--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,17 @@
 2009-11-14  Eric Blake  <ebb9@byu.net>
 
+	openat: detect Solaris fchownat bug
+	* lib/fchownat.c (rpl_fchownat): Work around Solaris bug.  Avoid
+	penalizing glibc chownat when only lchownat is broken.
+	* m4/openat.m4 (gl_FUNC_FCHOWNAT): Replace fchownat if there are
+	trailing slash bugs.
+	* doc/posix-functions/fchownat.texi (fchownat): Document the bug.
+	* modules/openat-tests (Files): Include more files.
+	(Depends-on): Add mgetgroups, sleep, stat-time.
+	(configure.ac): Add additional checks.
+	(Makefile.am): Build new test.
+	* tests/test-fchownat.c: New file.
+
 	lchown: detect Solaris and FreeBSD bug
 	* lib/lchown.c (rpl_lchown): Work around bug.
 	* m4/lchown.m4 (gl_FUNC_LCHOWN): Check for trailing slash bugs.

--- a/doc/posix-functions/fchownat.texi
+++ b/doc/posix-functions/fchownat.texi
@@ -9,10 +9,21 @@
 Portability problems fixed by Gnulib:
 @itemize
 @item
+Some platforms fail to detect trailing slash on non-directories, as in
+@code{fchown(dir,"link-to-file/",uid,gid,flag)}:
+Solaris 9.
+@item
+Some platforms mistakenly dereference symlinks when using
+@code{AT_SYMLINK_NOFOLLOW}:
+Linux kernel 2.6.17.
+@item
 This function is missing on some platforms:
 glibc 2.3.6, MacOS X 10.3, FreeBSD 6.0, NetBSD 3.0, OpenBSD 3.8, AIX
 5.1, HP-UX 11, IRIX 6.5, OSF/1 5.1, Cygwin 1.5.x, mingw, Interix 3.5, BeOS.
-But the replacement function is not safe to be used in libraries and is not multithread-safe.
+But the replacement function is not safe to be used in libraries and
+is not multithread-safe.  Also, the replacement may fail to change
+symlinks if @code{lchown} is unsupported, or fail altogether if
+@code{chown} is unsupported.
 @end itemize
 
 Portability problems not fixed by Gnulib:

--- a/lib/fchownat.c
+++ b/lib/fchownat.c
@@ -25,6 +25,13 @@
 
 #include <unistd.h>
 
+#include <errno.h>
+#include <string.h>
+
+#include "openat.h"
+
+#if !HAVE_FCHOWNAT
+
 /* Replacement for Solaris' function by the same name.
    Invoke chown or lchown on file, FILE, using OWNER and GROUP, in the
    directory open on descriptor FD.  If FLAG is AT_SYMLINK_NOFOLLOW, then
@@ -33,10 +40,68 @@
    then (chown|lchown)/restore_cwd.  If either the save_cwd or the
    restore_cwd fails, then give a diagnostic and exit nonzero.  */
 
-#define AT_FUNC_NAME fchownat
-#define AT_FUNC_F1 lchown
-#define AT_FUNC_F2 chown
-#define AT_FUNC_USE_F1_COND AT_SYMLINK_NOFOLLOW
-#define AT_FUNC_POST_FILE_PARAM_DECLS , uid_t owner, gid_t group, int flag
-#define AT_FUNC_POST_FILE_ARGS        , owner, group
-#include "at-func.c"
+# define AT_FUNC_NAME fchownat
+# define AT_FUNC_F1 lchown
+# define AT_FUNC_F2 chown
+# define AT_FUNC_USE_F1_COND AT_SYMLINK_NOFOLLOW
+# define AT_FUNC_POST_FILE_PARAM_DECLS , uid_t owner, gid_t group, int flag
+# define AT_FUNC_POST_FILE_ARGS        , owner, group
+# include "at-func.c"
+# undef AT_FUNC_NAME
+# undef AT_FUNC_F1
+# undef AT_FUNC_F2
+# undef AT_FUNC_USE_F1_COND
+# undef AT_FUNC_POST_FILE_PARAM_DECLS
+# undef AT_FUNC_POST_FILE_ARGS
+
+#else /* HAVE_FCHOWNAT */
+
+# undef fchownat
+
+# if FCHOWNAT_NOFOLLOW_BUG
+
+/* Failure to handle AT_SYMLINK_NOFOLLOW requires the /proc/self/fd or
+   fchdir workaround to call lchown for lchownat, but there is no need
+   to penalize chownat.  */
+static int
+local_lchownat (int fd, char const *file, uid_t owner, gid_t group);
+
+# define AT_FUNC_NAME local_lchownat
+# define AT_FUNC_F1 lchown
+# define AT_FUNC_POST_FILE_PARAM_DECLS , uid_t owner, gid_t group
+# define AT_FUNC_POST_FILE_ARGS        , owner, group
+# include "at-func.c"
+# undef AT_FUNC_NAME
+# undef AT_FUNC_F1
+# undef AT_FUNC_POST_FILE_PARAM_DECLS
+# undef AT_FUNC_POST_FILE_ARGS
+
+# endif
+
+/* Work around bugs with trailing slash, using the same workarounds as
+   chown and lchown.  */
+
+int
+rpl_fchownat (int fd, char const *file, uid_t owner, gid_t group, int flag)
+{
+# if FCHOWNAT_NOFOLLOW_BUG
+  if (flag == AT_SYMLINK_NOFOLLOW)
+    return local_lchownat (fd, file, owner, group);
+# endif
+# if CHOWN_TRAILING_SLASH_BUG
+  {
+    size_t len = strlen (file);
+    struct stat st;
+    if (len && file[len - 1] == '/')
+      {
+        if (statat (fd, file, &st))
+          return -1;
+        if (flag == AT_SYMLINK_NOFOLLOW)
+          return fchownat (fd, file, owner, group, 0);
+      }
+  }
+# endif
+  return fchownat (fd, file, owner, group, flag);
+}
+
+#endif /* HAVE_FCHOWNAT */

--- a/m4/openat.m4
+++ b/m4/openat.m4
@@ -1,4 +1,4 @@
-# serial 25
+# serial 26
 # See if we need to use our replacement for Solaris' openat et al functions.
 
 dnl Copyright (C) 2004-2009 Free Software Foundation, Inc.
@@ -102,9 +102,15 @@
 # Also use the replacement function if fchownat is simply not available.
 AC_DEFUN([gl_FUNC_FCHOWNAT],
 [
+  AC_REQUIRE([gl_FUNC_CHOWN])
   AC_CHECK_FUNC([fchownat],
-    [gl_FUNC_FCHOWNAT_DEREF_BUG([REPLACE_FCHOWNAT=1])],
+    [gl_FUNC_FCHOWNAT_DEREF_BUG([REPLACE_FCHOWNAT=1
+      AC_DEFINE([FCHOWNAT_NOFOLLOW_BUG], [1], [Define to 1 if your
+      platform has fchownat, but it cannot perform lchown tasks.])])],
     [HAVE_FCHOWNAT=0])
+  if test $REPLACE_CHOWN = 1; then
+    REPLACE_FCHOWNAT=1
+  fi
   if test $HAVE_FCHOWNAT = 0 || test $REPLACE_FCHOWNAT = 1; then
     AC_LIBOBJ([fchownat])
   fi

--- a/modules/openat-tests
+++ b/modules/openat-tests
@@ -1,24 +1,33 @@
 Files:
+tests/test-chown.h
+tests/test-lchown.h
 tests/test-lstat.h
 tests/test-mkdir.h
 tests/test-rmdir.h
 tests/test-stat.h
 tests/test-unlink.h
+tests/test-fchownat.c
 tests/test-fstatat.c
 tests/test-mkdirat.c
 tests/test-openat.c
 tests/test-unlinkat.c
 
 Depends-on:
+mgetgroups
 pathmax
+sleep
+stat-time
 symlink
 unlinkdir
 
 configure.ac:
+AC_CHECK_FUNCS_ONCE([getegid usleep])
 
 Makefile.am:
-TESTS += test-fstatat test-mkdirat test-openat test-unlinkat
-check_PROGRAMS += test-fstatat test-mkdirat test-openat test-unlinkat
+TESTS += test-fchownat test-fstatat test-mkdirat test-openat test-unlinkat
+check_PROGRAMS += test-fchownat test-fstatat test-mkdirat test-openat \
+  test-unlinkat
+test_fchownat_LDADD = $(LDADD) @LIBINTL@
 test_fstatat_LDADD = $(LDADD) @LIBINTL@
 test_mkdirat_LDADD = $(LDADD) @LIBINTL@
 test_openat_LDADD = $(LDADD) @LIBINTL@

new file mode 100644
--- /dev/null
+++ b/tests/test-fchownat.c
@@ -0,0 +1,89 @@
+/* Tests of fchownat.
+   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 <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+
+#include "mgetgroups.h"
+#include "openat.h"
+#include "stat-time.h"
+
+#define ASSERT(expr) \
+  do                                                                         \
+    {                                                                        \
+      if (!(expr))                                                           \
+        {                                                                    \
+          fprintf (stderr, "%s:%d: assertion failed\n", __FILE__, __LINE__);  \
+          fflush (stderr);                                                   \
+          abort ();                                                          \
+        }                                                                    \
+    }                                                                        \
+  while (0)
+
+#define BASE "test-fchownat.t"
+
+#include "test-chown.h"
+#include "test-lchown.h"
+
+static int dfd = AT_FDCWD;
+
+/* Wrapper around fchownat to test chown behavior.  */
+static int
+do_chown (char const *name, uid_t user, gid_t group)
+{
+  return chownat (dfd, name, user, group);
+}
+
+/* Wrapper around fchownat to test lchown behavior.  */
+static int
+do_lchown (char const *name, uid_t user, gid_t group)
+{
+  return lchownat (dfd, name, user, group);
+}
+
+int
+main (void)
+{
+  int result1; /* Skip because of no chown/symlink support.  */
+  int result2; /* Skip because of no lchown support.  */
+
+  /* Clean up any trash from prior testsuite runs.  */
+  ASSERT (system ("rm -rf " BASE "*") == 0);
+
+  /* Basic tests.  */
+  result1 = test_chown (do_chown, true);
+  result2 = test_lchown (do_lchown, result1 == 0);
+  dfd = open (".", O_RDONLY);
+  ASSERT (0 <= dfd);
+  ASSERT (test_chown (do_chown, false) == result1);
+  ASSERT (test_lchown (do_lchown, false) == result2);
+  /* We expect 0/0, 0/77, or 77/77, but not 77/0.  */
+  ASSERT (result1 <= result2);
+  ASSERT (close (dfd) == 0);
+
+  /* FIXME - add additional tests of dfd not at current directory.  */
+  return result1 | result2;
+}