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telldir.c revision 1.15 
      1 /*	$NetBSD: telldir.c,v 1.15 2003/08/07 16:42:58 agc 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 1.15 2003/08/07 16:42:58 agc Exp $");
     38 #endif
     39 #endif /* LIBC_SCCS and not lint */
     40 
     41 #include "namespace.h"
     42 #include "reentrant.h"
     43 #include <sys/param.h>
     44 
     45 #include <assert.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 	off_t	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)	(((int)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 	long idx;
     88 	struct ddloc *lp;
     89 
     90 #ifdef _REENTRANT
     91 	if (__isthreaded)
     92 		mutex_lock((mutex_t *)dirp->dd_lock);
     93 #endif
     94 
     95 	if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
     96 		return (-1);
     97 	idx = dd_loccnt++;
     98 	lp->loc_index = idx;
     99 	lp->loc_seek = dirp->dd_seek;
    100 	lp->loc_loc = dirp->dd_loc;
    101 	lp->loc_next = dd_hash[LOCHASH(idx)];
    102 	dd_hash[LOCHASH(idx)] = lp;
    103 #ifdef _REENTRANT
    104 	if (__isthreaded)
    105 		mutex_unlock((mutex_t *)dirp->dd_lock);
    106 #endif
    107 	return (idx);
    108 }
    109 
    110 /*
    111  * seek to an entry in a directory.
    112  * Only values returned by "telldir" should be passed to seekdir.
    113  */
    114 void
    115 __seekdir(dirp, loc)
    116 	DIR *dirp;
    117 	long loc;
    118 {
    119 	struct ddloc *lp;
    120 	struct ddloc **prevlp;
    121 	struct dirent *dp;
    122 
    123 	_DIAGASSERT(dirp != NULL);
    124 
    125 	prevlp = &dd_hash[LOCHASH(loc)];
    126 	lp = *prevlp;
    127 	while (lp != NULL) {
    128 		if (lp->loc_index == loc)
    129 			break;
    130 		prevlp = &lp->loc_next;
    131 		lp = lp->loc_next;
    132 	}
    133 	if (lp == NULL)
    134 		return;
    135 	if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
    136 		goto found;
    137 	(void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
    138 	dirp->dd_seek = lp->loc_seek;
    139 	dirp->dd_loc = 0;
    140 	while (dirp->dd_loc < lp->loc_loc) {
    141 		dp = readdir(dirp);
    142 		if (dp == NULL)
    143 			break;
    144 	}
    145 found:
    146 #ifdef SINGLEUSE
    147 	*prevlp = lp->loc_next;
    148 	free(lp);
    149 #endif
    150 }
    151