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

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Date:	Tue, 7 Jun 2016 15:45:27 -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>
Subject: Re: [PATCH net-next v10 2/5] openvswitch: set skb protocol and
 mac_len when receiving on internal device

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.
>> >
>> > * Set the mac_len which has been observed to not be set up correctly when
>> >   an ARP packet is generated and sent via an openvswitch bridge.
>> >   My test case is a scenario where there are two open vswtich bridges.
>> >   One outputs to a tunnel port which egresses on the other.
>> >
>> > The motivation for this is that support for outputting to layer 3 (non-tap)
>> > GRE tunnels as implemented by a subsequent patch depends on protocol and
>> > mac_len being set correctly on receive.
>> >
>> > Signed-off-by: Simon Horman <simon.horman@...ronome.com>
>> >
>> > ---
>> > v10
>> > * Set mac_len
>> >
>> > v9
>> > * New patch
>> > ---
>> >  net/openvswitch/vport-internal_dev.c | 4 ++++
>> >  1 file changed, 4 insertions(+)
>> >
>> > diff --git a/net/openvswitch/vport-internal_dev.c b/net/openvswitch/vport-internal_dev.c
>> > index 2ee48e447b72..f89b1efa88f1 100644
>> > --- a/net/openvswitch/vport-internal_dev.c
>> > +++ b/net/openvswitch/vport-internal_dev.c
>> > @@ -48,6 +48,10 @@ static int internal_dev_xmit(struct sk_buff *skb, struct net_device *netdev)
>> >  {
>> >         int len, err;
>> >
>> > +       skb->protocol = eth_type_trans(skb, netdev);
>> > +       skb_push(skb, ETH_HLEN);
>> > +       skb_reset_mac_len(skb);
>> > +
>> resetting mac-len breaks the assumption about mac_len for referencing
>> MPLS header ref: skb_mpls_header().
>
> Thanks I had overlooked this. I think it is actually safe as
> the mac_len is recalculated quite soon in key_extract() and IIRC
> the most important thing is for mac_len to be 0 or non-zero
> for the benefit of ovs_flow_key_extract(). None the less it does
> seem untidy and moreover inconsistent with the handling in
> netdev_port_receive() by a latter patch which does the following:
>
>         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()?