Re: [RFA] TLV fields for radiotap

On Tue, Nov 20, 2018 at 09:09:39PM +0100, Johannes Berg wrote:
> On Tue, 2018-09-04 at 14:14 +0200, Johannes Berg wrote:
> > On Mon, 2018-07-09 at 10:47 +0200, Johannes Berg wrote:
> > > Since there were no comments, let's make this more formal. Any
> > > objections now?
> > 
> > Does this look like a good idea/compromise?
> > 
> > It's hard to do an entirely new version, then at least in Linux we'd
> > probably have to be able to switch versions on the fly for some time,
> > which is awkward ... but OTOH this feels a bit hackish.
> > 
> > No comments at all? :)
> 
> *crickets*

Sorry, I keep meaning to but forgetting to respond to this.

I had a thought about this tonight: maybe the solution is to define
a new radiotap field, "hint," that contains a hint about the offset
to a field.  The field begins with a 16-bit (?) field number, f, to
be interpreted in the current namespace.  Following that is a 16-bit
(?) absolute offset from the end of the hint field to field f.  If you
introduce your vendor namespace when the last-assigned presence bit is
bit p, and later you reuse the vendor namespace with newly-assigned
presence bit p+k, then you can supply a hint for the vendor namespace
field so that old readers can still benefit from presence bits 0..p and
your vendor fields.

Anyway, I've only just thought-up the hint field, so I am not even sure
that it's well-defined.

Dave

-- 
David Young
[email protected]    Urbana, IL    (217) 721-9981