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

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Message-ID: <CA+ZOOTMxDnqVRFn52iKRBdM-KeNE=nk5Phnh1m4S1CwPaJQe+A@mail.gmail.com>
Date:	Wed, 14 May 2014 11:42:56 -0700
From:	Chema Gonzalez <chema@...gle.com>
To:	David Miller <davem@...emloft.net>
Cc:	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <dborkman@...hat.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2] net: filter: add insn for loading internal
 transport header offset

On Mon, May 5, 2014 at 12:12 PM, David Miller <davem@...emloft.net> wrote:
> 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.
I added a flow_keys variable in the packet runner function
(__sk_run_filter()) stack, and modified __skb_get_poff() to try to get
the results from there instead of calling the flow dissector every
time you call it. That will allow the packet filter to only perform a
single call to the flow dissector per packet.

I reworked the toff patch to use the same flow dissector output
approach (and share it with the poff load), and added a tproto patch.

Patches coming now.

-Chema
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