[PATCH net-next] openvswitch: allow linking a VRF to an OVS bridge

[Antoine Tenart <atenart@kernel.org>]

VRF devices are prevented from being added to upper devices since commit
1017e0987117 ("vrf: prevent adding upper devices") as they set the
IFF_NO_RX_HANDLER flag. However attaching a VRF to an OVS bridge is a
valid use case[1].

Allow a VRF device to be attached to an OVS bridge by having an OVS
specific tweak. This approach allows not to change a valid logic
elsewhere and the IFF_NO_RX_HANDLER limitation still applies for non-OVS
upper devices, even after a VRF was unlinked from an OVS bridge.

(Patch not sent as a fix as the commit introducing the limitation is not
recent).

[1] https://ltomasbo.wordpress.com/2021/06/25/openstack-networking-with-evpn/

Signed-off-by: Antoine Tenart <atenart@kernel.org>
---

Hi all,

I thought about other ways to fix this but did not want to add yet
another flag, nor to add specific logic outside of net/openvswitch/. A
custom netdev_rx_handler_register having priv_flags as a parameter could
also have been added, but again that seemed a bit invasive.

There might be questions about the setup in which a VRF is linked to an
OVS bridge; I cc'ed Luis Tomás who wrote the article.

Thanks,
Antoine

 net/openvswitch/vport-netdev.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/net/openvswitch/vport-netdev.c b/net/openvswitch/vport-netdev.c
index 8e1a88f13622..e76b2477d384 100644
--- a/net/openvswitch/vport-netdev.c
+++ b/net/openvswitch/vport-netdev.c
@@ -75,6 +75,7 @@ static struct net_device *get_dpdev(const struct datapath *dp)
 
 struct vport *ovs_netdev_link(struct vport *vport, const char *name)
 {
+	unsigned int saved_flags;
 	int err;
 
 	vport->dev = dev_get_by_name(ovs_dp_get_net(vport->dp), name);
@@ -98,8 +99,17 @@ struct vport *ovs_netdev_link(struct vport *vport, const char *name)
 	if (err)
 		goto error_unlock;
 
+	/* While IFF_NO_RX_HANDLER is rightly set for l3 masters (VRF) as they
+	 * don't work with upper devices, they can be attached to OVS bridges.
+	 */
+	saved_flags = vport->dev->priv_flags;
+	if (netif_is_l3_master(vport->dev))
+		vport->dev->priv_flags &= ~IFF_NO_RX_HANDLER;
+
 	err = netdev_rx_handler_register(vport->dev, netdev_frame_hook,
 					 vport);
+	vport->dev->priv_flags = saved_flags;
+
 	if (err)
 		goto error_master_upper_dev_unlink;
 
-- 
2.31.1