While the corresponding implementation has been in our trees for quite
a while, it's in a state that doesn't make it suitable for submission,
and the original author having left the company leaves open to find
someone to complete this work. Yet to prevent problems with other
interface extensions we'd like to keep the slot in the number space
reserved for the purpose it has been serving here.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- a/xen/include/public/io/blkif.h
+++ b/xen/include/public/io/blkif.h
@@ -76,6 +76,10 @@
  * "feature-flush-cache" node!
  */
 #define BLKIF_OP_FLUSH_DISKCACHE   3
+/*
+ * Device specific command packet contained within the request
+ */
+#define BLKIF_OP_PACKET            4
 
 /*
  * Maximum scatter/gather segments per request.