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

[Jiri Denemark <jdenemar@redhat.com>]

On Sun, Mar 25, 2012 at 10:26:57 -0500, Anthony Liguori wrote:
> On 03/25/2012 10:16 AM, Avi Kivity wrote:
> > On 03/25/2012 04:59 PM, Anthony Liguori wrote:
> So how about:
> 
> 1) Load ['@SYSCONFDIR@/qemu/qemu.cfg', '@SYSCONFDIR@/qemu/target-@ARCH@.cfg',
>           '@DATADIR@/system.cfg', '@DATADIR@/system-@ARCH@.cfg']
> 
> 2) system-@ARCH@.cfg will contain:
> 
> [system]
> readconfig=@DATADIR@/target-@ARCH@-cpus.cfg
> readconfig=@DATADIR@/target-@ARCH@-machine.cfg
> 
> 3) -nodefconfig will not load any configuration files from DATADIR or 
> SYSCONFDIR.  -no-user-config will not load any configuration files from SYSCONFDIR.
> 
...
> > 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.

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.

Jirka