Date:	Thu, 26 Apr 2012 16:13:21 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Jesse Gross <jesse@...ira.com>
Cc:	"Kyle Mestery (kmestery)" <kmestery@...co.com>,
	David Miller <davem@...emloft.net>, shemminger@...tta.com,
	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 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
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