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Date: Fri, 9 Dec 2011 17:32:33 +0530
From: Amit Shah <amit.shah@redhat.com>
Message-ID: <20111209120233.GD2464@amit-x200.redhat.com>
References: <cover.1323431083.git.amit.shah@redhat.com>
	<20111209115521.GB25940@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 0/3] balloon: error if guest driver is not
 initialised
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To: "Daniel P. Berrange" <berrange@redhat.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>, qemu list <qemu-devel@nongnu.org>, Markus Armbruster <armbru@redhat.com>

On (Fri) 09 Dec 2011 [11:55:21], Daniel P. Berrange wrote:
> On Fri, Dec 09, 2011 at 05:19:35PM +0530, Amit Shah wrote:
> > Hello,
> > 
> > These patches make qemu generate an error on failure in setting a
> > balloon value:
> > 
> > (qemu) balloon 400
> > Device 'balloon' has not been activated
> > 
> > This can happen when the guest hasn't yet loaded a balloon driver.
> 
> This is a pretty significant change in behaviour/semantics of the
> balloon driver interface.
> 
> eg, when libvirt starts a guest, it launches QEMU paused, and
> immediately sets a balloon target, which may be lower than the
> memory limit, and then starts CPUS to let the guest boot. The
> guest will utilize this target when it loads the balloon driver
> during bootup.
> 
> With this proposed change, libvirt will immediately get
> an error, and have to guess when the balloon driver might be
> loaded by the guest, in order to set the limit post-boot.
> 
> > Previously, such a ballooning attempt didn't produce an error, but the
> > virtio-balloon driver remembered the value nevertheless, causing a
> > module load in the guest using the attempted balloon value
> > originally.  This may not be the desired course of action.
> 
> This is *exactly* desired behaviour. Please don't change this.

OK, thanks.

I'll retract this patch series.

		Amit