Ladislav Lhotka <[email protected]> wrote:
> 
> > On 24 Feb 2016, at 15:48, Kent Watsen <[email protected]> wrote:
> > 
> > 
> > Hi Lada,
> > 
> > 
> > 
> > 
> > 
> > 
> >>> In yesterday's meeting, Lou (I think?) mentioned a use case for mount
> >>> that is not documented in draft-rtgyangdt-rtgwg-device-model; the need
> >>> for being able to specify modules to mount directly in the schema.
> >>> Something like this:
> >>> 
> >>> container root {
> >>>  ymnt:mount-point "lne" {
> >>>    ymnt:mount-module "ietf-interfaces";
> >>>  }
> >>> }
> >>> 
> >> 
> >> It is IMO impossible to use YANG extensions for similar purposes
> >> because it fundamentally changes YANG semantics.
> > 
> > 
> > Please say more.  I don’t see the issue.  Naturally there would need
> > to be an RFC that defines the semantics of this YANG extension, what
> > else would be missing?
> 
> Extensions are optional to implement and "MAY be ignored in its
> entirety" (sec. 6.3.1 in 6020bis). Otherwise, why have we bothered so
> much with backward compatibility in YANG 1.1? Somebody might define,
> via an extension, a new list with deep or optional keys, or a floating
> point data type or whatever. So in the end everybody would have YANG
> exactly to his or her own liking but there would be no standard at
> all.

Sure, this is possible.  For example we have an extension for YANG 1.0
called tailf:action (it is not needed anymore of course).  The point
is that we can define standard extensions with a well-defined meaning.
They would be optional to implement in general, but we can certainly
say that if you implement a module that uses ymnt:mount-point, you
MUST also implement the mount-point extension.  Just like we do with
nacm:default-deny-all.


/martin
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