Home | History | Annotate | Line # | Download | only in gen
telldir.c revision 1.6 
      1 /*	$NetBSD: telldir.c,v 1.6 1997/07/21 14:07:38 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 #include <sys/cdefs.h>
     37 #if defined(LIBC_SCCS) && !defined(lint)
     38 #if 0
     39 static char sccsid[] = "@(#)telldir.c	8.1 (Berkeley) 6/4/93";
     40 #else
     41 __RCSID("$NetBSD: telldir.c,v 1.6 1997/07/21 14:07:38 jtc Exp $");
     42 #endif
     43 #endif /* LIBC_SCCS and not lint */
     44 
     45 #include "namespace.h"
     46 #include <sys/param.h>
     47 #include <dirent.h>
     48 #include <stdlib.h>
     49 #include <unistd.h>
     50 
     51 #ifdef __weak_alias
     52 __weak_alias(telldir,_telldir);
     53 #endif
     54 
     55 /*
     56  * The option SINGLEUSE may be defined to say that a telldir
     57  * cookie may be used only once before it is freed. This option
     58  * is used to avoid having memory usage grow without bound.
     59  */
     60 #define SINGLEUSE
     61 
     62 /*
     63  * One of these structures is malloced to describe the current directory
     64  * position each time telldir is called. It records the current magic
     65  * cookie returned by getdirentries and the offset within the buffer
     66  * associated with that return value.
     67  */
     68 struct ddloc {
     69 	struct	ddloc *loc_next;/* next structure in list */
     70 	long	loc_index;	/* key associated with structure */
     71 	long	loc_seek;	/* magic cookie returned by getdirentries */
     72 	long	loc_loc;	/* offset of entry in buffer */
     73 };
     74 
     75 #define	NDIRHASH	32	/* Num of hash lists, must be a power of 2 */
     76 #define	LOCHASH(i)	((i)&(NDIRHASH-1))
     77 
     78 static long	dd_loccnt;	/* Index of entry for sequential readdir's */
     79 static struct	ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
     80 
     81 /*
     82  * return a pointer into a directory
     83  */
     84 long
     85 telldir(dirp)
     86 	const DIR *dirp;
     87 {
     88 	register int index;
     89 	register struct ddloc *lp;
     90 
     91 	if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
     92 		return (-1);
     93 	index = dd_loccnt++;
     94 	lp->loc_index = index;
     95 	lp->loc_seek = dirp->dd_seek;
     96 	lp->loc_loc = dirp->dd_loc;
     97 	lp->loc_next = dd_hash[LOCHASH(index)];
     98 	dd_hash[LOCHASH(index)] = lp;
     99 	return (index);
    100 }
    101 
    102 /*
    103  * seek to an entry in a directory.
    104  * Only values returned by "telldir" should be passed to seekdir.
    105  */
    106 void
    107 __seekdir(dirp, loc)
    108 	register DIR *dirp;
    109 	long loc;
    110 {
    111 	register struct ddloc *lp;
    112 	register struct ddloc **prevlp;
    113 	struct dirent *dp;
    114 
    115 	prevlp = &dd_hash[LOCHASH(loc)];
    116 	lp = *prevlp;
    117 	while (lp != NULL) {
    118 		if (lp->loc_index == loc)
    119 			break;
    120 		prevlp = &lp->loc_next;
    121 		lp = lp->loc_next;
    122 	}
    123 	if (lp == NULL)
    124 		return;
    125 	if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
    126 		goto found;
    127 	(void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
    128 	dirp->dd_seek = lp->loc_seek;
    129 	dirp->dd_loc = 0;
    130 	while (dirp->dd_loc < lp->loc_loc) {
    131 		dp = readdir(dirp);
    132 		if (dp == NULL)
    133 			break;
    134 	}
    135 found:
    136 #ifdef SINGLEUSE
    137 	*prevlp = lp->loc_next;
    138 	free((caddr_t)lp);
    139 #endif
    140 }
    141