+int para_chdir(const char *path);
+int mmap_full_file(const char *filename, int open_mode, void **map,
+ size_t *size, int *fd_ptr);
+int para_munmap(void *start, size_t length);
+int write_ok(int fd);
+void valid_fd_012(void);
+int write_nonblock(int fd, const char *buf, size_t len,
+ size_t max_bytes_per_write);