netdev - Re: [RFC PATCH v2 1/5] bpf: add PHYS_DEV prog type for early driver filter

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Message-ID: <CALx6S37x7FMfsn=T5e+=f7mz47nPgRBNpYYnA=NwmB-3cny1eg@mail.gmail.com>
Date:	Sat, 9 Apr 2016 10:17:27 -0300
From:	Tom Herbert <tom@...bertland.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Brenden Blanco <bblanco@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Edward Cree <ecree@...arflare.com>,
	john fastabend <john.fastabend@...il.com>,
	Thomas Graf <tgraf@...g.ch>,
	Johannes Berg <johannes@...solutions.net>,
	eranlinuxmellanox@...il.com, Lorenzo Colitti <lorenzo@...gle.com>
Subject: Re: [RFC PATCH v2 1/5] bpf: add PHYS_DEV prog type for early driver filter

On Sat, Apr 9, 2016 at 9:27 AM, Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
> On Sat, 9 Apr 2016 08:17:04 -0300
> Tom Herbert <tom@...bertland.com> wrote:
>
>> One other API issue is how to deal with encapsulation. In this case a
>> header may be prepended to the packet, I assume there are BPF helper
>> functions and we don't need to return a new length or start?
>
> That reminds me.  Do the BPF program need to know the head-room, then?
>
Right, that is basically my question. Can we have a helper function in
BPF that will prepend n bytes to the buffer? (I don't think we want
expose a notion of headroom).

Tom

> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   Author of http://www.iptv-analyzer.org
>   LinkedIn: http://www.linkedin.com/in/brouer