From 38f78286c730c14208621a29ccd8298fd5f7ba13 Mon Sep 17 00:00:00 2001
From: David Wragg <david@wragg.org>
Date: Mon, 2 Nov 2015 15:53:16 +0000
Subject: [PATCH] Probe whether the kernel has ODP vxlan support

It's possible to build that kernel with openvswitch, and vxlan, but
without the vport_vxlan module that glues them together.  And at
least one distro has actually done this.
---
 prog/weaver/main.go |  9 ++++++---
 router/odp.go       | 43 ++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/prog/weaver/main.go b/prog/weaver/main.go
index bf85b916..634bb46c 100644
--- a/prog/weaver/main.go
+++ b/prog/weaver/main.go
@@ -13,7 +13,6 @@ import (
 	"github.com/davecheney/profile"
 	"github.com/docker/docker/pkg/mflag"
 	"github.com/gorilla/mux"
-	"github.com/weaveworks/go-odp/odp"
 
 	. "github.com/weaveworks/weave/common"
 	"github.com/weaveworks/weave/common/docker"
@@ -119,8 +118,12 @@ func main() {
 		os.Exit(0)
 
 	case createDatapath:
-		err := weave.CreateDatapath(datapathName)
-		if odp.IsKernelLacksODPError(err) {
+		err, odp_supported := weave.CreateDatapath(datapathName)
+		if !odp_supported {
+			if err != nil {
+				Log.Error(err)
+			}
+
 			// When the kernel lacks ODP support, exit
 			// with a special status to distinguish it for
 			// the weave script.
diff --git a/router/odp.go b/router/odp.go
index cea42dd5..d772d930 100644
--- a/router/odp.go
+++ b/router/odp.go
@@ -1,25 +1,58 @@
 package router
 
 import (
+	"fmt"
+	"net"
+	"syscall"
+
 	"github.com/weaveworks/go-odp/odp"
 )
 
 // ODP admin functionality
 
-func CreateDatapath(dpname string) error {
+func CreateDatapath(dpname string) (err error, supported bool) {
 	dpif, err := odp.NewDpif()
 	if err != nil {
-		return err
+		if odp.IsKernelLacksODPError(err) {
+			return nil, false
+		}
+
+		return err, true
 	}
 
 	defer dpif.Close()
 
-	_, err = dpif.CreateDatapath(dpname)
+	dp, err := dpif.CreateDatapath(dpname)
 	if err != nil && !odp.IsDatapathNameAlreadyExistsError(err) {
-		return err
+		return err, true
 	}
 
-	return nil
+	// Pick an ephemeral port number to use in probing for vxlan
+	// support.
+	udpconn, err := net.ListenUDP("udp4", nil)
+	if err != nil {
+		return err, true
+	}
+
+	// we leave the UDP socket open, so creating a vxlan vport on
+	// the same port number should fail.  But that's fine: It's
+	// still sufficient to probe for support.
+	portno := uint16(udpconn.LocalAddr().(*net.UDPAddr).Port)
+	vpid, err := dp.CreateVport(odp.NewVxlanVportSpec(
+		fmt.Sprintf("vxlan-%d", portno), portno))
+	if nlerr, ok := err.(odp.NetlinkError); ok {
+		if syscall.Errno(nlerr) == syscall.EAFNOSUPPORT {
+			dp.Delete()
+			return fmt.Errorf("kernel does not have Open vSwitch VXLAN support"), false
+		}
+	}
+
+	if err == nil {
+		dp.DeleteVport(vpid)
+	}
+
+	udpconn.Close()
+	return nil, true
 }
 
 func DeleteDatapath(dpname string) error {