Re: [Qemu-devel] [PATCH] hw/i386: Deprecate the machines pc-0.10 to pc-0.15

[Markus Armbruster]

"Dr. David Alan Gilbert" <address@hidden> writes:

> * Daniel P. Berrange (address@hidden) wrote:
>> On Wed, May 10, 2017 at 03:51:25PM +0100, Dr. David Alan Gilbert wrote:
>> > * Daniel P. Berrange (address@hidden) wrote:
>> > > If we deprecate in this release (~Aug/Sep 2017), and kill in the next
>> > > release  (Dec 2017), that means our oldest machine type pc-1.0 is still
>> > > going to be 6 years, or 18 major releases, old. This raises some 
>> > > questions
>> > > 
>> > >   - Do we really think that we still have users with VMs that are
>> > >     stuck on a 6 year old machine type from 18 major releases ago ?
>> > 
>> > Our RHEL6 users are still on a 0.12 derivative.
>> 
>> Yep, but not using upstream machine types. So we can kill machine
>> types without affecting RHEL-6.  The separate question is whether
>> we can kill the associated features that are needed for RHEL to
>> create its legacy machine types (eg the rombar setting mentioned)
>
> Right, it just felt a bit odd to kill it off upstream if we know
> of users ourselves who use old versions like that.
>
> Also remember machine types are not just about migration compatibility;
> if we kill a machine type then:
>   a) The users will need to modify their libvirt xml for each VM to
> change machine type

Point taken.  But if this inconvenience is unacceptable, consider an
enterprise distribution, or maybe CentOS.

>   b) That change in guest view of the machine might upset the OS
> installed.

Unlikely, unless you migrate without a reboot.  Guests almost always
adapt to minor hardware changes on reboot just fine.

> I've certainly got VMs that were installed ages ago and are still using
> the XML from the old installation; so that probably means using an old
> machine type on a modern QEMU.

Eventually, that becomes as likely to actually work as rebooting with a
newer machine type :)