+bool io_fd_block(int fd, bool block);
+
+/**
+ * io_time_override - override the normal call for time.
+ * @nowfn: the function to call.
+ *
+ * io usually uses time_mono() internally, but this forces it
+ * to use your function (eg. for debugging). Returns the old
+ * one.
+ */
+struct timemono (*io_time_override(struct timemono (*now)(void)))(void);
+
+/**
+ * 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);
+