Re: [netmod] [Netconf] Retrieving Information Pointed by leafref

Igor Bryskin <Igor.Bryskin@huawei.com> Mon, 09 October 2017 17:22 UTC

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From: Igor Bryskin <Igor.Bryskin@huawei.com>
To: Martin Bjorklund <mbj@tail-f.com>
CC: "per@tail-f.com" <per@tail-f.com>, "xufeng.liu.ietf@gmail.com" <xufeng.liu.ietf@gmail.com>, "netconf@ietf.org" <netconf@ietf.org>, "netmod@ietf.org" <netmod@ietf.org>
Thread-Topic: [Netconf] [netmod] Retrieving Information Pointed by leafref
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Date: Mon, 9 Oct 2017 17:22:03 +0000
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Subject: Re: [netmod] [Netconf] Retrieving Information Pointed by leafref
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> But as Per explained, it only works in some cases (when the leafref
acts a "single pointer").

We think this is good enough. In all other cases leafref is simply not qualified for the expansion.
I am not an expert , but I believe there is a similar capability in SQL, no?

Igor

-----Original Message-----
From: Martin Bjorklund [mailto:mbj@tail-f.com] 
Sent: Monday, October 09, 2017 1:14 PM
To: Igor Bryskin
Cc: per@tail-f.com; xufeng.liu.ietf@gmail.com; netconf@ietf.org; netmod@ietf.org
Subject: Re: [Netconf] [netmod] Retrieving Information Pointed by leafref

Igor Bryskin <Igor.Bryskin@huawei.com> wrote:
> 
> Hi Per,
> 
> Basically, what we need is a way for a client to request something
> like this:
> 
> get <XPath> joint with <XPath1, XPath2, ..., XPathn>

... which is what Per's expression does!  Note that "|" in XPath means
"union".

But as Per explained, it only works in some cases (when the leafref
acts a "single pointer").

> with a server interpreting the request as follows:
> if a node pointed by XPath contains a pointer (e.g. key leafref)
> matching one of the XPath from the "joint with" list, then the server
> must provide the entire body of the node pointed by the pointer,
> otherwise, just the pointer (as it happens today, that is, when no
> "joint with" list specified).
> 
> We think that this would allow for the client to optimize the number
> of request-response iterations depending on application/use case.
> 
> Regards,
> Igor  



/martin


> 
> 
> 
> 
> 
> 
> -----Original Message-----
> From: Per Hedeland [mailto:per@tail-f.com] 
> Sent: Monday, October 09, 2017 12:06 PM
> To: Xufeng Liu
> Cc: Igor Bryskin; netconf@ietf.org; netmod@ietf.org
> Subject: Re: [Netconf] [netmod] Retrieving Information Pointed by
> leafref
> 
> I understand your use case, but a leaf of type leafref does not in
> general identify a single node in the data tree - the leafref path
> could
> be for a non-key leaf, and/or the path could traverse list nodes,
> and/or
> the "target" list could have multiple keys and thus multiple
> leafref-leafs be required to identify a specific list entry.
> 
> Thus it seems to me that your use case is not a reasonable basis for a
> new protocol operation. My XPath foo isn't very good either, but I do
> believe Robert's suggestion of using an XPath filter could be a way
> forward. I *think* the filter expression would be something along the
> lines of
> 
>  /te/tunnels/tunnel[name='foo'] |
>  /te/explicit-paths/explicit-path[name=/te/tunnels/tunnel[name='foo']/paths/path/explicit-path]
> 
> --Per
> 
> On 2017-10-09 15:42, Xufeng Liu wrote:
> > Hi Per,
> > 
> >  
> > 
> > *From:* Igor Bryskin [mailto:Igor.Bryskin@huawei.com]
> > *Sent:* Sunday, October 8, 2017 7:04 PM
> > *To:* Igor Bryskin <Igor.Bryskin@huawei.com>om>; per@tail-f.com;
> > *xufeng.liu.ietf@gmail.com
> > *Cc:* netconf@ietf.org; netmod@ietf.org
> > *Subject:* Re: [Netconf] [netmod] Retrieving Information Pointed by
> > *leafref
> > 
> >  
> > 
> > 
> > Hi Joel,
> > 
> > Thanks, I think I didnt explain our problem correctly.
> > 
> > In our case we have a leafref pointing to a te tunnel name, which
> > happens to be a key to lookup the (axilary) tunnel.  We need a way to
> > include the entire tunnel body (not just a name) into the get
> > response. This is to optimize the number of iterations between the
> > client and the server. As Xufeng put it something similar to SQL join,
> > 
> > Igor
> > 
> > *From:*Igor Bryskin
> > 
> > *To:*per@tail-f.com,xufeng.liu.ietf@gmail.com,
> > 
> > *Cc:*netconf@ietf.org,netmod@ietf.org,
> > 
> > *Date:*2017-10-08 17:36:47
> > 
> > *Subject:*Re: [Netconf] [netmod] Retrieving Information Pointed by
> > *leafref
> > 
> >  
> > 
> > Hi Per,
> > 
> > In a nutshell we would lika for a netconf client to have a way to
> > instruct the server on whether in response to the get request the
> > server needs to provide the entire body of a datastore node pointed
> > to by a leafref or just a pointer to said node, so that the node's
> > body could be retrieved by a subsequent separate request. This is
> > requested by implementors who want to optimise rhe number of
> > interactions between a client and its server.
> > 
> > Cheers,
> > Igor
> > 
> > *From:*Per Hedeland
> > 
> > *To:*Xufeng Liu,
> > 
> > *Cc:*netconf@ietf.org,'NetMod WG',
> > 
> > *Date:*2017-10-08 14:01:27
> > 
> > *Subject:*Re: [Netconf] [netmod] Retrieving Information Pointed by
> > *leafref
> > 
> >  
> > 
> > On 2017-10-06 23:11, Xufeng Liu wrote:
> >> During the design team discussion for TE and MPLS YANG modeling, we
> >> have received a request from implementers: How to minimize the number
> >> of NETCONF/RESTCONF RPCs to improve operation efficiency?
> >> Especially for the case when the operator or client software needs to
> >> retrieve the object contents pointed by a leafref.
> >> 
> >> For example, given the following simplified TE tunnel model,
> >> 
> >> +--rw te
> >> 
> >>      +--rw explicit-paths
> >> 
> >>      |  +--rw explicit-path* [name]
> >> 
> >>      |     +--rw name                      string
> >> 
> >>      |        +--rw explicit-route-object* [index]
> >> 
> >>      |           +--rw index                   uint32
> >> 
> >>      |           +--rw explicit-route-usage?   identityref
> >> 
> >>      +--rw tunnels
> >> 
> >>      |  +--rw tunnel* [name]
> >> 
> >>      |  |  +--rw name                   string
> >> 
> >>      |  |  +--rw paths
> >> 
> >>      |  |  |  +--rw path* [name]
> >> 
> >> |  |  |     +--rw explicit-path?  ->
> >> |  |  |     ../../../../../explicit-paths/explicit-path/name
> >> 
> >> when the client tries to retrieve a tunnels information based on the
> >> tunnel name, the get operation returns a list of leafrefs pointing
> >> to the paths of the tunnel.
> > 
> > Sorry, I'm afraid I don't follow. Can you explain exactly what your
> > "get" request is (protocol and payload), and where the "list of
> > leafref's" (whatever that may be) occurs in the reply?
> > 
> > */[Xufeng] The get operation is the NETCONF/RESTCON <get> protocol
> > *operation, or the <get-data> operation described in
> > *https://tools.ietf.org/html/draft-dsdt-nmda-netconf-01 and the GET
> > *operations
> > on {+restconf}/ds/<datastore> described in
> > https://tools.ietf.org/html/draft-ietf-netconf-nmda-restconf-00./*
> > 
> > */ /*
> > 
> > */We have a list of leafref values because in this example model, each
> > *tunnel contains a list of paths, each of them contains a leafref. The
> > *get returns a value for each instance of such a leafref,
> > which (as a string value) will be used as a constraint (foreign key)
> > to retrieve the instance of an explicit-path in the model above./*
> > 
> > 
> > 
> > JFYI, in case there is some fundamental misunderstanding here: a leaf
> > of
> > type leafref has a single value - *one* of those that satisfy the
> > leafref
> > constraint, in case there are multiple "candidates".
> > 
> > --Per
> > 
> >> The client needs to issue at 
> >> least one more get operation to retrieve the path information about
> >> the given tunnel. The request is to combine these two operations into
> >> one.
> >> 
> >> In the RDBMS SQL world, join can be used when SQL select is
> >> performed, but NETCONF/YANG currently does not have this capability.
> >> 
> >> Wed like to ask whether such a request is considered reasonable.
> >> 
> >> If the request is reasonable, the next question is how to
> >> proceed. This seems to be a protocol issue rather than YANG modeling
> >> issue. Is it acceptable to add a new operation to achieve such a
> >> <get-data> operation with expanded leafrefs?
> >> 
> >> Comments and suggestions are appreciated.
> >> 
> >> Thanks,
> >> 
> >> - Xufeng
> >> 
> >> 
> >> 
> >> _______________________________________________
> >> netmod mailing list
> >> netmod@ietf.org <mailto:netmod@ietf.org>
> >> https://www.ietf.org/mailman/listinfo/netmod
> >> 
> > 
> > _______________________________________________
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> > 
> 
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