when creating the tarball, only include the packages folder, repo and version

fixes #29

mirage/unikernel.ml

@@ -640,6 +640,13 @@ module Make
     let entries_of_git ~mtime store repo urls =
       let entries = Git.contents store in
       let to_entry path =
+        match Mirage_kv.Key.segments path with
+        (* from opam source code, src/repository/opamHTTP.ml:
+           include only three top-level dirs/files: packages, version, repo *)
+        | "packages" :: _
+        | "version" :: _
+        | "repo" :: _ ->
+          begin
             Store.get store path >|= function
             | Ok data ->
               let data =
@@ -655,7 +662,10 @@ module Make
                   (Mirage_kv.Key.to_string path) (Int64.of_int size) in
               urls := Git.find_urls !urls path data;
               Some (Some Tar.Header.Ustar, hdr, once data)
-        | Error _ -> None in
+            | Error _ -> None
+          end
+        | _ -> Lwt.return None
+      in
       let entries = Lwt_stream.filter_map_s to_entry entries in
       Lwt.return begin fun () -> Tar.High (High.inj (Lwt_stream.get entries >|= Result.ok)) end