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

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Message-ID: <AANLkTinREMV1bRhoJuiRV805-e1NKdZD6ejyhYczpw_E@mail.gmail.com>
Date:	Mon, 25 Oct 2010 15:45:09 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	John Fastabend <john.r.fastabend@...el.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC][net-next-2.6 PATCH 4/4] net: remove check for headroom in vlan_dev_create

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.

On the other hand, I agree that this check isn't actually necessary.
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