-/* Wrapper around read(2) to read all the data we requested (BLOCKING) */
-ssize_t
-readn(int fd, void *buffer, size_t len);
+/* Some platforms (FreeBSD, OpenBSD, Solaris) do not seem to define this */
+
+#ifndef POLLRDHUP
+# define POLLRDHUP (POLLIN | POLLHUP)
+#endif
+
+/* Some platforms (Darwin) have to define a larger limit on groups membership */
+
+#ifndef EXIM_GROUPLIST_SIZE
+# define EXIM_GROUPLIST_SIZE NGROUPS_MAX
+#endif
+
+/* Linux has TCP_CORK, FreeBSD has TCP_NOPUSH; they do pretty much the same */
+
+#ifdef TCP_CORK
+# define EXIM_TCP_CORK TCP_CORK
+#elif defined(TCP_NOPUSH)
+# define EXIM_TCP_CORK TCP_NOPUSH
+#endif