+
+dnl Prerequisites of lib/dirfd.c.
+AC_DEFUN([gl_PREREQ_DIRFD],
+[
+ AC_CACHE_CHECK([how to get the file descriptor associated with an open DIR*],
+ [gl_cv_sys_dir_fd_member_name],
+ [
+ dirfd_save_CFLAGS=$CFLAGS
+ for ac_expr in d_fd dd_fd; do
+
+ CFLAGS="$CFLAGS -DDIR_FD_MEMBER_NAME=$ac_expr"
+ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+ #include <sys/types.h>
+ #include <dirent.h>]],
+ [[DIR *dir_p = opendir("."); (void) dir_p->DIR_FD_MEMBER_NAME;]])],
+ [dir_fd_found=yes]
+ )
+ CFLAGS=$dirfd_save_CFLAGS
+ test "$dir_fd_found" = yes && break
+ done
+ test "$dir_fd_found" = yes || ac_expr=no_such_member
+
+ gl_cv_sys_dir_fd_member_name=$ac_expr
+ ]
+ )
+ if test $gl_cv_sys_dir_fd_member_name != no_such_member; then
+ AC_DEFINE_UNQUOTED([DIR_FD_MEMBER_NAME],
+ [$gl_cv_sys_dir_fd_member_name],
+ [the name of the file descriptor member of DIR])
+ fi
+ AH_VERBATIM([DIR_TO_FD],
+ [#ifdef DIR_FD_MEMBER_NAME
+# define DIR_TO_FD(Dir_p) ((Dir_p)->DIR_FD_MEMBER_NAME)
+#else
+# define DIR_TO_FD(Dir_p) -1
+#endif
+])
+])