Re: [Qemu-devel] [PATCH 0/3] Migrate with destination version

[Markus Armbruster]

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

> * Paolo Bonzini (address@hidden) wrote:
[...]
>> Version numbers open a huge compatibility can of worms (what is a version
>> number?)
>
> No, a version number here is very well defined; it's the output of
> query-version'
> (or 'info version' for the HMP world).

Okay, make it "version numbers are a huge, well-defined compatibility
can of worms" :)

> How you do comparisons on that, and in particular how you parse the 'package'
> text is a different matter, however I suggest that parsing the 'package'
> text is downstream's problem and they provide that text.

This means that a downstream has to examine and possibly adapt the
version number conditionals when it backports anything.

>> and don't solve the fundamental problem of migration receiving
>> insufficient testing with upstream QEMU versions.
>
> Indeed; and it's not meant to - in no way is this an excuse for inadequate
> testing - however, we're all human, and bugs happen, this is just providing
> a way to get out of some of the mess afterwards.

Understand.  It's a last resort, to be used only when the alternatives
are all even worse.

If we put this in, we'll have to review all attempts to use it very
critically: is there really, really no practical alternative?

Can you explain why we should put it in before we have a user?