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

From: Eric Garver <[email-masked]>
Date: Tue, 10 Oct 2017 11:09:49 -0400

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.