int xrename(const char *oldpath, const char *newpath);
int write_all(int fd, const char *buf, size_t len);
__printf_2_3 int write_va_buffer(int fd, const char *fmt, ...);
-int file_exists(const char *);
+bool file_exists(const char *);
int para_select(int n, fd_set *readfds, fd_set *writefds,
struct timeval *timeout_tv);
__must_check int mark_fd_nonblocking(int fd);