACCES;
+		return -1;
+	}
+
+	fl.l_type = rw_type;
+	fl.l_whence = SEEK_SET;
+	fl.l_start = offset;
+	fl.l_len = 1;
+	fl.l_pid = 0;
+
+	do {
+		ret = fcntl(tdb->fd,lck_type,&fl);
+	} while (ret == -1 && errno == EINTR);
+
+	if (ret == -1) {
+		if (!probe && lck_type != F_SETLK) {
+			/* Ensure error code is set for log fun to examine. */
+			tdb->ecode = TDB_ERR_LOCK;
+			TDB_LOG((tdb, 5,"tdb_brlock failed (fd=%d) at offset %d rw_type=%d lck_type=%d\n", 
+				 tdb->fd, offset, rw_type, lck_type));
+		}
+		/* Generic lock error. errno set by fcntl.
+		 * EAGAIN is an expected return from non-blocking
+		 * locks. */
+		if (errno != EAGAIN) {
+		TDB_LOG((tdb, 5, "tdb_brlock failed (fd=%d) at offset %d rw_type=%d lck_type=%d: %s\n", 
+				 tdb->fd, offset, rw_type, lck_type, 
+				 strerror(errno)));
+		}
+		return TDB_ERRCODE(TDB_ERR_LOCK, -1);
+	}
+	return 0;
+}
+
+/* lock a list in the database. list -1 is the alloc list */
+static int tdb_lock(TDB_CONTEXT *tdb, int list, int ltype)
+{
+	if (list < -1 || list >= (int)tdb->header.hash_size) {
+		TDB_LOG((tdb, 0,"tdb_lock: invalid list %d for ltype=%d\n", 
+			   list, ltype));
+		return -1;
+	}
+	if (tdb->flags & TDB_NOLOCK)
+		return 0;
+
+	/* Since fcntl locks don't nest, we do a lock for the first one,
+	   and simply bump the count for future ones */
+	if (tdb->locked[list+1].count == 0) {
+		if (tdb_brlock(tdb,FREELIST_TOP+4*list,ltype,F_SETLKW, 0)) {
+			TDB_LOG((tdb, 0,"tdb_lock failed on list %d ltype=%d (%s)\n", 
+					   list, ltype, strerror(errno)));
+			return -1;
+		}
+		tdb->locked[list+1].ltype = ltype;
+	}
+	tdb->locked[list+1].count++;
+	return 0;
+}
+
+/* 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 */
+static int tdb_unlock(TDB_CONTEXT *tdb, int list,
+		      int ltype __attribute__((unused)))
+{
+	int ret = -1;
+
+	if (tdb->flags & TDB_NOLOCK)
+		return 0;
+
+	/* Sanity checks */
+	if (list < -1 || list >= (int)tdb->header.hash_size) {
+		TDB_LOG((tdb, 0, "tdb_unlock: list %d invalid (%d)\n", list, tdb->header.hash_size));
+		return ret;
+	}
+
+	if (tdb->locked[list+1].count==0) {
+		TDB_LOG((tdb, 0, "tdb_unlock: count is 0\n"));
+		return ret;
+	}
+
+	if (tdb->locked[list+1].count == 1) {
+		/* Down to last nested lock: unlock underneath */
+		ret = tdb_brlock(tdb, FREELIST_TOP+4*list, F_UNLCK, F_SETLKW, 0);
+	} else {
+		ret = 0;
+	}
+	tdb->locked[list+1].count--;
+
+	if (ret)
+		TDB_LOG((tdb, 0,"tdb_unlock: An error occurred unlocking!\n")); 
+	return ret;
+}
+
+/* This is based on the hash algorithm from gdbm */
+static u32 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);  
+}
+
+/* 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(TDB_CONTEXT *tdb, tdb_off 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, 0,"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 < (off_t)len) {
+		if (!probe) {
+			/* Ensure ecode is set for log fn. */
+			tdb->ecode = TDB_ERR_IO;
+			TDB_LOG((tdb, 0,"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(TDB_CONTEXT *tdb, tdb_off off, void *buf, tdb_len len)
+{
+	if (tdb_oob(tdb, off + len, 0) != 0)
+		return -1;
+
+	if (tdb->map_ptr)
+		memcpy(off + (char *)tdb->map_ptr, buf, len);
+#ifdef HAVE_PWRITE
+	else if (pwrite(tdb->fd, buf, len, off) != (ssize_t)len) {
+#else
+	else if (lseek(tdb->fd, off, SEEK_SET) != (off_t)off
+		 || write(tdb->fd, buf, len) != (off_t)len) {
+#endif
+		/* Ensure ecode is set for log fn. */
+		tdb->ecode = TDB_ERR_IO;
+		TDB_LOG((tdb, 0,"tdb_write failed at %d len=%d (%s)\n",
+			   off, len, strerror(errno)));
+		return TDB_ERRCODE(TDB_ERR_IO, -1);
+	}
+	return 0;
+}
+
+/* read a lump of data at a specified offset, maybe convert */
+static int tdb_read(TDB_CONTEXT *tdb,tdb_off off,void *buf,tdb_len len,int cv)
+{
+	if (tdb_oob(tdb, off + len, 0) != 0)
+		return -1;
+
+	if (tdb->map_ptr)
+		memcpy(buf, off + (char *)tdb->map_ptr, len);
+#ifdef HAVE_PREAD
+	else if (pread(tdb->fd, buf, len, off) != (off_t)len) {
+#else
+	else if (lseek(tdb->fd, off, SEEK_SET) != (off_t)off
+		 || read(tdb->fd, buf, len) != (off_t)len) {
+#endif
+		/* Ensure ecode is set for log fn. */
+		tdb->ecode = TDB_ERR_IO;
+		TDB_LOG((tdb, 0,"tdb_read failed at %d len=%d (%s)\n",
+			   off, len, strerror(errno)));
+		return TDB_ERRCODE(TDB_ERR_IO, -1);
+	}
+	if (cv)
+		convert(buf, len);
+	return 0;
+}
+
+/* don't allocate memory: used in tdb_delete path. */
+static int tdb_key_eq(TDB_CONTEXT *tdb, tdb_off off, TDB_DATA key)
+{
+	char buf[64];
+	u32 len;
+
+	if (tdb_oob(tdb, off + key.dsize, 0) != 0)
+		return -1;
+
+	if (tdb->map_ptr)
+		return !memcmp(off + (char*)tdb->map_ptr, key.dptr, key.dsize);
+
+	while (key.dsize) {
+		len = key.dsize;
+		if (len > sizeof(buf))
+			len = sizeof(buf);
+		if (tdb_read(tdb, off, buf, len, 0) != 0)
+			return -1;
+		if (memcmp(buf, key.dptr, len) != 0)
+			return 0;
+		key.dptr += len;
+		key.dsize -= len;
+		off += len;
+	}
+	return 1;
+}
+
+/* read a lump of data, allocating the space for it */
+static char *tdb_alloc_read(TDB_CONTEXT *tdb, tdb_off offset, tdb_len len)
+{
+	char *buf;
+
+	if (!(buf = talloc_size(tdb, len))) {
+		/* Ensure ecode is set for log fn. */
+		tdb->ecode = TDB_ERR_OOM;
+		TDB_LOG((tdb, 0,"tdb_alloc_read malloc failed len=%d (%s)\n",
+			   len, strerror(errno)));
+		return TDB_ERRCODE(TDB_ERR_OOM, buf);
+	}
+	if (tdb_read(tdb, offset, buf, len, 0) == -1) {
+		SAFE_FREE(buf);
+		return NULL;
+	}
+	return buf;
+}
+
+/* read/write a tdb_off */
+static int ofs_read(TDB_CONTEXT *tdb, tdb_off offset, tdb_off *d)
+{
+	return tdb_read(tdb, offset, (char*)d, sizeof(*d), DOCONV());
+}
+static int ofs_write(TDB_CONTEXT *tdb, tdb_off offset, tdb_off *d)
+{
+	tdb_off off = *d;
+	return tdb_write(tdb, offset, CONVERT(off), sizeof(*d));
+}
+
+/* read/write a record */
+static int rec_read(TDB_CONTEXT *tdb, tdb_off offset, struct list_struct *rec)
+{
+	if (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, 0,"rec_read bad magic 0x%x at offset=%d\n", rec->magic, offset));
+		return TDB_ERRCODE(TDB_ERR_CORRUPT, -1);
+	}
+	return tdb_oob(tdb, rec->next+sizeof(*rec), 0);
+}
+static int rec_write(TDB_CONTEXT *tdb, tdb_off offset, struct list_struct *rec)
+{
+	struct list_struct r = *rec;
+	return tdb_write(tdb, offset, CONVERT(r), sizeof(r));
+}
+
+/* read a freelist record and check for simple errors */
+static int rec_free_read(TDB_CONTEXT *tdb, tdb_off off, struct list_struct *rec)
+{
+	if (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, 0,"rec_free_read non-free magic 0x%x at offset=%d - fixing\n", 
+			 rec->magic, off));
+		rec->magic = TDB_FREE_MAGIC;
+		if (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, 0,"rec_free_read bad magic 0x%x at offset=%d\n", 
+			   rec->magic, off));
+		return TDB_ERRCODE(TDB_ERR_CORRUPT, -1);
+	}
+	if (tdb_oob(tdb, rec->next+sizeof(*rec), 0) != 0)
+		return -1;
+	return 0;
+}
+
+/* update a record tailer (must hold allocation lock) */
+static int update_tailer(TDB_CONTEXT *tdb, tdb_off offset,
+			 const struct list_struct *rec)
+{
+	tdb_off totalsize;
+
+	/* Offset of tailer from record header */
+	totalsize = sizeof(*rec) + rec->rec_len;
+	return ofs_write(tdb, offset + totalsize - sizeof(tdb_off),
+			 &totalsize);
+}
+
+static tdb_off tdb_dump_record(TDB_CONTEXT *tdb, tdb_off offset)
+{
+	struct list_struct rec;
+	tdb_off tailer_ofs, tailer;
+
+	if (tdb_read(tdb, offset, (char *)&rec, sizeof(rec), DOCONV()) == -1) {
+		printf("ERROR: failed to read record at %u\n", offset);
+		return 0;
+	}
+
+	printf(" rec: offset=0x%08x next=0x%08x rec_len=%d key_len=%d data_len=%d full_hash=0x%x magic=0x%x\n",
+	       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);
+	if (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(TDB_CONTEXT *tdb, int i)
+{
+	tdb_off rec_ptr, top;
+
+	top = TDB_HASH_TOP(i);
+
+	if (tdb_lock(tdb, i, F_WRLCK) != 0)
+		return -1;
+
+	if (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, rec_ptr);
+	}
+
+	return tdb_unlock(tdb, i, F_WRLCK);
+}
+
+void tdb_dump_all(TDB_CONTEXT *tdb)
+{
+	unsigned 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(TDB_CONTEXT *tdb)
+{
+	int ret;
+	long total_free = 0;
+	tdb_off 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 (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_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);
+}
+
+/* Remove an element from the freelist.  Must have alloc lock. */
+static int remove_from_freelist(TDB_CONTEXT *tdb, tdb_off off, tdb_off next)
+{
+	tdb_off last_ptr, i;
+
+	/* read in the freelist top */
+	last_ptr = FREELIST_TOP;
+	while (ofs_read(tdb, last_ptr, &i) != -1 && i != 0) {
+		if (i == off) {
+			/* We've found it! */
+			return ofs_write(tdb, last_ptr, &next);
+		}
+		/* Follow chain (next offset is at start of record) */
+		last_ptr = i;
+	}
+	TDB_LOG((tdb, 0,"remove_from_freelist: not on list at off=%d\n", off));
+	return TDB_ERRCODE(TDB_ERR_CORRUPT, -1);
+}
+
+/* Add an element into the freelist. Merge adjacent records if
+   neccessary. */
+static int tdb_free(TDB_CONTEXT *tdb, tdb_off offset, struct list_struct *rec)
+{
+	tdb_off 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, 0, "tdb_free: upfate_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_read(tdb, right, &r, sizeof(r), DOCONV()) == -1) {
+			TDB_LOG((tdb, 0, "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, 0, "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);
+	if (left > TDB_DATA_START(tdb->header.hash_size)) {
+		struct list_struct l;
+		tdb_off leftsize;
+		
+		/* Read in tailer and jump back to header */
+		if (ofs_read(tdb, left, &leftsize) == -1) {
+			TDB_LOG((tdb, 0, "tdb_free: left offset read failed at %u\n", left));
+			goto update;
+		}
+		left = offset - leftsize;
+
+		/* Now read in record */
+		if (tdb_read(tdb, left, &l, sizeof(l), DOCONV()) == -1) {
+			TDB_LOG((tdb, 0, "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, 0, "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, 0, "tdb_free: update_tailer failed at %u\n", offset));
+		goto fail;
+	}
+
+	/* Now, prepend to free list */
+	rec->magic = TDB_FREE_MAGIC;
+
+	if (ofs_read(tdb, FREELIST_TOP, &rec->next) == -1 ||
+	    rec_write(tdb, offset, rec) == -1 ||
+	    ofs_write(tdb, FREELIST_TOP, &offset) == -1) {
+		TDB_LOG((tdb, 0, "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;
+}
+
+
+/* expand a file.  we prefer to use ftruncate, as that is what posix
+  says to use for mmap expansion */
+static int expand_file(TDB_CONTEXT *tdb, tdb_off size, tdb_off addition)
+{
+	char buf[1024];
+#if HAVE_FTRUNCATE_EXTEND
+	if (ftruncate(tdb->fd, size+addition) != 0) {
+		TDB_LOG((tdb, 0, "expand_file ftruncate to %d failed (%s)\n", 
+			   size+addition, strerror(errno)));
+		return -1;
+	}
+#else
+	char b = 0;
+
+#ifdef HAVE_PWRITE
+	if (pwrite(tdb->fd,  &b, 1, (size+addition) - 1) != 1) {
+#else
+	if (lseek(tdb->fd, (size+addition) - 1, SEEK_SET) != (off_t)(size+addition) - 1 || 
+	    write(tdb->fd, &b, 1) != 1) {
+#endif
+		TDB_LOG((tdb, 0, "expand_file to %d failed (%s)\n", 
+			   size+addition, strerror(errno)));
+		return -1;
+	}
+#endif
+
+	/* 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, 0x42, sizeof(buf));
+	while (addition) {
+		int n = addition>sizeof(buf)?sizeof(buf):addition;
+#ifdef HAVE_PWRITE
+		int ret = pwrite(tdb->fd, buf, n, size);
+#else
+		int ret;
+		if (lseek(tdb->fd, size, SEEK_SET) != (off_t)size)
+			return -1;
+		ret = write(tdb->fd, buf, n);
+#endif
+		if (ret != n) {
+			TDB_LOG((tdb, 0, "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 */
+static int tdb_expand(TDB_CONTEXT *tdb, tdb_off size)
+{
+	struct list_struct rec;
+	tdb_off offset;
+
+	if (tdb_lock(tdb, -1, F_WRLCK) == -1) {
+		TDB_LOG((tdb, 0, "lock failed in tdb_expand\n"));
+		return -1;
+	}
+
+	/* must know about any previous expansions by another process */
+	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 TDB_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 (expand_file(tdb, tdb->map_size, size) != 0)
+			goto fail;
+	}
+
+	tdb->map_size += size;
+
+	if (tdb->flags & TDB_INTERNAL) {
+		char *new_map_ptr = talloc_realloc_size(tdb, 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;
+}
+
+
+/* 
+   the core of tdb_allocate - called when we have decided which
+   free list entry to use
+ */
+static tdb_off tdb_allocate_ofs(TDB_CONTEXT *tdb, tdb_len length, tdb_off rec_ptr,
+				struct list_struct *rec, tdb_off last_ptr)
+{
+	struct list_struct newrec;
+	tdb_off 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 (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 (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
+ */
+static tdb_off tdb_allocate(TDB_CONTEXT *tdb, tdb_len length,
+			    struct list_struct *rec)
+{
+	tdb_off rec_ptr, last_ptr, newrec_ptr;
+	struct {
+		tdb_off rec_ptr, last_ptr;
+		tdb_len rec_len;
+	} bestfit = { 0, 0, 0 };
+
+	if (tdb_lock(tdb, -1, F_WRLCK) == -1)
+		return 0;
+
+	/* Extra bytes required for tailer */
+	length += sizeof(tdb_off);
+
+ again:
+	last_ptr = FREELIST_TOP;
+
+	/* read in the freelist top */
+	if (ofs_read(tdb, FREELIST_TOP, &rec_ptr) == -1)
+		goto fail;
+
+	bestfit.rec_ptr = 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 (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 (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;
+}
+
+/* initialise a new database with a specified hash size */
+static int tdb_new_database(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);
+	if (!(newdb = talloc_zero_size(tdb, size)))
+		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;
+}
+
+/* Returns 0 on fail.  On success, return offset of record, and fills
+   in rec */
+static tdb_off tdb_find(TDB_CONTEXT *tdb, TDB_DATA key, u32 hash,
+			struct list_struct *r)
+{
+	tdb_off rec_ptr;
+	
+	/* read in the hash top */
+	if (ofs_read(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1)
+		return 0;
+
+	/* keep looking until we find the right record */
+	while (rec_ptr) {
+		if (rec_read(tdb, rec_ptr, r) == -1)
+			return 0;
+
+		if (!TDB_DEAD(r) && hash==r->full_hash && key.dsize==r->key_len) {
+			/* a very likely hit - read the key */
+			int cmp = tdb_key_eq(tdb, rec_ptr + sizeof(*r), key);
+			if (cmp < 0)
+				return 0;
+			else if (cmp > 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 */
+static tdb_off tdb_find_lock_hash(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;
+}
+
+enum TDB_ERROR tdb_error(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_NOEXIST, "Record does not exist"} };
+
+/* Error string for the last tdb error */
+const char *tdb_errorstr(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";
+}
+
+/* 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(TDB_CONTEXT *tdb, TDB_DATA key, u32 hash, TDB_DATA dbuf)
+{
+	struct list_struct rec;
+	tdb_off 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)) {
+		tdb->ecode = TDB_SUCCESS; /* Not really an error */
+		return -1;
+	}
+
+	if (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 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(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	tdb_off 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;
+}
+
+/* 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(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(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	u32 hash = tdb->hash_fn(&key);
+	return tdb_exists_hash(tdb, key, hash);
+}
+
+/* record lock stops delete underneath */
+static int lock_record(TDB_CONTEXT *tdb, tdb_off off)
+{
+	return off ? tdb_brlock(tdb, off, F_RDLCK, F_SETLKW, 0) : 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.
+*/
+ 
+static int write_lock_record(TDB_CONTEXT *tdb, tdb_off off)
+{
+	struct tdb_traverse_lock *i;
+	for (i = &tdb->travlocks; i; i = i->next)
+		if (i->off == off)
+			return -1;
+	return tdb_brlock(tdb, off, F_WRLCK, F_SETLK, 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.
+*/
+
+static int write_unlock_record(TDB_CONTEXT *tdb, tdb_off off)
+{
+	return tdb_brlock(tdb, off, F_UNLCK, F_SETLK, 0);
+}
+/* fcntl locks don't stack: avoid unlocking someone else's */
+static int unlock_record(TDB_CONTEXT *tdb, tdb_off 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_brlock(tdb, off, F_UNLCK, F_SETLKW, 0) : 0);
+}
+
+/* actually delete an entry in the database given the offset */
+static int do_delete(TDB_CONTEXT *tdb, tdb_off rec_ptr, struct list_struct*rec)
+{
+	tdb_off last_ptr, i;
+	struct list_struct lastrec;
+
+	if (tdb->read_only) return -1;
+
+	if (write_lock_record(tdb, rec_ptr) == -1) {
+		/* Someone traversing here: mark it as dead */
+		rec->magic = TDB_DEAD_MAGIC;
+		return rec_write(tdb, rec_ptr, rec);
+	}
+	if (write_unlock_record(tdb, rec_ptr) != 0)
+		return -1;
+
+	/* find previous record in hash chain */
+	if (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 (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 (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;
+}
+
+/* Uses traverse lock: 0 = finish, -1 = error, other = record offset */
+static int tdb_next_lock(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++) {
+
+		/* 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).
+		 */
+		if (!tlock->off && tlock->hash != 0) {
+			u32 off;
+			if (tdb->map_ptr) {
+				for (;tlock->hash < tdb->header.hash_size;tlock->hash++) {
+					if (0 != *(u32 *)(TDB_HASH_TOP(tlock->hash) + (unsigned char *)tdb->map_ptr)) {
+						break;
+					}
+				}
+				if (tlock->hash == tdb->header.hash_size) {
+					continue;
+				}
+			} else {
+				if (ofs_read(tdb, TDB_HASH_TOP(tlock->hash), &off) == 0 &&
+				    off == 0) {
+					continue;
+				}
+			}
+		}
+
+		if (tdb_lock(tdb, tlock->hash, F_WRLCK) == -1)
+			return -1;
+
+		/* No previous record?  Start at top of chain. */
+		if (!tlock->off) {
+			if (ofs_read(tdb, TDB_HASH_TOP(tlock->hash),
+				     &tlock->off) == -1)
+				goto fail;
+		} else {
+			/* Otherwise unlock the previous record. */
+			if (unlock_record(tdb, tlock->off) != 0)
+				goto fail;
+		}
+
+		if (want_next) {
+			/* We have offset of old record: grab next */
+			if (rec_read(tdb, tlock->off, rec) == -1)
+				goto fail;
+			tlock->off = rec->next;
+		}
+
+		/* Iterate through chain */
+		while( tlock->off) {
+			tdb_off current;
+			if (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, 0, "tdb_next_lock: loop detected.\n"));
+				goto fail;
+			}
+
+			if (!TDB_DEAD(rec)) {
+				/* Woohoo: we found one! */
+				if (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 && 
+			    do_delete(tdb, current, rec) != 0)
+				goto fail;
+		}
+		tdb_unlock(tdb, tlock->hash, F_WRLCK);
+		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, F_WRLCK) != 0)
+		TDB_LOG((tdb, 0, "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
+  */
+int tdb_traverse(TDB_CONTEXT *tdb, tdb_traverse_func fn, void *private)
+{
+	TDB_DATA key, dbuf;
+	struct list_struct rec;
+	struct tdb_traverse_lock tl = { NULL, 0, 0 };
+	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, F_WRLCK) != 0)
+				goto out;
+			if (unlock_record(tdb, tl.off) != 0)
+				TDB_LOG((tdb, 0, "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, F_WRLCK) != 0) {
+			ret = -1;
+			goto out;
+		}
+		if (fn && fn(tdb, key, dbuf, private)) {
+			/* They want us to terminate traversal */
+			ret = count;
+			if (unlock_record(tdb, tl.off) != 0) {
+				TDB_LOG((tdb, 0, "tdb_traverse: unlock_record failed!\n"));;
+				ret = -1;
+			}
+			tdb->travlocks.next = tl.next;
+			SAFE_FREE(key.dptr);
+			return count;
+		}
+		SAFE_FREE(key.dptr);
+	}
+out:
+	tdb->travlocks.next = tl.next;
+	if (ret < 0)
+		return -1;
+	else
+		return count;
+}
+
+/* find the first entry in the database and return its key */
+TDB_DATA tdb_firstkey(TDB_CONTEXT *tdb)
+{
+	TDB_DATA key;
+	struct list_struct rec;
+
+	/* release any old lock */
+	if (unlock_record(tdb, tdb->travlocks.off) != 0)
+		return tdb_null;
+	tdb->travlocks.off = tdb->travlocks.hash = 0;
+
+	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);
+	if (tdb_unlock(tdb, BUCKET(tdb->travlocks.hash), F_WRLCK) != 0)
+		TDB_LOG((tdb, 0, "tdb_firstkey: error occurred while tdb_unlocking!\n"));
+	return key;
+}
+
+/* find the next entry in the database, returning its key */
+TDB_DATA tdb_nextkey(TDB_CONTEXT *tdb, TDB_DATA oldkey)
+{
+	u32 oldhash;
+	TDB_DATA key = tdb_null;
+	struct list_struct rec;
+	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,F_WRLCK))
+			return tdb_null;
+		if (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 (unlock_record(tdb, tdb->travlocks.off) != 0)
+				return tdb_null;
+			if (tdb_unlock(tdb, tdb->travlocks.hash, F_WRLCK) != 0)
+				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), F_WRLCK, &rec);
+		if (!tdb->travlocks.off)
+			return tdb_null;
+		tdb->travlocks.hash = BUCKET(rec.full_hash);
+		if (lock_record(tdb, tdb->travlocks.off) != 0) {
+			TDB_LOG((tdb, 0, "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, F_WRLCK) != 0)
+			TDB_LOG((tdb, 0, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
+	}
+	/* Unlock the chain of old record */
+	if (tdb_unlock(tdb, BUCKET(oldhash), F_WRLCK) != 0)
+		TDB_LOG((tdb, 0, "tdb_nextkey: WARNING tdb_unlock failed!\n"));
+	return key;
+}
+
+/* delete an entry in the database given a key */
+static int tdb_delete_hash(TDB_CONTEXT *tdb, TDB_DATA key, u32 hash)
+{
+	tdb_off rec_ptr;
+	struct list_struct rec;
+	int ret;
+
+	if (!(rec_ptr = tdb_find_lock_hash(tdb, key, hash, F_WRLCK, &rec)))
+		return -1;
+	ret = do_delete(tdb, rec_ptr, &rec);
+	if (tdb_unlock(tdb, BUCKET(rec.full_hash), F_WRLCK) != 0)
+		TDB_LOG((tdb, 0, "tdb_delete: WARNING tdb_unlock failed!\n"));
+	return ret;
+}
+
+int tdb_delete(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	u32 hash = tdb->hash_fn(&key);
+	return tdb_delete_hash(tdb, key, hash);
+}
+
+/* store an element in the database, replacing any existing element
+   with the same key 
+
+   return 0 on success, -1 on failure
+*/
+int tdb_store(TDB_CONTEXT *tdb, TDB_DATA key, TDB_DATA dbuf, int flag)
+{
+	struct list_struct rec;
+	u32 hash;
+	tdb_off rec_ptr;
+	char *p = NULL;
+	int ret = 0;
+
+	/* 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 out;
+		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 *)talloc_size(tdb, 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);
+
+	/* we have to allocate some space */
+	if (!(rec_ptr = tdb_allocate(tdb, key.dsize + dbuf.dsize, &rec)))
+		goto fail;
+
+	/* Read hash top into next ptr */
+	if (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 (rec_write(tdb, rec_ptr, &rec) == -1
+	    || tdb_write(tdb, rec_ptr+sizeof(rec), p, key.dsize+dbuf.dsize)==-1
+	    || ofs_write(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1) {
+		/* Need to tdb_unallocate() here */
+		goto fail;
+	}
+ out:
+	SAFE_FREE(p); 
+	tdb_unlock(tdb, BUCKET(hash), F_WRLCK);
+	return ret;
+fail:
+	ret = -1;
+	goto out;
+}
+
+/* Attempt to append data to 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. Record must be locked before calling.
+*/
+static int tdb_append_inplace(TDB_CONTEXT *tdb, TDB_DATA key, u32 hash, TDB_DATA new_dbuf)
+{
+	struct list_struct rec;
+	tdb_off rec_ptr;
+
+	/* find entry */
+	if (!(rec_ptr = tdb_find(tdb, key, hash, &rec)))
+		return -1;
+
+	/* Append of 0 is always ok. */
+	if (new_dbuf.dsize == 0)
+		return 0;
+
+	/* must be long enough for key, old data + new data and tailer */
+	if (rec.rec_len < key.dsize + rec.data_len + new_dbuf.dsize + sizeof(tdb_off)) {
+		/* No room. */
+		tdb->ecode = TDB_SUCCESS; /* Not really an error */
+		return -1;
+	}
+
+	if (tdb_write(tdb, rec_ptr + sizeof(rec) + rec.key_len + rec.data_len,
+		      new_dbuf.dptr, new_dbuf.dsize) == -1)
+		return -1;
+
+	/* update size */
+	rec.data_len += new_dbuf.dsize;
+	return rec_write(tdb, rec_ptr, &rec);
+}
+
+/* Append to an entry. Create if not exist. */
+
+int tdb_append(TDB_CONTEXT *tdb, TDB_DATA key, TDB_DATA new_dbuf)
+{
+	struct list_struct rec;
+	u32 hash;
+	tdb_off rec_ptr;
+	char *p = NULL;
+	int ret = 0;
+	size_t new_data_size = 0;
+
+	/* find which hash bucket it is in */
+	hash = tdb->hash_fn(&key);
+	if (tdb_lock(tdb, BUCKET(hash), F_WRLCK) == -1)
+		return -1;
+
+	/* first try in-place. */
+	if (tdb_append_inplace(tdb, key, hash, new_dbuf) == 0)
+		goto out;
+
+	/* reset the error code potentially set by the tdb_append_inplace() */
+	tdb->ecode = TDB_SUCCESS;
+
+	/* find entry */
+	if (!(rec_ptr = tdb_find(tdb, key, hash, &rec))) {
+		if (tdb->ecode != TDB_ERR_NOEXIST)
+			goto fail;
+
+		/* Not found - create. */
+
+		ret = tdb_store(tdb, key, new_dbuf, TDB_INSERT);
+		goto out;
+	}
+
+	new_data_size = rec.data_len + new_dbuf.dsize;
+
+	/* Copy key+old_value+value *before* allocating free space in case malloc
+	   fails and we are left with a dead spot in the tdb. */
+
+	if (!(p = (char *)talloc_size(tdb, key.dsize + new_data_size))) {
+		tdb->ecode = TDB_ERR_OOM;
+		goto fail;
+	}
+
+	/* Copy the key in place. */
+	memcpy(p, key.dptr, key.dsize);
+
+	/* Now read the old data into place. */
+	if (rec.data_len &&
+		tdb_read(tdb, rec_ptr + sizeof(rec) + rec.key_len, p + key.dsize, rec.data_len, 0) == -1)
+			goto fail;
+
+	/* Finally append the new data. */
+	if (new_dbuf.dsize)
+		memcpy(p+key.dsize+rec.data_len, new_dbuf.dptr, new_dbuf.dsize);
+
+	/* 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. */
+
+	tdb_delete_hash(tdb, key, hash);
+
+	if (!(rec_ptr = tdb_allocate(tdb, key.dsize + new_data_size, &rec)))
+		goto fail;
+
+	/* Read hash top into next ptr */
+	if (ofs_read(tdb, TDB_HASH_TOP(hash), &rec.next) == -1)
+		goto fail;
+
+	rec.key_len = key.dsize;
+	rec.data_len = new_data_size;
+	rec.full_hash = hash;
+	rec.magic = TDB_MAGIC;
+
+	/* write out and point the top of the hash chain at it */
+	if (rec_write(tdb, rec_ptr, &rec) == -1
+	    || tdb_write(tdb, rec_ptr+sizeof(rec), p, key.dsize+new_data_size)==-1
+	    || ofs_write(tdb, TDB_HASH_TOP(hash), &rec_ptr) == -1) {
+		/* Need to tdb_unallocate() here */
+		goto fail;
+	}
+
+ out:
+	SAFE_FREE(p); 
+	tdb_unlock(tdb, BUCKET(hash), F_WRLCK);
+	return ret;
+
+fail:
+	ret = -1;
+	goto out;
+}
+
+static int tdb_already_open(dev_t device,
+			    ino_t ino)
+{
+	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. */
+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(TDB_CONTEXT *tdb __attribute__((unused)),
+			int level __attribute__((unused)),
+			const char *fmt __attribute__((unused)), ...)
+{
+}
+
+
+TDB_CONTEXT *tdb_open_ex(const char *name, int hash_size, int tdb_flags,
+			 int open_flags, mode_t mode,
+			 tdb_log_func log_fn,
+			 tdb_hash_func hash_fn)
+{
+	TDB_CONTEXT *tdb;
+	struct stat st;
+	int rev = 0, locked = 0;
+	uint8_t *vp;
+	u32 vertest;
+
+	if (!(tdb = talloc_zero(name, TDB_CONTEXT))) {
+		/* Can't log this */
+		errno = ENOMEM;
+		goto fail;
+	}
+	tdb->fd = -1;
+	tdb->name = NULL;
+	tdb->map_ptr = NULL;
+	tdb->flags = tdb_flags;
+	tdb->open_flags = open_flags;
+	tdb->log_fn = log_fn?log_fn:null_log_fn;
+	tdb->hash_fn = hash_fn ? hash_fn : default_tdb_hash;
+
+	if ((open_flags & O_ACCMODE) == O_WRONLY) {
+		TDB_LOG((tdb, 0, "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, 0, "tdb_open_ex: tdb_new_database failed!"));
+			goto fail;
+		}
+		goto internal;
+	}
+
+	if ((tdb->fd = open(name, open_flags, mode)) == -1) {
+		TDB_LOG((tdb, 5, "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_brlock(tdb, GLOBAL_LOCK, F_WRLCK, F_SETLKW, 0) == -1) {
+		TDB_LOG((tdb, 0, "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_brlock(tdb, ACTIVE_LOCK, F_WRLCK, F_SETLK, 0) == 0))) {
+		open_flags |= O_CREAT;
+		if (ftruncate(tdb->fd, 0) == -1) {
+			TDB_LOG((tdb, 0, "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 = (uint8_t *)&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;
+		convert(&tdb->header, sizeof(tdb->header));
+	}
+	if (fstat(tdb->fd, &st) == -1)
+		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, 2, "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 *)talloc_strdup(tdb, name))) {
+		errno = ENOMEM;
+		goto fail;
+	}
+
+	tdb->map_size = st.st_size;
+	tdb->device = st.st_dev;
+	tdb->inode = st.st_ino;
+	tdb->locked = talloc_zero_array(tdb, struct tdb_lock_type,
+					tdb->header.hash_size+1);
+	if (!tdb->locked) {
+		TDB_LOG((tdb, 2, "tdb_open_ex: "
+			 "failed to allocate lock structure for %s\n",
+			 name));
+		errno = ENOMEM;
+		goto fail;
+	}
+	tdb_mmap(tdb);
+	if (locked) {
+		if (tdb_brlock(tdb, ACTIVE_LOCK, F_UNLCK, F_SETLK, 0) == -1) {
+			TDB_LOG((tdb, 0, "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_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0) == -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_brlock(tdb, GLOBAL_LOCK, F_UNLCK, F_SETLKW, 0) == -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, 5, "tdb_open_ex: failed to close tdb->fd on error!\n"));
+	SAFE_FREE(tdb->locked);
+	SAFE_FREE(tdb);
+	errno = save_errno;
+	return NULL;
+	}
+}
+
+/**
+ * Close a database.
+ *
+ * @returns -1 for error; 0 for success.
+ **/
+int tdb_close(TDB_CONTEXT *tdb)
+{
+	TDB_CONTEXT **i;
+	int ret = 0;
+
+	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->locked);
+
+	/* 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;
+}
+
+/* lock/unlock entire database */
+int tdb_lockall(TDB_CONTEXT *tdb)
+{
+	u32 i;
+
+	/* There are no locks on read-only dbs */
+	if (tdb->read_only)
+		return TDB_ERRCODE(TDB_ERR_LOCK, -1);
+	for (i = 0; i < tdb->header.hash_size; i++) 
+		if (tdb_lock(tdb, i, F_WRLCK))
+			break;
+
+	/* If error, release locks we have... */
+	if (i < tdb->header.hash_size) {
+		u32 j;
+
+		for ( j = 0; j < i; j++)
+			tdb_unlock(tdb, j, F_WRLCK);
+		return TDB_ERRCODE(TDB_ERR_NOLOCK, -1);
+	}
+
+	return 0;
+}
+void tdb_unlockall(TDB_CONTEXT *tdb)
+{
+	u32 i;
+	for (i=0; i < tdb->header.hash_size; i++)
+		tdb_unlock(tdb, i, F_WRLCK);
+}
+
+/* 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(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	return tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK);
+}
+
+int tdb_chainunlock(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_WRLCK);
+}
+
+int tdb_chainlock_read(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	return tdb_lock(tdb, BUCKET(tdb->hash_fn(&key)), F_RDLCK);
+}
+
+int tdb_chainunlock_read(TDB_CONTEXT *tdb, TDB_DATA key)
+{
+	return tdb_unlock(tdb, BUCKET(tdb->hash_fn(&key)), F_RDLCK);
+}
+
+
+/* register a loging function */
+void tdb_logging_function(TDB_CONTEXT *tdb, void (*fn)(TDB_CONTEXT *, int , const char *, ...))
+{
+	tdb->log_fn = fn?fn:null_log_fn;
+}
+
+
+/* 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(TDB_CONTEXT *tdb)
+{
+	struct stat st;
+
+	if (tdb->flags & TDB_INTERNAL)
+		return 0; /* Nothing to do. */
+	if (tdb_munmap(tdb) != 0) {
+		TDB_LOG((tdb, 0, "tdb_reopen: munmap failed (%s)\n", strerror(errno)));
+		goto fail;
+	}
+	if (close(tdb->fd) != 0)
+		TDB_LOG((tdb, 0, "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, 0, "tdb_reopen: open failed (%s)\n", strerror(errno)));
+		goto fail;
+	}
+	if (fstat(tdb->fd, &st) != 0) {
+		TDB_LOG((tdb, 0, "tdb_reopen: fstat failed (%s)\n", strerror(errno)));
+		goto fail;
+	}
+	if (st.st_ino != tdb->inode || st.st_dev != tdb->device) {
+		TDB_LOG((tdb, 0, "tdb_reopen: file dev/inode has changed!\n"));
+		goto fail;
+	}
+	tdb_mmap(tdb);
+	if ((tdb->flags & TDB_CLEAR_IF_FIRST) && (tdb_brlock(tdb, ACTIVE_LOCK, F_RDLCK, F_SETLKW, 0) == -1)) {
+		TDB_LOG((tdb, 0, "tdb_reopen: failed to obtain active lock\n"));
+		goto fail;
+	}
+
+	return 0;
+
+fail:
+	tdb_close(tdb);
+	return -1;
+}
+
+/* Not general: only works if single writer. */
+TDB_CONTEXT *tdb_copy(TDB_CONTEXT *tdb, const char *outfile)
+{
+	int fd, saved_errno;
+	TDB_CONTEXT *copy;
+
+	fd = open(outfile, O_TRUNC|O_CREAT|O_WRONLY, 0640);
+	if (fd < 0)
+		return NULL;
+	if (tdb->map_ptr) {
+		if (write(fd,tdb->map_ptr,tdb->map_size) != (int)tdb->map_size)
+			goto fail;
+	} else {
+		char buf[65536];
+		int r;
+
+		lseek(tdb->fd, 0, SEEK_SET);
+		while ((r = read(tdb->fd, buf, sizeof(buf))) > 0) {
+			if (write(fd, buf, r) != r)
+				goto fail;
+		}
+		if (r < 0)
+			goto fail;
+	}
+	copy = tdb_open(outfile, 0, 0, O_RDWR, 0);
+	if (!copy)
+		goto fail;
+	close(fd);
+	return copy;
+
+fail:
+	saved_errno = errno;
+	close(fd);
+	unlink(outfile);
+	errno = saved_errno;
+	return NULL;
+}
+
+/* reopen all tdb's */
+int tdb_reopen_all(void)
+{
+	TDB_CONTEXT *tdb;
+
+	for (tdb=tdbs; tdb; tdb = tdb->next) {
+		/* Ensure no clear-if-first. */
+		tdb->flags &= ~TDB_CLEAR_IF_FIRST;
+		if (tdb_reopen(tdb) != 0)
+			return -1;
+	}
+
+	return 0;
+}