netdev - Re: [patch net-next v3 8/9] net: move vlan pop/push functions into common code

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Date:	Wed, 19 Nov 2014 14:03:57 +0100
From:	Jiri Benc <jbenc@...hat.com>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	Jiri Pirko <jiri@...nulli.us>, netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Tom Herbert <therbert@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Daniel Borkmann <dborkman@...hat.com>, mst@...hat.com,
	fw@...len.de, Paul.Durrant@...rix.com, Thomas Graf <tgraf@...g.ch>,
	Cong Wang <cwang@...pensource.com>
Subject: Re: [patch net-next v3 8/9] net: move vlan pop/push functions into
 common code

On Wed, 19 Nov 2014 00:06:19 -0800, Pravin Shelar wrote:
> skb_reset_mac_len() sets length according to ethernet and network
> offsets, but mpls expects mac-length to be offset to mpls header (ref.
> skb_mpls_header()). Therefore rather than reset we need to subtract
> VLAN_HLEN from mac_len. Same goes for vlan-push(), we can add
> VLAN_HLEN.

Subtracting VLAN_HLEN from mac_len would break the common vlan cases,
where skb->protocol is ETH_P_8021Q and skb->mac_len is 14 on input to
__skb_vlan_pop. After __skb_vlan_pop pops the vlan header, it changes
skb->protocol to the protocol of the actual frame and has to leave
skb->mac_len at 14.

You'll need something more sophisticated to support MPLS here, I'm
afraid.

 Jiri

-- 
Jiri Benc
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