Re: [netmod] XPath questions about revised datastores

[Martin Bjorklund <[e-mail]>]

Andy Bierman <[e-mail]> wrote:
> On Thu, Jun 15, 2017 at 9:08 AM, Martin Bjorklund <[e-mail]> wrote:
> 
> > Andy Bierman <[e-mail]> wrote:
> > > On Thu, Jun 15, 2017 at 8:41 AM, Martin Bjorklund <[e-mail]>
> > wrote:
> > >
> > > > Andy Bierman <[e-mail]> wrote:
> > > > > On Thu, Jun 15, 2017 at 5:27 AM, Juergen Schoenwaelder <
> > > > > [e-mail]> wrote:
> > > > >
> > > > > > 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.
> > > > > >
> > > > > >
> > > > >
> > > > > So the usual method of "augment when" is broken:
> > > > >
> > > > > WRONG: Will evaluate when-stmt against config
> > > > >
> > > > >    augment /foo {
> > > > >        when "some condition";
> > > > >        container stats { }
> > > > >   }
> > > >
> > > > Do you mean that stats is a config true container?  And presumably in
> > > > the stats containter you have config false leafs?
> > > >
> > > >
> > > no -- stats is a config false container
> >
> > Ok.  Well, then this is also ok.  The stats container will exist if
> > "some condition" is true in the operational state datastore.
> >
> > > > I think this works as expected.  In a conventional datastore
> > > > (e.g. running), the stats container exists if "some condition" is true
> > > > in that datastore.
> > > >
> > >
> > >
> > > no -- in my example the desire is to augment the operational state based
> > on
> > > the
> > > operational value of a config=true leaf
> >
> > Yes, that will happen in both cases.
> >
> > > > In the operational state, the stats container exists if "some
> > > > condition" is true in that the operational state datastore.
> > > >
> > > > >  Correct: Will evaluate when-stmt against operational:
> > > > >
> > > > >    augment /foo {
> > > > >        container stats {
> > > > >          config false;
> > > > >          when "different condition";
> > > > >        }
> > > > >    }
> > > >
> > > > In this case the stats container will never exist in any conventional
> > > > datastore, since it is config false.
> > > >
> > > > In the operational state, the stats container exists if "different
> > > > condition" is true in that the operational state datastore.
> > > >
> > > > > Forcing the augmenting node to be the XPath context node impacts the
> > > > > possible expressions.
> > > > > I think the RD draft should make all this clear.
> > > >
> > > > This is not different from how it works today wrt candidate vs running
> > > > for example.
> > > >
> > >
> > > no -- the datastore doesn't change based on the context node config-stmt
> > > value
> > > for candidate and running.
> >
> > The datastore doesn't change with NMDA either - an XPath expression is
> > always evaluated in a particular datastore, just like before.  There
> > is no mechanism to read data from a different datastore in the XPath
> > expressions.
> >
> >
> >
> 
> But in the first example the when-stmt is evaluated in the context of /foo
> which is config=true.
> Doesn't that mean the configuration values will be used?

No, the values of these nodes in the operational state datastore will
be used (these are the "applied configuration" values).

> The config=false nodes added if the when-stmt is true are not the context
> nodes in the first form.
> Authors need to be careful to put the when-stmt in a config=false context
> node in order
> to evaluate in the operational datastore.

No, see above.


/martin



> 
> 
> 
> > /martin
> >
> 
> 
> Andy
> 
> 
> >
> >
> >
> >
> > >
> > >
> > >
> > > >
> > > >
> > > > /martin
> > > >
> > > >
> > > >
> > >
> > > Andy
> > >
> > >
> > > >
> > > > >
> > > > >
> > > > >
> > > > > /js
> > > > > >
> > > > >
> > > > >
> > > > > Andy
> > > > >
> > > > >
> > > > > >
> > > > > > 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
> > > > > >
> > > > > > > _______________________________________________
> > > > > > > netmod mailing list
> > > > > > > [e-mail]
> > > > > > > https://www.ietf.org/mailman/listinfo/netmod
> > > > > >
> > > > > >
> > > > > > --
> > > > > > Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> > > > > > Phone: [phone]         Campus Ring 1 | 28759 Bremen |
> > Germany
> > > > > > Fax:   [phone]         <http://www.jacobs-university.de/>
> > > > > >
> > > >
> >