Refactor all the 'H5VL_*_optional' callbacks to move the type of operation out

of the va_list, so it's at least possible for another connector to know what
the operation is and decide whether to implement it or not.

Added a new VOL sub-class called "introspect" where callbacks that report
information about the connector or container can be placed.  Added an
'opt_query' callback to this sub-class, for a connector to report back
to the library whether a particular optional callback operation is supported.
Also added a 'get_conn_cls' introspection callback, to retrieve the H5VL_class_t
of a connector (either the "current" connector, H5VL_GET_CONN_LVL_CURR, or
the terminal connector, H5VL_GET_CONN_LVL_TERM).

Moved the "post open" operation from a file 'specific' operation to a file
'optional' operation, now that it's possible to detect (with the 'opt_query'
introspection callback) whether a VOL connector implements an optional
operation, without just returning an error.

Added new internal VOL helper routines: H5VL_object_is_native, to determine
if an object is in (or is a) native file, and H5VL_file_is_same, to determine
if two objects are in (or are) the same terminal VOL connector's container.
(And moved the special handling for FILE_IS_EQUAL operation out of internal VOL
callback routine into H5VL_file_is_same)

Made new dataset 'get' operation for H5Dvlen_get_buf_size, aligning it better
with other 'get' operations in API.

Fixed several issues with pass-through connectors, which are now passing the
'make check-passthrough-vol' tests again.

A bunch of warning and style cleanups as well.

1 files changed, 3 insertions, 5 deletions

diff --git a/src/H5VLnative_attr.c b/src/H5VLnative_attr.c
index 85af320..e54c49f 100644
--- a/src/H5VLnative_attr.c
+++ b/src/H5VLnative_attr.c
@@ -524,16 +524,14 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5VL__native_attr_optional(void H5_ATTR_UNUSED *obj, hid_t H5_ATTR_UNUSED dxpl_id,
-    void H5_ATTR_UNUSED **req, va_list arguments)
+H5VL__native_attr_optional(void H5_ATTR_UNUSED *obj, H5VL_attr_optional_t opt_type,
+    hid_t H5_ATTR_UNUSED dxpl_id, void H5_ATTR_UNUSED **req, va_list arguments)
 {
-    H5VL_native_attr_optional_t optional_type;
     herr_t ret_value = SUCCEED;    /* Return value */
 
     FUNC_ENTER_PACKAGE
 
-    optional_type = HDva_arg(arguments, H5VL_native_attr_optional_t);
-    switch(optional_type) {
+    switch(opt_type) {
 #ifndef H5_NO_DEPRECATED_SYMBOLS
         case H5VL_NATIVE_ATTR_ITERATE_OLD:
             {