Re: [netmod] Differentiating the types of Mount

[STUART VENTERS <[e-mail]>]

Eric,

I did the suggested OpenDaylight  (ODL)search, and yes there is a lot of activity there.  There are a lot of trees in that forest.

The best overview I found seems to be here.
https://wiki.opendaylight.org/view/OpenDaylight_Controller:_SAL_Architecture_Overview#Nested_Subsystems

Mapping my words to ODL,
My Sibling is the ODL Nested system.
My Parent might be ODL Top-level Subsystem?

Having had lunch to think about it, I don't think I should have picked NetConf as a place to choose what data to mount.
I suspect it should be somewhere in the application, separate for both Yang and Netconf.
ODL appears to use the Northbound Restconf interface to do this function
<module xmlns="urn:opendaylight:params:xml:ns:yang:controller:config">

Stepping back, for this mounting stuff, there are at least 3 issues:
1) Specifying a where in the Parent schema to put the sibling schema.
2) Specifying the type of the sibling.
3) Specifying what sibling data instance to put at a specific parent node data instance.

I think Yang would be a great place to do 1 and 2, but  I think the application should handle 3.
ODL appears to put 1) in Yang,  I'm not sure about 2), and 3) in the application.
Your proposed definition's mention of data-tree appears to put 3 into Yang with appears to conflict with ODL.

Since you clearly don't want however Yang turns out to collide with ODL, but appear to be proposing something that collides, I must not understand?


Another use case:
ODL Yang device mounting is about grafting and removing whole, existing devices as branches in a single tree on a running system.
For this, there may be some benefit in treating the grafted branch as a special sort of node in the tree.
Having a special keyword like 'mount' might help this, or the application function that does 3) above could handle it.

Another use case is simply making a big device model by grafting together smaller, whole, existing models.
In this case, the benefit may be to make the grafted branch look like a non-special vanilla node in the tree.
In this case, I don't see the benefit over a special keyword like 'mount' over an existing one like 'uses'.

Regards,

Stuart


-----Original Message-----
From: Eric Voit (evoit) [mailto:[e-mail]] 
Sent: Wednesday, March 16, 2016 12:20 PM
To: STUART VENTERS
Cc: [e-mail]; Martin Bjorklund (mbjorklu); 'Juergen Schoenwaelder'
Subject: RE: [netmod] Differentiating the types of Mount

> From: STUART VENTERS, March 16, 2016 12:58 PM
> 
> Defining a schema-tree seems Yang's strong suite.
> I'm not sure if the suite extends to defining what goes into a 
> data-tree governed by the schema-tree.

Hi Stuart,

Open Daylight has found Mounting YANG data from one device to another has proven central to their effort.  Doing a quick Google search for "mount site:opendaylight.org" gives 800+ results.

Based on that, I was hoping that being defining the variants of Mount across different constituencies would help us not collide as the technologies evolve.  This includes a shared definition of "YANG Mount" which shows what is common across all efforts.

Thanks,
Eric
 
> Perhaps:
> 
> YANG Mount
>  ----------------
>  Definition: An abstracted term for a YANG mechanism that grafts a 
> sibling schema-tree as a subtree of a parent schema-tree.
>  Purpose: Provides flexibility by enabling the growth of YANG models 
> via an explicit reference to other YANG models defined elsewhere.
> 
> Given the ability to specify a combined schema-tree, maybe something 
> at the protocol level could specify what data to use to populate the grafted tree.
> This could provide a place to specify details like who has ownership 
> of the data, if it is RW, etc.
> 
> NETCONF Mount
> ------------------
> Definition: An abstracted term for a NETCONF mechanism to construct a 
> combined data-tree according to a schema defined with YANG mount.
> Purpose: ...
> 
> 
> 
> -----Original Message-----
> From: netmod [mailto:[e-mail]] On Behalf Of Juergen 
> Schoenwaelder
> Sent: Wednesday, March 16, 2016 6:23 AM
> To: Eric Voit (evoit)
> Cc: [e-mail]; Martin Bjorklund (mbjorklu)
> Subject: Re: [netmod] Differentiating the types of Mount
> 
> On Wed, Mar 16, 2016 at 03:59:50AM +0000, Eric Voit (evoit) wrote:
> > To help differentiate between concepts and drafts, below are 
> > strawman
> definitions for the various types of Mount which we have been discussing over
> the last year in Netmod.   Thoughts/suggestions?
> >
> > YANG Mount
> > ----------------
> > Definition: An abstracted term for a mechanism that a parent YANG 
> > model can
> use to link in YANG information defined or located elsewhere.
> > Purpose: Provides model flexibility by enabling the growth of YANG 
> > trees via
> an explicit reference to other YANG information and structures.
> 
> Trying to rewrite the definition to be more consistent with existing
> terminology:
> 
>   The abstract concept of incorporating a YANG-defined data tree (the
>   mounted data tree) into a existing YANG-defined data tree (the
>   parent data tree).
> 
> Well, this is not really correct, perhaps we have to just say 'tree'
> instead of 'data tree' since a schema mount (as I understand it) seems 
> to incorporate a schema tree into another schema tree while the other 
> two mounts incorporate a data tree into a data tree. So perhaps the 
> general definition is something like this:
> 
>   The abstract concept of incorporating a YANG-defined data tree or
>   schema tree (the mounted data or schema tree) into a existing
>   YANG-defined data tree or schema tree (the parent data tree).
> 
> The schema mount then essentially removes data tree and the other two 
> mounts remove the schema tree from this definition.
> 
> Is your alias mount simply a special case of a peer mount where the 
> peer is local? Or is there more to it? In other words, would it be 
> reasonable to think of the terms in this way:
> 
>          +-> schema (tree) mount
> 	 |
> mount -> |                        +-> local data tree (alias) mount
>          +-> data (tree) mount -> |
>                                   +-> remote data tree (peer) mount
> 
> /js
> 
> --
> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
> Fax:   [phone]         <http://www.jacobs-university.de/>
> 
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