[bug-gnulib] new unlinkdir module for gnulib

[Paul Eggert]

I installed this, imported from coreutils.  It addresses the issue
that `unlink ("directory")' works on some hosts (e.g., Solaris,
OpenBSD) but not others (e.g., GNU/Linux, FreeBSD).  Solaris 10 has a
new wrinkle: you can add/remove the privilege of unlinking a
directory.

2005-05-14  Paul Eggert  <address@hidden>

        New unlinkdir module.
        * MODULES.html.sh (File system functions): Add unlinkdir.
        * lib/unlinkdir.c, lib/unlinkdir.h, m4/unlinkdir.m4, modules/unlinkdir:
        New file.

Index: MODULES.html.sh
===================================================================
RCS file: /cvsroot/gnulib/gnulib/MODULES.html.sh,v
retrieving revision 1.81
diff -p -u -r1.81 MODULES.html.sh
--- MODULES.html.sh     14 May 2005 06:03:57 -0000      1.81
+++ MODULES.html.sh     15 May 2005 06:07:19 -0000
@@ -1826,6 +1826,7 @@ func_all_modules ()
   func_module same
   func_module save-cwd
   func_module savedir
+  func_module unlinkdir
   func_module utimecmp
   func_module utimens
   func_module xgetcwd
--- /dev/null   2003-03-18 13:55:57 -0800
+++ lib/unlinkdir.c     2005-05-14 22:53:47 -0700
@@ -0,0 +1,70 @@
+/* unlinkdir.c - determine (and maybe change) whether we can unlink directories
+
+   Copyright (C) 2005 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 and Jim Meyering.  */
+
+#include <config.h>
+
+#include "unlinkdir.h"
+
+#if HAVE_PRIV_H
+# include <priv.h>
+#endif
+#if HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+
+#if ! UNLINK_CANNOT_UNLINK_DIR
+
+/* Return true if we cannot unlink directories, false if we might be
+   able to unlink directories.  If possible, tell the kernel we don't
+   want to be able to unlink directories, so that we can return true.  */
+
+bool
+cannot_unlink_dir (void)
+{
+  static bool initialized;
+  static bool cannot;
+
+  if (! initialized)
+    {
+# if defined PRIV_EFFECTIVE && defined PRIV_SYS_LINKDIR
+      /* We might be able to unlink directories if we cannot
+        determine our privileges, or if we have the
+        PRIV_SYS_LINKDIR privilege and cannot delete it.  */
+      priv_set_t *pset = priv_allocset ();
+      if (pset)
+       {
+         cannot =
+           (getppriv (PRIV_EFFECTIVE, pset) == 0
+            && (! priv_ismember (pset, PRIV_SYS_LINKDIR)
+                || (priv_delset (pset, PRIV_SYS_LINKDIR) == 0
+                    && setppriv (PRIV_SET, PRIV_EFFECTIVE, pset) == 0)));
+         priv_freeset (pset);
+       }
+# else
+      /* In traditional Unix, only root can unlink directories.  */
+      cannot = (geteuid () != 0);
+# endif
+      initialized = true;
+    }
+
+  return cannot;
+}
+
+#endif
--- /dev/null   2003-03-18 13:55:57 -0800
+++ lib/unlinkdir.h     2005-05-14 21:51:47 -0700
@@ -0,0 +1,27 @@
+/* unlinkdir.h - determine (and maybe change) whether we can unlink directories
+
+   Copyright (C) 2005 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 and Jim Meyering.  */
+
+#include <stdbool.h>
+
+#if UNLINK_CANNOT_UNLINK_DIR
+static bool cannot_unlink_dir (void) { return true; }
+#else
+bool cannot_unlink_dir (void);
+#endif
--- /dev/null   2003-03-18 13:55:57 -0800
+++ m4/unlinkdir.m4     2005-05-14 21:51:54 -0700
@@ -0,0 +1,34 @@
+#serial 2
+
+# Copyright (C) 2005 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_UNLINKDIR],
+[
+  AC_REQUIRE([AC_CANONICAL_HOST])
+  AC_CHECK_HEADERS_ONCE(priv.h unistd.h)
+
+  AC_LIBSOURCES([unlinkdir.c, unlinkdir.h])
+  AC_LIBOBJ([unlinkdir])
+
+  # The Hurd, the Linux kernel, the FreeBSD kernel version 2.2 and later,
+  # and Cygwin never let anyone (even root) unlink directories.
+  # If anyone knows of another system for which unlink can never
+  # remove a directory, please report it to <address@hidden>.
+  # Unfortunately this is difficult to test for, since it requires root access
+  # and might create garbage in the file system,
+  # so the code below simply relies on the kernel name and version number.
+  case $host in
+  *-*-gnu[0-9]* | \
+  *-*-linux-* | *-*-linux | \
+  *-*-freebsd2.2* | *-*-freebsd[3-9]* | *-*-freebsd[1-9][0-9]* | \
+  *-cygwin)
+    AC_DEFINE([UNLINK_CANNOT_UNLINK_DIR], 1,
+      [Define to 1 if unlink (dir) cannot possibly succeed.]);;
+  esac
+])
--- /dev/null   2003-03-18 13:55:57 -0800
+++ modules/unlinkdir   2005-05-14 21:54:20 -0700
@@ -0,0 +1,24 @@
+Description:
+Determine (and maybe change) whether we can unlink directories.
+
+Files:
+lib/unlinkdir.h
+lib/unlinkdir.c
+m4/unlinkdir.m4
+
+Depends-on:
+stdbool
+
+configure.ac:
+gl_UNLINKDIR
+
+Makefile.am:
+
+Include:
+"unlinkdir.h"
+
+License:
+GPL
+
+Maintainer:
+Paul Eggert, Jim Meyering