On Wed, Nov 23, 2022 at 10:36:25AM +0100, Cornelia Huck wrote:
> On Tue, Nov 22 2022, "Michael S. Tsirkin" <> wrote:
>
>
> On Tue, Nov 22, 2022 at 03:46:38PM +0100, Cornelia Huck wrote:
> >> On Sun, Nov 20 2022, "Michael S. Tsirkin" <> wrote:
> >>
> >>
> Add new registers to the PCI common configuration structure.
> >> >
> >>
> These registers will be used for querying the indices of the admin
> >>
> virtqueues of the owner device. To configure, reset or enable the admin
> >>
> virtqueues, the driver should follow existing queue configuration/setup
> >>
> sequence.
> >> >
> >>
> Signed-off-by: Max Gurtovoy <>
> >>
> Signed-off-by: Michael S. Tsirkin <>
> >> > ---
> >>
> content.tex | 34 ++++++++++++++++++++++++++++++++++
> >>
> 1 file changed, 34 insertions(+)
> >>
> >> (...)
> >>
> >> > @@ -1112,6 +1129,14 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
> >>
> were used before the queue reset.
> >> > (see \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}).
> >> >
> >> > +If VIRTIO_F_ADMIN_VQ has been negotiated, and if the driver
> >> > +configures any administration virtqueues, the driver MUST
> >> > +configure the administration virtqueues using the index
> >> > +in the range \field{admin_queue_index} to
> >> > +\field{admin_queue_index} + \field{admin_queue_num} inclusive.
> >> > +The driver MAY configure less administration virtqueues than
> >> > +supported by the device.
> >>
> >> Is the driver allowed to pick any admin queue from within the range,
> >> e.g. queues 2 and 5, and leave the rest?
> >
>
> I was split on this. In the end I don't see why not.
>
> Do you feel we need to document this?
>
> It should work fine, I guess; probably no need to spell it out
> explicitly.
>
> >
> >> > +
> >> > \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
> >> >
> >>
> The notification location is found using the VIRTIO_PCI_CAP_NOTIFY_CFG
> >> > @@ -6986,6 +7011,15 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
> >>
>
See \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Reset}.
> >> >
> >> >
\item[VIRTIO_F_ADMIN_VQ (41)] This feature indicates that an administration virtqueue is supported.
> >> > + At the moment this feature is only supported for devices using
> >> > + \ref{sec:Virtio Transport Options / Virtio Over PCI
> >> > + Bus}~\nameref{sec:Virtio Transport Options / Virtio Over PCI Bus}
> >> > + as the transport and is reserved for future use for
> >> > + devices using other transports (see
> >> > + \ref{drivernormative:Basic Facilities of a Virtio Device / Feature Bits}
> >> > + and
> >> > + \ref{devicenormative:Basic Facilities of a Virtio Device / Feature Bits} for
> >> > + handling features reserved for future use.
> >> >
> >> > \end{description}
> >> >
> >>
> >> We don't say for any other feature which transports support it; do we
> >> really need to state it here explicitly if we have the rules for
> >> reserved feature bits in place? It simply will be neither offered nor
> >> accepted if the device and driver use an unsupported transport.
> >
>
> It's just easy for someone to add code for feature in transport
>
> agnostic part and then it will be negotiated mistakenly when
>
> we add it for a new transport.
>
> Potential for such a bug is what worries me and this is why I add
>
> this in so many places. Harmless no?
>
> By this reasoning, we probably should also add a comment for
> NOTIFICATION_DATA and RING_RESET? (On top, of course.)
Yes I think we should.
--
MST
