sysdeps/unix/bsd/telldir.c

   1 /* Copyright (C) 1994, 1995, 1996 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 __libc_lock_define_initialized(static, lock) /* Locks above data.  */
  40
  41
  42 /* Return the current position of DIRP.  */
  43 off_t
  44 DEFUN(telldir, (dirp), DIR *dirp)
  45 {
  46   struct record *new;
  47   off_t pos;
  48
  49   __libc_lock_lock (lock);
  50
  51   new = malloc (sizeof *new);
  52   if (new == NULL)
  53     return (off_t) -1;
  54
  55   new->pos = dirp->filepos;
  56   new->offset = dirp->offset;
  57   new->cookie = ++lastpos;
  58   new->next = records[new->cookie % NBUCKETS];
  59   records[new->cookie % NBUCKETS] = new;
  60
  61   pos = new->cookie;
  62
  63   __libc_lock_unlock (lock);
  64
  65   return pos;
  66 }
  67
  68 \f
  69
  70 /* Seek to position POS in DIRP.  */
  71 void
  72 DEFUN(seekdir, (dirp, pos), DIR *dirp AND __off_t pos)
  73 {
  74   struct record *r, **prevr;
  75
  76   __libc_lock_lock (lock);
  77
  78   for (prevr = &records[pos % NBUCKETS], r = *prevr;
  79        r != NULL;
  80        prevr = &r->next, r = r->next)
  81     if (r->cookie == pos)
  82       {
  83         __libc_lock_lock (dirp->__lock);
  84         if (dirp->filepos != r->pos || dirp->offset != r->offset)
  85           {
  86             dirp->size = 0;     /* Must read a fresh buffer.  */
  87             /* Move to the saved position.  */
  88             __lseek (dirp->fd, r->pos, SEEK_SET);
  89             dirp->filepos = r->pos;
  90             dirp->offset = 0;
  91             /* Read entries until we reach the saved offset.  */
  92             while (dirp->offset < r->offset)
  93               {
  94                 struct dirent *scan;
  95                 __libc_lock_unlock (dirp->__lock);
  96                 scan = readdir (dirp);
  97                 __libc_lock_lock (dirp->__lock);
  98                 if (! scan)
  99                   break;
 100               }
 101           }
 102         __libc_lock_unlock (dirp->__lock);
 103
 104         /* To prevent leaking memory, cookies returned from telldir
 105            can only be used once.  So free this one's record now.  */
 106         *prevr = r->next;
 107         free (r);
 108         break;
 109       }
 110
 111   __libc_lock_unlock (lock);
 112
 113   /* If we lost there is no way to indicate it.  Oh well.  */
 114 }