Re: [netmod] YANG Versioning Weekly Call Minutes - 2021-04-13

[Balázs Lengyel <[e-mail]>]

Hello Andy,

I remember when we wrote these rules, we were concentrating on config and did not spend much time considering state data.

 

There are rules that are good for config but not for state. E.g.

*	RFC7950 does not allow changing the mandatory statement from false to true; as this could make a valid configuration that does not include an optional leaf invalid.
*	On the other hand, changing a state leaf from mandatory false to true means always including the leaf in a <get> response. That should be a compatible change. 

Do you agree, that at least in some cases different compatibility rules for state and configuration data makes sense?

Regards Balazs

 

From: netmod <[e-mail]> On Behalf Of Sterne, Jason (Nokia - CA/Ottawa)
Sent: 2021. április 13., kedd 20:30
To: Andy Bierman <[e-mail]>
Cc: [e-mail]
Subject: Re: [netmod] YANG Versioning Weekly Call Minutes - 2021-04-13

 

Hi Andy,

 

Thx for taking a look.

 

Yes - agree with the "orderly" comment. That was very brief shorthand for the minutes. By "remove" it could even just mean marking as "obsolete" (with deprecated as an optional intermediate step).

 

We aren't trying to redefine the rules for config. But it is worth considering whether some of those aren't really good for state.  Implementations may be ignoring some of those rules for state because they don't really fit.

 

Jason 

 

From: Andy Bierman <[e-mail] <mailto:[e-mail]> > 
Sent: Tuesday, April 13, 2021 2:16 PM
To: Sterne, Jason (Nokia - CA/Ottawa) <[e-mail] <mailto:[e-mail]> >
Cc: [e-mail] <mailto:[e-mail]> 
Subject: Re: [netmod] YANG Versioning Weekly Call Minutes - 2021-04-13

 

 

 

On Tue, Apr 13, 2021 at 7:12 AM Sterne, Jason (Nokia - CA/Ottawa) <[e-mail] <mailto:[e-mail]> > wrote:

YANG Versioning Weekly Call Minutes - 2021-04-13

 

Primary discussion was around the BC/NBC rules for state.

 

Value space for config false:

- more informative if you actually remove the enum from the model if it isn't used anymore (vs leaving it in and servers just not returning it)

- a server implementation should deviate if it doesn't return something ever (schema should try to accurately define the API)

- standard module -> remove the item if it isn't part of the API anymore

 

 

I assume you mean to use the status-stmt to transition from current -> deprecated -> obsolete

in an orderly fashion. Especially since sec 11 is very clear:

 

   Obsolete definitions MUST NOT be removed from published modules,
   since their identifiers may still be referenced by other modules.

 

 

 

- NMDA operational DS has a copy of config true, so increased value space in config automatically casues increased value space in "state" (operational)

- a config true MTU in the operational DS and a dedicated config false "oper-mtu" leaf should have the same rules for increasing value space

 

Maybe a better formulation of the state rules is to take the 7950 rules and apply minimal text changes. Rob will take a stab at this.

 

7950:

   o  A "must" statement may be removed or its constraint relaxed.

   

Adjusted 7950 text:

   o  A "must" statement may be added, removed, or changed

  

 

7950:

   o  A "range", "length", or "pattern" statement may expand the allowed

      value space.

Adjusted 7950:

   o  A "range", "length", or "pattern" statement may expand or reduce the allowed

      value space.

 

 

I strongly object to this WG creating an "adjusted YANG 1.1" standard.

IMO there is no need or WG consensus to create any sort of replacement for RFC 7950.

 

If YANG 1.1 needs non-backward-compatible changes  (which it doesn't IMO) then a new

YANG 2.0 RFC must be written to accomplish that.

 

It is possible to introduce support for NBC changes in a way that does not change YANG 1.1

at all. E.g.:

 

Rule 1 of 1:

  - If any change is made that violates a MUST or MUST NOT provision of RFC 7950,

    sec. 11, then the major revision number in the semver string MUST be incremented.

 

 

 

 

Jason

 

Andy

 

 

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