On Mon, May 19, 2014 at 06:34:05PM -0700, Jesse Gross wrote:
> I have some miscellaneous comments on things that I noticed, all of
> which are pretty small. I will probably have a few more tomorrow but
> my hope is that we can get this in soon.
>
> On Thu, May 15, 2014 at 4:07 PM, Simon Horman <ho...@verge.net.au> wrote:
> > diff --git a/datapath/actions.c b/datapath/actions.c
> > index 603c7cb..7c3ae0c 100644
> > --- a/datapath/actions.c
> > +++ b/datapath/actions.c
> > +static int push_mpls(struct sk_buff *skb,
> > + const struct ovs_action_push_mpls *mpls)
> > +{
> > + __be32 *new_mpls_lse;
> > + struct ethhdr *hdr;
> > +
> > + if (skb_cow_head(skb, MPLS_HLEN) < 0) {
> > + kfree_skb(skb);
> > + return -ENOMEM;
> > + }
>
> I think it would be better to not free the skb on error here - it
> introduces an exception case in the call to push_mpls() that would be
> otherwise handled if we didn't free it.
Thanks, I have fixed it up as you suggest.
> When we set the EtherType at the bottom of the function, I don't think
> that it is correct in the presence of VLAN tags because it will set
> the outer EtherType.
I believe this comes back to the problem we have with tag ordering. A
problem which after the most recent discussion of this topic I planned to
kick into the long grass by only allowing push MPLS actions on packets with
a well defined tag order.
This is the purpose of the white list in ovs_nla_copy_actions__(). It is
supposed to only push MPLS actions for flows with an IPv4, IPv6, ARP, RARP
or MPLS ethtype. However, I now think that the white list likely does not
work for VLAN packets as their flow's ethtype will be the inner-ethtype
(the one inside the VLAN tag) rather than a VLAN ethtype.
I'm unsure how you would like to handle this but one possibility would be
simply for push_mpls() to return an error if it is called on an skb with a
VLAN tag present or if the ethtype doesn't match a white list. Another is
to set the inner ethtype.
> > +static int pop_mpls(struct sk_buff *skb, const __be16 ethertype)
> > +{
> > + struct ethhdr *hdr;
> > + int err;
> > +
> > + if (unlikely(skb->len < skb->mac_len + MPLS_HLEN))
> > + return -EINVAL;
>
> I don't think this check is necessary since we would have rejected
> such packets at flow validation time.
Thanks, I have removed it.
> > +static int set_mpls(struct sk_buff *skb, const __be32 *mpls_lse)
> > +{
> > + __be32 *stack = (__be32 *)mac_header_end(skb);
> > + int err;
> > +
> > + err = make_writable(skb, skb->mac_len + MPLS_HLEN);
> > + if (unlikely(err))
> > + return err;
> > +
> > + if (skb->ip_summed == CHECKSUM_COMPLETE) {
> > + __be32 diff[] = { ~(*stack), *mpls_lse };
> > + skb->csum = ~csum_partial((char *)diff, sizeof(diff),
> > + ~skb->csum);
> > + }
>
> Is it possible to use csum_replace4() to simplify this?
I'm not sure that it can be due to its use of csum_fold() and csum_unfold().
In particular I notice that inet_proto_csum_replace4() uses code
similar to the above rather than csum_replace4().
> > @@ -701,6 +815,8 @@ int ovs_execute_actions(struct datapath *dp, struct
> > sk_buff *skb, bool recirc)
> > goto out_loop;
> > }
> >
> > + ovs_skb_init_inner_protocol(skb);
>
> I think we talked about some time ago but it seems like this will get
> reset by recirculation (although maybe it's unlikely that
> recirculation will get used on output).
Thanks, I think that can be fixed as follows:
if (!recirc)
ovs_skb_init_inner_protocol(skb);
> Also, maybe I'm missing something but I don't see where we actually
> set the inner protocol.
Thanks, I noticed that too. I have added the following back into push_mpls(),
just before skb->protocol is updated.
if (!ovs_skb_get_inner_protocol(skb))
ovs_skb_set_inner_protocol(skb, skb->protocol);
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