[xfer] Send xfer_window_changed() after xfer_vredirect()

Modify the default action for xfer_vredirect() to automatically send
xfer_window_changed() messages to both the new child and the parent
interfaces.  This will allow the elimination of processes that simply
poll on xfer_window() to determine when a redirection has completed
successfully.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/xfer.c

  * @ret rc		Return status code
  */
 int xfer_vredirect ( struct interface *intf, int type, va_list args ) {
+	struct interface tmp = INTF_INIT ( null_intf_desc );
 	struct interface *dest;
 	xfer_vredirect_TYPE ( void * ) *op =
 		intf_get_dest_op_no_passthru ( intf, xfer_vredirect, &dest );
 	if ( op ) {
 		rc = op ( object, type, args );
 	} else {
-		/* Default is to reopen the interface as instructed */
+		/* Default is to reopen the interface as instructed,
+		 * then send xfer_window_changed() messages to both
+		 * new child and parent interfaces.  Since our
+		 * original child interface is likely to be closed and
+		 * unplugged as a result of the call to
+		 * xfer_vreopen(), we create a temporary interface in
+		 * order to be able to send xfer_window_changed() to
+		 * the parent.
+		 */
+		intf_plug ( &tmp, dest );
 		rc = xfer_vreopen ( dest, type, args );
+		if ( rc == 0 ) {
+			xfer_window_changed ( dest );
+			xfer_window_changed ( &tmp );
+		}
+		intf_unplug ( &tmp );
 	}
 
 	if ( rc != 0 ) {