Home | History | Annotate | Line # | Download | only in gen
telldir.c revision 1.2 
      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[] = "@(#)telldir.c	8.1 (Berkeley) 6/4/93";
     36 #endif /* LIBC_SCCS and not lint */
     37 
     38 #include <sys/param.h>
     39 #include <dirent.h>
     40 #include <stdlib.h>
     41 #include <unistd.h>
     42 
     43 /*
     44  * The option SINGLEUSE may be defined to say that a telldir
     45  * cookie may be used only once before it is freed. This option
     46  * is used to avoid having memory usage grow without bound.
     47  */
     48 #define SINGLEUSE
     49 
     50 /*
     51  * One of these structures is malloced to describe the current directory
     52  * position each time telldir is called. It records the current magic
     53  * cookie returned by getdirentries and the offset within the buffer
     54  * associated with that return value.
     55  */
     56 struct ddloc {
     57 	struct	ddloc *loc_next;/* next structure in list */
     58 	long	loc_index;	/* key associated with structure */
     59 	long	loc_seek;	/* magic cookie returned by getdirentries */
     60 	long	loc_loc;	/* offset of entry in buffer */
     61 };
     62 
     63 #define	NDIRHASH	32	/* Num of hash lists, must be a power of 2 */
     64 #define	LOCHASH(i)	((i)&(NDIRHASH-1))
     65 
     66 static long	dd_loccnt;	/* Index of entry for sequential readdir's */
     67 static struct	ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
     68 
     69 /*
     70  * return a pointer into a directory
     71  */
     72 long
     73 telldir(dirp)
     74 	const DIR *dirp;
     75 {
     76 	register int index;
     77 	register struct ddloc *lp;
     78 
     79 	if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
     80 		return (-1);
     81 	index = dd_loccnt++;
     82 	lp->loc_index = index;
     83 	lp->loc_seek = dirp->dd_seek;
     84 	lp->loc_loc = dirp->dd_loc;
     85 	lp->loc_next = dd_hash[LOCHASH(index)];
     86 	dd_hash[LOCHASH(index)] = lp;
     87 	return (index);
     88 }
     89 
     90 /*
     91  * seek to an entry in a directory.
     92  * Only values returned by "telldir" should be passed to seekdir.
     93  */
     94 void
     95 __seekdir(dirp, loc)
     96 	register DIR *dirp;
     97 	long loc;
     98 {
     99 	register struct ddloc *lp;
    100 	register struct ddloc **prevlp;
    101 	struct dirent *dp;
    102 
    103 	prevlp = &dd_hash[LOCHASH(loc)];
    104 	lp = *prevlp;
    105 	while (lp != NULL) {
    106 		if (lp->loc_index == loc)
    107 			break;
    108 		prevlp = &lp->loc_next;
    109 		lp = lp->loc_next;
    110 	}
    111 	if (lp == NULL)
    112 		return;
    113 	if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
    114 		goto found;
    115 	(void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
    116 	dirp->dd_seek = lp->loc_seek;
    117 	dirp->dd_loc = 0;
    118 	while (dirp->dd_loc < lp->loc_loc) {
    119 		dp = readdir(dirp);
    120 		if (dp == NULL)
    121 			break;
    122 	}
    123 found:
    124 #ifdef SINGLEUSE
    125 	*prevlp = lp->loc_next;
    126 	free((caddr_t)lp);
    127 #endif
    128 }
    129