--- a/ChangeLog	Fri Mar 23 13:11:28 2007 +0000
+++ b/ChangeLog	Fri Mar 23 17:33:07 2007 +0000
@@ -1,3 +1,9 @@
+2007-03-23  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* MODULES.html.sh (File system functions): New module write-any-file.
+	* modules/write-any-file, lib/write-any-file.c, lib/write-any-file.h:
+	* m4/write-any-file.m4: New files.
+
 2007-03-23  Eric Blake  <ebb9@byu.net>
 
 	* gnulib-tool: Rearrange space-tab sequences, since some editors

--- a/MODULES.html.sh	Fri Mar 23 13:11:28 2007 +0000
+++ b/MODULES.html.sh	Fri Mar 23 17:33:07 2007 +0000
@@ -2072,6 +2072,7 @@
   func_module unlinkdir
   func_module utimecmp
   func_module utimens
+  func_module write-any-file
   func_module xgetcwd
   func_module xreadlink
   func_module xreadlink-with-size

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/write-any-file.c	Fri Mar 23 17:33:07 2007 +0000
@@ -0,0 +1,59 @@
+/* Determine whether we can write any file.
+
+   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 St, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+/* Written by Paul Eggert.  */
+
+#include <config.h>
+
+#include "write-any-file.h"
+
+#if HAVE_PRIV_H
+# include <priv.h>
+#endif
+#include <unistd.h>
+
+/* Return true if we know that we can write any file, including
+   writing directories.  */
+
+bool
+can_write_any_file (void)
+{
+  static bool initialized;
+  static bool can;
+
+  if (! initialized)
+    {
+#if defined PRIV_EFFECTIVE && defined PRIV_FILE_DAC_WRITE
+      priv_set_t *pset = priv_allocset ();
+      if (pset)
+	{
+	  can =
+	    (getppriv (PRIV_EFFECTIVE, pset) == 0
+	     && priv_ismember (pset, PRIV_FILE_DAC_WRITE));
+	  priv_freeset (pset);
+	}
+      else
+#else
+      /* In traditional Unix, only root can unlink directories.  */
+      can = (geteuid () == 0);
+#endif
+      initialized = true;
+    }
+
+  return can;
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/write-any-file.h	Fri Mar 23 17:33:07 2007 +0000
@@ -0,0 +1,2 @@
+#include <stdbool.h>
+bool can_write_any_file (void);

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/m4/write-any-file.m4	Fri Mar 23 17:33:07 2007 +0000
@@ -0,0 +1,15 @@
+# Determine whether we can write any file.
+
+# Copyright (C) 2007 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.
+
+# Written by Paul Eggert.
+
+AC_DEFUN([gl_WRITE_ANY_FILE],
+[
+  AC_CHECK_HEADERS_ONCE(priv.h)
+  AC_LIBOBJ([write-any-file])
+])

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/write-any-file	Fri Mar 23 17:33:07 2007 +0000
@@ -0,0 +1,24 @@
+Description:
+Determine whether we can write any file.
+
+Files:
+lib/write-any-file.h
+lib/write-any-file.c
+m4/write-any-file.m4
+
+Depends-on:
+stdbool
+
+configure.ac:
+gl_WRITE_ANY_FILE
+
+Makefile.am:
+
+Include:
+"write-any-file.h"
+
+License:
+GPL
+
+Maintainer:
+Paul Eggert, Jim Meyering