Lou Berger <[email protected]> wrote:
> 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:
Yes I saw that.
> 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?
Note that the extension yangmnt:mount-point can only be present in a
container or list, not in a choice/case.
But what is the point of a choice with three different mount points?
> 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?
See above; the current definition is invalid.
> > "parent-reference": [
> > "/if:interfaces/if:interface
> > [ni:bind-network-instance-name = ../ni:name]"
Correction. This should be:
"/if:interfaces/if:interface
[ni:bind-network-instance-name = current()/../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?
No it would be:
/if:interfaces-state/if:interface[
if:name = /if:interfaces/if:interface[
ni:bind-ni-name = current()/../ni:name]/if:name]
etc.
I.e., the interfaces in -state that that has the same names as the
interfaces in config that has the correct bind-ni-name.
> 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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