netdev - DSA and underlying 802.1Q encapsulation

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Date:	Tue, 26 May 2015 18:29:57 -0400 (EDT)
From:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:	netdev <netdev@...r.kernel.org>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Florian Fainelli <f.fainelli@...il.com>,
	Andrew Lunn <andrew@...n.ch>, Chris Healy <cphealy@...il.com>,
	Jérome Oufella 
	<jerome.oufella@...oirfairelinux.com>
Subject: DSA and underlying 802.1Q encapsulation

Hi,

I'm doing tests with VLAN support in DSA and I noticed that the EDSA 
frame is prepended with a 802.1q header once queued to the underlying 
network device, in net/dsa/tag_edsa.c:

    skb->dev = p->parent->dst->master_netdev;
    dev_queue_xmit(skb);

This issue can be observed with the following dump:

    curl -s http://ix.io/iIv | tcpdump -en -r -

I suspect that the DSA code must clear some VLAN flags in the skb
structure, in order to prevent the additional encapsulation by the lower
level. Does this make sense?

Thanks,
-v
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