linux-kernel - Re: [Xen-devel] [PATCH] xen/xenbus: Add quirk to deal with misconfigured backends.

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Message-ID: <alpine.DEB.2.00.1203221511380.15151@kaball-desktop>
Date:	Thu, 22 Mar 2012 15:16:43 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Ian Campbell <Ian.Campbell@...rix.com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen/xenbus: Add quirk to deal with misconfigured
 backends.

On Thu, 22 Mar 2012, Konrad Rzeszutek Wilk wrote:
> On Thu, Mar 22, 2012 at 10:52:26AM +0000, Ian Campbell wrote:
> > On Thu, 2012-03-22 at 10:44 +0000, Stefano Stabellini wrote:
> > > On Thu, 22 Mar 2012, Konrad Rzeszutek Wilk wrote:
> > > > A rather annoying and common case is when booting a PVonHVM guest
> > > > and exposing the PV KBD and PV VFB - as both of those do not
> > > > make any sense. The HVM guest is using the VGA driver and the emulated
> > > > keyboard for this. So we provide a very basic quirk framework
> > > > (can be expanded in the future) to not wait for 6 minutes for those devices
> > > > to initialize - they never wont.
> > > > 
> > > > To trigger this, put this in your guest config:
> > > > 
> > > > vfb = [ 'vnc=1, vnclisten=0.0.0.0 ,vncunused=1']
> > > > 
> > > > instead of this:
> > > > vnc=1
> > > > vnclisten="0.0.0.0"
> > > 
> > > While I do understand the issue you are trying to solve, it actually
> > > makes sense to have PV KBD (and PV VFB maybe in the future) in a PVonHVM
> > > guest. In particular PV KVB is already enabled in upstream QEMU for
> > > PVonHVM guests because it allows users to have a keyboard and mouse
> 
> How about looking for a particular Xen version? The patch
> could check for anything less than 4.2 (does 4.2 use that version of
> QEMU that has this implemented?). I can't find any way to get the QEMU
> version from within the guest - DMI reports:
> 
> DMI: Xen HVM domU, BIOS 4.1-120322 03/22/2012

I am not a great fun of enabling/disabling features depending on the Xen
version. What happens for example if a Linux distro decided to patch
QEMU 4.1 to enable PV KBD for PVonHVM guests?
I realize that it is unlikely but it is possible.
Maybe we can reduce the timeout for non essential devices (everything
expect disk, network and console) like Ian suggested?
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