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

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Date:	Wed, 19 Feb 2014 22:02:11 -0300
From:	Flavio Leitner <fbl@...hat.com>
To:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
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

On Wed, Feb 19, 2014 at 02:22:06PM +0900, Toshiaki Makita wrote:
> (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
> 

Alright, the code looks good and I didn't notice anything
different on my testing env.

Acked-by: Flavio Leitner <fbl@...hat.com>

Thanks!
fbl
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