int write_all(int fd, const char *buf, size_t len);
__printf_2_3 int write_va_buffer(int fd, const char *fmt, ...);
bool file_exists(const char *);
-int para_select(int n, fd_set *readfds, fd_set *writefds, int timeout);
+int xpoll(struct pollfd *fds, nfds_t nfds, int timeout);
__must_check int mark_fd_nonblocking(int fd);
__must_check int mark_fd_blocking(int fd);
int para_mmap(size_t length, int prot, int flags, int fd, void *map);