Re: [Qemu-devel] [PATCH v2 0/5] q35: Remove old machines and unused compat code

[Paolo Bonzini]

On 11/02/2016 17:33, Michael S. Tsirkin wrote:
>> They won't start unless the QEMU command-line is changed, because
>> they are using a feature QEMU won't support anymore. Why is that
>> a problem?
> 
> We don't support installing one machine type, then switching.

Uhm, we definitely support people using qemu directly with no -M option
at all with installed VMs.  That's the same as switching machine types
every time a new QEMU is released.

At least RHEV supports switching machine types, even RHEL6->RHEL7.
There are constraints on when to do that because it affects the whole
datacenter, but it is done routinely because each RHEV release only
supports two machine types IIRC.

Paolo