Re: [PATCH V3 Resend] virtio-transport: Clarify requirements

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

On Mon, May 20, 2024 at 09:42:02AM +0000, Parav Pandit wrote:
> Michael,
> 
> > From: Viresh Kumar <viresh.kumar@linaro.org>
> > Sent: Monday, May 20, 2024 3:00 PM
> > To: virtio-comment@lists.linux.dev; virtio-dev@lists.linux.dev
> 
> There is still cross posting to virtio-dev.

Well we say "do not do this" in the list subscription form.
Viresh, what gives?

> Is the list open to community now?

It's been open for a week. I think it's fair to say whoever wanted to
subscribe, has subscribed.

> If not, can you please send out the guidance and timeline to open it on virtio-comment list?
> 
> This way contributors can avoid resending it multiple times.
> 
> > Cc: Viresh Kumar <viresh.kumar@linaro.org>; Vincent Guittot
> > <vincent.guittot@linaro.org>; Alex Bennée <alex.bennee@linaro.org>; stratos-
> > dev@op-lists.linaro.org; Manos Pitsidianakis
> > <manos.pitsidianakis@linaro.org>; Cornelia Huck <cohuck@redhat.com>;
> > Michael S. Tsirkin <mst@redhat.com>
> > Subject: [PATCH V3 Resend] virtio-transport: Clarify requirements
> > 
> > The virtio documentation currently doesn't define any generic requirements
> > that are applicable to all transports. They can be useful while adding support
> > for a new transport.
> > 
> > This commit tries to define the same.
> > 
> > Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
> > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> > ---
> > V2->V3:
> > - Minor fixes.
> > - Added Reviewed by from Alex.
> > 
> > V1->V2:
> > - Lot of changes after discussions with Alex and Cornelia.
> > - Almost a rewrite of the first commit.
> > - Add Transport normative sections.
> > 
> >  commands.tex    |  3 +-
> >  conformance.tex | 14 +++++++++
> >  content.tex     | 78
> > +++++++++++++++++++++++++++++++++++++++++++++++--
> >  3 files changed, 92 insertions(+), 3 deletions(-)
> > 
> > diff --git a/commands.tex b/commands.tex index
> > 25ea8ee3bc78..b64b14424bd2 100644
> > --- a/commands.tex
> > +++ b/commands.tex
> > @@ -7,7 +7,8 @@
> >  % How we format a field name
> >  \newcommand{\field}[1]{\emph{#1}}
> > 
> > -% Mark a normative section (driver or device)
> > +% Mark a normative section (driver or device, or transport)
> > +\newcommand{\transportnormative}[3]{#1{Transport Requirements:
> > +#2}\label{transportnormative:#3}}
> >  \newcommand{\drivernormative}[3]{#1{Driver Requirements:
> > #2}\label{drivernormative:#3}}
> > \newcommand{\devicenormative}[3]{#1{Device Requirements:
> > #2}\label{devicenormative:#3}}  \newcounter{clausecounter} diff --git
> > a/conformance.tex b/conformance.tex index dc00e84e75ae..4a873169ce63
> > 100644
> > --- a/conformance.tex
> > +++ b/conformance.tex
> > @@ -11,6 +11,10 @@ \section{Conformance Targets}\label{sec:Conformance
> > / Conformance Targets}
> > 
> >  Conformance targets:
> >  \begin{description}
> > +\item[Transport] A transport MUST conform to one conformance clauses:
> > +  \begin{itemize}
> > +    \item Clause \ref{sec:Conformance / Transport Conformance}.
> > +  \end{itemize}
> >  \item[Driver] A driver MUST conform to four conformance clauses:
> >    \begin{itemize}
> >      \item Clause \ref{sec:Conformance / Driver Conformance}.
> > @@ -66,6 +70,14 @@ \section{Conformance Targets}\label{sec:Conformance
> > / Conformance Targets}
> >    \end{itemize}
> >  \end{description}
> > 
> > +\conformance{\section}{Transport Conformance}\label{sec:Conformance /
> > +Transport Conformance}
> > +
> > +A transport MUST conform to the following normative statements:
> > +
> > +\begin{itemize}
> > +\item \ref{transportnormative:Virtio Transport Options / Virtio
> > +Transport Requirements} \end{itemize}
> > +
> >  \conformance{\section}{Driver Conformance}\label{sec:Conformance / Driver
> > Conformance}
> > 
> >  A driver MUST conform to the following normative statements:
> > @@ -93,6 +105,7 @@ \section{Conformance Targets}\label{sec:Conformance
> > / Conformance Targets}  \item \ref{drivernormative:Basic Facilities of a Virtio
> > Device / Packed Virtqueues / Supplying Buffers to The Device / Sending
> > Available Buffer Notifications}  \item \ref{drivernormative:General Initialization
> > And Device Operation / Device Initialization}  \item
> > \ref{drivernormative:General Initialization And Device Operation / Device
> > Cleanup}
> > +\item \ref{drivernormative:Virtio Transport Options / Virtio Transport
> > +Requirements}
> >  \item \ref{drivernormative:Reserved Feature Bits}  \end{itemize}
> > 
> > @@ -172,6 +185,7 @@ \section{Conformance
> > Targets}\label{sec:Conformance / Conformance Targets}  \item
> > \ref{devicenormative:Basic Facilities of a Virtio Device / Packed Virtqueues /
> > The Virtqueue Descriptor Table}  \item \ref{devicenormative:Basic Facilities of
> > a Virtio Device / Packed Virtqueues / Scatter-Gather Support}  \item
> > \ref{devicenormative:Basic Facilities of a Virtio Device / Shared Memory
> > Regions}
> > +\item \ref{devicenormative:Virtio Transport Options / Virtio Transport
> > +Requirements}
> >  \item \ref{devicenormative:Reserved Feature Bits}  \end{itemize}
> > 
> > diff --git a/content.tex b/content.tex
> > index 0a62dce5f65f..a79993b5ed69 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -631,8 +631,82 @@ \section{Device Cleanup}\label{sec:General
> > Initialization And Device Operation /
> > 
> >  \chapter{Virtio Transport Options}\label{sec:Virtio Transport Options}
> > 
> > -Virtio can use various different buses, thus the standard is split -into virtio
> > general and bus-specific sections.
> > +Devices and drivers can use different transport methods to enable
> > +interaction, for example PCI, MMIO, or Channel I/O. The transport
> > +methods define various aspects of the communication between the device
> > +and the driver, like device discovery, exchanging capabilities,
> > +interrupt handling, data transfer, etc. For example, in a host/guest
> > +architecture, the host might expose a device to the guest on a PCI bus,
> > +and the guest will use a PCI-specific driver to interact with it.
> > +
> > +The standard is split into sections describing general virtio
> > +implementation and transport-specific sections.
> > +
> > +\section{Virtio Transport Requirements}\label{sec:Virtio Transport
> > +Options / Virtio Transport Requirements}
> > +
> > +\transportnormative{\subsection}{Virtio Transport Requirements}{Virtio
> > +Transport Options / Virtio Transport Requirements} The transport MUST
> > +provide a mechanism for the driver to discover the device.
> > +
> > +The transport MUST provide a mechanism for the driver to identify the
> > +device type.
> > +
> > +The transport MUST provide a mechanism for communicating virtqueue
> > +configurations between the device and the driver.
> > +
> > +The transport MUST allow multiple virtqueues per device. The number of
> > +virtqueues for a pair of device-driver are governed by the individual
> > +device protocol.
> > +
> > +The transport MUST provide a mechanism that the device and the driver
> > +use to access memory for implementing virtqueues.
> > +
> > +The transport MUST provide a mechanism for the device to notify the
> > +driver and a mechanism for the driver to notify the device, for example
> > +regarding availability of a buffer on the virtqueue.
> > +
> > +The transport MAY provide a mechanism for the driver to initiate a
> > +reset of the virtqueues and device.
> > +
> > +The transport SHOULD provide a mechanism for the driver to read the
> > +device status. The transport MUST provide a mechanism for the driver to
> > +change the device status.
> > +
> > +The transport MUST provide a mechanism to implement config space
> > +between the device and the driver.
> > +
> > +\devicenormative{\subsection}{Virtio Transport Requirements}{Virtio
> > +Transport Options / Virtio Transport Requirements}
> > +
> > +The device MUST keep any data associated with a device-initiated
> > +transaction accessible to the driver until the driver acknowledges the
> > +transaction to be complete.
> > +
> > +The device MUST NOT access the contents of a virtqueue before the
> > +driver notifies, in a transport defined way, the device that the
> > +virtqueue is ready to be accessed.
> > +
> > +The device MUST NOT access or modify buffers on a virtqueue after it
> > +has notified the driver about their availability.
> > +
> > +The device MUST reset the virtqueues if requested by the driver, in a
> > +transport defined way, if the transport provides such a method.
> > +
> > +\drivernormative{\subsection}{Virtio Transport Requirements}{Virtio
> > +Transport Options / Virtio Transport Requirements}
> > +
> > +The driver MUST acknowledge device notifications, as mandated by the
> > +transport.
> > +
> > +The driver MUST NOT access virtqueue contents before the device
> > +notifies about the readiness of the same.
> > +
> > +The driver MUST NOT access buffers, after it has added them to the
> > +virtqueue and notified the device about their availability. The driver
> > +MAY access them after the device has processed them and notified the
> > +driver of their availability, in a transport defined way.
> > +
> > +The driver MAY ask the device to reset the virtqueues if, for example,
> > +the driver times out waiting for a notification from the device for a
> > +previously queued request.
> > 
> >  \input{transport-pci.tex}
> >  \input{transport-mmio.tex}
> > --
> > 2.31.1.272.g89b43f80a514
> > 
>