netdev - Re: [PATCH v2.41 5/5] datapath: Add basic MPLS support to kernel

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Message-ID: <20131003002052.GA13111@verge.net.au>
Date:	Thu, 3 Oct 2013 09:20:54 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	netdev <netdev@...r.kernel.org>, Jesse Gross <jesse@...ira.com>,
	Ben Pfaff <blp@...ira.com>, Ravi K <rkerur@...il.com>,
	Isaku Yamahata <yamahata@...inux.co.jp>,
	Joe Stringer <joe@...d.net.nz>
Subject: Re: [PATCH v2.41 5/5] datapath: Add basic MPLS support to kernel

On Wed, Oct 02, 2013 at 11:03:57AM -0700, Pravin Shelar wrote:
> On Mon, Sep 30, 2013 at 11:47 PM, Simon Horman <horms@...ge.net.au> wrote:
> > Allow datapath to recognize and extract MPLS labels into flow keys
> > and execute actions which push, pop, and set labels on packets.
> >
> > Based heavily on work by Leo Alterman, Ravi K, Isaku Yamahata and Joe Stringer.
> >
> > Cc: Ravi K <rkerur@...il.com>
> > Cc: Leo Alterman <lalterman@...ira.com>
> > Cc: Isaku Yamahata <yamahata@...inux.co.jp>
> > Cc: Joe Stringer <joe@...d.net.nz>
> > Signed-off-by: Simon Horman <horms@...ge.net.au>
> >
> > ---
> >
> > +
> > +       /* this hack needed to get regular skb_gso_segment() */
> > +#ifdef HAVE___SKB_GSO_SEGMENT
> > +#undef __skb_gso_segment
> > +       skb_gso = __skb_gso_segment(skb, features, tx_path);
> > +#else
> > +#undef skb_gso_segment
> > +       skb_gso = skb_gso_segment(skb, features);
> > +#endif
> > +
> 
> We can get rid of #ifdefs by just using different name for
> rpl___skb_gso_segment(), something like mpls_vlan_skb_gso_segment().
> The way it is done for tnl-gso.

Thanks.

The reason that I had the code arranged this way was so that
calls to __skb_gso_segment() would go via rpl___skb_gso_segment()
on kernels older than v3.11. In particular calls outside of gso.c.

On closer examination the only such case is in ovs_dp_upcall().
Currently there should be no need to perform MPLS GSO segmentation in that
case because MPLS GSO segmentation can only be needed after actions are
applied.

However, I am concerned that it may be necessary later when
recirculation is introduced as in that case an upcall may occur
on a packet which has had actions applied.
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