Re: [netmod] Proposal to enhance the YANG tree output

Martin Bjorklund <mbj@tail-f.com> Wed, 20 September 2017 06:33 UTC

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Date: Wed, 20 Sep 2017 08:34:39 +0200 (CEST)
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To: lberger@labn.net
Cc: rwilton@cisco.com, netmod@ietf.org
From: Martin Bjorklund <mbj@tail-f.com>
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Subject: Re: [netmod] Proposal to enhance the YANG tree output
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Lou Berger <lberger@labn.net> wrote:
> 
> 
> On 9/19/2017 9:42 AM, Martin Bjorklund wrote:
> > Lou Berger <lberger@labn.net> wrote:
> >>
> >> On 9/19/2017 7:29 AM, Martin Bjorklund wrote:
> >>> Lou Berger <lberger@labn.net> wrote:
> >>>> Martin,
> >>>>
> >>>> Speaking as a contributor:
> >>>>
> >>>>
> >>>> On 9/15/2017 7:40 AM, Martin Bjorklund wrote:
> >>>>> Robert Wilton <rwilton@cisco.com> wrote:
> >>>>>> On 15/09/2017 11:21, Ladislav Lhotka wrote:
> >>>>>>> Andy Bierman píše v Čt 14. 09. 2017 v 08:43 -0700:
> >>>>>>>> Hi,
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> Actually I liked the early pyang output that was concise and easy to
> >>>>>>>> remember.
> >>>>>>>> The current format gets very cluttered and there are too many little
> >>>>>>>> symbols
> >>>>>>>> to remember them all.
> >>>>>>> I agree.
> >>>>> Me too.  The current draft adds three new magic symbols: "mp" "@" and
> >>>>> "/".
> >>>>>
> >>>>> "mp" is for a mount point, and it can be generated directly from the
> >>>>> YANG modules.
> >>>>>
> >>>>> Directly under a "mp", "/" and "@" are used to indicate that a node is mounted
> >>>>> or available through a parent reference, respectively.
> >>>>>
> >>>>> I actually question the usability of "/" and "@".  
> >>>> I agree that / and @ are something new, and enabled by schema mount. 
> >>>> There have been repeated comments in the RTG WG that there needs to be
> >>>> some way for vendors to convey what they have implemented with Schema
> >>>> mount
> >>> If that's the requirement, using the tree diagram is probably not the
> >>> best way.  The tree diagram is intended to provide an overview of a
> >>> given (set of) YANG module(s).
> >>>
> >>> A perhaps better way to convey the information is to create a file
> >>> with an instantiated /schema-mounts tree.
> >> using what syntax?  JSON and XML really isn't that easy for the (human)
> >> reader to parse.
> > Either JSON or XML.
> This is fine for code, less so for humans.  We include both in the NI
> draft, the tree provides a quick overview, the JSON provides the details. 
> 
> >
> >>>> and this is one way to help convey (a) what is expected of server
> >>>> implementors and (b) what client implementors should expect.
> >>>>
> >>>    Hence the
> >>>> current draft text:
> >>>>
> >>>>   In describing the intended use of a module containing a mount point,
> >>>>    it is helpful to show how the mount point would look with mounted
> >>>>    modules.
> >>>>
> >>>> The whole point of trees is to facilitate understanding for those who
> >>>> are less familiar with a model than the authors, and IMO that's the
> >>>> paramount perspective in this discussion.
> >>> Fully agree!  I would say that we have to make sure that the diagrams
> >>> can be understood by people less familiar with the technology than the
> >>> authors.  Mixing schema and instance data does not help here.
> >> Can you propose an alternative?
> > As I have written before, I think the "/" is not needed, so I would
> > remove that.  I would also not list the nodes from "parent-references"
> > in the same tree ouput.  It is not clear to me that this level of
> > detail is needed in the tree, and - as noted before - it isn't even
> > correct to list e.g. "interfaces" when the parent-reference in fact
> > selects a single interface.
> >
> >> The routing WG participants seem to
> >> find these useful, we can also ask there for broader input if you'd like.
> > One approach is to add the union of eveything that some people find
> > useful.  In the end we have to look for WG consensus.  Several people
> > have said that they prefer a less cluttered format.
> In the context of listing enums...
> 
> >
> >>>>> Since a parent
> >>>>> reference can be very specific, e.g. one specific interface, it isn't
> >>>>> really accurate to show:
> >>>>>
> >>>>>                   +--mp vrf-root
> >>>>>                      +--rw rt:routing/
> >>>>>                      |  ...
> >>>>>                      +--ro if:interfaces@
> >>>> This is just a conditional and we have precedent on how to handle
> >>>> conditional representation.   
> >>>>
> >>>>> And the trailing "/" on rt:routing doesn't add any information we
> >>>>> don't already know.  Since vrf-root is a mount point, it follows that
> >>>>> its children are mounted.
> >>>> The issue is a bit more complex when considering some real use cases,
> >>>> particularity when parent references and augmentations are used.  For
> >>>> example consider the following *without* the use / or @:
> >>>>
> >>>> module: ietf-network-instance
> >>>>   +--rw network-instances
> >>>>      +--rw network-instance* [name]
> >>>>         | ...
> >>>>         +--rw (root-type)
> >>>>            +--:(vrf-root)
> >>>>               +--mp vrf-root
> >>>>                  +--ro rt:routing-state
> >>>>                  |  +--ro router-id?                 yang:dotted-quad
> >>>>                  |  +--ro control-plane-protocols
> >>>>                  |     +--ro control-plane-protocol* [type name]
> >>>>                  |        +--ro ospf:ospf
> >>>>                  |           +--ro instance* [af]
> >>>>                  +--rw rt:routing
> >>>>                  |  +--rw router-id?                 yang:dotted-quad
> >>>>                  |  +--rw control-plane-protocols
> >>>>                  |     +--rw control-plane-protocol* [type name]
> >>>>                  |     +--rw ospf:ospf
> >>>>                  |        +--rw instance* [af]
> >>>>                  |           +--rw areas
> >>>>                  |              +--rw area* [area-id]
> >>>>                  |                 +--rw interfaces
> >>>>                  |                    +--rw interface* [name]
> >>>>                  |                       +--rw name if:interface-ref
> >>>>                  |                       +--rw cost?   uint16
> >>>>                  +--ro if:interfaces
> >>>>                  |  ...
> >>>>                  +--ro if:interfaces-state
> >>>>                  |  ...
> >>>>
> >>>>
> >>>> It's certainly not too hard to spot the top level mounts, but it is
> >>>> impossible to distinguish the parent references from the actual mounts. 
> >>> My proposal would be to not even show the parent references in the
> >>> diagram.  If we do that, the '/' is not needed.
> >>>
> >>>> Further more, some mounts are hard to spot.  For example, notice ospf. 
> >>>> Did you notice that it's a mount?
> >>> This is actually not correct.  ospf is *not* a mount; it is an augment.
> >>>
> >> it's a mounted module that augments another mounted module.
> > But why would it have a "/" just b/c it is augmented, when its sibling
> > 'control-plan-protocol' doesn't have the "/"?  What addition info does
> > the "/" convey?
> That it is a (sub)tree that is present due to a mounted module.

So is 'control-plane-protocol', so then it should also have '/',
right?


/martin