Ladislav Lhotka <lho...@nic.cz> wrote:
> Martin Bjorklund <m...@tail-f.com> writes:
>
> > Hi,
> >
> > [replying to the first post in this (old) thread; the thread got a bit
> > off-topic]
> >
> > Balazs Lengyel <balazs.leng...@ericsson.com> wrote:
> >> Hello,
> >>
> >> As I understand it, Schema-mount today does not support an important
> >> use-case which we definitely need, but others also indicated they
> >> want.
> >>
> >> I want to specify off-line in design time which models will be mounted
> >> where. Many of my nodes know in design-time what their model structure
> >> will be, so I want a way to be able to document this in YANG.
> >
> > I'd like to understand this use case in more detail. You say that
> > that a "node knows in design-time" that YANG models it will use. Thus
> > it seems natural to be able to specify which other modules to mount in
> > the YANG module itself.
>
> Did you have a chance to look into my slides from Berlin? I sketched some
> solutions there.
Well, that's a *solution*. I'd like to understand the *problem* first ;)
> > The problem I see with this is that it is very limited to the use case
> > where each implementation defines its own YANG modules. Suppose you
> > have such a model, for example:
> >
> > module A {
> > ...
> > mount ... {
> > mount-module B;
> > mount-module C;
> > }
> > }
> >
> > [pseudo-code for module A that specifies that it mounts B and C]
> >
> > Now, suppose you take this module A to another implementation, and it
> > needs to augment something into module C; essentially this means that
> > it would like to mount B, C and new module D. This will not be
> > possible unless it modifies module A.
>
> Not necessarily, D could contain an augment with a target specified by a
> schema node identifier that uses nodes from both A and C.
Not if B and D are defined as standalone modules, e.g. if B is
ietf-interfaces and D is ietf-ip.
> Imagine that instead of "ietf-ip" augmenting "ietf-interfaces" it would
> be the other way around: "ietf-interfaces" mounts "ietf-ip". Then the
> augment in ietf-ipv6-router-advertisements
>
> augment "/if:interfaces-state/if:interface/ip:ipv6" { ... }
>
> needn't be changed.
This would be an entirely different kind of mount! The current mount
doesn't work like that; it doesn't give you visibility into the
combined models - by design.
> The major problem with this IMO is that it needs a new YANG statement.
>
> >
> >> In
> >> today's proposal the only way to find the Yang-Mounts is to read it
> >> from the live node.
> >>
> >> * OAM integrators or operators want to be able to write CLI scripts
> >> and Netconf messages without accessing (expensive) real nodes. For
> >> this they need to know the mounts
> >> * We want to generate some fancy documentation from YANG automatically
> >> in design-time.
> >
> > In a way this is no different from the situation today - in order to
> > learn what YANG modules a device supports you need to connect and
> > parse the <hello> message (or ietf-yang-library data in the near
> > future). This info could also be made available off-line in a file.
>
> Yup. So we just need some machine-readable description of the structure
> of mounted schemas.
>
> >
> > It should certainly be possible to define a file format that a device
> > somehow could "publish" off-line that contained all the info that is
> > available at run-time. This file format could be exactly the same as
> > you would get if you did a NETCONF <get/> operation with some filter
> > to only retreive the ietf-yang-library data at the mount points.
>
> Well, if you have multiple levels of mounts, it will get messy: you
> wouldn't know which yang-library data belongs to which mount point.
Why not - imagine that you do a full <get/> on such a device, it will
return the nested yang library data just fine.
/martin
> I believe some variation on YSDL could work, and as I wrote in another
> thread, we could also incorporate datastores: after defining the
> (multilevel) schemas, each datastore will get one assigned - and they
> can also share them where needed.
>
> Lada
>
> >
> >
> >
> > /martin
> >
> >
> >>
> >> * Many use cases need the possibility to mount schemas, but do not
> >> need the added complexity of schema changes in run-time.
> >> Notwithstanding the case of "YANG Features", for me the model schema
> >> is a mostly static description of a nodes capabilities. Most of the
> >> time I do not want to worry about the node changing its schema on
> >> the fly.
> >>
> >>
> >> For this I propose 2 YANG extensions
> >>
> >> extension schema-mount {
> >> description "Indicates that a YANG Module is to be mounted into
> >> another module.
> >> The argument specifies the name of the module to be mounted.";
> >> argument mounted-module;
> >> }
> >>
> >> extension schema-mount-target {
> >> description "Specifies the target node under which a YANG module is to
> >> be mounted.
> >> The statement can only be used inside a schema-mount statement.
> >> The argument follows the same rules as an augment statement's target.
> >> argument target-node;
> >> }
> >>
> >> The two extension statements can be placed in a separate module or the
> >> mounted module.
> >>
> >> I don't insist on the solution, but I need the off-line/design-time
> >> specification of yang-mount to be possible. IMHO the design-time mount
> >> use-case is more important than the dynamic-mount.
> >>
> >> regards Balazs
> >> --
> >> Balazs Lengyel Ericsson Hungary Ltd.
> >> Senior Specialist
> >> Mobile: +36-70-330-7909 email: balazs.leng...@ericsson.com
> >
> > _______________________________________________
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> > https://www.ietf.org/mailman/listinfo/netmod
>
> --
> Ladislav Lhotka, CZ.NIC Labs
> PGP Key ID: E74E8C0C
>
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