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telldir.c revision 1.4.4.1 
      1 /*	$NetBSD: telldir.c,v 1.4.4.1 1996/09/16 18:40:38 jtc Exp $	*/
      2 
      3 /*
      4  * Copyright (c) 1983, 1993
      5  *	The Regents of the University of California.  All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  * 3. All advertising materials mentioning features or use of this software
     16  *    must display the following acknowledgement:
     17  *	This product includes software developed by the University of
     18  *	California, Berkeley and its contributors.
     19  * 4. Neither the name of the University nor the names of its contributors
     20  *    may be used to endorse or promote products derived from this software
     21  *    without specific prior written permission.
     22  *
     23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     33  * SUCH DAMAGE.
     34  */
     35 
     36 #if defined(LIBC_SCCS) && !defined(lint)
     37 #if 0
     38 static char sccsid[] = "@(#)telldir.c	8.1 (Berkeley) 6/4/93";
     39 #else
     40 static char rcsid[] = "$NetBSD: telldir.c,v 1.4.4.1 1996/09/16 18:40:38 jtc Exp $";
     41 #endif
     42 #endif /* LIBC_SCCS and not lint */
     43 
     44 #include "namespace.h"
     45 #include <sys/param.h>
     46 #include <dirent.h>
     47 #include <stdlib.h>
     48 #include <unistd.h>
     49 
     50 #ifdef __weak_alias
     51 __weak_alias(telldir,_telldir);
     52 #endif
     53 
     54 /*
     55  * The option SINGLEUSE may be defined to say that a telldir
     56  * cookie may be used only once before it is freed. This option
     57  * is used to avoid having memory usage grow without bound.
     58  */
     59 #define SINGLEUSE
     60 
     61 /*
     62  * One of these structures is malloced to describe the current directory
     63  * position each time telldir is called. It records the current magic
     64  * cookie returned by getdirentries and the offset within the buffer
     65  * associated with that return value.
     66  */
     67 struct ddloc {
     68 	struct	ddloc *loc_next;/* next structure in list */
     69 	long	loc_index;	/* key associated with structure */
     70 	long	loc_seek;	/* magic cookie returned by getdirentries */
     71 	long	loc_loc;	/* offset of entry in buffer */
     72 };
     73 
     74 #define	NDIRHASH	32	/* Num of hash lists, must be a power of 2 */
     75 #define	LOCHASH(i)	((i)&(NDIRHASH-1))
     76 
     77 static long	dd_loccnt;	/* Index of entry for sequential readdir's */
     78 static struct	ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
     79 
     80 /*
     81  * return a pointer into a directory
     82  */
     83 long
     84 telldir(dirp)
     85 	const DIR *dirp;
     86 {
     87 	register int index;
     88 	register struct ddloc *lp;
     89 
     90 	if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
     91 		return (-1);
     92 	index = dd_loccnt++;
     93 	lp->loc_index = index;
     94 	lp->loc_seek = dirp->dd_seek;
     95 	lp->loc_loc = dirp->dd_loc;
     96 	lp->loc_next = dd_hash[LOCHASH(index)];
     97 	dd_hash[LOCHASH(index)] = lp;
     98 	return (index);
     99 }
    100 
    101 /*
    102  * seek to an entry in a directory.
    103  * Only values returned by "telldir" should be passed to seekdir.
    104  */
    105 void
    106 __seekdir(dirp, loc)
    107 	register DIR *dirp;
    108 	long loc;
    109 {
    110 	register struct ddloc *lp;
    111 	register struct ddloc **prevlp;
    112 	struct dirent *dp;
    113 
    114 	prevlp = &dd_hash[LOCHASH(loc)];
    115 	lp = *prevlp;
    116 	while (lp != NULL) {
    117 		if (lp->loc_index == loc)
    118 			break;
    119 		prevlp = &lp->loc_next;
    120 		lp = lp->loc_next;
    121 	}
    122 	if (lp == NULL)
    123 		return;
    124 	if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
    125 		goto found;
    126 	(void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
    127 	dirp->dd_seek = lp->loc_seek;
    128 	dirp->dd_loc = 0;
    129 	while (dirp->dd_loc < lp->loc_loc) {
    130 		dp = readdir(dirp);
    131 		if (dp == NULL)
    132 			break;
    133 	}
    134 found:
    135 #ifdef SINGLEUSE
    136 	*prevlp = lp->loc_next;
    137 	free((caddr_t)lp);
    138 #endif
    139 }
    140