netdev - Re: [RFC PATCH 1/5] bpf: add PHYS_DEV prog type for early driver filter

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Date:	Mon, 04 Apr 2016 07:33:40 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Daniel Borkmann <daniel@...earbox.net>,
	Brenden Blanco <bblanco@...mgrid.com>, davem@...emloft.net,
	netdev@...r.kernel.org, tom@...bertland.com,
	alexei.starovoitov@...il.com, gerlitz@...lanox.com,
	john.fastabend@...il.com
Subject: Re: [RFC PATCH 1/5] bpf: add PHYS_DEV prog type for early driver
 filter

On Mon, 2016-04-04 at 15:07 +0200, Jesper Dangaard Brouer wrote:

> Argh... maybe the minimal pseudo/fake SKB is the wrong "signal" to send
> to users of this API.
> 
> The hole idea is that an SKB is NOT allocated yet, and not needed at
> this level.  If we start supporting calling underlying SKB functions,
> then we will end-up in the same place (performance wise).

A BPF program can access many skb fields.

If you plan to support BPF, your fake skb needs to be populated like a
real one. Looks like some code will be replicated in all drivers that
want this facility...

Or accept (document ?) that some BPF instructions are just not there.
(hash, queue_mapping ...)