Combo set of async and other changes (#161)

* Update API tracing for new H5VL_request_status_t typedef

* Finish converting internal event set operations to use list iterator callbacks, instead of directly accessing the list structure

* Add H5VL_REQUEST_GET_ERR_STACK operation to request subclass, for retrieving a copy of the error stack for a failed asynchronous operation

* Remove 'canceled' event status from Java constants

* Be safer about releasing resources when inserting a newly opened/created object or file into an event set

* Remove H5EStest, add H5ES_WAIT_NONE for 0 timeout, and revise parameters to H5ESwait, to make it more "aggregate".

* Remove H5ES_STATUS_CANCELED from Java wrappers also

* Apply patch for dynamically registering optional VOL operations

* (a) Add async APIs for H5O module as listed in jira issue ID-283.
(b) Remove verification of name parameter in async related routines for H55A and H5L modules
    because it is checked in H5VL_setup* routine.
(c) Modify h5dump expected output due to the async changes.

* Corrections based on PR feedback.

* Further changes to make based on PR feedback.

* Remove H5Dwait & H5Fwait (moved to the async connector).  Added H5atclose
routine.  Updated 'optional op' operations.

* Fix missed merge marker, and reformatted line

* Update API tracing infrastructure for H5atclose callback

* Clean up some warnings

* Normalize against develop branch

* Correct level of indirection

* Add doxygen info for H5is_library_terminating and regression tests for it and H5atclose

* Relocate prototype (and doxygen info) for H5Aclose

* Align w/changes on develop

* Move group package initialization code to H5Gint.c, and update tracing macros

* Change non-static function declarations to be static

* Correct GCC diagnostic macro

* Ensure that H5TSpublic.h header gets installed (#129)

* Finish moving API routines that invoke VOL framework to main source files.

* Fix position of H5Fmount and H5Funmount

* Add 'wrapper' versions of async calls, to allow language wrappers and layers on top of HDF5 to pass in their application information.

* Add wrappers for dynamically registered optional operations

* Fix typo

* Update doxygen comment for H5atclose with additional detail.

* Add H5VL\*_vararg versions of H5VL routines that use va_list parameters

* Implement and test H5S_BLOCK

* Switch H5Aexists\*_async and H5Lexists\*_async to use flag to return status, instead of return value.  Make the corresponding changes through most of the v1 and v2 B-tree code.  Clean up warnings in H5public.h and cmpd_dtransform.c.

* Add H5Iregister_future routine and tests.

* Correct return value for H5Lexists_async

* Add H5_DLL macro to public H5ES API routines

* Update supported -> flags parameter for introspect_query callback

* Remove my email address.  Update passthrough VOL connector ID.

* Fix comment for post_open_api_common

* Remove unused non-blocking VOL connector

* Minor cleanup in async branch in preparation for merge to develop

* Update CMake and the Autotools to use the new pass-through VOL ID

* Finish another iteration on public H5ES routines, along with running the code reformatter

* Another round of reformatting

* Fix for SWMR daily test failures (#160)

The H5I_register_using_existing_id() call did not initialize the future
ID callbacks, causing the library to segfault when it tried to
resolve those function pointers.

* Added selective async APIs (#150)

* Added selective async APIs

Description:
    Added the following APIs:
        H5Ropen_attr_async
        H5Ropen_object_async
        H5Ropen_region_async

        H5Mcreate_async
        H5Mopen_async
        H5Mput_async
        H5Mget_async
        H5Mclose_async

        H5Tcommit_async
        H5Topen_async
        H5Tcopy_async
        H5Tclose_async
    - Updated an expected output file to include a new internal function
      in the error stack for the failure case.

* Updated async APIs per reviews, including removing async version of
H5Tcopy.

* Removed statements that were added by mistake in the previous commit.

* Fix compile issues in H5M and warnings elsewhere

* Reformat code

* Brings VOL_LIST changes from develop. (#163)

* Remove H5Dwait and H5Fwait calls, which were incorrectly brought back in

* Tiny cleanup of H5Lcreate_hard_async

* Run source formatter

* Allow for canceled operation in wait_cb

* Attempt to fix switch on string value

* Re-run source formatter

* Add H5S_BLOCK testfile to CMake clean target

* Add H5Pset_vol_async API routine and 'get_cap_flags' VOL introspection callback

* Clean up warnings

* Add H5P(set\|get)_vol_implicit_async API routines to allow \/ disallow implicit asynchronous operations (default is disallowed)

* Run formatting script

* Remove H5VL_REQUEST_WAIT\*

* Warning cleanup

* Eliminate strdup()s on statically allocated strings

* Warning cleanup

* Split H5VLrestore_lib_state into H5VLstart_lib_state and H5VLrestore_lib_state, and rename H5VLreset_lib_state to H5VLfinish_lib_state.

* Duplicate strings when building err_info to return to applicatin

* Move connector author routines into seperate header files, all included in the new hdf5dev.h header

* Run bin/trace to add TRACE macros

* Allow H5ES_NONE as a valid, but no-op, parameter to all H5ES API routines that accept an event set ID

* Clean up formatting

* Remove H5Pset/get_vol_implicit_async

* Clean up warning

* Remove H5Pget_vol_async and replace with more generic H5Pget_vol_cap_flags

* Clean up warnings

* Add H5ESfree_err_info convenience routine

* Fix typo

* Correct matching for cached VOL plugins

* Add developer header file

* Update for C99 compatibility

* Add missing trace macro

* Stop clang-format from messing with the trace macros.  Don't set up VOL wrappers for 'infrastructure' objects like requests and blobs

* Fix warning about formatting a directory

* Clean up formatting for H5E_BEGIN_TRY / H5E_END_TRY

* Reduce scope of H5ES__close

* Enable CMake checks for various types on MacOS

* Clean up properly when H5CX_retrieve_state() fails.  Also clean up many compiler warnings.

* Committing clang-format changes

* Merge from develop

* Fix mis-placed assert

* Remove commented-out code

* Re-add macro for unsetenv on Windows (I think it accidentally was merged out)

* Strengthen sanity check from error report to assertion

* Committing clang-format changes

* Add units to the comments for a few fields

* Switch 'get execution time' operation for async request tokens to be an optional operation and query if connector supports operation before retrieving it.

* Committing clang-format changes

* Remove H5ESget_time_estimate

* Committing clang-format changes

* Create developer header for datatype routines and move type conversion register/unregister routines there.

* Simplify internal H5VL_setup_name_args and H5VL_setup_idx_args routines

* Add H5VLlink_optional_op, allowing dynamicly registered optional operations for the link VOL subclass, also added H5VL_loc_params argument to the link 'optional' callback to allow them to work correctly.

* Run bin/format_source on current code

* Add H5VLobject_optional_op, allowing dynamicly registered optional operations for the object VOL subclass, also added H5VL_loc_params argument to the object 'optional' callback to allow them to work correctly.

* Run bin/format_source on current code

* Committing clang-format changes

* Revert "Switch 'get execution time' operation for async request tokens to be an optional operation and query if connector supports operation before retrieving it."

This reverts commit 5ac92014da2682bdba62d7a2524b8d90e38f6b19.

* Committing clang-format changes

* Convert attribute 'get' operation to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.

* Update tracing macros

* Convert attribute 'specific' operation to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.

* Convert dataset 'get' and 'specific' operations to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.  Also, minor tweaks to attribute 'get' and 'specific' operation parameters.

* Convert datatype 'get' and 'specific' operations to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.  Also, minor tweaks to H5O_refresh_metadata arguments.

* Reduce warnings

* Reduce warnings

* Track change to datatype 'get' callback

* Fix bug with file pointer getting invalidated when object closed

* Reformat source

* Convert file and group VOL classes 'get' and 'specific' operations to use
struct-of-tagged-union pattern for VOL callback arguments, instead of using
varargs.  Also small cleanup to the attribute get name operation.  Also moved
'mount' and 'unmount' operations to be group specific operations, instead of
file specific, to better align with their behavior (mounted files are on
groups, so a group is what is operated on).

* Remove remainder of merge conflict marking

* Convert link VOL class 'create' operations to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.

* Remove some unused local variables

* Convert link VOL class 'get' operations to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.  Also refactor 'get name by idx' routines to return actual length of name with a parameter instead of the return value, and move some callback context structs for the link interface from the private header file into the source code module, to reduce their visibility scope.

* Update tracing macros

* Convert link VOL class 'specific' operations to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.

* Convert object VOL class 'get' operations to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.

* Convert object VOL class 'specific' operations to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.  Also refactor H5G_loc_exists, et al, to return 'exists' flag in a parameter and errors with the function return value, instead of overloading both into the return value.  And, corrected logic error in test/links.c around non-existant objects in a file.

* Convert request VOL class 'specific' operations to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.

* Convert blob VOL class 'specific' operations to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.  Also removes the H5VL_BLOB_GETSIZE operation, as it's unused in the library and the blob ID size for a container is now returned with H5VL_FILE_GET_CONT_INFO.

* Add 'const' to several parameters that are only queried.

* Convert all VOL classes' 'optional' operations to use struct-of-tagged-union pattern for VOL callback arguments, instead of using varargs.  Convert several 'get' routines to return the length of an array in a parameter instead of combining it into the return value.  Move several routines to be in less public namespace.  Correct direct_chunk test to verify that parameters aren't modified on error.

* Switch get/specific/optional VOL callback argument structures to be 'async-friendly'.  Also other minor cleanups and bug-fixes.

* Add H5Pset_dataset_io_hyperslab_selection / H5S_PLIST feature, to allow skipping H5Dget_space + H5Sselect_hyperslab for async operation

* Add dynamic optional operations for request objects

* Update dynamic operation test for optional request operations

* Update a comment for an operation argument

* Run trace and format_source scripts

* Committing clang-format changes

* Committing clang-format changes

Co-authored-by: vchoi <vchoi@jelly.ad.hdfgroup.org>
Co-authored-by: vchoi-hdfgroup <55293060+vchoi-hdfgroup@users.noreply.github.com>
Co-authored-by: jhendersonHDF <jhenderson@hdfgroup.org>
Co-authored-by: Dana Robinson <derobins@hdfgroup.org>
Co-authored-by: Dana Robinson <43805+derobins@users.noreply.github.com>
Co-authored-by: bmribler <39579120+bmribler@users.noreply.github.com>
Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

1 files changed, 242 insertions, 442 deletions

diff --git a/src/H5VLpassthru.c b/src/H5VLpassthru.c
index 5ccc082..ede2f5f 100644
--- a/src/H5VLpassthru.c
+++ b/src/H5VLpassthru.c
@@ -36,7 +36,7 @@
 #include <string.h>
 
 /* Public HDF5 file */
-#include "hdf5.h"
+#include "hdf5dev.h"
 
 /* This connector's header */
 #include "H5VLpassthru.h"
@@ -77,15 +77,6 @@ typedef struct H5VL_pass_through_wrap_ctx_t {
 /********************* */
 
 /* Helper routines */
-static herr_t H5VL_pass_through_file_specific_reissue(void *obj, hid_t connector_id,
-                                                      H5VL_file_specific_t specific_type, hid_t dxpl_id,
-                                                      void **req, ...);
-static herr_t H5VL_pass_through_request_specific_reissue(void *obj, hid_t connector_id,
-                                                         H5VL_request_specific_t specific_type, ...);
-static herr_t H5VL_pass_through_link_create_reissue(H5VL_link_create_type_t create_type, void *obj,
-                                                    const H5VL_loc_params_t *loc_params, hid_t connector_id,
-                                                    hid_t lcpl_id, hid_t lapl_id, hid_t dxpl_id, void **req,
-                                                    ...);
 static H5VL_pass_through_t *H5VL_pass_through_new_obj(void *under_obj, hid_t under_vol_id);
 static herr_t               H5VL_pass_through_free_obj(H5VL_pass_through_t *obj);
 
@@ -117,13 +108,11 @@ static herr_t H5VL_pass_through_attr_read(void *attr, hid_t mem_type_id, void *b
                                           void **req);
 static herr_t H5VL_pass_through_attr_write(void *attr, hid_t mem_type_id, const void *buf, hid_t dxpl_id,
                                            void **req);
-static herr_t H5VL_pass_through_attr_get(void *obj, H5VL_attr_get_t get_type, hid_t dxpl_id, void **req,
-                                         va_list arguments);
+static herr_t H5VL_pass_through_attr_get(void *obj, H5VL_attr_get_args_t *args, hid_t dxpl_id, void **req);
 static herr_t H5VL_pass_through_attr_specific(void *obj, const H5VL_loc_params_t *loc_params,
-                                              H5VL_attr_specific_t specific_type, hid_t dxpl_id, void **req,
-                                              va_list arguments);
-static herr_t H5VL_pass_through_attr_optional(void *obj, H5VL_attr_optional_t opt_type, hid_t dxpl_id,
-                                              void **req, va_list arguments);
+                                              H5VL_attr_specific_args_t *args, hid_t dxpl_id, void **req);
+static herr_t H5VL_pass_through_attr_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id,
+                                              void **req);
 static herr_t H5VL_pass_through_attr_close(void *attr, hid_t dxpl_id, void **req);
 
 /* Dataset callbacks */
@@ -137,12 +126,12 @@ static herr_t H5VL_pass_through_dataset_read(void *dset, hid_t mem_type_id, hid_
 static herr_t H5VL_pass_through_dataset_write(void *dset, hid_t mem_type_id, hid_t mem_space_id,
                                               hid_t file_space_id, hid_t plist_id, const void *buf,
                                               void **req);
-static herr_t H5VL_pass_through_dataset_get(void *dset, H5VL_dataset_get_t get_type, hid_t dxpl_id,
-                                            void **req, va_list arguments);
-static herr_t H5VL_pass_through_dataset_specific(void *obj, H5VL_dataset_specific_t specific_type,
-                                                 hid_t dxpl_id, void **req, va_list arguments);
-static herr_t H5VL_pass_through_dataset_optional(void *obj, H5VL_dataset_optional_t opt_type, hid_t dxpl_id,
-                                                 void **req, va_list arguments);
+static herr_t H5VL_pass_through_dataset_get(void *dset, H5VL_dataset_get_args_t *args, hid_t dxpl_id,
+                                            void **req);
+static herr_t H5VL_pass_through_dataset_specific(void *obj, H5VL_dataset_specific_args_t *args, hid_t dxpl_id,
+                                                 void **req);
+static herr_t H5VL_pass_through_dataset_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id,
+                                                 void **req);
 static herr_t H5VL_pass_through_dataset_close(void *dset, hid_t dxpl_id, void **req);
 
 /* Datatype callbacks */
@@ -151,12 +140,12 @@ static void *H5VL_pass_through_datatype_commit(void *obj, const H5VL_loc_params_
                                                hid_t tapl_id, hid_t dxpl_id, void **req);
 static void *H5VL_pass_through_datatype_open(void *obj, const H5VL_loc_params_t *loc_params, const char *name,
                                              hid_t tapl_id, hid_t dxpl_id, void **req);
-static herr_t H5VL_pass_through_datatype_get(void *dt, H5VL_datatype_get_t get_type, hid_t dxpl_id,
-                                             void **req, va_list arguments);
-static herr_t H5VL_pass_through_datatype_specific(void *obj, H5VL_datatype_specific_t specific_type,
-                                                  hid_t dxpl_id, void **req, va_list arguments);
-static herr_t H5VL_pass_through_datatype_optional(void *obj, H5VL_datatype_optional_t opt_type, hid_t dxpl_id,
-                                                  void **req, va_list arguments);
+static herr_t H5VL_pass_through_datatype_get(void *dt, H5VL_datatype_get_args_t *args, hid_t dxpl_id,
+                                             void **req);
+static herr_t H5VL_pass_through_datatype_specific(void *obj, H5VL_datatype_specific_args_t *args,
+                                                  hid_t dxpl_id, void **req);
+static herr_t H5VL_pass_through_datatype_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id,
+                                                  void **req);
 static herr_t H5VL_pass_through_datatype_close(void *dt, hid_t dxpl_id, void **req);
 
 /* File callbacks */
@@ -164,12 +153,11 @@ static void * H5VL_pass_through_file_create(const char *name, unsigned flags, hi
                                             hid_t dxpl_id, void **req);
 static void * H5VL_pass_through_file_open(const char *name, unsigned flags, hid_t fapl_id, hid_t dxpl_id,
                                           void **req);
-static herr_t H5VL_pass_through_file_get(void *file, H5VL_file_get_t get_type, hid_t dxpl_id, void **req,
-                                         va_list arguments);
-static herr_t H5VL_pass_through_file_specific(void *file, H5VL_file_specific_t specific_type, hid_t dxpl_id,
-                                              void **req, va_list arguments);
-static herr_t H5VL_pass_through_file_optional(void *file, H5VL_file_optional_t opt_type, hid_t dxpl_id,
-                                              void **req, va_list arguments);
+static herr_t H5VL_pass_through_file_get(void *file, H5VL_file_get_args_t *args, hid_t dxpl_id, void **req);
+static herr_t H5VL_pass_through_file_specific(void *file, H5VL_file_specific_args_t *args, hid_t dxpl_id,
+                                              void **req);
+static herr_t H5VL_pass_through_file_optional(void *file, H5VL_optional_args_t *args, hid_t dxpl_id,
+                                              void **req);
 static herr_t H5VL_pass_through_file_close(void *file, hid_t dxpl_id, void **req);
 
 /* Group callbacks */
@@ -178,18 +166,17 @@ static void * H5VL_pass_through_group_create(void *obj, const H5VL_loc_params_t
                                              void **req);
 static void * H5VL_pass_through_group_open(void *obj, const H5VL_loc_params_t *loc_params, const char *name,
                                            hid_t gapl_id, hid_t dxpl_id, void **req);
-static herr_t H5VL_pass_through_group_get(void *obj, H5VL_group_get_t get_type, hid_t dxpl_id, void **req,
-                                          va_list arguments);
-static herr_t H5VL_pass_through_group_specific(void *obj, H5VL_group_specific_t specific_type, hid_t dxpl_id,
-                                               void **req, va_list arguments);
-static herr_t H5VL_pass_through_group_optional(void *obj, H5VL_group_optional_t opt_type, hid_t dxpl_id,
-                                               void **req, va_list arguments);
+static herr_t H5VL_pass_through_group_get(void *obj, H5VL_group_get_args_t *args, hid_t dxpl_id, void **req);
+static herr_t H5VL_pass_through_group_specific(void *obj, H5VL_group_specific_args_t *args, hid_t dxpl_id,
+                                               void **req);
+static herr_t H5VL_pass_through_group_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id,
+                                               void **req);
 static herr_t H5VL_pass_through_group_close(void *grp, hid_t dxpl_id, void **req);
 
 /* Link callbacks */
-static herr_t H5VL_pass_through_link_create(H5VL_link_create_type_t create_type, void *obj,
+static herr_t H5VL_pass_through_link_create(H5VL_link_create_args_t *args, void *obj,
                                             const H5VL_loc_params_t *loc_params, hid_t lcpl_id, hid_t lapl_id,
-                                            hid_t dxpl_id, void **req, va_list arguments);
+                                            hid_t dxpl_id, void **req);
 static herr_t H5VL_pass_through_link_copy(void *src_obj, const H5VL_loc_params_t *loc_params1, void *dst_obj,
                                           const H5VL_loc_params_t *loc_params2, hid_t lcpl_id, hid_t lapl_id,
                                           hid_t dxpl_id, void **req);
@@ -197,13 +184,11 @@ static herr_t H5VL_pass_through_link_move(void *src_obj, const H5VL_loc_params_t
                                           const H5VL_loc_params_t *loc_params2, hid_t lcpl_id, hid_t lapl_id,
                                           hid_t dxpl_id, void **req);
 static herr_t H5VL_pass_through_link_get(void *obj, const H5VL_loc_params_t *loc_params,
-                                         H5VL_link_get_t get_type, hid_t dxpl_id, void **req,
-                                         va_list arguments);
+                                         H5VL_link_get_args_t *args, hid_t dxpl_id, void **req);
 static herr_t H5VL_pass_through_link_specific(void *obj, const H5VL_loc_params_t *loc_params,
-                                              H5VL_link_specific_t specific_type, hid_t dxpl_id, void **req,
-                                              va_list arguments);
-static herr_t H5VL_pass_through_link_optional(void *obj, H5VL_link_optional_t opt_type, hid_t dxpl_id,
-                                              void **req, va_list arguments);
+                                              H5VL_link_specific_args_t *args, hid_t dxpl_id, void **req);
+static herr_t H5VL_pass_through_link_optional(void *obj, const H5VL_loc_params_t *loc_params,
+                                              H5VL_optional_args_t *args, hid_t dxpl_id, void **req);
 
 /* Object callbacks */
 static void * H5VL_pass_through_object_open(void *obj, const H5VL_loc_params_t *loc_params,
@@ -213,17 +198,16 @@ static herr_t H5VL_pass_through_object_copy(void *src_obj, const H5VL_loc_params
                                             const H5VL_loc_params_t *dst_loc_params, const char *dst_name,
                                             hid_t ocpypl_id, hid_t lcpl_id, hid_t dxpl_id, void **req);
 static herr_t H5VL_pass_through_object_get(void *obj, const H5VL_loc_params_t *loc_params,
-                                           H5VL_object_get_t get_type, hid_t dxpl_id, void **req,
-                                           va_list arguments);
+                                           H5VL_object_get_args_t *args, hid_t dxpl_id, void **req);
 static herr_t H5VL_pass_through_object_specific(void *obj, const H5VL_loc_params_t *loc_params,
-                                                H5VL_object_specific_t specific_type, hid_t dxpl_id,
-                                                void **req, va_list arguments);
-static herr_t H5VL_pass_through_object_optional(void *obj, H5VL_object_optional_t opt_type, hid_t dxpl_id,
-                                                void **req, va_list arguments);
+                                                H5VL_object_specific_args_t *args, hid_t dxpl_id, void **req);
+static herr_t H5VL_pass_through_object_optional(void *obj, const H5VL_loc_params_t *loc_params,
+                                                H5VL_optional_args_t *args, hid_t dxpl_id, void **req);
 
 /* Container/connector introspection callbacks */
 static herr_t H5VL_pass_through_introspect_get_conn_cls(void *obj, H5VL_get_conn_lvl_t lvl,
                                                         const H5VL_class_t **conn_cls);
+static herr_t H5VL_pass_through_introspect_get_cap_flags(const void *info, unsigned *cap_flags);
 static herr_t H5VL_pass_through_introspect_opt_query(void *obj, H5VL_subclass_t cls, int opt_type,
                                                      uint64_t *flags);
 
@@ -231,19 +215,15 @@ static herr_t H5VL_pass_through_introspect_opt_query(void *obj, H5VL_subclass_t
 static herr_t H5VL_pass_through_request_wait(void *req, uint64_t timeout, H5VL_request_status_t *status);
 static herr_t H5VL_pass_through_request_notify(void *obj, H5VL_request_notify_t cb, void *ctx);
 static herr_t H5VL_pass_through_request_cancel(void *req, H5VL_request_status_t *status);
-static herr_t H5VL_pass_through_request_specific(void *req, H5VL_request_specific_t specific_type,
-                                                 va_list arguments);
-static herr_t H5VL_pass_through_request_optional(void *req, H5VL_request_optional_t opt_type,
-                                                 va_list arguments);
+static herr_t H5VL_pass_through_request_specific(void *req, H5VL_request_specific_args_t *args);
+static herr_t H5VL_pass_through_request_optional(void *req, H5VL_optional_args_t *args);
 static herr_t H5VL_pass_through_request_free(void *req);
 
 /* Blob callbacks */
 static herr_t H5VL_pass_through_blob_put(void *obj, const void *buf, size_t size, void *blob_id, void *ctx);
 static herr_t H5VL_pass_through_blob_get(void *obj, const void *blob_id, void *buf, size_t size, void *ctx);
-static herr_t H5VL_pass_through_blob_specific(void *obj, void *blob_id, H5VL_blob_specific_t specific_type,
-                                              va_list arguments);
-static herr_t H5VL_pass_through_blob_optional(void *obj, void *blob_id, H5VL_blob_optional_t opt_type,
-                                              va_list arguments);
+static herr_t H5VL_pass_through_blob_specific(void *obj, void *blob_id, H5VL_blob_specific_args_t *args);
+static herr_t H5VL_pass_through_blob_optional(void *obj, void *blob_id, H5VL_optional_args_t *args);
 
 /* Token callbacks */
 static herr_t H5VL_pass_through_token_cmp(void *obj, const H5O_token_t *token1, const H5O_token_t *token2,
@@ -254,8 +234,7 @@ static herr_t H5VL_pass_through_token_from_str(void *obj, H5I_type_t obj_type, c
                                                H5O_token_t *token);
 
 /* Generic optional callback */
-static herr_t H5VL_pass_through_optional(void *obj, int op_type, hid_t dxpl_id, void **req,
-                                         va_list arguments);
+static herr_t H5VL_pass_through_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id, void **req);
 
 /*******************/
 /* Local variables */
@@ -355,8 +334,9 @@ static const H5VL_class_t H5VL_pass_through_g = {
     },
     {
         /* introspect_cls */
-        H5VL_pass_through_introspect_get_conn_cls, /* get_conn_cls */
-        H5VL_pass_through_introspect_opt_query,    /* opt_query */
+        H5VL_pass_through_introspect_get_conn_cls,  /* get_conn_cls */
+        H5VL_pass_through_introspect_get_cap_flags, /* get_cap_flags */
+        H5VL_pass_through_introspect_opt_query,     /* opt_query */
     },
     {
         /* request_cls */
@@ -1025,7 +1005,7 @@ H5VL_pass_through_attr_write(void *attr, hid_t mem_type_id, const void *buf, hid
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_attr_get(void *obj, H5VL_attr_get_t get_type, hid_t dxpl_id, void **req, va_list arguments)
+H5VL_pass_through_attr_get(void *obj, H5VL_attr_get_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -1034,7 +1014,7 @@ H5VL_pass_through_attr_get(void *obj, H5VL_attr_get_t get_type, hid_t dxpl_id, v
     printf("------- PASS THROUGH VOL ATTRIBUTE Get\n");
 #endif
 
-    ret_value = H5VLattr_get(o->under_object, o->under_vol_id, get_type, dxpl_id, req, arguments);
+    ret_value = H5VLattr_get(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -1055,8 +1035,7 @@ H5VL_pass_through_attr_get(void *obj, H5VL_attr_get_t get_type, hid_t dxpl_id, v
  */
 static herr_t
 H5VL_pass_through_attr_specific(void *obj, const H5VL_loc_params_t *loc_params,
-                                H5VL_attr_specific_t specific_type, hid_t dxpl_id, void **req,
-                                va_list arguments)
+                                H5VL_attr_specific_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -1065,8 +1044,7 @@ H5VL_pass_through_attr_specific(void *obj, const H5VL_loc_params_t *loc_params,
     printf("------- PASS THROUGH VOL ATTRIBUTE Specific\n");
 #endif
 
-    ret_value = H5VLattr_specific(o->under_object, loc_params, o->under_vol_id, specific_type, dxpl_id, req,
-                                  arguments);
+    ret_value = H5VLattr_specific(o->under_object, loc_params, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -1086,8 +1064,7 @@ H5VL_pass_through_attr_specific(void *obj, const H5VL_loc_params_t *loc_params,
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_attr_optional(void *obj, H5VL_attr_optional_t opt_type, hid_t dxpl_id, void **req,
-                                va_list arguments)
+H5VL_pass_through_attr_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -1096,7 +1073,7 @@ H5VL_pass_through_attr_optional(void *obj, H5VL_attr_optional_t opt_type, hid_t
     printf("------- PASS THROUGH VOL ATTRIBUTE Optional\n");
 #endif
 
-    ret_value = H5VLattr_optional(o->under_object, o->under_vol_id, opt_type, dxpl_id, req, arguments);
+    ret_value = H5VLattr_optional(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -1285,8 +1262,7 @@ H5VL_pass_through_dataset_write(void *dset, hid_t mem_type_id, hid_t mem_space_i
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_dataset_get(void *dset, H5VL_dataset_get_t get_type, hid_t dxpl_id, void **req,
-                              va_list arguments)
+H5VL_pass_through_dataset_get(void *dset, H5VL_dataset_get_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)dset;
     herr_t               ret_value;
@@ -1295,7 +1271,7 @@ H5VL_pass_through_dataset_get(void *dset, H5VL_dataset_get_t get_type, hid_t dxp
     printf("------- PASS THROUGH VOL DATASET Get\n");
 #endif
 
-    ret_value = H5VLdataset_get(o->under_object, o->under_vol_id, get_type, dxpl_id, req, arguments);
+    ret_value = H5VLdataset_get(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -1315,8 +1291,7 @@ H5VL_pass_through_dataset_get(void *dset, H5VL_dataset_get_t get_type, hid_t dxp
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_dataset_specific(void *obj, H5VL_dataset_specific_t specific_type, hid_t dxpl_id,
-                                   void **req, va_list arguments)
+H5VL_pass_through_dataset_specific(void *obj, H5VL_dataset_specific_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     hid_t                under_vol_id;
@@ -1326,12 +1301,12 @@ H5VL_pass_through_dataset_specific(void *obj, H5VL_dataset_specific_t specific_t
     printf("------- PASS THROUGH VOL H5Dspecific\n");
 #endif
 
-    // Save copy of underlying VOL connector ID and prov helper, in case of
-    // refresh destroying the current object
+    /* Save copy of underlying VOL connector ID, in case of
+     * 'refresh' operation destroying the current object
+     */
     under_vol_id = o->under_vol_id;
 
-    ret_value =
-        H5VLdataset_specific(o->under_object, o->under_vol_id, specific_type, dxpl_id, req, arguments);
+    ret_value = H5VLdataset_specific(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -1351,8 +1326,7 @@ H5VL_pass_through_dataset_specific(void *obj, H5VL_dataset_specific_t specific_t
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_dataset_optional(void *obj, H5VL_dataset_optional_t opt_type, hid_t dxpl_id, void **req,
-                                   va_list arguments)
+H5VL_pass_through_dataset_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -1361,7 +1335,7 @@ H5VL_pass_through_dataset_optional(void *obj, H5VL_dataset_optional_t opt_type,
     printf("------- PASS THROUGH VOL DATASET Optional\n");
 #endif
 
-    ret_value = H5VLdataset_optional(o->under_object, o->under_vol_id, opt_type, dxpl_id, req, arguments);
+    ret_value = H5VLdataset_optional(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -1488,8 +1462,7 @@ H5VL_pass_through_datatype_open(void *obj, const H5VL_loc_params_t *loc_params,
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_datatype_get(void *dt, H5VL_datatype_get_t get_type, hid_t dxpl_id, void **req,
-                               va_list arguments)
+H5VL_pass_through_datatype_get(void *dt, H5VL_datatype_get_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)dt;
     herr_t               ret_value;
@@ -1498,7 +1471,7 @@ H5VL_pass_through_datatype_get(void *dt, H5VL_datatype_get_t get_type, hid_t dxp
     printf("------- PASS THROUGH VOL DATATYPE Get\n");
 #endif
 
-    ret_value = H5VLdatatype_get(o->under_object, o->under_vol_id, get_type, dxpl_id, req, arguments);
+    ret_value = H5VLdatatype_get(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -1518,8 +1491,7 @@ H5VL_pass_through_datatype_get(void *dt, H5VL_datatype_get_t get_type, hid_t dxp
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_datatype_specific(void *obj, H5VL_datatype_specific_t specific_type, hid_t dxpl_id,
-                                    void **req, va_list arguments)
+H5VL_pass_through_datatype_specific(void *obj, H5VL_datatype_specific_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     hid_t                under_vol_id;
@@ -1529,12 +1501,12 @@ H5VL_pass_through_datatype_specific(void *obj, H5VL_datatype_specific_t specific
     printf("------- PASS THROUGH VOL DATATYPE Specific\n");
 #endif
 
-    // Save copy of underlying VOL connector ID and prov helper, in case of
-    // refresh destroying the current object
+    /* Save copy of underlying VOL connector ID, in case of
+     * 'refresh' operation destroying the current object
+     */
     under_vol_id = o->under_vol_id;
 
-    ret_value =
-        H5VLdatatype_specific(o->under_object, o->under_vol_id, specific_type, dxpl_id, req, arguments);
+    ret_value = H5VLdatatype_specific(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -1554,8 +1526,7 @@ H5VL_pass_through_datatype_specific(void *obj, H5VL_datatype_specific_t specific
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_datatype_optional(void *obj, H5VL_datatype_optional_t opt_type, hid_t dxpl_id, void **req,
-                                    va_list arguments)
+H5VL_pass_through_datatype_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -1564,7 +1535,7 @@ H5VL_pass_through_datatype_optional(void *obj, H5VL_datatype_optional_t opt_type
     printf("------- PASS THROUGH VOL DATATYPE Optional\n");
 #endif
 
-    ret_value = H5VLdatatype_optional(o->under_object, o->under_vol_id, opt_type, dxpl_id, req, arguments);
+    ret_value = H5VLdatatype_optional(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -1732,7 +1703,7 @@ H5VL_pass_through_file_open(const char *name, unsigned flags, hid_t fapl_id, hid
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_file_get(void *file, H5VL_file_get_t get_type, hid_t dxpl_id, void **req, va_list arguments)
+H5VL_pass_through_file_get(void *file, H5VL_file_get_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)file;
     herr_t               ret_value;
@@ -1741,7 +1712,7 @@ H5VL_pass_through_file_get(void *file, H5VL_file_get_t get_type, hid_t dxpl_id,
     printf("------- PASS THROUGH VOL FILE Get\n");
 #endif
 
-    ret_value = H5VLfile_get(o->under_object, o->under_vol_id, get_type, dxpl_id, req, arguments);
+    ret_value = H5VLfile_get(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -1751,31 +1722,6 @@ H5VL_pass_through_file_get(void *file, H5VL_file_get_t get_type, hid_t dxpl_id,
 } /* end H5VL_pass_through_file_get() */
 
 /*-------------------------------------------------------------------------
- * Function:    H5VL_pass_through_file_specific_reissue
- *
- * Purpose:     Re-wrap vararg arguments into a va_list and reissue the
- *              file specific callback to the underlying VOL connector.
- *
- * Return:      Success:    0
- *              Failure:    -1
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5VL_pass_through_file_specific_reissue(void *obj, hid_t connector_id, H5VL_file_specific_t specific_type,
-                                        hid_t dxpl_id, void **req, ...)
-{
-    va_list arguments;
-    herr_t  ret_value;
-
-    va_start(arguments, req);
-    ret_value = H5VLfile_specific(obj, connector_id, specific_type, dxpl_id, req, arguments);
-    va_end(arguments);
-
-    return ret_value;
-} /* end H5VL_pass_through_file_specific_reissue() */
-
-/*-------------------------------------------------------------------------
  * Function:    H5VL_pass_through_file_specific
  *
  * Purpose:     Specific operation on file
@@ -1786,106 +1732,109 @@ H5VL_pass_through_file_specific_reissue(void *obj, hid_t connector_id, H5VL_file
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_file_specific(void *file, H5VL_file_specific_t specific_type, hid_t dxpl_id, void **req,
-                                va_list arguments)
+H5VL_pass_through_file_specific(void *file, H5VL_file_specific_args_t *args, hid_t dxpl_id, void **req)
 {
-    H5VL_pass_through_t *o            = (H5VL_pass_through_t *)file;
-    hid_t                under_vol_id = -1;
-    herr_t               ret_value;
+    H5VL_pass_through_t *      o = (H5VL_pass_through_t *)file;
+    H5VL_pass_through_t *      new_o;
+    H5VL_file_specific_args_t  my_args;
+    H5VL_file_specific_args_t *new_args;
+    H5VL_pass_through_info_t * info;
+    hid_t                      under_vol_id = -1;
+    herr_t                     ret_value;
 
 #ifdef ENABLE_PASSTHRU_LOGGING
     printf("------- PASS THROUGH VOL FILE Specific\n");
 #endif
 
-    /* Unpack arguments to get at the child file pointer when mounting a file */
-    if (specific_type == H5VL_FILE_MOUNT) {
-        H5I_type_t           loc_type;
-        const char *         name;
-        H5VL_pass_through_t *child_file;
-        hid_t                plist_id;
-
-        /* Retrieve parameters for 'mount' operation, so we can unwrap the child file */
-        loc_type   = (H5I_type_t)va_arg(arguments, int); /* enum work-around */
-        name       = va_arg(arguments, const char *);
-        child_file = (H5VL_pass_through_t *)va_arg(arguments, void *);
-        plist_id   = va_arg(arguments, hid_t);
-
-        /* Keep the correct underlying VOL ID for possible async request token */
-        under_vol_id = o->under_vol_id;
-
-        /* Re-issue 'file specific' call, using the unwrapped pieces */
-        ret_value = H5VL_pass_through_file_specific_reissue(o->under_object, o->under_vol_id, specific_type,
-                                                            dxpl_id, req, (int)loc_type, name,
-                                                            child_file->under_object, plist_id);
-    } /* end if */
-    else if (specific_type == H5VL_FILE_IS_ACCESSIBLE || specific_type == H5VL_FILE_DELETE) {
-        H5VL_pass_through_info_t *info;
-        hid_t                     fapl_id, under_fapl_id;
-        const char *              name;
-        htri_t *                  ret;
-
-        /* Get the arguments for the 'is accessible' check */
-        fapl_id = va_arg(arguments, hid_t);
-        name    = va_arg(arguments, const char *);
-        ret     = va_arg(arguments, htri_t *);
+    if (args->op_type == H5VL_FILE_IS_ACCESSIBLE) {
+        /* Shallow copy the args */
+        memcpy(&my_args, args, sizeof(my_args));
 
         /* Get copy of our VOL info from FAPL */
-        H5Pget_vol_info(fapl_id, (void **)&info);
+        H5Pget_vol_info(args->args.is_accessible.fapl_id, (void **)&info);
 
         /* Make sure we have info about the underlying VOL to be used */
         if (!info)
             return (-1);
 
+        /* Keep the correct underlying VOL ID for later */
+        under_vol_id = info->under_vol_id;
+
         /* Copy the FAPL */
-        under_fapl_id = H5Pcopy(fapl_id);
+        my_args.args.is_accessible.fapl_id = H5Pcopy(args->args.is_accessible.fapl_id);
 
         /* Set the VOL ID and info for the underlying FAPL */
-        H5Pset_vol(under_fapl_id, info->under_vol_id, info->under_vol_info);
+        H5Pset_vol(my_args.args.is_accessible.fapl_id, info->under_vol_id, info->under_vol_info);
 
-        /* Keep the correct underlying VOL ID for possible async request token */
+        /* Set argument pointer to new arguments */
+        new_args = &my_args;
+
+        /* Set object pointer for operation */
+        new_o = NULL;
+    } /* end else-if */
+    else if (args->op_type == H5VL_FILE_DELETE) {
+        /* Shallow copy the args */
+        memcpy(&my_args, args, sizeof(my_args));
+
+        /* Get copy of our VOL info from FAPL */
+        H5Pget_vol_info(args->args.del.fapl_id, (void **)&info);
+
+        /* Make sure we have info about the underlying VOL to be used */
+        if (!info)
+            return (-1);
+
+        /* Keep the correct underlying VOL ID for later */
         under_vol_id = info->under_vol_id;
 
-        /* Re-issue 'file specific' call */
-        ret_value = H5VL_pass_through_file_specific_reissue(NULL, info->under_vol_id, specific_type, dxpl_id,
-                                                            req, under_fapl_id, name, ret);
+        /* Copy the FAPL */
+        my_args.args.del.fapl_id = H5Pcopy(args->args.del.fapl_id);
 
-        /* Close underlying FAPL */
-        H5Pclose(under_fapl_id);
+        /* Set the VOL ID and info for the underlying FAPL */
+        H5Pset_vol(my_args.args.del.fapl_id, info->under_vol_id, info->under_vol_info);
 
-        /* Release copy of our VOL info */
-        H5VL_pass_through_info_free(info);
+        /* Set argument pointer to new arguments */
+        new_args = &my_args;
+
+        /* Set object pointer for operation */
+        new_o = NULL;
     } /* end else-if */
     else {
-        va_list my_arguments;
-
-        /* Make a copy of the argument list for later, if reopening */
-        if (specific_type == H5VL_FILE_REOPEN)
-            va_copy(my_arguments, arguments);
-
-        /* Keep the correct underlying VOL ID for possible async request token */
+        /* Keep the correct underlying VOL ID for later */
         under_vol_id = o->under_vol_id;
 
-        ret_value =
-            H5VLfile_specific(o->under_object, o->under_vol_id, specific_type, dxpl_id, req, arguments);
-
-        /* Wrap file struct pointer, if we reopened one */
-        if (specific_type == H5VL_FILE_REOPEN) {
-            if (ret_value >= 0) {
-                void **ret = va_arg(my_arguments, void **);
+        /* Set argument pointer to current arguments */
+        new_args = args;
 
-                if (ret && *ret)
-                    *ret = H5VL_pass_through_new_obj(*ret, o->under_vol_id);
-            } /* end if */
+        /* Set object pointer for operation */
+        new_o = o->under_object;
+    } /* end else */
 
-            /* Finish use of copied vararg list */
-            va_end(my_arguments);
-        } /* end if */
-    }     /* end else */
+    ret_value = H5VLfile_specific(new_o, under_vol_id, new_args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
         *req = H5VL_pass_through_new_obj(*req, under_vol_id);
 
+    if (args->op_type == H5VL_FILE_IS_ACCESSIBLE) {
+        /* Close underlying FAPL */
+        H5Pclose(my_args.args.is_accessible.fapl_id);
+
+        /* Release copy of our VOL info */
+        H5VL_pass_through_info_free(info);
+    } /* end else-if */
+    else if (args->op_type == H5VL_FILE_DELETE) {
+        /* Close underlying FAPL */
+        H5Pclose(my_args.args.del.fapl_id);
+
+        /* Release copy of our VOL info */
+        H5VL_pass_through_info_free(info);
+    } /* end else-if */
+    else if (args->op_type == H5VL_FILE_REOPEN) {
+        /* Wrap file struct pointer for 'reopen' operation, if we reopened one */
+        if (ret_value >= 0 && *args->args.reopen.file)
+            *args->args.reopen.file = H5VL_pass_through_new_obj(*args->args.reopen.file, under_vol_id);
+    } /* end else */
+
     return ret_value;
 } /* end H5VL_pass_through_file_specific() */
 
@@ -1900,8 +1849,7 @@ H5VL_pass_through_file_specific(void *file, H5VL_file_specific_t specific_type,
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_file_optional(void *file, H5VL_file_optional_t opt_type, hid_t dxpl_id, void **req,
-                                va_list arguments)
+H5VL_pass_through_file_optional(void *file, H5VL_optional_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)file;
     herr_t               ret_value;
@@ -1910,7 +1858,7 @@ H5VL_pass_through_file_optional(void *file, H5VL_file_optional_t opt_type, hid_t
     printf("------- PASS THROUGH VOL File Optional\n");
 #endif
 
-    ret_value = H5VLfile_optional(o->under_object, o->under_vol_id, opt_type, dxpl_id, req, arguments);
+    ret_value = H5VLfile_optional(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2036,8 +1984,7 @@ H5VL_pass_through_group_open(void *obj, const H5VL_loc_params_t *loc_params, con
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_group_get(void *obj, H5VL_group_get_t get_type, hid_t dxpl_id, void **req,
-                            va_list arguments)
+H5VL_pass_through_group_get(void *obj, H5VL_group_get_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -2046,7 +1993,7 @@ H5VL_pass_through_group_get(void *obj, H5VL_group_get_t get_type, hid_t dxpl_id,
     printf("------- PASS THROUGH VOL GROUP Get\n");
 #endif
 
-    ret_value = H5VLgroup_get(o->under_object, o->under_vol_id, get_type, dxpl_id, req, arguments);
+    ret_value = H5VLgroup_get(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2066,8 +2013,7 @@ H5VL_pass_through_group_get(void *obj, H5VL_group_get_t get_type, hid_t dxpl_id,
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_group_specific(void *obj, H5VL_group_specific_t specific_type, hid_t dxpl_id, void **req,
-                                 va_list arguments)
+H5VL_pass_through_group_specific(void *obj, H5VL_group_specific_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     hid_t                under_vol_id;
@@ -2077,11 +2023,27 @@ H5VL_pass_through_group_specific(void *obj, H5VL_group_specific_t specific_type,
     printf("------- PASS THROUGH VOL GROUP Specific\n");
 #endif
 
-    // Save copy of underlying VOL connector ID and prov helper, in case of
-    // refresh destroying the current object
+    /* Save copy of underlying VOL connector ID, in case of
+     * 'refresh' operation destroying the current object
+     */
     under_vol_id = o->under_vol_id;
 
-    ret_value = H5VLgroup_specific(o->under_object, o->under_vol_id, specific_type, dxpl_id, req, arguments);
+    /* Unpack arguments to get at the child file pointer when mounting a file */
+    if (args->op_type == H5VL_GROUP_MOUNT) {
+        H5VL_group_specific_args_t vol_cb_args; /* New group specific arg struct */
+
+        /* Set up new VOL callback arguments */
+        vol_cb_args.op_type         = H5VL_GROUP_MOUNT;
+        vol_cb_args.args.mount.name = args->args.mount.name;
+        vol_cb_args.args.mount.child_file =
+            ((H5VL_pass_through_t *)args->args.mount.child_file)->under_object;
+        vol_cb_args.args.mount.fmpl_id = args->args.mount.fmpl_id;
+
+        /* Re-issue 'group specific' call, using the unwrapped pieces */
+        ret_value = H5VLgroup_specific(o->under_object, under_vol_id, &vol_cb_args, dxpl_id, req);
+    } /* end if */
+    else
+        ret_value = H5VLgroup_specific(o->under_object, under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2101,8 +2063,7 @@ H5VL_pass_through_group_specific(void *obj, H5VL_group_specific_t specific_type,
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_group_optional(void *obj, H5VL_group_optional_t opt_type, hid_t dxpl_id, void **req,
-                                 va_list arguments)
+H5VL_pass_through_group_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -2111,7 +2072,7 @@ H5VL_pass_through_group_optional(void *obj, H5VL_group_optional_t opt_type, hid_
     printf("------- PASS THROUGH VOL GROUP Optional\n");
 #endif
 
-    ret_value = H5VLgroup_optional(o->under_object, o->under_vol_id, opt_type, dxpl_id, req, arguments);
+    ret_value = H5VLgroup_optional(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2154,33 +2115,6 @@ H5VL_pass_through_group_close(void *grp, hid_t dxpl_id, void **req)
 } /* end H5VL_pass_through_group_close() */
 
 /*-------------------------------------------------------------------------
- * Function:    H5VL_pass_through_link_create_reissue
- *
- * Purpose:     Re-wrap vararg arguments into a va_list and reissue the
- *              link create callback to the underlying VOL connector.
- *
- * Return:      Success:    0
- *              Failure:    -1
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5VL_pass_through_link_create_reissue(H5VL_link_create_type_t create_type, void *obj,
-                                      const H5VL_loc_params_t *loc_params, hid_t connector_id, hid_t lcpl_id,
-                                      hid_t lapl_id, hid_t dxpl_id, void **req, ...)
-{
-    va_list arguments;
-    herr_t  ret_value;
-
-    va_start(arguments, req);
-    ret_value = H5VLlink_create(create_type, obj, loc_params, connector_id, lcpl_id, lapl_id, dxpl_id, req,
-                                arguments);
-    va_end(arguments);
-
-    return ret_value;
-} /* end H5VL_pass_through_link_create_reissue() */
-
-/*-------------------------------------------------------------------------
  * Function:    H5VL_pass_through_link_create
  *
  * Purpose:     Creates a hard / soft / UD / external link.
@@ -2191,9 +2125,8 @@ H5VL_pass_through_link_create_reissue(H5VL_link_create_type_t create_type, void
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_link_create(H5VL_link_create_type_t create_type, void *obj,
-                              const H5VL_loc_params_t *loc_params, hid_t lcpl_id, hid_t lapl_id,
-                              hid_t dxpl_id, void **req, va_list arguments)
+H5VL_pass_through_link_create(H5VL_link_create_args_t *args, void *obj, const H5VL_loc_params_t *loc_params,
+                              hid_t lcpl_id, hid_t lapl_id, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o            = (H5VL_pass_through_t *)obj;
     hid_t                under_vol_id = -1;
@@ -2208,32 +2141,22 @@ H5VL_pass_through_link_create(H5VL_link_create_type_t create_type, void *obj,
         under_vol_id = o->under_vol_id;
 
     /* Fix up the link target object for hard link creation */
-    if (H5VL_LINK_CREATE_HARD == create_type) {
-        void *             cur_obj;
-        H5VL_loc_params_t *cur_params;
+    if (H5VL_LINK_CREATE_HARD == args->op_type) {
+        void *cur_obj = args->args.hard.curr_obj;
 
-        /* Retrieve the object & loc params for the link target */
-        cur_obj    = va_arg(arguments, void *);
-        cur_params = va_arg(arguments, H5VL_loc_params_t *);
-
-        /* If it's a non-NULL pointer, find the 'under object' and re-set the property */
+        /* If cur_obj is a non-NULL pointer, find its 'under object' and update the pointer */
         if (cur_obj) {
-            /* Check if we still need the "under" VOL ID */
+            /* Check if we still haven't set the "under" VOL ID */
             if (under_vol_id < 0)
                 under_vol_id = ((H5VL_pass_through_t *)cur_obj)->under_vol_id;
 
-            /* Set the object for the link target */
-            cur_obj = ((H5VL_pass_through_t *)cur_obj)->under_object;
+            /* Update the object for the link target */
+            args->args.hard.curr_obj = ((H5VL_pass_through_t *)cur_obj)->under_object;
         } /* end if */
+    }     /* end if */
 
-        /* Re-issue 'link create' call, using the unwrapped pieces */
-        ret_value = H5VL_pass_through_link_create_reissue(create_type, (o ? o->under_object : NULL),
-                                                          loc_params, under_vol_id, lcpl_id, lapl_id, dxpl_id,
-                                                          req, cur_obj, cur_params);
-    } /* end if */
-    else
-        ret_value = H5VLlink_create(create_type, (o ? o->under_object : NULL), loc_params, under_vol_id,
-                                    lcpl_id, lapl_id, dxpl_id, req, arguments);
+    ret_value = H5VLlink_create(args, (o ? o->under_object : NULL), loc_params, under_vol_id, lcpl_id,
+                                lapl_id, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2347,8 +2270,8 @@ H5VL_pass_through_link_move(void *src_obj, const H5VL_loc_params_t *loc_params1,
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_link_get(void *obj, const H5VL_loc_params_t *loc_params, H5VL_link_get_t get_type,
-                           hid_t dxpl_id, void **req, va_list arguments)
+H5VL_pass_through_link_get(void *obj, const H5VL_loc_params_t *loc_params, H5VL_link_get_args_t *args,
+                           hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -2357,7 +2280,7 @@ H5VL_pass_through_link_get(void *obj, const H5VL_loc_params_t *loc_params, H5VL_
     printf("------- PASS THROUGH VOL LINK Get\n");
 #endif
 
-    ret_value = H5VLlink_get(o->under_object, loc_params, o->under_vol_id, get_type, dxpl_id, req, arguments);
+    ret_value = H5VLlink_get(o->under_object, loc_params, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2378,8 +2301,7 @@ H5VL_pass_through_link_get(void *obj, const H5VL_loc_params_t *loc_params, H5VL_
  */
 static herr_t
 H5VL_pass_through_link_specific(void *obj, const H5VL_loc_params_t *loc_params,
-                                H5VL_link_specific_t specific_type, hid_t dxpl_id, void **req,
-                                va_list arguments)
+                                H5VL_link_specific_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -2388,8 +2310,7 @@ H5VL_pass_through_link_specific(void *obj, const H5VL_loc_params_t *loc_params,
     printf("------- PASS THROUGH VOL LINK Specific\n");
 #endif
 
-    ret_value = H5VLlink_specific(o->under_object, loc_params, o->under_vol_id, specific_type, dxpl_id, req,
-                                  arguments);
+    ret_value = H5VLlink_specific(o->under_object, loc_params, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2409,8 +2330,8 @@ H5VL_pass_through_link_specific(void *obj, const H5VL_loc_params_t *loc_params,
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_link_optional(void *obj, H5VL_link_optional_t opt_type, hid_t dxpl_id, void **req,
-                                va_list arguments)
+H5VL_pass_through_link_optional(void *obj, const H5VL_loc_params_t *loc_params, H5VL_optional_args_t *args,
+                                hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -2419,7 +2340,7 @@ H5VL_pass_through_link_optional(void *obj, H5VL_link_optional_t opt_type, hid_t
     printf("------- PASS THROUGH VOL LINK Optional\n");
 #endif
 
-    ret_value = H5VLlink_optional(o->under_object, o->under_vol_id, opt_type, dxpl_id, req, arguments);
+    ret_value = H5VLlink_optional(o->under_object, loc_params, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2509,8 +2430,8 @@ H5VL_pass_through_object_copy(void *src_obj, const H5VL_loc_params_t *src_loc_pa
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_object_get(void *obj, const H5VL_loc_params_t *loc_params, H5VL_object_get_t get_type,
-                             hid_t dxpl_id, void **req, va_list arguments)
+H5VL_pass_through_object_get(void *obj, const H5VL_loc_params_t *loc_params, H5VL_object_get_args_t *args,
+                             hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -2519,8 +2440,7 @@ H5VL_pass_through_object_get(void *obj, const H5VL_loc_params_t *loc_params, H5V
     printf("------- PASS THROUGH VOL OBJECT Get\n");
 #endif
 
-    ret_value =
-        H5VLobject_get(o->under_object, loc_params, o->under_vol_id, get_type, dxpl_id, req, arguments);
+    ret_value = H5VLobject_get(o->under_object, loc_params, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2541,8 +2461,7 @@ H5VL_pass_through_object_get(void *obj, const H5VL_loc_params_t *loc_params, H5V
  */
 static herr_t
 H5VL_pass_through_object_specific(void *obj, const H5VL_loc_params_t *loc_params,
-                                  H5VL_object_specific_t specific_type, hid_t dxpl_id, void **req,
-                                  va_list arguments)
+                                  H5VL_object_specific_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     hid_t                under_vol_id;
@@ -2552,12 +2471,12 @@ H5VL_pass_through_object_specific(void *obj, const H5VL_loc_params_t *loc_params
     printf("------- PASS THROUGH VOL OBJECT Specific\n");
 #endif
 
-    // Save copy of underlying VOL connector ID and prov helper, in case of
-    // refresh destroying the current object
+    /* Save copy of underlying VOL connector ID, in case of
+     * 'refresh' operation destroying the current object
+     */
     under_vol_id = o->under_vol_id;
 
-    ret_value = H5VLobject_specific(o->under_object, loc_params, o->under_vol_id, specific_type, dxpl_id, req,
-                                    arguments);
+    ret_value = H5VLobject_specific(o->under_object, loc_params, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2577,8 +2496,8 @@ H5VL_pass_through_object_specific(void *obj, const H5VL_loc_params_t *loc_params
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_object_optional(void *obj, H5VL_object_optional_t opt_type, hid_t dxpl_id, void **req,
-                                  va_list arguments)
+H5VL_pass_through_object_optional(void *obj, const H5VL_loc_params_t *loc_params, H5VL_optional_args_t *args,
+                                  hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -2587,7 +2506,7 @@ H5VL_pass_through_object_optional(void *obj, H5VL_object_optional_t opt_type, hi
     printf("------- PASS THROUGH VOL OBJECT Optional\n");
 #endif
 
-    ret_value = H5VLobject_optional(o->under_object, o->under_vol_id, opt_type, dxpl_id, req, arguments);
+    ret_value = H5VLobject_optional(o->under_object, loc_params, o->under_vol_id, args, dxpl_id, req);
 
     /* Check for async request */
     if (req && *req)
@@ -2597,7 +2516,7 @@ H5VL_pass_through_object_optional(void *obj, H5VL_object_optional_t opt_type, hi
 } /* end H5VL_pass_through_object_optional() */
 
 /*-------------------------------------------------------------------------
- * Function:    H5VL_pass_through_introspect_get_conn_clss
+ * Function:    H5VL_pass_through_introspect_get_conn_cls
  *
  * Purpose:     Query the connector class.
  *
@@ -2627,6 +2546,36 @@ H5VL_pass_through_introspect_get_conn_cls(void *obj, H5VL_get_conn_lvl_t lvl, co
 } /* end H5VL_pass_through_introspect_get_conn_cls() */
 
 /*-------------------------------------------------------------------------
+ * Function:    H5VL_pass_through_introspect_get_cap_flags
+ *
+ * Purpose:     Query the capability flags for this connector and any
+ *              underlying connector(s).
+ *
+ * Return:      SUCCEED / FAIL
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5VL_pass_through_introspect_get_cap_flags(const void *_info, unsigned *cap_flags)
+{
+    const H5VL_pass_through_info_t *info = (const H5VL_pass_through_info_t *)_info;
+    herr_t                          ret_value;
+
+#ifdef ENABLE_PASSTHRU_LOGGING
+    printf("------- PASS THROUGH VOL INTROSPECT GetCapFlags\n");
+#endif
+
+    /* Invoke the query on the underlying VOL connector */
+    ret_value = H5VLintrospect_get_cap_flags(info->under_vol_info, info->under_vol_id, cap_flags);
+
+    /* Bitwise OR our capability flags in */
+    if (ret_value >= 0)
+        *cap_flags |= H5VL_pass_through_g.cap_flags;
+
+    return ret_value;
+} /* end H5VL_pass_through_introspect_get_cap_flags() */
+
+/*-------------------------------------------------------------------------
  * Function:    H5VL_pass_through_introspect_opt_query
  *
  * Purpose:     Query if an optional operation is supported by this connector
@@ -2743,31 +2692,6 @@ H5VL_pass_through_request_cancel(void *obj, H5VL_request_status_t *status)
 } /* end H5VL_pass_through_request_cancel() */
 
 /*-------------------------------------------------------------------------
- * Function:    H5VL_pass_through_request_specific_reissue
- *
- * Purpose:     Re-wrap vararg arguments into a va_list and reissue the
- *              request specific callback to the underlying VOL connector.
- *
- * Return:      Success:    0
- *              Failure:    -1
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5VL_pass_through_request_specific_reissue(void *obj, hid_t connector_id,
-                                           H5VL_request_specific_t specific_type, ...)
-{
-    va_list arguments;
-    herr_t  ret_value;
-
-    va_start(arguments, specific_type);
-    ret_value = H5VLrequest_specific(obj, connector_id, specific_type, arguments);
-    va_end(arguments);
-
-    return ret_value;
-} /* end H5VL_pass_through_request_specific_reissue() */
-
-/*-------------------------------------------------------------------------
  * Function:    H5VL_pass_through_request_specific
  *
  * Purpose:     Specific operation on a request
@@ -2778,139 +2702,16 @@ H5VL_pass_through_request_specific_reissue(void *obj, hid_t connector_id,
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_request_specific(void *obj, H5VL_request_specific_t specific_type, va_list arguments)
+H5VL_pass_through_request_specific(void *obj, H5VL_request_specific_args_t *args)
 {
-    herr_t ret_value = -1;
+    H5VL_pass_through_t *o         = (H5VL_pass_through_t *)obj;
+    herr_t               ret_value = -1;
 
 #ifdef ENABLE_PASSTHRU_LOGGING
     printf("------- PASS THROUGH VOL REQUEST Specific\n");
 #endif
 
-    if (H5VL_REQUEST_WAITANY == specific_type || H5VL_REQUEST_WAITSOME == specific_type ||
-        H5VL_REQUEST_WAITALL == specific_type) {
-        va_list tmp_arguments;
-        size_t  req_count;
-
-        /* Sanity check */
-        assert(obj == NULL);
-
-        /* Get enough info to call the underlying connector */
-        va_copy(tmp_arguments, arguments);
-        req_count = va_arg(tmp_arguments, size_t);
-
-        /* Can only use a request to invoke the underlying VOL connector when there's >0 requests */
-        if (req_count > 0) {
-            void **              req_array;
-            void **              under_req_array;
-            uint64_t             timeout;
-            H5VL_pass_through_t *o;
-            size_t               u; /* Local index variable */
-
-            /* Get the request array */
-            req_array = va_arg(tmp_arguments, void **);
-
-            /* Get a request to use for determining the underlying VOL connector */
-            o = (H5VL_pass_through_t *)req_array[0];
-
-            /* Create array of underlying VOL requests */
-            under_req_array = (void **)malloc(req_count * sizeof(void **));
-            for (u = 0; u < req_count; u++)
-                under_req_array[u] = ((H5VL_pass_through_t *)req_array[u])->under_object;
-
-            /* Remove the timeout value from the vararg list (it's used in all the calls below) */
-            timeout = va_arg(tmp_arguments, uint64_t);
-
-            /* Release requests that have completed */
-            if (H5VL_REQUEST_WAITANY == specific_type) {
-                size_t *               idx;    /* Pointer to the index of completed request */
-                H5VL_request_status_t *status; /* Pointer to the request's status */
-
-                /* Retrieve the remaining arguments */
-                idx = va_arg(tmp_arguments, size_t *);
-                assert(*idx <= req_count);
-                status = va_arg(tmp_arguments, H5VL_request_status_t *);
-
-                /* Reissue the WAITANY 'request specific' call */
-                ret_value = H5VL_pass_through_request_specific_reissue(o->under_object, o->under_vol_id,
-                                                                       specific_type, req_count,
-                                                                       under_req_array, timeout, idx, status);
-
-                /* Release the completed request, if it completed */
-                if (ret_value >= 0 && *status != H5ES_STATUS_IN_PROGRESS) {
-                    H5VL_pass_through_t *tmp_o;
-
-                    tmp_o = (H5VL_pass_through_t *)req_array[*idx];
-                    H5VL_pass_through_free_obj(tmp_o);
-                } /* end if */
-            }     /* end if */
-            else if (H5VL_REQUEST_WAITSOME == specific_type) {
-                size_t *               outcount;          /* # of completed requests */
-                unsigned *             array_of_indices;  /* Array of indices for completed requests */
-                H5VL_request_status_t *array_of_statuses; /* Array of statuses for completed requests */
-
-                /* Retrieve the remaining arguments */
-                outcount = va_arg(tmp_arguments, size_t *);
-                assert(*outcount <= req_count);
-                array_of_indices  = va_arg(tmp_arguments, unsigned *);
-                array_of_statuses = va_arg(tmp_arguments, H5VL_request_status_t *);
-
-                /* Reissue the WAITSOME 'request specific' call */
-                ret_value = H5VL_pass_through_request_specific_reissue(
-                    o->under_object, o->under_vol_id, specific_type, req_count, under_req_array, timeout,
-                    outcount, array_of_indices, array_of_statuses);
-
-                /* If any requests completed, release them */
-                if (ret_value >= 0 && *outcount > 0) {
-                    unsigned *idx_array; /* Array of indices of completed requests */
-
-                    /* Retrieve the array of completed request indices */
-                    idx_array = va_arg(tmp_arguments, unsigned *);
-
-                    /* Release the completed requests */
-                    for (u = 0; u < *outcount; u++) {
-                        H5VL_pass_through_t *tmp_o;
-
-                        tmp_o = (H5VL_pass_through_t *)req_array[idx_array[u]];
-                        H5VL_pass_through_free_obj(tmp_o);
-                    }                                     /* end for */
-                }                                         /* end if */
-            }                                             /* end else-if */
-            else {                                        /* H5VL_REQUEST_WAITALL == specific_type */
-                H5VL_request_status_t *array_of_statuses; /* Array of statuses for completed requests */
-
-                /* Retrieve the remaining arguments */
-                array_of_statuses = va_arg(tmp_arguments, H5VL_request_status_t *);
-
-                /* Reissue the WAITALL 'request specific' call */
-                ret_value = H5VL_pass_through_request_specific_reissue(
-                    o->under_object, o->under_vol_id, specific_type, req_count, under_req_array, timeout,
-                    array_of_statuses);
-
-                /* Release the completed requests */
-                if (ret_value >= 0) {
-                    for (u = 0; u < req_count; u++) {
-                        if (array_of_statuses[u] != H5ES_STATUS_IN_PROGRESS) {
-                            H5VL_pass_through_t *tmp_o;
-
-                            tmp_o = (H5VL_pass_through_t *)req_array[u];
-                            H5VL_pass_through_free_obj(tmp_o);
-                        } /* end if */
-                    }     /* end for */
-                }         /* end if */
-            }             /* end else */
-
-            /* Release array of requests for underlying connector */
-            free(under_req_array);
-        } /* end if */
-
-        /* Finish use of copied vararg list */
-        va_end(tmp_arguments);
-    } /* end if */
-    else {
-        H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
-
-        ret_value = H5VLrequest_specific(o->under_object, o->under_vol_id, specific_type, arguments);
-    } /* end else */
+    ret_value = H5VLrequest_specific(o->under_object, o->under_vol_id, args);
 
     return ret_value;
 } /* end H5VL_pass_through_request_specific() */
@@ -2926,7 +2727,7 @@ H5VL_pass_through_request_specific(void *obj, H5VL_request_specific_t specific_t
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5VL_pass_through_request_optional(void *obj, H5VL_request_optional_t opt_type, va_list arguments)
+H5VL_pass_through_request_optional(void *obj, H5VL_optional_args_t *args)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -2935,7 +2736,7 @@ H5VL_pass_through_request_optional(void *obj, H5VL_request_optional_t opt_type,
     printf("------- PASS THROUGH VOL REQUEST Optional\n");
 #endif
 
-    ret_value = H5VLrequest_optional(o->under_object, o->under_vol_id, opt_type, arguments);
+    ret_value = H5VLrequest_optional(o->under_object, o->under_vol_id, args);
 
     return ret_value;
 } /* end H5VL_pass_through_request_optional() */
@@ -3027,8 +2828,7 @@ H5VL_pass_through_blob_get(void *obj, const void *blob_id, void *buf, size_t siz
  *-------------------------------------------------------------------------
  */
 herr_t
-H5VL_pass_through_blob_specific(void *obj, void *blob_id, H5VL_blob_specific_t specific_type,
-                                va_list arguments)
+H5VL_pass_through_blob_specific(void *obj, void *blob_id, H5VL_blob_specific_args_t *args)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -3037,7 +2837,7 @@ H5VL_pass_through_blob_specific(void *obj, void *blob_id, H5VL_blob_specific_t s
     printf("------- PASS THROUGH VOL BLOB Specific\n");
 #endif
 
-    ret_value = H5VLblob_specific(o->under_object, o->under_vol_id, blob_id, specific_type, arguments);
+    ret_value = H5VLblob_specific(o->under_object, o->under_vol_id, blob_id, args);
 
     return ret_value;
 } /* end H5VL_pass_through_blob_specific() */
@@ -3052,7 +2852,7 @@ H5VL_pass_through_blob_specific(void *obj, void *blob_id, H5VL_blob_specific_t s
  *-------------------------------------------------------------------------
  */
 herr_t
-H5VL_pass_through_blob_optional(void *obj, void *blob_id, H5VL_blob_optional_t opt_type, va_list arguments)
+H5VL_pass_through_blob_optional(void *obj, void *blob_id, H5VL_optional_args_t *args)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -3061,7 +2861,7 @@ H5VL_pass_through_blob_optional(void *obj, void *blob_id, H5VL_blob_optional_t o
     printf("------- PASS THROUGH VOL BLOB Optional\n");
 #endif
 
-    ret_value = H5VLblob_optional(o->under_object, o->under_vol_id, blob_id, opt_type, arguments);
+    ret_value = H5VLblob_optional(o->under_object, o->under_vol_id, blob_id, args);
 
     return ret_value;
 } /* end H5VL_pass_through_blob_optional() */
@@ -3168,7 +2968,7 @@ H5VL_pass_through_token_from_str(void *obj, H5I_type_t obj_type, const char *tok
  *-------------------------------------------------------------------------
  */
 herr_t
-H5VL_pass_through_optional(void *obj, int op_type, hid_t dxpl_id, void **req, va_list arguments)
+H5VL_pass_through_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id, void **req)
 {
     H5VL_pass_through_t *o = (H5VL_pass_through_t *)obj;
     herr_t               ret_value;
@@ -3177,7 +2977,7 @@ H5VL_pass_through_optional(void *obj, int op_type, hid_t dxpl_id, void **req, va
     printf("------- PASS THROUGH VOL generic Optional\n");
 #endif
 
-    ret_value = H5VLoptional(o->under_object, o->under_vol_id, op_type, dxpl_id, req, arguments);
+    ret_value = H5VLoptional(o->under_object, o->under_vol_id, args, dxpl_id, req);
 
     return ret_value;
 } /* end H5VL_pass_through_optional() */