+static int connect_ctrl_ring(struct backend_info *be)
+{
+ struct xenbus_device *dev = be->dev;
+ struct xenvif *vif = be->vif;
+ unsigned int val;
+ grant_ref_t ring_ref;
+ unsigned int evtchn;
+ int err;
+
+ err = xenbus_gather(XBT_NIL, dev->otherend,
+ "ctrl-ring-ref", "%u", &val, NULL);
+ if (err)
+ goto done; /* The frontend does not have a control ring */
+
+ ring_ref = val;
+
+ err = xenbus_gather(XBT_NIL, dev->otherend,
+ "event-channel-ctrl", "%u", &val, NULL);
+ if (err) {
+ xenbus_dev_fatal(dev, err,
+ "reading %s/event-channel-ctrl",
+ dev->otherend);
+ goto fail;
+ }
+
+ evtchn = val;
+
+ err = xenvif_connect_ctrl(vif, ring_ref, evtchn);
+ if (err) {
+ xenbus_dev_fatal(dev, err,
+ "mapping shared-frame %u port %u",
+ ring_ref, evtchn);
+ goto fail;
+ }
+
+done:
+ return 0;
+
+fail:
+ return err;
+}
+