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Re: [PATCH] docs: clarify absence of set_features in vhost-user
From: |
Alex Bennée |
Subject: |
Re: [PATCH] docs: clarify absence of set_features in vhost-user |
Date: |
Thu, 01 Sep 2022 13:12:06 +0100 |
User-agent: |
mu4e 1.9.0; emacs 28.1.91 |
Alyssa Ross <hi@alyssa.is> writes:
> The previous wording was (at least to me) ambiguous about whether a
> backend should enable features immediately after they were set using
> VHOST_USER_SET_PROTOCOL_FEATURES, or wait for support for protocol
> features to be acknowledged if it hasn't been yet before enabling
> those features.
>
> This patch attempts to make it clearer that
> VHOST_USER_SET_PROTOCOL_FEATURES should immediately enable features,
> even if support for protocol features has not yet been acknowledged,
> while still also making clear that the frontend SHOULD acknowledge
> support for protocol features.
>
> Previous discussion begins here:
> <https://lore.kernel.org/qemu-devel/87sgd1ktx9.fsf@alyssa.is/>
>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Alyssa Ross <hi@alyssa.is>
> ---
> docs/interop/vhost-user.rst | 14 +++++++++-----
> 1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
> index 3f18ab424e..c8b9771a16 100644
> --- a/docs/interop/vhost-user.rst
> +++ b/docs/interop/vhost-user.rst
> @@ -906,9 +906,9 @@ Front-end message types
> ``VHOST_USER_SET_FEATURES``.
>
> .. Note::
> - Back-ends that report ``VHOST_USER_F_PROTOCOL_FEATURES`` must
> - support this message even before ``VHOST_USER_SET_FEATURES`` was
> - called.
> + While QEMU should acknowledge ``VHOST_USER_F_PROTOCOL_FEATURES``, a
> + back-end must allow ``VHOST_USER_GET_PROTOCOL_FEATURES`` even if
> + ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been acknowledged yet.
I think this is just restating the same logic from above introduced in:
fa9972662c (vhost-user.rst: add clarifying language about protocol
negotiation)
that we don't need VHOST_USER_F_PROTOCOL_FEATURES to be acked by
VHOST_USER_SET_FEATURES? I agree the wording is hard to follow though. I
suspect what would really help is some clear message sequence diagrams
in the document showing the negotiation steps.
>
> ``VHOST_USER_SET_PROTOCOL_FEATURES``
> :id: 16
> @@ -923,8 +923,12 @@ Front-end message types
> ``VHOST_USER_SET_FEATURES``.
>
> .. Note::
> - Back-ends that report ``VHOST_USER_F_PROTOCOL_FEATURES`` must support
> - this message even before ``VHOST_USER_SET_FEATURES`` was called.
> + While QEMU should acknowledge ``VHOST_USER_F_PROTOCOL_FEATURES``, a
> + back-end must allow ``VHOST_USER_SET_PROTOCOL_FEATURES`` even if
> + ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been acknowledged yet.
> + The back-end must not wait for ``VHOST_USER_SET_FEATURES`` before
> + enabling protocol features requested with
> + ``VHOST_USER_SET_PROTOCOL_FEATURES``.
>
> ``VHOST_USER_SET_OWNER``
> :id: 3
>
> base-commit: e93ded1bf6c94ab95015b33e188bc8b0b0c32670
--
Alex Bennée