Re: [netmod] schema mount open issue #1

[Lou Berger <[e-mail]>]

Hi Martin,

See below.


On 8/22/2017 6:20 AM, Martin Bjorklund wrote:
> Hi,
>
> Lada presented an open issue in schema mount in Prague.  (See slide 6
> in
> https://datatracker.ietf.org/meeting/99/materials/slides-99-netmod-sessb-schema-mount)
>
> The original problem comes from the NI use case
> (https://tools.ietf.org/html/draft-ietf-rtgwg-ni-model).  In this
> use case, interfaces are assigned to NIs by:
>
>    augment /if:interfaces/if:interface:
>      +--rw bind-ni-name?   -> /network-instances/network-instance/name
>
> Modules that are mounted within the NI might have references to
> interfaces.  The idea is that a specific NI can only reference the
> interfaces that has been assigned to it.
>
> In schema mount, we have the "parent-reference" XPath expression that
> in this case will be "/if:interfaces/if:interface".  The problem is
> that this XPath expression will evaluate to a node set that contains
> *all* interfaces in the system.  We would like this to contain just
> the interfaces assigned to the NI.
>
> It turns out that this can be done with a simple change to the
> "parent-reference" node.  If we state that this XPath expression is
> evaluated in an XPath context where the context node is the node in
> the data tree where the mount point is defined (instead of "/"), we
> can use as parent-reference:
>
>   /if:interfaces/if:interface[ni:bind-network-instance-name = ../ni:name]
>
> Putting this together we'd have:
>
>   augment "/if:interfaces/if:interface" {
>     leaf bind-ni-name {
>       type leafref {
>         path "/network-instances/network-instance/name";
>       }
>     }
>   }
>
>   container network-instances {
>     list network-instance {
>       key name;
>       leaf name { ... }
>       ...
>       container root {
>         // this would be the XPath context root for parent-reference
>         yangmnt:mount-point ni-root;
>       }
>     }
>   }

note that the current NI definition is:


   module: ietf-network-instance
     +--rw network-instances
        +--rw network-instance* [name]
           +--rw name           string
           +--rw enabled?       boolean
           +--rw description?   string
           +--rw (ni-type)?
           +--rw (root-type)?
              +--:(vrf-root)
              |  +--mp vrf-root?
              +--:(vsi-root)
              |  +--mp vsi-root?
              +--:(vv-root)
                 +--mp vv-root?
   augment /if:interfaces/if:interface:
     +--rw bind-ni-name?   -> /network-instances/network-instance/name
   augment /if:interfaces/if:interface/ip:ipv4:
     +--rw bind-ni-name?   -> /network-instances/network-instance/name
   augment /if:interfaces/if:interface/ip:ipv6:
     +--rw bind-ni-name?   -> /network-instances/network-instance/name

> And in state data:
>
>
> "ietf-yang-schema-mount:schema-mounts": {
>   "namespace": [
>     {
>       "prefix": "ni",
>       "uri": "urn:ietf:params:xml:ns:yang:ietf-network-instance"
>     },
>     {
>       "prefix": "if",
>       "uri": "urn:ietf:params:xml:ns:yang:ietf-interfaces"
>     }
>   ]
>   "mount-point": [
>     {
>       "target": "/ni:network-instances/ni:network-instance/ni:root",
Can you confirm that with the current definition the target is:

      "target": "/ni:network-instances/ni:network-instance",

correct?

>       "parent-reference": [
>             "/if:interfaces/if:interface
>              [ni:bind-network-instance-name = ../ni:name]"
>                           ],
Also, can you confirm that if we wanted to cover v4, v6 (for example
purposes) interfaces-state, the full parent reference list would be:

      "parent-reference": [
            "/if:interfaces/if:interface
             [ni:bind-ni-name = ./ni:name]",
            "/if:interfaces/if:interface/ip:ipv4
             [ni:bind-ni-name = ./ni:name]",
            "/if:interfaces/if:interface/ip:ipv6
             [ni:bind-ni-name = ./ni:name]",
             "/if:interfaces-state/if:interface"

 correct?

Note that interfaces-state isn't filtered as the bind-ni-name isn't
present in -state.

>       "use-schema": [
>         {
>           "name": "ni-schema"
>         }
>       ]
>     }
>   ]
>
>
>
> Note that this does NOT affect the schema that is mounted; it only
> affects the result of the parent-reference XPath expressions.
>
>
> I think that we should make this change, since it allows for more
> precise parent-references.
I'm okay with the change (just want to see the draft moved forward ;-)

Lou
(As contributor)


>
>
> /martin
>
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