Re: [PATCH 1/3] migration/colo: Deprecate COLO migration framework

[Markus Armbruster <armbru@redhat.com>]

Zhang Chen <zhangckid@gmail.com> writes:

> On Fri, Jan 16, 2026 at 2:26 PM Markus Armbruster <armbru@redhat.com> wrote:
>>
>> Lukas Straub <lukasstraub2@web.de> writes:
>>
>> > On Wed, 14 Jan 2026 15:11:55 -0500
>> > Peter Xu <peterx@redhat.com> wrote:
>> >
>> >> On Wed, Jan 14, 2026 at 02:56:57PM -0500, Peter Xu wrote:
>> >> > COLO was broken for QEMU release 10.0/10.1 without anyone noticed.  One
>> >> > reason might be that we don't have an unit test for COLO (which we
>> >> > explicitly require now for any new migration feature).  The other reason
>> >> > should be that there are just no more active COLO users, at least based on
>> >> > the latest development of QEMU.
>> >> >
>> >> > I don't remember seeing anything really active in the past few years in
>> >> > COLO development.
>> >> >
>> >> > Meanwhile, COLO migration framework maintainer (Hailiang Zhang)'s last
>> >> > email to qemu-devel is in Dec 2021 where the patch proposed an email
>> >> > change (<20211214075424.6920-1-zhanghailiang@xfusion.com>).
>> >> >
>> >> > We've discussed this for a while, see latest discussions here (our thoughts
>> >> > of deprecating COLO framework might be earlier than that, but still):
>> >> >
>> >> > https://lore.kernel.org/r/aQu6bDAA7hnIPg-y@x1.local/
>> >> > https://lore.kernel.org/r/20251230-colo_unit_test_multifd-v1-0-f9734bc74c71@web.de
>> >> >
>> >> > Let's make it partly official and put COLO into deprecation list.  If
>> >> > anyone cares about COLO and is deploying it, please send an email to
>> >> > qemu-devel to discuss.
>> >> >
>> >> > Otherwise, let's try to save some energy for either maintainers or
>> >> > developers who is looking after QEMU. Let's save the work if we don't even
>> >> > know what the work is for.
>> >> >
>> >> > Cc: Lukáš Doktor <ldoktor@redhat.com>
>> >>
>> >> My apologize, I copied the wrong email.
>> >>
>> >> Cc: Lukas Straub <lukasstraub2@web.de>
>> >
>> > Nack.
>> >
>> > This code has users, as explained in my other email:
>> > https://lore.kernel.org/qemu-devel/20260115224516.7f0309ba@penguin/T/#mc99839451d6841366619c4ec0d5af5264e2f6464
>>
>> Code being useful is not enough.  We must have people to maintain it
>> adequately.  This has not been the case for COLO in years.
>>
>> Deprecating a feature with intent to remove it is not a death sentence.
>> It's a *suspended* death sentence: if somebody steps up to maintain it,
>> we can revert the deprecation, or extend the grace period to give them a
>> chance.
>>
>> I think we should deprecate COLO now to send a clear distress signal.
>> The deprecation notice should explain it doesn't work, and will be
>> removed unless people step up to fix it and to maintain it.  This will
>> ensure progress one way or the other.  Doing nothing now virtually
>> ensures we'll have the same discussion again later.
>>
>> "Broken for two releases without anyone noticing" and "maintainer absent
>> for more than four years" doesn't exacltly inspire hope, though.  We
>> should seriously consider removing it right away.
>>
>> Lukas, can you give us hope?
>>
>
> Hi Markus,
> Maybe you missed something?
> I think Lukas is ready to maintain this code in his previous emails.
> https://lore.kernel.org/qemu-devel/20260115224516.7f0309ba@penguin/T/#mc99839451d6841366619c4ec0d5af5264e2f6464

Patch to MAINTAINERS or it didn't happen ;)