netdev - Re: [RFC v4] Add TCP encap

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Message-ID: <CAEP_g=8EVOVgDaWnu3sd+qHxNZ7+ogjzBkuWvfVHNAqX2DRf=g@mail.gmail.com>
Date:	Mon, 23 Apr 2012 13:53:42 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	David Miller <davem@...emloft.net>
Cc:	shemminger@...tta.com, horms@...ge.net.au, jhs@...atatu.com,
	stephen.hemminger@...tta.com, netdev@...r.kernel.org,
	dev@...nvswitch.org, eric.dumazet@...il.com
Subject: Re: [RFC v4] Add TCP encap_rcv hook (repost)

On Mon, Apr 23, 2012 at 1:13 PM, David Miller <davem@...emloft.net> wrote:
> From: Jesse Gross <jesse@...ira.com>
> Date: Mon, 23 Apr 2012 13:08:49 -0700
>
>> Assuming that the TCP stack generates large TSO frames on transmit
>> (which could be the local stack; something sent by a VM; or packets
>> received, coalesced by GRO and then encapsulated by STT) then you can
>> just prepend the STT header (possibly slightly adjusting things like
>> requested MSS, number of segments, etc. slightly).  After that it's
>> possible to just output the resulting frame through the IP stack like
>> all tunnels do today.
>
> Which seems to potentially suggest a stronger intergration of the STT
> tunnel transmit path into our IP stack rather than the approach Simon
> is taking

Did you have something in mind?  Since the originating stack already
generates TSO frames today, it's just a few lines of code to adjust
for the addition of the STT header as the skb is encapsulated.
Otherwise, the transmit path is the same as something like GRE.  L2TP
follows a fairly similar path - on receive it binds to a listening UDP
socket and on transmit it prepends a header, setups up checksum
offloading, and outputs directly via ip_queue_xmit().
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