[ovs-dev] [PATCH v2.57] datapath: Add basic MPLS support to kernel

Jesse Gross jesse at nicira.com
Wed May 21 23:53:37 UTC 2014


On Wednesday, May 21, 2014, Simon Horman <horms at verge.net.au> wrote:

> 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 at verge.net.au<javascript:;>>
> 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 at verge.net.au<javascript:;>>
> 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?
>

Yes, that's fine.
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