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

Lou Berger <lberger@labn.net> Tue, 19 September 2017 13:28 UTC

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To: Martin Bjorklund <mbj@tail-f.com>
Cc: rwilton@cisco.com, netmod@ietf.org
References: <5b512435-cebd-3534-eeb3-649154450d81@cisco.com> <20170915.134007.262763963470255554.mbj@tail-f.com> <c5352dde-4026-7549-bafa-30b19d7bb789@labn.net> <20170919.132947.358857445863848356.mbj@tail-f.com>
From: Lou Berger <lberger@labn.net>
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Subject: Re: [netmod] Proposal to enhance the YANG tree output
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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.

>
>> 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?  The routing WG participants seem to
find these useful, we can also ask there for broader input if you'd like.

>>> 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.

Lou
> /martin
>
>
>
>> Is it a mount or parent reference? 
>> With the / and @ both cases are transparent:
>>
>> 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@
>>                  |  ...
>>
>>> Also, what is mounted under a mount point is not defined in the
>>> schema, so a tool cannot generate this from the YANG modules.
>> I think this is a limitation in the current schema-mount definition that
>> perhaps will be revisited to support design time mounts, but
>> nonetheless  still has value to model any reader and implementor.
>> ...
>>
>> Lou
>>