Re: [Qemu-devel] [PATCH v3 2/2] Add configure option --enable-pc-1-0-qemu-kvm

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Sep 22, 2014 at 05:45:28PM +0200, Andreas Färber wrote:
> Am 22.09.2014 um 15:05 schrieb Alex Bligh:
> >>> Sadly that is not true. For instance on Ubuntu Precise
> >>> it's invoked as qemu-system-x86_64 by at least one
> >>> management application known to me.
> >>
> >> Well change it to call qemu-kvm then :)
> >> Also what happens if you install qemu as well?
> >> Does it conflict?
> > 
> > I'm not an Ubuntu maintainer but AFAIK qemu-kvm is deprecated.
> > It may only be there to support upgrades.
> > 
> > We still need to support migration from qemu running on Precise
> > to qemu running on Trusty. The trusty instance may not have
> > qemu-kvm installed. If we were looking at argv[0], we'd
> > really want to look at it on the /sending/ machine.
> > 
> > Forcing qemu to be involved as qemu-kvm solely on the basis
> > some users might want to migrate a VM in from a previous
> > version does not sound practical.
> > 
> >>> I'm not quite sure why you say "legacy management
> >>> applications".
> >>
> >> Because any non legacy one can be patched.
> > 
> > Well this is where we diverge. I think the distro needs
> > a way to change the default behaviour, i.e. so the existing
> > command line will do something different.
> > 
> >>> This applies to /any/ management application.
> >>> Unless we're going to burden every management application
> >>> with this problem, we need to fix it.
> >>>
> >>> Just as a reminder, the ./configure value defaults to
> >>> off, which means there is no change in current behaviour.
> >>
> >> Yes but this still perpetuates the mess.
> >>
> >> If you prefer using -M pc-1.0, add a new property
> >> and teach management to set it.
> >>
> >> But no silent compile-time behind the scenes changes please.
> > 
> > OK, how about we keep the aliases, and make pc-1.0
> > default to the pc-1.0-qemu-git. We then add a command
> > line option to make pc-1.0 mean pc-1.0-qemu-kvm, with
> > that obviously defaulting to off.
> > 
> > Then distros can then put the option in
> > /etc/qemu/target-x86_64.conf or whatever.
> 
> What about adding a bool property "qemu-kvm-compat" to the MachineClass?
> Then a qemu-kvm shell script (like SUSE uses) can pass -global
> machine.qemu-kvm-compat=on whereas qemu-system-x86_64 would run in the
> default non-qemu-kvm mode (config on disk would affect both). It would
> also allow running -machine pc-0.15,qemu-kvm-compat=on, ditching lots of
> new machine names and avoiding the name bikeshedding.
> 
> Regards,
> Andreas

Ack. Exactly.

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