[ovs-dev] [runt-flows 5/8] datapath: Report memory allocation errors in flow_extract().

[Ben Pfaff]

On Thu, Aug 26, 2010 at 02:56:04PM -0700, Jesse Gross wrote:
> On Fri, Aug 13, 2010 at 10:55 AM, Ben Pfaff <blp at nicira.com> wrote:
> > Until now flow_extract() has simply returned a bogus flow when memory
> > allocation errors occurred.  This fixes the problem by propagating the
> > error to the caller.
> >
> > Signed-off-by: Ben Pfaff <blp at nicira.com>
> 
> Hmm, that's pretty nasty behavior that we had before.
> 
> One general comment about this is that the behavior seems a little
> asymmetrical for the different protocol types: why switch to this new
> style for IP but not for ARP?  Why are the L4 protocols different from
> L3?  Why can't we just do all of this at the beginning?  The answer to
> all of these questions is (I assume) "IP options".  However, it took a
> little more thought to convince myself that it is OK than seems
> necessary.

We could do it all at the beginning, if we are willing to pull 98 bytes
of headers:

        14      Ethernet
        4       VLAN
        60      max IP header
        20      TCP/UDP/ICMP header
        --
        98

The 64 bytes we currently pull covers any of the protocols we support as
long as there are no IP options.  I was reluctant to increase the amount
we pull.  But maybe it's not a big deal.  What do you think?