Re: [yang-doctors] Small modules discussion from LSR [Fwd: [Lsr] When to augment LSR base YANG modules...]

Martin Bjorklund <mbj@tail-f.com> Tue, 02 April 2019 12:15 UTC

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Subject: Re: [yang-doctors] Small modules discussion from LSR [Fwd: [Lsr] When to augment LSR base YANG modules...]
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"Rob Wilton (rwilton)" <rwilton@cisco.com>; wrote:
> 
> 
> > -----Original Message-----
> > From: Martin Bjorklund <mbj@tail-f.com>;
> > Sent: 02 April 2019 12:29
> > To: Rob Wilton (rwilton) <rwilton@cisco.com>;
> > Cc: chopps@chopps.org; yang-doctors@ietf.org; yingzhen.qu@huawei.com
> > Subject: Re: [yang-doctors] Small modules discussion from LSR [Fwd:
> > [Lsr]
> > When to augment LSR base YANG modules...]
> > 
> > "Rob Wilton (rwilton)" <rwilton@cisco.com>; wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Christian Hopps <chopps@chopps.org>;
> > > > Sent: 02 April 2019 11:31
> > > > To: Rob Wilton (rwilton) <rwilton@cisco.com>;
> > > > Cc: Christian Hopps <chopps@chopps.org>;; YANG Doctors <yang-
> > > > doctors@ietf.org>;; Yingzhen Qu <yingzhen.qu@huawei.com>;
> > > > Subject: Re: [yang-doctors] Small modules discussion from LSR [Fwd:
> > > > [Lsr]
> > > > When to augment LSR base YANG modules...]
> > > >
> > > >
> > > > > On Apr 2, 2019, at 5:52 AM, Rob Wilton (rwilton)
> > > > > <rwilton@cisco.com>;
> > > > wrote:
> > > > >
> > > > > Hi Chris,
> > > > >
> > > > > I don’t think that there is a one size fits all answer here.
> > > > >
> > > > > If the enhancement is small, and is likely to be reasonably widely
> > > > > used then
> > > > my view is that adding it as an optional feature to the base module
> > > > is a better choice in the long term.
> > > > >
> > > > > If the feature is larger, or esoteric, and perhaps won’t be widely
> > > > > deployed
> > > > then I would think that putting it into a separate module might be a
> > > > better choice.
> > > > >
> > > > > I actually think that it is the IETF process that is perhaps the
> > > > > difficult thing
> > > > here.  I.e. I think that you want to republish a new revision of the
> > > > base module, but in a way that gets processed more quickly by the
> > > > IESG.
> > > > E.g.
> > > > request that they only review/comment on the diffs between the
> > > > current revision and the previous one.  Or somehow publish an
> > > > updated revision of the module on github without assigning it a new
> > > > RFC number every time.
> > > >
> > > > Yes, although I'm trying to do a couple things:
> > > >
> > > > - Get YANG management support added at the same time as the
> > > > functionality, not as an after thought maybe someday, maybe never.
> > >
> > > I agree that this is definitely the right thing to do.
> > >
> > >
> > > > - Reduce the cost of adding the YANG support. A stand-alone document
> > > > is very expensive time and effort wise, separate IESG reviews,
> > > > directorate reviews, last-calls.
> > >
> > > I agree.  And rev'ing the base ISIS YANG model is likely to be just as
> > > expensive.
> > 
> > My suggestion was not to rev the base model, but have _one_ model with
> > these "optional features", and rev that every time.
> 
> [RW] I'm not sure I see the difference.

Just less to update all the time.

> Whatever minimal base draft that does the includes has to be updated
> if a new include is added or changed.

Yes.

> Where would that updated base be published?  Would that be included in
> the extension RFC?

Yes.

> > > > I had wondered if we could use errata on the base vs doing a brand
> > > > new bis version of the base module; however, this seems to be
> > > > trading too much process overhead with perhaps not quite enough.
> > > >
> > > > To the first goal, I wrote that reverse metric module a couple days
> > > > ago as an example. I have to wonder when or even if it would have
> > > > gotten written (or the equivalent feature added) otherwise. Instead
> > > > I suspect it would just get added into N vendors models as people
> > > > move on to other things in the WG.
> > > >
> > > > In a perfect world I would add a YANG section to my functionality
> > > > RFC that updated (not augment) the base module, but with augment
> > > > style definition (i.e., so the entire huge base module doesn't need
> > > > to be re-represented in the document). This would then cause the
> > > > base document to get reissued with the changes. Sort of like IANA
> > > > sections are capable of updating a registry.
> > >
> > > We almost want to just include a diff/patch to the base model into the
> > > document.  This is actually a little bit like how IEEE 802 update
> > > their documents, and then they periodically roll their updates into
> > > the base model.
> > >
> > >
> > > >
> > > > So maybe your github idea is like this, we create a module
> > > > definition registry where the most up-to-date module definitions go,
> > > > and then RFCs can update that using something like (or exactly like)
> > > > augment to document the changes to the module in the individual
> > > > RFCs.
> > >
> > > Yes.  We want the review to only focus on the stuff that is new/added
> > > rather than reviewing the whole module every time.
> > >
> > > Martin's suggestion of using submodules is another way to achieve
> > > this.  E.g. the actual module definition is split over multiple RFCs,
> > > but I'm not that keen on submodules and I suspect that this will make
> > > them hard to read in future.
> > 
> > Note that we can "gc" the submodules and fold their contents into the
> > main
> > module, or perhaps a "top" submodule, when you have N submodules.
> 
> True.
> 
> > 
> > 
> > > I think that the real answer here is that YANG modules should not be
> > > published in RFCs.  Yes, they should go through a similar formal
> > > review process for changes to the modules but without the overhead of
> > > reviewing every change as a new document.
> > 
> > Right.  This is longer term though, since it requires a process
> > update!
> 
> Yes.
> 
> But, if we think that this is the right long term plan perhaps we
> should be writing up a draft to propose this to see what the WG
> reaction is?

Actually, Ignas is currently driving this.


/martin