Subject: [netmod] mount-point in anydata

From: Martin Bjorklund <[email-masked]>
Date: Tue, 17 Jan 2017 13:29:13 +0100 (CET)

Hi,

Currently, the schema mount draft says that the "mount-point"
extension only can be defined in an "anydata" node.  However, this
doesn't really work, since RFC 7950 says:

   An anydata node is treated as an opaque chunk of data.  This data
   can be modified in its entirety only.

But the idea with schema mount is to build a composite model that can
be manipulated just like a normal model, or a model that is
augmented.  If we mount models in an "anydata" node, clients would
have to replace the enitire mounted subtree in order to change e.g. a
single leaf.

For this reason, I propose that we go back to the previous model where
"mount-point" would be allowed in "container" and "list".  Note that a
client that doesn't know anything about these mounts would see some
nodes in some unknown namespace; just like in the case that there is
an augment that the client doesn't know about.

/martin

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From: Lou Berger <[email-masked]>
Date: Thu, 19 Jan 2017 12:21:04 -0500

Martin,

> an augment that the client doesn't know about.

would it be better to have the  schema mount draft updates 7950 to allow
for sub-tree changes under anydata?  It "feels" cleaner and I'd expect
to have no real impact on servers as this would only impact servers
supporting the draft.  I'm unsure about client impact though...

Thanks,
Lou

>
> /martin
>
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From: Martin Bjorklund <[email-masked]>
Date: Thu, 19 Jan 2017 18:55:21 +0100 (CET)

> supporting the draft.  I'm unsure about client impact though...

Actually, this would have bigger impact on servers, than on clients; a
client could still treat the entire thing as an opaque blob - but
that's not what we want.  I prefer a solution that doesn't change the
core YANG semantics.  The text in 7950 is pretty clear, e.g.,:

   Any "operation" attributes present on subelements of an anydata node
   are ignored by the NETCONF server.

/martin

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From: Robert Varga <[email-masked]>
Date: Fri, 20 Jan 2017 00:52:15 +0100

> an augment that the client doesn't know about.

+1, although I think the situation is not quite equal to an unknown
augmentation: the mount point itself would be in an unknown namespace,
but the nodes beneath it could actually match a namespace known to the
client, right?

Thanks,
Robert

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From: Martin Bjorklund <[email-masked]>
Date: Fri, 20 Jan 2017 08:35:51 +0100 (CET)

> but the nodes beneath it could actually match a namespace known to the

Yes, the namespace might be known to the client, but in a different
place.

/martin