+/**
+ * io_poll_override - override the normal call for poll.
+ * @pollfn: the function to call.
+ *
+ * io usually uses poll() internally, but this forces it to use your
+ * function (eg. for debugging, suppressing fds, or polling on others unknown
+ * to ccan/io). Returns the old one.
+ */
+int (*io_poll_override(int (*poll)(struct pollfd *fds, nfds_t nfds, int timeout)))(struct pollfd *, nfds_t, int);
+