netdev - Re: [PATCH net-next] net-gre-gro: Fix a bug that breaks the forwarding path

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Date:	Wed, 16 Jul 2014 15:15:53 +0300
From:	Or Gerlitz <or.gerlitz@...il.com>
To:	Jerry Chu <hkchu@...gle.com>
Cc:	Tom Herbert <therbert@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Wolfgang Walter <linux@...m.de>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net-gre-gro: Fix a bug that breaks the
 forwarding path

On Tue, Jul 15, 2014 at 11:22 PM, Jerry Chu <hkchu@...gle.com> wrote:
> On Tue, Jul 15, 2014 at 11:21 AM, Or Gerlitz <or.gerlitz@...il.com> wrote:

>> I am not near the code now, but AFAIK, the "stack" sets it in the TX path
>> and the driver sets it in the RX path, any deviation you see there for this
>> convension except for the change introduced by this patch.

> Where does the forwarding path (e.g., the case at hand) belong then?

yep, so forwarding flow is something like

HW --> driver RX --> stack RX --> some stack processing --> stack TX
--> driver TX --> HW

and this is different from a path of

application --> stack TX --> driver TX --> HW

It seems as of even before we throw in the tunneling thing, the GRO stack
which is part of that "stack RX" code I mentioned above sets the
gso_type of SKBs
for the sake of forwarding  so these things already happen.

> AFAICT the current dev_hard_start_xmit() code pretty much requires
> skb->encapsulation to be set on all tunneled pkts in order for the proper
> TX offload to be possible.
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