--- xen-4.2.2/tools/libxl/libxl.c.orig	2013-06-26 19:10:38.850364477 +0100
+++ xen-4.2.2/tools/libxl/libxl.c	2013-06-26 19:10:45.953275678 +0100
@@ -1710,6 +1710,26 @@
     return;
 }
 
+/* common function to get next device id */
+static int libxl__device_nextid(libxl__gc *gc, uint32_t domid, char *device)
+{
+    char *dompath, **l;
+    unsigned int nb;
+    int nextid = -1;
+
+    if (!(dompath = libxl__xs_get_dompath(gc, domid)))
+        return nextid;
+
+    l = libxl__xs_directory(gc, XBT_NULL,
+                            GCSPRINTF("%s/device/%s", dompath, device), &nb);
+    if (l == NULL || nb == 0)
+        nextid = 0;
+    else
+        nextid = strtoul(l[nb - 1], NULL, 10) + 1;
+
+    return nextid;
+}
+
 /******************************************************************************/
 
 int libxl__device_disk_setdefault(libxl__gc *gc, libxl_device_disk *disk)
@@ -2550,8 +2570,7 @@
     flexarray_t *front;
     flexarray_t *back;
     libxl__device *device;
-    char *dompath, **l;
-    unsigned int nb, rc;
+    unsigned int rc;
 
     rc = libxl__device_nic_setdefault(gc, nic, domid);
     if (rc) goto out;
@@ -2568,17 +2587,10 @@
     }
 
     if (nic->devid == -1) {
-        if (!(dompath = libxl__xs_get_dompath(gc, domid))) {
+        if ((nic->devid = libxl__device_nextid(gc, domid, "vif")) < 0) {
             rc = ERROR_FAIL;
             goto out_free;
         }
-        if (!(l = libxl__xs_directory(gc, XBT_NULL,
-                                     libxl__sprintf(gc, "%s/device/vif", dompath), &nb)) ||
-            nb == 0) {
-            nic->devid = 0;
-        } else {
-            nic->devid = strtoul(l[nb - 1], NULL, 10) + 1;
-        }
     }
 
     GCNEW(device);
@@ -2976,6 +2988,13 @@
         goto out_free;
     }
 
+    if (vkb->devid == -1) {
+        if ((vkb->devid = libxl__device_nextid(gc, domid, "vkb")) < 0) {
+            rc = ERROR_FAIL;
+            goto out_free;
+        }
+    }
+
     rc = libxl__device_from_vkb(gc, domid, vkb, &device);
     if (rc != 0) goto out_free;
 
@@ -3078,6 +3097,13 @@
         goto out_free;
     }
 
+    if (vfb->devid == -1) {
+        if ((vfb->devid = libxl__device_nextid(gc, domid, "vfb")) < 0) {
+            rc = ERROR_FAIL;
+            goto out_free;
+        }
+    }
+
     rc = libxl__device_from_vfb(gc, domid, vfb, &device);
     if (rc != 0) goto out_free;