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

William Tu u9012063 at gmail.com
Fri Jun 1 18:23:12 UTC 2018

On Fri, Jun 1, 2018 at 9:38 AM, Jiri Benc <jbenc at redhat.com> 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.
Thanks for the feedback.

Looking at the dpif_netlink_rtnl_probe_oot_tunnels(), since now we
added ERSPAN feature, instead of probing geneve module,
we should probe ip_gre module with a nlattr of ERSPAN (ex: HWID).
If it does not return -ENOSUPPORT, then use the upstream ip_gre module.

And the next added feature should change this function to determine
whether to use compat mode or not.  Do I understand it right?


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