netdev - Re: [PATCH net] veth: Fix vlan_features so as to be able to use stacked vlan interfaces

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Message-ID: <53043F7E.804@lab.ntt.co.jp>
Date:	Wed, 19 Feb 2014 14:22:06 +0900
From:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:	fbl@...hat.com
CC:	"David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net] veth: Fix vlan_features so as to be able to use stacked
 vlan interfaces

(2014/02/19 13:13), Flavio Leitner wrote:
> On Tue, Feb 18, 2014 at 09:20:08PM +0900, Toshiaki Makita wrote:
>> Even if we create a stacked vlan interface such as veth0.10.20, it sends
>> single tagged frames (tagged with only vid 10).
>> Because vlan_features of a veth interface has the
>> NETIF_F_HW_VLAN_[CTAG/STAG]_TX bits, veth0.10 also has that feature, so
>> dev_hard_start_xmit(veth0.10) doesn't call __vlan_put_tag() and
>> vlan_dev_hard_start_xmit(veth0.10) overwrites vlan_tci.
>> This prevents us from using a combination of 802.1ad and 802.1Q
>> in containers, etc.
>>
>> Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
>> ---
>>  drivers/net/veth.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
>> index 2ec2041..5b37437 100644
>> --- a/drivers/net/veth.c
>> +++ b/drivers/net/veth.c
>> @@ -285,7 +285,8 @@ static void veth_setup(struct net_device *dev)
>>  	dev->ethtool_ops = &veth_ethtool_ops;
>>  	dev->features |= NETIF_F_LLTX;
>>  	dev->features |= VETH_FEATURES;
>> -	dev->vlan_features = dev->features;
>> +	dev->vlan_features = dev->features &
>> +			     ~(NETIF_F_HW_VLAN_CTAG_TX | NETIF_F_HW_VLAN_STAG_TX);
>>  	dev->destructor = veth_dev_free;
>>  
>>  	dev->hw_features = VETH_FEATURES;
>> -- 
>> 1.8.1.2
>>
> 
> Why that isn't a problem with another software device?
> Although this patch might fix the issue, it seems to me that
> the middle devices shouldn't use the same feature flags.
> I mean, vlan.20 should add the header, then vlan.10 should
> offload the tag to veth.  Otherwise, for any vlan on top of
> veth there will be an unneeded memmove().

In this case with this patch, vlan_dev_hard_start_xmit(veth0.10.20) set
vlan_tci, dev_hard_start_xmit(veth0.10) put it into skb->data, and
vlan_dev_hard_start_xmit(veth0.10) set vlan_tci again.
dev_hard_start_xmit(veth0) doesn't put it into skb->data because veth0
has NETIF_F_HW_VLAN_*TAG_TX feature.

Similarly, in not stacked vlan case, for example if veth0.10 has no vlan
intarface on it, vlan_dev_hard_start_xmit(veth0.10) set vlan_tci and
dev_hard_start_xmit(veth0) doesn't put it into skb->data.
There will be no unnecessary memmove().

Although I haven't looked over all, other drivers don't seem to have
NETIF_F_HW_VLAN_*TAG_TX in vlan_features (at least, bridge, vxlan,
e1000e, and bnx2x don't).

Thanks,
Toshiaki Makita
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