Re: [netmod] yang-data-ext issues
Robert Wilton <rwilton@cisco.com> Fri, 27 April 2018 11:19 UTC
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To: Ladislav Lhotka <lhotka@nic.cz>, Martin Bjorklund <mbj@tail-f.com>
Cc: netmod@ietf.org
References: <87muxq1pk9.fsf@nic.cz> <CABCOCHSwB8m6Uk82MZHnjnVi=0ofRohqEPT0Q06NM=+3n5gtFA@mail.gmail.com> <065a363753a67ee12f8bde6224009207b5fe7ee7.camel@nic.cz> <20180427.120325.419501937185262392.mbj@tail-f.com> <11da9315-40d9-60cd-d32f-b0ac4a5640c4@cisco.com> <45f5a97d205a9251b382687f54865c62250787cb.camel@nic.cz>
From: Robert Wilton <rwilton@cisco.com>
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Date: Fri, 27 Apr 2018 12:19:41 +0100
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Subject: Re: [netmod] yang-data-ext issues
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On 27/04/2018 12:03, Ladislav Lhotka wrote: > On Fri, 2018-04-27 at 11:23 +0100, Robert Wilton wrote: >> On 27/04/2018 11:03, Martin Bjorklund wrote: >>> Hi, >>> >>> Ladislav Lhotka <lhotka@nic.cz> wrote: >>>> On Thu, 2018-04-26 at 17:52 -0700, Andy Bierman wrote: >>>>> On Wed, Apr 25, 2018 at 10:53 PM, Ladislav Lhotka <lhotka@nic.cz> wrote: >>>>>> Ladislav Lhotka <lhotka@nic.cz> writes: >>>>>> >>>>>>> On Wed, 2018-04-25 at 08:04 -0700, Andy Bierman wrote: >>>>>>>> On Wed, Apr 25, 2018 at 7:05 AM, Ladislav Lhotka <lhotka@nic.cz> >>>>>>>> wrote: >>>>>>>>> On Wed, 2018-04-25 at 15:55 +0200, Juergen Schoenwaelder wrote: >>>>>>>>>> On Tue, Apr 24, 2018 at 04:36:01PM +0200, Martin Bjorklund >>>>>>>>>> wrote: >>>>>>>>>>> Ladislav Lhotka <lhotka@nic.cz> wrote: >>>>>>>>>>>> Martin Bjorklund <mbj@tail-f.com> writes: >>>>>>>>>>>> >>>>>>>>>>>>> Hi, >>>>>>>>>>>>> >>>>>>>>>>>>> I am not sure what this statement tells us re. the issue >>>>>>>>>>>>> in >>>>>> this >>>>>>>>> email >>>>>>>>>>>>> thread. >>>>>>>>>>>> It tells us that, in my view, the approach taken in this >>>>>>>>>>>> document >>>>>> is a >>>>>>>>>>>> bad idea. >>>>>>>>>>> Do you mean that the WG shoud drop this document? And >>>>>>>>>>> people that >>>>>>>>>>> need yang-data should continue to use the version in >>>>>>>>>>> 8040? Or that >>>>>>>>>>> people that need yang-data do not have a valid use case and >>>>>>>>>>> they >>>>>>>>>>> should do something else? >>>>>>>>>> One option is that people use yang-data as defined in RFC 8040 >>>>>>>>>> until >>>>>>>>> IMO, people should use plain YANG. With the new YANG library it >>>>>>>>> will be >>>>>>>>> possible >>>>>>>>> to confine such non-NM schemas in a special datastore so that >>>>>>>>> the >>>>>> intention >>>>>>>>> should be clear and multi-module schemas with all the additional >>>>>>>>> data >>>>>>>>> (versions, >>>>>>>>> features, deviations) can be used. >>>>>>>>> >>>>>>>> I don't see how yang-data interferes with "plain YANG" at all. >>>>>>>> It is for data that is not in scope for plain YANG. >>>>>>> My question is why this extension is needed in the first place. >>>>>> For example, RFC 8040 could have used two modules instead of >>>>>> "ietf-restconf", one with the contents of grouping "errors" and the >>>>>> other with the contents of grouping "restconf". No extension. >>>>>> >>>>> This is true. We used to do this before yang-data was available. >>>> If I remember correctly, the stuff was inside groupings that were not used >>>> anywhere. >>> Which doesn't quite work, since no namespace is attached to the nodes. > Note that this is not what I was proposing. For RESTCONF errors, the module I > had in mind could be like this: > > module ietf-restconf-errors { > > container errors { // same content as in RFC 8040 > ... > } > > ... > > } > > Please explain why this cannot serve the given purpose, apart from the fact that > it looks like configuration which it isn't - but this can be explained in the > module description. It is the "because it looks like configuration" that I don't like. If the server supports and advertises this module then it is reasonable to expect that a client should be able to configure the errors container, since it is configuration ... At least marking it as config false would be slightly better. > > With this module, one could validate error messages using generic YANG tools > etc. > > (I am not proposing to update RFC 8040, just using it as an example.) > >> OK. So, using plain groupings doesn't work. >> >> In cases where groupings are being used within a YANG defined RPC, then >> presumably they do work OK? >> >> Is the specific problem scenario where the data is external to YANG >> defined RPCs, but yet it is still desirable to use a YANG schema and one >> of the associated YANG encodings to describe/encode the data? >> >> >>>>>> What would be wrong with this solution? Instead, the reader is >>>>>> overwhelmed with the complexity of the "yang-data" definition, and >>>>>> most >>>>>> tools cannot process the module. >>>>> There are tools that can use yang-data. >>>>> Not all use-cases involve a server to query for a yang-library. >>>> Sure, but it is not necessary, I meant it just as an option. Such YANG >>>> modules >>>> can be passed straight to tools. >>>> >>>>> Offline tools need to know about the special data somehow. >>>> Why? Let's say I want the ascii tree, and pyang will be able to generate >>>> it. All >>>> right, there will be "rw" labels that don't apply but it is not a big >>>> deal. >>>> >>>>> The yang-data extension prevents data-def-stmts from being treated >>>>> as if they were configuration or operational data. >>>> This would be a problem if this yang-data is mixed with standard data in >>>> the >>>> same module. IMO this can be avoided, and then for it is essentially >>>> irrelevant >>>> for tools whether it is normal data or not. >>>> >>>>> I agree with you that unconstrained use of yang-data is questionable >>>>> for a standard extension. The bar should be that all tools which choose >>>>> to implement the extension should provide the user with the same >>>>> behavior. >>>>> Declaring that behavior out-of-scope does not help interoperability at >>>>> all. >>>> Yes, and so my proposal here is to silently misuse YANG somewhat where >>>> necessary >>>> rather than spend cycles on a Standard Track document that gives a false >>>> impression of a general solution. >>> I am strongly opposed to this. IMO it is much better to put such >>> structures in an extension, which tools that don't understand it will >>> ignore, than relying on description statements in normal data nodes, >>> which no tool can understand without hard coding special cases. >> I'm also opposed to this. >> >> Stuff that looks like configuration should be configuration, and stuff >> that looks like state should be state. If this data is going to be >> described in YANG then I think that there must be a programmatic way to >> indicate that the resultant schema is not configuration or operational >> state, but something else instead. An extension seems to achieve this. > YANG spec deals exclusively with configuration and state data, and using its > statements inside an extension doesn't make this basic fact go away. Specifying > all necessary changes properly inside a description of an extension is simply > impossible. If an implementation needs to support generating the error messages then they can support the yang-data extension if they want (or just hard code what they expect to receive). Otherwise, devices can also ignore the yang-data extension and it doesn't seem to do any harm since its doesn't change the behaviour in any way. Thanks, Rob > > Lada > >> Thanks, >> Rob >> >> >>> >>>> It would be great to remove NETCONF specifics from YANG and I'd be willing >>>> to >>>> contribute to this work. >>> This is a different topic though. >>> >>> >>> /martin >>> >>> >>>> Lada >>>> >>>>>> Lada >>>>>> >>>>> Andy >>>>> >>>>>>>> A plain client can ignore yang-data and not affect and RPC, >>>>>>>> notification, >>>>>> or >>>>>>>> data >>>>>>>> definitions in plain YANG. >>>>>>> A plain (NC/RC) client should never see such data even if it is not >>>>>> protected by >>>>>>> yang-data in YANG. On the other hand, tools will be able to process >>>>>>> such >>>>>> schemas >>>>>>> (generate the ascii tree, convert it to something else, generate >>>>>>> sample >>>>>>> instances etc.) without explicitly supporting yang-data. >>>>>>> >>>>>>> Lada >>>>>>> >>>>>>>> >>>>>>>>> Lada >>>>>>>>> >>>>>>>> Andy >>>>>>>> >>>>>>>>>> there is a version of YANG that has a proper and complete >>>>>>>>>> integrated >>>>>>>>>> solution. (If for example yang-data is used to declare error >>>>>>>>>> content >>>>>>>>>> for RPCs, then more extensions are needed or a proper >>>>>>>>>> integration >>>>>> into >>>>>>>>>> YANG. Is it really good to introduce augment-yang-data >>>>>>>>>> (instead of >>>>>>>>>> making augment work with say 'data' in YANG 1.2)? And then we >>>>>>>>>> do >>>>>>>>>> uses-yang-data etc. >>>>>>>>>> >>>>>>>>>> /js >>>>>>>>>> >>>>>>>>> -- >>>>>>>>> Ladislav Lhotka >>>>>>>>> Head, CZ.NIC Labs >>>>>>>>> PGP Key ID: 0xB8F92B08A9F76C67 >>>>>>>>> >>>>>>>>> _______________________________________________ >>>>>>>>> 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 >>>>>> _______________________________________________ >>>>>> 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 >>>> >>> _______________________________________________ >>> netmod mailing list >>> netmod@ietf.org >>> https://www.ietf.org/mailman/listinfo/netmod >>> . >>> >>
- Re: [netmod] yang-data-ext issues Kent Watsen
- Re: [netmod] yang-data-ext issues Joe Clarke
- Re: [netmod] yang-data-ext issues Kent Watsen
- [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Joe Clarke
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Robert Wilton
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Robert Wilton
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Kent Watsen
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Kent Watsen
- Re: [netmod] yang-data-ext issues Robert Varga
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Robert Varga
- Re: [netmod] yang-data-ext issues Juergen Schoenwaelder
- Re: [netmod] yang-data-ext issues Robert Varga
- Re: [netmod] yang-data-ext issues Juergen Schoenwaelder
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Andy Bierman
- [netmod] Extensions vs new YANG versions [was Re:… Robert Wilton
- Re: [netmod] yang-data-ext issues Robert Wilton
- Re: [netmod] Extensions vs new YANG versions [was… Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Kent Watsen
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Juergen Schoenwaelder
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Robert Wilton
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Robert Wilton
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Juergen Schoenwaelder
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Juergen Schoenwaelder
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Kent Watsen
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Kent Watsen
- Re: [netmod] yang-data-ext issues Juergen Schoenwaelder
- Re: [netmod] yang-data-ext issues Kent Watsen
- Re: [netmod] yang-data-ext issues Juergen Schoenwaelder
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Robert Wilton
- Re: [netmod] yang-data-ext issues Martin Bjorklund
- Re: [netmod] yang-data-ext issues Juergen Schoenwaelder
- Re: [netmod] yang-data-ext issues Ladislav Lhotka
- Re: [netmod] yang-data-ext issues Robert Varga
- Re: [netmod] yang-data-ext issues Robert Varga
- Re: [netmod] yang-data-ext issues Kent Watsen
- Re: [netmod] yang-data-ext issues Juergen Schoenwaelder
- Re: [netmod] yang-data-ext issues Andy Bierman
- Re: [netmod] yang-data-ext issues Kent Watsen
- Re: [netmod] yang-data-ext issues Ladislav Lhotka