Re: [netmod] augment and if-feature

[Robert Wilton <[e-mail]>]

Hi Andy,


On 16/03/2017 16:17, Andy Bierman wrote:
>
>
> On Thu, Mar 16, 2017 at 2:54 AM, Robert Wilton <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>     Hi Dale,
>
>
>     On 15/03/2017 19:02, Dale R. Worley wrote:
>
>         JOEY BOYD <[e-mail] <mailto:[e-mail]>>
>         writes:
>
>             module base-module {
>                prefix bmod;
>
>                feature do-things;
>
>                container things {
>                  if-feature do-things;
>                  ...
>                }
>             }
>
>             module augment-module {
>                prefix amod;
>
>                augment "/bmod:do-things" {
>                  container other-things {
>                  }
>                }
>             }
>
>         First question:  I'm not expert in Yang, but as far as I can
>         figure out,
>         the augment statement is augmenting "container things",
>         right?  So the
>         augment statement should be 'augment "/bmod:things"' not 'augment
>         "/bmod:do-things"'.
>
>     Yes, the augment should be to "things".
>
>
>         But on the important question, I don't see it as at all
>         unreasonable
>         that the augment needs to be qualified by the same
>         if-feature.  The
>         reason is that if you're reading the text of module
>         augment-module, it's
>         helpful to have documented, right there, that the augmentation
>         depends
>         on the presence of a particular feature in the augmented
>         module.  And
>         it's helpful to know that the designer did, at least for one
>         moment,
>         think about the fact that the augmentation is conditional.
>
>
>     It isn't just any if-feature on the container that is being
>     augmented that needs to be considered.  You would have to consider
>     all if-feature statements by walking up the augmented node's
>     ancestors to the top of the tree and combine them, or have
>     multiple if-feature statements.
>
>     Further, the 7950 YANG update rules allow for the augmented module
>     to be revised and some of those if-feature statements to be
>     subsequently removed.  If the augmenting module had restated the
>     if-feature conditions then this would probably leave the
>     augmenting module unintentionally out of sync with the module that
>     it is augmenting.
>
>     In short, I think that if-feature statements work better if they
>     act on the given node and all descendant nodes, regardless of
>     which module those descendants are defined in.
>
>
> "work better"
>
> Please explain which protocol you are using that allows you to manage 
> descendant nodes of unimplemented nodes.
>
> NETCONF and RESTCONF do not work at all wrt/ accessing such nodes.
I think that we may be crossing wires:

It was NETCONF/RESTCONF that I was thinking of, and I am not considering 
managing descendant nodes of unimplemented nodes.

I think that the question is only whether an augmentation of a node that 
has an if-feature statement also requires the same if-feature statement 
on the augment statement.

To quote Joey's example,  I think that both of the following modules are 
valid (presuming that they are both implemented by a device) regardless 
of which features are enabled.  Do you agree?

module base-module {
   prefix bmod;

   feature things;
   feature widgets;

   container things {
     if-feature things;
     ...
     container widgets {
       if-feature widgets;
       ...
     }
   }
}

module augment-module {
   prefix amod;

   augment "/bmod:things" {
     container other-things {
     }
   }

   augment "/bmod:things/bmod:widgets" {
     container other-widgets {
     }
   }
}

Thanks,
Rob


>     Rob
>
>
> Andy
>
>
>
>         Dale
>
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