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 [off-list ref] wrote:

On Thu, Jun 02, 2016 at 03:01:47PM -0700, pravin shelar wrote:

quoted

On Wed, Jun 1, 2016 at 11:24 PM, Simon Horman
[off-list ref] wrote:

quoted

* 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 <redacted>

---
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()?
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