Subject: Re: Cannot move macvlan interface on top of bonding device

From: Vlad Yasevich <[email-masked]>
Date: Wed, 17 Sep 2014 16:51:53 -0400

On 09/17/2014 04:46 PM, Cong Wang wrote:
> On Wed, Sep 17, 2014 at 1:39 PM, Vlad Yasevich <[email-masked]> wrote:
>> On 09/17/2014 03:06 PM, Florian Westphal wrote:
>>> Cong Wang <[email-masked]> wrote:
>>>> On Wed, Sep 17, 2014 at 8:56 AM, Francesco Ruggeri <[email-masked]> wrote:
>>>>> This used to work in older releases.
>>>>> The problem seems to be that commit f939981492 sets NETIF_F_NETNS_LOCAL
>>>>> on bonding interfaces, and commit 797f87f83 causes macvlan interfaces
>>>>> to inherit its features from the lower device.
>>>>>
>>>>> Is there a reason why NETIF_F_NETNS_LOCAL should be inherited from the
>>>>> lower device
>>>>> by macvlan interfaces?
>>>>
>>>> commit 797f87f83 looks wrong, it should not inherit NETIF_F_NETNS_LOCAL,
>>>> so just clear this flag. Please submit a patch.
>>>
>>> Under which conditions would NETIF_F_NETNS_LOCAL have to be inherited?
>>> (i.e., why is it inheritable in the first place?)
>>
>> macvlan code calls
>>         features = netdev_increment_features(vlan->lowerdev->features,
>>                                              features,
>>                                              mask);
>>
>> where lowerdev->features contains the NETIF_F_NETNS_LOCAL bit.  That
>> bit is not set in features or in mask.  It is also not one of the ALL_FOR_ALL
>> bits so it's not turned off.
>>
>> As an example, here are the values from a quit test I ran:
>>
>> bond features = 0x400f3888
>> features = 0x3b5a09  (mask is the same).
>> incremented features = 0x41bf389
>>
>> NETIF_F_NETNS_LOCAL is still on.
> 

No, it is not.  NETIF_F_NETNS_LOCAL is bit 13 and that's off.  Bits
14 (GRO) and 12 (LLTX) are set.

-vlad

> I think the comment on netdev_increment_features() is clear:
> 
>  *      Computes a new feature set after adding a device with feature set
>  *      @one to the master device with current feature set @all.  Will not
>  *      enable anything that is off in @mask. Returns the new feature set.
> 
> And NETIF_F_NETNS_LOCAL is on in mask.
> 
>>
>> May be a better solution is:
>>
>>         features = netdev_increment_features(vlan->lowerdev->features & MACVLAN_FEATURS,
>>                                              features,
>>                                              mask);
>>
>> This way we start with only the feature MACVLAN is interested in.
>>
> 
> Or clear it in mask?
>