netdev - Re: [PATCH net-next 2/6] bpf: add meta pointer for direct access

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Date:   Thu, 28 Sep 2017 21:40:40 +0000
From:   "Waskiewicz Jr, Peter" <peter.waskiewicz.jr@...el.com>
To:     John Fastabend <john.fastabend@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
        "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "mchan@...adcom.com" <mchan@...adcom.com>
Subject: Re: [PATCH net-next 2/6] bpf: add meta pointer for direct access

On 9/28/17 2:23 PM, John Fastabend wrote:
> [...]
> 
>> 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