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Date:   Sat, 19 Sep 2020 19:34:17 -0700
From:   Florian Fainelli <>
To:     Vladimir Oltean <>,,
Subject: Re: [RFC PATCH 3/9] net: dsa: convert check for 802.1Q upper when
 bridged into PRECHANGEUPPER

On 9/19/2020 6:47 PM, Vladimir Oltean wrote:
> DSA tries to prevent having a VLAN added by a bridge and by an 802.1Q
> upper at the same time. It does that by checking the VID in
> .ndo_vlan_rx_add_vid(), since that's something that the 8021q module
> calls, via vlan_vid_add(). When a VLAN matches in both subsystems, this
> check returns -EBUSY.
> However the vlan_vid_add() function isn't specific to the 8021q module
> in any way at all. It is simply the kernel's way to tell an interface to
> add a VLAN to its RX filter and not drop that VLAN. So there's no reason
> to return -EBUSY when somebody tries to call vlan_vid_add() for a VLAN
> that was installed by the bridge. The proper behavior is to accept that
> configuration.
> So what's wrong is how DSA checks that it has an 8021q upper. It should
> look at the actual uppers for that, not just assume that the 8021q
> module was somewhere in the call stack of .ndo_vlan_rx_add_vid().
> Signed-off-by: Vladimir Oltean <>

Reviewed-by: Florian Fainelli <>

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