netdev - Re: [PATCH RFC 1/3] xdp: Infrastructure to generalize XDP

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Date:   Wed, 21 Sep 2016 16:48:00 +0200
From:   Thomas Graf <tgraf@...g.ch>
To:     Tom Herbert <tom@...bertland.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Kernel Team <kernel-team@...com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Brenden Blanco <bblanco@...mgrid.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH RFC 1/3] xdp: Infrastructure to generalize XDP

On 09/21/16 at 07:19am, Tom Herbert wrote:
> certain design that because of constraints on one kernel interface. As
> a kernel developer I want flexibility on how we design and implement
> things!

Perfectly valid argument. I reviewed your ILA changes and did not
object to them.

> I think there are two questions that this patch set poses for the
> community wrt XDP:
> 
> #1: Should we allow alternate code to run in XDP other than BPF?
> #2: If #1 is true what is the best way to implement that?
> 
> If the answer to #1 is "no" then the answer to #2 is irrelevant. So
> with this RFC I'm hoping we can come the agreement on questions #1.

I'm not opposed to running non-BPF code at XDP. I'm against adding
a linked list of hook consumers.

Would anyone require to run XDP-BPF in combination ILA? Or XDP-BPF
in combination with a potential XDP-nftables? We don't know yet I
guess.

Maybe exclusive access to the hook for one consumer as selected by
the user is good enough.

If that is not good enough: BPF (and potentially nftables in the
future) could provide means to perform a selection process where a
helper call can run another XDP prog or return a verdict to trigger
another XDP prog. Definitely more flexible and faster than a linear
list doing  if, else if, else if, else if, ...