Re: [Qemu-devel] [PATCH v5 1/2 (for 2.10)] docs: document support lifetime for features

[Paolo Bonzini]

On 24/07/2017 16:11, Daniel P. Berrange wrote:
>>> +
>>> +The supported lifetime for versioned machine types is 12 releases,
>>> +which is equivalent to 4 years worth of previous QEMU releases.
>> I think there's still no consensus on this.
> 
> Indeed, which is exactly why I sent this patch - we need to come up
> with a sensible policy here, so we can stop repeating the same debate
> over & over & over each time some proposes a patch to kill off some
> random old machine type.
> 
> The 12 release / 4 year figure was a fairly arbitrary starting
> point to which I'd be hoping to see critical reviewer feedback
> on (with possible counterproposals) so we can try to get something
> documented, to put an end to the repeated debates in this area
> each time someone proposes a patch.

I agree.  At the moment, the status is "machine types never die".

We can change it, but I think that we should also make a decision on
whether removing machine types implies removing properties that only
exist for backwards-compatibility reasons.

4 year seems like a long time, but it can actually be pretty taxing for
RHEL.  I'm pretty sure that around RHEL 8.4 (some time between
2020-2022) we'll need a 1.5-ish machine type (2016).

Paolo

>>                                              The first two paragraphs
>> should be added to the documentation for -machine in qemu-options.hx,
>> since "-machine [type=]foo" is currently not documented at all.
> I'll happily send a patch for the docs for qemu-options.hx.