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 *);
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 *);