Alyssa Ross <h...@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....@alyssa.is/> I totally missed this when I posted a similar attempt at clarification: Subject: [PATCH v2] vhost-user.rst: add clarifying language about protocol negotiation Date: Wed, 3 Mar 2021 14:50:11 +0000 Message-Id: <20210303145011.14547-1-alex.ben...@linaro.org> > > Cc: Michael S. Tsirkin <m...@redhat.com> > Signed-off-by: Alyssa Ross <h...@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 d6085f7045..c42150331d 100644 > --- a/docs/interop/vhost-user.rst > +++ b/docs/interop/vhost-user.rst > @@ -871,9 +871,9 @@ Master message types > ``VHOST_USER_GET_FEATURES``. > > .. Note:: > - Slave that reported ``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 > + backend must allow ``VHOST_USER_GET_PROTOCOL_FEATURES`` even if > + ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been acknowledged yet. > > ``VHOST_USER_SET_PROTOCOL_FEATURES`` > :id: 16 > @@ -886,8 +886,12 @@ Master message types > ``VHOST_USER_GET_FEATURES``. > > .. Note:: > - Slave that reported ``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 > + backend must allow ``VHOST_USER_SET_PROTOCOL_FEATURES`` even if > + ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been acknowledged yet. > + The backend must not wait for ``VHOST_USER_SET_FEATURES`` before > + enabling protocol features requested with > + ``VHOST_USER_SET_PROTOCOL_FEATURES``. I think this is perfectly fine clarification although I think there might be a patch in flight which changes some of the master slave terminology so with that resolved: Reviewed-by: Alex Bennée <alex.ben...@linaro.org> However there is still the edge case of what happens after the vhost pair have negotiated protocol features like REPLY_ACK should VHOST_USER_F_PROTOCOL_FEATURES still be acknowledged by VHOST_USER_SET_FEATURES. Stefan's proposed wording which I incorporated in my patch made it clear that VHOST_USER_F_PROTOCOL_FEATURES is never exposed to the guest by the VMM due to it's UNUSED status. I would just like it explicit if it needs to be preserved between the two sides of the VHOST_USER_*_FEATURES for the negotiated protocol features to remain valid. Perhaps you could incorporate some wording for that? > > ``VHOST_USER_SET_OWNER`` > :id: 3 -- Alex Bennée
