Hi Martin,
That works.
Thanks,
Acee
On 2/1/18, 5:15 PM, "Martin Bjorklund" <mbj@xxxxxxxxxx> wrote:
Hi,
The second argument must be a string, so you should add quotes:
must "derived-from( "
+ "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol[rt:name=current()]/"
+ "rt:type, 'ospf:ospf-protocol')";
-------------^------------------^
/martin
"Acee Lindem (acee)" <acee@xxxxxxxxx> wrote:
> Martin, Lada,
>
> I believe this got lost with all the discussion of schema mount/yang
> library during roughly the same time frame. You have both advocated
> using derived-from()/dervived-from-or-self() for ietf-ospf.yang
> checking. However, either I have misinterpreted the RFC 7950
> description of these YANG functions or the yangvalidator validation is
> broken. Please see below.
>
> Thanks,
> Acee
>
> On 1/22/18, 1:42 PM, "Acee Lindem (acee)" <acee@xxxxxxxxx> wrote:
>
> Hi Martin, Lada,
>
> In experimenting with this, I get YANGLINT validation errors. I’m not
> sure what I’m missing but the first argument to
> derived-from()/derive-from-or-self() is the schema node and the second
> is the identity – correct?
> For example, the following YANG leaf:
>
> identity ospf-protocol {
> base "rt:routing-protocol";
> description "Any version the OSPF protocol";
> }
>
> identity ospfv2 {
> base "ospf-protocol";
> description "OSPFv2";
> }
>
> identity ospfv3 {
> base "ospf-protocol";
> description "OSPFv3";
> }
>
> leaf routing-protocol-name {
> type leafref {
> path "/rt:routing/rt:control-plane-protocols/"
> + "rt:control-plane-protocol/rt:name";
> }
> must "derived-from( "
> + "/rt:routing/rt:control-plane-protocols/"
> + "rt:control-plane-protocol[rt:name=current()]/"
> + "rt:type, ospf:ospf-protocol)";
> description
> "OSPF routing protocol instance name.";
> }
>
> Gives me:
>
> warn: Schema node "ietf-ospf:ospf-protocol" not found (derived-from(
> /ietf-routing:routing/ietf-routing:control-plane-protocols/ietf-routing:control-plane-protocol[ietf-routing:name=current()]/ietf-routing:type,
> ietf-ospf:ospf-protocol) with context node
> "/ietf-ospf:if-state-change/routing-protocol-name".
>
> Thanks
> Acee
>
> On 1/10/18, 4:36 AM, "Martin Bjorklund" <mbj@xxxxxxxxxx> wrote:
>
> Hi,
>
> I think we can agree that the model in this I-D should use
> derived-from-or-self() instead of string comparison, and conclude this
> discussion here. I suggest that if we need to further discuss the
> representation of identityrefs, then we start a new thred on the
> NETMOD ML.
>
>
> /martin
>
>
>
> Ladislav Lhotka <lhotka@xxxxxx> wrote:
> > On Tue, 2018-01-09 at 16:23 +0100, Martin Bjorklund wrote:
> > > Ladislav Lhotka <lhotka@xxxxxx> wrote:
> > > > On Tue, 2018-01-09 at 09:06 +0100, Martin Bjorklund wrote:
> > >
> > > > > Hi,
> > >
> > > > >
> > >
> > > > > Ladislav Lhotka <lhotka@xxxxxx> wrote:
> > >
> > > > > > Hi Acee,
> > >
> > > > >
> > >
> > > > > >
> > >
> > > > >
> > >
> > > > > > please see inline.
> > >
> > > > >
> > >
> > > > > >
> > >
> > > > >
> > >
> > > > > > On Mon, 2018-01-08 at 19:28 +0000, Acee Lindem (acee) wrote:
> > >
> > > > >
> > >
> > > > > > > Hi Lada,
> > >
> > > > >
> > >
> > > > > > >
> > >
> > > > >
> > >
> > > > > > > Apologies for the delay. We somewhat got hung up on 4 and
> > > > > > > 6. See
> > > inline.
> > >
> > > > >
> > >
> > > > > > >
> > >
> > > > >
> > >
> > > > > > > On 12/6/17, 6:26 AM, "Ladislav Lhotka" <lhotka@xxxxxx>
> > > > > > > wrote:
> > >
> > > > >
> > >
> > > > > > >
> > >
> > > > >
> > >
> > > > > > > > Reviewer: Ladislav Lhotka
> > >
> > > > >
> > >
> > > > > > > > Review result: Ready with Issues
> > >
> > > > >
> > >
> > > > > >
> > >
> > > > >
> > >
> > > > > > ...
> > >
> > > > >
> > >
> > > > > >
> > >
> > > > >
> > >
> > > > > > > >
> > >
> > > > >
> > >
> > > > > > > > 3. Maybe the draft could mention that implementations
> > > > > > > > should supply
> > > a
> > >
> > > > >
> > >
> > > > > > > > default routing domain as a system-controlled resource.
> > >
> > > > >
> > >
> > > > > > >
> > >
> > > > >
> > >
> > > > > > > Isn’t this more of an RFC8022BIS statement? I guess we
> > > > > > > could state
> > > this as
> > >
> > > > >
> > >
> > > > > > > an assumption.
> > >
> > > > >
> > >
> > > > > >
> > >
> > > > >
> > >
> > > > > > Probably, but it is not a YANG issue, so I'd leave it to you
> > > > > > routing
> > > folks
> > >
> > > > > to
> > >
> > > > >
> > >
> > > > > > decide.
> > >
> > > > >
> > >
> > > > > >
> > >
> > > > >
> > >
> > > > > > >
> > >
> > > > >
> > >
> > > > > > >
> > >
> > > > >
> > >
> > > > > > > > 4. In "when" expressions, the module uses literal strings
> > > > > > > > for
> > >
> > > > >
> > >
> > > > > > > > identities. This is known to be problematic, the XPath
> > > > > > > > functions
> > >
> > > > >
> > >
> > > > > > > > derived-from() or derived-from-or-self() should be used
> > > > > > > > instead.
> > >
> > > > >
> > >
> > > > > > >
> > >
> > > > >
> > >
> > > > > > > Why is this problematic? Is it because the types can be
> > > > > > > extended?
> > >
> > > > >
> > >
> > > > > >
> > >
> > > > >
> > >
> > > > > > That's one reason: derived identities should often also
> > > > > > satisfy the
> > >
> > > > > constraint.
> > >
> > > > >
> > >
> > > > > >
> > >
> > > > >
> > >
> > > > > > But the more serious problem is that things like
> > >
> > > > >
> > >
> > > > > >
> > >
> > > > >
> > >
> > > > > > when "../../../../../../../rt:type = 'ospf:ospfv3'"
> > >
> > > > >
> > >
> > > > > >
> > >
> > > > >
> > >
> > > > > > rely on plain string comparison that depends od the actual
> > > > > > prefix used
> > > for
> > >
> > > > > the
> > >
> > > > >
> > >
> > > > > > "rt:type" value. For one, according to RFC 7951 the JSON
> > > > > > encoding of
> > > this
> > >
> > > > > value
> > >
> > > > >
> > >
> > > > > > would be "ietf-ospf:ospfv3" so the above expression is always
> > > > > > false.
> > >
> > > > >
> > >
> > > > >
> > >
> > > > > This is not correct; the when expression is not evaluated on
> > > > > the JSON
> > >
> > > > > encoding. See the last paragraph of section 9.10.3 in RFC
> > > > > 7950:
> > >
> > > > >
> > >
> > > > > The string value of a node of type "identityref" in a "must"
> > > > > or
> > >
> > > > > "when" XPath expression is the referred identity's qualified
> > > > > name
> > >
> > > > > with the prefix present. If the referred identity is
> > > > > defined in an
> > >
> > > > > imported module, the prefix in the string value is the
> > > > > prefix defined
> > >
> > > > > in the corresponding "import" statement. Otherwise, the
> > > > > prefix in
> > >
> > > > > the string value is the prefix for the current module.
> > >
> > > >
> > >
> > > > This is weird, to say the least. The leafref instance may have an
> > > > identity
> > > value
> > >
> > > > that is defined in a module that (has to be implemented by the
> > > > server but)
> > >
> > > > needn't be imported in the module that contains the XPath
> > > > expression. So I
> > > don't
> > >
> > > > know what 'corresponding "import" statement' this paragraph is
> > > > talking
> > > about.
> > >
> > >
> > > It has to import the module in order to give a prefix, which then
> > > can
> > > be used in the XPath expression.
> >
> > In the XPath expression above, do you mean the "rt" prefix of
> > "rt:type"? If so,
> > it is irrelevant for the string comparison, what's important is the
> > *value* of
> > the "rt:type" instance, which can be an identity defined in a module
> > that
> > needn't be imported by ietf-routing, ietf-ospf or
> > whatever. Sec. 9.10.2:
> >
> > On a particular server, the valid values are further restricted to
> > the set of
> > identities defined in the modules implemented by the server.
> >
> > >
> > > > Also, potentially there can be a collision in prefixes and then
> > > > this also
> > > breaks
> > >
> > > > down.
> > >
> > >
> > > No, two modules cannot be imported with the same prefix.
> >
> > I have to disagree. An identity derived from the
> > "ietf-routing:control-protocol-
> > type" base identity can be defined in a module that is not imported
> > anywhere. If
> > a server declares such a module as implemented, then "rt:type" may
> > have this
> > value per sec. 9.10.2.
> >
> > And, consequently, there may be two different modules with
> > conflicting prefixes
> > defining identities that are derived from
> > "ietf-routing:control-protocol-type".
> >
> > >
> > > > A moral of the namespace/prefix story in XML was that relying of
> > > > namespace
> > >
> > > > prefixes having a particular value is a really bad idea. I know
> > > > that the
> > > cited
> > >
> > > > paragraph was intended to make such XPath string comparisons more
> > > deterministic,
> > >
> > > > but it is also problematic and should be avoided if possible.
> > >
> > >
> > > Note that this prefix is under the control of the module designer
> > > writing the XPath expression. The same identityref value might use
> > > a
> >
> > No, it is not. The prefixes appear in instance data.
> >
> > Lada
> >
> > > different prefix in some other module.
> > >
> > >
> > > /martin
> > >
> > >
> > >
> > > >
> > >
> > > > Lada
> > >
> > > >
> > >
> > > > >
> > >
> > > > > So the equality test of the identityref is correct.
> > >
> > > > >
> > >
> > > > > However, I agree that in most cases 'derived-from-or-self'
> > > > > should be
> > >
> > > > > used, in order to handle derived identities.
> > >
> > > > >
> > >
> > > > >
> > >
> > > > > /martin
> > >
> > > > --
> > >
> > > > Ladislav Lhotka
> > >
> > > > Head, CZ.NIC Labs
> > >
> > > > PGP Key ID: 0xB8F92B08A9F76C67
> > >
> > > >
> > >
> > --
> > Ladislav Lhotka
> > Head, CZ.NIC Labs
> > PGP Key ID: 0xB8F92B08A9F76C67
> >
>
>
>
>
>