[ovs-dev] [PATCH 2/3] [RFC] datapath: tunnelling: Pass l4_offset to update_header callback

Simon Horman horms at verge.net.au
Fri Apr 6 02:10:34 UTC 2012


On Thu, Apr 05, 2012 at 05:34:21PM -0700, Jesse Gross wrote:
> On Tue, Apr 3, 2012 at 10:14 PM, Simon Horman <horms at verge.net.au> wrote:
> > The STT protocol's header includes a field for the offset
> > to the start of the l4 header. It seems that this
> > is the value of the transport_offset of the original SKB and
> > making that value available to the update_header callback avoids
> > STT needing to calculate the offset.
> >
> > Signed-off-by: Simon Horman <horms at verge.net.au>
> 
> Isn't it possible to quickly compute the L4 offset if you know the
> size of the header (which in STT is fixed)?  I'm just trying to
> minimize the amount of protocol-specific code in the generic tunneling
> code as we add more protocols.

To be honest I'm not sure that I really understand the motivation for the
l4_offset in STT. But it seems to me the difficulty in calculating
l4_offset lies in calculating the size of the IP header in the inner
packet, especially in the case of IPv6. I'm quite happy to accept that I
have missed the point somehow.



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