Re: [netmod] Order of evaluation for when?

Balazs Lengyel Fri, 16 Oct 2015 08:43:01 -0700

Hello,
I don't have a problem with the when in rpc/action as it is a simple case, it is meaningful understandable. I have problems with the undespecified behavior of when in edit-config and with the MANY! complicated "corner" cases. I would love to just prohibit 90% of them.
regards Balazs

On 2015-10-16 17:03, Andy Bierman wrote:

Hi,

I find all this fretting over when-stmt corner-cases to be a waste of time.

I certainly have no intention of spending 100s of hours coding for corner-cases

that have no operational value whatsoever. When-stmt has always been full

of problems that exist on paper but not in real servers.

There is no need for the YANG spec to point out that the constraints

only apply to YANG. That is self-evident.

Why doesn't when-stmt apply to a plain rpc?

rpc plot-point {

input {

leaf 3d {

type boolean;

default false;

}

leaf X { type uint32; }

leaf Y { type uint32; }

leaf Z {

when "../3d";

type uint32;

}

}

}

Are you saying that the when-stmt for Z is not allowed?

Or that it gets ignored and not enforced?

IMO this section was rather clear -- it applies to when-stmt

in the RPC input.

Andy

On Fri, Oct 16, 2015 at 5:01 AM, Martin Bjorklund <[email protected]> wrote:

Hi,

Balazs Lengyel <[email protected]> wrote:
> Hello Andy, Martin,
> If that is what is meant by 8.2.1 then I have a few comments

Sorry for the confusion on this topic. I have now done some digging
in the archives and I think that section 8.2 is really intended to
apply only to *configuration data* (which it actually says upfront).
The text in 8.2.1 is not intended to be for generic rpcs; it is
intended for rpcs that modify configuration datastores (edit-config).

The whole idea is that there are really three points in time where
"checks" are done - (1) simple type checks and structural checks when
the edit-config is parsed (2) check that the requested _operations_
are valid and (3) check that the _resulting datastore_ is valid.

This said, note that section 8.1 applies to *all* valid data trees,
including rpc/action input/output.

So, in summary, 8.1 defines the generic rules for valid data trees,
and 8.2 defines the NETCONF-specific behavior for edit-config
processing.

In order to resolve Balazs' original issue, we need to agree what
should happen in these cases *for NETCONF*.

Suppose we have:

leaf a {
when "../b = 42";
type int32;
}
leaf b {
type int32;
}

Scenario A
----------
The DB contains b=10

The server gets an edit-config with:

<a>2</a>

What is the result?

1) an error is returned
2) ok; the request to set a to 2 is silently dropped

Scenario B
----------
The DB contains b=10.

The server gets an edit-config with:

<a>2</a>
<b>42</b>

What is the result?

1) an error is returned
2) ok, db now has b=42; the request to set a to 2 is silently
dropped
3) ok, db now has a=2 and b=42

Scenario C (same as 2, but different order in edit-config)
----------
The DB contains b=10.

The server gets an edit-config with:

<b>42</b>
<a>2</a>

What is the result?

1) an error is returned
2) ok, db now has b=42; the request to set a to 2 is silently
dropped
3) ok, db now has a=2 and b=42

/martin

-- 
Balazs Lengyel                       Ericsson Hungary Ltd.
Senior Specialist
ECN: 831 7320                        
Mobile: +36-70-330-7909              email: [email protected]

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Re: [netmod] Order of evaluation for when?

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