+ /* REVISIT the fault reporting model here is weak:
+ *
+ * - When we get an error after receiving N bytes from a slave,
+ * there is no way to report "N".
+ *
+ * - When we get a NAK after transmitting N bytes to a slave,
+ * there is no way to report "N" ... or to let the master
+ * continue executing the rest of this combined message, if
+ * that's the appropriate response.
+ *
+ * - When for example "num" is two and we successfully complete
+ * the first message but get an error part way through the
+ * second, it's unclear whether that should be reported as
+ * one (discarding status on the second message) or errno
+ * (discarding status on the first one).
+ */
+