[virtio] Re: [virtio-dev] [PATCH v3] conformance: clarify transitional/non-transitional

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

On Tue, Mar 12, 2019 at 04:00:41PM +0100, Halil Pasic wrote:
> On Mon, 11 Mar 2019 12:00:46 -0400
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > Clarify that:
> > - non-transitional just satisfy 3 main clauses
> > - transitional also has a legacy interface:
> >   however note that it's not an optional component
> >   *for transitional devices* so MAY is inappropriate
> > - legacy device descriptions are non-normative.
> >   In fact virtio 0.9 is non-normative as a whole
> >   and always was by design: it was early days and
> >   spec evolved to document bugs in implementations.
> > 
> > VIRTIO-167
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > 
> > Changes from v1:
> > 	address remaining comments by Cornelia
> > Changes from v1:
> > 	address comments by Cornelia
> > 
> >  conformance.tex | 26 ++++++++++++++++++--------
> >  1 file changed, 18 insertions(+), 8 deletions(-)
> > 
> > diff --git a/conformance.tex b/conformance.tex
> > index 1577c0c..c0df2a2 100644
> > --- a/conformance.tex
> > +++ b/conformance.tex
> > @@ -344,16 +344,26 @@ Interface: Terminology}.
> >  
> >  A non-transitional implementation conforms to this specification
> >  if it satisfies all of the MUST or REQUIRED level requirements
> > -defined above.
> > +defined in section \ref{sec:Conformance / Conformance Targets} above.
> 
> I think 'above' is superfluous. 
> 
> >  
> > -An implementation MAY choose to implement OPTIONAL support for the
> > -legacy interface, including support for legacy drivers
> > -or devices, by additionally conforming to all of the MUST or
> > -REQUIRED level requirements for the legacy interface
> > -for the transitional devices and drivers.
> > +A transitional implementation conforms to this specification
> > +if it satisfies all of the MUST or REQUIRED level requirements
> > +defined in section \ref{sec:Conformance / Conformance Targets} above
> 
> I would prefer 'above' dropped, but no biggie.
> 
> > +and additionally implements the legacy interface
> > +for devices and drivers, described in
> > +\hyperref[intro:Virtio PCI Draft]{[Virtio PCI Draft]}.
> >  
> > -The requirements for the legacy interface for transitional implementations
> > -are located in sections named ``Legacy Interface'' listed below:
> > +\begin{note}
> > +No normative specification for the legacy interface exists,
> > +instead the ability of the device or the driver to inter-operate
> > +with the existing body of devices and drivers is a quality of
> > +implementation issue.
> > +\end{note}
> 
> I don't like 'existing body of devices and drivers' because IMHO this is
> only about legacy devices and drivers. I.e. an implementation that
> conforms to this specification (or a previous version of this
> specification) is guaranteed to be inter-operable. 
> 
> > +
> > +To facilitate creating transitional implementations, as well as
> > +to assist in converting legacy interfaces to conforming ones,
> > +the requirements for the legacy interface for transitional implementations
> > +are located in non-normative sections named ``Legacy Interface'' listed below:
> 
> I have a hard time to tell if this change makes transitional vs
> non-transitional clearer or not.
> 
> I think there is a dissonance between 'no normative specification for
> the legacy interface exists' and 'transitional implementation conforms
> to this specification if ...'.
> 
> The latter suggests that based on this specification and the referenced
> draft together do provide, what is necessary to decide if a given
> implementation is a transitional implementation that conforms to this
> specification.
> 
> The former suggests that only the non-transitional, i.e. virtio
> conforming, part of the transitional device is actually well specified.
> Please note that the non-normative sections do contain constructs that
> are normally reserved for normative statements (e.g. MUST).
> AFAIU a transitional implementation is any implementation that is
> conforming to this specification and aims to provide some
> inter-operability with some legacy implementations that do not conform
> this specification. A non-transitional implementation is an
> implementation that is conforms to this specification and does not care
> about inter-operability with implementation that don not conform to this
> specification.
> 
> I think people familiar with virtio already have a good understanding of
> transitional and non-transitional. Because of this I'm going to abstain
> on this.
> 
> Regards,
> Halil

OK I'm convinced, I've send v2 which is a much smaller change.
Pls review that before I start another ballot.

-- 
MST

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