-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, Solaris 10, Cygwin 1.5.x, mingw, Interix 3.5, BeOS.
+This function always fails on platforms that don't support symlinks:
+mingw, MSVC 9.
+@item
+When @code{readlink} is called on a directory: In the case of NFS mounted
+directories, Cygwin sets @code{errno} to @code{ENOENT} or @code{EIO} instead of
+@code{EINVAL}. To avoid this problem, check for a directory before calling
+@code{readlink}.
+@item
+When @code{readlink} is called on a file that is not a symbolic link:
+Irix may set @code{errno} to @code{ENXIO} instead of @code{EINVAL}. Cygwin
+may set errno to @code{EACCES} instead of @code{EINVAL}.
+@item
+Symlink contents do not always have a trailing null byte, and there is
+no indication if symlink contents were truncated if the return value
+matches the length. Furthermore, AIX 5.1 and HP-UX 11 set
+@code{errno} to @code{ERANGE} rather than returning truncated
+contents, and Linux sets @code{errno} to @code{EINVAL} if the
+requested length is zero. Use the gnulib module areadlink for
+improved ability to read symlink contents.