Try to use FetchContent to install ckf ported from Belle.

CMakeLists.txt

@@ -29,6 +29,7 @@ endif()
 
 list(PREPEND CMAKE_MODULE_PATH $ENV{PANDORAPFA}/cmakemodules)
 list(PREPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake") # (Find*.cmake)
+include(cmake/CEPCSWOptions.cmake)
 include(cmake/CEPCSWDependencies.cmake)
 
 add_subdirectory(Analysis)

cmake/CEPCSWOptions.cmake

+# Define necessary options
+
+##############################################################################
+## CKF Belle
+##############################################################################
+
+option(CEPCSW_USE_SYSTEM_CKF_BELLE 
+       "Use the existing installation of CKF BELLE"
+       TRUE)
+
+if (CEPCSW_USE_SYSTEM_CKF_BELLE)
+  message("Try to use an existing installation of CKF BELLE")
+else()
+  message("Try to use an internal installation of CKF BELLE")
+
+  include(FetchContent)
+
+  FetchContent_Declare(
+    ckf_belle
+    GIT_REPOSITORY https://code.ihep.ac.cn/cepc/externals/ckf_belle.git
+    GIT_TAG        11624a552a9d2382bba3ce9ed9b0cf2d05a89b6e
+  )
+
+  FetchContent_MakeAvailable(ckf_belle)
+endif()