RE: [virtio-comment] RE: [PATCH v3 2/2] content: Support enabling virtqueue after DRIVER_OK stage

[Parav Pandit <parav@nvidia.com>]

Hi Michael, Cornelia,

> From: Parav Pandit
> Sent: Thursday, October 19, 2023 7:27 PM
> 
> Hi Cornelia, Michael,
> 
> > From: virtio-comment@lists.oasis-open.org <virtio-comment@lists.oasis-
> > open.org> On Behalf Of Parav Pandit
> > Sent: Wednesday, October 18, 2023 4:43 PM
> >
> > > From: Cornelia Huck <cohuck@redhat.com>
> > > Sent: Wednesday, October 18, 2023 4:34 PM
> >
> > > On Wed, Oct 18 2023, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > >
> > > > On Wed, Oct 18, 2023 at 12:25:23PM +0200, Cornelia Huck wrote:
> > > >> On Tue, Oct 17 2023, Parav Pandit <parav@nvidia.com> wrote:
> > > >>
> > > >> >> From: Cornelia Huck <cohuck@redhat.com>
> > > >> >> Sent: Tuesday, October 17, 2023 5:55 PM
> > > >> >>
> > > >> >> On Mon, Oct 02 2023, Parav Pandit <parav@nvidia.com> wrote:
> > > >> >> > +When VIRTIO_F_RING_DYNAMIC is not negotiated, the driver
> > > >> >> > +MUST enable the required number of virtqueues before
> > > >> >> > +setting the
> > > DRIVER_OK status bit.
> > > >> >>
> > > >> >> What does "required" mean here? It just chooses to enable the
> > > >> >> queues it wants to use, right?
> > > >> > Right.
> > > >> > Required meaning, whatever number of queues that driver choose
> > > >> > to
> > > enable, those must be enabled before driver_ok.
> > > >> > So it is "required by the driver".
> > > >> > Would that be ok?
> > > >>
> > > >> I'd write it as "the driver MUST enable any virtqueue it plans to use"
> > > >> or something like that.
> > > >>
> > > >> (...)
> > > >
> > > > It would have to be SHOULD - we can't add new MUST requirements
> > > > not contingent on a feature bit, we can give recommendation based
> > > > on existing installed base.
> > >
> > It is not just installed base.
> > Spec clearly says that:
> > "Perform device-specific setup, including discovery of virtqueues for
> > the device, optional per-bus setup, reading and possibly writing the
> > device's virtio configuration space, and population of virtqueues."
> >
> > There is no feature bit or any text that says "population of
> > virtqueues" can be done later outside of the device initialization phase.
> > Only reference is _F_RESET bit which is only for re-enabling. (not enabling).
> >
> > > Then I wonder whether we need to add any normative statement at all
> > > -- prior to the introduction of this new feature, the driver had to
> > > enable anything it wanted to use before DRIVER_OK, and if it does
> > > not negotiate the new feature, nothing changes. Spelling that out in
> > > non-normative sections should be enough?
> > It is already implied in the spec that queues must be enabled before
> > DRIVER_OK.
> > So what is written in normative is not changing any behavior.
> > It is only making the implied behavior explicit.
> >
> > If it says SHOULD, that means, one can enable the queue for the first
> > time after DRIVER_OK stage too.
> > And that would violate the "Driver Requirements: Device Initialization".
> >
> 
> I have addressed the comments of v3 in v4 at [1].
> The device requirement is kept as MUST to keep it aligned with the "driver
> requirements section".'
> 
> [1] https://lore.kernel.org/virtio-comment/20231017143135.758523-1-
> parav@nvidia.com/T/#mc49b6e54186c5f1b1e8c743bc440ca0cc0938212
> 
> Please review.

If no comments in v4 which was a week ago, please raise the voting ballot.

[1] https://lists.oasis-open.org/archives/virtio-comment/202310/msg00183.html

Parav