Subject: Re: [PATCH net-next v4 3/3] openvswitch: New MPLS actions for layer 2 tunnelling

From: Martin Varghese <[email-masked]>
Date: Fri, 20 Dec 2019 08:34:28 +0530

On Thu, Dec 19, 2019 at 05:07:25PM -0800, Pravin Shelar wrote:
> On Wed, Dec 18, 2019 at 8:12 PM Martin Varghese
> <[email-masked]> wrote:
> >
> > On Wed, Dec 18, 2019 at 07:50:52PM -0800, Pravin Shelar wrote:
> > > On Tue, Dec 17, 2019 at 10:56 PM Martin Varghese
> > > <[email-masked]> wrote:
> > > >
> > > > From: Martin Varghese <[email-masked]>
> > > >
> > > > The existing PUSH MPLS action inserts MPLS header between ethernet header
> > > > and the IP header. Though this behaviour is fine for L3 VPN where an IP
> > > > packet is encapsulated inside a MPLS tunnel, it does not suffice the L2
> > > > VPN (l2 tunnelling) requirements. In L2 VPN the MPLS header should
> > > > encapsulate the ethernet packet.
> > > >
> > > > The new mpls action PTAP_PUSH_MPLS inserts MPLS header at the start of the
> > > > packet or at the start of the l3 header depending on the value of l2 tunnel
> > > > flag in the PTAP_PUSH_MPLS arguments.
> > > >
> > > > POP_MPLS action is extended to support ethertype 0x6558.
> > > >
> > > > Signed-off-by: Martin Varghese <[email-masked]>
> > > > ---
> > > > Changes in v2:
> > > >    - PTAP_POP_MPLS action removed.
> > > >    - Special handling for ethertype 0 added in PUSH_MPLS.
> > > >    - Refactored push_mpls function to cater existing push_mpls and
> > > >      ptap_push_mpls actions.
> > > >    - mac len to specify the MPLS header location added in PTAP_PUSH_MPLS
> > > >      arguments.
> > > >
> > > > Changes in v3:
> > > >    - Special handling for ethertype 0 removed.
> > > >    - Added support for ether type 0x6558.
> > > >    - Removed mac len from PTAP_PUSH_MPLS argument list
> > > >    - used l2_tun flag to distinguish l2 and l3 tunnelling.
> > > >    - Extended PTAP_PUSH_MPLS handling to cater PUSH_MPLS action also.
> > > >
> > > > Changes in v4:
> > > >    - Removed extra blank lines.
> > > >    - Replaced bool l2_tun with u16 tun flags in
> > > >      struct ovs_action_ptap_push_mpls.
> > > >
> > > The patch looks almost ready. I have couple of comments.
> > >
> > > >  include/uapi/linux/openvswitch.h | 31 +++++++++++++++++++++++++++++++
> > > >  net/openvswitch/actions.c        | 30 ++++++++++++++++++++++++------
> > > >  net/openvswitch/flow_netlink.c   | 34 ++++++++++++++++++++++++++++++++++
> > > >  3 files changed, 89 insertions(+), 6 deletions(-)
> > > >
> > > > diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
> > > > index a87b44c..d9461ce 100644
> > > > --- a/include/uapi/linux/openvswitch.h
> > > > +++ b/include/uapi/linux/openvswitch.h
> > > > @@ -673,6 +673,32 @@ struct ovs_action_push_mpls {
> > > >  };
> > > >
> > > ...
> > > ...
> > > > diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
> > > > index 65c2e34..85fe7df 100644
> > > > --- a/net/openvswitch/flow_netlink.c
> > > > +++ b/net/openvswitch/flow_netlink.c
> > > > @@ -79,6 +79,7 @@ static bool actions_may_change_flow(const struct nlattr *actions)
> > > >                 case OVS_ACTION_ATTR_SET_MASKED:
> > > >                 case OVS_ACTION_ATTR_METER:
> > > >                 case OVS_ACTION_ATTR_CHECK_PKT_LEN:
> > > > +               case OVS_ACTION_ATTR_PTAP_PUSH_MPLS:
> > > >                 default:
> > > >                         return true;
> > > >                 }
> > > > @@ -3005,6 +3006,7 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
> > > >                         [OVS_ACTION_ATTR_METER] = sizeof(u32),
> > > >                         [OVS_ACTION_ATTR_CLONE] = (u32)-1,
> > > >                         [OVS_ACTION_ATTR_CHECK_PKT_LEN] = (u32)-1,
> > > > +                       [OVS_ACTION_ATTR_PTAP_PUSH_MPLS] = sizeof(struct ovs_action_ptap_push_mpls),
> > > >                 };
> > > >                 const struct ovs_action_push_vlan *vlan;
> > > >                 int type = nla_type(a);
> > > > @@ -3072,6 +3074,33 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
> > > >                 case OVS_ACTION_ATTR_RECIRC:
> > > >                         break;
> > > >
> > > > +               case OVS_ACTION_ATTR_PTAP_PUSH_MPLS: {
> > > Can you change name of this action given this can handle both L2 and
> > > L3 MPLS tunneling?
> > >
> > > > +                       const struct ovs_action_ptap_push_mpls *mpls = nla_data(a);
> > > > +
> > > > +                       if (!eth_p_mpls(mpls->mpls_ethertype))
> > > > +                               return -EINVAL;
> > > > +
> > > > +                       if (!(mpls->tun_flags & OVS_MPLS_L2_TUNNEL_FLAG_MASK)) {
> > > > +                               if (vlan_tci & htons(VLAN_CFI_MASK) ||
> > > > +                                   (eth_type != htons(ETH_P_IP) &&
> > > > +                                    eth_type != htons(ETH_P_IPV6) &&
> > > > +                                    eth_type != htons(ETH_P_ARP) &&
> > > > +                                    eth_type != htons(ETH_P_RARP) &&
> > > > +                                    !eth_p_mpls(eth_type)))
> > > > +                                       return -EINVAL;
> > > > +                               mpls_label_count++;
> > > > +                       } else {
> > > > +                               if (mac_proto != MAC_PROTO_NONE) {
> > > It is better to check for 'MAC_PROTO_ETHERNET', rather than this negative test.
> > >
> > The idea is that if you have a l2 header you need to reset the mpls label count
> > Either way fine for me.Let me know
> Lets change it to  "if (mac_proto  == MAC_PROTO_ETHERNET)"
> 
Yes, but it will not work for a hypothetical case where l2
is no ethernet.
> > > > +                                       mpls_label_count = 1;
> > > > +                                       mac_proto = MAC_PROTO_NONE;
> > > > +                               } else {
> > > > +                                       mpls_label_count++;
> > > > +                               }
> > > We need to either disallow combination of L3 and L2 MPLS_PUSH, POP
> > > actions in a action list or keep separate label count. Otherwise it is
> > > impossible to validate mpls labels stack depth in POP actions.
> > >
> >
> > I assume it is taken in care in the above block
> >
> > let us consider the different cases
> >
> > 1.
> >   Incoming Packet - ETH|IP|Payload
> >   Actions = push_mpls(0x1),push_mpls(0x2),ptap_push_mpls(0x03)
> >   Resulting packet - MPLS(3)|Eth|MPLS(2)|MPLS(1)|IP|Payload
> >   Total Mpls count = 1
> >
> >   Since the total MPLS count = 1,ony one POP will be allowed and a recirc is need to
> >   parse the inner packets
> >
> > 2. Incoming Packet - ETH|MPLS(1)|IP|Payload
> >    Actions = ptap_push_mpls(0x03)
> >    Resulting packet - MPLS(3)|Eth|MPLS(1)|IP|Payload
> >    Total Mpls count = 1
> >
> >    Since the total MPLS count = 1,ony one POP will be allowed and a recirc is need to
> >    parse the inner packets
> >
> > 3. Incoming Packet - MPLS(1)|IP|Payload
> >    Actions = ptap_push_mpls(0x03)
> >    Resulting packet - MPLS(3)|MPLS(1)|IP|Payload
> >    Total Mpls count = 2
> >
> >    Since the total MPLS acount is 2 , 2 pops are allowd
> >
> >
> > Is there any other case ?
> >
> I was think case of action list: PUSH_MPLS_L2, PUSH_MPLS_L3, ....,
> POP_MPLS_L2, POP_MPLS_L2
> This action will pass the validation. It would also work fine in
> datapath since POP action can detect L2 and L3 packet dynamically. But
> it is inconsistent with actions intention.

I couldnt get the concern correctly.
THere is no POPMPLS l2.There is only one type of MPLS POP
the pop MPLS always removes MPLS header after mac header

In the case of POP_MPLS:0x6558 the ethernet header should not be
present as we dont support ethernet in ethernet.We have the validation
in flow_netlink.c
So for the POP_MPLS:0x6558 to work ,it should be preceeded by a pop_eth
if is a ethernet packet.

Considering the action above.
Incomming packet - ETH|IP|Payload
1 Actions - push_mpls_l2
outgoing packet -  l2 MPLS label|eth|IP - ( Packet is l3 now)
2 Actions  - Push_mpls_l2
outgoing packet  | L3 MPLS Label| l2 MPLS label|eth|IP.

2 actions - POP_MPLS,POP_MPLS
outgoing packet - ETH |IP|Payload  (Packet is l2 now)