Re: [netmod] XPath questions about revised datastores

Andy,

section 5.1 of draft-ietf-netmod-revised-datastores-02.txt discusses
the XPath context. An xpath expression in a config-false container
will resolve to the operational state.

/js

On Wed, Jun 14, 2017 at 11:07:35AM -0700, Andy Bierman wrote:
> Hi,
> 
> I don't know if getting rid of /foo-state is such a great idea,
> especially wrt/ counters and other objects that are not
> related to intended config vs. applied config.
> 
> Q1) how does a client know the difference between an auto-generated
> foo-state.yang and a real foo-state.yang?  Seem like a YANG extension
> is needed to flag an auto-generated foo-state.yang
> 
> Q2) How does XPath reference an operational node if the /foo-state
> subtree has been moved to the /foo config subtree?
> 
> module foo {
> 
>      container foo {
>           leaf stat-collect-type {
>              type enumeration {
>                enum stat-set1;
>                enum stat-set2;
>              }
>            }
>       }
> 
>      container foo-state {
>           config false;
>           leaf stat-collect-type {
>              type enumeration {
>                enum stat-set1;
>                enum stat-set2;
>              }
>            }
>            container stat-set1 {
>               when "../stat-collect-type = 'stat-set1'";
>               ...
>            }
>            container stat-set2 {
>               when "../stat-collect-type = 'stat-set2'";
>               ...
>            }
>      }
> }
> 
> In this example, there is a request stat collect type /foo/stat-collect-type
> and there is an operational value (what the server/device is capable
> of collecting -- e.g. client requests stat-set2 knowing the server
> will change it to stat-set1 if set2 not supported)
> 
> So if /foo-state is folded into /foo (because that is the intent -- to get
> rid of this extra stat-collect-type leaf), then how do the when-stmts
> get applied to the operational value instead of the configured value?
> The same issue applies if the when-stmts are within an augment-stmt
> 
> WANT:
> 
>  augment /foo-state {
>     when "stat-collect-type = 'stat-set1'";
>     container stat-set1 {
>        ...
>     }
>  }
> 
> RD Provides:
> 
>   augment /foo {
>     when "stat-collect-type = 'stat-set1'";
>     container stat-set1 {
>        config false;
>        ...
>     }
>  }
> 
> There is no way to use when-stmt to reference the operational value.
> This is a rather common usage of the when-stmt, so it should not
> be removed if RD is used.
> 
> 
> 
> Andy

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-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
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