Re: [netmod] import-by-semver issue

Martin Bjorklund <mbj@tail-f.com> Sun, 24 March 2019 15:21 UTC

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Subject: Re: [netmod] import-by-semver issue
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"Rob Wilton (rwilton)" <rwilton@cisco.com> wrote:
> Hi Juergen,
> 
> > -----Original Message-----
> > From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
> > Sent: 24 March 2019 15:31
> > To: Rob Wilton (rwilton) <rwilton@cisco.com>
> > Cc: Andy Bierman <andy@yumaworks.com>om>; NetMod WG <netmod@ietf.org>
> > Subject: Re: [netmod] import-by-semver issue
> > 
> > On Sun, Mar 24, 2019 at 02:07:15PM +0000, Rob Wilton (rwilton) wrote:
> > > Hi Andy,
> > >
> > > There are many ways to write and design compilers.
> > >
> > > Compilers that don’t understand import-by-semver just ignore the
> > > extension,
> > no deviation is required.  They just import whichever arbitrary
> > revision that they
> > would have imported anyway, as specified by YANG 1.1.  The
> > import-by-semver
> > statement just reduces the set of valid modules revisions that can be
> > used for
> > import.
> > >
> > 
> > If two compilers (one supporting semver, the other not) resolve
> > imports
> > differently, then the design is in my view somewhat broken, in
> > particular if you
> > allow NBC changes.
> 
> But that is true of YANG compilers today.  If there are multiple
> revisions of a module that could be chosen, then each compiler is at
> liberty to decide which revision to choose (last paragraph of section
> 5.1.1 in RFC 7950).

This is by design, of course.  With an "open" import (not import by
revision), the server implementor is free to implement any set of
modules that work together.

> So, I would argue that "import-by-version" doesn't make YANG compilers
> any less consistent that they are already today, since that
> inconsistency already exists.

I don't think I understand Andy's objection.   I also think that this
is just another implementation detail.

> I presume that the real solution here is to explicitly define the full
> set of implemented, import-only-modules to the compiler so that it
> always compiles a consistent schema.  Perhaps other compilers have
> different ways to solve this problem.
> 
> Note, I also think that YANG library has a similar inconsistency.
> I.e. there is no guarantee that two different compilers will construct
> exactly the same datastore schema from the YANG library output.

Can you elaborate?  Given an instance of YANG library, it should be
clear which set of modules are used.



> I
> think that this is a design bug, but also one that we attempt to
> address in draft-verdt-netmod-yang-semver-00.
> 
> Thanks,
> Rob
> 
> > 
> > /js
> > 
> > --
> > Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> > Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
> > Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>
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