diff --git a/src/xrt/auxiliary/CMakeLists.txt b/src/xrt/auxiliary/CMakeLists.txt
index 16d2caae5..51fa0facb 100644
--- a/src/xrt/auxiliary/CMakeLists.txt
+++ b/src/xrt/auxiliary/CMakeLists.txt
@@ -111,6 +111,7 @@ set(UTIL_SOURCE_FILES
 	util/u_distortion_mesh.h
 	util/u_documentation.h
 	util/u_file.c
+	util/u_file.cpp
 	util/u_file.h
 	util/u_format.c
 	util/u_format.h
diff --git a/src/xrt/auxiliary/util/u_file.c b/src/xrt/auxiliary/util/u_file.c
index d711f5676..b40295860 100644
--- a/src/xrt/auxiliary/util/u_file.c
+++ b/src/xrt/auxiliary/util/u_file.c
@@ -104,6 +104,8 @@ u_file_open_file_in_config_dir(const char *filename, const char *mode)
 	return fopen(file_str, mode);
 }
 
+#endif
+
 char *
 u_file_read_content(FILE *file)
 {
@@ -128,5 +130,3 @@ u_file_read_content(FILE *file)
 
 	return buffer;
 }
-
-#endif
diff --git a/src/xrt/auxiliary/util/u_file.cpp b/src/xrt/auxiliary/util/u_file.cpp
new file mode 100644
index 000000000..4a2054fce
--- /dev/null
+++ b/src/xrt/auxiliary/util/u_file.cpp
@@ -0,0 +1,94 @@
+// Copyright 2019-2021, Collabora, Ltd.
+// SPDX-License-Identifier: BSL-1.0
+/*!
+ * @file
+ * @brief  Very simple file opening functions, mostly using std::filesystem for portability.
+ * @author Ryan Pavlik <ryan.pavlik@collabora.com>
+ * @author Jakob Bornecrantz <jakob@collabora.com>
+ * @author Pete Black <pblack@collabora.com>
+ * @ingroup aux_util
+ */
+
+#include "xrt/xrt_config_os.h"
+#include "util/u_file.h"
+
+#ifndef XRT_OS_LINUX
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#if __cplusplus >= 201703L
+#include <filesystem>
+namespace fs = std::filesystem;
+#else
+#define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
+#include <experimental/filesystem>
+namespace fs = std::experimental::filesystem;
+#endif
+
+static inline fs::path
+get_config_path()
+{
+#ifdef XRT_OS_WINDOWS
+	auto local_app_data = fs::path{getenv("LOCALAPPDATA")};
+	return local_app_data / "monado";
+#else
+
+	const char *xdg_home = getenv("XDG_CONFIG_HOME");
+	const char *home = getenv("HOME");
+	if (xdg_home != NULL) {
+		return fs::path(xdg_home) / "monado";
+	}
+	if (home != NULL) {
+		return fs::path(home) / "monado";
+	}
+	return {};
+#endif
+}
+ssize_t
+u_file_get_config_dir(char *out_path, size_t out_path_size)
+{
+	auto config_path = get_config_path();
+	if (config_path.empty()) {
+		return -1;
+	}
+	auto config_path_string = config_path.string();
+	return snprintf(out_path, out_path_size, "%s", config_path_string.c_str());
+}
+
+ssize_t
+u_file_get_path_in_config_dir(const char *filename, char *out_path, size_t out_path_size)
+{
+	auto config_path = get_config_path();
+	if (config_path.empty()) {
+		return -1;
+	}
+	auto path_string = (config_path / filename).string();
+	return snprintf(out_path, out_path_size, "%s", path_string.c_str());
+}
+
+FILE *
+u_file_open_file_in_config_dir(const char *filename, const char *mode)
+{
+	auto config_path = get_config_path();
+	if (config_path.empty()) {
+		return NULL;
+	}
+
+	auto file_path_string = (config_path / filename).string();
+	FILE *file = fopen(file_path_string.c_str(), mode);
+	if (file != NULL) {
+		return file;
+	}
+
+	// Try creating the path.
+	auto directory = (config_path / filename).parent_path();
+	fs::create_directories(directory);
+
+	// Do not report error.
+	return fopen(file_path_string.c_str(), mode);
+}
+
+#endif