+extern off_t bb_copyfd_size(int fd1, int fd2, off_t size);
+extern void bb_copyfd_exact_size(int fd1, int fd2, off_t size);
+/* "short" copy can be detected by return value < size */
+/* this helper yells "short read!" if param is not -1 */
+extern void complain_copyfd_and_die(off_t sz) ATTRIBUTE_NORETURN;