Derived metrics vs metrics with instances

[Nathan Scott <nathans@xxxxxxxxxx>]

Hi Ken,

Paul and I were wondering if its possible to build a derived metric that
uses specific instances of a metric as part of the _expression_.  For example,
something like:

my.new.metric = network.interface.in.bytes["eth1"] + network.interface.out.bytes["eth1"]

... appears to be unsupported?  (or, at least, I can't see code that parses
the square braces anywhere).  Is that correct, or is there a way to do this?

cheers.

--

Nathan