Re: [Qemu-devel] [PATCH v3] hw/i386: Deprecate the machines pc-0.10 to pc-1.2

[Eduardo Habkost <ehabkost@redhat.com>]

On Thu, Jul 13, 2017 at 04:00:00AM +0300, Michael S. Tsirkin wrote:
> On Wed, Jul 12, 2017 at 10:22:33AM +0200, Thomas Huth wrote:
> > We don't want to carry along old machine types forever. If we are able to
> > remove the pc machines up to 0.13 one day for example, this would allow
> > us to eventually kill the code for rombar=0 (i.e. where QEMU copies ROM
> > BARs directly to low memory). Everything up to pc-1.2 is also known to
> > have issues with migration.  So let's start with a deprecation message
> > for the old machine types so that the (hopefully) few users of these old
> > systems start switching over to newer machine types instead.
> > 
> > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > ---
> >  Note: Even if we mark all these old machines as deprecated, this ofcourse
> >  doesn't mean that we also have to remove them all at once later when we
> >  decide to finally really remove some. We could then also start by removing
> >  0.10 and 0.11 only, for example (since there should really be no users left
> >  for these), or only up to 0.13 (to be able to kill rombar=0).
> 
> So I generally think the main issue is that machine types are conflating
> two things. One is saying "I want to be able to migrate from/to QEMU X".
> Another is saying "I want to look to guests as if I am QEMU X
> but I restart gurst on the new QEMU".
> 
> First is generally a superset of the second, but only a subset of
> users needs the first. And while there's a very good chance we
> are actually pretty close to supporting the second even for very
> old machine types, I doubt we are actually able to migrate to/from
> these old QEMU versions since it is so hard to test.
> 
> So IMHO, a more significant step with a long term impact would be to
> support splitting these things up.

I agree they are different things, but do we really have
volunteers willing to maintain a machine-type just because of the
latter?  Setting the same deprecation policy for the two features
sounds simpler to me.

-- 
Eduardo