Re: [netmod] Guideline on modeling including features and phased support by a device
Robert Wilton <rwilton@cisco.com> Tue, 06 March 2018 09:37 UTC
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To: "Bogaert, Bart (Nokia - BE/Antwerp)" <bart.bogaert@nokia.com>, "netmod@ietf.org" <netmod@ietf.org>
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From: Robert Wilton <rwilton@cisco.com>
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Date: Tue, 06 Mar 2018 09:37:44 +0000
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Subject: Re: [netmod] Guideline on modeling including features and phased support by a device
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Hi Bart, I think that the best solution to problem is perhaps to avoid it altogether. I.e. I don't think that the only-if-feature leaf should be marked mandatory. Instead, it would be better to define a sensible default value/behaviour if the leaf is absent even when the feature is supported. Alternatively, you can simulate something similar to an if-feature statement by using a when or must expression instead that is predicated on a leaf that the client must explicitly set to enable the feature, giving control back to the client. E.g. something along the lines of ... leaf enable-super-feature { if-feature test-feature; type boolean; default "false"; } ... leaf only-if-feature { when '/enable-super-feature = "true"'; type string; mandatory true; } It would be interesting if you have a concrete example where neither of the above suggestions would work or be appropriate. Thanks, Rob On 05/03/2018 09:25, Bogaert, Bart (Nokia - BE/Antwerp) wrote: > > Hi, > > We have a question with respect to YANG models using features. Assume > that a part of the model is defined under a feature and that this > feature-dependent part defines a leaf as mandatory. > > module servers { > > namespace "http://www.example.com/servers"; > > prefix servers; > > import ietf-inet-types { > > prefix inet; > > } > > revision 2018-03-01 { > > description > > "Initial version."; > > } > > feature test-feature { > > description "testing feature"; > > } > > container servers { > > list server { > > key name; > > max-elements 64; > > leaf name { > > type string; > > } > > leaf ip { > > type inet:ip-address; > > mandatory true; > > } > > leaf port { > > type inet:port-number; > > mandatory true; > > } > > leaf only-if-feature { > > if-feature test-feature; > > type string; > > mandatory true; > > } > > } > > } > > } > > Now assume that we have a device that implements the model step-wise > by first not supporting this feature and in a sub-sequent release by > supporting this feature (and uses a persistent running datastore). > The question arising now is how to deal with this mandatory leaf? > Normally this can only be configured by a client, meaning that without > any “help”, the NC server will not be able to startup with the data > contained in the device’s persistent datastore unless a value is set > for the mandatory leaf that now becomes available as a result of > supporting the feature. > > When modeling as follows it seems the NC server can start with the > model supporting the feature that was not supported before: > > module servers { > > namespace "http://www.example.com/servers"; > > prefix servers; > > import ietf-inet-types { > > prefix inet; > > } > > revision 2018-03-01 { > > description > > "Initial version."; > > } > > feature test-feature { > > description "testing feature"; > > } > > container servers { > > list server { > > key name; > > max-elements 64; > > leaf name { > > type string; > > } > > leaf ip { > > type inet:ip-address; > > mandatory true; > > } > > leaf port { > > type inet:port-number; > > mandatory true; > > } > > container only-if-feature { > > presence "see if this helps"; > > if-feature test-feature; > > leaf only-if-feature { > > type string; > > mandatory true; > > } > > } > > } > > } > > } > > Are recommendations or guidelines in place to deal with this? > > Regards, Bart > > > > _______________________________________________ > netmod mailing list > netmod@ietf.org > https://www.ietf.org/mailman/listinfo/netmod
- [netmod] Guideline on modeling including features… Bogaert, Bart (Nokia - BE/Antwerp)
- Re: [netmod] Guideline on modeling including feat… Alex Campbell
- Re: [netmod] Guideline on modeling including feat… Robert Wilton
- Re: [netmod] Guideline on modeling including feat… Bogaert, Bart (Nokia - BE/Antwerp)
- Re: [netmod] Guideline on modeling including feat… Robert Wilton
- Re: [netmod] Guideline on modeling including feat… Bogaert, Bart (Nokia - BE/Antwerp)
- Re: [netmod] Guideline on modeling including feat… Robert Wilton
- Re: [netmod] Guideline on modeling including feat… Juergen Schoenwaelder