netdev - Re: [PATCH 2/3] offloading: Support multiple vlan tags in GSO.

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Date:	Mon, 1 Nov 2010 18:31:46 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 2/3] offloading: Support multiple vlan tags in GSO.

On Mon, Nov 1, 2010 at 1:33 PM, Ben Hutchings <bhutchings@...arflare.com> wrote:
> On Fri, 2010-10-29 at 15:14 -0700, Jesse Gross wrote:
>> We assume that hardware TSO can't support multiple levels of vlan tags
>> but we allow it to be done.  Therefore, enable GSO to parse these tags
>> so we can fallback to software.
>>
>> Signed-off-by: Jesse Gross <jesse@...ira.com>
>> CC: Ben Hutchings <bhutchings@...arflare.com>
> [...]
>
> I can't see how TSO would be enabled on a second-level VLAN device;
> presumably you're thinking about GSO being enabled there?

Right, TSO can't be enabled on a stacked vlan device.  However, there
are a few ways that I can think of to hit this code path.  One is GSO,
another is encapsulating a bridged packet that is already tagged.

These are definitely corner cases and I can think of a few other
caveats when using them.  Mostly I'm just thinking about making it
robust in the face of weird corner cases, one piece at a time at
least.
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