vhost-user(?) breaking changes

[Alyssa Ross <hi@alyssa.is>]

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[Trimming CC substantially.]

Alex Bennée <alex.bennee@linaro.org> writes:

> Manos Pitsidianakis <manos.pitsidianakis@linaro.org> writes:
>
>> On Mon, May 25, 2026 at 5:03 AM Demi Marie Obenour
>> <demiobenour@gmail.com> wrote:
>>>
>>> The first is whether vhost-user memory regions
>>> are guaranteed to not overlap.  I sent a patch in
>>> https://lore.kernel.org/qemu-devel/20260522-vhost-user-dev-v1-1-b31646cf19b8@gmail.com
>>> to guarantee this is not the case.  However, this is technically a
>>> breaking spec change.  The virtio vhost-user device I'm working on
>>> requires this.
>
> Breaking spec changes are always a red flag because of whats already
> deployed. Are you sure there is no way to make changes optional with use
> of feature flags?

There's some nuance between breaking changes and clarifications though,
right?  e.g. 97f24a0496 ("vhost-user.rst: clarify when FDs can be sent")
tightened things up, so could also have been in principle have been seen
as a breaking change, but not practically.

Are there likely to be devices that use overlapping memory regions
today?  Would we expect that to work?

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