Re: [Qemu-devel] [PATCH] Migration compatibility for serial

[Paolo Bonzini <pbonzini@redhat.com>]

On 17/06/2015 14:07, Dr. David Alan Gilbert wrote:
> Of course for us on RHEL our minor releases don't correspond to
> QEMU minor releases, so we already support migrating from our
> downstream 7.1 (QEMU 2.1) derivative to our 7.0 (1.5.3) version.  
> And the reason for this patch series is to support something >2.2
> migrating back to that 2.1 (or maybe even to that 1.5.3).
> 
> I don't believe we're alone in wanting to be able to do that type
> of thing;

Others may prefer to have migration only work when it is absolutely sure
that it works.  It is much easier to add hacks on top of what upstream
QEMU does (e.g. using the static checker), than to remove the hacks.

If we really didn't care about others' support for bidirectional
migration, we would have kept the static checker internal to Red Hat.
Or we wouldn't have bothered to refine the .needed functions, and so on.

Paolo

> so you can either worry about not burdening upstream
> with compatibility patches like this, or think it's not fair
> to leave them out if others upstream might want them.  How many
> others? Well I'd say it's got to be more than some of the other
> obscure features in QEMU!