src/libcaptive/storage/size.c

   1 /* $Id$
   2  * Detect media size of given GIOChannel for libcaptive
   3  * Copyright (C) 2002 Jan Kratochvil <project-captive@jankratochvil.net>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; exactly version 2 of June 1991 is required
   8  *
   9  * This program 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
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  17  */
  18
  19
  20 #include "config.h"
  21
  22 #include "captive/storage.h"    /* self */
  23 #include <glib/gmessages.h>
  24 #include <glib/gtypes.h>
  25
  26
  27 guint64 captive_giochannel_size(GIOChannel *iochannel)
  28 {
  29 gint fd;
  30 gint64 low,high,mid;
  31 GIOStatus erriostatus;
  32 gchar bufchar;
  33 gsize bufchargot;
  34
  35         g_return_val_if_fail(iochannel!=NULL,0);
  36         /* Default "UTF-8" encoding is not much usable for us */
  37         g_return_val_if_fail(g_io_channel_get_encoding(iochannel)==NULL,0);
  38
  39         fd=g_io_channel_unix_get_fd(iochannel);
  40         g_return_val_if_fail(fd!=-1,0);
  41
  42         /* FIXME: TODO: ioctl() detection */
  43
  44         /* low  ==high: low (high)
  45          * low+1==high: mid==low; NORMAL: no change: high
  46          * low+1==high: mid==low; EOF   : high=mid => 'low==high' case
  47          */
  48         for (low=0,
  49                         high=
  50                                         G_MAXINT;       /* FIXME: 'G_MAXINT64' fails on g_io_channel_seek_position() */
  51                         low+1<high;) {
  52                 mid=low+(high-low)/2;   /* beware of 'gint64' overflow! */
  53
  54                 erriostatus=g_io_channel_seek_position(iochannel,mid,G_SEEK_SET,
  55                                 NULL);  /* error */
  56                 /* During seek in block device such as on URL file:///dev/hda1#captive-fastfat.sys-ro:/
  57                  * we will do llseek(2) on "/dev/hda1" device from captive_giochannel_size().
  58                  * Although we are allowed to seek behind EOF on regular files
  59                  * at least linux-kernel-2.4.19-ac4/fs/block_dev.c/block_llseek() will give
  60                  * EINVAL on seek behind EOF therefore it must be accepted without complaints by us.
  61                  */
  62                 if (erriostatus!=G_IO_STATUS_NORMAL) {
  63                         erriostatus=G_IO_STATUS_EOF;
  64                         bufchargot=0;
  65                         }
  66                 else {
  67                         g_assert(sizeof(bufchar)==1);
  68                         erriostatus=g_io_channel_read_chars(iochannel,
  69                                         &bufchar, /* buf */
  70                                         sizeof(bufchar),        /* count */
  71                                         &bufchargot,    /* bytes_read */
  72                                         NULL);  /* error */
  73                         g_assert(erriostatus==G_IO_STATUS_NORMAL || erriostatus==G_IO_STATUS_EOF);
  74                         g_assert(0
  75                                         || (erriostatus==G_IO_STATUS_NORMAL && bufchargot==1)
  76                                         || (erriostatus==G_IO_STATUS_EOF    && bufchargot==0));
  77                         }
  78
  79                 if (erriostatus==G_IO_STATUS_NORMAL)
  80                         low=mid;
  81                 else
  82                         high=mid;
  83                 }
  84
  85         g_assert(high>=0);
  86         return high;
  87 }