port/gen/ndbm.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 * Copyright (c) 2016 by Delphix. All rights reserved.
 */

/*	Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T	*/
/*	  All Rights Reserved	*/

/*
 * University Copyright- Copyright (c) 1982, 1986, 1988
 * The Regents of the University of California
 * All Rights Reserved
 *
 * University Acknowledgment- Portions of this document are derived from
 * software developed by the University of California, Berkeley, and its
 * contributors.
 */

#include "lint.h"
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/file.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <ndbm.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>

/* add support for batched writing for NIS */

#define	_DBM_DEFWRITE 0x4
#define	_DBM_DIRTY 0x8
#define	_DBM_DIRDIRTY 0x10
#define	dbm_dirty(db) ((db)->dbm_flags & _DBM_DIRTY)
#define	dbm_dirdirty(db) ((db)->dbm_flags & _DBM_DIRDIRTY)
#define	dbm_defwrite(db) ((db)->dbm_flags & _DBM_DEFWRITE)
#define	dbm_setdirty(db) (db)->dbm_flags |= _DBM_DIRTY
#define	dbm_clrdirty(db) (db)->dbm_flags &= ~_DBM_DIRTY
#define	dbm_setdirdirty(db) (db)->dbm_flags |= _DBM_DIRDIRTY
#define	dbm_clrdirdirty(db) (db)->dbm_flags &= ~_DBM_DIRDIRTY

/*
 * forward declarations
 */
static datum makdatum(char *, int);
static unsigned long dcalchash(datum);
static void dbm_access(DBM *, unsigned long);
static int finddatum(char *, datum);
static int delitem(char *, int);
static int additem(char *, datum, datum);
static int cmpdatum(datum, datum);
static int setbit(DBM *);
static int getbit(DBM *);
static int dbm_flushdir(DBM *);
static int dbm_flushpag(DBM *db);

/* the following three are required by mapfile-vers */
datum dbm_do_nextkey(DBM *, datum);
int dbm_close_status(DBM *);

/* used to make a dbm file all at once instead of incrementally */
void
dbm_setdefwrite(DBM *db)
{
	db->dbm_flags |= _DBM_DEFWRITE;
}

#undef	dbm_error

int
dbm_error(DBM *db)
{
	return (db->dbm_flags & _DBM_IOERR);
}

#undef	dbm_clearerr

int
dbm_clearerr(DBM *db)
{
	return (db->dbm_flags &= ~_DBM_IOERR);
}

int
dbm_flush(DBM *db)
{
	int ok = 0;
	if (dbm_flushpag(db) < 0)
		ok = -1;
	if (dbm_flushdir(db) < 0)
		ok = -1;
	return (ok);
}

static int
dbm_flushpag(DBM *db)
{
	int ok = 0;
	off64_t where;

	if (dbm_dirty(db)) { /* must page out the page */
		where = (((off64_t)db->dbm_pagbno) * PBLKSIZ);
		if ((lseek64(db->dbm_pagf, where, L_SET) != where) ||
		    (write(db->dbm_pagf, db->dbm_pagbuf, PBLKSIZ) != PBLKSIZ)) {
			db->dbm_flags |= _DBM_IOERR;
			ok = -1;
		}
		dbm_clrdirty(db);
	}
	return (ok);
}

static int
dbm_flushdir(DBM *db)
{
	int ok = 0;
	off64_t where;
	if (dbm_dirdirty(db)) { /* must page out the dir */
		where = (((off64_t)db->dbm_dirbno) * DBLKSIZ);
		if ((lseek64(db->dbm_dirf, where, L_SET) != where) ||
		    (write(db->dbm_dirf, db->dbm_dirbuf, DBLKSIZ) != DBLKSIZ)) {
			ok = -1;
		}
		dbm_clrdirdirty(db);
	}
	return (ok);
}

#define	BYTESIZ 8
#undef setbit

DBM *
dbm_open(const char *file, int flags, mode_t mode)
{
	struct stat64 statb;
	DBM *db;
	int	serrno;

	if ((db = (DBM *)malloc(sizeof (*db))) == 0) {
		errno = ENOMEM;
		return ((DBM *)0);
	}
	db->dbm_flags = (flags & 03) == O_RDONLY ? _DBM_RDONLY : 0;
	if ((flags & 03) == O_WRONLY)
		flags = (flags & ~03) | O_RDWR;
	if (strlcpy(db->dbm_pagbuf, file, sizeof (db->dbm_pagbuf)) >=
	    sizeof (db->dbm_pagbuf) ||
	    strlcat(db->dbm_pagbuf, ".pag", sizeof (db->dbm_pagbuf)) >=
	    sizeof (db->dbm_pagbuf)) {
		/*
		 * file.pag does not fit into dbm_pagbuf.
		 * fail with ENAMETOOLONG.
		 */
		serrno = ENAMETOOLONG;
		goto bad;
	}
	db->dbm_pagf = open64(db->dbm_pagbuf, flags, mode);
	if (db->dbm_pagf < 0) {
		serrno = errno;
		goto bad;
	}
	/*
	 * We know this won't overflow so it is safe to ignore the
	 * return value; we use strl* to prevent false hits in
	 * code sweeps.
	 */
	(void) strlcpy(db->dbm_pagbuf, file, sizeof (db->dbm_pagbuf));
	(void) strlcat(db->dbm_pagbuf, ".dir", sizeof (db->dbm_pagbuf));
	db->dbm_dirf = open64(db->dbm_pagbuf, flags, mode);
	if (db->dbm_dirf < 0) {
		serrno = errno;
		goto bad1;
	}
	(void) fstat64(db->dbm_dirf, &statb);
	db->dbm_maxbno = statb.st_size * BYTESIZ-1;
	db->dbm_pagbno = db->dbm_dirbno = -1;
	return (db);
bad1:
	(void) close(db->dbm_pagf);
bad:
	free((char *)db);
	errno = serrno;
	return ((DBM *)0);
}

void
dbm_close(DBM *db)
{
(void) dbm_close_status(db);
}

/* close with return code */
int
dbm_close_status(DBM *db)
{
	int ok;
	ok = 0;

	if (dbm_flush(db) < 0)
		ok = -1;
	if (close(db->dbm_dirf) < 0)
		ok = -1;
	if (close(db->dbm_pagf) < 0)
		ok = -1;
	free((char *)db);
	return (ok);
}

long
dbm_forder(DBM *db, datum key)
{
	unsigned long hash;

	hash = dcalchash(key);
	for (db->dbm_hmask = 0; ; db->dbm_hmask = (db->dbm_hmask<<1)+1) {
		db->dbm_blkno = hash & db->dbm_hmask;
		db->dbm_bitno = db->dbm_blkno + db->dbm_hmask;
		if (getbit(db) == 0)
			break;
	}
	return (db->dbm_blkno);
}

datum
dbm_fetch(DBM *db, datum key)
{
	int i;
	datum item;

	if (dbm_error(db))
		goto err;
	dbm_access(db, dcalchash(key));
	if ((i = finddatum(db->dbm_pagbuf, key)) >= 0) {
		item = makdatum(db->dbm_pagbuf, i+1);
		if (item.dptr != NULL)
			return (item);
	}
err:
	item.dptr = NULL;
	item.dsize = 0;
	return (item);
}

int
dbm_delete(DBM *db, datum key)
{
	int i;
	off64_t where;

	if (dbm_error(db))
		return (-1);
	if (dbm_rdonly(db)) {
		errno = EPERM;
		return (-1);
	}
	dbm_access(db, dcalchash(key));
	if ((i = finddatum(db->dbm_pagbuf, key)) < 0)
		return (-1);
	if (!delitem(db->dbm_pagbuf, i))
		goto err;
	db->dbm_pagbno = db->dbm_blkno;
	if (dbm_defwrite(db)) {
		dbm_setdirty(db);
	} else {
		where = (((off64_t)db->dbm_blkno) * PBLKSIZ);
		if ((lseek64(db->dbm_pagf, where, L_SET) != where) ||
		    (write(db->dbm_pagf, db->dbm_pagbuf, PBLKSIZ) != PBLKSIZ)) {
			err:
				db->dbm_flags |= _DBM_IOERR;
				return (-1);
		}
	}
	return (0);
}

int
dbm_store(DBM *db, datum key, datum dat, int replace)
{
	int i;
	datum item, item1;
	char ovfbuf[PBLKSIZ];
	unsigned long hashdiff, key_hash, item_hash;
	off64_t where;

	if (dbm_error(db))
		return (-1);
	if (dbm_rdonly(db)) {
		errno = EPERM;
		return (-1);
	}
loop:
	key_hash = dcalchash(key);
	dbm_access(db, key_hash);
	if ((i = finddatum(db->dbm_pagbuf, key)) >= 0) {
		if (!replace)
			return (1);
		if (!delitem(db->dbm_pagbuf, i)) {
			db->dbm_flags |= _DBM_IOERR;
			return (-1);
		}
	}
	if (!additem(db->dbm_pagbuf, key, dat))
		goto split;
	db->dbm_pagbno = db->dbm_blkno;
	if (dbm_defwrite(db)) {
		dbm_setdirty(db);
	} else {
		where = (((off64_t)db->dbm_blkno) * PBLKSIZ);
		if ((lseek64(db->dbm_pagf, where, L_SET) != where) ||
		    (write(db->dbm_pagf, db->dbm_pagbuf, PBLKSIZ) != PBLKSIZ)) {
			db->dbm_flags |= _DBM_IOERR;
			return (-1);
		}
	}
	return (0);
split:
	hashdiff = 0;
	if (key.dsize + dat.dsize + 3 * (int)sizeof (short) >= PBLKSIZ) {
		db->dbm_flags |= _DBM_IOERR;
		errno = ENOSPC;
		return (-1);
	}
	(void) memset(ovfbuf, 0, PBLKSIZ);
	for (i = 0; ; ) {
		item = makdatum(db->dbm_pagbuf, i);
		if (item.dptr == NULL)
			break;
		item_hash = dcalchash(item);
		if (item_hash != key_hash) {
			hashdiff++;
		}

		if (item_hash & (db->dbm_hmask+1)) {
			item1 = makdatum(db->dbm_pagbuf, i+1);
			if (item1.dptr == NULL) {
				/* (void) fprintf(stderr, "ndbm: */
				/* split not paired\n"); */
				db->dbm_flags |= _DBM_IOERR;
				break;
			}
			if (!additem(ovfbuf, item, item1) ||
			    !delitem(db->dbm_pagbuf, i)) {
				db->dbm_flags |= _DBM_IOERR;
				return (-1);
			}
			continue;
		}
		i += 2;
	}
	db->dbm_pagbno = db->dbm_blkno;
	where = (((off64_t)db->dbm_blkno) * PBLKSIZ);
	if ((lseek64(db->dbm_pagf, where, L_SET) != where) ||
	    (write(db->dbm_pagf, db->dbm_pagbuf, PBLKSIZ) != PBLKSIZ)) {
		db->dbm_flags |= _DBM_IOERR;
		return (-1);
	}
	dbm_clrdirty(db); /* clear dirty */
	where = (((off64_t)db->dbm_blkno + db->dbm_hmask + 1) * PBLKSIZ);
	if ((lseek64(db->dbm_pagf, where, L_SET) != where) ||
	    (write(db->dbm_pagf, ovfbuf, PBLKSIZ) != PBLKSIZ)) {
		db->dbm_flags |= _DBM_IOERR;
		return (-1);
	}
	if (setbit(db) < 0) {
		db->dbm_flags |= _DBM_IOERR;
		return (-1);
	}
	if (hashdiff == 0) {
		db->dbm_flags |= _DBM_IOERR;
		return (-1);
	}
	goto loop;
}

static unsigned long
dbm_hashinc(DBM *db, unsigned long hash)
{
	long bit;

	hash &= db->dbm_hmask;
	bit = db->dbm_hmask+1;
	for (;;) {
		bit >>= 1;
		if (bit == 0)
			return (0L);
		if ((hash&bit) == 0)
			return (hash|bit);
		hash &= ~bit;
	}
}


static datum nullkey = {NULL, 0};

datum
dbm_firsthash(DBM *db, unsigned long hash)
{
	int i, j;
	datum item, bitem;

loop:
	dbm_access(db, hash);
	j = 0;
	bitem = makdatum(db->dbm_pagbuf, 0);
	for (i = 2; ; i += 2) {
		item = makdatum(db->dbm_pagbuf, i);
		if (item.dptr == NULL)
			break;
		if (cmpdatum(bitem, item) < 0) {
			j = i;
			bitem = item;
		}
	}
	if (bitem.dptr != NULL) {
		db->dbm_keyptr = j + 2;
		db->dbm_blkptr = db->dbm_blkno;
		return (bitem);
	}
	hash = dbm_hashinc(db, hash);
	if (hash == 0)
		return (item); /* null item */
	goto loop;

}

datum
dbm_firstkey(DBM *db)
{
	/*
	 * For some reason, the Posix specification (SUSv3)
	 * says that dbm_firstkey() is not a cancellation point.
	 * It really should be, but in order to pass the SUSv3
	 * test suite we make it not a cancellation point.
	 * XXX: fix me when the SUSv3 specification gets fixed.
	 */
	int cancel_state;
	datum rval;

	db->dbm_blkptr = 0L;
	db->dbm_keyptr = 0;
	(void) pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cancel_state);
	rval = dbm_firsthash(db, 0L);
	(void) pthread_setcancelstate(cancel_state, NULL);
	return (rval);
}

datum
dbm_nextkey(DBM *db)
{

	return (dbm_do_nextkey(db, nullkey));
}

/*
 * this is used if keyptr-2, blocknum doesn't point to the previous
 * specific key allowing the fast hash order search --
 * its use indicates user tampering with our state variables,
 * which some evil users might do to search from some specific place.
 * It finds the first key at or after blkptr, keyptr in block seq order
 * this requires looking at all sorts of emtpy blocks in many cases
 */

static
datum
dbm_slow_nextkey(DBM *db)
{

	struct stat64 statb;
	datum item;
	off64_t where;

	if (dbm_error(db) || fstat64(db->dbm_pagf, &statb) < 0)
		goto err;
	statb.st_size /= PBLKSIZ;

	for (;;) {
		if (db->dbm_blkptr != db->dbm_pagbno) {

			if (dbm_dirty(db)) (void) dbm_flushpag(db);

			db->dbm_pagbno = db->dbm_blkptr;
			where = (((off64_t)db->dbm_blkptr) * PBLKSIZ);
			if ((lseek64(db->dbm_pagf, where, L_SET) != where) ||
			    (read(db->dbm_pagf, db->dbm_pagbuf, PBLKSIZ) !=
			    PBLKSIZ))
				(void) memset(db->dbm_pagbuf, 0, PBLKSIZ);
#ifdef DEBUG
			else if (chkblk(db->dbm_pagbuf) < 0)
				db->dbm_flags |= _DBM_IOERR;
#endif
		}
		/* Am I an empty block? */
		if (((short *)(uintptr_t)db->dbm_pagbuf)[0] != 0) {
			item = makdatum(db->dbm_pagbuf, db->dbm_keyptr);
			if (item.dptr != NULL) {
				db->dbm_keyptr += 2;
				return (item);
			}
			db->dbm_keyptr = 0;
		}
		/* go to next sequential block */
		if (++db->dbm_blkptr >= statb.st_size)
			break;
	}
err:
	item.dptr = NULL;
	item.dsize = 0;
	return (item);
}


datum
dbm_do_nextkey(DBM *db, datum inkey)
{
	datum item, bitem;
	unsigned long hash;
	datum key;
	int f;
	int i;
	int j;
	short *sp;
	long n;
	char *p1, *p2;
	off64_t where;

	if (dbm_error(db)) {
		item.dptr = NULL;
		item.dsize = 0;
		return (item);
	}

	/* user has supplied lastkey */

	if (inkey.dptr != NULL) {
		dbm_access(db, (hash = dcalchash(inkey)));
		if ((i = finddatum(db->dbm_pagbuf, inkey)) >= 0) {
			db->dbm_keyptr = i + 2;
			db->dbm_blkptr = db->dbm_blkno;
		}
		key = inkey;
	} else  {
		/* is this a manual firstkey request? */

		if (db->dbm_blkptr == 0L &&
		    db->dbm_keyptr == 0)
			return (dbm_firsthash(db, 0L));

		/* no -- get lastkey this is like dbm_access by blkptr */

		if (db->dbm_blkptr != db->dbm_pagbno) {

			if (dbm_dirty(db)) (void) dbm_flushpag(db);
			db->dbm_pagbno = db->dbm_blkptr;
			where = (((off64_t)db->dbm_blkptr) * PBLKSIZ);
			if ((lseek64(db->dbm_pagf, where, L_SET) != where) ||
			    (read(db->dbm_pagf, db->dbm_pagbuf, PBLKSIZ) !=
			    PBLKSIZ))
				(void) memset(db->dbm_pagbuf, 0, PBLKSIZ);
#ifdef DEBUG
			else if (chkblk(db->dbm_pagbuf) < 0)
			db->dbm_flags |= _DBM_IOERR;
#endif
		}
		/* now just make up last key datum */
		if (db->dbm_keyptr >= 2)
			key = makdatum(db->dbm_pagbuf, (db->dbm_keyptr-2));
		else key = nullkey;

		/*
		 * the keyptr pagbuf have failed us, the user must
		 * be an extra clever moron who depends on
		 * these variables and their former meaning.
		 * If we set the variables this would have got
		 * us the key for sure! So give it the old algorithm.
		 */
		if (key.dptr == NULL)
			return (dbm_slow_nextkey(db));
	}

	/*
	 * at this point the last key is paged in and
	 * we can proceed as in old dbm -- like Ken did his.
	 */

	f = 1;
	j = 0;
	sp = (short *)(uintptr_t)db->dbm_pagbuf;

	for (i = 0; ; i += 2) {

		/* begin put makdatum inline */

		if ((unsigned)i >= sp[0]) {
			item.dptr = NULL;
			item.dsize = 0;
			break; /* from below */
		} else {
			if (i > 0) item.dsize = sp[i] - sp[i + 1];
			else item.dsize = PBLKSIZ - sp[i + 1];
			item.dptr = db->dbm_pagbuf+sp[i + 1];
		}

		/* item = makdatum(db->dbm_pagbuf, i); */
		/* end put makdatum inline */

		if (item.dptr == NULL)
			break;
/* inline cmpdatum */


		n = key.dsize;
		if (n != item.dsize) {
			if ((n - item.dsize) <= 0)
				continue;
		} else {
			if (n == 0) continue;
			p1 = key.dptr;
			p2 = item.dptr;
			do {
				if (*p1++ != *p2++)
					if ((*--p1 - *--p2) > 0)
						goto keep_going;
					else continue;
			} while (--n);
			continue;
		}

keep_going:

/* end inline cmpdatum */
		/*
		 * if (cmpdatum(key, item) <= 0)
		 *	continue;
		 */

		if (f) {
			bitem = item;
			j = i;
			f = 0;
		} else {

			/* if (cmpdatum(bitem, item) < 0) */

			n = bitem.dsize;
			if (n != item.dsize) {
				if ((n - item.dsize) < 0) {
					bitem = item;
					j = i;
				}
			} else
				if (n != 0) {
					p1 = bitem.dptr;
					p2 = item.dptr;
					do {
					if (*p1++ != *p2++) {
						if ((*--p1 - *--p2) < 0) {
							bitem = item;
							j = i;
						}
						break;
					}
					} while (--n);
				}
			}
	}

	if (f == 0) {
		db->dbm_keyptr = j + 2;
		db->dbm_blkptr = db->dbm_blkno;
		return (bitem);
	}

	/* really need hash at this point */
	/* if it gave us a key we have already calculated the hash */
	/* if not get the hash */
	if (inkey.dptr == NULL)
		hash = dcalchash(key);
	hash = dbm_hashinc(db, hash);

	if (hash == 0)
		return (item); /* null */
	/* get first item on next page in hash table order */
	return (dbm_firsthash(db, hash));


}

static void
dbm_access(DBM *db, unsigned long hash)
{
	long b, i, n;
	long bn;
	long my_bitno;
	long my_hmask;
	long my_blkno;
	int j = (sizeof (my_hmask)) * 8;
	off64_t where;

	for (my_hmask = 0; j-- > 0; my_hmask = (my_hmask<<1) + 1) {
		my_blkno = hash & my_hmask;
		my_bitno = my_blkno + my_hmask;
		/* getbit inline */
		if (my_bitno > db->dbm_maxbno) break;
		n = my_bitno % BYTESIZ;
		bn = my_bitno / BYTESIZ;
		i = bn % DBLKSIZ;
		b = bn / DBLKSIZ;
		if (b != db->dbm_dirbno) {
			if (dbm_dirdirty(db))
				(void) dbm_flushdir(db); /* must flush */
			db->dbm_dirbno = b;
			where = (((off64_t)b) * DBLKSIZ);
			if ((lseek64(db->dbm_dirf, where, L_SET) != where) ||
			    (read(db->dbm_dirf, db->dbm_dirbuf, DBLKSIZ) !=
			    DBLKSIZ))
				(void) memset(db->dbm_dirbuf, 0, DBLKSIZ);
		}
		if ((db->dbm_dirbuf[i] & (1<<n)) == 0) break;

		/*
		 * if (getbit(db) == 0)
		 *	break;
		 */
	}
	/* copy */
	db->dbm_blkno = my_blkno;
	db->dbm_bitno = my_bitno;
	db->dbm_hmask = my_hmask;

	if (my_blkno != db->dbm_pagbno) {
		if (dbm_dirty(db)) { /* must page out the page */
			where = (((off64_t)db->dbm_pagbno) * PBLKSIZ);
			if ((lseek64(db->dbm_pagf, where, L_SET) != where) ||
			    (write(db->dbm_pagf, db->dbm_pagbuf, PBLKSIZ) !=
			    PBLKSIZ)) {
				db->dbm_flags |= _DBM_IOERR;
			}
		dbm_clrdirty(db);
		}

		db->dbm_pagbno = my_blkno;
		where = (((off64_t)my_blkno) * PBLKSIZ);
		if ((lseek64(db->dbm_pagf, where, L_SET) != where) ||
		    (read(db->dbm_pagf, db->dbm_pagbuf, PBLKSIZ) != PBLKSIZ))
			(void) memset(db->dbm_pagbuf, 0, PBLKSIZ);
#ifdef DEBUG
		else if (chkblk(db->dbm_pagbuf) < 0)
			db->dbm_flags |= _DBM_IOERR;
#endif
	}
}

static int
getbit(DBM *db)
{
	long bn;
	long b, i, n;
	off64_t where;

	if (db->dbm_bitno > db->dbm_maxbno)
		return (0);
	n = db->dbm_bitno % BYTESIZ;
	bn = db->dbm_bitno / BYTESIZ;
	i = bn % DBLKSIZ;
	b = bn / DBLKSIZ;
	if (b != db->dbm_dirbno) {
		if (dbm_dirdirty(db))
			(void) dbm_flushdir(db); /* must flush */
		db->dbm_dirbno = b;
		where = (((off64_t)b) * DBLKSIZ);
		if ((lseek64(db->dbm_dirf, where, L_SET) != where) ||
		    (read(db->dbm_dirf, db->dbm_dirbuf, DBLKSIZ) != DBLKSIZ))
			(void) memset(db->dbm_dirbuf, 0, DBLKSIZ);
	}
	return (db->dbm_dirbuf[i] & (1<<n));
}

static int
setbit(DBM *db)
{
	long bn;
	long i, n, b;
	off64_t where;

	if (db->dbm_bitno > db->dbm_maxbno)
		db->dbm_maxbno = db->dbm_bitno;
	n = db->dbm_bitno % BYTESIZ;
	bn = db->dbm_bitno / BYTESIZ;
	i = bn % DBLKSIZ;
	b = bn / DBLKSIZ;
	if (b != db->dbm_dirbno) {
		if (dbm_dirdirty(db))
			(void) dbm_flushdir(db);
		db->dbm_dirbno = b;
		where = (((off64_t)b) * DBLKSIZ);
		if ((lseek64(db->dbm_dirf, where, L_SET) != where) ||
		    (read(db->dbm_dirf, db->dbm_dirbuf, DBLKSIZ) != DBLKSIZ))
			(void) memset(db->dbm_dirbuf, 0, DBLKSIZ);
	}
	db->dbm_dirbuf[i] |= 1<<n;
	db->dbm_dirbno = b;
	if (dbm_defwrite(db)) {
		dbm_setdirdirty(db);
	} else {
		where = (((off64_t)b) * DBLKSIZ);
		if ((lseek64(db->dbm_dirf, where, L_SET) != where) ||
		    (write(db->dbm_dirf, db->dbm_dirbuf, DBLKSIZ) != DBLKSIZ)) {
			return (-1);
		}
	}
	return (0);
}

static datum
makdatum(char *buf, int n)
{
	short *sp;
	int t;
	datum item;

	sp = (short *)(uintptr_t)buf;
	if ((unsigned)n >= sp[0]) {
		item.dptr = NULL;
		item.dsize = 0;
		return (item);
	}
	t = PBLKSIZ;
	if (n > 0)
		t = sp[n];
	item.dptr = buf + sp[n + 1];
	item.dsize = t - sp[n + 1];
	return (item);
}

static int
cmpdatum(datum d1, datum d2)
{
	long n;
	char *p1, *p2;

	n = d1.dsize;
	if (n != d2.dsize)
		return ((int)(n - d2.dsize));
	if (n == 0)
		return (0);
	p1 = d1.dptr;
	p2 = d2.dptr;
	do {
		if (*p1 != *p2)
			return (*p1 - *p2);
		else {
			p1++;
			p2++;
		}
	} while (--n);
	return (0);
}

static int
finddatum(char *buf, datum item)
{
	short *sp;
	int i, n, j;

	sp = (short *)(uintptr_t)buf;
	n = PBLKSIZ;
	for (i = 0, j = sp[0]; i < j; i += 2, n = sp[i]) {
		n -= sp[i + 1];
		if (n != item.dsize)
			continue;
		if (n == 0 || memcmp(&buf[sp[i+1]], item.dptr, n) == 0)
			return (i);
	}
	return (-1);
}

static const int hitab[16]
/*
 * ken's
 * {
 *	055, 043, 036, 054, 063, 014, 004, 005,
 *	010, 064, 077, 000, 035, 027, 025, 071,
 * };
 */
	= {    61, 57, 53, 49, 45, 41, 37, 33,
		29, 25, 21, 17, 13,  9,  5,  1,
};

/* could consider to make it 32-bit int table to minimize memory usage */
static const long hltab[64]
	= {
	06100151277L, 06106161736L, 06452611562L, 05001724107L,
	02614772546L, 04120731531L, 04665262210L, 07347467531L,
	06735253126L, 06042345173L, 03072226605L, 01464164730L,
	03247435524L, 07652510057L, 01546775256L, 05714532133L,
	06173260402L, 07517101630L, 02431460343L, 01743245566L,
	00261675137L, 02433103631L, 03421772437L, 04447707466L,
	04435620103L, 03757017115L, 03641531772L, 06767633246L,
	02673230344L, 00260612216L, 04133454451L, 00615531516L,
	06137717526L, 02574116560L, 02304023373L, 07061702261L,
	05153031405L, 05322056705L, 07401116734L, 06552375715L,
	06165233473L, 05311063631L, 01212221723L, 01052267235L,
	06000615237L, 01075222665L, 06330216006L, 04402355630L,
	01451177262L, 02000133436L, 06025467062L, 07121076461L,
	03123433522L, 01010635225L, 01716177066L, 05161746527L,
	01736635071L, 06243505026L, 03637211610L, 01756474365L,
	04723077174L, 03642763134L, 05750130273L, 03655541561L,
};

static unsigned long
dcalchash(datum item)
{
	long s;
	int c, j;
	char *cp;
	unsigned long hashl;
	long hashi;

	hashl = 0;
	hashi = 0;
	for (cp = item.dptr, s = item.dsize; --s >= 0; ) {
		c = *cp++;
		for (j = 0; j < BYTESIZ; j += 4) {
			hashi += hitab[c&017];
			hashl += hltab[hashi&63];
			c >>= 4;
		}
	}
	return (hashl);
}

/*
 * Delete pairs of items (n & n+1).
 */
static int
delitem(char *buf, int n)
{
	short *sp, *sp1;
	int i1, i2;

	sp = (short *)(uintptr_t)buf;
	i2 = sp[0];
	if ((unsigned)n >= i2 || (n & 1))
		return (0);
	if (n == i2-2) {
		sp[0] -= 2;
		return (1);
	}
	i1 = PBLKSIZ;
	if (n > 0)
		i1 = sp[n];
	i1 -= sp[n+2];
	if (i1 > 0) {
		i2 = sp[i2];
		(void) memmove(&buf[i2 + i1], &buf[i2], sp[n+2] - i2);
	}
	sp[0] -= 2;
	for (sp1 = sp + sp[0], sp += n+1; sp <= sp1; sp++)
		sp[0] = sp[2] + i1;
	return (1);
}

/*
 * Add pairs of items (item & item1).
 */
static int
additem(char *buf, datum item, datum item1)
{
	short *sp;
	int i1, i2;

	sp = (short *)(uintptr_t)buf;
	i1 = PBLKSIZ;
	i2 = sp[0];
	if (i2 > 0)
		i1 = sp[i2];
	i1 -= item.dsize + item1.dsize;
	if (i1 <= (i2+3) * (int)sizeof (short))
		return (0);
	sp[0] += 2;
	sp[++i2] = (short)(i1 + item1.dsize);
	(void) memmove(&buf[i1 + item1.dsize], item.dptr, item.dsize);
	sp[++i2] = i1;
	(void) memmove(&buf[i1], item1.dptr, item1.dsize);
	return (1);
}

#ifdef DEBUG
static int
chkblk(char buf[PBLKSIZ])
{
	short *sp;
	int t, i;

	sp = (short *)buf;
	t = PBLKSIZ;
	for (i = 0; i < sp[0]; i++) {
		if (sp[i + 1] > t)
			return (-1);
		t = sp[i + 1];
	}
	if (t < (sp[0] + 1) * sizeof (short))
		return (-1);
	return (0);
}
#endif