void valid_fd_012(void);
int readv_nonblock(int fd, struct iovec *iov, int iovcnt, size_t *num_bytes);
int read_nonblock(int fd, void *buf, size_t sz, size_t *num_bytes);
-int read_pattern(int fd, const char *pattern, size_t bufsize);
+int read_and_compare(int fd, const char *expectation);
int xwrite(int fd, const char *buf, size_t len);
int xwritev(int fd, struct iovec *iov, int iovcnt);
int for_each_file_in_dir(const char *dirname,