netdev - Re: [PATCH net-next 1/2] net: More fine-grained support for encapsulated GSO features

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Date:	Tue, 23 Apr 2013 14:00:19 -0700 (PDT)
From:	Joseph Gasparakis <joseph.gasparakis@...el.com>
To:	Simon Horman <horms@...ge.net.au>
cc:	dev@...nvswitch.org, netdev@...r.kernel.org,
	Jesse Gross <jesse@...ira.com>, jarno.rajahalme@....com,
	Joseph Gasparakis <joseph.gasparakis@...el.com>,
	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Maciej Żenczykowski <maze@...gle.com>
Subject: Re: [PATCH net-next 1/2] net: More fine-grained support for encapsulated
 GSO features



On Mon, 22 Apr 2013, Simon Horman wrote:

> "net: Add support for hardware-offloaded encapsulation" introduced
> the encapsulation field of struct skb, which when set provides hints
> that GSO should handle an skb that encapsulates a packet.
> 
> This patch adds an encapsulation_features field which provides
> a hint to dev dev_hard_start_xmit() that harware-offload encapsulation
> features should be used. Previously this hint was provided by the
> encapsulation field.
> 
> The other uses of the encapsulation field are left unchanged.
> 
> The two in-tree locations that set the encapsulation have been updated to
> also set encapsulation_field.
> 
> The motivation for this is to provide support segmentation of GSO MPLS skbs.
> This may be necessary when a non-MPLS GSO skb is turned into an MPLS GSO
> skb by Open vSwtich and its MPLS push action.
> 
> In this case it  harware-offload encapsulation features should be used,
> actually to be more exact software segmentation should be selected, but
> other hints provided by the encapsulation field are not applicable.
> 
> Cc: Joseph Gasparakis <joseph.gasparakis@...el.com>
> Cc: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>
> Cc: Alexander Duyck <alexander.h.duyck@...el.com>
> Signed-off-by: Simon Horman <horms@...ge.net.au>
> ---
>  include/linux/skbuff.h | 9 ++++++++-
>  net/core/dev.c         | 2 +-
>  net/core/skbuff.c      | 1 +
>  net/ipv4/gre.c         | 1 +
>  net/ipv4/ipip.c        | 1 +
>  5 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 2e0ced1..d9ec1de 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -494,7 +494,14 @@ struct sk_buff {
>  	 * headers if needed
>  	 */
>  	__u8			encapsulation:1;
> -	/* 7/9 bit hole (depending on ndisc_nodetype presence) */
> +	/* Encapsulation protocol and NIC drivers should use
> +	 * this flag to indicate to each other if the skb contains
> +	 * encapsulated packet and GSO should use encapsulation features
> +	 * instead of standard features for the netdev. This is typically
> +	 * a subset of cases where skb->encapsulation is set.
> +	 */
> +	__u8			encapsulation_features:1;
> +	/* 6/8 bit hole (depending on ndisc_nodetype presence) */
>  	kmemcheck_bitfield_end(flags2);
>  
>  #ifdef CONFIG_NET_DMA
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 9e26b8d..53236c5 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2498,7 +2498,7 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
>  		 * hardware encapsulation features instead of standard
>  		 * features for the netdev
>  		 */
> -		if (skb->encapsulation)
> +		if (skb->encapsulation_features)
>  			features &= dev->hw_enc_features;
>  
>  		if (netif_needs_gso(skb, features)) {
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 898cf5c..f23d136 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -708,6 +708,7 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
>  	new->l4_rxhash		= old->l4_rxhash;
>  	new->no_fcs		= old->no_fcs;
>  	new->encapsulation	= old->encapsulation;
> +	new->encapsulation_features = old->encapsulation_features;
>  #ifdef CONFIG_XFRM
>  	new->sp			= secpath_get(old->sp);
>  #endif
> diff --git a/net/ipv4/gre.c b/net/ipv4/gre.c
> index 0ae998b..8420f29 100644
> --- a/net/ipv4/gre.c
> +++ b/net/ipv4/gre.c
> @@ -157,6 +157,7 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
>  	}
>  
>  	skb->encapsulation = 0;
> +	skb->encapsulation_features = 0;
>  
>  	if (unlikely(!pskb_may_pull(skb, ghl)))
>  		goto out;
> diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
> index 77bfcce..a6db3c0 100644
> --- a/net/ipv4/ipip.c
> +++ b/net/ipv4/ipip.c
> @@ -220,6 +220,7 @@ static netdev_tx_t ipip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev)
>  	if (likely(!skb->encapsulation)) {
>  		skb_reset_inner_headers(skb);
>  		skb->encapsulation = 1;
> +		skb->encapsulation_features = 1;
>  	}
>  
>  	ip_tunnel_xmit(skb, dev, tiph);
> 

Any particular reason to introduce skb->encapsulation_features instead of 
using the existing skb->encapsulation? Also I don't see it used in your 
second patch either.
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