netdev - Re: XDP question: best API for returning/setting egress port?

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Date:   Thu, 20 Apr 2017 00:51:31 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Andy Gospodarek <andy@...yhouse.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>
CC:     Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Alexei Starovoitov <ast@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "xdp-newbies@...r.kernel.org" <xdp-newbies@...r.kernel.org>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: XDP question: best API for returning/setting egress port?

On 04/19/2017 10:02 PM, Andy Gospodarek wrote:
[...]
> and then lookup this dest in a table we have the option to make that
> dest an ifindex/socket/other.
>
> I did also look at JohnF's patch and I do like the simplicity of the redirect
> action and new ndo_xdp_xmit and how it moves towards a way to transmit the
> frame.  The downside is that it presumes an ifindex, so it might not be ideal
> we want the lookup to return something other than an ifindex.
>
[...]
> would be handled.  If we are ultimately going to need a new netdev op to
> handle the redirect then what may be the issue with not providing the
> destination port the return code and the option proposed by JohnF looks
> good to me with maybe a small tweak to not presume ifindex in some manner.

Is there a concrete reason that all the proposed future cases like sockets
have to be handled within the very same XDP_REDIRECT return code? F.e. why
not XDP_TX_NIC that only assumes ifindex as proposed in the patch, and future
ones would get a different return code f.e. XDP_TX_SK only handling sockets
when we get there implementation-wise?