chdir-safer: port to mingw

[Bruno Haible]

Hi Jim,

While trying to compile all of gnulib on mingw, this module caused a
compilation error:

chdir-safer.c: In function `chdir_no_follow':
chdir-safer.c:60: error: `ELOOP' undeclared (first use in this function)
chdir-safer.c:60: error: (Each undeclared identifier is reported only once
chdir-safer.c:60: error: for each function it appears in.)
make[3]: *** [chdir-safer.o] Error 1

mingw does not have ELOOP, since that platform does not have symbolic
links. But on a platform without symbolic links, the main test done by
chdir_no_follow is not necessary. Such platforms can be recognized
through the absence of the readlink() function (see also
doc/posix-functions/readlink.texi).

Here is a proposed patch:


2008-04-20  Bruno Haible  <address@hidden>

        Port chdir-safer to mingw.
        * lib/chdir-safer.c (chdir_no_follow): Don't test for a symlink on
        platforms without readlink().
        * m4/chdir-safer.m4 (gl_CHDIR_SAFER): Test for readlink function.

--- lib/chdir-safer.c.orig      2008-04-20 09:22:10.000000000 +0200
+++ lib/chdir-safer.c   2008-04-20 09:21:20.000000000 +0200
@@ -1,6 +1,6 @@
 /* much like chdir(2), but safer
 
-   Copyright (C) 2005, 2006 Free Software Foundation, Inc.
+   Copyright (C) 2005, 2006, 2008 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
@@ -43,6 +43,7 @@
   if (fd < 0)
     return -1;
 
+#if HAVE_READLINK /* only on platforms which have symbolic links */
   /* If open follows symlinks, lstat DIR and fstat FD to ensure that
      they are the same file; if they are different files, set errno to
      ELOOP (the same value that open uses for symlinks with
@@ -62,6 +63,7 @@
            }
        }
     }
+#endif
 
   if (result == 0)
     result = fchdir (fd);
--- m4/chdir-safer.m4.orig      2008-04-20 09:22:10.000000000 +0200
+++ m4/chdir-safer.m4   2008-04-20 09:20:02.000000000 +0200
@@ -1,5 +1,5 @@
-#serial 3
-dnl Copyright (C) 2005, 2006 Free Software Foundation, Inc.
+#serial 4
+dnl Copyright (C) 2005, 2006, 2008 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.
@@ -7,4 +7,5 @@
 AC_DEFUN([gl_CHDIR_SAFER],
 [
   AC_LIBOBJ([chdir-safer])
+  AC_CHECK_FUNCS_ONCE([readlink])
 ])