(gl_PREREQ_CHOWN): Check for fcntl.h.

See if we need an fchown replacement.
(gl_FUNC_CHOWN_FOLLOWS_SYMLINK): New macro.
(gl_FUNC_CHOWN): Require gl_FUNC_CHOWN_FOLLOWS_SYMLINK,
and use the replacement function if we detect either defect.

1 files changed, 61 insertions, 9 deletions

diff --git a/m4/chown.m4 b/m4/chown.m4
index f723cb576..430bc8073 100644
--- a/m4/chown.m4
+++ b/m4/chown.m4
@@ -1,15 +1,24 @@
-#serial 9
-
-dnl From Jim Meyering.
-dnl Determine whether chown accepts arguments of -1 for uid and gid.
-dnl If it doesn't, arrange to use the replacement function.
-dnl
+#serial 10
+# Determine whether we need the chown wrapper.  chown should accept
+# arguments of -1 for uid and gid, and it should dereference symlinks.
+# If it doesn't, arrange to use the replacement function.
+# From Jim Meyering.
 
 AC_DEFUN([gl_FUNC_CHOWN],
 [
-  AC_REQUIRE([AC_TYPE_UID_T])dnl
+  AC_REQUIRE([AC_TYPE_UID_T])
   AC_REQUIRE([AC_FUNC_CHOWN])
-  if test $ac_cv_func_chown_works = no; then
+  AC_REQUIRE([gl_FUNC_CHOWN_FOLLOWS_SYMLINK])
+
+  if test $ac_cv_func_chown_works = yes; then
+    AC_DEFINE(CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE, 1,
+      [Define if chown is not POSIX compliant regarding IDs of -1.])
+  fi
+
+  # If chown has either of the above problems, then we need the wrapper.
+  if test $ac_cv_func_chown_works$gl_cv_func_chown_follows_symlink = yesyes; then
+    : # no wrapper needed
+  else
     AC_LIBOBJ(chown)
     AC_DEFINE(chown, rpl_chown,
       [Define to rpl_chown if the replacement function should be used.])
@@ -17,8 +26,51 @@ AC_DEFUN([gl_FUNC_CHOWN],
   fi
 ])
 
+# Determine whether chown follows symlinks (it should).
+AC_DEFUN([gl_FUNC_CHOWN_FOLLOWS_SYMLINK],
+[
+  AC_CACHE_CHECK(
+    [whether chown(2) dereferences symlinks],
+    gl_cv_func_chown_follows_symlink,
+    [
+      AC_RUN_IFELSE([AC_LANG_SOURCE([[
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+#include <stdlib.h>
+#include <errno.h>
+
+	int
+	main ()
+	{
+	  char const *dangling_symlink = "conftest.dangle";
+
+	  unlink (dangling_symlink);
+	  if (symlink ("conftest.no-such", dangling_symlink))
+	    abort ();
+
+	  /* Exit successfully on a conforming system,
+	     i.e., where chown must fail with ENOENT.  */
+	  exit ( ! (chown (dangling_symlink, getuid (), getgid ()) != 0
+		    && errno == ENOENT));
+	}
+	]])],
+	[gl_cv_func_chown_follows_symlink=yes],
+	[gl_cv_func_chown_follows_symlink=no],
+	[gl_cv_func_chown_follows_symlink=no]
+      )
+    ]
+  )
+
+  if test $gl_cv_func_chown_follows_symlink = no; then
+    AC_DEFINE(CHOWN_MODIFIES_SYMLINK, 1,
+      [Define if chown modifies symlinks.])
+  fi
+])
+
 # Prerequisites of lib/chown.c.
 AC_DEFUN([gl_PREREQ_CHOWN],
 [
-  AC_CHECK_HEADERS_ONCE(unistd.h)
+  AC_CHECK_HEADERS_ONCE(unistd.h fcntl.h)
+  AC_CHECK_FUNC([fchown], , [AC_LIBOBJ(fchown-stub)])
 ])