sysdeps/unix/bsd/telldir.c

   1 /* Copyright (C) 1994, 1995 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 #include "dirstream.h"
  27
  28 /* Internal data structure for telldir and seekdir.  */
  29 struct record
  30   {
  31     struct record *next; /* Link in chain.  */
  32     off_t cookie;               /* Value returned by `telldir'.  */
  33     off_t pos;
  34     size_t offset;
  35   };
  36 #define NBUCKETS 32
  37 static struct record *records[32];
  38 static off_t lastpos;
  39
  40
  41 /* Return the current position of DIRP.  */
  42 off_t
  43 DEFUN(telldir, (dirp), DIR *dirp)
  44 {
  45   struct record *new;
  46
  47   new = malloc (sizeof *new);
  48   if (new == NULL)
  49     return (off_t) -1;
  50
  51   new->pos = dirp->__pos;
  52   new->offset = dirp->__offset;
  53   new->cookie = ++lastpos;
  54   new->next = records[new->cookie % NBUCKETS];
  55   records[new->cookie % NBUCKETS] = new;
  56
  57   return new->cookie;
  58 }
  59
  60 \f
  61
  62 /* Seek to position POS in DIRP.  */
  63 void
  64 DEFUN(seekdir, (dirp, pos), DIR *dirp AND __off_t pos)
  65 {
  66   struct record *r, **prevr;
  67
  68   for (prevr = &records[pos % NBUCKETS], r = *prevr;
  69        r != NULL;
  70        prevr = &r->next, r = r->next)
  71     if (r->cookie == pos)
  72       {
  73         if (dirp->__pos != r->pos || dirp->__offset != r->offset)
  74           {
  75             dirp->__size = 0;   /* Must read a fresh buffer.  */
  76             /* Move to the saved position.  */
  77             __lseek (dirp->__fd, r->pos, SEEK_SET);
  78             dirp->__pos = r->pos;
  79             dirp->__offset = 0;
  80             /* Read entries until we reach the saved offset.  */
  81             while (dirp->__offset < r->offset)
  82               if (readdir (dirp) == NULL)
  83                 break;
  84           }
  85
  86         /* To prevent leaking memory, cookies returned from telldir
  87            can only be used once.  So free this one's record now.  */
  88         *prevr = r->next;
  89         free (r);
  90         return;
  91       }
  92
  93   /* We lost, but have no way to indicate it.  Oh well.  */
  94 }