Subject: Re: [PATCH v2 net] vlan: Mask off vlan acceleration features on vlan device.

From: Vlad Yasevich <[email-masked]>
Date: Wed, 26 Mar 2014 20:53:12 -0400

On 03/26/2014 05:15 PM, Patrick McHardy wrote:
> On Wed, Mar 26, 2014 at 05:10:38PM -0400, David Miller wrote:
>> From: Vlad Yasevich <[email-masked]>
>> Date: Wed, 26 Mar 2014 16:28:31 -0400
>>
>>> Some drivers incorrectly assign vlan acceleration features to
>>> vlan_features thus causing issues for Q-in-Q vlan configurations.
>>> Prevent this once and for all by masking off acceleration features
>>> for vlan devices until such time as we support stacked acceleration.
>>>
>>> Signed-off-by: Vlad Yasevich <[email-masked]>
>>
>> So what if we do have chips that can offload Q-in-Q?  Will we use
>> a new flag?
> 
> For 802.1ad that was the intention, using the NETIF_F_HW_VLAN_STAG_* flags.
> 

But we can't really do that as we don't carry multiple vlan_tci in the
skb.  If the card advertises VLAN_STAG_*, then we'll offload that, but
CTAG will have to be computed by software.  More infrastructure is
needed to support nested vlan offloads.

-vlad