netdev - Re: [PATCH v2.57] datapath: Add basic MPLS support to kernel

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Date:	Fri, 16 May 2014 17:48:10 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	dev@...nvswitch.org, netdev@...r.kernel.org,
	Jesse Gross <jesse@...ira.com>,
	Pravin B Shelar <pshelar@...ira.com>
Cc:	Ben Pfaff <blp@...ira.com>, Ravi K <rkerur@...il.com>,
	Joe Stringer <joe@...d.net.nz>
Subject: Re: [PATCH v2.57] datapath: Add basic MPLS support to kernel

On Fri, May 16, 2014 at 08:07:07AM +0900, Simon Horman wrote:
> Allow datapath to recognize and extract MPLS labels into flow keys
> and execute actions which push, pop, and set labels on packets.

[snip]

> diff --git a/datapath/linux/compat/gso.h b/datapath/linux/compat/gso.h
> index b83a4c3..98b2aba 100644
> --- a/datapath/linux/compat/gso.h
> +++ b/datapath/linux/compat/gso.h
> @@ -4,6 +4,7 @@
>  #include <linux/version.h>
>  #if LINUX_VERSION_CODE < KERNEL_VERSION(3,12,0)
>  
> +#include <linux/netdevice.h>
>  #include <linux/skbuff.h>
>  #include <net/protocol.h>
>  
> @@ -14,6 +15,9 @@ struct ovs_gso_cb {
>  	sk_buff_data_t	inner_network_header;
>  	sk_buff_data_t	inner_mac_header;
>  	void (*fix_segment)(struct sk_buff *);
> +#if LINUX_VERSION_CODE < KERNEL_VERSION(3,11,0)
> +	__be16			inner_protocol;
> +#endif
>  };
>  #define OVS_GSO_CB(skb) ((struct ovs_gso_cb *)(skb)->cb)

Unfortunately it seems that at least for v3.11 on x86_64 the above now
results in struct ovs_gso_cb being larger than the cb field of struct
skb_buff.

(It also seems that the call to ovs_skb_set_inner_protocol() is
 missing from push_mpls() so it is likely that GSO segmentation
 is broken.)

I apologise for not noticing this earlier.

One idea I had is so make inner_protocol union of some other member of
either struct ovs_gso_cb or struct ovs_skb_cb. But its not clear to me that
would fly.

Another possibility is to simply drop compatibility for segmentation of GSO
packets that become MPLS.  But I gather that is not the preferred way for
datapath features.

Any suggestions would be much appreciated.
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