Subject: Re: [ovs-dev] [PATCH net-next] openvswitch: add ct_clear action

From: Eric Garver <[email-masked]>
Date: Tue, 10 Oct 2017 15:13:29 -0400

On Tue, Oct 10, 2017 at 10:24:20AM -0700, Joe Stringer wrote:
> On 10 October 2017 at 08:09, Eric Garver <[email-masked]> wrote:
> > On Tue, Oct 10, 2017 at 05:33:48AM -0700, Joe Stringer wrote:
> >> On 9 October 2017 at 21:41, Pravin Shelar <[email-masked]> wrote:
> >> > On Fri, Oct 6, 2017 at 9:44 AM, Eric Garver <[email-masked]> wrote:
> >> >> This adds a ct_clear action for clearing conntrack state. ct_clear is
> >> >> currently implemented in OVS userspace, but is not backed by an action
> >> >> in the kernel datapath. This is useful for flows that may modify a
> >> >> packet tuple after a ct lookup has already occurred.
> >> >>
> >> >> Signed-off-by: Eric Garver <[email-masked]>
> >> > Patch mostly looks good. I have following comments.
> >> >
> >> >> ---
> >> >>  include/uapi/linux/openvswitch.h |  2 ++
> >> >>  net/openvswitch/actions.c        |  5 +++++
> >> >>  net/openvswitch/conntrack.c      | 12 ++++++++++++
> >> >>  net/openvswitch/conntrack.h      |  7 +++++++
> >> >>  net/openvswitch/flow_netlink.c   |  5 +++++
> >> >>  5 files changed, 31 insertions(+)
> >> >>
> >> >> diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
> >> >> index 156ee4cab82e..1b6e510e2cc6 100644
> >> >> --- a/include/uapi/linux/openvswitch.h
> >> >> +++ b/include/uapi/linux/openvswitch.h
> >> >> @@ -806,6 +806,7 @@ struct ovs_action_push_eth {
> >> >>   * packet.
> >> >>   * @OVS_ACTION_ATTR_POP_ETH: Pop the outermost Ethernet header off the
> >> >>   * packet.
> >> >> + * @OVS_ACTION_ATTR_CT_CLEAR: Clear conntrack state from the packet.
> >> >>   *
> >> >>   * Only a single header can be set with a single %OVS_ACTION_ATTR_SET.  Not all
> >> >>   * fields within a header are modifiable, e.g. the IPv4 protocol and fragment
> >> >> @@ -835,6 +836,7 @@ enum ovs_action_attr {
> >> >>         OVS_ACTION_ATTR_TRUNC,        /* u32 struct ovs_action_trunc. */
> >> >>         OVS_ACTION_ATTR_PUSH_ETH,     /* struct ovs_action_push_eth. */
> >> >>         OVS_ACTION_ATTR_POP_ETH,      /* No argument. */
> >> >> +       OVS_ACTION_ATTR_CT_CLEAR,     /* No argument. */
> >> >>
> >> >>         __OVS_ACTION_ATTR_MAX,        /* Nothing past this will be accepted
> >> >>                                        * from userspace. */
> >> >> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> >> >> index a54a556fcdb5..db9c7f2e662b 100644
> >> >> --- a/net/openvswitch/actions.c
> >> >> +++ b/net/openvswitch/actions.c
> >> >> @@ -1203,6 +1203,10 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> >> >>                                 return err == -EINPROGRESS ? 0 : err;
> >> >>                         break;
> >> >>
> >> >> +               case OVS_ACTION_ATTR_CT_CLEAR:
> >> >> +                       err = ovs_ct_clear(skb, key);
> >> >> +                       break;
> >> >> +
> >> >>                 case OVS_ACTION_ATTR_PUSH_ETH:
> >> >>                         err = push_eth(skb, key, nla_data(a));
> >> >>                         break;
> >> >> @@ -1210,6 +1214,7 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> >> >>                 case OVS_ACTION_ATTR_POP_ETH:
> >> >>                         err = pop_eth(skb, key);
> >> >>                         break;
> >> >> +
> >> >>                 }
> >> > Unrelated change.
> >> >
> >> >>
> >> >>                 if (unlikely(err)) {
> >> >> diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
> >> >> index d558e882ca0c..f9b73c726ad7 100644
> >> >> --- a/net/openvswitch/conntrack.c
> >> >> +++ b/net/openvswitch/conntrack.c
> >> >> @@ -1129,6 +1129,18 @@ int ovs_ct_execute(struct net *net, struct sk_buff *skb,
> >> >>         return err;
> >> >>  }
> >> >>
> >> >> +int ovs_ct_clear(struct sk_buff *skb, struct sw_flow_key *key)
> >> >> +{
> >> >> +       if (skb_nfct(skb)) {
> >> >> +               nf_conntrack_put(skb_nfct(skb));
> >> >> +               nf_ct_set(skb, NULL, 0);
> >> > Can the new conntract state be appropriate? may be IP_CT_UNTRACKED?
> >> >
> >> >> +       }
> >> >> +
> >> >> +       ovs_ct_fill_key(skb, key);
> >> >> +
> >> > I do not see need to refill the key if there is no skb-nf-ct.
> >>
> >> Really this is trying to just zero the CT key fields, but reuses
> >> existing functions, right? This means that subsequent upcalls, for
> >
> > Right.
> >
> >> instance, won't have the outdated view of the CT state from the
> >> previous lookup (that was prior to the ct_clear). I'd expect these key
> >> fields to be cleared.
> >
> > I assumed Pravin was saying that we don't need to clear them if there is
> > no conntrack state. They should already be zero.
> 
> The conntrack calls aren't going to clear it, so I don't see what else
> would clear it?
> 
> If you execute ct(),ct_clear(), then the first ct will set the
> values.. what will zero them?

I meant move ovs_ct_fill_key() to inside the if statement.
i.e.

       if (skb_nfct(skb)) {
               nf_conntrack_put(skb_nfct(skb));
               nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
               ovs_ct_fill_key(skb, key);
       }

Should be nothing to fill/zero if we have not yet done conntrack.
Is there a case where we may lose skb->_nfct, but the key still has
conntrack data?