Re: [netmod] Y34

[Andy Bierman <[e-mail]>]

On Sun, Jul 26, 2015 at 5:31 PM, Lou Berger <[e-mail]> wrote:

>   Andy,
>
> Have you thought through implications / possibilities for existing
> models,  e.g., interfaces?
>


First we have to define various forms of relocation.

(1) Aggregation of datastores

The simplest form is aggregation.
It is possible to define a YANG container that is a conceptual
document root, such that the set of child nodes matches the set
of top-level YANG data nodes supported by the server.

A YANG extension can mark a YANG container or anyxml as a docroot.
Yuma-based code has been doing this for years with a YANG
extension called "root"

http://www.netconfcentral.org/modules/yuma-ncx/2013-09-23#root.554

http://svn.tools.ietf.org/svn/wg/netmod/yang-1.1/issues.html
(See Y34-04)

The <config> node below is a document root:

container servers {
  list server {
      key addr;
      leaf addr { type inet:ip-address; }
      anydata config {
          ncx:root;
      }
  }
}

XPath evaluation requires certain inputs, including a context node
and a document root.  The 'root' extension tells the tool to use
the node with the 'root' tag as the document root, when processing
XPath within its descendant nodes. Without the tag, the XPath parser
would use 'servers' as the document root, which is incorrect for
the relocated YANG nodes within 'config'.

(2) Move a subtree within the datastore

This is the hardest (of course) because it involves moving the context node
not the document root. It is possible for tools to get fooled about the
intent
of the XPath writer.  Basically the tool has to remember the original
context node,
and do some complicated data manipulation, processing [4] Step
in XPath 1.0.  Multiple relocated subtrees gets even more complicated.

It may be possible to come up with some guidelines on XPath to avoid.
Basically any Xpath that selects nodes by specific names can be
relocated automatically.  Nodes selected by function, wildcard, axis, etc.
will not be so easy.




> Thanks,
> Lou
>


Andy


>   On July 26, 2015 4:41:32 PM Andy Bierman <[e-mail]> wrote:
>
>> Hi Acee,
>>
>> I agree that "Relocatable YANG" would be very useful, and have been
>> thinking about the problem for awhile.  I think the key is to precisely
>> define a protocol-independent document root for each of the various
>> YANG XPath contexts.  In most cases the expression can be
>> automatically relocated to an ancestor root.  For the rest, a
>> YANG mechanism is needed to tell the compiler to force evaluation
>> on the old docroot (not the new docroot ancestor).
>>
>>
>> Andy
>>
>>
>> On Sun, Jul 26, 2015 at 10:49 AM, Acee Lindem (acee) <[e-mail]>
>> wrote:
>>
>>> I think being able to place a given model anywhere in the device tree
>>> would be useful and this would allow a model to be rooted in different
>>> locations on different devices. Similarly, we’d need the ability to
>>> prefix
>>> XPATH references to data nodes in the model with the root.
>>> Thanks,
>>> Acee
>>>
>>> On 7/20/15, 11:00 PM, "netmod on behalf of Juergen Schoenwaelder"
>>> <[e-mail] on behalf of
>>> [e-mail]> wrote:
>>>
>>> >Lada,
>>> >
>>> >Y34 is closed and I have not seen any new argument here that indicates
>>> >we made a major mistake with the resolution of Y34. As such, Y34
>>> >remains closed.
>>> >
>>> >If you want to discuss new ideas to relocate or "symlink" data models,
>>> >please do so in a separate thread. (And no, we do not accept new
>>> >issues for YANG 1.1 either at this point in time.)
>>> >
>>> >/js
>>> >
>>> >On Mon, Jul 20, 2015 at 07:42:49PM +0200, Ladislav Lhotka wrote:
>>> >>
>>> >> > On 20 Jul 2015, at 19:29, Andy Bierman <[e-mail]> wrote:
>>> >> >
>>> >> >
>>> >> >
>>> >> > On Mon, Jul 20, 2015 at 10:15 AM, Ladislav Lhotka <[e-mail]>
>>> >>wrote:
>>> >> >
>>> >> > > On 20 Jul 2015, at 17:00, Andy Bierman <[e-mail]>
>>> wrote:
>>> >> > >
>>> >> > >
>>> >> > >
>>> >> > > On Mon, Jul 20, 2015 at 6:08 AM, Ladislav Lhotka <[e-mail]>
>>> >>wrote:
>>> >> > >
>>> >> > > > On 20 Jul 2015, at 14:55, Andy Bierman <[e-mail]>
>>> wrote:
>>> >> > > >
>>> >> > > > Hi,
>>> >> > > >
>>> >> > > > Can you explain why we need 2 broken anyxmls?
>>> >> > > > (The original and a synonym?)  The whole point of
>>> >> > > > anydata is that it does not have XML cruft in it.
>>> >> > >
>>> >> > > Yes, I understand this was your main priority. For implementors
>>> >>using off-the-shelf XML parsers and tools the XML cruft is not an issue
>>> >>at all.
>>> >> > >
>>> >> > >
>>> >> > > yes it is an issue.
>>> >> > > We need something to model a container full of arbitrary YANG data
>>> >>nodes.
>>> >> > > This is something that can be applied to the contents of a
>>> >>datastore.
>>> >> >
>>> >> > anyxml can do that, too.
>>> >> >
>>> >> >
>>> >> > the WG already decided it can't.
>>> >> > The extra XML PIs, etc. are not accepted by all servers, remember?
>>> >> > There is no use for the extra stuff in the datastore.
>>> >> >  I don't see why we need 2 anyxml constructs that are not
>>> >> > supported by the industry.  One is already too many.
>>> >>
>>> >> I agree, but this is what we are going to have. My proposal was to
>>> have
>>> >>just one with two different names.
>>> >>
>>> >> >
>>> >> >
>>> >> > >
>>> >> > >
>>> >> > > Anyway, I believe there are use cases for arbitrary
>>> XML/JSON/CBOR/…
>>> >>with no (YANG) schema available. My only complaint to “anyxml” has
>>> >>always been that it is a misnomer for encodings other than XML.
>>> >> > >
>>> >> > > The message encoding on the wire is not the same issue
>>> >> > > as the contents of a datastore.  Our server stores its own
>>> >> > > internal data structures.  XML, JSON, CBOR are just message
>>> >> > > encoding formats between client and server.  The datastore
>>> >> > > is not encoded in any of these formats.
>>> >> >
>>> >> > The payload of anyxml needn’t directly map to a data subtree in the
>>> >>usual sense.
>>> >> >
>>> >> > that's precisely the difference between anyxml and anydata.
>>> >> > The anydata node MUST map directly into data subtrees.
>>> >>
>>> >> If the server doesn’t know the YANG data model at run time (which is
>>> >>possible) then it cannot do it - for instance, it cannot properly map
>>> >>module names to namespace URI or handle lists.
>>> >>
>>> >> >
>>> >> >
>>> >> >
>>> >> > >
>>> >> > >
>>> >> > >
>>> >> > >
>>> >> > >
>>> >> > > >
>>> >> > > > I also don't get the value of a single top-level node called
>>> >>'device'
>>> >> > > > that every YANG model on the planet is supposed to augment.
>>> >> > > > Can you explain why a protocol operation to retrieve the
>>> >> > > > document root (/) is not sufficient for the top-level node?
>>> >> > >
>>> >> > > I don’t intend to defend their model, the more serious problem IMO
>>> >>is that a model for a single device/function may be needed in another
>>> >>device that hosts many virtualised devices/functions of the former
>>> type.
>>> >>We don’t have a good solution for this rather typical situation.
>>> >> > >
>>> >> > > But a single container called "whatever" provides no such
>>> >>aggregation.
>>> >> > > You would need a list for that. And the NMS might have multiple
>>> >> > > layers of hierarchy to represent various aggregations.  The NP
>>> >> > > container called "device" is not helpful for aggregation.
>>> >> >
>>> >> > The parent node can be a list as well. The “root” node would be like
>>> >>a mount point in a Unix filesystem.
>>> >> >
>>> >> >
>>> >> > Are you saying all data on a device needs to be in a top-level list
>>> >>called 'device'
>>> >> > because an NMS might exist that  wants to have the datastores from
>>> >>lots of devices?
>>> >> > As Martin pointed out several times, the NMS can make its own
>>> >>container or
>>> >> > lists.  It does not need the device to mirror its own structure.
>>> >>
>>> >> As I said, I don’t care that much about the “device” container. What
>>> >>would be really useful is to have the possibility to do e.g. this:
>>> >>
>>> >> virtual-node* [name]
>>> >>     name
>>> >>     if:interfaces
>>> >>         ...
>>> >>
>>> >> to support the use case where all virtual nodes are managed by the
>>> same
>>> >>NETCONF/RESTCONF server.
>>> >>
>>> >> Lada
>>> >>
>>> >> >
>>> >> >
>>> >> >
>>> >> > Lada
>>> >> >
>>> >> > Andy
>>> >> >
>>> >> >
>>> >> > >
>>> >> > >
>>> >> > >
>>> >> > > Lada
>>> >> > >
>>> >> > >
>>> >> > > Andy
>>> >> > >
>>> >> > >
>>> >> > > >
>>> >> > > > Andy
>>> >> > > >
>>> >> > > >
>>> >> > > >
>>> >> > > > On Mon, Jul 20, 2015 at 5:48 AM, Ladislav Lhotka <[e-mail]
>>> >
>>> >>wrote:
>>> >> > > >
>>> >> > > > > On 20 Jul 2015, at 14:45, Ladislav Lhotka <[e-mail]>
>>> wrote:
>>> >> > > > >
>>> >> > > > > Hi,
>>> >> > > > >
>>> >> > > > > after listening to the presentation of
>>> >> > > > > draft-rtgyangdt-rtgwg-device-model-00 at RTGWG session, I am
>>> >>wondering
>>> >> > > > > whether the solution chosen for Y34 is really useful.
>>> >> > > > >
>>> >> > > > > The draft states they want to reuse ietf-interfaces but their
>>> >>tree in
>>> >> > > > > fact is
>>> >> > > > >
>>> >> > > > >   +--rw device
>>> >> > > > >          +--rw info
>>> >> > > > >          |  +--rw device-type?   enumeration
>>> >> > > > >          +--rw hardware
>>> >> > > > >          +--rw interfaces
>>> >> > > > >          |  +--rw interface* [name]
>>> >> > > > >          |     ...
>>> >> > > > >          +--rw qos
>>> >> > > > >
>>> >> > > > > So the "interfaces" container is no more a top-level node.
>>> >>There are
>>> >> > > > > three possible options:
>>> >> > > > >
>>> >> > > > > 1. Change the ietf-interfaces module.
>>> >> > > > > 2. Replicate its contents in another module.
>>> >> > > > > 3. Extend YANG so that a *specific* schema tree can be grafted
>>> >>at a
>>> >> > > > >   given data node.
>>> >> > > > >
>>> >> > > > > IMO #1 & #2 are really bad. I thought Y34-04 was essentially
>>> #3
>>> >>but it
>>> >> > > > > seems it is not so because it doesn't specify a concrete data
>>> >>model
>>> >> > > > > that's allowed at a given location.
>>> >> > > > >
>>> >> > > > > On the other hand, the only real contribution of "anydata"
>>> over
>>> >>"anyxml"
>>> >> > > > > is that is doesn't permit mixed content in XML, which is IMO
>>> >>not much.
>>> >> > > > >
>>> >> > > > > I know Y34 was already closed but I think it is more important
>>> >>to do
>>> >> > > > > things right before YANG 1.1 becomes an RFC.
>>> >> > > > >
>>> >> > > > > What I want to propose is this:
>>> >> > > > >
>>> >> > > > > - Rename "anydata" as a synonym to "anyxml", and deprecate
>>> >>"anyxml" (but
>>> >> > > > >  keep it for backward compatibility).
>>> >> > > >
>>> >> > > > s/Rename/Introduce/
>>> >> > > >
>>> >> > > > >
>>> >> > > > > - Introduce a new statement and data node type, e.g. "root",
>>> >>that will
>>> >> > > > >  extend the schema tree starting from that data node with a
>>> >>precisely
>>> >> > > > >  specified data model. The specification can be same or
>>> similar
>>> >>as
>>> >> > > > >  in yang-library.
>>> >> > > > >
>>> >> > > > > I believe there are other use cases in the existing modules.
>>> For
>>> >> > > > > example, the ietf-routing module could simply define the data
>>> >>model for
>>> >> > > > > a single routing instance (i.e. without "routing-instance"
>>> list
>>> >>at the
>>> >> > > > > top), and it can be then used without changes on simple
>>> >>devices, and
>>> >> > > > > more complex router implementations can graft it as a subtree
>>> >>under
>>> >> > > > > "routing-instance", "networking-instance" or whatever.
>>> >> > > > >
>>> >> > > > > Lada
>>> >> > > > >
>>> >> > > > > --
>>> >> > > > > Ladislav Lhotka, CZ.NIC Labs
>>> >> > > > > PGP Key ID: E74E8C0C
>>> >> > > > >
>>> >> > > > > _______________________________________________
>>> >> > > > > netmod mailing list
>>> >> > > > > [e-mail]
>>> >> > > > > https://www.ietf.org/mailman/listinfo/netmod
>>> >> > > >
>>> >> > > > --
>>> >> > > > Ladislav Lhotka, CZ.NIC Labs
>>> >> > > > PGP Key ID: E74E8C0C
>>> >> > > >
>>> >> > > >
>>> >> > > >
>>> >> > > >
>>> >> > > > _______________________________________________
>>> >> > > > netmod mailing list
>>> >> > > > [e-mail]
>>> >> > > > https://www.ietf.org/mailman/listinfo/netmod
>>> >> > > >
>>> >> > >
>>> >> > > --
>>> >> > > Ladislav Lhotka, CZ.NIC Labs
>>> >> > > PGP Key ID: E74E8C0C
>>> >> > >
>>> >> > >
>>> >> > >
>>> >> > >
>>> >> > >
>>> >> >
>>> >> > --
>>> >> > Ladislav Lhotka, CZ.NIC Labs
>>> >> > PGP Key ID: E74E8C0C
>>> >> >
>>> >> >
>>> >> >
>>> >> >
>>> >> > _______________________________________________
>>> >> > netmod mailing list
>>> >> > [e-mail]
>>> >> > https://www.ietf.org/mailman/listinfo/netmod
>>> >>
>>> >> --
>>> >> Ladislav Lhotka, CZ.NIC Labs
>>> >> PGP Key ID: E74E8C0C
>>> >>
>>> >>
>>> >>
>>> >>
>>> >> _______________________________________________
>>> >> netmod mailing list
>>> >> [e-mail]
>>> >> https://www.ietf.org/mailman/listinfo/netmod
>>> >
>>> >--
>>> >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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>>>
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>>
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