netdev - Re: [PATCH v9 net-next 4/7] openvswitch: add layer 3 flow/port support

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Message-ID: <20160509081818.GB4470@vergenet.net>
Date:	Mon, 9 May 2016 17:18:20 +0900
From:	Simon Horman <simon.horman@...ronome.com>
To:	Jiri Benc <jbenc@...hat.com>
Cc:	netdev@...r.kernel.org, dev@...nvswitch.org,
	Lorand Jakab <lojakab@...co.com>,
	Thomas Morin <thomas.morin@...nge.com>
Subject: Re: [PATCH v9 net-next 4/7] openvswitch: add layer 3 flow/port
 support

On Fri, May 06, 2016 at 11:35:04AM +0200, Jiri Benc wrote:
> On Wed,  4 May 2016 16:36:30 +0900, Simon Horman wrote:
> > +static int push_eth(struct sk_buff *skb, struct sw_flow_key *key,
> > +		    const struct ovs_action_push_eth *ethh)
> > +{
> > +	int err;
> > +
> > +	/* De-accelerate any hardware accelerated VLAN tag added to a previous
> > +	 * Ethernet header */
> > +	err = skb_vlan_deaccel(skb);
> > +	if (unlikely(err))
> > +		return err;
> > +
> > +	/* Add the new Ethernet header */
> > +	if (skb_cow_head(skb, ETH_HLEN) < 0)
> > +		return -ENOMEM;
> > +
> > +	skb_push(skb, ETH_HLEN);
> > +	skb_reset_mac_header(skb);
> > +	skb_reset_mac_len(skb);
> > +
> > +	ether_addr_copy(eth_hdr(skb)->h_source, ethh->addresses.eth_src);
> > +	ether_addr_copy(eth_hdr(skb)->h_dest, ethh->addresses.eth_dst);
> > +	eth_hdr(skb)->h_proto = ethh->eth_type;
> 
> This doesn't seem right. We know the packet type, it's skb->protocol.
> We should fill in that.

I think that makes sense. Possibly the eth_type field
can be removed from ovs_action_push_eth.

> In addition, we should check whether mac_len > 0 and in such case,
> change skb->protocol to ETH_P_TEB first (and store that value in the
> pushed eth header).
> 
> Similarly on pop_eth, we need to check skb->protocol and if it is
> ETH_P_TEB, call eth_type_trans on the modified frame to set the new
> skb->protocol correctly. It's probably not that simple, as we'd need a
> version of eth_type_trans that doesn't need a net device.

I'm not sure I understand the interaction with ETH_P_TEB here.

In my mind skb->protocol == ETH_P_TEB may be used early on in OvS's receive
processing to find the inner protocol from the packet and at that point
skb->protocol is set to that value. And that for further packet processing
the fact the packet was received as TEB is transparent.

Conversely, skb->protocol may be set as necessary on transmit as a packet
exits OvS.