-off_t written;
-return sendfile(in, out, *off, cnt, NULL, &written, 0) < 0
- ? (ssize_t) -1 : (ssize_t) written;
+off_t loff = *offp, written;
+
+if (sendfile(in, out, loff, cnt, NULL, &written, 0) < 0) return (ssize_t)-1;
+*offp = loff + written;
+return (ssize_t)written;