On 9/28/17 2:23 PM, John Fastabend wrote:

[...]

quoted

I'm pretty sure I misunderstood what you were going after with
XDP_REDIRECT reserving the headroom.  Our use case (patches coming in a
few weeks) will populate the headroom coming out of the driver to XDP,
and then once the XDP program extracts whatever hints it wants via
helpers, I fully expect that area in the headroom to get stomped by
something else.  If we want to send any of that hint data up farther,
we'll already have it extracted via the helpers, and the eBPF program
can happily assign it to wherever in the outbound metadata area.

In case its not obvious with the latest xdp metadata patches the outbound
metadata can then be pushed into skb fields via a tc_cls program if needed.

Yes, that was what I was alluding to with "can happily assign it to 
wherever."  The patches we're working on are driver->XDP, then anything 
else using the latest meta-data patches would be XDP->anywhere else.  So 
I don't think we're going to step on any toes.

Thanks John,
-PJ