On Thu, Sep 04, 2014 at 09:18:53AM -0700, Andy Bierman wrote:
> It makes a big difference to YANG XPath whether there is a separate
> datastore.
> YANG only supports 1 static context for each document type
> (rpc/input, rpc/output, config-data, all-data, notification). A new
> datastore might
> require many changes to YANG, depending on I2RS requirements.
> 
> There are problems mixing local config and I2RS nodes in "must" or "when"
> expressions.
> One important detail is whether I2RS objects are config=true (or false) in
> YANG.
> This impacts how must, when, and other constructs will behave.
> 
> If I2RS is config=false, It should be OK to reference local config from
> I2RS must/when stmts,
> but a config object must/when statement is not allowed to reference an I2RS
> object.
> Is this OK? Are there any requirements for "YANG integration" between the
> local config
> and the I2RS datastore?

An example use case that may cover this is a BGP dynamic peer I2RS
interface.  In such a case (ideally):

- Configuration exists for BGP.  This implies an IDR BGP yang module.
- Some re-usable components from the BGP module have been made into
  groupings to permit I2RS re-use.  For example, a "neighbor template".
- The I2RS portion of this module would rely on some amount of local BGP
  configuration outside of the I2RS module.  As a trivial example,
  "router autonomous system number" is a property that is device-wide that may
  be owned by BGP config; the I2RS neighbor configuration would have a "must"
  dependency on the presence of the ASN config.

(Those who are interested in working on such a BGP I2RS module please hold
your nitpicking of the example.  Yes, we'll probably want to permit local
configuration of the neighbor ASN as well, but it highlights the issue...
:-)

If we can't do this sort of thing by using a separate datastore, that may
push the solution a given direction.

-- Jeff

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