RE: [PATCH 1/2] virtio: introduce selective queue enabling

[Parav Pandit <parav@nvidia.com>]

Hi Eugenio,

> From: Eugenio PÃrez <eperezma@redhat.com>
> Sent: Tuesday, June 6, 2023 1:55 PM
> 
> This patch allows the driver to start the device (as set DRIVER_OK) with only
> some queues enabled, and then enable another queues later.
> 
> This is the current way to migrate net device state through control virtqueue, in
> a software assisted framework with vDPA:
> * First, only net CVQ is enabled at DRIVER_OK
> * All the control commands (mac address, mq, etc) needed for the device to
> behave the same as the source of migration are sent
> * Finally all the dataplane queues are enabled.
> 
> Signed-off-by: Eugenio PÃrez <eperezma@redhat.com>
> ---
>  content.tex | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/content.tex b/content.tex
> index d2ab9eb..ea4a6d8 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -99,10 +99,10 @@ \section{Feature Bits}\label{sec:Basic Facilities of a
> Virtio Device / Feature B  \begin{description}
>  \item[0 to 23, and 50 to 127] Feature bits for the specific device type
> 
> -\item[24 to 41] Feature bits reserved for extensions to the queue and
> +\item[24 to 42] Feature bits reserved for extensions to the queue and
>    feature negotiation mechanisms
> 
> -\item[42 to 49, and 128 and above] Feature bits reserved for future extensions.
> +\item[43 to 49, and 128 and above] Feature bits reserved for future
> extensions.
>  \end{description}
> 
>  \begin{note}
> @@ -398,6 +398,13 @@ \section{Virtqueues}\label{sec:Basic Facilities of a
> Virtio Device / Virtqueues}  Every driver and device supports either the Packed
> or the Split  Virtqueue format, or both.
> 
> +\subsection{Virtqueue selective enabling}\label{sec:Basic Facilities of
> +a Virtio Device / Virtqueues / Selective Virtqueue Enable}
> +
> +If the driver negotiates VIRTIO\_F\_RING\_ENABLE\_ANYTIME, it can
> +enable individual virtqueues both before and after the DRIVER\_OK. The
> +way to enable a virtqueue is transport specific, but it mimics the
> +re-enabling after an hypothetical reset.
> +
>  \subsection{Virtqueue Reset}\label{sec:Basic Facilities of a Virtio Device /
> Virtqueues / Virtqueue Reset}
> 
>  When VIRTIO_F_RING_RESET is negotiated, the driver can reset a virtqueue
> @@ -870,6 +877,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved
> Feature Bits}
>  	\ref{devicenormative:Basic Facilities of a Virtio Device / Feature Bits} for
>  	handling features reserved for future use.
> 
> +  \item[VIRTIO_F_RING_ENABLE_ANYTIME(42)] This feature indicates  that
> + the driver can enable a queue both before and after DRIVER\_OK.
> +  See \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Selective
> Virtqueue Enable}.
> +

Can you please highlight, current spec normative which indicates that all queues must be enabled before DRIVER_OK and more queues cannot be enabled after DRIVER_OK?