[virtio] [PATCH v2] conformance: clarify transitional/non-transitional

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

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:

Accept all changes proposed by Cornelia Huck <cohuck@redhat.com>

 conformance.tex | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/conformance.tex b/conformance.tex
index 1577c0c..518b9c7 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.
 
-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
+and additionally implements the legacy interface
+for the transitional 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 device and driver's ability to interoperate with
+the existing body of installed devices and drivers is a quality
+of implementation issue.
+\begin{note}
+
+To facilitate creating transitional implementations, as well as
+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:
 \begin{itemize}
 \item Section \ref{sec:Basic Facilities of a Virtio Device /
 Feature Bits / Legacy Interface: A Note on Feature Bits}
-- 
MST

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