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Re: [Xen-devel] Xen & Automated Disk Management for Domains

To: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] Xen & Automated Disk Management for Domains
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>
Date: Sat, 07 Aug 2004 14:11:39 +0100
Cc: =?iso-8859-1?Q? Bj=F6rn=20Sessler ?= <bjoern.sessler@xxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx, Ian.Pratt@xxxxxxxxxxxx
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> On Sat, Aug 07, 2004 at 01:33:12PM +0200, =?iso-8859-1?Q? Bj=F6rn=20Sessler 
> ?= wrote:
> > 
> > disk = [ 'phy:hdb5,hdb5,w' , 'phy:hda6,hda6,w' , 
> > 'phy:/dev/vg0/rootvm101,hdx1,w' ]
> > before:
> > disk = [ 'phy:hdb5,hdb5,w' , 'phy:hda6,hda6,w' ]
> There's a couple of things wrong with that entry:
> - the destination device has to have a /dev/ entry in the
> domain where you run xend (i.e. /dev/hdx1 would have to exist in
> dom0's filesystem).

At some point (probably post 2.0) we need to modify the vbd
interface so that both the backend and frontend drivers get
passed device _names_ rather than numbers, that they each resolve
in their own context (within the kernel).

The current situation where xend looks up both device names and
passes 32bit device numbers is not ideal, particularly when
booting a non-Linux OS. (Christian pointed this out many months
ago while doing the NetBSD port, but we haven't gotten around to
fixing it).

> - like with all devices, xend will prepend /dev/ to the device name.

xend appends /dev/ if it's not already there, but it should be
safe to leave it on.
> For completeness, let me also mention that the destination
> device has to be a hd or sd with an existing major number in
> the domain where the device will be used.
> (in 2.4, cciss might work as well ans here might be support for it to
> be an xbd but that can go away anytime...).

It's somewhat bizarre that the cciss driver uses its own
major/minor rather that the normal scsi disk ones. I'm surprised
they were allowed to...


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