Re: [PATCH 3/9] change order of kvm_init call.

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Jul 27, 2009 at 03:38:57PM -0300, Glauber Costa wrote:
> On Mon, Jul 27, 2009 at 07:28:17PM +0100, Daniel P. Berrange wrote:
> > On Mon, Jul 27, 2009 at 03:20:08PM -0300, Glauber Costa wrote:
> > > On Mon, Jul 27, 2009 at 08:10:24PM +0200, Jan Kiszka wrote:
> > > > 
> > > > I think we should simply resolves this the way upstream does: Do not
> > > > start if modules are missing and -no-kvm is omitted - or even switch
> > > > over to -enable-kvm as I think you already suggested in some other
> > > > thread. Then we can either fail or succeed, but not fall back more or
> > > > less silently. This falling back of qemu-kvm to tcg is a constant source
> > > > of confusion anyway.
> > > 
> > > switching to --enable-kvm would be my preferred solution, but guys from
> > > mgmt tools may not like it.
> > 
> > Totally agree that it should never ever fallback to a  different mode than
> > the one requested, since falling  back from KVM to QEMU simply means the 
> > user doesn't discover the problem till their  VM install has wasted an 
> > hour of their time. Personally I would vote for --accelmode qemu|kvm|kqemu 
> > since it is more future proof, but I'm not too bothered if people prefer 
> > to have --enable-kvm on the grounds that kqemu is being killed off. 
> > libvirt just needs a reliable way to request one of qemu, kvm, or kqemu, 
> > and either get an error message, or have the requested mode work.
> The big problem here is that in qemu-kvm.git, kvm happens without any user request.
> That would be the advantage of --enable-kvm or --accelmode, or whatever.
> Simply changing the default to kill the VM if we fail to initialize KVM is cumbersome,
> because it would mean that users of pure tcg would have to add an option for a
> basic VM to work.

Well, we could go for logic like:

 * No arg given          => try kvm, try kqemu, try tcg
 * --accelmode arg given => try $arg, and fail if unavailable

then libvirt would simply always supply --accelmode for all VMs,
while people running qemu manually would get best available 

Daniel
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