netdev - Re: [PATCH net-next 2/2] openvswitch: remove skb_mpls

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Date:   Fri, 30 Sep 2016 09:05:07 -0700
From:   pravin shelar <pshelar@....org>
To:     Jiri Benc <jbenc@...hat.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Ahern <dsa@...ulusnetworks.com>
Subject: Re: [PATCH net-next 2/2] openvswitch: remove skb_mpls_header

On Fri, Sep 30, 2016 at 1:06 AM, Jiri Benc <jbenc@...hat.com> wrote:
> On Thu, 29 Sep 2016 16:03:19 -0700, pravin shelar wrote:
>> > --- a/include/net/mpls.h
>> > +++ b/include/net/mpls.h
>> > @@ -25,15 +25,4 @@ static inline bool eth_p_mpls(__be16 eth_type)
>> >                 eth_type == htons(ETH_P_MPLS_MC);
>> >  }
>> >
>> > -/*
>> > - * For non-MPLS skbs this will correspond to the network header.
>> > - * For MPLS skbs it will be before the network_header as the MPLS
>> > - * label stack lies between the end of the mac header and the network
>> > - * header. That is, for MPLS skbs the end of the mac header
>> > - * is the top of the MPLS label stack.
>> > - */
>> > -static inline unsigned char *skb_mpls_header(struct sk_buff *skb)
>> > -{
>> > -       return skb_mac_header(skb) + skb->mac_len;
>> > -}
>>
>> I think we should keep this API, so that it is clear that MPLS header
>> mapped skb network header.
>
> I was pondering this but I don't think it really gains us anything.
> Wrappers like ip_hdr() are useful as they do type conversion; it's much
> nicer to write
>         ip_hdr(skb)->daddr
> than
>         (struct iphdr *)skb_network_header(skb)->daddr.
>
> But we don't really have a good type to return from skb_mpls_header, it
> boils down to be 100% equivalent to skb_network_header. In fact, you
> could just do:
> #define skb_mpls_header skb_network_header
>
I am fine with this too.

> In the code, I don't think there's much benefit from calling the
> wrapper, meaning of skb_network_header itself is clear enough. It *is*
> the network header, after all. In the whole openvswitch code, MPLS is
> treated as L3 header - no dissection is performed after the MPLS
> headers, the network header and mac_len is set as expected now, etc.
>

It makes it easier to locate which modules are using this API. That
also helps if in future we decide to change MPLS header mapping again.