Re: [netmod] [Netconf] Retrieving Information Pointed by leafref
Robert Wilton <rwilton@cisco.com> Wed, 11 October 2017 10:49 UTC
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To: "t.petch" <ietfc@btconnect.com>, Igor Bryskin <Igor.Bryskin@huawei.com>, netconf@ietf.org, netmod@ietf.org
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From: Robert Wilton <rwilton@cisco.com>
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Date: Wed, 11 Oct 2017 11:49:07 +0100
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Subject: Re: [netmod] [Netconf] Retrieving Information Pointed by leafref
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I've also been thinking about this problem a bit more :-) The XPath solution works, but the expression isn't particularly nice to write, and I suspect that implementations may struggle to implement it efficiently (if they support XPath filtering at all). A nicer solution here might be to allow the XPath filters to be combined with a subtree filter along the lines of a more advanced type of "Attribute Match Expression" sec 6.2.2 of rfc6241. E.g. rather than this XPath filter: /te:te/te:tunnels/te:tunnel[te:name='foo'] | /te:te/te:connections/te:connection[te:name=/te:te/te:tunnels/te:tunnel[te:name='foo']/te:connections/te:connection/te:name] Here is example of what a subtree filter combined with an XPath filter could potentially look like (which of course isn't valid NETCONF/YANG today): <filter type="subtree-xpath"> <te:te xmlns:te="..."> <te:tunnels te:name="foo"/> <te:connections> <filter type="xpath" select="te:name = ../te:tunnels/te:tunnel[te:name='foo']/te:connections/te:connection/te:name)"/> </te:connections> </te:te> </filter> Any opinions on whether this would be beneficial or is this just reinventing the wheel? Thanks, Rob On 11/10/2017 10:41, t.petch wrote: > Igor > > Thinking laterally, this is a problem that DNS encountered a few decades > ago and solved, by allowing the server to include additional information > not specifically requested that the server can see is going to be needed > for the next step, so if the client asks only about a CNAME, then the > server can provide the relevant IP address as well. > > I suspect that the current rules for Netconf do not allow the server to > send anything not explicitly requested, which is a shame (IMO). > > The DNS approach works very well, in fact I do not think we would > survive without it. > > Tom Petch > > ----- Original Message ----- > From: "Igor Bryskin" <Igor.Bryskin@huawei.com> > Sent: Tuesday, October 10, 2017 2:35 PM > > Hi Rob, > > This helps a lot. What you wrote will work. > > The only difference is that if we would have the "joimt with" clause as > we proposed, the server would be able to tailor the te-tunnel > presentation to the client's requirements, e.g. substituting the > connection pointers with connection bodies, while, according to your > suggestion, the server will provide the te-tunnel body as is, and then > augment it with the cobbection information, thus, leaving > for the client to "shuffle " the received data. But I do agree, this > would be a minor inconvinience for the client, the important thing is > that the client will get all the data in one piece. > > Thanks a lot, > Igor > > c > > From:Robert Wilton > To:Igor Bryskin, > Cc:Per Hedeland,netmod@ietf.org,netconf@ietf.org, > Date:2017-10-10 06:41:04 > Subject:Re: [netmod] [Netconf] Retrieving Information Pointed by leafref > > Hi Igor, > > On 09/10/2017 23:11, Igor Bryskin wrote: >> Hi Per, >> >> This is a good news, but, please, help us out. >> Consider, we have a node - "te-tunnel" - which among other attributes > has two key leafref lists: >> 1) each member of the 1st list points to a "connection" supporting the > te-tunnel. All connections supporting all te-tunnels are stored in a > single list of connections. >> 2) each member of the 2nd list points to a supporting "te-tunnel" - > the te-tunnel in question depends on. All te=tunnels including the > te-tunnel in question, are stored in a single list of te-tunnels. >> The question: how the client can retrieve via a single request all > attributes of the te-tunnel in question along with all parameters of all > connections supporting the te-tunnel, but with just pointers to > supporting te-tunnels (so that the interested client can use the > pointers to retrieve full data via subsequent separate requests) ? > I think that it might be something like this (for tunnel name foo): > > /te/tunnels/tunnel[name='foo'] | > > /te/connections/connection[name=/te/tunnels/tunnel[name='foo']/connectio > ns/connection/name] > > E.g. in English, this should equate to something like: > > Return all information for tunnel foo AND ALSO > Return all information for all connections where the connection name > matches one of the connections listed in tunnel foo. > >> Likewise, how the client can ask for full data of the te-tunnel and > all supporting te-tunnels and just pointers for supporting connections? > If my xpath above is right, then this would be something roughly like > this: > > /te/tunnels/tunnel[name='foo'] | > > /te/tunnels/tunnel[name=/te/tunnels/tunnel[name='foo']/supporting-tunnel > s/supporting-tunnel/name] > > > I'm an XPath novice, so the expressions might be wrong. > > https://www.freeformatter.com/xpath-tester.html might be useful. E.g. if > you can construct a simple XML instance tree of your data, you could > validate whether the XPath expression works. > > I hope that this is of some help, > Rob > > >> I really appreciate your help, >> >> Igor >> >> >> -----Original Message----- >> From: Per Hedeland [mailto:per@tail-f.com] >> Sent: Monday, October 09, 2017 5:21 PM >> To: Igor Bryskin >> Cc: mbj@tail-f.com; xufeng.liu.ietf@gmail.com; netconf@ietf.org; > netmod@ietf.org >> Subject: Re: [Netconf] [netmod] Retrieving Information Pointed by > leafref >> Just to be clear: what we're suggesting is that you can use the >> already-existing standard NETCONF XPath capability to achieve the > desired >> result - see https://tools.ietf.org/html/rfc6241#section-8.9 >> >> --Per >> >> On 2017-10-09 21:52, Igor Bryskin wrote: >>> I agree. For example, a leafref may point not to a singls entity, but > to a list of entities, and the client might want to expand all of them > into the joint get response. >>> Igor >>> >>> *From:*Per Hedeland >>> *To:*Martin Bjorklund, >>> *Cc:*Igor > Bryskin,xufeng.liu.ietf@gmail.com,netconf@ietf.org,netmod@ietf.org, >>> *Date:*2017-10-09 15:12:22 >>> *Subject:*Re: [Netconf] [netmod] Retrieving Information Pointed by > leafref >>> On 2017-10-09 19:13, Martin Bjorklund wrote: >>>> 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"). >>> Well, that particular expression works only in that case - but since > it >>> is effectively the client that (perhaps based on the data model) > decides >>> what the leafref-leafs "mean" (in this case the single key of a > single >>> list), other cases can be handled the same way. E.g. multiple >>> leafref-to-key leafs that together give the keys of a multi-key list >>> just amounts to a slightly hairier XPath filter... >>> >>> --Per >>> >>>>> 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']/pat > hs/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>; 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 >>>>>>> >>>>>> _______________________________________________ >>>>>> Netconf mailing list >>>>>> Netconf@ietf.org <mailto:Netconf@ietf.org> >>>>>> https://www.ietf.org/mailman/listinfo/netconf >>>>>> >>>>> _______________________________________________ >>>>> Netconf mailing list >>>>> Netconf@ietf.org >>>>> https://www.ietf.org/mailman/listinfo/netconf >>>>> >> _______________________________________________ >> netmod mailing list >> netmod@ietf.org >> https://www.ietf.org/mailman/listinfo/netmod >> . >> > > > > ------------------------------------------------------------------------ > -------- > > >> _______________________________________________ >> netmod mailing list >> netmod@ietf.org >> https://www.ietf.org/mailman/listinfo/netmod >> > . >
- [netmod] Retrieving Information Pointed by leafref Xufeng Liu
- Re: [netmod] Retrieving Information Pointed by le… Kent Watsen
- Re: [netmod] Retrieving Information Pointed by le… Kent Watsen
- Re: [netmod] Retrieving Information Pointed by le… Per Hedeland
- Re: [netmod] [Netconf] Retrieving Information Poi… Igor Bryskin
- Re: [netmod] [Netconf] Retrieving Information Poi… Igor Bryskin
- Re: [netmod] [Netconf] Retrieving Information Poi… Xufeng Liu
- Re: [netmod] [Netconf] Retrieving Information Poi… Robert Wilton
- Re: [netmod] [Netconf] Retrieving Information Poi… Per Hedeland
- Re: [netmod] [Netconf] Retrieving Information Poi… Igor Bryskin
- Re: [netmod] [Netconf] Retrieving Information Poi… Martin Bjorklund
- Re: [netmod] [Netconf] Retrieving Information Poi… Igor Bryskin
- Re: [netmod] [Netconf] Retrieving Information Poi… Per Hedeland
- Re: [netmod] [Netconf] Retrieving Information Poi… Igor Bryskin
- Re: [netmod] [Netconf] Retrieving Information Poi… Per Hedeland
- Re: [netmod] [Netconf] Retrieving Information Poi… Igor Bryskin
- Re: [netmod] [Netconf] Retrieving Information Poi… Per Hedeland
- Re: [netmod] [Netconf] Retrieving Information Poi… Robert Wilton
- Re: [netmod] [Netconf] Retrieving Information Poi… Igor Bryskin
- Re: [netmod] [Netconf] Retrieving Information Poi… t.petch
- Re: [netmod] [Netconf] Retrieving Information Poi… Robert Wilton
- Re: [netmod] [Netconf] Retrieving Information Poi… Xufeng Liu
- Re: [netmod] [Netconf] Retrieving Information Poi… Robert Wilton