Re: [netmod] yanglint and implemented versus imported YANG modules

Ladislav Lhotka <lhotka@nic.cz> Tue, 07 March 2017 09:30 UTC

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From: Ladislav Lhotka <lhotka@nic.cz>
To: Robert Wilton <rwilton@cisco.com>, William Lupton <wlupton@broadband-forum.org>, netmod@ietf.org
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Date: Tue, 07 Mar 2017 10:30:51 +0100
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Subject: Re: [netmod] yanglint and implemented versus imported YANG modules
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Robert Wilton <rwilton@cisco.com> writes:

> Hi William,
>
> I think that what yanglint is doing here is sane, i.e. I think that its 
> interpretation/split between imported vs implemented modules is 
> supported by the YANG RFC.
>
> However, for validation purposes it seems that it would be useful if 
> yanglint had an option to assume that all imported modules are 
> implicitly implemented without requiring them to be explicitly
> specified.

This will fail if a module just wants to use a grouping or typedef from
an imported module but not data nodes that may also be there. 

It is exactly the problem that I mentioned in the discussion about
NETMOD charter: we need a way to specify a complete data model. In my
YANG/I-D development environment [1], a hello XML file is used for this
purpose.

Lada

[1] https://github.com/llhotka/YANG-I-D

>
> Thanks,
> Rob
>
>
> On 06/03/2017 16:44, William Lupton wrote:
>> All,
>>
>> This message arose from a yang-multicast@ietf.org 
>> <mailto:yang-multicast@ietf.org> “draft-ietf-pim-igmp-mld-yang-02.txt: 
>> YANG compilation isuse” (sic) thread 
>> <https://www.ietf.org/mail-archive/web/yang-multicast/current/threads.html#00232> initiated 
>> by Benoit.
>>
>> I thought it would be useful for NETMOD to see the part of the 
>> discussion that relates to implemented versus imported YANG modules.
>>
>>  1. Benoit Claise reported this warning:
>>       * warn: Schema node "ietf-ip:ipv4" not found
>>         (/ietf-interfaces:interfaces/ietf-interfaces:interface[ietf-interfaces:name
>>         = current()]/ietf-ip:ipv4)
>>  2. Radek Krejčí replied:
>>       * These warnings are printed because in yanglint, until
>>         explicitly stated, the imported modules (such as
>>         ietf-interfaces and ietf-ip), are supposed to be only
>>         imported, not implemented. The data nodes in imported schemas
>>         are not available, which is the reason of these warnings.
>>  3. William Lupton (that’s me!) asked / commented:
>>       * Why are the complaints only about ip:ipv4 (etc) and not about
>>         if:interfaces (etc), which are also referenced in the must
>>         statements?
>>       * This makes it hard for an automated tool (such as Benoit’s)
>>         because it needs to know which other YANG files to process in
>>         addition to the “file of interest”.
>>  4. Radek Krejčí replied:
>>       * According to RFC 7950, sec 5.6.6 (3rd paragraph) [ED: 5.6.5?],
>>         when an implemented module augments another module
>>         (ietf-interfaces), the augmented module MUST be also
>>         implemented. So libyang automatically changes the augmented
>>         module from imported to the implemented. The same rule applies
>>         also in case of referring a module in path (leafref) and
>>         by deviating a module. But it does not apply when a module
>>         data is used in must or when conditions. That's the reason why
>>         it complains just about ietf-ip and not about ietf-interfaces.
>>       * YANG actually does not provide a way to specify that a
>>         particular import is also expected to be implemented.
>>         Therefore, libyang needs some help with setting modules
>>         implemented - all the explicitly loaded modules are supposed
>>         to be implemented, if the module is just implicitly loaded
>>         from the search directory and user did not expressed that it
>>         is supposed to be implemented, it is kept only imported to
>>         provide groupings or type definitions
>>  5. Benoit Claise asked (referring to my reference to automated tools):
>>       * Would it be possible to improve the warning (and the related
>>         test, by testing implemented instead of import), basically
>>         telling that the module itself is fine?
>>
>>
>> I’m interested to know that NETMOD thinks about this distinction 
>> between implemented versus imported (in the absence of any instance 
>> documents). I guess my (maybe naive) view is that if all I’m doing is 
>> checking for errors in my YANG model then I don’t care about this. If 
>> my YANG is good I want to see no warnings or errors, and if it’s bad 
>> then I want to be told this (and why).
>>
>> Thanks,
>> William
>>
>>
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Ladislav Lhotka, CZ.NIC Labs
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