Re: [PATCHv2 net-next 5/9] openvswitch: Add conntrack action

[Joe Stringer]

On 5 August 2015 at 15:31, Pravin Shelar <pshelar@xxxxxxxxxx> wrote:
> On Tue, Aug 4, 2015 at 9:49 PM, Joe Stringer <joestringer@xxxxxxxxxx> wrote:
> I got sparse warning:
>
> net/openvswitch/actions.c:634:1: warning: symbol 'ovs_dst_get_mtu' was
> not declared. Should it be static?
>
> net/openvswitch/actions.c:703:17: warning: cast from restricted __be16
>
> net/openvswitch/actions.c:703:17: warning: incorrect type in argument
> 1 (different base types)
>
> net/openvswitch/actions.c:703:17:    expected unsigned short
> [unsigned] [usertype] val
>
> net/openvswitch/actions.c:703:17:    got restricted __be16 [usertype] ethertype
>
> net/openvswitch/actions.c:703:17: warning: cast from restricted __be16
>
> net/openvswitch/actions.c:703:17: warning: cast from restricted __be16

Hrm, thanks. I'll figure out why I wasn't getting any warnings and fix these up.

>> -static void do_output(struct datapath *dp, struct sk_buff *skb, int out_port)
>> +static int ovs_vport_output(struct sock *sock, struct sk_buff *skb)
>> +{
>> +       struct ovs_frag_data *data = this_cpu_ptr(&ovs_frag_data_storage);
>> +       struct vport *vport = data->vport;
>> +
>> +       if (skb_cow_head(skb, data->l2_len) < 0)
>> +               return -ENOMEM;
>> +
> Need to free skb here.

OK.

>> +       skb->_skb_refdst = data->dst;
> I think we need to clone dst if there are multiple fragments.
> Can you test this code with vxlan flow based tunnels?

In prepare_frag(), we're currently doing:
data->dst = skb->_skb_refdst & SKB_DST_NOREF

Which means that the fragments shouldn't need an additional reference.
However it also means that the original reference is never freed. I
think we just need to add the final free of the original reference
after fragmentation is finished, in ovs_fragment(). I'll do this.

I assume that's the same as just setting up OVS with a vxlan tunnel
and sending some traffic across it with different sizes. I have a test
case for that:
https://github.com/joestringer/openvswitch/blob/dev/ct_20150806/tests/kmod-traffic.at#L964

>> +       *OVS_CB(skb) = data->cb;
>> +
>> +       /* Reconstruct the MAC header.  */
>> +       skb_push(skb, data->l2_len);
>> +       memcpy(skb->data, &data->l2_data, data->l2_len);
>> +       skb_reset_mac_header(skb);
>> +       skb->protocol = eth_hdr(skb)->h_proto;
> why do we need to restore skb->protocol?
>> +       skb->vlan_tci = 0;
>> +
> Why is vlan_tci set to zero.

Right, leftovers from an earlier approach where I pushed the vlan tci
into the packet before copying. I'll remove them.

>> +static void ovs_fragment(struct vport *vport, struct sk_buff *skb,
>> +                        unsigned int mru, __be16 ethertype)
>> +{
>> +       if (skb_network_offset(skb) > MAX_L2_LEN) {
>> +               OVS_NLERR(1, "L2 header too long to fragment");
>> +               return;
>> +       }
>> +
>> +       if (ethertype == htons(ETH_P_IP)) {
>> +               struct dst_entry ovs_dst;
>> +
>> +               prepare_frag(vport, skb);
>> +               dst_init(&ovs_dst, &ovs_dst_ops, NULL, 1,
>> +                        DST_OBSOLETE_NONE, DST_NOCOUNT);
>> +               ovs_dst.dev = vport->dev;
>> +
>> +               skb_dst_set_noref(skb, &ovs_dst);
>> +               IPCB(skb)->frag_max_size = mru;
>> +
>> +               ip_do_fragment(skb->sk, skb, ovs_vport_output);
>> +       } else if (ethertype == htons(ETH_P_IPV6)) {
>> +               const struct nf_ipv6_ops *v6ops = nf_get_ipv6_ops();
>> +               struct rt6_info ovs_rt;
>> +
>> +               if (!v6ops) {
>> +                       kfree_skb(skb);
>> +                       return;
>> +               }
>> +
>> +               prepare_frag(vport, skb);
>> +               memset(&ovs_rt, 0, sizeof(ovs_rt));
>> +               dst_init(&ovs_rt.dst, &ovs_dst_ops, NULL, 1,
>> +                        DST_OBSOLETE_NONE, DST_NOCOUNT);
>> +               ovs_rt.dst.dev = vport->dev;
>> +
>> +               skb_dst_set_noref(skb, &ovs_rt.dst);
>> +               IP6CB(skb)->frag_max_size = mru;
>> +
>> +               v6ops->fragment(skb->sk, skb, ovs_vport_output);
>> +       } else {
>> +               WARN_ONCE(1, "Failed fragment ->%s: eth=%04x, MRU=%d, MTU=%d.",
>> +                         ovs_vport_name(vport), htons(ethertype), mru,
>> +                         vport->dev->mtu);
>> +               kfree_skb(skb);
>> +       }
>> +}
>> +
> We also need something similar of this packet is going to userspace so
> that we can send original packets to userspace. Otherwise we would
> send defragmented packet to userspace.

OK, in that case we'll need to get an MTU from somewhere. I'll look at
using the MRU as the MTU for this path, since corner cases where the
MRU is greater than the netlink payload size seems pretty unlikely
(and the netlink sending code should already handle such cases). The
other concern I have is exactly how this should be presented to
userspace. Currently the conntrack action is treated an an implicit
reassembly, which will implicitly refragment on output. In between, it
remains defragmented. If we fragment on miss, then lookup will use the
key representing the defragmented packet (ie no OVS_FRAG_TYPE_* bits
set), so we should send the same up to userspace. I assume that
userspace would then re-parse the packets and see that they are
fragments for representing up to the higher layers like OpenFlow, but
for flow installation it would reuse the key passed up from the
kernel. Is that the model you have in mind?

>> +static void do_output(struct datapath *dp, struct sk_buff *skb, int out_port,
>> +                     struct sw_flow_key *key)
>>  {
>>         struct vport *vport = ovs_vport_rcu(dp, out_port);
>>
>> -       if (likely(vport))
>> -               ovs_vport_send(vport, skb);
>> -       else
>> +       if (likely(vport)) {
>> +               unsigned int mru = OVS_CB(skb)->mru;
>> +
>> +               if (likely(!mru || (skb->len <= mru + ETH_HLEN))) {
>> +                       ovs_vport_send(vport, skb);
>> +               } else if (mru <= vport->dev->mtu) {
>> +                       __be16 ethertype = key->eth.type;
>> +
>> +                       if (!is_flow_key_valid(key)) {
>> +                               if (eth_p_mpls(skb->protocol))
>> +                                       ethertype = skb->inner_protocol;
>> +                               else
>> +                                       ethertype = vlan_get_protocol(skb);
>> +                       }
>> +
> This looks nice!
A bit tidier:)

>> +int ovs_ct_copy_action(struct net *net, const struct nlattr *attr,
>> +                      const struct sw_flow_key *key,
>> +                      struct sw_flow_actions **sfa,  bool log)
>> +{
>> +       struct ovs_conntrack_info ct_info;
>> +       u16 family;
>> +       int err;
>> +
>> +       family = key_to_nfproto(key);
>> +       if (family == NFPROTO_UNSPEC) {
>> +               OVS_NLERR(log, "ct family unspecified");
>> +               return -EINVAL;
>> +       }
>> +
>> +       memset(&ct_info, 0, sizeof(ct_info));
>> +       ct_info.family = family;
>> +
>> +       err = parse_ct(attr, &ct_info, log);
>> +       if (err)
>> +               return err;
>> +
>> +       /* Set up template for tracking connections in specific zones. */
>> +       ct_info.ct = nf_ct_tmpl_alloc(net, ct_info.zone, GFP_KERNEL);
> Do we need to take any lock to add the template?

Since 0838aa7fcfcd875caa7bcc5dab0c3fd40444553d, templates aren't held
in any lists.
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