[ovs-dev] [PATCH] dpif: Ensure ERSPAN GRE support

Ben Pfaff blp at ovn.org
Tue Jun 5 17:39:58 UTC 2018

On Fri, Jun 01, 2018 at 06:38:53PM +0200, Jiri Benc wrote:
> On Fri, 1 Jun 2018 09:15:33 -0700, Gregory Rose wrote:
> > Since ERSPAN over gre/ip_gre was added to the Linux 4.16 kernel the 
> > compat interface is needed
> > for kernels up to 4.15 so that we can support ERSPAN.  If the built-in 
> > gre/ip_gre kernel modules
> > don't have the ERSPAN support in them then we have to use the compat 
> > interface.
> That's very wrong. The compat interface should not be used with
> upstream kernel (except perhaps for very very very old kernels). We
> converted the API to the standard rtnetlink for good reasons. New
> features are not supported using the compat API. You are potentially
> breaking future distribution kernels by reverting to an obsolete and
> deprecated API.
> You'll have to find a different way to do what you need. Eric described
> pretty nicely a way to achieve that and how the fallbacks work, please
> re-read his emails and modify the code accordingly.
> > The target for USE_UPSTREAM_TUNNEL is moved to 4.16 now.  That's when 
> > ERSPAN becomes
> > fully supported.  Going forward the ERSPAN feature is the determinant 
> > for whether gr/ip_gre
> > compat mode is used or not.
> And with the next added feature to the kernel, that next feature will be
> what determines whether the compat mode will be used? And then next and
> so on? This doesn't work. ERSPAN must not be the decision factor.
> Instead, rtnetlink must be tried first and if and only if it fails,
> compat mode can be used.
> Please go read what Eric described about reading the value back.
> As for the patch,
> Nacked-by: Jiri Benc <jbenc at redhat.com>

These patches have been reverted now, see



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