Re: [Qemu-devel] [libvirt] Modern CPU models cannot be used with libvirt

[Eduardo Habkost]

On Mon, Mar 26, 2012 at 02:03:21PM +0200, Gleb Natapov wrote:
> On Mon, Mar 26, 2012 at 01:59:05PM +0200, Avi Kivity wrote:
> > On 03/26/2012 01:24 PM, Jiri Denemark wrote:
> > > ...
> > > > > The command line becomes unstable if you use -nodefconfig.
> > > > 
> > > > -no-user-config solves this but I fully expect libvirt would continue 
> > > > to use 
> > > > -nodefconfig.
> > >
> > > Libvirt uses -nodefaults -nodefconfig because it wants to fully control 
> > > how
> > > the virtual machine will look like (mainly in terms of devices). In other
> > > words, we don't want any devices to just magically appear without libvirt
> > > knowing about them. -nodefaults gets rid of default devices that are built
> > > directly in qemu. Since users can set any devices or command line options
> > > (such as enable-kvm) into qemu configuration files in @SYSCONFDIR@, we 
> > > need to
> > > avoid reading those files as well. Hence we use -nodefconfig. However, we
> > > would still like qemu to read CPU definitions, machine types, etc. once 
> > > they
> > > become externally loaded configuration (or however we decide to call it). 
> > > That
> > > said, when CPU definitions are moved into @DATADIR@, and -no-user-config 
> > > is
> > > introduced, I don't see any reason for libvirt to keep using -nodefconfig.

ACK.

> > >
> > > I actually like
> > > -no-user-config
> > > more than
> > > -nodefconfig -readconfig @DATADIR@/...
> > > since it would avoid additional magic to detect what files libvirt should
> > > explicitly pass to -readconfig but basically any approach that would 
> > > allow us
> > > to do read files only from @DATADIR@ is much better than what we have with
> > > -nodefconfig now.
> > 
> > That's how I see it as well.
> > 
> +1
> 
> except that instead of -no-user-config we can do what most other
> programs do. If config file is specified during invocation default one
> is not used. After implementing -no-user-config (or similar) we can drop
> -nodefconfig entirely since its only user will be gone it its semantics
> is not clear.

Awesome. It looks like we have a solution now? Anthony, do you agree
with that? Daniel, it looks good for you?

It looks like in the end, no one will ever use -nodefconfig because it's
optimizing for a use-case that nobody cares about. Maybe I'm wrong and
somebody somewhere will use -nodefconfig, maybe Anthony has a specific
use-case or specific tools in mind, I don't know. But personally I will
probably simply ignore the existence of -nodefconfig because it is
absolutely useless for me and for libvirt.

-- 
Eduardo