Probe whether the kernel has ODP vxlan support

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.

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
+	}
+
+	// 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)
 	}
 
-	return nil
+	udpconn.Close()
+	return nil, true
 }
 
 func DeleteDatapath(dpname string) error {