ttm_ref_object_add
ret = ttm_ref_object_add(tfile, base, NULL, false);
ret = ttm_ref_object_add(tfile, base, NULL, false);
extern int ttm_ref_object_add(struct ttm_object_file *tfile,
ret = ttm_ref_object_add(vmw_fp->tfile, base,
ret = ttm_ref_object_add(tfile, base, NULL, require_exist);
ret = ttm_ref_object_add(tfile, base, NULL, false);