Re: [netmod] draft-ietf-netmod-rfc8407bis: must + error-message for "config false"

["Rob Wilton (rwilton)" <[e-mail]>]

Specifically regarding MUST statements on state date, RFC 8342 section 5.3, also has this statement (which effectively aligns to Jürgen's last paragraph):

   <operational> SHOULD conform to any constraints specified in the data
   model, but given the principal aim of returning "in use" values, it
   is possible that constraints MAY be violated under some circumstances
   (e.g., an abnormal value is "in use", the structure of a list is
   being modified, or remnant configuration (see Section 5.3.1) still
   exists).  Note that deviations SHOULD be used when it is known in
   advance that a device does not fully conform to the <operational>
   schema.

   Only semantic constraints MAY be violated.  These are the YANG
   "when", "must", "mandatory", "unique", "min-elements", and
   "max-elements" statements; and the uniqueness of key values.
 
   Syntactic constraints MUST NOT be violated, including hierarchical
   organization, identifiers, and type-based constraints.  If a node in
   <operational> does not meet the syntactic constraints, then it
   MUST NOT be returned, and some other mechanism should be used to flag
   the error.

Regards,
Rob


-----Original Message-----
From: netmod <[e-mail]> On Behalf Of Jürgen Schönwälder
Sent: Wednesday, November 1, 2023 7:46 AM
To: [e-mail]
Cc: [e-mail]
Subject: Re: [netmod] draft-ietf-netmod-rfc8407bis: must + error-message for "config false"

Here is what RFC 7950 says:

  7.5.4.1.  The "error-message" Statement

     The "error-message" statement, which is optional, takes a string as
     an argument.  If the constraint evaluates to "false", the string is
     passed as <error-message> in the <rpc-error> in NETCONF.

Since state data is not (directly) modified by processing RPCs, which
<rpc-error> would carry the <error-message>? If the answer is 'none',
then why define an <error-message> for state data?

My take has always been that operational state data should report as
much as possible the true state of the device - even if the current
state violates certain constraints. The entity to check constraints
would be a managing system, not the managed system. That said, the
wording in section 7.5.4.1 indicates that the designers had servers
processing RPCs in mind.

/js

On Tue, Oct 31, 2023 at 10:40:15AM +0000, [e-mail] wrote:
> Hi all,
> 
> In the context of https://datatracker.ietf.org/doc/draft-ietf-pce-pcep-yang/, Dhruv has received in the past a comment about the use of "must + error-message" for "config false" data nodes. He reported that comment at https://mailarchive.ietf.org/arch/msg/yang-doctors/gWnXnyNHPVv_nZB1PQjThAwP1JY/, but without any follow-up.
> 
> rfc7950#section-8.1 includes a provision for the use of "must" for state data, but silent about the use of error-message. Some guidance for authors may be useful here.
> 
> The following options are being considered:
> 
> (1) Remove both must and error-message for config false data nodes
> (2) Remove error-message but keep the must
> (3) keep both
> 
> I think that (3) is OK as this is a formal way to detect anomalies in state data, but I'm open to hear what the WG thinks.
> 
> Opinions whether we need to include a mention about this in draft-ietf-netmod-rfc8407bis are welcome.
> 
> Thank you.
> 
> Cheers,
> Med
> 
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-- 
Jürgen Schönwälder              Constructor University Bremen gGmbH
Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
Fax:   [phone]         <https://constructor.university/>

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