[ovs-dev] [PATCH v2.39 7/7] datapath: Add basic MPLS support to kernel

[Simon Horman]

On Mon, Sep 23, 2013 at 06:38:23PM -0700, Jesse Gross wrote:
> On Mon, Sep 23, 2013 at 6:32 PM, Simon Horman <horms at verge.net.au> wrote:
> > On Mon, Sep 23, 2013 at 02:17:50PM -0700, Jesse Gross wrote:
> >> On Sat, Sep 21, 2013 at 10:34 PM, Simon Horman <horms at verge.net.au> wrote:
> >> > On Thu, Sep 19, 2013 at 12:21:33PM -0500, Jesse Gross wrote:
> >> >> On Thu, Sep 19, 2013 at 10:57 AM, Simon Horman <horms at verge.net.au> wrote:
> >> >> > On Mon, Sep 16, 2013 at 03:38:21PM -0500, Jesse Gross wrote:
> >> >> >> On Mon, Sep 9, 2013 at 12:20 AM, Simon Horman <horms at verge.net.au> wrote:
> >> >> One other consideration in the OVS case - with recirculation we may
> >> >> hit this code multiple times and the difference in behavior could be
> >> >> surprising. However, on the other hand, we need to be careful because
> >> >> skb->cb is not guaranteed to be initialized to zero.
> >> >
> >> > Thanks, that is also not something that I had considered.
> >> >
> >> > I'm not sure, but I think that we can rely on skb->cb
> >> > not being clobbered between rounds of recirculation.
> >> > Or at the very least I think we could save and restore it
> >> > as necessary.
> >>
> >> Yes, it should be safe to assume this.
> >>
> >> > So I think if we could be careful to make sure that inner_protocol
> >> > is in a sane state the first time we see the skb but not
> >> > each time it is recirculated then I think things should work out.
> >> >
> >> > In my current implementation of recirculation the datapath
> >> > side is driven ovs_dp_process_received_packet(). So by my reasoning
> >> > above I think it would make sense to reset the inner_protocol there
> >> > and in ovs_packet_cmd_execute() rather than in ovs_execute_actions()
> >> > which each of those functions call.
> >>
> >> I think that would work, however, I wonder if it's the right place in
> >> general, independent of this compatibility issue. I guess it still
> >> seems like the ideal thing to do is to move this as close to where it
> >> is necessary as possible, specifically in mpls_push(). Is there a
> >> reason to not put it there (again, other than the out-of-tree
> >> compatibility issues)?
> >
> > I agree that should work, out-of-tree compatibility issues aside.
> >
> > Perhaps a solution is to have a conditional set_inner_protocol call inside
> > push_mpls, where the condition is that inner_protocol is zero.
> > And a reset_inner_protocol call earlier on, a call that sets inner_protocol
> > to zero only if the compatibility code is in use and thus it resides in
> > struct ovs_gso_cb. This call could be remove once the compatibility
> > code is no longer needed, that is once kernels older than 3.11 are no
> > longer supported.
> 
> I agree that's probably the right solution.

Thanks, I will see about making it so.