Re: [babel] [netmod] NULL value for uint16

Mahesh Jethanandani <mjethanandani@gmail.com> Tue, 14 September 2021 22:51 UTC

Return-Path: <mjethanandani@gmail.com>
X-Original-To: babel@ietfa.amsl.com
Delivered-To: babel@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 110F13A3495; Tue, 14 Sep 2021 15:51:07 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.097
X-Spam-Level:
X-Spam-Status: No, score=-2.097 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, HTML_MESSAGE=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id XvLXbO7h4fba; Tue, 14 Sep 2021 15:51:01 -0700 (PDT)
Received: from mail-pg1-x52f.google.com (mail-pg1-x52f.google.com [IPv6:2607:f8b0:4864:20::52f]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 9E2013A34C1; Tue, 14 Sep 2021 15:51:01 -0700 (PDT)
Received: by mail-pg1-x52f.google.com with SMTP id w8so737136pgf.5; Tue, 14 Sep 2021 15:51:01 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:message-id:mime-version:subject:date:in-reply-to:cc:to :references; bh=Qi288jpIEntwg6YFTY3A6n48C/qAkL4edjtpSYTtoDI=; b=Jp50YlGXggx8juHGLQTRpt6B2CHIhh70WoQOe4wGJ//eTzNNOyaqHjDdWi+OLZ/4PP 4bzeqklt+nim4sX0BrGuHfFFsCOLO4sfaBB5d9QEDntnFJxXhC+1wC2+Plpmy+4vBOq9 gwivtdTtW27SOiZksXWse22UdHbXe2A777ANhH118wNWQjKtYilI6/bz3MbtXKX4F4WS 3JQql09cpcfAUAC93xKVZKKZehUy5r/woHb5WT6EucieaVoFj8TprvQiBMMATqoSUhW0 QtrXGXwBfYSKU6+eSCEgMgUMF0c8R+hVL3euKWufjg4K45Ks2J0PgeHqUxQI2Pe8xfOD Cjag==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:message-id:mime-version:subject:date :in-reply-to:cc:to:references; bh=Qi288jpIEntwg6YFTY3A6n48C/qAkL4edjtpSYTtoDI=; b=OutHTp55xYpZD9kFmresjRm2hUdmRjHBMn/hK2SY6MWXo2BeCgiPrAg4YROkNDPFTD 31k/WFGnMcigXn1zEyPSnhjuR6GgkoI8thU0Wxa6GUW0ZADH5n2IRxa3CfzJp0ecJTFN mJVkzMMsr0CVJ7Ib0n95+Io12TtIfckKS3sSt0Hw1vhA6tx4fk446nb1M97eYuKm789e hpfiSRHf90yTHipRf04GLApTPH9yNisFOqZAV/19xQmbGY/9IXiPbA1EIMwspqg6DLy8 eOsAL8B0hblWWCpSh7Tf9mosPaNPBUs3xzUJFt0pKIbVqjWUPiqxfNSakbek0/Eli0Rv sXhA==
X-Gm-Message-State: AOAM5309XEqpjk1Ku3gKi0W9TaxNGIH/CvKtCECBXN1XORdOfoxm7DDq 586vcD61z2NPS9H089cEFmQ=
X-Google-Smtp-Source: ABdhPJyW1FftbbAv1tKA8hN9PJqC4fpA8yP/dIjAWkaGsDKzZGUlZcv3/sBMDNe6b7cReHGNKVSE2w==
X-Received: by 2002:a63:798c:: with SMTP id u134mr17725084pgc.479.1631659859928; Tue, 14 Sep 2021 15:50:59 -0700 (PDT)
Received: from [192.168.1.133] (c-69-181-169-15.hsd1.ca.comcast.net. [69.181.169.15]) by smtp.gmail.com with ESMTPSA id a71sm11666550pfd.86.2021.09.14.15.50.58 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 14 Sep 2021 15:50:59 -0700 (PDT)
From: Mahesh Jethanandani <mjethanandani@gmail.com>
Message-Id: <C8C1F5DC-A7E2-403B-B308-0191893E23CD@gmail.com>
Content-Type: multipart/alternative; boundary="Apple-Mail=_83D425F1-5AEF-4183-8B9A-989202EE4F35"
Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.7\))
Date: Tue, 14 Sep 2021 15:50:58 -0700
In-Reply-To: <3CCE870C-9D69-450F-A795-84B791DDAA8E@gmail.com>
Cc: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>, Babel at IETF <babel@ietf.org>, "STARK, BARBARA H" <bs7652@att.com>, netmod@ietf.org
To: =?utf-8?Q?Martin_Bj=C3=B6rklund?= <mbj+ietf@4668.se>
References: <DM6PR02MB692446F49506791E90B0D23EC3DA9@DM6PR02MB6924.namprd02.prod.outlook.com> <20210914171729.ph5q77zm46z3zvxi@anna.jacobs.jacobs-university.de> <5F6A0BF9-06F9-41E9-8B9A-701608875934@gmail.com> <20210914.201758.1827806402442755510.id@4668.se> <3CCE870C-9D69-450F-A795-84B791DDAA8E@gmail.com>
X-Mailer: Apple Mail (2.3608.120.23.2.7)
Archived-At: <https://mailarchive.ietf.org/arch/msg/babel/cA85ldZhmKi3Ce4avinPNyI2Ndo>
Subject: Re: [babel] [netmod] NULL value for uint16
X-BeenThere: babel@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "A list for discussion of the Babel Routing Protocol." <babel.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/babel>, <mailto:babel-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/babel/>
List-Post: <mailto:babel@ietf.org>
List-Help: <mailto:babel-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/babel>, <mailto:babel-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 14 Sep 2021 22:51:08 -0000

A related question.

> On Sep 14, 2021, at 12:31 PM, Mahesh Jethanandani <mjethanandani@gmail.com> wrote:
> 
> Hi Martin,
> 
>> On Sep 14, 2021, at 11:17 AM, Martin Björklund <mbj+ietf@4668.se <mailto:mbj+ietf@4668.se>> wrote:
>> 
>> Mahesh Jethanandani <mjethanandani@gmail.com <mailto:mjethanandani@gmail.com>> wrote:
>>> Hi Juergen,
>>> 
>>>> On Sep 14, 2021, at 10:17 AM, Jürgen Schönwälder <j.schoenwaelder@jacobs-university.de <mailto:j.schoenwaelder@jacobs-university.de>> wrote:
>>>> 
>>>> On Tue, Sep 14, 2021 at 01:51:36PM +0000, STARK, BARBARA H wrote:
>>>> 
>>>>> As I mentioned, BBF TR-181 uses int with range 	-1:65535 with -1 meaning NULL. So I certainly have no issue with that approach. The language in RFC9046 was intended to make sure this approach was allowed, since this is how it's done in TR-181.
>>>>> I guess I am a bit surprised to learn that YANG doesn't seem to have a preferred way to handle this. Unfortunately, given my considerable lack of YANG expertise, I can't recommend the "right" way to model this in YANG. I can only insist that the model be able to express a value in the range 0 to 2^16 and NULL value for these parameters. 
>>>>> Independent of the fact that the words in RFC9046 don't seem to have expressed this perfectly clearly, that is absolutely the intent of those words. I apologize that the RFC9046 words don't seem to be sufficiently clear. 
>>>>> 
>>>>> Since you do mention the possibility of using -1 for NULL, I'd like to understand who might find this approach unacceptable? The language in the information model was definitely intended to express the acceptability of using this approach from a Babel WG perspective (because I knew that's how it would be done in TR-181). Would this be unacceptable to people with YANG expertise? I think my preference would be to use this approach, since it would provide additional consistency between the TR-181 and YANG models.
>>>> 
>>>> If other data models use an extended integer range and -1 to indicate
>>>> a special case, then this may be a strong reason to do the same in the
>>>> IETF YANG data model. Consistency across data models is a value, in
>>>> particular for systems that may have to support multiple. While the
>>>> conversion of different notations no hard, its one more thing to
>>>> potentially get wrong.
>>>> 
>>>> If you were starting with a blank sheet of paper, then the YANG idiom
>>>> would likely be to use a union of a 16-bit integer and a special
>>>> (string) value, which might even be of type empty.
>>> 
>>> I hear two suggestions on what the “other” construct should be in the union statement. Use ‘empty’ as you suggest, or use ‘boolean’. Are there any pros/cons for either of the approaches?
>> 
>> 'boolean' doesn't seem right, since that would mean that you could see
>> the values 'true' | 'false' | <uint16>.
>> 
>> If you want a union I suggest a union with one enum, perhaps:
>> 
>>  type union {
>>    type enumeration {
>>      enum null;
>>    }
>>    type uint16;
>>  }
>> 
>> But Jürgens point about using a solution that other data models use
>> makes sense.
> 
> That would mean something like this:
> 
> type union {
>   type empty;
>   type uint16;
> }
> 
> Right?

RFC 7950 says that the empty type cannot have a default value. The model had the value 0, which represented NULL as the default value for some of the attributes. With the suggested change, is there a way in the union for the empty type to be the default?

If not, I will have to use Martin’s suggestion above of using a null enumeration.

Thanks.

> 
>> 
>> Yet another alternative could be to not instantiate this leaf when the
>> value in the information model is null.
> 
> I have never been very clear on what happens when the leaf goes from a defined value to null. In other words, how do you “un-instantiate” a leaf? Do you delete it?
> 
> Cheers.
> 
>> 
>> 
>> 
>> /martin
>> 
>> 
>> 
>> 
>> 
>>> 
>>>> 
>>>> One of the reasons to have no common approach to these kind of
>>>> questions is to provide the flexibility needed to do the right thing
>>>> in different contexts. Of course, you may want to stay consistent in a
>>>> data model or a collection of related data model.
>>>> 
>>>> I skimmed RFC 8407 and it seems we do not have text discussion this
>>>> specific situation. Perhaps we should have text, perhaps I have
>>>> overlooked it. ;-) I think there are different patterns to choose from
>>>> to handle this situation with their various pros and cons.
>>>> 
>>>> /js
>>>> 
>>>> -- 
>>>> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
>>>> Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
>>>> Fax:   +49 421 200 3103         <https://www.jacobs-university.de/ <https://www.jacobs-university.de/>>
>>> 
>>> Mahesh Jethanandani
>>> mjethanandani@gmail.com <mailto:mjethanandani@gmail.com>
> Mahesh Jethanandani
> mjethanandani@gmail.com <mailto:mjethanandani@gmail.com>
Mahesh Jethanandani
mjethanandani@gmail.com