netdev - Re: [PATCH net-next v2] net: filter: add insn for loading internal transport header offset

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Date:	Mon, 05 May 2014 15:12:00 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	chema@...gle.com
Cc:	edumazet@...gle.com, dborkman@...hat.com, ast@...mgrid.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2] net: filter: add insn for loading internal
 transport header offset

From: Chema Gonzalez <chema@...gle.com>
Date: Mon, 5 May 2014 11:42:00 -0700

> On Fri, May 2, 2014 at 7:52 PM, David Miller <davem@...emloft.net> wrote:
>> We can probably add an extension to AF_PACKET which provides the flow
>> key at the end of the tpacket3_hdr if a certain socket option is set.
>>
>> That would provide the transport header as well as a side effect, and
>> be much more powerful and efficient than this particular BPF
>> instruction.
> I'm not sure whether I follow this. The goal is to be able to access
> the inner-most headers inside BPF, not in userland by calling
> getsockopt().

You're missing my entire point.

You can use AF_PACKET mmap() rings and in those ring entries all of the
flow dissection information can be put in the ring entry headers before
the packet contents.  Ports, header offsets, everything.
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