netdev - Re: [PATCH net-next v10 2/5] openvswitch: set skb protocol and mac

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Date:	Tue, 21 Jun 2016 11:25:01 +0900
From:	Simon Horman <simon.horman@...ronome.com>
To:	pravin shelar <pshelar@....org>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	ovs dev <dev@...nvswitch.org>, Jiri Benc <jbenc@...hat.com>
Subject: Re: [PATCH net-next v10 2/5] openvswitch: set skb protocol and
 mac_len when receiving on internal device

[Cc Jiri Benc]

On Sat, Jun 18, 2016 at 06:38:54PM -0700, pravin shelar wrote:
> On Thu, Jun 16, 2016 at 10:53 PM, Simon Horman
> <simon.horman@...ronome.com> wrote:
> > On Tue, Jun 07, 2016 at 03:45:27PM -0700, pravin shelar wrote:
> >> On Mon, Jun 6, 2016 at 8:08 PM, Simon Horman <simon.horman@...ronome.com> wrote:
> >> > On Thu, Jun 02, 2016 at 03:01:47PM -0700, pravin shelar wrote:
> >> >> On Wed, Jun 1, 2016 at 11:24 PM, Simon Horman
> >> >> <simon.horman@...ronome.com> wrote:
> >> >> > * Set skb protocol based on contents of packet. I have observed this is
> >> >> >   necessary to get actual protocol of a packet when it is injected into an
> >> >> >   internal device e.g. by libnet in which case skb protocol will be set to
> >> >> >   ETH_ALL.
> ....
> ....
> >> >         eth_type = eth_type_trans(skb, skb->dev);
> >> >         skb->mac_len = skb->data - skb_mac_header(skb);
> >> >         __skb_push(skb, skb->mac_len);
> >> >
> >> >         if (eth_type == htons(ETH_P_8021Q))
> >> >                 skb->mac_len += VLAN_HLEN;
> >> >
> >> > Perhaps that logic ought to be in a helper used by both internal_dev_xmit()
> >> > and netdev_port_receive(). Or somehow centralised in ovs_vport_receive().
> >>
> >> This does looks bit complex. Can we use other skb metadata like
> >> skb_mac_header_was_set()?
> >
> > Yes, I think that can be made to work if skb->mac_header is unset
> > for l3 packets in netdev_port_receive(). The following is an incremental
> > patch on the entire series. Is this the kind of thing you had in mind?
> >
> > diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
> > index 86f2cfb19de3..42587d5bf894 100644
> > --- a/net/openvswitch/flow.c
> > +++ b/net/openvswitch/flow.c
> > @@ -729,7 +729,7 @@ int ovs_flow_key_extract(const struct ip_tunnel_info *tun_info,
> >         key->phy.skb_mark = skb->mark;
> >         ovs_ct_fill_key(skb, key);
> >         key->ovs_flow_hash = 0;
> > -       key->phy.is_layer3 = skb->mac_len == 0;
> > +       key->phy.is_layer3 = skb_mac_header_was_set(skb) == 0;
> >         key->recirc_id = 0;
> >
> >         err = key_extract(skb, key);
> > diff --git a/net/openvswitch/vport-internal_dev.c b/net/openvswitch/vport-internal_dev.c
> > index 484ba529c682..8973d4db509b 100644
> > --- a/net/openvswitch/vport-internal_dev.c
> > +++ b/net/openvswitch/vport-internal_dev.c
> > @@ -50,7 +50,6 @@ static int internal_dev_xmit(struct sk_buff *skb, struct net_device *netdev)
> >
> >         skb->protocol = eth_type_trans(skb, netdev);
> >         skb_push(skb, ETH_HLEN);
> > -       skb_reset_mac_len(skb);
> >
> >         len = skb->len;
> >         rcu_read_lock();
> > diff --git a/net/openvswitch/vport-netdev.c b/net/openvswitch/vport-netdev.c
> > index 3df36df62ee9..4cf3f12ffc99 100644
> > --- a/net/openvswitch/vport-netdev.c
> > +++ b/net/openvswitch/vport-netdev.c
> > @@ -60,22 +60,9 @@ static void netdev_port_receive(struct sk_buff *skb)
> >         if (vport->dev->type == ARPHRD_ETHER) {
> >                 skb_push(skb, ETH_HLEN);
> >                 skb_postpush_rcsum(skb, skb->data, ETH_HLEN);
> > -       } else if (vport->dev->type == ARPHRD_NONE) {
> > -               if (skb->protocol == htons(ETH_P_TEB)) {
> > -                       __be16 eth_type;
> > -
> > -                       if (unlikely(skb->len < ETH_HLEN))
> > -                               goto error;
> > -
> > -                       eth_type = eth_type_trans(skb, skb->dev);
> > -                       skb->mac_len = skb->data - skb_mac_header(skb);
> > -                       __skb_push(skb, skb->mac_len);
> > -
> > -                       if (eth_type == htons(ETH_P_8021Q))
> > -                               skb->mac_len += VLAN_HLEN;
> > -               } else {
> > -                       skb->mac_len = 0;
> > -               }
> > +       } else if (vport->dev->type == ARPHRD_NONE &&
> > +                  skb->protocol != htons(ETH_P_TEB)) {
> > +               skb->mac_header = (typeof(skb->mac_header))~0U;
> >         }
> >
> >         ovs_vport_receive(vport, skb, skb_tunnel_info(skb));
> 
> This certainly looks better. I was wondering if we can unset the mac
> header offset in L3 tunnel devices itself. So there is no need to have
> this check here.

I think that might be possible for GRE by modifying the following in
__ipgre_rcv().

                if (tunnel->dev->type != ARPHRD_NONE)
                        skb_pop_mac_header(skb);
                else
                        skb_reset_mac_header(skb);

But I am unsure what side effects this might have on other users of the
code.

Jiri, do you have any thoughts on this?