Re: [netconf] YANG Library 1.1: a deviation module may exist without a module entry?

"Sterne, Jason (Nokia - CA/Ottawa)" <jason.sterne@nokia.com> Thu, 13 May 2021 15:40 UTC

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From: "Sterne, Jason (Nokia - CA/Ottawa)" <jason.sterne@nokia.com>
To: Jernej Tuljak <jernej.tuljak@mg-soft.si>, Netconf <netconf@ietf.org>
Thread-Topic: [netconf] YANG Library 1.1: a deviation module may exist without a module entry?
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Date: Thu, 13 May 2021 15:39:56 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/netconf/NivBb0ndDe29j3GNGlkjC0YCtEE>
Subject: Re: [netconf] YANG Library 1.1: a deviation module may exist without a module entry?
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The concept of "deviation module" is a bit odd IMO in RFC8525.

Deviation statements can sit in any module and can be mixed in a module that declares other schema nodes (containers, lists, etc).

Maybe it is a nice idea for authors to gather deviations into modules that contain nothing but deviation statements, but that would just be a convention of how to organize your modules. Nothing in the specs really requires that.

Jason

> -----Original Message-----
> From: netconf <netconf-bounces@ietf.org> On Behalf Of Jernej Tuljak
> Sent: Wednesday, May 12, 2021 7:44 AM
> To: Netconf <netconf@ietf.org>
> Subject: Re: [netconf] YANG Library 1.1: a deviation module may exist
> without a module entry?
> 
> Somehow it slipped my mind that require-instance defaults to true in
> YANG 1.1. Everything checks out.
> 
> A server implementation that announces a deviation module in the
> "/yang-library/module-set/module/deviation" leaf-list, but lacks a
> corresponding entry in "/yang-library/module-set/module" list is
> non-RFC8525 compliant.
> 
> Jernej
> 
> On 12/05/2021 11:18, Jernej Tuljak wrote:
> > Hi,
> >
> > is there a particular reason for the deviation leaf-list in
> > ietf-yang-library@2019-01-04 not having require-instance true for its
> > leafref path, therefore allowing servers to report "incomplete" module
> > sets/schemas to the client?
> >
> >      grouping module-implementation-parameters {
> >        description
> >          "Parameters for describing the implementation of a module.";
> >        leaf-list feature {
> >          type yang:yang-identifier;
> >          description
> >            "List of all YANG feature names from this module that are
> >             supported by the server, regardless whether they are defined
> >             in the module or any included submodule.";
> >        }
> >        leaf-list deviation {
> >          type leafref {
> >            path "../../module/name";
> >          }
> >
> >          description
> >            "List of all YANG deviation modules used by this server to
> >             modify the conformance of the module associated with this
> >             entry.  Note that the same module can be used for deviations
> >             for multiple modules, so the same entry MAY appear within
> >             multiple 'module' entries.
> >
> >             This reference MUST NOT (directly or indirectly)
> >             refer to the module being deviated.
> >
> >             Robust clients may want to make sure that they handle a
> >             situation where a module deviates itself (directly or
> >             indirectly) gracefully.";
> >        }
> >      }
> >
> > Why are deviation modules allowed to exist without a module entry
> > within YANG Library instances? Why would a server choose to withhold
> > namespace information for a deviation module?
> >
> > Jernej
> >
> > _______________________________________________
> > netconf mailing list
> > netconf@ietf.org
> > https://www.ietf.org/mailman/listinfo/netconf
> 
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