sysdeps/unix/bsd/telldir.c

   1 /* Copyright (C) 1994 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 The GNU C Library is free software; you can redistribute it and/or
   5 modify it under the terms of the GNU Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 License, or (at your option) any later version.
   8
   9 The GNU C Library is distributed in the hope that it will be useful,
  10 but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <errno.h>
  21 #include <stddef.h>
  22 #include <dirent.h>
  23 #include <unistd.h>
  24 #include <sys/types.h>
  25 #include <stdlib.h>
  26
  27 /* Internal data structure for telldir and seekdir.  */
  28 struct record
  29   {
  30     struct record *next; /* Link in chain.  */
  31     off_t cookie;               /* Value returned by `telldir'.  */
  32     off_t pos;
  33     size_t offset;
  34   };
  35 #define NBUCKETS 32
  36 static struct record *records[32];
  37 static off_t lastpos;
  38
  39
  40 /* Return the current position of DIRP.  */
  41 off_t
  42 DEFUN(telldir, (dirp), DIR *dirp)
  43 {
  44   struct record *new;
  45
  46   new = malloc (sizeof *new);
  47   if (new == NULL)
  48     return (off_t) -1;
  49
  50   new->pos = dirp->__pos;
  51   new->offset = dirp->__offset;
  52   new->cookie = ++lastpos;
  53   new->next = records[new->cookie % NBUCKETS];
  54   records[new->cookie % NBUCKETS] = new;
  55
  56   return new->cookie;
  57 }
  58
  59 \f
  60
  61 /* Seek to position POS in DIRP.  */
  62 void
  63 DEFUN(seekdir, (dirp, pos), DIR *dirp AND __off_t pos)
  64 {
  65   struct record *r, **prevr;
  66
  67   for (prevr = &records[pos % NBUCKETS], r = *prevr;
  68        r != NULL;
  69        prevr = &r->next, r = r->next)
  70     if (r->cookie == pos)
  71       {
  72         if (dirp->__pos != r->pos || dirp->__offset != r->offset)
  73           {
  74             dirp->__size = 0;   /* Must read a fresh buffer.  */
  75             /* Move to the saved position.  */
  76             __lseek (dirp->__fd, r->pos, SEEK_SET);
  77             dirp->__pos = r->pos;
  78             dirp->__offset = 0;
  79             /* Read entries until we reach the saved offset.  */
  80             while (dirp->__offset < r->offset)
  81               if (readdir (dirp) == NULL)
  82                 break;
  83           }
  84
  85         /* To prevent leaking memory, cookies returned from telldir
  86            can only be used once.  So free this one's record now.  */
  87         *prevr = r->next;
  88         free (r);
  89         return;
  90       }
  91
  92   /* We lost, but have no way to indicate it.  Oh well.  */
  93 }