Re: [Xen-devel] [RFC] Xen PV Drivers Lifecycle

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 20 Dec 2016, Jan Beulich wrote:
> >>> On 20.12.16 at 01:47, <sstabellini@xxxxxxxxxx> wrote:
> > ## Design Phase
> > 
> > The first step toward acceptance of a new PV protocol is to write a
> > design document and send it to xen-devel. It should cover the xenstore
> > handshake mechanism, the ABI, how the protocol works and anything else
> > which is required to write an implementation of it. The usage of C-like
> > structs to describe language and platform agnostic protocols is
> > discouraged.
> > 
> > An attempt should be made for the protocol ABI to be backward compatible
> > and OS agnostic, but, realistically, backward and cross-platform
> > compatibility are not fully expected at this stage.
> 
> How does backward compatibility matter for a new protocol? Is
> this perhaps rather about forward compatibility provisions
> (like requiring reserved fields to be zero to allow future use)?

By "backward compatibility" I mean promising that, in 5 years time, a
new frontend will still be able to connect to a backend written in 2016.

This level of support requires an understanding of the protocol and its
subtleties which usually only comes from experience. Hence, I am
suggesting to make this kind of promises only after the code has lived
in-tree for a while and has been subject to wider testing.

Maybe I should call it cross-versions compatibility?

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