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

[William Tu]

On Fri, Jun 1, 2018 at 9:56 AM, Gregory Rose <gvrose8192 at gmail.com> wrote:
> On 6/1/2018 9:38 AM, 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.
>
>
> Jiri,
>
> I think there must be some confusion here.  The compat interface should be
> used to support
> features that are not in the kernel. ERSPAN in this case.  ERSPAN is
> introduced in 4.16 (let's
> just agree to ignore 4.15 since it's not LTS).
>
> So in kernels up to and including 4.14 we must use the compat interface to
> get ERSPAN support
> correct?
>
> If there is another way to do it I'm all ears.
>

IIUC, I think Jiri and Eric consider the case where there is already a
backport of ERSPAN in the order kernel, ex: RedHat backport ERSPAN
to the older kernel.  As a result, OVS needs to use the rtnetlink interface
mentioned by Eric to probe the older kernel.  If it has ERSPAN, then use
the upstream module.

Most of the cases for example ubuntu, it is a simple version check.
If > 4.16 then use the upstream, otherwise use compat module.

Regards,
William