Re: [PATCH v1 4/5] Add virtio Admin virtqueue

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Mar 02, 2022 at 05:56:07PM +0200, Max Gurtovoy wrote:
> In one of the many use cases a user wants to manipulate features and
> configuration of the virtio devices regardless of the device type
> (net/block/console). Some of this configuration is generic enough. i.e
> Number of MSI-X vectors of a virtio PCI VF device. There is a need to do
> such features query and manipulation by its parent PCI PF. For that the
> Admin Command Set introduced. The Admin virtqueue will be the first
> management interface to issue Admin commands.
> 
> Currently virtio specification defines control virtqueue to manipulate
> features and configuration of the device it operates on. However,
> control virtqueue commands are device type specific, which makes it very
> difficult to extend for device agnostic commands.
> 
> To support this requirement in elegant way, this patch introduces a new
> admin virtqueue interface.
> 
> Manipulate features via admin virtqueue is asynchronous, scalable, easy
> to extend and doesn't require additional and expensive on-die resources
> to be allocated for every new feature that will be added in the future.
> 
> Reviewed-by: Parav Pandit <parav@nvidia.com>
> Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
> ---
>  admin.tex       | 17 +++++++++++++++++
>  conformance.tex |  1 +
>  content.tex     |  6 ++++--
>  3 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/admin.tex b/admin.tex
> index 9a8969b..ed9f6bd 100644
> --- a/admin.tex
> +++ b/admin.tex
> @@ -158,3 +158,20 @@ \subsection{VIRTIO ADMIN DEVICE INFO command}\label{sec:Basic Facilities of a Vi
>  specification and can't be equal to zero. If bit 0 is not set, the driver will ignore \field{vf_number}.}
>  \end{note}
>  
> +\section{Admin Virtqueues}\label{sec:Basic Facilities of a Virtio Device / Admin Virtqueues}
> +
> +An admin virtqueue is a management interface of a device that can be used to send administrative
> +commands to manipulate various features of the device and/or to manipulate
> +various features, if possible, of another device within the same virtio subsystem
> +(see \ref{sec:Introduction / Definitions / virtio subsystem}).
> +
> +An admin virtqueue exists for a certain device if VIRTIO_F_ADMIN_VQ is
> +negotiated. The index of the admin virtqueue is exposed by the device in a
> +transport specific manner.
> +
> +If VIRTIO_F_ADMIN_VQ has been negotiated, the driver will use the admin virtqueue to send all admin commands.
> +

Add links please, and explain how do commands map to VQ buffers.
E.g. I guess device readable an output buffer and device writeable an input
buffer...

> +\devicenormative{\subsection}{Admin Virtqueues}{Basic Facilities of a Virtio Device / Admin Virtqueues}
> +A device that advertises VIRTIO_F_ADMIN_VQ capability MUST support all the mandatory admin commands.
> +
> +A device that advertises VIRTIO_F_ADMIN_VQ capability MAY support one or more optional admin commands.
> diff --git a/conformance.tex b/conformance.tex
> index 42f8537..129831c 100644
> --- a/conformance.tex
> +++ b/conformance.tex
> @@ -341,6 +341,7 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
>  \item \ref{devicenormative:Basic Facilities of a Virtio Device / Virtqueues / Available Buffer Notification Suppression}
>  \item \ref{devicenormative:Basic Facilities of a Virtio Device / Shared Memory Regions}
>  \item \ref{devicenormative:Reserved Feature Bits}
> +\item \ref{devicenormative:Basic Facilities of a Virtio Device / Admin Virtqueues}
>  \end{itemize}
>  
>  \conformance{\subsection}{PCI Device Conformance}\label{sec:Conformance / Device Conformance / PCI Device Conformance}
> diff --git a/content.tex b/content.tex
> index 2e1df84..163cb34 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 40] Feature bits reserved for extensions to the queue and
> +\item[24 to 41] Feature bits reserved for extensions to the queue and
>    feature negotiation mechanisms
>  
> -\item[41 to 49, and 128 and above] Feature bits reserved for future extensions.
> +\item[42 to 49, and 128 and above] Feature bits reserved for future extensions.
>  \end{description}
>  
>  \begin{note}
> @@ -6849,6 +6849,8 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
>    that the driver can reset a queue individually.
>    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.
> +
>  \end{description}
>  
>  \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
> -- 
> 2.21.0