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telldir.c revision 1.17 
      1 /*	$NetBSD: telldir.c,v 1.17 2006/01/24 19:33:10 christos 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. Neither the name of the University nor the names of its contributors
     16  *    may be used to endorse or promote products derived from this software
     17  *    without specific prior written permission.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     29  * SUCH DAMAGE.
     30  */
     31 
     32 #include <sys/cdefs.h>
     33 #if defined(LIBC_SCCS) && !defined(lint)
     34 #if 0
     35 static char sccsid[] = "@(#)telldir.c	8.1 (Berkeley) 6/4/93";
     36 #else
     37 __RCSID("$NetBSD: telldir.c,v 1.17 2006/01/24 19:33:10 christos Exp $");
     38 #endif
     39 #endif /* LIBC_SCCS and not lint */
     40 
     41 #include "namespace.h"
     42 #include "reentrant.h"
     43 #include "extern.h"
     44 #include <sys/param.h>
     45 
     46 #include <assert.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 	off_t	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)	(((int)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 long
     82 telldir(const DIR *dirp)
     83 {
     84 	long rv;
     85 #ifdef _REENTRANT
     86 	if (__isthreaded) {
     87 		mutex_lock((mutex_t *)dirp->dd_lock);
     88 		rv = _telldir_unlocked(dirp);
     89 		mutex_unlock((mutex_t *)dirp->dd_lock);
     90 	} else
     91 #endif
     92 		rv = _telldir_unlocked(dirp);
     93 	return rv;
     94 }
     95 
     96 /*
     97  * return a pointer into a directory
     98  */
     99 long
    100 _telldir_unlocked(const DIR *dirp)
    101 {
    102 	long idx;
    103 	struct ddloc *lp;
    104 
    105 	if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
    106 		return (-1);
    107 	idx = dd_loccnt++;
    108 	lp->loc_index = idx;
    109 	lp->loc_seek = dirp->dd_seek;
    110 	lp->loc_loc = dirp->dd_loc;
    111 	lp->loc_next = dd_hash[LOCHASH(idx)];
    112 	dd_hash[LOCHASH(idx)] = lp;
    113 	return (idx);
    114 }
    115 
    116 /*
    117  * seek to an entry in a directory.
    118  * Only values returned by "telldir" should be passed to seekdir.
    119  */
    120 void
    121 _seekdir_unlocked(DIR *dirp, long loc)
    122 {
    123 	struct ddloc *lp;
    124 	struct ddloc **prevlp;
    125 	struct dirent *dp;
    126 
    127 	_DIAGASSERT(dirp != NULL);
    128 
    129 	prevlp = &dd_hash[LOCHASH(loc)];
    130 	lp = *prevlp;
    131 	while (lp != NULL) {
    132 		if (lp->loc_index == loc)
    133 			break;
    134 		prevlp = &lp->loc_next;
    135 		lp = lp->loc_next;
    136 	}
    137 	if (lp == NULL)
    138 		return;
    139 	if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
    140 		goto found;
    141 	(void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
    142 	dirp->dd_seek = lp->loc_seek;
    143 	dirp->dd_loc = 0;
    144 	while (dirp->dd_loc < lp->loc_loc) {
    145 		dp = _readdir_unlocked(dirp);
    146 		if (dp == NULL)
    147 			break;
    148 	}
    149 found:
    150 #ifdef SINGLEUSE
    151 	*prevlp = lp->loc_next;
    152 	free(lp);
    153 #endif
    154 }
    155