Re: Question to recent xentools3 update

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

On Thursday 27 March 2008 15:59:35 Juergen Hannken-Illjes wrote:
> On Thu, Mar 27, 2008 at 03:51:51PM +0100, Manuel Bouyer wrote:
> > On Thu, Mar 27, 2008 at 02:18:57PM +0100, Christoph Egger wrote:
> > > Hi!
> > >
> > > In pkgsrc/sysutils/xentools3/patches/patch-di there is a comment,
> > > which says, reads from raw disk must be sector-aligned.
> > >
> > > a) Why is that?
> >
> > The raw device pass requests directly to the underlying device, with
> > only check/adjustements against the partition bounds. Especially it won't
> > try to do read/modify/write for write requests, or expand the read if
> > it's not sector-aligned.

I guess, these aren't desirable in this case.

> >
> > > b) Is there a non-raw device w/o this requirement?
> >
> > The block device doesn't have this restriction. But it has other side
> > effects (as it goes though the buffer cache), I don't know if it would be
> > suitable for pygrub ... it's definitively not usaeable for the block
> > device backend, or for qemu-dm I/O.
>
> As of -current the block device allows only ONE open, therefore it is not
> usable by pygrub.

So the problem is, pygrub wants to open the disk multiple times ?
Or is it that xend has already plumbed in the device to qemu-dm ?
Is there something that prevents a second open?

Isn't it possible to pass pygrub an edited version of the device name or
have pygrub edit it itself? If we were to use the non-raw device for pygrub
and the raw device for qemu-dm, would things work?

Christoph