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

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Message-ID: <CAOrHB_B2mUqUOgwZroRqaYwsHCKd-Vj5nMWMvPxfF=quxhJ2cA@mail.gmail.com>
Date:	Tue, 21 Jun 2016 09:30:17 -0700
From:	pravin shelar <pshelar@....org>
To:	Simon Horman <simon.horman@...ronome.com>
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

On Mon, Jun 20, 2016 at 7:25 PM, Simon Horman
<simon.horman@...ronome.com> wrote:
> [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.
>
I think it is fine with device of type ARPHRD_NONE. metadata tunnel
devices would be of this type anyways.

> Jiri, do you have any thoughts on this?