Factor out the wait-for-interface code

net/if.go

@@ -0,0 +1,28 @@
+package net
+
+import (
+	"fmt"
+	"net"
+	"time"
+)
+
+func EnsureInterface(ifaceName string, wait int) (iface *net.Interface, err error) {
+	if iface, err = findInterface(ifaceName); err == nil || wait == 0 {
+		return
+	}
+	for ; err != nil && wait > 0; wait -= 1 {
+		time.Sleep(1 * time.Second)
+		iface, err = findInterface(ifaceName)
+	}
+	return
+}
+
+func findInterface(ifaceName string) (iface *net.Interface, err error) {
+	if iface, err = net.InterfaceByName(ifaceName); err != nil {
+		return iface, fmt.Errorf("Unable to find interface %s", ifaceName)
+	}
+	if 0 == (net.FlagUp & iface.Flags) {
+		return iface, fmt.Errorf("Interface %s is not up", ifaceName)
+	}
+	return
+}