netdev - Re: [RFC][net-next-2.6 PATCH 4/4] net: remove check for headroom in vlan_dev

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Message-ID: <AANLkTimYGADLrfYrY6kth7EDeiGXsvSY8wS=3dxVQ3cC@mail.gmail.com>
Date:	Tue, 26 Oct 2010 19:07:54 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	John Fastabend <john.r.fastabend@...el.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RFC][net-next-2.6 PATCH 4/4] net: remove check for headroom in vlan_dev_create

On Tue, Oct 26, 2010 at 3:05 PM, John Fastabend
<john.r.fastabend@...el.com> wrote:
> On 10/25/2010 3:45 PM, Jesse Gross wrote:
>> On Thu, Oct 21, 2010 at 3:10 PM, John Fastabend
>> <john.r.fastabend@...el.com> wrote:
>>> It is possible for the headroom to be smaller then the
>>> hard_header_len for a short period of time after toggling
>>> the vlan offload setting.
>>>
>>> This is not a hard error and skb_cow_head is called in
>>> __vlan_put_tag() to resolve this.
>>>
>>> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
>>
>> How is it possible that the hard_header_len changes on the vlan
>> device?  It looks like the header length never gets changed after it
>> is initialized.  There's no set_flags method in the vlan device to
>> toggle whether it is using offloading or not, it just rides on top of
>> the underlying device.
>
> Your right and I think this is why my previous patch was broken. If we
> can toggle the underlying offloads we should set the header length as
> well. With the updated patch I just sent this should be true now.

OK, it makes sense it that context.
Acked-by: Jesse Gross <jesse@...ira.com>

Thanks.
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