Re: [Xen-users] can't mount vfat fs on lvm created by winxp guest

[Nico Kadel-Garcia <nkadel@xxxxxxxxx>]

Yann Boutin wrote:
> On 23:02 Fri 27 Apr     , Yann Boutin wrote:
>   
> > Greetings, 
> > I've had no success with mounting a vfat file system created by a 
> > Windows XP guest on a lvm volume.
> > # mount -t vfat /dev/vg1/win1 /mnt/
> > mount: wrong fs type, bad option, bad superblock on /dev/vg1/win1,
> >        missing codepage or other error
> >        In some cases useful info is found in syslog - try
> >        dmesg | tail  or so
> >
> > # dmesg
> > FAT: invalid media value (0xb9)
> > VFS: Can't find a valid FAT filesystem on dev dm-0.
> >
> > # lvm version
> >   LVM version:     2.02.10 (2006-09-19)
> >   Library version: 1.02.10 (2006-09-19)
> >   Driver version:  4.7.0
> >
> > # uname -a
> > Linux gentoo 2.6.18-xen #6 SMP Sun Apr 22 12:11:43 CEST 2007 i686 
> > Intel(R) Core(TM)2 CPU          6300  @ 1.86GHz GenuineIntel GNU/Linux
> > Help  would be greatly appreciated.
> >
> > Thanks!
> >     
> Finally I've found a solution. Actually the real FAT32 partition starts
> 63 sectors ahead the first sector of the logical volume. I think that's
> because Windows XP guest consider this volume as a physical disk and not as a 
> partition. As a result the MediaDescriptor (15th word in boot sector) contained 
> a wrong value, b9 as reported in previous error message (FAT: invalid media 
> value (0xb9)). For information it appears that the MediaDescriptor should 
> contain F8 see : http://averstak.tripod.com/fatdox/bootsec.htm. Well to solve 
> my problem I use device-mapper to remap the logical volume 63 sectors ahead as 
> follow:
>
> printing actual map table
> # dmsetup table
> vg1-win2: 0 12582912 linear 8:6 14680448
>
> we can see that it starts at 14680448. So 14680448 + 63 = 14680511 and
> then we can remap it with this value:
> # dmsetup create vg1-win2-p1 --table "0 12582912 linear /dev/sda6
> 14680511"
>
> for further explanation of this command see
> #man 8 dmsetup
>
> and then I could mount my partition without problem
> # mount /dev/mapper/vg1-win2-p1 /mnt/
>
> I'm aware that it's not really a xen related problem but I hope that it
> could help someone, one day, someone who should consider accessing
> windows guest fs with lvm. Note that this problem is exactly the same with NTFS 
> and is solved the same too.
>
>   Yann.
>   
Ahh. I think I see what's going on. The logical volume you're using is 
being seen by Windows as a whole *disk*, not a single partition. In the 
Linux world, you'd use "kpartx" to get that set up.
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