Re: [Qemu-devel] [PATCH 0/3] balloon: error if guest driver is not initialised

[Amit Shah <amit.shah@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