Re: [netmod] datastore-specific constraints

On Wed, 2018-12-12 at 15:23 +0000, Robert Wilton wrote:
> Hi Lada,
> I basically agree with Jan's suggestion.
> I don't think that I would use a when statement for this scenario since you
> want a leaf to report the operational value that is in effect, and one of the
> aims of NMDA is to try and get the configured and operational value onto the
> same path wherever possible.
> But, I think that the question about validity of must statements is more
> interesting.  RFC 8342 states that these can be violated in operational, but
> the intention is that the constraints in <operational> should generally apply
> (but never be actually checked by the server).  In this case, it might be
> useful to be able to annotate a must statement to indicate that it only
> applies to configuration data and not operational data.

Another option could be that "must" constraints on config data do not apply in
<operational>, whereas constraints on "config false" data serve as binding
guidelines for implementors.

Anyway, the logic of my example could then be implemented using "must". I agree
though that ignoring the configured value if auto-foo is true may be preferable.

Lada

> Thanks,
> Rob
> 
> On 12/12/2018 14:52, Jan Lindblad wrote:
> > Lada,
> > 
> > Maybe you could just skip the when and explain the behavior in the
> > description? E.g.
> > 
> > leaf foo {
> >  ...
> >  description "Foo controls bla, bla. 
> >   Any configured value will be ignored when auto-foo is true.";
> > }
> > 
> > Best Regards,
> > /jan
> > 
> > > On 12 Dec 2018, at 15:33, Ladislav Lhotka <lhotka@nic.cz> wrote:
> > > 
> > > Hi,
> > > 
> > > in some cases, constraints expressed with "when" or "must" may only be
> > > intended for configuration datastores. A typical example is an
> > > auto-negotiable parameter:
> > > 
> > > leaf auto-foo {
> > >  type boolean;
> > >  default true;
> > >  description "If true, parameter 'foo' will be auto-negotiated.";
> > > }
> > > leaf foo {
> > >  when "../auto-foo = 'false'";
> > >  ...
> > > }
> > > 
> > > This means that if auto-foo is true, it is impossible to configure the
> > > foo parameter. However, even with auto-foo = true, it is desirable to
> > > see the auto-negotiated value in <operational>, so, ideally, the "when"
> > > constraint should not apply in <operational>.
> > > 
> > > How can this logic be modelled under NMDA? Is an extra leaf
> > > "foo-operational" needed?
> > > 
> > > Thanks, Lada
> > > 
> > > -- 
> > > 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