Integrate QCOW2 import-export

ocaml/xapi/export_raw_vdi.ml

@@ -49,7 +49,7 @@ let localhost_handler rpc session_id vdi (req : Http.Request.t)
               debug "Copying VDI contents..." ;
               match format with
               | Qcow ->
-                  Qcow_tool_wrapper.send
+                  Qcow_tool_wrapper.send ?relative_to:base_path
                     (Qcow_tool_wrapper.update_task_progress __context)
                     s path size
               | Vhd | Tar | Raw ->

ocaml/xapi/qcow_tool_wrapper.ml

@@ -50,7 +50,9 @@ let receive (progress_cb : int -> unit) (unix_fd : Unix.file_descr)
   debug "Calling Qcow_stream.stream_decode (output_path = '%s')" path ;
   Qcow_stream.stream_decode ~progress_cb unix_fd path
 
-let send (progress_cb : int -> unit) (unix_fd : Unix.file_descr) (path : string)
-    (_size : Int64.t) =
-  let args = [path] in
+let send ?relative_to (progress_cb : int -> unit) (unix_fd : Unix.file_descr)
+    (path : string) (_size : Int64.t) =
+  let args =
+    [path] @ match relative_to with None -> [] | Some vdi -> ["--diff"; vdi]
+  in
   run_qcow_tool progress_cb args unix_fd

ocaml/xapi/qcow_tool_wrapper.mli

@@ -0,0 +1,25 @@
+(*
+ * Copyright (C) 2025 Vates.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *)
+
+val update_task_progress : Context.t -> int -> unit
+
+val receive : (int -> unit) -> Unix.file_descr -> string -> unit
+
+val send :
+     ?relative_to:string
+  -> (int -> unit)
+  -> Unix.file_descr
+  -> string
+  -> int64
+  -> unit