netdev - Re: [RFC v4] Add TCP encap

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Date:	Thu, 26 Apr 2012 16:16:36 +0000
From:	"Kyle Mestery (kmestery)" <kmestery@...co.com>
To:	Jesse Gross <jesse@...ira.com>
CC:	Simon Horman <horms@...ge.net.au>,
	David Miller <davem@...emloft.net>,
	"<shemminger@...tta.com>" <shemminger@...tta.com>,
	"<jhs@...atatu.com>" <jhs@...atatu.com>,
	"<stephen.hemminger@...tta.com>" <stephen.hemminger@...tta.com>,
	"<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
	"<dev@...nvswitch.org>" <dev@...nvswitch.org>,
	"<eric.dumazet@...il.com>" <eric.dumazet@...il.com>
Subject: Re: [RFC v4] Add TCP encap_rcv hook (repost)


On Apr 26, 2012, at 11:13 AM, Jesse Gross wrote:

> On Thu, Apr 26, 2012 at 12:13 AM, Simon Horman <horms@...ge.net.au> wrote:
>> On Wed, Apr 25, 2012 at 10:17:25AM -0700, Jesse Gross wrote:
>>> On Wed, Apr 25, 2012 at 1:39 AM, Simon Horman <horms@...ge.net.au> wrote:
>>>> 
>>>> Hi Kyle,
>>>> 
>>>> the component that is of most interest to me is enabling OVS to use in-tree
>>>> tunnelling code - as it seems that makes most sense for an implementation
>>>> of STT. I have taken a brief look over your vxlan work and it isn't clear
>>>> to me if it is moving towards being an in-tree implementation.  Moreover,
>>>> I'm a rather unclear on what changes need to be made to OVS in order for
>>>> in-tree tunneling to be used.
>>>> 
>>>> My recollection is that OVS did make use of in-tree tunnelling code
>>>> but this was removed in favour of the current implementation for various
>>>> reasons (performance being one IIRC). I gather that revisiting in-tree
>>>> tunnelling won't revisit the previous set of problems. But I'm unclear how.
>>>> 
>>>> Jesse, is it possible for you to describe that in a little detail
>>>> or point me to some information?
>>> 
>>> This was what I had originally written a while back, although it's
>>> more about OVS internally and less about how to connect to the in-tree
>>> code:
>>> http://openvswitch.org/pipermail/dev/2012-February/014779.html
>>> 
>>> In order to flexibly implement support for current and future tunnel
>>> protocols OVS needs to be able to get/set information about the outer
>>> tunnel header when processing the inner packet.  At the very least
>>> this is src/dst IP addresses and the key/ID/VNI/etc.  In the upstream
>>> tunnel implementations those are implicitly encoded in the device that
>>> sends or receives the packet.  However, this has a two problems:
>>> number of devices and ability to handle unknown values.  We addressed
>>> part of this problem by allowing the tunnel ID to be set and matched
>>> through the OVS flow table and an action.  In order to do this with
>>> the in-tree tunneling code, we obviously need a way of passing this
>>> information around since it would currently get lost as we pass
>>> through the Linux device layer.
>>> 
>>> The plan to deal with that is to add a function to the in-tree
>>> tunneling code that allows a skb to be encapsulated with specific
>>> parameters and conversely a hook to receive decapsulated packets along
>>> with header info.  This would make all of the kernel tunneling code
>>> common, while still giving OVS userspace the ability to implement
>>> essentially any type of tunneling policy.  In many ways, this is very
>>> similar to how vlans look in OVS today.
>>> 
>>> While it would be possible to implement the hook to use the in-tree
>>> tunnel code today without a lot of changes, we already know that we
>>> want to move away from port-based model in the OVS kernel module
>>> towards the flow model.  As we push this upstream the userspace/kernel
>>> API should be the correct one, so that's why these two things are tied
>>> together.
>> 
>> 
>> Thanks, that explanation along with Kyle's response helps a lot.
>> 
>> It seems to me that something I could help out with is the implementation
>> of the set_tunnel action which extents and replaces the tun_id action.
>> It seems that is a requirement for the scheme you describe above.
>> 
>> http://openvswitch.org/pipermail/dev/2012-April/016239.html
> 
> I agree that's probably the best place to start unless Kyle has some
> specific plans otherwise.

Simon and I chatted off-list, and this is indeed where we plan to start.--
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