--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2011-02-05  Eric Blake  <eblake@redhat.com>
+
+	strerror_r-posix: port to cygwin
+	* lib/strerror_r.c (strerror_r) [__CYGWIN__]: Add cygwin
+	implementation.
+	* m4/strerror_r.m4 (gl_FUNC_STRERROR_R): Adjust comment.
+	* tests/test-strerror_r.c (main): Fix test.
+	* doc/posix-functions/strerror_r.texi (strerror_r): Document the
+	issue.
+
 2011-02-05  Bruno Haible  <bruno@clisp.org>
 
 	New module 'wmemchr'.

--- a/doc/posix-functions/strerror_r.texi
+++ b/doc/posix-functions/strerror_r.texi
@@ -12,7 +12,8 @@
 This function is missing on some platforms:
 NetBSD 3.0, HP-UX 11.23, IRIX 6.5, Solaris 9, mingw.
 @item
-glibc has an incompatible version of this function.  The POSIX compliant code
+glibc and Cygwin have an incompatible version of this function.  The
+POSIX compliant code
 @smallexample
 char *s = (strerror_r (err, buf, buflen) == 0 ? buf : NULL);
 @end smallexample

--- a/lib/strerror_r.c
+++ b/lib/strerror_r.c
@@ -27,7 +27,7 @@
 #if HAVE_DECL_STRERROR_R && !(__GLIBC__ >= 2 || defined __UCLIBC__) && !EXTEND_STRERROR_R
 
 /* The system's strerror_r function is OK, except that its third argument
-   is 'int', not 'size_t'.  */
+   is 'int', not 'size_t', or its return type is wrong.  */
 
 # include <limits.h>
 
@@ -61,6 +61,11 @@
     else
       ret = strerror_r (errnum, buf, buflen);
   }
+# elif defined __CYGWIN__
+  /* Cygwin only provides the glibc interface, is thread-safe, and
+     always succeeds (although it may truncate). */
+  strerror_r (errnum, buf, buflen);
+  ret = 0;
 # else
   ret = strerror_r (errnum, buf, buflen);
 # endif

--- a/m4/strerror_r.m4
+++ b/m4/strerror_r.m4
@@ -24,7 +24,7 @@
   if test $ac_cv_func_strerror_r = yes; then
     if test -z "$ERRNO_H"; then
       dnl The POSIX prototype is:  int strerror_r (int, char *, size_t);
-      dnl glibc's prototype:       char *strerror_r (int, char *, size_t);
+      dnl glibc, Cygwin:           char *strerror_r (int, char *, size_t);
       dnl AIX 5.1, OSF/1 5.1:      int strerror_r (int, char *, int);
       AC_CACHE_CHECK([for strerror_r with POSIX signature],
         [gl_cv_func_strerror_r_posix_signature],

--- a/tests/test-strerror_r.c
+++ b/tests/test-strerror_r.c
@@ -74,8 +74,8 @@
         if (ret == 0)
           {
             /* Truncated result.  POSIX allows this, and it actually
-               happens on AIX 6.1.  */
-            ASSERT (strcmp (buf, "BADFACE") != 0);
+               happens on AIX 6.1 and Cygwin.  */
+            ASSERT ((strcmp (buf, "BADFACE") == 0) == (i == 0));
           }
         else
           {