On Mon, Sep 23, 2013 at 02:17:50PM -0700, Jesse Gross wrote: > On Sat, Sep 21, 2013 at 10:34 PM, Simon Horman <ho...@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 <ho...@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 <ho...@verge.net.au> > >> >> wrote: > >> >> > @@ -616,6 +736,13 @@ int ovs_execute_actions(struct datapath *dp, > >> >> > struct sk_buff *skb) > >> >> > goto out_loop; > >> >> > } > >> >> > > >> >> > + /* Needed to initialise inner protocol on kernels older > >> >> > + * than v3.11 where skb->inner_protocol is not present > >> >> > + * and compatibility code uses the OVS_CB(skb) to store > >> >> > + * the inner protocol. > >> >> > + */ > >> >> > + ovs_skb_set_inner_protocol(skb, skb->protocol); > >> >> > >> >> The comment makes it sound like this code should just be deleted when > >> >> upstreaming. However, I believe that we still need to initialize this > >> >> field, right? Is this the best place do it or should it be conditional > >> >> on adding a first MPLS header? (i.e. what happens if inner_protocol is > >> >> already set and the packet simply passes through OVS?) > >> > > >> > I believe there are several problems here. > >> > > >> > The first one, which my comment was written around is that I think that > >> > if > >> > inner_protocol is a field of struct sk_buff then we can rely on it > >> > already > >> > being initialised. However, if we are using compatibility code, where > >> > inner_protcol is called in the callback field of struct sk_buff then I > >> > think that OVS needs to initialise it. > >> > >> I'm not sure that it's true that inner_protocol is already initialized > >> - I grepped the tree and the only assignment that I found is in > >> skbuff.c in __copy_skb_header(). > > > > My assumption was that it would be initialised to zero, > > primarily due to the behaviour of __alloc_skb_head(). > > Perhaps the core code should be fixed to make my assumption true? > > I misunderstood then - I think you can assume that it is initialized > to zero, I though you meant that it was initialized to a protocol > value. However, I then still have my original question - don't we need > to set it here in both cases since we're not just 'initializing' it > but actually setting a protocol?
I believe that you are correct and it needs to be set in both cases. > >> 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. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
