sysdeps/unix/bsd/telldir.c

   1 /* Copyright (C) 1994, 1995, 1996, 1997, 1999 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 Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the 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    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <errno.h>
  20 #include <stddef.h>
  21 #include <dirent.h>
  22 #include <unistd.h>
  23 #include <sys/types.h>
  24 #include <stdlib.h>
  25 #include "dirstream.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 __libc_lock_define_initialized(static, lock) /* Locks above data.  */
  39
  40
  41 /* Return the current position of DIRP.  */
  42 long int
  43 telldir (dirp)
  44      DIR *dirp;
  45 {
  46   struct record *new;
  47   long int pos;
  48
  49   new = malloc (sizeof *new);
  50   if (new == NULL)
  51     return -1l;
  52
  53   __libc_lock_lock (lock);
  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 seekdir (dirp, pos)
  73      DIR *dirp;
  74      long int pos;
  75 {
  76   struct record *r, **prevr;
  77
  78   __libc_lock_lock (lock);
  79
  80   for (prevr = &records[pos % NBUCKETS], r = *prevr;
  81        r != NULL;
  82        prevr = &r->next, r = r->next)
  83     if (r->cookie == pos)
  84       {
  85         __libc_lock_lock (dirp->__lock);
  86         if (dirp->filepos != r->pos || dirp->offset != r->offset)
  87           {
  88             dirp->size = 0;     /* Must read a fresh buffer.  */
  89             /* Move to the saved position.  */
  90             __lseek (dirp->fd, r->pos, SEEK_SET);
  91             dirp->filepos = r->pos;
  92             dirp->offset = 0;
  93             /* Read entries until we reach the saved offset.  */
  94             while (dirp->offset < r->offset)
  95               {
  96                 struct dirent *scan;
  97                 __libc_lock_unlock (dirp->__lock);
  98                 scan = readdir (dirp);
  99                 __libc_lock_lock (dirp->__lock);
 100                 if (! scan)
 101                   break;
 102               }
 103           }
 104         __libc_lock_unlock (dirp->__lock);
 105
 106         /* To prevent leaking memory, cookies returned from telldir
 107            can only be used once.  So free this one's record now.  */
 108         *prevr = r->next;
 109         free (r);
 110         break;
 111       }
 112
 113   __libc_lock_unlock (lock);
 114
 115   /* If we lost there is no way to indicate it.  Oh well.  */
 116 }