--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2008-09-13  Bruno Haible  <bruno@clisp.org>
+
+	* lib/errno.in.h: New file.
+	* m4/errno_h.m4: New file, borrowing from m4/eoverflow.m4.
+	* modules/errno: New file.
+	* doc/posix-headers/errno.texi: Update documentation.
+	* MODULES.html.sh (Support for systems lacking POSIX:2001): Add errno.
+
 2008-09-13  Bruno Haible  <bruno@clisp.org>
 
 	* tests/test-poll.c: Use #if for native Windows, rather than testing

--- a/MODULES.html.sh
+++ b/MODULES.html.sh
@@ -2082,6 +2082,7 @@
   func_module chown
   func_module dup2
   func_module environ
+  func_module errno
   func_module EOVERFLOW
   func_module fchdir
   func_module fcntl

--- a/doc/posix-headers/errno.texi
+++ b/doc/posix-headers/errno.texi
@@ -3,13 +3,28 @@
 
 POSIX specification: @url{http://www.opengroup.org/susv3xbd/errno.h.html}
 
-Gnulib module: EOVERFLOW
+Gnulib module: errno, EOVERFLOW
 
 Portability problems fixed by Gnulib:
 @itemize
 @item
-The macro @code{EOVERFLOW} is not defined on some platforms:
-OSF/1 4.0, mingw.
+The macros @code{EOVERFLOW}, @code{ENOLINK}, @code{EMULTIHOP} are not defined
+on some platforms:
+OpenBSD 4.0, OSF/1 4.0, mingw.
+@item
+The macros @code{ENOMSG}, @code{EIDRM}, @code{EPROTO}, @code{EBADMSG},
+@code{ENOTSUP}, @code{ECANCELED} are not defined on some platforms:
+OpenBSD 4.0, mingw.
+@item
+The macros @code{EWOULDBLOCK}, @code{ETXTBSY}, @code{ELOOP}, @code{ENOTSOCK},
+@code{EDESTADDRREQ}, @code{EMSGSIZE}, @code{EPROTOTYPE}, @code{ENOPROTOOPT},
+@code{EPROTONOSUPPORT}, @code{EOPNOTSUPP}, @code{EAFNOSUPPORT},
+@code{EADDRINUSE}, @code{EADDRNOTAVAIL}, @code{ENETDOWN}, @code{ENETUNREACH},
+@code{ENETRESET}, @code{ECONNABORTED}, @code{ECONNRESET}, @code{ENOBUFS},
+@code{EISCONN}, @code{ENOTCONN}, @code{ETIMEDOUT}, @code{ECONNREFUSED},
+@code{EHOSTUNREACH}, @code{EALREADY}, @code{EINPROGRESS}, @code{ESTALE},
+@code{EDQUOT} are not defined on some platforms:
+mingw.
 @end itemize
 
 Portability problems not fixed by Gnulib:

new file mode 100644
--- /dev/null
+++ b/lib/errno.in.h
@@ -0,0 +1,150 @@
+/* A POSIX-like <errno.h>.
+
+   Copyright (C) 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
+   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 Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
+
+#ifndef _GL_ERRNO_H
+
+@PRAGMA_SYSTEM_HEADER@
+
+/* The include_next requires a split double-inclusion guard.  */
+#@INCLUDE_NEXT@ @NEXT_ERRNO_H@
+
+#ifndef _GL_ERRNO_H
+#define _GL_ERRNO_H
+
+
+/* On native Windows platforms, many macros are not defined.  */
+# if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+
+/* Values >= 100 seem safe to use.  */
+#  define ETXTBSY   100
+#  define GNULIB_defined_ETXTBSY 1
+
+/* These are intentionally the same values as the WSA* error numbers, defined
+   in <winsock2.h>.  */
+#  define EWOULDBLOCK     10035
+#  define EINPROGRESS     10036
+#  define EALREADY        10037
+#  define ENOTSOCK        10038
+#  define EDESTADDRREQ    10039
+#  define EMSGSIZE        10040
+#  define EPROTOTYPE      10041
+#  define ENOPROTOOPT     10042
+#  define EPROTONOSUPPORT 10043
+#  define ESOCKTNOSUPPORT 10044  /* not required by POSIX */
+#  define EOPNOTSUPP      10045
+#  define EPFNOSUPPORT    10046  /* not required by POSIX */
+#  define EAFNOSUPPORT    10047
+#  define EADDRINUSE      10048
+#  define EADDRNOTAVAIL   10049
+#  define ENETDOWN        10050
+#  define ENETUNREACH     10051
+#  define ENETRESET       10052
+#  define ECONNABORTED    10053
+#  define ECONNRESET      10054
+#  define ENOBUFS         10055
+#  define EISCONN         10056
+#  define ENOTCONN        10057
+#  define ESHUTDOWN       10058  /* not required by POSIX */
+#  define ETOOMANYREFS    10059  /* not required by POSIX */
+#  define ETIMEDOUT       10060
+#  define ECONNREFUSED    10061
+#  define ELOOP           10062
+#  define EHOSTDOWN       10064  /* not required by POSIX */
+#  define EHOSTUNREACH    10065
+#  define EPROCLIM        10067  /* not required by POSIX */
+#  define EUSERS          10068  /* not required by POSIX */
+#  define EDQUOT          10069
+#  define ESTALE          10070
+#  define EREMOTE         10071  /* not required by POSIX */
+#  define GNULIB_defined_ESOCK 1
+
+# endif
+
+
+/* On OSF/1 5.1, when _XOPEN_SOURCE_EXTENDED is not defined, the macros
+   EMULTIHOP, ENOLINK, EOVERFLOW are not defined.  */
+# if @EMULTIHOP_HIDDEN@
+#  define EMULTIHOP @EMULTIHOP_VALUE@
+#  define GNULIB_defined_EMULTIHOP 1
+# endif
+# if @ENOLINK_HIDDEN@
+#  define ENOLINK   @ENOLINK_VALUE@
+#  define GNULIB_defined_ENOLINK 1
+# endif
+# if @EOVERFLOW_HIDDEN@
+#  define EOVERFLOW @EOVERFLOW_VALUE@
+#  define GNULIB_defined_EOVERFLOW 1
+# endif
+
+
+/* On OpenBSD 4.0 and on native Windows, the macros ENOMSG, EIDRM, ENOLINK,
+   EPROTO, EMULTIHOP, EBADMSG, EOVERFLOW, ENOTSUP, ECANCELED are not defined.
+   Define them here.  Values >= 128 seem safe to use.
+
+   Note: When one of these systems defines some of these macros some day,
+   binaries will have to be recompiled so that they recognizes the new
+   errno values from the system.  */
+
+# ifndef ENOMSG
+#  define ENOMSG    128
+#  define GNULIB_defined_ENOMSG 1
+# endif
+
+# ifndef EIDRM
+#  define EIDRM     129
+#  define GNULIB_defined_EIDRM 1
+# endif
+
+# ifndef ENOLINK
+#  define ENOLINK   130
+#  define GNULIB_defined_ENOLINK 1
+# endif
+
+# ifndef EPROTO
+#  define EPROTO    131
+#  define GNULIB_defined_EPROTO 1
+# endif
+
+# ifndef EMULTIHOP
+#  define EMULTIHOP 132
+#  define GNULIB_defined_EMULTIHOP 1
+# endif
+
+# ifndef EBADMSG
+#  define EBADMSG   133
+#  define GNULIB_defined_EBADMSG 1
+# endif
+
+# ifndef EOVERFLOW
+#  define EOVERFLOW 134
+#  define GNULIB_defined_EOVERFLOW 1
+# endif
+
+# ifndef ENOTSUP
+#  define ENOTSUP   135
+#  define GNULIB_defined_ENOTSUP 1
+# endif
+
+# ifndef ECANCELED
+#  define ECANCELED 136
+#  define GNULIB_defined_ECANCELED 1
+# endif
+
+
+#endif /* _GL_ERRNO_H */
+#endif /* _GL_ERRNO_H */

new file mode 100644
--- /dev/null
+++ b/m4/errno_h.m4
@@ -0,0 +1,89 @@
+# errno_h.m4 serial 1
+dnl Copyright (C) 2004, 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.
+
+AC_DEFUN([gl_HEADER_ERRNO_H],
+[
+  dnl Use AC_REQUIRE here, so that the default behavior below is expanded
+  dnl once only, before all statements that occur in other macros.
+  AC_REQUIRE([gl_HEADER_ERRNO_H_BODY])
+])
+
+AC_DEFUN([gl_HEADER_ERRNO_H_BODY],
+[
+  AC_REQUIRE([AC_PROG_CC])
+  AC_CACHE_CHECK([for complete errno.h], gl_cv_header_errno_h_complete, [
+    AC_EGREP_CPP(booboo,[
+#include <errno.h>
+#ifndef EOVERFLOW
+booboo
+#endif
+      ],
+      [gl_cv_header_errno_h_complete=no],
+      [gl_cv_header_errno_h_complete=yes])
+  ])
+  if test $gl_cv_header_errno_h_complete = yes; then
+    ERRNO_H=''
+  else
+    gl_CHECK_NEXT_HEADERS([errno.h])
+    ERRNO_H='errno.h'
+  fi
+  AC_SUBST([ERRNO_H])
+  gl_REPLACE_ERRNO_VALUE([EMULTIHOP])
+  gl_REPLACE_ERRNO_VALUE([ENOLINK])
+  gl_REPLACE_ERRNO_VALUE([EOVERFLOW])
+])
+
+# Assuming $1 = EOVERFLOW.
+# The EOVERFLOW errno value ought to be defined in <errno.h>, according to
+# POSIX.  But some systems (like OpenBSD 4.0 or AIX 3) don't define it, and
+# some systems (like OSF/1) define it when _XOPEN_SOURCE_EXTENDED is defined.
+# Check for the value of EOVERFLOW.
+# Set the variables EOVERFLOW_HIDDEN and EOVERFLOW_VALUE.
+AC_DEFUN([gl_REPLACE_ERRNO_VALUE],
+[
+  if test -n "$ERRNO_H"; then
+    AC_CACHE_CHECK([for ]$1[ value], [gl_cv_header_errno_h_]$1, [
+      AC_EGREP_CPP(yes,[
+#include <errno.h>
+#ifdef ]$1[
+yes
+#endif
+      ],
+      [gl_cv_header_errno_h_]$1[=yes],
+      [gl_cv_header_errno_h_]$1[=no])
+      if test $gl_cv_header_errno_h_]$1[ = no; then
+        AC_EGREP_CPP(yes,[
+#define _XOPEN_SOURCE_EXTENDED 1
+#include <errno.h>
+#ifdef ]$1[
+yes
+#endif
+          ], [gl_cv_header_errno_h_]$1[=hidden])
+        if test $gl_cv_header_errno_h_]$1[ = hidden; then
+          dnl The macro exists but is hidden.
+          dnl Define it to the same value.
+          AC_COMPUTE_INT([gl_cv_header_errno_h_]$1, $1, [
+#define _XOPEN_SOURCE_EXTENDED 1
+#include <errno.h>
+/* The following two lines are a workaround against an autoconf-2.52 bug.  */
+#include <stdio.h>
+#include <stdlib.h>
+])
+        fi
+      fi
+    ])
+    case $gl_cv_header_errno_h_]$1[ in
+      yes | no)
+        ]$1[_HIDDEN=0; ]$1[_VALUE=
+        ;;
+      *)
+        ]$1[_HIDDEN=1; ]$1[_VALUE="$gl_cv_header_errno_h_]$1["
+        ;;
+    esac
+    AC_SUBST($1[_HIDDEN])
+    AC_SUBST($1[_VALUE])
+  fi
+])
\ No newline at end of file

new file mode 100644
--- /dev/null
+++ b/modules/errno
@@ -0,0 +1,44 @@
+Description:
+A POSIX-like <errno.h>.
+
+Files:
+lib/errno.in.h
+m4/errno_h.m4
+
+Depends-on:
+include_next
+
+configure.ac:
+gl_HEADER_ERRNO_H
+
+Makefile.am:
+BUILT_SOURCES += $(ERRNO_H)
+
+# We need the following in order to create <errno.h> when the system
+# doesn't have one that is POSIX compliant.
+errno.h: errno.in.h
+	rm -f $@-t $@
+	{ echo '/* DO NOT EDIT! GENERATED AUTOMATICALLY! */' && \
+	  sed -e 's|@''INCLUDE_NEXT''@|$(INCLUDE_NEXT)|g' \
+	      -e 's|@''PRAGMA_SYSTEM_HEADER''@|@PRAGMA_SYSTEM_HEADER@|g' \
+	      -e 's|@''NEXT_ERRNO_H''@|$(NEXT_ERRNO_H)|g' \
+	      -e 's|@''EMULTIHOP_HIDDEN''@|$(EMULTIHOP_HIDDEN)|g' \
+	      -e 's|@''EMULTIHOP_VALUE''@|$(EMULTIHOP_VALUE)|g' \
+	      -e 's|@''ENOLINK_HIDDEN''@|$(ENOLINK_HIDDEN)|g' \
+	      -e 's|@''ENOLINK_VALUE''@|$(ENOLINK_VALUE)|g' \
+	      -e 's|@''EOVERFLOW_HIDDEN''@|$(EOVERFLOW_HIDDEN)|g' \
+	      -e 's|@''EOVERFLOW_VALUE''@|$(EOVERFLOW_VALUE)|g' \
+	      < $(srcdir)/errno.in.h; \
+	} > $@-t
+	mv $@-t $@
+MOSTLYCLEANFILES += errno.h errno.h-t
+
+Include:
+<errno.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+Bruno Haible
+