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

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Date:	Thu, 22 May 2014 08:03:51 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Jesse Gross <jesse@...ira.com>
Cc:	"dev@...nvswitch.org" <dev@...nvswitch.org>,
	netdev <netdev@...r.kernel.org>,
	Pravin B Shelar <pshelar@...ira.com>,
	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 Wed, May 21, 2014 at 01:31:55PM -0700, Jesse Gross wrote:
> On Wed, May 21, 2014 at 8:31 AM, Simon Horman <horms@...ge.net.au> wrote:
> > On Tue, May 20, 2014 at 07:30:38PM -0700, Jesse Gross wrote:
> >> On Thu, May 15, 2014 at 4:07 PM, Simon Horman <horms@...ge.net.au> wrote:
> >> > diff --git a/datapath/linux/compat/include/linux/netdevice.h b/datapath/linux/compat/include/linux/netdevice.h
> >> > index d726390..0381002 100644
> >> > --- a/datapath/linux/compat/include/linux/netdevice.h
> >> > +++ b/datapath/linux/compat/include/linux/netdevice.h
> >> > +#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,38)
> >> >  #define netif_skb_features rpl_netif_skb_features
> >> >  netdev_features_t rpl_netif_skb_features(struct sk_buff *skb);
> >>
> >> Currently this function doesn't look at mpls_features. Should it for
> >> things other than TSO?
> >
> > It seems to me that rpl_netif_skb_features is only used by
> > rpl_dev_queue_xmit().
> >
> > If that is the case then I don't think it is necessary to examine
> > mpls_features, which was introduced in v3.11, as rpl_dev_queue_xmit()
> > only exists for older kernel versions.
> 
> Sorry, I actually meant for upstream. I agree that the compatibility
> code reflects current kernels as written.
> 
> It seems like the checks in dev_hard_start_xmit() won't take
> mpls_features (or the presence of MPLS) into account when deciding
> whether to emulate the offload or pass the skb directly to the NIC. In
> the GSO code itself, we look at mpls_features but if we never get
> there then it will be too late.

I am reasonably sure that when I merged the MPLS GSO code into mainline
that it worked for the case where a non-MPLS GSO packet became an MPLS GSO
packet (due to a push MPLS action). But that was a while ago and looking
over the code its not obvious to my why that case would work.

I'll do some testing an analysis and propose a fix if necessary.

Would that address your concern?
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