Re: [netmod] Clarify the meaning of property in RFC7950

[Andy Bierman <[e-mail]>]

Hi,

On Sat, May 13, 2023 at 12:02 PM Jason Sterne (Nokia) <
[e-mail]> wrote:

> Hi Frank,
>
>
>
> The table just after the text has this:
>
>
>
> +--------------+--------------+-------------+
>
>                | substatement | section      | cardinality |
>
>                +--------------+--------------+-------------+
>
>                | config       | 7.21.1       | 0..1        |
>
>                | default      | 7.6.4, 7.7.4 | 0..n        |
>
>                | mandatory    | 7.6.5        | 0..1        |
>
>                | max-elements | 7.7.6        | 0..1        |
>
>                | min-elements | 7.7.5        | 0..1        |
>
>                | must         | 7.5.3        | 0..n        |
>
>                | type         | 7.4          | 0..1        |
>
>                | unique       | 7.8.3        | 0..n        |
>
>                | units        | 7.3.3        | 0..1        |
>
>                +--------------+--------------+-------------+
>
>
>
>                         The deviate's Substatements
>
>
>
> That implies to me (since it says “deviate’s substatements”, not just
> “delete substatements”) that only those items can be added/changed/deleted.
> That table is the list of “properties”.
>
>
>
> But the other part of your question here isn’t so clear to me either.
> Every node does have a config true or false property associated with them
> (either explicitly, by default, or inherited from an ancestor). But does
> that mean it “exists” (from the ‘replace’ paragraph)? Does that mean it
> “matches a corresponding keyword in the targer node (from the ‘delete’
> paragraph)?
>
>
>


IMO libyang is correct.

Maybe the RFC text refers to the actual 'config' statement, and 'property'
is not precise terminology.
Every node has an effective config property so it would never be possible
to "add" a config-stmt, only "replace" it.



> In some ways maybe either add or replace should just work in this case
> since it isn’t really ambiguous what the result should be.
>
>
>

Agreed.
I just checked, and our compiler works this way.
It does the patch for add or replace, whether the node has an existing
config-stmt or not.  (oops),


Jason
>


Andy


>
>
> *From:* netmod <[e-mail]> *On Behalf Of *Fengchong (frank)
> *Sent:* Monday, May 8, 2023 2:15 AM
> *To:* [e-mail]
> *Subject:* [netmod] Clarify the meaning of property in RFC7950
>
>
>
>
>
> *CAUTION:* This is an external email. Please be very careful when
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>
>
>
> Hi all,
>
>
>
> In RFC7950 sec *7.20.3.2 <https://datatracker.ietf.org/doc/html/rfc7950#section-7.20.3.2>:*
>
>
>
>    The argument "add" adds properties to the target node.  The
>
>    properties to add are identified by substatements to the "deviate"
>
>    statement.  If a property can only appear once, the property MUST NOT
>
>    exist in the target node.
>
>
>
>    The argument "replace" replaces properties of the target node.  The
>
>    properties to replace are identified by substatements to the
>
>    "deviate" statement.  The properties to replace MUST exist in the
>
>    target node.
>
>
>
>    The argument "delete" deletes properties from the target node.  The
>
>    properties to delete are identified by substatements to the "delete"
>
>    statement.  The substatement's keyword MUST match a corresponding
>
>    keyword in the target node, and the argument's string MUST be equal
>
>    to the corresponding keyword's argument string in the target node.
>
>
>
> What’s the meaning of property? Is it a sub-statement?
>
>
>
> I see pyang and libyang have two different explanation. Pyang treat ‘config’ property as always exist property, because ‘config’ statement has default value (true or derived from parent).
>
> But libyang think if there is no ‘config’ sub-statement, then the ‘config’ property will be not exist.
>
>
>
> So there is a conflict when using pyang/libyang to parse YANG module.
>
> For example,
>
> Module a {
>
> Container a {
>
>
>
>    Leaf b {
>
>      Type string;
>
>    }
>
> }
>
>
>
> }
>
>
>
> Module a-dev {
>
>    Deviation  “/a:a/a:b” {
>
>      Deviate add {
>
>        Config false;
>
>     }
>
>    }
>
> }
>
>
>
> This example, pyang will report error, because pyang think ‘config’ property is always exist, so this propery should not be added. But libyang think it’s valid.
>
>
>
> If we change the type of deviate from ‘add’ to ‘replace’.
>
>
>
> Module a-dev {
>
>    Deviation  “/a:a/a:b” {
>
>      Deviate replace {
>
>        Config false;
>
>     }
>
>    }
>
> }
>
>
>
> Pyang will think it’s valid. But libyang think it’s invalid.
>
>
>
> So I think WG should clarify what’s the meaning of property.
>
>
>
> Ref:
>
> Issue on pyang: https://github.com/mbj4668/pyang/issues/815
>
>
>
> Issue on libyang: https://github.com/CESNET/libyang/issues/2010
>
>
>
>
>
>
>
>
>
>
>
>
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