netdev - Re: [PATCH net-next 2/3] net: mpls: Fixups for GSO

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Date:	Wed, 17 Aug 2016 17:23:34 -0600
From:	David Ahern <dsa@...ulusnetworks.com>
To:	Alexander Duyck <alexander.duyck@...il.com>
Cc:	Netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Lennert Buytenhek <buytenh@...tstofly.org>,
	Simon Horman <simon.horman@...ronome.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, rshearma@...cade.com,
	Tom Herbert <tom@...bertland.com>, Thomas Graf <tgraf@...g.ch>,
	olivier.dugeon@...nge.com
Subject: Re: [PATCH net-next 2/3] net: mpls: Fixups for GSO

On 8/17/16 5:16 PM, Alexander Duyck wrote:
>> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
>> index 1ecbd7715f6d..6d78f162a88b 100644
>> --- a/net/openvswitch/actions.c
>> +++ b/net/openvswitch/actions.c
>> @@ -167,6 +167,12 @@ static int push_mpls(struct sk_buff *skb, struct sw_flow_key *key,
>>                 skb->mac_len);
>>         skb_reset_mac_header(skb);
>>
>> +       /* for GSO: set MPLS as network header and encapsulated protocol
>> +        * header as inner network header
>> +        */
>> +       skb_set_network_header(skb, skb->mac_len);
>> +       skb_set_inner_network_header(skb, skb->mac_len + MPLS_HLEN);
>> +
>>         new_mpls_lse = (__be32 *)skb_mpls_header(skb);
>>         *new_mpls_lse = mpls->mpls_lse;
>>
> 
> So the one question I would have about this is how attached are you to
> using the network_header to record the offset for the MPLS header?  I
> ask because I think from a hardware offloading perspective it would
> make it much easier if instead you used the inner_mac_header to
> represent the offset for the MPLS header.  This way device drivers
> could just skip over it like a VLAN and just use network and transport
> header values like they would otherwise.
> 

Where does the network_header relate to if I change the marker to inner_mac_header? Would it be skipped?

skb->protocol is set to MPLS.
mac_header points to ethernet address
network_header points to ???

inner protocol is set to what is encapsulated (e.g., ipv4 or ipv6)
inner_mac_header points to start of mpls label.
inner_network points to start of network header.

Is that sufficient for h/w drivers?