Deprecating stuff for 4.2 (was: [Qemu-devel] Exposing feature deprecation to machine clients)

From: Markus Armbruster <armbru@redhat.com>
To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Cc: "kwolf@redhat.com" <kwolf@redhat.com>,
	"Thomas Huth" <thuth@redhat.com>,
	"Denis Lunev" <den@virtuozzo.com>,
	"qemu-block@nongnu.org" <qemu-block@nongnu.org>,
	"libvir-list@redhat.com" <libvir-list@redhat.com>,
	"John Snow" <jsnow@redhat.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	"Alistair Francis" <alistair.francis@wdc.com>,
	"Gerd Hoffmann" <kraxel@redhat.com>,
	"mreitz@redhat.com" <mreitz@redhat.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>
Subject: Deprecating stuff for 4.2 (was: [Qemu-devel] Exposing feature deprecation to machine clients)
Date: Fri, 08 Nov 2019 07:41:29 +0100	[thread overview]
Message-ID: <87eeyirht2.fsf_-_@dusky.pond.sub.org> (raw)
In-Reply-To: <e0448126-3371-fcf7-20ed-0d682dd8ca97@virtuozzo.com> (Vladimir Sementsov-Ogievskiy's message of "Thu, 7 Nov 2019 19:13:18 +0000")

Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> writes:

> 07.11.2019 21:52, Philippe Mathieu-Daudé wrote:
[...]
>> Pre-release period, time to deprecate some stuffs :)
>> 
>> How should we proceed? Do you have something in mind?
>> 
>> There are older threads about this. Should we start a new thread? Gather the different ideas on the Wiki?
>> 
>> (Obviously you are not the one responsible of this topic, you just happen to be the last one worried about it on the list).
>> 
>> Regards,
>> 
>> Phil.

4.2.0-rc0 has been tagged, i.e. we're in hard freeze already.  Only bug
fixes are accepted during hard freeze.  We've occasionally bent this
rule after -rc0 for borderline cases, e.g. to tweak a new external
interface before the release calcifies it.  Making a case for bending
the rules becomes harder with each -rc.

Ideally, we'd double-check new interfaces for gaffes before a release,
and whether old interfaces that have been replaced now should be
deprecated.  There's rarely time for that, and pretty much never for
releases right after KVM Forum.

So no, I don't have anything in mind for 4.2.

We intend to tag -rc1 next Tuesday.  To make that deadline, we'd need
patches, not just ideas.

> Hi!
>
> I wanted to resend, but faced some problems, and understand that I can't do it in time before soft-freeze..
> But you say, that we can deprecate something even after hard-freeze?

See above.

> Ok, the problem that I faced, is that deprecation warnings breaks some iotests.. What can we do?
>
> 1. Update iotests...
>    1.1 Just update iotests outputs to show warnings. Then, in next release cycle, update iotests, to not use deprecated things

Sounds workable to me, but I'm not the maintainer.

>    or
>    1.2 Update iotests to not use deprecated things.. Not appropriate for hard freeze.

Unnecessarily risky compared to 1.1.

> or
> 2. Commit deprecations without warnings.. But how do people find out about this?

Not nice.

We do it for QMP, but only because we still lack the means to warn
there.

> Next, what exactly to deprecate? As I understand, we can't deprecate drive-mirror now?
> So I propose to:
>
> 1. deprecate drive-backup
> 2. add optional filter-node-name parameter to drive-mirror, to correspond to commit and mirror
> 3. deprecate that filter-node-name is optional for commit and mirror.

To have a chance there, we need patches a.s.a.p.