VDI.export_changed_blocks: lock vdi_to during SMAPIv2 call

This is to avoid the VDI being attached and written to while the
VDI.export_changed_blocks SMAPIv2 call is running.

The caller has to ensure that the "sr" parameter is the SR of the second
VDI, "vdi_to".

Signed-off-by: Gabor Igloi <[email protected]>

Author: gaborigloi

ocaml/xapi/storage_impl.ml

@@ -592,9 +592,13 @@ module Wrapper = functor(Impl: Server_impl) -> struct
            Impl.VDI.disable_cbt context ~dbg ~sr ~vdi
         )
 
+    (** The [sr] parameter is the SR of VDI [vdi_to]. *)
     let export_changed_blocks context ~dbg ~sr ~vdi_from ~vdi_to =
       info "VDI.export_changed_blocks dbg:%s sr:%s vdi_from:%s vdi_to:%s" dbg sr vdi_from vdi_to;
-      Impl.VDI.export_changed_blocks context ~dbg ~sr ~vdi_from ~vdi_to
+      with_vdi sr vdi_to
+        (fun () ->
+           Impl.VDI.export_changed_blocks context ~dbg ~sr ~vdi_from ~vdi_to
+        )
 
   end