netdev - Re: Cannot move macvlan interface on top of bonding device

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Date:	Wed, 17 Sep 2014 13:46:55 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Vlad Yasevich <vyasevich@...il.com>
Cc:	Florian Westphal <fw@...len.de>,
	Francesco Ruggeri <fruggeri@...sta.com>,
	netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Weilong Chen <chenweilong@...wei.com>
Subject: Re: Cannot move macvlan interface on top of bonding device

On Wed, Sep 17, 2014 at 1:39 PM, Vlad Yasevich <vyasevich@...il.com> wrote:
> On 09/17/2014 03:06 PM, Florian Westphal wrote:
>> Cong Wang <cwang@...pensource.com> wrote:
>>> On Wed, Sep 17, 2014 at 8:56 AM, Francesco Ruggeri <fruggeri@...sta.com> 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.

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?
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