Martin Bjorklund <[email protected]> writes:
> Hi,
>
> [replying to the first post in this (old) thread; the thread got a bit
> off-topic]
>
> Balazs Lengyel <[email protected]> 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.
>
> 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.
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.
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.
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: [email protected]
>
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--
Ladislav Lhotka, CZ.NIC Labs
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