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telldir.c revision 1.4 
      1 /*	$NetBSD: telldir.c,v 1.4 1995/02/25 08:51:51 cgd 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 1995/02/25 08:51:51 cgd Exp $";
     41 #endif
     42 #endif /* LIBC_SCCS and not lint */
     43 
     44 #include <sys/param.h>
     45 #include <dirent.h>
     46 #include <stdlib.h>
     47 #include <unistd.h>
     48 
     49 /*
     50  * The option SINGLEUSE may be defined to say that a telldir
     51  * cookie may be used only once before it is freed. This option
     52  * is used to avoid having memory usage grow without bound.
     53  */
     54 #define SINGLEUSE
     55 
     56 /*
     57  * One of these structures is malloced to describe the current directory
     58  * position each time telldir is called. It records the current magic
     59  * cookie returned by getdirentries and the offset within the buffer
     60  * associated with that return value.
     61  */
     62 struct ddloc {
     63 	struct	ddloc *loc_next;/* next structure in list */
     64 	long	loc_index;	/* key associated with structure */
     65 	long	loc_seek;	/* magic cookie returned by getdirentries */
     66 	long	loc_loc;	/* offset of entry in buffer */
     67 };
     68 
     69 #define	NDIRHASH	32	/* Num of hash lists, must be a power of 2 */
     70 #define	LOCHASH(i)	((i)&(NDIRHASH-1))
     71 
     72 static long	dd_loccnt;	/* Index of entry for sequential readdir's */
     73 static struct	ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
     74 
     75 /*
     76  * return a pointer into a directory
     77  */
     78 long
     79 telldir(dirp)
     80 	const DIR *dirp;
     81 {
     82 	register int index;
     83 	register struct ddloc *lp;
     84 
     85 	if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
     86 		return (-1);
     87 	index = dd_loccnt++;
     88 	lp->loc_index = index;
     89 	lp->loc_seek = dirp->dd_seek;
     90 	lp->loc_loc = dirp->dd_loc;
     91 	lp->loc_next = dd_hash[LOCHASH(index)];
     92 	dd_hash[LOCHASH(index)] = lp;
     93 	return (index);
     94 }
     95 
     96 /*
     97  * seek to an entry in a directory.
     98  * Only values returned by "telldir" should be passed to seekdir.
     99  */
    100 void
    101 __seekdir(dirp, loc)
    102 	register DIR *dirp;
    103 	long loc;
    104 {
    105 	register struct ddloc *lp;
    106 	register struct ddloc **prevlp;
    107 	struct dirent *dp;
    108 
    109 	prevlp = &dd_hash[LOCHASH(loc)];
    110 	lp = *prevlp;
    111 	while (lp != NULL) {
    112 		if (lp->loc_index == loc)
    113 			break;
    114 		prevlp = &lp->loc_next;
    115 		lp = lp->loc_next;
    116 	}
    117 	if (lp == NULL)
    118 		return;
    119 	if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
    120 		goto found;
    121 	(void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
    122 	dirp->dd_seek = lp->loc_seek;
    123 	dirp->dd_loc = 0;
    124 	while (dirp->dd_loc < lp->loc_loc) {
    125 		dp = readdir(dirp);
    126 		if (dp == NULL)
    127 			break;
    128 	}
    129 found:
    130 #ifdef SINGLEUSE
    131 	*prevlp = lp->loc_next;
    132 	free((caddr_t)lp);
    133 #endif
    134 }
    135