Subject: Re: how to mix bridges and bonding inc. vlans correctly on Kernel > 3.10

From: Veaceslav Falico <[email-masked]>
Date: Thu, 14 Nov 2013 12:54:51 +0100

On Wed, Nov 13, 2013 at 10:09:30PM -0500, Vlad Yasevich wrote:
>Can you try out attached patch please.  I ran it in my environment and
>always get promisc link when attaching devices to the bridge.

It's interesting, actually, why do we need to check for IFF_UP at all when
changing flags.

The addition of IFF_UP goes up to:

commit b6c40d68ff6498b7f63ddf97cf0aa818d748dee7
Author: Patrick McHardy <[email-masked]>
Date:   Tue Oct 7 15:26:48 2008 -0700

     net: only invoke dev->change_rx_flags when device is UP

     Jesper Dangaard Brouer <[email-masked]> reported a bug when setting a VLAN
     device down that is in promiscous mode:

     When the VLAN device is set down, the promiscous count on the real
     device is decremented by one by vlan_dev_stop(). When removing the
     promiscous flag from the VLAN device afterwards, the promiscous
     count on the real device is decremented a second time by the
     vlan_change_rx_flags() callback.

... snip ...

However, I'm not sure that this is still needed, cause:

commit deede2fabe24e00bd7e246eb81cd5767dc6fcfc7
Author: Matthijs Kooijman <[email-masked]>
Date:   Mon Oct 31 04:53:13 2011 +0000

     vlan: Don't propagate flag changes on down interfaces.

     When (de)configuring a vlan interface, the IFF_ALLMULTI ans IFF_PROMISC
     flags are cleared or set on the underlying interface. So, if these flags
     are changed on a vlan interface that is not up, the flags underlying
     interface might be set or cleared twice.

     Only propagating flag changes when a device is up makes sure this does
     not happen. It also makes sure that an underlying device is not set to
     promiscuous or allmulti mode for a vlan device that is down.

... snip ...

which fixed completely the initial issue with vlans.

Maybe we should just remove the IFF_UP check in dev_change_rx_flags(), and
let the drivers using it handle its own logic, as vlan does?

Something like this:

diff --git a/net/core/dev.c b/net/core/dev.c
index 8ffc52e..9615cd7 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4995,7 +4995,7 @@ static void dev_change_rx_flags(struct net_device *dev, int flags)
  {
  	const struct net_device_ops *ops = dev->netdev_ops;
  
-	if ((dev->flags & IFF_UP) && ops->ndo_change_rx_flags)
+	if (ops->ndo_change_rx_flags)
  		ops->ndo_change_rx_flags(dev, flags);
  }

>Thanks
>-vlad