+void valid_fd_012(void);
+int readv_nonblock(int fd, struct iovec *iov, int iovcnt, fd_set *rfds,
+ size_t *num_bytes);
+int read_nonblock(int fd, void *buf, size_t sz, fd_set *rfds, size_t *num_bytes);
+int read_pattern(int fd, const char *pattern, size_t bufsize, fd_set *rfds);
+int write_nonblock(int fd, const char *buf, size_t len);
+int for_each_file_in_dir(const char *dirname,
+ int (*func)(const char *, void *), void *private_data);