[ovs-dev] [PATCH] datapath: Handle packets with precomputed checksums.

[Jesse Gross]

Ben Pfaff wrote:
> On Fri, Jan 22, 2010 at 08:12:39PM -0500, Jesse Gross wrote:
>> Some devices are capable of computing checksums of received packets
>> in hardware (the GRE module also falls into this category).
>> Unfortunately before CHECKSUM_HW was split into two different values
>> it was impossible to tell the checksum status of a packet during
>> bridging.  It turns out that a workaround that we already had in the
>> GRE module is very similar to that in mainline kernel, so this
>> generalizes that workaround.
> 
> Could you add something to the changelog and possibly to the comment
> that explains how to test this, e.g. how to set up a machine such that
> this code will be triggered and thus fix a problem.  It's not obvious to
> me...

I'll add something to the commit message but here is the quick version: 
sending a packet with a GRE checksum will cause a panic.  This code 
previously lived in the GRE module, which is why there aren't panics all 
the time.  I ran into this again when I bought a NIC that sets the 
appropriate ip_summed value.  Before I had thought that this was just a 
temporary workaround but after a little digging it turns out that the 
bridge does something similar.