Ladislav Lhotka <[email protected]> wrote:
>
> > On 23 May 2016, at 16:10, Martin Bjorklund <[email protected]> wrote:
> >
> > Hi,
> >
> > This comment from the Gen-ART review deserves it's own thread.
> >
> > gen-art> - section 9.9
> > gen-art>
> > gen-art> The leafref type is used to declare a constraint on the value
> > space
> > gen-art> of a leaf, based on a reference to a set of leaf instances in
> > the
> > gen-art> data tree. The "path" substatement (Section 9.9.2) selects a
> > set of
> > gen-art> leaf instances, and the leafref value space is the set of
> > values of
> > gen-art> these leaf instances.
> > gen-art>
> > gen-art> The first sentence isn't quite right. Perhaps:
> > gen-art>
> > gen-art> The value space of a leaf with leafref type is one of the
> > values of
> > gen-art> a set of leaf instances in the data tree. The "path"
> > substatement
> > gen-art> (Section 9.9.2) selects the set of leaf instances, and the
> > leafref
> > gen-art> value space is the set of values of these leaf instances.
> > gen-art>
> > gen-art> - section 9.9.3
> > gen-art>
> > gen-art> If "require-instance" is "true", it means that the instance
> > being
> > gen-art> referred MUST exist for the data to be valid. This constraint
> > is
> > gen-art> enforced according to the rules in Section 8.
> > gen-art>
> > gen-art> If "require-instance" is "false", it means that the instance
> > being
> > gen-art> referred MAY exist in valid data.
> > gen-art>
> > [...]
> > gen-art> Also, I think the second paragraph means that if require-instance
> > is
> > gen-art> false, the referred-to instance need not exist. But it's not
> > clear to
> > gen-art> me what that would mean -- if there are no instances referenced by
> > the
> > gen-art> XPath expression, then the set of value values of the leafref
> > would be
> > gen-art> empty and the leafref would necessarily be invalid. ... I think
> > these
> > gen-art> paragraphs need to be expanded in some way.
> >
> > mbj> Right; so what we want to say is:
> > mbj>
> > mbj> - the value space is the same as the value space of the referred
> > mbj> leaf
> > mbj>
> > mbj> - there is an additional constraint if require-instance is true that
> > mbj> the referred to leaf instance must exist
> > mbj>
> > mbj> How about
> > mbj>
> > mbj> OLD:
> > mbj>
> > mbj> The leafref type is used to declare a constraint on the value space
> > mbj> of a leaf, based on a reference to a set of leaf instances in the
> > mbj> data tree. The "path" substatement (Section 9.9.2) selects a set of
> > mbj> leaf instances, and the leafref value space is the set of values of
> > mbj> these leaf instances.
> > mbj>
> > mbj> If the leaf with the leafref type represents configuration data, and
> > mbj> the "require-instance" property (Section 9.9.3) is "true", the leaf
> > mbj> it refers to MUST also represent configuration. Such a leaf puts a
> > mbj> constraint on valid data. All such nodes MUST reference existing
> > mbj> leaf instances or leafs with default values in use (see Section
> > 7.6.1
> > mbj> and Section 7.7.2) for the data to be valid. This constraint is
> > mbj> enforced according to the rules in Section 8.
> > mbj>
> > mbj> NEW:
> > mbj>
> > mbj> The leafref type is used to declare a constraint on the value space
> > mbj> of a leaf, based on a reference to a set of leaf instances in the
> > mbj> data tree. The "path" substatement (Section 9.9.2) is used to refer
> > mbj> to another leaf node. The leafref value space is the value space of
> > mbj> this leaf node.
>
> This mixes up paths in the data tree with those in the schema
> tree. The XPath expression in the "path" statement is evaluated in
> the context of a data tree, but if the result is an empty node set,
> then "this leaf node" makes no sense.
The fact is that the path statement refers to instances of one leaf
node which exists in the schema tree. The current text doesn't really
work with "require-instance false". For example:
list interface
leaf name {
type string;
}
}
leaf if-ref {
type leafref {
path /interface/name;
require-instance false;
}
}
The idea is that this would be valid:
<interface>
<name>eth0</name>
</interface>
<if-ref>eth2</if-ref>
The current text says that the value space of "if-ref" is { "eth0" },
but the intention is to be able to refer to "non-existing values".
The current text also doesn't allow non-existing references in
the candidate.
> A specific example:
>
> leaf fooref {
> type leafref {
> path "../foo";
> require-instance false;
> }
> }
>
> leaf foo {
> type uint8;
> when "../bar < 42";
> }
>
> leaf bar {
> type uint8;
> default 100;
> }
>
> If there is neither "foo" nor "bar" in the data tree, what is the
> value space of "fooref"?
With the new text it would be uint8.
/martin
>
> Lada
>
> > mbj>
> > mbj> If the "require-instance" property is "true", there MUST exist an
> > mbj> instance, or a leaf with a default value in use (see Section 7.6.1
> > mbj> and Section 7.7.2), of the leaf being referred to with the same
> > value
> > mbj> as the leafref value in a valid data tree.
> > mbj>
> > mbj> If the leaf with the leafref type represents configuration data, and
> > mbj> the "require-instance" property (Section 9.9.3) is "true", the leaf
> > mbj> it refers to MUST also represent configuration.
> >
> >
> > Does anyone have comments on this proposal?
> >
> >
> > /martin
> >
> > _______________________________________________
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>
> --
> Ladislav Lhotka, CZ.NIC Labs
> PGP Key ID: E74E8C0C
>
>
>
>
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