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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] Re: [PATCH 0/9] Virtio cleanups
Date: Tue, 23 Mar 2010 11:40:46 +0000
References: <cover.1268765204.git.quintela@redhat.com>
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>, qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>

> > Right.  The only real challenge is dealing with legacy save/restore and
> > command line syntax.  For save/restore, we can possibly have a dummy
> > device that can split the VirtioPCI device state from the virtio device
> > states and do the right thing.
> >
> > I'm not sure what we should do for command line syntax.  We can keep
> > -drive working as is.  Do we need to support -device based creation?  I
> > don't think we've really considered what to do in a situation like this.
> 
> If we need to change command line because of an implementation
> change, IMO something is wrong with the design.
> Users shouldn't care about non-existent virtio bus.

I don't find this argument convincing. If we need to change the internal 
structure of a machine, then users who manipulate the machine configuration 
are going to have to compensate for this.  This kind of change is pretty much 
unavoidable when we get the device model wrong. The best we can realistically 
do is avoid making these changes on a stable branch, and arrange for outdated 
configs to be rejected rather than silently doing the wrong thing.

Paul