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telldir.c revision 1.13 
      1 /*	$NetBSD: telldir.c,v 1.13 2001/12/30 19:27:42 thorpej 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 1.13 2001/12/30 19:27:42 thorpej Exp $");
     42 #endif
     43 #endif /* LIBC_SCCS and not lint */
     44 
     45 #include "namespace.h"
     46 #include <sys/param.h>
     47 
     48 #include <assert.h>
     49 #include <dirent.h>
     50 #include <stdlib.h>
     51 #include <unistd.h>
     52 
     53 #ifdef __weak_alias
     54 __weak_alias(telldir,_telldir)
     55 #endif
     56 
     57 /*
     58  * The option SINGLEUSE may be defined to say that a telldir
     59  * cookie may be used only once before it is freed. This option
     60  * is used to avoid having memory usage grow without bound.
     61  */
     62 #define SINGLEUSE
     63 
     64 /*
     65  * One of these structures is malloced to describe the current directory
     66  * position each time telldir is called. It records the current magic
     67  * cookie returned by getdirentries and the offset within the buffer
     68  * associated with that return value.
     69  */
     70 struct ddloc {
     71 	struct	ddloc *loc_next;/* next structure in list */
     72 	long	loc_index;	/* key associated with structure */
     73 	off_t	loc_seek;	/* magic cookie returned by getdirentries */
     74 	long	loc_loc;	/* offset of entry in buffer */
     75 };
     76 
     77 #define	NDIRHASH	32	/* Num of hash lists, must be a power of 2 */
     78 #define	LOCHASH(i)	(((int)i)&(NDIRHASH-1))
     79 
     80 static long	dd_loccnt;	/* Index of entry for sequential readdir's */
     81 static struct	ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
     82 
     83 /*
     84  * return a pointer into a directory
     85  */
     86 long
     87 telldir(dirp)
     88 	const DIR *dirp;
     89 {
     90 	long idx;
     91 	struct ddloc *lp;
     92 
     93 
     94 	if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
     95 		return (-1);
     96 	idx = dd_loccnt++;
     97 	lp->loc_index = idx;
     98 	lp->loc_seek = dirp->dd_seek;
     99 	lp->loc_loc = dirp->dd_loc;
    100 	lp->loc_next = dd_hash[LOCHASH(idx)];
    101 	dd_hash[LOCHASH(idx)] = lp;
    102 	return (idx);
    103 }
    104 
    105 /*
    106  * seek to an entry in a directory.
    107  * Only values returned by "telldir" should be passed to seekdir.
    108  */
    109 void
    110 __seekdir(dirp, loc)
    111 	DIR *dirp;
    112 	long loc;
    113 {
    114 	struct ddloc *lp;
    115 	struct ddloc **prevlp;
    116 	struct dirent *dp;
    117 
    118 	_DIAGASSERT(dirp != NULL);
    119 
    120 	prevlp = &dd_hash[LOCHASH(loc)];
    121 	lp = *prevlp;
    122 	while (lp != NULL) {
    123 		if (lp->loc_index == loc)
    124 			break;
    125 		prevlp = &lp->loc_next;
    126 		lp = lp->loc_next;
    127 	}
    128 	if (lp == NULL)
    129 		return;
    130 	if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
    131 		goto found;
    132 	(void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
    133 	dirp->dd_seek = lp->loc_seek;
    134 	dirp->dd_loc = 0;
    135 	while (dirp->dd_loc < lp->loc_loc) {
    136 		dp = readdir(dirp);
    137 		if (dp == NULL)
    138 			break;
    139 	}
    140 found:
    141 #ifdef SINGLEUSE
    142 	*prevlp = lp->loc_next;
    143 	free(lp);
    144 #endif
    145 }
    146