dirfd.m4

gnu tar 源码包。 tar 软件是 Unix 系统下的一个打包软件

#serial 14   -*- Autoconf -*-

dnl Find out how to get the file descriptor associated with an open DIR*.

# Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006 Free Software
# Foundation, Inc.
# This file is free software; the Free Software Foundation
# gives unlimited permission to copy and/or distribute it,
# with or without modifications, as long as this notice is preserved.

dnl From Jim Meyering

AC_DEFUN([gl_FUNC_DIRFD],
[
  dnl Work around a bug of AC_EGREP_CPP in autoconf-2.57.
  AC_REQUIRE([AC_PROG_CPP])
  AC_REQUIRE([AC_PROG_EGREP])
  AC_CHECK_FUNCS(dirfd)
  AC_CHECK_DECLS([dirfd], , ,
    [#include <sys/types.h>
     #include <dirent.h>])

  AC_CACHE_CHECK([whether dirfd is a macro],
    gl_cv_func_dirfd_macro,
    [AC_EGREP_CPP([dirent_header_defines_dirfd], [
#include <sys/types.h>
#include <dirent.h>
#ifdef dirfd
 dirent_header_defines_dirfd
#endif],
       gl_cv_func_dirfd_macro=yes,
       gl_cv_func_dirfd_macro=no)])

  # Use the replacement only if we have no function, macro,
  # or declaration with that name.
  if test $ac_cv_func_dirfd,$ac_cv_have_decl_dirfd,$gl_cv_func_dirfd_macro \
      = no,no,no; then
    AC_REPLACE_FUNCS([dirfd])
    AC_CACHE_CHECK(
	      [how to get the file descriptor associated with an open DIR*],
		   gl_cv_sys_dir_fd_member_name,
      [
	dirfd_save_CFLAGS=$CFLAGS
	for ac_expr in d_fd dd_fd; do

	  CFLAGS="$CFLAGS -DDIR_FD_MEMBER_NAME=$ac_expr"
	  AC_TRY_COMPILE(
	    [#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
])
  fi
])