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telldir.c revision 1.3.4.2 
      1 /*
      2  * Copyright (c) 1983, 1993
      3  *	The Regents of the University of California.  All rights reserved.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions
      7  * are met:
      8  * 1. Redistributions of source code must retain the above copyright
      9  *    notice, this list of conditions and the following disclaimer.
     10  * 2. Redistributions in binary form must reproduce the above copyright
     11  *    notice, this list of conditions and the following disclaimer in the
     12  *    documentation and/or other materials provided with the distribution.
     13  * 3. All advertising materials mentioning features or use of this software
     14  *    must display the following acknowledgement:
     15  *	This product includes software developed by the University of
     16  *	California, Berkeley and its contributors.
     17  * 4. Neither the name of the University nor the names of its contributors
     18  *    may be used to endorse or promote products derived from this software
     19  *    without specific prior written permission.
     20  *
     21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     31  * SUCH DAMAGE.
     32  */
     33 
     34 #if defined(LIBC_SCCS) && !defined(lint)
     35 /*static char sccsid[] = "from: @(#)telldir.c	8.1 (Berkeley) 6/4/93";*/
     36 static char rcsid[] = "$Id: telldir.c,v 1.3.4.2 1995/05/02 19:35:19 jtc Exp $";
     37 #endif /* LIBC_SCCS and not lint */
     38 
     39 #include "namespace.h"
     40 #include <sys/param.h>
     41 #include <dirent.h>
     42 #include <stdlib.h>
     43 #include <unistd.h>
     44 
     45 /*
     46  * The option SINGLEUSE may be defined to say that a telldir
     47  * cookie may be used only once before it is freed. This option
     48  * is used to avoid having memory usage grow without bound.
     49  */
     50 #define SINGLEUSE
     51 
     52 /*
     53  * One of these structures is malloced to describe the current directory
     54  * position each time telldir is called. It records the current magic
     55  * cookie returned by getdirentries and the offset within the buffer
     56  * associated with that return value.
     57  */
     58 struct ddloc {
     59 	struct	ddloc *loc_next;/* next structure in list */
     60 	long	loc_index;	/* key associated with structure */
     61 	long	loc_seek;	/* magic cookie returned by getdirentries */
     62 	long	loc_loc;	/* offset of entry in buffer */
     63 };
     64 
     65 #define	NDIRHASH	32	/* Num of hash lists, must be a power of 2 */
     66 #define	LOCHASH(i)	((i)&(NDIRHASH-1))
     67 
     68 static long	dd_loccnt;	/* Index of entry for sequential readdir's */
     69 static struct	ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
     70 
     71 /*
     72  * return a pointer into a directory
     73  */
     74 long
     75 telldir(dirp)
     76 	const DIR *dirp;
     77 {
     78 	register int index;
     79 	register struct ddloc *lp;
     80 
     81 	if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
     82 		return (-1);
     83 	index = dd_loccnt++;
     84 	lp->loc_index = index;
     85 	lp->loc_seek = dirp->dd_seek;
     86 	lp->loc_loc = dirp->dd_loc;
     87 	lp->loc_next = dd_hash[LOCHASH(index)];
     88 	dd_hash[LOCHASH(index)] = lp;
     89 	return (index);
     90 }
     91 #pragma weak telldir=_telldir
     92 
     93 
     94 /*
     95  * seek to an entry in a directory.
     96  * Only values returned by "telldir" should be passed to seekdir.
     97  */
     98 void
     99 __seekdir(dirp, loc)
    100 	register DIR *dirp;
    101 	long loc;
    102 {
    103 	register struct ddloc *lp;
    104 	register struct ddloc **prevlp;
    105 	struct dirent *dp;
    106 
    107 	prevlp = &dd_hash[LOCHASH(loc)];
    108 	lp = *prevlp;
    109 	while (lp != NULL) {
    110 		if (lp->loc_index == loc)
    111 			break;
    112 		prevlp = &lp->loc_next;
    113 		lp = lp->loc_next;
    114 	}
    115 	if (lp == NULL)
    116 		return;
    117 	if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
    118 		goto found;
    119 	(void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
    120 	dirp->dd_seek = lp->loc_seek;
    121 	dirp->dd_loc = 0;
    122 	while (dirp->dd_loc < lp->loc_loc) {
    123 		dp = readdir(dirp);
    124 		if (dp == NULL)
    125 			break;
    126 	}
    127 found:
    128 #ifdef SINGLEUSE
    129 	*prevlp = lp->loc_next;
    130 	free((caddr_t)lp);
    131 #endif
    132 }
    133