[ovs-dev] adding an option for GRE tunneling without an Ethernet header

[thomas.morin at orange.com]

Hello,

Currently, OVS GRE tunnels use Ethertype 6558 and the GRE packets 
produced by OVS hence always are xxx-over-Ethernet-over-GRE. 
Symmetrically OVS expects received GRE packets to be of the same 
ethertype and carry an Ethernet payload.

I have written the included patch, which does the following:
- add a "noeth" option for a GRE tunnel, so that the Ethernet header is 
stripped before GRE encapsulation (the option, of course, defaults to 
the current behavior)
- on reception, recreates a fake Ethernet header if the ethertype of the 
received packet is not 6558 -- this behavior is similar to what the LISP 
tunneling code does

Note that, in both cases, the code takes care of preserving correct 
ethertypes.

As a result, this patch allows to setup GRE tunnels to interconnect OVS 
with network devices doing a usual x-over-GRE approach such as IP/MPLS 
routers.

The patch builds and passes unit tests.
It has been tested to confirm with a packet capture that:
- with the option set on a tunnel, the GRE packets from this tunnel are 
send and received as expected
- for a tunnel without this option, or we the option disabled, the 
current behavior is preserved

Caveats:
- documentation and unit test are missing, but I'll be happy to 
contribute these later
- I not an experimented C coder, please be kind :)
- some parts of the code are a bit of a guess work from me: I'm unsure 
of what needs to be done for GSO (possibly it can be done later?), or if 
re-checksumming is really needed after recreating a fake Ethernet header

I'd be happy to have comments on the approach and on the patch and to 
take them into account.

Thank you,

-Thomas

  datapath/datapath.c                            |    1
  datapath/flow_netlink.c                        |    7 +++
  datapath/linux/compat/include/net/gre.h        |    4 +
  datapath/linux/compat/include/net/ip_tunnels.h |    1
  datapath/vport-gre.c                           |   57 
++++++++++++++++++++++++-
  include/linux/openvswitch.h                    |    1
  lib/flow.c                                     |    2
  lib/flow.h                                     |    1
  lib/netdev-vport.c                             |    9 +++
  lib/netdev.h                                   |    1
  lib/odp-util.c                                 |   11 ++++
  lib/odp-util.h                                 |    3 -
  ofproto/tunnel.c                               |    7 ++-
  13 files changed, 101 insertions(+), 4 deletions(-)

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