netdev - Re: [ovs-dev] [PATCH v3 net-next] MPLS: Use mpls_features to activate software MPLS GSO segmentation

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Message-ID: <20140602043947.GA28083@verge.net.au>
Date:	Mon, 2 Jun 2014 13:39:50 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	YAMAMOTO Takashi <yamamoto@...inux.co.jp>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, dev@...nvswitch.org
Subject: Re: [ovs-dev] [PATCH v3 net-next] MPLS: Use mpls_features to
 activate software MPLS GSO segmentation

On Mon, Jun 02, 2014 at 12:51:53PM +0900, YAMAMOTO Takashi wrote:
> > If an MPLS packet requires segmentation then use mpls_features
> > to determine if the software implementation should be used.
> > 
> > As no driver advertises MPLS GSO segmentation this will always be
> > the case.
> > 
> > I had not noticed that this was necessary before as software MPLS GSO
> > segmentation was already being used in my test environment. I believe that
> > the reason for that is the skbs in question always had fragments and the
> > driver I used does not advertise NETIF_F_FRAGLIST (which seems to be the
> > case for most drivers). Thus software segmentation was activated by
> > skb_gso_ok().
> > 
> > Thanks to Jesse Gross for prompting me to investigate this.
> > 
> > Acked-by: Jesse Gross <jesse@...ira.com>
> > Signed-off-by: Simon Horman <horms@...ge.net.au>
> > 
> > ---
> > v3
> > * As requested by David Miller
> >   - Do not mark net_mpls_features as inline
> >   - Correct alignment of parameters
> > 
> > v2
> > * Added Ack from Jesse Gross
> > * Removed duplicate 'Thus' from changelog
> > ---
> >  net/core/dev.c | 38 ++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 38 insertions(+)
> > 
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index 0355ca5..1aa7004 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -2540,6 +2540,42 @@ netdev_features_t netif_skb_features(struct sk_buff *skb)
> >  }
> >  EXPORT_SYMBOL(netif_skb_features);
> >  
> > +/* If MPLS offload request, verify we are testing hardware MPLS features
> > + * instead of standard features for the netdev.
> > + */
> > +#ifdef CONFIG_NET_MPLS_GSO
> > +static netdev_features_t net_mpls_features(struct sk_buff *skb,
> > +					   struct net_device *dev,
> > +					   netdev_features_t features)
> > +{
> > +	/* There is no support for MPLS LRO. So the only way that
> > +	 * an MPLS skb could require GSO segmentation is if it
> > +	 * was received as a non-MPLS skb and then became an MPLS skb.
> > +	 * This may be effected by Open vSwitch in which case the
> > +	 * mac_len will non-zero and not equal to skb_network_offset
> > +	 * as the former indicates the end of L2 the latter indicates
> 
> s/L2/& and/
> 
> > +	 * the beginning of L3 and there is a gap between them occupied
> > +	 * by the MPLS label stack.
> > +	 *
> > +	 * Thus it is possible to avoid traversing any VLAN tags that are
> > +	 * present to determine if the ethtype is MPLS. Instead the
> > +	 * inequality of mac_llen and skb_network_offset are used to
> 
> s/mac_llen/mac_len/
> 
> Acked-by: YAMAMOTO Takashi <yamamoto@...inux.co.jp>

Thanks, I will fix that and post v4.
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