--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2007-04-13  Bruno Haible  <bruno@clisp.org>
+
+	* modules/fbufmode: New file.
+	* lib/fbufmode.h: New file.
+	* lib/fbufmode.c: New file.
+	* m4/fbufmode.m4: New file.
+
 2007-04-13  Bruno Haible  <bruno@clisp.org>
 
 	* modules/fwritable-tests: New file.

new file mode 100644
--- /dev/null
+++ b/lib/fbufmode.c
@@ -0,0 +1,64 @@
+/* Retrieve information about a FILE stream.
+   Copyright (C) 2007 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License along
+   with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include "fbufmode.h"
+
+#if HAVE___FLBF
+# include <stdio_ext.h>
+#endif
+
+int
+fbufmode (FILE *fp)
+{
+  /* Most systems provide FILE as a struct and the necessary bitmask in
+     <stdio.h>, because they need it for implementing getc() and putc() as
+     fast macros.  */
+#if defined _IO_ferror_unlocked     /* GNU libc, BeOS */
+# if HAVE___FLBF                    /* glibc >= 2.2 */
+  if (__flbf (fp))
+    return _IOLBF;
+# else
+  if (fp->_flags & _IO_LINE_BUF)
+    return _IOLBF;
+# endif
+  if (fp->_flags & _IO_UNBUFFERED)
+    return _IONBF;
+  return _IOFBF;
+#elif defined __sferror             /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
+  if (fp->_flags & __SLBF)
+    return _IOLBF;
+  if (fp->_flags & __SNBF)
+    return _IONBF;
+  return _IOFBF;
+#elif defined _IOERR                /* AIX, HP-UX, IRIX, OSF/1, Solaris, mingw */
+# if HAVE___FLBF                    /* Solaris >= 7 */
+  if (__flbf (fp))
+    return _IOLBF;
+# else
+  if (fp->_flag & _IOLBF)
+    return _IOLBF;
+# endif
+  if (fp->_flag & _IONBF)
+    return _IONBF;
+  return _IOFBF;
+#else
+ #error "Please port gnulib fbufmode.c to your platform! Look at the setvbuf implementation."
+#endif
+}

new file mode 100644
--- /dev/null
+++ b/lib/fbufmode.h
@@ -0,0 +1,37 @@
+/* Retrieve information about a FILE stream.
+   Copyright (C) 2007 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License along
+   with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#include <stdio.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Return the buffering mode of the stream STREAM.
+
+   Result    means
+   ------   -------
+   _IONBF  unbuffered
+   _IOLBF  line buffered
+   _IOFBF  fully buffered
+
+   STREAM must not be wide-character oriented.  */
+extern int fbufmode (FILE *stream);
+
+#ifdef __cplusplus
+}
+#endif

new file mode 100644
--- /dev/null
+++ b/m4/fbufmode.m4
@@ -0,0 +1,11 @@
+# fbufmode.m4 serial 1
+dnl Copyright (C) 2007 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_FBUFMODE],
+[
+  dnl Prerequisites of lib/fbufmode.c.
+  AC_CHECK_FUNCS_ONCE([__flbf])
+])

new file mode 100644
--- /dev/null
+++ b/modules/fbufmode
@@ -0,0 +1,25 @@
+Description:
+fbufmode() function: Determine the buffering mode of a FILE stream.
+
+Files:
+lib/fbufmode.h
+lib/fbufmode.c
+m4/fbufmode.m4
+
+Depends-on:
+
+configure.ac:
+gl_FUNC_FBUFMODE
+
+Makefile.am:
+lib_SOURCES += fbufmode.c
+
+Include:
+"fbufmode.h"
+
+License:
+LGPL
+
+Maintainer:
+Bruno Haible, Eric Blake
+