Move os-util.[ch] to basic/

parse_os_release() will be used basic/hostname-util.c later on.

src/basic/os-util.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include <stdio.h>
+
+/* The *_extension_release flavours will look for /usr/lib/extension-release/extension-release.NAME
+ * in accordance with the OS extension specification, rather than for /usr/lib/ or /etc/os-release. */
+
+bool image_name_is_valid(const char *s) _pure_;
+
+int path_is_extension_tree(const char *path, const char *extension);
+static inline int path_is_os_tree(const char *path) {
+        return path_is_extension_tree(path, NULL);
+}
+
+int open_extension_release(const char *root, const char *extension, char **ret_path, int *ret_fd);
+static inline int open_os_release(const char *root, char **ret_path, int *ret_fd) {
+        return open_extension_release(root, NULL, ret_path, ret_fd);
+}
+
+int fopen_extension_release(const char *root, const char *extension, char **ret_path, FILE **ret_file);
+static inline int fopen_os_release(const char *root, char **ret_path, FILE **ret_file) {
+        return fopen_extension_release(root, NULL, ret_path, ret_file);
+}
+
+int parse_extension_release(const char *root, const char *extension, ...) _sentinel_;
+int parse_os_release(const char *root, ...) _sentinel_;
+int load_extension_release_pairs(const char *root, const char *extension, char ***ret);
+int load_os_release_pairs(const char *root, char ***ret);
+int load_os_release_pairs_with_prefix(const char *root, const char *prefix, char ***ret);