Add check-datapath to weaveutil

The utility is used to check whether a datapath can be created.

prog/weaveutil/datapath.go

@@ -31,6 +31,19 @@ func deleteDatapath(args []string) error {
 	return odp.DeleteDatapath(args[0])
 }
 
+// Checks whether a datapath can be created by actually creating and destroying it
+func checkDatapath(args []string) error {
+	if len(args) != 1 {
+		cmdUsage("check-datapath", "<datapath>")
+	}
+
+	if err := createDatapath(args); err != nil {
+		return err
+	}
+
+	return odp.DeleteDatapath(args[0])
+}
+
 func addDatapathInterface(args []string) error {
 	if len(args) != 2 {
 		cmdUsage("add-datapath-interface", "<datapath> <interface>")

prog/weaveutil/main.go

@@ -15,6 +15,7 @@ func init() {
 		"docker-tls-args":        dockerTLSArgs,
 		"create-datapath":        createDatapath,
 		"delete-datapath":        deleteDatapath,
+		"check-datapath":         checkDatapath,
 		"add-datapath-interface": addDatapathInterface,
 		"create-plugin-network":  createPluginNetwork,
 		"remove-plugin-network":  removePluginNetwork,

weave

@@ -639,8 +639,7 @@ create_bridge() {
     else
         if [ -n "$LAUNCHING_ROUTER" ] ; then
             if [ "$BRIDGE_TYPE" = bridge -a -z "$WEAVE_NO_FASTDP" ] &&
-                util_op create-datapath $DATAPATH 2>/dev/null &&
-                util_op delete-datapath $DATAPATH 2>/dev/null ; then
+                util_op check-datapath $DATAPATH 2>/dev/null ; then
                 cat <<EOF >&2
 WEAVE_NO_FASTDP is not set, but there is already a bridge present of
 the wrong type for fast datapath.  Please do 'weave reset' to remove