1 files changed, 71 insertions, 0 deletions
diff --git a/src/H5FDpublic.h b/src/H5FDpublic.h
index 0cfb072..b8f4f12 100644
--- a/src/H5FDpublic.h
+++ b/src/H5FDpublic.h
@@ -138,6 +138,77 @@
  */
 #define H5FD_FEAT_DEFAULT_VFD_COMPATIBLE 0x00008000
 
+/* ctl function definitions: */
+#define H5FD_CTL_OPC_RESERVED 512 /* Opcodes below this value are reserved for library use */
+#define H5FD_CTL_OPC_EXPER_MIN                                                                               \
+    H5FD_CTL_OPC_RESERVED /* Minimum opcode value available for experimental use                             \
+                           */
+#define H5FD_CTL_OPC_EXPER_MAX                                                                               \
+    (H5FD_CTL_OPC_RESERVED + 511) /* Maximum opcode value available for experimental use */
+
+/* ctl function op codes: */
+#define H5FD_CTL__INVALID_OPCODE              0
+#define H5FD_CTL__TEST_OPCODE                 1
+#define H5FD_CTL__GET_MPI_COMMUNICATOR_OPCODE 2
+#define H5FD_CTL__GET_MPI_RANK_OPCODE         3
+#define H5FD_CTL__GET_MPI_SIZE_OPCODE         4
+
+/* ctl function flags: */
+
+/* Definitions:
+ *
+ * WARNING: While the following definitions of Terminal
+ * and Passthrough VFDs should be workable for now, they
+ * have to be adjusted as our use cases for VFDs expand.
+ *
+ *                                   JRM -- 8/4/21
+ *
+ *
+ * Terminal VFD: Lowest VFD in the VFD stack through
+ * which all VFD calls pass.  Note that this definition
+ * is situational.  For example, the sec2 VFD is typically
+ * terminal.  However, in the context of the family file
+ * driver, it is not -- the family file driver is the
+ * bottom VFD through which all VFD calls pass, and thus
+ * it is terminal.
+ *
+ * Similarly, on the splitter VFD, a sec2 VFD on the
+ * R/W channel is terminal, but a sec2 VFD on the W/O
+ * channel is not.
+ *
+ *
+ * Pass through VFD:  Any VFD that relays all VFD calls
+ * (with the possible exception of some non-I/O related
+ * calls) to underlying VFD(s).
+ */
+
+/* Unknown op codes should be ignored silently unless the
+ * H5FD_CTL__FAIL_IF_UNKNOWN_FLAG is set.
+ *
+ * On terminal VFDs, unknown op codes should generate an
+ * error unconditionally if this flag is set.
+ *
+ * On pass through VFDs, unknown op codes should be routed
+ * to the underlying VFD(s) as indicated by any routing
+ * flags.  In the absence of such flags, the VFD should
+ * generate an error.
+ */
+#define H5FD_CTL__FAIL_IF_UNKNOWN_FLAG 0x0001
+
+/* The H5FD_CTL__ROUTE_TO_TERMINAL_VFD_FLAG is used only
+ * by non-ternminal VFDs, and only applies to unknown
+ * opcodes. (known op codes should be handled as
+ * appropriate.)
+ *
+ * If this flag is set for an uknown op code, that
+ * op code should be passed to the next VFD down
+ * the VFD stack en-route to the terminal VFD.
+ * If that VFD does not support the ctl call, the
+ * pass through VFD should fail or succeed as directed
+ * by the  H5FD_CTL__FAIL_IF_UNKNOWN_FLAG.
+ */
+#define H5FD_CTL__ROUTE_TO_TERMINAL_VFD_FLAG 0x0002
+
 /*******************/
 /* Public Typedefs */
 /*******************/