int para_munmap(void *start, size_t length);
int write_ok(int fd);
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 write_nonblock(int fd, const char *buf, size_t len,
size_t max_bytes_per_write);
int for_each_file_in_dir(const char *dirname,