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telldir.c revision 1.5 
      1 /*	$NetBSD: telldir.c,v 1.5 1997/07/13 19:46:20 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. 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 1.5 1997/07/13 19:46:20 christos Exp $");
     42 #endif
     43 #endif /* LIBC_SCCS and not lint */
     44 
     45 #include <sys/param.h>
     46 #include <dirent.h>
     47 #include <stdlib.h>
     48 #include <unistd.h>
     49 
     50 /*
     51  * The option SINGLEUSE may be defined to say that a telldir
     52  * cookie may be used only once before it is freed. This option
     53  * is used to avoid having memory usage grow without bound.
     54  */
     55 #define SINGLEUSE
     56 
     57 /*
     58  * One of these structures is malloced to describe the current directory
     59  * position each time telldir is called. It records the current magic
     60  * cookie returned by getdirentries and the offset within the buffer
     61  * associated with that return value.
     62  */
     63 struct ddloc {
     64 	struct	ddloc *loc_next;/* next structure in list */
     65 	long	loc_index;	/* key associated with structure */
     66 	long	loc_seek;	/* magic cookie returned by getdirentries */
     67 	long	loc_loc;	/* offset of entry in buffer */
     68 };
     69 
     70 #define	NDIRHASH	32	/* Num of hash lists, must be a power of 2 */
     71 #define	LOCHASH(i)	((i)&(NDIRHASH-1))
     72 
     73 static long	dd_loccnt;	/* Index of entry for sequential readdir's */
     74 static struct	ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
     75 
     76 /*
     77  * return a pointer into a directory
     78  */
     79 long
     80 telldir(dirp)
     81 	const DIR *dirp;
     82 {
     83 	register int index;
     84 	register struct ddloc *lp;
     85 
     86 	if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
     87 		return (-1);
     88 	index = dd_loccnt++;
     89 	lp->loc_index = index;
     90 	lp->loc_seek = dirp->dd_seek;
     91 	lp->loc_loc = dirp->dd_loc;
     92 	lp->loc_next = dd_hash[LOCHASH(index)];
     93 	dd_hash[LOCHASH(index)] = lp;
     94 	return (index);
     95 }
     96 
     97 /*
     98  * seek to an entry in a directory.
     99  * Only values returned by "telldir" should be passed to seekdir.
    100  */
    101 void
    102 __seekdir(dirp, loc)
    103 	register DIR *dirp;
    104 	long loc;
    105 {
    106 	register struct ddloc *lp;
    107 	register struct ddloc **prevlp;
    108 	struct dirent *dp;
    109 
    110 	prevlp = &dd_hash[LOCHASH(loc)];
    111 	lp = *prevlp;
    112 	while (lp != NULL) {
    113 		if (lp->loc_index == loc)
    114 			break;
    115 		prevlp = &lp->loc_next;
    116 		lp = lp->loc_next;
    117 	}
    118 	if (lp == NULL)
    119 		return;
    120 	if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
    121 		goto found;
    122 	(void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
    123 	dirp->dd_seek = lp->loc_seek;
    124 	dirp->dd_loc = 0;
    125 	while (dirp->dd_loc < lp->loc_loc) {
    126 		dp = readdir(dirp);
    127 		if (dp == NULL)
    128 			break;
    129 	}
    130 found:
    131 #ifdef SINGLEUSE
    132 	*prevlp = lp->loc_next;
    133 	free((caddr_t)lp);
    134 #endif
    135 }
    136