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

Per Hedeland <per@tail-f.com> Mon, 09 October 2017 16:09 UTC

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To: Xufeng Liu <xufeng.liu.ietf@gmail.com>
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Cc: 'Igor Bryskin' <Igor.Bryskin@huawei.com>, netconf@ietf.org, netmod@ietf.org
From: Per Hedeland <per@tail-f.com>
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Subject: Re: [netmod] [Netconf] Retrieving Information Pointed by leafref
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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
>> 
>> 
>> 
>> _______________________________________________
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>> netmod@ietf.org <mailto:netmod@ietf.org>
>> https://www.ietf.org/mailman/listinfo/netmod
>> 
> 
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