linux domU's and partitioning

http://www
.netbsd.org/Ports/xen/howto.html says:

   A virtual block device can't be partitioned in the Linux
domain as
   it is in the NetBSD domain. This means that each
partition that
   will be available in the Linux system have to be exported
from the
   domain0 system.

This appears to be untrue, at least for gentoo xen kernels.

I have a disk image file that I can dual-boot using both a
normal
linux i386 kernel with hvm, and using a domU xen kernel.  It
was
installed as the former and 'upgraded' to xen native, pretty
much just
by adding the xen kernel (also building with
-mno-tls-direct-seg-refs,
but that's only a performance issue).

All that was necessary was mapping the image as the linux
'hda'
device, and then linux finds hda1 etc partitions as normal:

 disk = [ 'file:/home/xen/gentoo/gentoo.img,0x300,w' ]
 root = "/dev/hda3 ro"

I have no reason to suspect this is particular to gentoo
kernels, but
no real inclination to test other distributions right now to
confirm
it either.  If someone else can provide that confirmation,
I'll fix
the page accordingly.

--
Dan.

On Monday 04 December 2006 14:23, Daniel Carosone wrote:
>   A virtual block device can't be partitioned in the
Linux domain as
>    it is in the NetBSD domain. This means that each
partition that
>    will be available in the Linux system have to be
exported from the
>    domain0 system.
>
> This appears to be untrue, at least for gentoo xen
kernels.
>
> I have a disk image file


I'm pretty sure the documentation is referring to a virtual
block device 
whereas you are referring to a vnd pseudo device.

An image file can contain all required information to
effectively mimic an 
entire disk. This can't be said for a single physical slice.

Sarton

On Monday 04 December 2006 14:23, Daniel Carosone wrote:
>   A virtual block device can't be partitioned in the
Linux domain as
>    it is in the NetBSD domain. This means that each
partition that
>    will be available in the Linux system have to be
exported from the
>    domain0 system.
>
> This appears to be untrue, at least for gentoo xen
kernels.
>
> I have a disk image file


I'm pretty sure the documentation is referring to a virtual
block device 
whereas you are referring to a vnd pseudo device.

An image file can contain all required information to
effectively mimic an 
entire disk. This can't be said for a single physical slice.

Sarton

On Mon, Dec 04, 2006 at 05:12:14PM +1100, Sarton O'Brien
wrote:
> On Monday 04 December 2006 14:23, Daniel Carosone
wrote:
> >   A virtual block device can't be partitioned in
the Linux domain as
> >    it is in the NetBSD domain. This means that
each partition that
> >    will be available in the Linux system have to
be exported from the
> >    domain0 system.
> >
> > This appears to be untrue, at least for gentoo xen
kernels.
> >
> > I have a disk image file
> 
> 
> I'm pretty sure the documentation is referring to a
virtual block device 
> whereas you are referring to a vnd pseudo device.
> 
> An image file can contain all required information to
effectively mimic an 
> entire disk. This can't be said for a single physical
slice.

A physical slice can also be sub-partitionned when used as
virtual disk.

-- 
Manuel Bouyer, LIP6, Universite Paris VI.          
Manuel.Bouyerlip6.fr
     NetBSD: 26 ans d'experience feront toujours la
difference
--

On Mon, Dec 04, 2006 at 02:23:52PM +1100, Daniel Carosone
wrote:
> http://www
.netbsd.org/Ports/xen/howto.html says:
> 
>    A virtual block device can't be partitioned in the
Linux domain as
>    it is in the NetBSD domain. This means that each
partition that
>    will be available in the Linux system have to be
exported from the
>    domain0 system.
> 
> This appears to be untrue, at least for gentoo xen
kernels.
> 
> I have a disk image file that I can dual-boot using
both a normal
> linux i386 kernel with hvm, and using a domU xen
kernel.  It was
> installed as the former and 'upgraded' to xen native,
pretty much just
> by adding the xen kernel (also building with
-mno-tls-direct-seg-refs,
> but that's only a performance issue).
> 
> All that was necessary was mapping the image as the
linux 'hda'
> device, and then linux finds hda1 etc partitions as
normal:
> 
>  disk = [ 'file:/home/xen/gentoo/gentoo.img,0x300,w' ]
>  root = "/dev/hda3 ro"
> 
> I have no reason to suspect this is particular to
gentoo kernels, but
> no real inclination to test other distributions right
now to confirm
> it either.  If someone else can provide that
confirmation, I'll fix
> the page accordingly.

It's possible that this has changed with Xen3. With Xen2 I'm
sure using 
0x300 didn't work; the linux kernel simply didn't read the
partition table
from the virtal disk.

-- 
Manuel Bouyer, LIP6, Universite Paris VI.          
Manuel.Bouyerlip6.fr
     NetBSD: 26 ans d'experience feront toujours la
difference
--

On Monday 04 December 2006 20:55, you wrote:
> > I'm pretty sure the documentation is referring to
a virtual block device
> > whereas you are referring to a vnd pseudo device.
> >
> > An image file can contain all required information
to effectively mimic
> > an entire disk. This can't be said for a single
physical slice.
>
> A physical slice can also be sub-partitionned when used
as virtual disk.

I thought it possible so long as you have something similar
to the NetBSD 
install kernel. I was probably being a little pedantic about
the wording of 
the howto and the fact an image can be pre-prepared. My
knowledge of linux 
under xen outside of an image is rather limited  ... I'd
image it would be 
difficult to prepare a slice appropriately without an
install kernel, but not 
impossible.

Has anyone here accomplished this without hvm? I haven't
used hvm but I assume 
it would function in a similar way to using an install
kernel.

Sarton

On Monday 04 December 2006 14:23, Daniel Carosone wrote:
>   A virtual block device can't be partitioned in the
Linux domain as
>    it is in the NetBSD domain. This means that each
partition that
>    will be available in the Linux system have to be
exported from the
>    domain0 system.
>
> This appears to be untrue, at least for gentoo xen
kernels.
>
> I have a disk image file


I'm pretty sure the documentation is referring to a virtual
block device 
whereas you are referring to a vnd pseudo device.

An image file can contain all required information to
effectively mimic an 
entire disk. This can't be said for a single physical slice.

Sarton

On Mon, Dec 04, 2006 at 10:57:04AM +0100, Manuel Bouyer
wrote:
> 
> It's possible that this has changed with Xen3.?With
Xen2 I'm sure using 
> 0x300 didn't work; the linux kernel simply didn't read
the partition table
> from the virtal disk.

Wait, 0x300 actually means something?  What does it mean? 
I've
just been numbering the disks 0x1, 0x2, etc...  the galaxy
hasn't
exploded yet, so i figured i was okay...
  --david


> 
> -- 
> Manuel Bouyer, LIP6, Universite Paris VI.          
Manuel.Bouyerlip6.fr
>      NetBSD: 26 ans d'experience feront toujours la
difference
> --

On Mon, Dec 04, 2006 at 08:23:58AM -0600, david l goodrich
wrote:
> On Mon, Dec 04, 2006 at 10:57:04AM +0100, Manuel Bouyer
wrote:
> > 
> > It's possible that this has changed with
Xen3.?With Xen2 I'm sure using 
> > 0x300 didn't work; the linux kernel simply didn't
read the partition table
> > from the virtal disk.
> 
> Wait, 0x300 actually means something?  What does it
mean?

For linux it's a device number: 0x300 is hda, 0x301 hda1,
etc
NetBSD doesn't care.

>I've
> just been numbering the disks 0x1, 0x2, etc...  the
galaxy hasn't
> exploded yet, so i figured i was okay...

With NetBSD guests it's OK, but with linux guest the kernel
should print
an "unknown device" error

-- 
Manuel Bouyer, LIP6, Universite Paris VI.          
Manuel.Bouyerlip6.fr
     NetBSD: 26 ans d'experience feront toujours la
difference
--

On Monday 04 December 2006 14:23, Daniel Carosone wrote:
>   A virtual block device can't be partitioned in the
Linux domain as
>    it is in the NetBSD domain. This means that each
partition that
>    will be available in the Linux system have to be
exported from the
>    domain0 system.
>
> This appears to be untrue, at least for gentoo xen
kernels.
>
> I have a disk image file


I'm pretty sure the documentation is referring to a virtual
block device 
whereas you are referring to a vnd pseudo device.

An image file can contain all required information to
effectively mimic an 
entire disk. This can't be said for a single physical slice.

Sarton