newlib/libc/sys/sysvi386/telldir.c

   1 /*
   2  * Copyright (c) 1983 Regents of the University of California.
   3  * 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. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  */
  29
  30 #if defined(LIBC_SCCS) && !defined(lint)
  31 static char sccsid[] = "@(#)telldir.c   5.9 (Berkeley) 2/23/91";
  32 #endif /* LIBC_SCCS and not lint */
  33
  34 #include <sys/param.h>
  35 #include <dirent.h>
  36 #include <stdlib.h>
  37 #include <unistd.h>
  38
  39 /*
  40  * The option SINGLEUSE may be defined to say that a telldir
  41  * cookie may be used only once before it is freed. This option
  42  * is used to avoid having memory usage grow without bound.
  43  */
  44 #define SINGLEUSE
  45
  46 /*
  47  * One of these structures is malloced to describe the current directory
  48  * position each time telldir is called. It records the current magic
  49  * cookie returned by getdirentries and the offset within the buffer
  50  * associated with that return value.
  51  */
  52 struct ddloc {
  53         struct  ddloc *loc_next;/* next structure in list */
  54         long    loc_index;      /* key associated with structure */
  55         long    loc_seek;       /* magic cookie returned by getdirentries */
  56         long    loc_loc;        /* offset of entry in buffer */
  57 };
  58
  59 #define NDIRHASH        32      /* Num of hash lists, must be a power of 2 */
  60 #define LOCHASH(i)      ((i)&(NDIRHASH-1))
  61
  62 static long     dd_loccnt;      /* Index of entry for sequential readdir's */
  63 static struct   ddloc *dd_hash[NDIRHASH];   /* Hash list heads for ddlocs */
  64
  65 /*
  66  * return a pointer into a directory
  67  */
  68 long
  69 telldir(dirp)
  70         const DIR *dirp;
  71 {
  72         register int index;
  73         register struct ddloc *lp;
  74
  75         if ((lp = (struct ddloc *)malloc(sizeof(struct ddloc))) == NULL)
  76                 return (-1);
  77         index = dd_loccnt++;
  78         lp->loc_index = index;
  79         lp->loc_seek = dirp->dd_seek;
  80         lp->loc_loc = dirp->dd_loc;
  81         lp->loc_next = dd_hash[LOCHASH(index)];
  82         dd_hash[LOCHASH(index)] = lp;
  83         return (index);
  84 }
  85
  86 /*
  87  * seek to an entry in a directory.
  88  * Only values returned by "telldir" should be passed to seekdir.
  89  */
  90 void
  91 _seekdir(dirp, loc)
  92         register DIR *dirp;
  93         long loc;
  94 {
  95         register struct ddloc *lp;
  96         register struct ddloc **prevlp;
  97         struct dirent *dp;
  98         extern long lseek();
  99
 100         prevlp = &dd_hash[LOCHASH(loc)];
 101         lp = *prevlp;
 102         while (lp != NULL) {
 103                 if (lp->loc_index == loc)
 104                         break;
 105                 prevlp = &lp->loc_next;
 106                 lp = lp->loc_next;
 107         }
 108         if (lp == NULL)
 109                 return;
 110         if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
 111                 goto found;
 112         (void) lseek(dirp->dd_fd, lp->loc_seek, 0);
 113         dirp->dd_seek = lp->loc_seek;
 114         dirp->dd_loc = 0;
 115         while (dirp->dd_loc < lp->loc_loc) {
 116                 dp = readdir(dirp);
 117                 if (dp == NULL)
 118                         break;
 119         }
 120 found:
 121 #ifdef SINGLEUSE
 122         *prevlp = lp->loc_next;
 123         free((caddr_t)lp);
 124 #endif
 125 }