Re: [netmod] Adding a pre-existing leaf into a new 'choice' - NBC change?

Martin Bjorklund <mbj@tail-f.com> Thu, 22 November 2018 13:39 UTC

Return-Path: <mbj@tail-f.com>
X-Original-To: netmod@ietfa.amsl.com
Delivered-To: netmod@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 46DC8130EE0 for <netmod@ietfa.amsl.com>; Thu, 22 Nov 2018 05:39:52 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.9
X-Spam-Level:
X-Spam-Status: No, score=-1.9 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id noVQi1x1GohE for <netmod@ietfa.amsl.com>; Thu, 22 Nov 2018 05:39:49 -0800 (PST)
Received: from mail.tail-f.com (mail.tail-f.com [46.21.102.45]) by ietfa.amsl.com (Postfix) with ESMTP id 33EE0130EDC for <netmod@ietf.org>; Thu, 22 Nov 2018 05:39:49 -0800 (PST)
Received: from localhost (h-39-108.A165.priv.bahnhof.se [213.136.39.108]) by mail.tail-f.com (Postfix) with ESMTPSA id 7624D1AE018C; Thu, 22 Nov 2018 14:39:48 +0100 (CET)
Date: Thu, 22 Nov 2018 14:39:48 +0100 (CET)
Message-Id: <20181122.143948.1543843065251732639.mbj@tail-f.com>
To: lhotka@nic.cz
Cc: andy@yumaworks.com, jason.sterne@nokia.com, netmod@ietf.org
From: Martin Bjorklund <mbj@tail-f.com>
In-Reply-To: <87wop5kzgb.fsf@nic.cz>
References: <VI1PR07MB3981A171F18213B030D289A79BD80@VI1PR07MB3981.eurprd07.prod.outlook.com> <CABCOCHQM9Y_+ENB_sFGDQ6NufGm=mBRU-Ns4xiLXddMWXTUO6w@mail.gmail.com> <87wop5kzgb.fsf@nic.cz>
X-Mailer: Mew version 6.7 on Emacs 25.2 / Mule 6.0 (HANACHIRUSATO)
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Archived-At: <https://mailarchive.ietf.org/arch/msg/netmod/biqXxujGLP_cf_Vq1_46AOlsHXw>
Subject: Re: [netmod] Adding a pre-existing leaf into a new 'choice' - NBC change?
X-BeenThere: netmod@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: NETMOD WG list <netmod.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/netmod>, <mailto:netmod-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/netmod/>
List-Post: <mailto:netmod@ietf.org>
List-Help: <mailto:netmod-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/netmod>, <mailto:netmod-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 22 Nov 2018 13:39:52 -0000

Hi,

Ladislav Lhotka <lhotka@nic.cz> wrote:
> Andy Bierman <andy@yumaworks.com> writes:
> 
> > On Mon, Nov 19, 2018 at 12:32 PM Sterne, Jason (Nokia - CA/Ottawa) <
> > jason.sterne@nokia.com> wrote:
> >
> >> Hi all,
> >>
> >>
> >>
> >> If we have a YANG model with a leaf:
> >>
> >>
> >>
> >> MODEL VERSION 1:
> >>
> >> container my-model {
> >>
> >>     leaf a { type string; }
> >>
> >> }
> >>
> >>
> >>
> >> And then later we produce another version of the model where that leaf is
> >> placed into a choice construct:
> >>
> >>
> >>
> >> MODEL VERSION 2:
> >>
> >> container my-model {
> >>
> >>     choice some-choice {
> >>
> >>         case x {
> >>
> >>             leaf a { type string; }
> >>
> >>         }
> >>
> >>     }
> >>
> >> }
> >>
> >>
> >>
> >> Is that considered a non-backwards-compatible change?
> >>
> >
> >
> > yes -- even though the data node /my-model/x did not change,
> > the schema node /my-model/a changed to /my-model/some-choice/x/a.
> > Any leafref path pointing at this leaf will break.
> 
> This is not correct. A leafref path is a special XPath, and as such
> includes only data nodes, i.e. NOT choice and case nodes.
> 
> What does change are schema node identifier. This could be significant
> in an augment statement, but not ini this example because a leaf cannot
> be augmented anyway.
> 
> I don't see anything else that could break, so Jason's change seems
> backward compatible to me.

Since it does change the schema tree, this is not legal according to
7950.  So in that sense it is not backwards compatible.  The rules in
7950 protect both clients and other modules that import the module.


/martin



> 
> Lada
> 
> >
> >
> > Andy
> >
> >
> >>
> >> Does the answer depend on whether the choice contains other cases (or
> >> other cases that are the default case)?
> >>
> >>
> >>
> >
> > no
> >
> >
> >> MODEL VERSION 3:
> >>
> >> container my-model {
> >>
> >>     choice some-choice {
> >>
> >>         case x {
> >>
> >>             leaf a { type string; }
> >>
> >>         }
> >>
> >>         case y {
> >>
> >>             leaf b { type string; }
> >>
> >>         }
> >>
> >>     }
> >>
> >> }
> >>
> >>
> >>
> >> A client 'foo' using VERSION 1 would still be able to set & read back leaf
> >> a in the same way as it always did.
> >>
> >>
> >>
> >> But if another client 'bar' (using VERSION 3) sets leaf 'b', then leaf 'a'
> >> would disappear. That could be surprising to client 'foo' although perhaps
> >> no more surprising than if another client simply deletes leaf 'a' (using
> >> VERSION 1).
> >>
> >>
> >>
> >> Jason
> >>
> >>
> >>
> >>
> >>
> >>
> >> _______________________________________________
> >> netmod mailing list
> >> netmod@ietf.org
> >> https://www.ietf.org/mailman/listinfo/netmod
> >>
> > _______________________________________________
> > netmod mailing list
> > netmod@ietf.org
> > https://www.ietf.org/mailman/listinfo/netmod
> 
> -- 
> Ladislav Lhotka
> Head, CZ.NIC Labs
> PGP Key ID: 0xB8F92B08A9F76C67
> 
> _______________________________________________
> netmod mailing list
> netmod@ietf.org
> https://www.ietf.org/mailman/listinfo/netmod
>