On Mon, Aug 24, 2015 at 9:35 AM, Ladislav Lhotka <lho...@nic.cz> wrote:
> Ladislav Lhotka <lho...@nic.cz> writes:
> Hi,
>
> >
> > 2. The rogue vendor can use a must statement to achieve the same
> > effect (or perhaps just state it in a description?). What’s important
> > is whether the server that advertises such an extension rejects a
> > configuration where the new parameter is missing or not.
>
> As a follow-up to the discussion during the interim call, here is an
> example of a module snippet that augments "ietf-interfaces" with a
> mandatory node:
>
> import ietf-interfaces {
> prefix if;
> }
>
> augment "/if:interfaces" {
> container top {
> must "foo";
> leaf accept {
> type boolean;
> default true;
> }
> leaf foo {
> type empty;
> }
> }
> }
>
> If a server advertises this module along with "ietf-interfaces", then,
> according to the rules of YANG 1.0, a datastore without the "foo"
> instance is invalid.
>
>
When a datastore is validated, all "must" constraints are
conceptually evaluated once for each data node in the data tree, and
for all leafs with default values in use (see Section 7.6.1). If a
data node does not exist in the data tree, and it does not have a
default value, its "must" statements are not evaluated.
According to sec. 7.5.3, para 2, the must statement is not evaluated
for a missing NP container because it has no default-stmt.
> Therefore, I think it really makes no practical sense to insist on
> restricting augments to non-mandatory nodes.
>
>
It does because the current YANG conformance model does not
require the augmenting modules to be present. They are considered
optional so a client can be written to work with the base module
and not break every time a new augments is added.
> Lada
>
>
Andy
> --
> Ladislav Lhotka, CZ.NIC Labs
> PGP Key ID: E74E8C0C
>
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