--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,17 @@
 2009-09-19  Eric Blake  <ebb9@byu.net>
 
+	unlink: new module, for Solaris 9 bug
+	* modules/unlink: New file.
+	* lib/unlink.c: Likewise.
+	* m4/unlink.m4 (gl_FUNC_UNLINK): Likewise.
+	* m4/unistd_h.m4 (gl_UNISTD_H_DEFAULTS): Add witnesses.
+	* modules/unistd (Makefile.am): Use them.
+	* lib/unistd.in.h (stat): Declare replacement.
+	* MODULES.html.sh (systems lacking POSIX:2008): Mention module.
+	* doc/posix-functions/unlink.texi (unlink): Likewise.
+	* modules/unlink-tests: New test.
+	* tests/test-unlink.c: Likewise.
+
 	lstat: fix Solaris 9 bug
 	* lib/lstat.c (lstat): Also check for trailing slash on
 	non-symlink, non-directories.  Use stat module to simplify logic.

--- a/MODULES.html.sh
+++ b/MODULES.html.sh
@@ -2359,6 +2359,7 @@
   func_module sys_wait
   func_module tsearch
   func_module unistd
+  func_module unlink
   func_module utime
   func_module vasnprintf-posix
   func_module vasprintf-posix

--- a/doc/posix-functions/unlink.texi
+++ b/doc/posix-functions/unlink.texi
@@ -4,15 +4,28 @@
 
 POSIX specification: @url{http://www.opengroup.org/onlinepubs/9699919799/functions/unlink.html}
 
-Gnulib module: ---
+Gnulib module: unlink
 
 Portability problems fixed by Gnulib:
 @itemize
+@item
+Some systems mistakenly succeed on @code{unlink("file/")}:
+Solaris 9.
 @end itemize
 
 Portability problems not fixed by Gnulib:
 @itemize
 @item
+Some systems allow a superuser to unlink directories, even though this
+can cause file system corruption.  The error given if a process is not
+permitted to unlink directories varies across implementations; it is
+not always the POSIX value of @code{EPERM}.  Meanwhile, if a process
+has the ability to unlink directories, POSIX requires that
+@code{unlink("symlink-to-dir/")} remove @file{dir} and leave
+@file{symlink-to-dir} dangling; this behavior is counter-intuitive.
+The gnulib module unlinkdir can help determine whether code must be
+cautious of unlinking directories.
+@item
 Removing an open file is non-portable: On Unix this allows the programs that
 have the file already open to continue working with it; the file's storage
 is only freed when the no process has the file open any more.  On Windows,

--- a/lib/unistd.in.h
+++ b/lib/unistd.in.h
@@ -164,6 +164,21 @@
 #endif
 
 
+#if @GNULIB_UNLINK@
+# if @REPLACE_UNLINK@
+#  undef unlink
+#  define unlink rpl_unlink
+extern int unlink (char const *file);
+# endif
+#elif defined GNULIB_POSIXCHECK
+# undef unlink
+# define unlink(n)                         \
+    (GL_LINK_WARNING ("unlink is not portable - " \
+                      "use gnulib module unlink for portability"), \
+     unlink (n))
+#endif
+
+
 #if @GNULIB_UNLINKAT@
 # if !@HAVE_UNLINKAT@
 extern int unlinkat (int fd, char const *file, int flag);

new file mode 100644
--- /dev/null
+++ b/lib/unlink.c
@@ -0,0 +1,85 @@
+/* Work around unlink bugs.
+
+   Copyright (C) 2009 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 3 of the License, 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, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#include <unistd.h>
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+
+#undef unlink
+
+/* Remove file NAME.
+   Return 0 if successful, -1 if not.  */
+
+int
+rpl_unlink (char const *name)
+{
+  /* Work around Solaris 9 bug where unlink("file/") succeeds.  */
+  size_t len = strlen (name);
+  int result = 0;
+  if (len && ISSLASH (name[len - 1]))
+    {
+      /* We can't unlink(2) something if it doesn't exist.  If it does
+	 exist, then it resolved to a directory, due to the trailing
+	 slash, and POSIX requires that the unlink attempt to remove
+	 that directory (which would leave the symlink dangling).
+	 Unfortunately, Solaris 9 is one of the platforms where the
+	 root user can unlink directories, and we don't want to
+	 cripple this behavior on real directories, even if it is
+	 seldom needed (at any rate, it's nicer to let coreutils'
+	 unlink(1) give the correct errno for non-root users).  But we
+	 don't know whether name was an actual directory, or a symlink
+	 to a directory; and due to the bug of ignoring trailing
+	 slash, Solaris 9 would end up successfully unlinking the
+	 symlink instead of the directory.  Technically, we could use
+	 realpath to find the canonical directory name to attempt
+	 deletion on.  But that is a lot of work for a corner case; so
+	 we instead just use an lstat on the shortened name, and
+	 reject symlinks with trailing slashes.  The root user of
+	 unlink(1) will just have to live with the rule that they
+	 can't delete a directory via a symlink.  */
+      struct stat st;
+      result = lstat (name, &st);
+      if (result == 0)
+	{
+	  /* Trailing NUL will overwrite the trailing slash.  */
+	  char *short_name = malloc (len);
+	  if (!short_name)
+	    {
+	      errno = EPERM;
+	      return -1;
+	    }
+	  memcpy (short_name, name, len);
+	  while (len && ISSLASH (short_name[len - 1]))
+	    short_name[--len] = '\0';
+	  if (len && (lstat (short_name, &st) || S_ISLNK (st.st_mode)))
+	    {
+	      free (short_name);
+	      errno = EPERM;
+	      return -1;
+	    }
+	  free (short_name);
+	}
+    }
+  if (!result)
+    result = unlink (name);
+  return result;
+}

--- a/m4/unistd_h.m4
+++ b/m4/unistd_h.m4
@@ -1,4 +1,4 @@
-# unistd_h.m4 serial 27
+# unistd_h.m4 serial 28
 dnl Copyright (C) 2006-2009 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -61,6 +61,7 @@
   GNULIB_SYMLINKAT=0;        AC_SUBST([GNULIB_SYMLINKAT])
   GNULIB_UNISTD_H_GETOPT=0;  AC_SUBST([GNULIB_UNISTD_H_GETOPT])
   GNULIB_UNISTD_H_SIGPIPE=0; AC_SUBST([GNULIB_UNISTD_H_SIGPIPE])
+  GNULIB_UNLINK=0;           AC_SUBST([GNULIB_UNLINK])
   GNULIB_UNLINKAT=0;         AC_SUBST([GNULIB_UNLINKAT])
   GNULIB_WRITE=0;            AC_SUBST([GNULIB_WRITE])
   dnl Assume proper GNU behavior unless another module says otherwise.
@@ -99,6 +100,7 @@
   REPLACE_LINK=0;         AC_SUBST([REPLACE_LINK])
   REPLACE_LSEEK=0;        AC_SUBST([REPLACE_LSEEK])
   REPLACE_RMDIR=0;        AC_SUBST([REPLACE_RMDIR])
+  REPLACE_UNLINK=0;       AC_SUBST([REPLACE_UNLINK])
   REPLACE_WRITE=0;        AC_SUBST([REPLACE_WRITE])
   UNISTD_H_HAVE_WINSOCK2_H=0; AC_SUBST([UNISTD_H_HAVE_WINSOCK2_H])
   UNISTD_H_HAVE_WINSOCK2_H_AND_USE_SOCKETS=0;

new file mode 100644
--- /dev/null
+++ b/m4/unlink.m4
@@ -0,0 +1,27 @@
+# unlink.m4 serial 1
+dnl Copyright (C) 2009 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_UNLINK],
+[
+  AC_REQUIRE([gl_AC_DOS])
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  dnl Detect Solaris 9 bug.
+  AC_CACHE_CHECK([whether unlink honors trailing slashes],
+    [gl_cv_func_unlink_works],
+    [touch conftest.file
+     AC_RUN_IFELSE(
+       [AC_LANG_PROGRAM(
+         [[#include <stdio.h>
+           #include <errno.h>
+]], [[return !unlink ("conftest.file/") || errno != ENOTDIR;]])],
+      [gl_cv_func_unlink_works=yes], [gl_cv_func_unlink_works=no],
+      [gl_cv_func_unlink_works="guessing no"])
+     rm -f conftest.file])
+  if test x"$gl_cv_func_unlink_works" != xyes; then
+    REPLACE_UNLINK=1
+    AC_LIBOBJ([unlink])
+  fi
+])

--- a/modules/unistd
+++ b/modules/unistd
@@ -54,6 +54,7 @@
 	      -e 's|@''GNULIB_SYMLINKAT''@|$(GNULIB_SYMLINKAT)|g' \
 	      -e 's|@''GNULIB_UNISTD_H_GETOPT''@|$(GNULIB_UNISTD_H_GETOPT)|g' \
 	      -e 's|@''GNULIB_UNISTD_H_SIGPIPE''@|$(GNULIB_UNISTD_H_SIGPIPE)|g' \
+	      -e 's|@''GNULIB_UNLINK''@|$(GNULIB_UNLINK)|g' \
 	      -e 's|@''GNULIB_UNLINKAT''@|$(GNULIB_UNLINKAT)|g' \
 	      -e 's|@''GNULIB_WRITE''@|$(GNULIB_WRITE)|g' \
 	      -e 's|@''HAVE_DUP2''@|$(HAVE_DUP2)|g' \
@@ -91,6 +92,7 @@
 	      -e 's|@''REPLACE_LINK''@|$(REPLACE_LINK)|g' \
 	      -e 's|@''REPLACE_LSEEK''@|$(REPLACE_LSEEK)|g' \
 	      -e 's|@''REPLACE_RMDIR''@|$(REPLACE_RMDIR)|g' \
+	      -e 's|@''REPLACE_UNLINK''@|$(REPLACE_UNLINK)|g' \
 	      -e 's|@''REPLACE_WRITE''@|$(REPLACE_WRITE)|g' \
 	      -e 's|@''UNISTD_H_HAVE_WINSOCK2_H''@|$(UNISTD_H_HAVE_WINSOCK2_H)|g' \
 	      -e 's|@''UNISTD_H_HAVE_WINSOCK2_H_AND_USE_SOCKETS''@|$(UNISTD_H_HAVE_WINSOCK2_H_AND_USE_SOCKETS)|g' \

new file mode 100644
--- /dev/null
+++ b/modules/unlink
@@ -0,0 +1,26 @@
+Description:
+unlink(): remove a file.
+
+Files:
+lib/unlink.c
+m4/dos.m4
+m4/unlink.m4
+
+Depends-on:
+lstat
+unistd
+
+configure.ac:
+gl_FUNC_UNLINK
+gl_UNISTD_MODULE_INDICATOR([unlink])
+
+Makefile.am:
+
+Include:
+<unistd.h>
+
+License:
+LGPL
+
+Maintainer:
+Eric Blake

new file mode 100644
--- /dev/null
+++ b/modules/unlink-tests
@@ -0,0 +1,12 @@
+Files:
+tests/test-unlink.c
+
+Depends-on:
+unlinkdir
+
+configure.ac:
+AC_CHECK_FUNCS_ONCE([symlink])
+
+Makefile.am:
+TESTS += test-unlink
+check_PROGRAMS += test-unlink

new file mode 100644
--- /dev/null
+++ b/tests/test-unlink.c
@@ -0,0 +1,110 @@
+/* Tests of unlink.
+   Copyright (C) 2009 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 3 of the License, 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, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Eric Blake <ebb9@byu.net>, 2009.  */
+
+#include <config.h>
+
+#include <unistd.h>
+
+#include <fcntl.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+
+#include "unlinkdir.h"
+
+#if !HAVE_SYMLINK
+# define symlink(a,b) (-1)
+#endif
+
+#define ASSERT(expr) \
+  do                                                                         \
+    {                                                                        \
+      if (!(expr))                                                           \
+	{                                                                    \
+	  fprintf (stderr, "%s:%d: assertion failed\n", __FILE__, __LINE__);  \
+	  fflush (stderr);                                                   \
+	  abort ();                                                          \
+	}                                                                    \
+    }                                                                        \
+  while (0)
+
+#define BASE "test-unlink.t"
+
+int
+main ()
+{
+  /* Remove any leftovers from a previous partial run.  */
+  ASSERT (system ("rm -rf " BASE "*") == 0);
+
+  /* Setup.  */
+  ASSERT (mkdir (BASE "dir", 0700) == 0);
+  ASSERT (close (creat (BASE "dir/file", 0600)) == 0);
+
+  /* Basic error conditions.  */
+  errno = 0;
+  ASSERT (unlink ("") == -1);
+  ASSERT (errno == ENOENT);
+  errno = 0;
+  ASSERT (unlink (BASE "nosuch") == -1);
+  ASSERT (errno == ENOENT);
+  errno = 0;
+  ASSERT (unlink (BASE "nosuch/") == -1);
+  ASSERT (errno == ENOENT);
+  /* Resulting errno after directories is rather varied across
+     implementations (EPERM, EINVAL, EACCES, EBUSY, EISDIR, ENOTSUP);
+     however, we must be careful to not attempt unlink on a directory
+     unless we know it must fail.  */
+  if (cannot_unlink_dir ())
+    {
+      ASSERT (unlink (".") == -1);
+      ASSERT (unlink ("..") == -1);
+      ASSERT (unlink ("/") == -1);
+      ASSERT (unlink (BASE "dir") == -1);
+      ASSERT (mkdir (BASE "dir1", 0700) == 0);
+      ASSERT (unlink (BASE "dir1") == -1);
+      ASSERT (rmdir (BASE "dir1") == 0);
+    }
+  errno = 0;
+  ASSERT (unlink (BASE "dir/file/") == -1);
+  ASSERT (errno == ENOTDIR);
+
+  /* Test symlink behavior.  Specifying trailing slash will attempt
+     unlink of a directory, so only attempt it if we know it must
+     fail.  */
+  if (symlink (BASE "dir", BASE "link") != 0)
+    {
+      ASSERT (unlink (BASE "dir/file") == 0);
+      ASSERT (rmdir (BASE "dir") == 0);
+      fputs ("skipping test: symlinks not supported on this filesystem\n",
+             stderr);
+      return 77;
+    }
+  if (cannot_unlink_dir ())
+    ASSERT (unlink (BASE "link/") == -1);
+  ASSERT (unlink (BASE "link") == 0);
+  ASSERT (symlink (BASE "dir/file", BASE "link") == 0);
+  /* Order here proves unlink of a symlink does not follow through to
+     the file.  */
+  ASSERT (unlink (BASE "link") == 0);
+  ASSERT (unlink (BASE "dir/file") == 0);
+  ASSERT (rmdir (BASE "dir") == 0);
+
+  return 0;
+}