+extern int head_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data);
+extern int for_each_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data);
+extern int for_each_ref_in_submodule(const char *submodule, const char *prefix,
+ each_ref_fn fn, void *cb_data);
+extern int for_each_tag_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data);
+extern int for_each_branch_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data);
+extern int for_each_remote_ref_submodule(const char *submodule, each_ref_fn fn, void *cb_data);
+