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>

16 files changed, 1428 insertions, 61 deletions

diff --git a/test/CMakeTests.cmake b/test/CMakeTests.cmake
index 17931cf..e840559 100644
--- a/test/CMakeTests.cmake
+++ b/test/CMakeTests.cmake
@@ -402,6 +402,8 @@ set (test_CLEANFILES
     mirror_rw/*
     mirror_wo/*
     event_set_*.h5
+    h5s_block.h5
+    h5s_plist.h5
 )
 
 # Remove any output file left over from previous test run
diff --git a/test/Makefile.am b/test/Makefile.am
index 4bf9620..d465664 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -175,7 +175,7 @@ CHECK_CLEANFILES+=accum.h5 cmpd_dset.h5 compact_dataset.h5 dataset.h5 dset_offse
     zero_chunk.h5 chunk_single.h5 swmr_non_latest.h5 \
     earray_hdr_fd.h5 farray_hdr_fd.h5 bt2_hdr_fd.h5 \
     storage_size.h5 dls_01_strings.h5 power2up.h5 version_bounds.h5 \
-    alloc_0sized.h5 \
+    alloc_0sized.h5 h5s_block.h5 h5s_plist.h5 \
     extend.h5 istore.h5 extlinks*.h5 frspace.h5 links*.h5 \
     sys_file1 tfile[1-7].h5 th5s[1-4].h5 lheap.h5 fheap.h5 ohdr.h5 \
     stab.h5 extern_[1-5].h5 extern_[1-4][rw].raw gheap[0-4].h5 \
diff --git a/test/chunk_info.c b/test/chunk_info.c
index 7104941..7c6dcc1 100644
--- a/test/chunk_info.c
+++ b/test/chunk_info.c
@@ -1676,7 +1676,7 @@ test_basic_query(hid_t fapl)
 
     /* iterate over all chunks */
     cptr = &(chunk_infos[0]);
-    if (H5Dchunk_iter(dset, &iter_cb, &cptr) < 0)
+    if (H5Dchunk_iter(dset, H5P_DEFAULT, &iter_cb, &cptr) < 0)
         TEST_ERROR;
 
     VERIFY(cptr, &(chunk_infos[2]), "Iterator did not iterate all chunks");
@@ -1690,7 +1690,7 @@ test_basic_query(hid_t fapl)
 
     /* iterate and stop after one iteration */
     cptr = &(chunk_infos[0]);
-    if (H5Dchunk_iter(dset, &iter_cb_stop, &cptr) < 0)
+    if (H5Dchunk_iter(dset, H5P_DEFAULT, &iter_cb_stop, &cptr) < 0)
         TEST_ERROR;
     VERIFY(cptr, &(chunk_infos[1]), "Verification of halted iterator failed\n");
 
@@ -1698,7 +1698,7 @@ test_basic_query(hid_t fapl)
     cptr = &(chunk_infos[0]);
     H5E_BEGIN_TRY
     {
-        ret = H5Dchunk_iter(dset, &iter_cb_fail, &cptr);
+        ret = H5Dchunk_iter(dset, H5P_DEFAULT, &iter_cb_fail, &cptr);
     }
     H5E_END_TRY;
     if (ret >= 0)
diff --git a/test/direct_chunk.c b/test/direct_chunk.c
index 61e3df9..0d270bd 100644
--- a/test/direct_chunk.c
+++ b/test/direct_chunk.c
@@ -1990,23 +1990,23 @@ test_read_unallocated_chunk(hid_t file)
 
     /* Create the data space with unlimited dimensions. */
     if ((dataspace = H5Screate_simple(RANK, dims, maxdims)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
     if ((mem_space = H5Screate_simple(RANK, chunk_dims, NULL)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     /* Modify dataset creation properties, i.e. enable chunking, no compression */
     if ((cparms = H5Pcreate(H5P_DATASET_CREATE)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
     if ((status = H5Pset_chunk(cparms, RANK, chunk_dims)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     /* Create a new dataset within the file using cparms creation properties. */
     if ((dataset = H5Dcreate2(file, DATASETNAME11, H5T_NATIVE_INT, dataspace, H5P_DEFAULT, cparms,
                               H5P_DEFAULT)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     if ((dxpl = H5Pcreate(H5P_DATASET_XFER)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     /* Write a single chunk to intialize the chunk storage */
     HDmemset(direct_buf, 0, CHUNK_NX * CHUNK_NY * sizeof(int));
@@ -2014,7 +2014,7 @@ test_read_unallocated_chunk(hid_t file)
     offset[1] = 0;
 
     if (H5Dwrite_chunk(dataset, dxpl, filter_mask, offset, chunk_nbytes, direct_buf) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     /* Attempt to read each chunk in the dataset. Chunks are not allocated,
      * therefore we expect the result of H5Dread_chunk to fail. Chunk idx starts
@@ -2034,7 +2034,7 @@ test_read_unallocated_chunk(hid_t file)
 
             /* Check that the chunk read call does not succeed. */
             if (status != -1)
-                goto error;
+                TEST_ERROR
 
             /* Query the size of the non-existant chunk */
             direct_chunk_nbytes = ULONG_MAX;
@@ -2046,18 +2046,23 @@ test_read_unallocated_chunk(hid_t file)
 
             /* Check that the chunk storage size call does not succeed. */
             if (status != -1)
-                goto error;
-            if (direct_chunk_nbytes != 0)
-                goto error;
+                TEST_ERROR
+            if (direct_chunk_nbytes != ULONG_MAX)
+                TEST_ERROR
         }
     }
 
     /* Close/release resources. */
-    H5Dclose(dataset);
-    H5Sclose(mem_space);
-    H5Sclose(dataspace);
-    H5Pclose(cparms);
-    H5Pclose(dxpl);
+    if (H5Dclose(dataset) < 0)
+        FAIL_STACK_ERROR;
+    if (H5Sclose(mem_space) < 0)
+        FAIL_STACK_ERROR;
+    if (H5Sclose(dataspace) < 0)
+        FAIL_STACK_ERROR;
+    if (H5Pclose(cparms) < 0)
+        FAIL_STACK_ERROR;
+    if (H5Pclose(dxpl) < 0)
+        FAIL_STACK_ERROR;
 
     PASSED();
     return 0;
@@ -2121,103 +2126,100 @@ test_single_chunk(unsigned config)
     TESTING("Single chunk I/O");
 
     /* Initialize data */
-    for (i = 0; i < DIM0; i++) {
+    for (i = 0; i < DIM0; i++)
         for (j = 0; j < DIM1; j++)
             wdata[i][j] = j / CHUNK0;
-    }
 
     /* Create a new file with the latest format  */
     if ((fapl = H5Pcreate(H5P_FILE_ACCESS)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
     if (config & CONFIG_LATEST)
         if (H5Pset_libver_bounds(fapl, H5F_LIBVER_LATEST, H5F_LIBVER_LATEST) < 0)
-            goto error;
+            FAIL_STACK_ERROR;
     if ((fid = H5Fcreate(FILE, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     /* Create dataspace */
     if ((sid = H5Screate_simple(2, dims, NULL)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     /* Create the dataset creation property list and set the chunk size */
     if ((dcpl = H5Pcreate(H5P_DATASET_CREATE)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
     if (H5Pset_chunk(dcpl, 2, chunk) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     /* Create the dataset */
     if ((did = H5Dcreate2(fid, DATASET, H5T_NATIVE_INT, sid, H5P_DEFAULT, dcpl, H5P_DEFAULT)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     if (config & CONFIG_DIRECT_WRITE) {
         /* Write the data directly to the dataset */
         if (H5Dwrite_chunk(did, H5P_DEFAULT, 0, offset, CHUNK0 * CHUNK1 * 4, (void *)wdata) < 0)
-            goto error;
+            FAIL_STACK_ERROR;
     } /* end if */
     else
         /* Write the data to the dataset */
         if (H5Dwrite(did, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, (void *)wdata) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     /*
      * Close and release resources.
      */
     if (H5Pclose(dcpl) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
     if (config & CONFIG_REOPEN_DSET)
         if (H5Dclose(did) < 0)
-            goto error;
+            FAIL_STACK_ERROR;
     if (H5Sclose(sid) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
     if (H5Pclose(fapl) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
     if (config & CONFIG_REOPEN_FILE)
         if (H5Fclose(fid) < 0)
-            goto error;
+            FAIL_STACK_ERROR;
 
     /* Open the file and dataset with default properties  */
     if (config & CONFIG_REOPEN_FILE)
         if ((fid = H5Fopen(FILE, H5F_ACC_RDONLY, H5P_DEFAULT)) < 0)
-            goto error;
+            FAIL_STACK_ERROR;
     if (config & CONFIG_REOPEN_DSET)
         if ((did = H5Dopen2(fid, DATASET, H5P_DEFAULT)) < 0)
-            goto error;
+            FAIL_STACK_ERROR;
 
     /* Retrieve dataset creation property list */
     if ((dcpl = H5Dget_create_plist(did)) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     if (config & CONFIG_DIRECT_READ) {
         /* Read the data directly */
         if (H5Dread_chunk(did, H5P_DEFAULT, offset, &filters, rdata) < 0)
-            goto error;
+            FAIL_STACK_ERROR;
 
         /* Verify returned filter mask */
         if (filters != 0)
-            goto error;
+            TEST_ERROR
     } /* end if */
     else
         /* Read the data */
         if (H5Dread(did, H5T_NATIVE_INT, H5S_ALL, H5S_ALL, H5P_DEFAULT, rdata) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     /* Verify that the data read was correct.  */
-    for (i = 0; i < DIM0; i++) {
-        for (j = 0; j < DIM1; j++) {
+    for (i = 0; i < DIM0; i++)
+        for (j = 0; j < DIM1; j++)
             if (rdata[i][j] != wdata[i][j])
-                goto error;
-        }
-    }
+                TEST_ERROR
 
     /*
      * Close and release resources
      */
     if (H5Pclose(dcpl) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
     if (H5Dclose(did) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
     if (H5Fclose(fid) < 0)
-        goto error;
+        FAIL_STACK_ERROR;
 
     PASSED();
     return 0;
diff --git a/test/dsets.c b/test/dsets.c
index 96f8b81..cc35fe3 100644
--- a/test/dsets.c
+++ b/test/dsets.c
@@ -83,6 +83,8 @@ const char *FILENAME[] = {"dataset",             /* 0 */
                           "power2up",            /* 24 */
                           "version_bounds",      /* 25 */
                           "alloc_0sized",        /* 26 */
+                          "h5s_block",           /* 27 */
+                          "h5s_plist",           /* 28 */
                           NULL};
 
 #define OHMIN_FILENAME_A "ohdr_min_a"
@@ -14963,6 +14965,370 @@ error:
 } /* end test_object_header_minimization_dcpl() */
 
 /*-----------------------------------------------------------------------------
+ * Function:   test_h5s_block
+ *
+ * Purpose:    Test the H5S_BLOCK feature.
+ *
+ * Return:     Success/pass:   0
+ *             Failure/error: -1
+ *
+ * Programmer: Quincey Koziol
+ *             3 November 2020
+ *
+ *-----------------------------------------------------------------------------
+ */
+static herr_t
+test_h5s_block(void)
+{
+    hid_t    file_id                     = H5I_INVALID_HID; /* File ID */
+    char     filename[FILENAME_BUF_SIZE] = "";
+    hid_t    dset_id                     = H5I_INVALID_HID; /* Dataset ID */
+    hsize_t  dims[1]                     = {20};            /* Dataset's dataspace size */
+    hsize_t  start                       = 2;               /* Starting offset of hyperslab selection */
+    hsize_t  count                       = 10;              /* Count of hyperslab selection */
+    hid_t    file_space_id               = H5I_INVALID_HID; /* File dataspace ID */
+    int      buf[20];                                       /* Memory buffer for I/O */
+    unsigned u;                                             /* Local index variable */
+    herr_t   ret;
+
+    TESTING("contiguous memory buffers with H5S_BLOCK");
+
+    /*********/
+    /* SETUP */
+    /*********/
+    if (NULL == h5_fixname(FILENAME[27], H5P_DEFAULT, filename, sizeof(filename)))
+        TEST_ERROR
+    if (H5I_INVALID_HID == (file_id = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT)))
+        FAIL_STACK_ERROR
+    if ((file_space_id = H5Screate_simple(1, dims, NULL)) < 0)
+        FAIL_STACK_ERROR
+    if ((dset_id = H5Dcreate2(file_id, "dset", H5T_NATIVE_INT, file_space_id, H5P_DEFAULT, H5P_DEFAULT,
+                              H5P_DEFAULT)) < 0)
+        FAIL_STACK_ERROR
+
+    for (u = 0; u < 20; u++)
+        buf[u] = (int)u;
+
+    /*********/
+    /* TESTS */
+    /*********/
+
+    /* Check error cases */
+    H5E_BEGIN_TRY
+    {
+        ret = H5Dwrite(dset_id, H5T_NATIVE_INT, H5S_ALL, H5S_BLOCK, H5P_DEFAULT, buf);
+    }
+    H5E_END_TRY;
+    if (ret == SUCCEED)
+        TEST_ERROR
+
+    /* Write the entire dataset */
+    if (H5Dwrite(dset_id, H5T_NATIVE_INT, H5S_BLOCK, H5S_ALL, H5P_DEFAULT, buf) < 0)
+        FAIL_STACK_ERROR
+
+    /* Reset the memory buffer */
+    HDmemset(buf, 0, sizeof(buf));
+
+    /* Read the entire dataset */
+    if (H5Dread(dset_id, H5T_NATIVE_INT, H5S_BLOCK, H5S_ALL, H5P_DEFAULT, buf) < 0)
+        FAIL_STACK_ERROR
+
+    /* Verify the data read in */
+    for (u = 0; u < 20; u++)
+        if (buf[u] != (int)u)
+            TEST_ERROR
+
+    /* Read a hyperslab from the file to the first 10 elements of the buffer */
+    if (H5Sselect_hyperslab(file_space_id, H5S_SELECT_SET, &start, NULL, &count, NULL) < 0)
+        FAIL_STACK_ERROR
+    if (H5Dread(dset_id, H5T_NATIVE_INT, H5S_BLOCK, file_space_id, H5P_DEFAULT, buf) < 0)
+        FAIL_STACK_ERROR
+
+    /* Verify the data read in */
+    for (u = 0; u < count; u++)
+        if (buf[u] != (int)(u + start))
+            TEST_ERROR
+
+    /* Verify that reading 0 elements is handled correctly and doesn't modify buffer */
+    if (H5Sselect_none(file_space_id) < 0)
+        FAIL_STACK_ERROR
+    if (H5Dread(dset_id, H5T_NATIVE_INT, H5S_BLOCK, file_space_id, H5P_DEFAULT, buf) < 0)
+        FAIL_STACK_ERROR
+
+    /* Verify the data read in */
+    for (u = 0; u < count; u++)
+        if (buf[u] != (int)(u + start))
+            TEST_ERROR
+
+    /************/
+    /* TEARDOWN */
+    /************/
+    if (FAIL == H5Sclose(file_space_id))
+        FAIL_STACK_ERROR
+    if (FAIL == H5Dclose(dset_id))
+        FAIL_STACK_ERROR
+    if (FAIL == H5Fclose(file_id))
+        FAIL_STACK_ERROR
+
+    PASSED();
+
+    return SUCCEED;
+
+error:
+    H5E_BEGIN_TRY
+    {
+        H5Sclose(file_space_id);
+        H5Dclose(dset_id);
+        H5Fclose(file_id);
+    }
+    H5E_END_TRY;
+
+    return FAIL;
+} /* end test_h5s_block() */
+
+/*-----------------------------------------------------------------------------
+ * Function:   test_h5s_plist
+ *
+ * Purpose:    Test the H5S_PLIST feature.
+ *
+ * Return:     Success/pass:   0
+ *             Failure/error: -1
+ *
+ * Programmer: Quincey Koziol
+ *             28 January 2021
+ *
+ *-----------------------------------------------------------------------------
+ */
+static herr_t
+test_h5s_plist(void)
+{
+    hid_t    file_id                     = H5I_INVALID_HID; /* File ID */
+    char     filename[FILENAME_BUF_SIZE] = "";
+    hid_t    dset_id                     = H5I_INVALID_HID; /* Dataset ID */
+    hsize_t  dims[1]                     = {20};            /* Dataset's dataspace size */
+    hid_t    dxpl_id                     = H5I_INVALID_HID; /* Dataset xfer property list ID */
+    hid_t    dxpl_id_copy                = H5I_INVALID_HID; /* Copy of dataset xfer property list ID */
+    hsize_t  start                       = 2;               /* Starting offset of hyperslab selection */
+    hsize_t  stride                      = 1;               /* Stride of hyperslab selection */
+    hsize_t  count                       = 10;              /* Count of hyperslab selection */
+    hsize_t  start2                      = 14;              /* Starting offset of hyperslab selection */
+    hsize_t  count2                      = 4;               /* Count of hyperslab selection */
+    hsize_t  block                       = 1;               /* Block size of hyperslab selection */
+    hid_t    file_space_id               = H5I_INVALID_HID; /* File dataspace ID */
+    int      buf[20];                                       /* Memory buffer for I/O */
+    unsigned u;                                             /* Local index variable */
+    herr_t   ret;
+
+    TESTING("dataset's dataspace selection for I/O in DXPL with H5S_PLIST");
+
+    /*********/
+    /* SETUP */
+    /*********/
+    if (NULL == h5_fixname(FILENAME[28], H5P_DEFAULT, filename, sizeof(filename)))
+        TEST_ERROR
+    if (H5I_INVALID_HID == (file_id = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT)))
+        FAIL_STACK_ERROR
+    if ((file_space_id = H5Screate_simple(1, dims, NULL)) < 0)
+        FAIL_STACK_ERROR
+    if ((dset_id = H5Dcreate2(file_id, "dset", H5T_NATIVE_INT, file_space_id, H5P_DEFAULT, H5P_DEFAULT,
+                              H5P_DEFAULT)) < 0)
+        FAIL_STACK_ERROR
+    if ((dxpl_id = H5Pcreate(H5P_DATASET_XFER)) < 0)
+        FAIL_STACK_ERROR
+
+    for (u = 0; u < 20; u++)
+        buf[u] = (int)u;
+
+    /*********/
+    /* TESTS */
+    /*********/
+
+    /* Check error cases */
+    H5E_BEGIN_TRY
+    {
+        /* Bad rank */
+        ret = H5Pset_dataset_io_hyperslab_selection(dxpl_id, 0, H5S_SELECT_SET, &start, &stride, &count,
+                                                    &block);
+    }
+    H5E_END_TRY;
+    if (ret == SUCCEED)
+        TEST_ERROR
+    H5E_BEGIN_TRY
+    {
+        /* Bad selection operator */
+        ret = H5Pset_dataset_io_hyperslab_selection(dxpl_id, 1, H5S_SELECT_NOOP, &start, &stride, &count,
+                                                    &block);
+    }
+    H5E_END_TRY;
+    if (ret == SUCCEED)
+        TEST_ERROR
+    H5E_BEGIN_TRY
+    {
+        /* Bad start pointer */
+        ret =
+            H5Pset_dataset_io_hyperslab_selection(dxpl_id, 1, H5S_SELECT_SET, NULL, &stride, &count, &block);
+    }
+    H5E_END_TRY;
+    if (ret == SUCCEED)
+        TEST_ERROR
+    H5E_BEGIN_TRY
+    {
+        /* Bad stride value (stride of NULL is OK) */
+        stride = 0;
+        ret    = H5Pset_dataset_io_hyperslab_selection(dxpl_id, 1, H5S_SELECT_SET, &start, &stride, &count,
+                                                    &block);
+        stride = 1;
+    }
+    H5E_END_TRY;
+    if (ret == SUCCEED)
+        TEST_ERROR
+    H5E_BEGIN_TRY
+    {
+        /* Bad count pointer */
+        ret =
+            H5Pset_dataset_io_hyperslab_selection(dxpl_id, 1, H5S_SELECT_SET, &start, &stride, NULL, &block);
+    }
+    H5E_END_TRY;
+    if (ret == SUCCEED)
+        TEST_ERROR
+
+    /* Block pointer is allowed to be NULL */
+
+    H5E_BEGIN_TRY
+    {
+        /* H5S_PLIST for memory dataspace */
+        ret = H5Dwrite(dset_id, H5T_NATIVE_INT, H5S_PLIST, H5S_ALL, H5P_DEFAULT, buf);
+    }
+    H5E_END_TRY;
+    if (ret == SUCCEED)
+        TEST_ERROR
+
+    /* Write the entire dataset */
+    if (H5Dwrite(dset_id, H5T_NATIVE_INT, H5S_BLOCK, H5S_ALL, H5P_DEFAULT, buf) < 0)
+        FAIL_STACK_ERROR
+
+    /* Reset the memory buffer */
+    HDmemset(buf, 0, sizeof(buf));
+
+    /* Read the entire dataset */
+    if (H5Dread(dset_id, H5T_NATIVE_INT, H5S_BLOCK, H5S_ALL, H5P_DEFAULT, buf) < 0)
+        FAIL_STACK_ERROR
+
+    /* Verify the data read in */
+    for (u = 0; u < 20; u++)
+        if (buf[u] != (int)u)
+            TEST_ERROR
+
+    /* Reset the memory buffer */
+    HDmemset(buf, 0, sizeof(buf));
+
+    /* Set valid selection in DXPL */
+    if (H5Pset_dataset_io_hyperslab_selection(dxpl_id, 1, H5S_SELECT_SET, &start, &stride, &count, &block) <
+        0)
+        FAIL_STACK_ERROR
+
+    /* Read a hyperslab from the file to the first 10 elements of the buffer */
+    if (H5Dread(dset_id, H5T_NATIVE_INT, H5S_BLOCK, H5S_PLIST, dxpl_id, buf) < 0)
+        FAIL_STACK_ERROR
+
+    /* Verify the data read in */
+    for (u = 0; u < count; u++)
+        if (buf[u] != (int)(u + start))
+            TEST_ERROR
+
+    /* Reset the memory buffer */
+    HDmemset(buf, 0, sizeof(buf));
+
+    /* Check for copying property list w/selection */
+    if ((dxpl_id_copy = H5Pcopy(dxpl_id)) < 0)
+        FAIL_STACK_ERROR
+
+    /* Read a hyperslab from the file to the first 10 elements of the buffer */
+    if (H5Dread(dset_id, H5T_NATIVE_INT, H5S_BLOCK, H5S_PLIST, dxpl_id_copy, buf) < 0)
+        FAIL_STACK_ERROR
+
+    /* Verify the data read in */
+    for (u = 0; u < count; u++)
+        if (buf[u] != (int)(u + start))
+            TEST_ERROR
+
+    /* Attempt to 'OR' block with invalid dimensions into the selection */
+    H5E_BEGIN_TRY
+    {
+        ret = H5Pset_dataset_io_hyperslab_selection(dxpl_id_copy, 2, H5S_SELECT_OR, &start, &stride, &count,
+                                                    &block);
+    }
+    H5E_END_TRY;
+    if (ret == SUCCEED)
+        TEST_ERROR
+
+    /* Set new valid selection in DXPL */
+    if (H5Pset_dataset_io_hyperslab_selection(dxpl_id_copy, 1, H5S_SELECT_SET, &start, &stride, &count,
+                                              &block) < 0)
+        FAIL_STACK_ERROR
+
+    /* Read a hyperslab from the file to the first 10 elements of the buffer */
+    if (H5Dread(dset_id, H5T_NATIVE_INT, H5S_BLOCK, H5S_PLIST, dxpl_id_copy, buf) < 0)
+        FAIL_STACK_ERROR
+
+    /* Verify the data read in */
+    for (u = 0; u < count; u++)
+        if (buf[u] != (int)(u + start))
+            TEST_ERROR
+
+    /* Close the copy */
+    if (FAIL == H5Pclose(dxpl_id_copy))
+        FAIL_STACK_ERROR
+    dxpl_id_copy = H5I_INVALID_HID;
+
+    /* 'OR' valid block into the existing selection in original DXPL */
+    if (H5Pset_dataset_io_hyperslab_selection(dxpl_id, 1, H5S_SELECT_OR, &start2, &stride, &count2, &block) <
+        0)
+        FAIL_STACK_ERROR
+
+    /* Read a disjoint hyperslab from the file to the first 10 elements of the buffer */
+    if (H5Dread(dset_id, H5T_NATIVE_INT, H5S_BLOCK, H5S_PLIST, dxpl_id, buf) < 0)
+        FAIL_STACK_ERROR
+
+    /* Verify the data read in */
+    for (u = 0; u < count; u++)
+        if (buf[u] != (int)(u + start))
+            TEST_ERROR
+    for (u = 0; u < count2; u++)
+        if (buf[u + count] != (int)(u + start2))
+            TEST_ERROR
+
+    /************/
+    /* TEARDOWN */
+    /************/
+    if (FAIL == H5Pclose(dxpl_id))
+        FAIL_STACK_ERROR
+    if (FAIL == H5Sclose(file_space_id))
+        FAIL_STACK_ERROR
+    if (FAIL == H5Dclose(dset_id))
+        FAIL_STACK_ERROR
+    if (FAIL == H5Fclose(file_id))
+        FAIL_STACK_ERROR
+
+    PASSED();
+
+    return SUCCEED;
+
+error:
+    H5E_BEGIN_TRY
+    {
+        H5Pclose(dxpl_id_copy);
+        H5Pclose(dxpl_id);
+        H5Sclose(file_space_id);
+        H5Dclose(dset_id);
+        H5Fclose(file_id);
+    }
+    H5E_END_TRY;
+
+    return FAIL;
+} /* end test_h5s_plist() */
+
+/*-----------------------------------------------------------------------------
  * Function:   test_0sized_dset_metadata_alloc
  *
  * Purpose:    Tests the metadata allocation for 0-sized datasets.
@@ -15407,7 +15773,10 @@ main(void)
     /* Tests version bounds using its own file */
     nerrors += (test_versionbounds() < 0 ? 1 : 0);
 
+    /* Tests that use their own file */
     nerrors += (test_object_header_minimization_dcpl() < 0 ? 1 : 0);
+    nerrors += (test_h5s_block() < 0 ? 1 : 0);
+    nerrors += (test_h5s_plist() < 0 ? 1 : 0);
 
     /* Run misc tests */
     nerrors += (dls_01_main() < 0 ? 1 : 0);
diff --git a/test/event_set.c b/test/event_set.c
index 6568663..5df49e9 100644
--- a/test/event_set.c
+++ b/test/event_set.c
@@ -94,6 +94,71 @@ error:
 }
 
 /*-------------------------------------------------------------------------
+ * Function:    test_es_none
+ *
+ * Purpose:     Tests for passing H5ES_NONE to H5ES routines
+ *
+ * Return:      Success:    0
+ *              Failure:    number of errors
+ *
+ * Programmer:  Quincey Koziol
+ *              Friday, February 26, 2021
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+test_es_none(void)
+{
+    TESTING("event set H5ES_NONE");
+
+    /* Wait */
+    if (H5ESwait(H5ES_NONE, 0, NULL, NULL) < 0)
+        TEST_ERROR;
+
+    /* Cancel */
+    if (H5EScancel(H5ES_NONE, NULL, NULL) < 0)
+        TEST_ERROR;
+
+    /* Get count */
+    if (H5ESget_count(H5ES_NONE, NULL) < 0)
+        TEST_ERROR;
+
+    /* Get op counter */
+    if (H5ESget_op_counter(H5ES_NONE, NULL) < 0)
+        TEST_ERROR;
+
+    /* Get error status */
+    if (H5ESget_err_status(H5ES_NONE, NULL) < 0)
+        TEST_ERROR;
+
+    /* Get error count */
+    if (H5ESget_err_count(H5ES_NONE, NULL) < 0)
+        TEST_ERROR;
+
+    /* Get error info */
+    if (H5ESget_err_info(H5ES_NONE, 0, NULL, NULL) < 0)
+        TEST_ERROR;
+
+    /* Register insert function */
+    if (H5ESregister_insert_func(H5ES_NONE, NULL, NULL) < 0)
+        TEST_ERROR;
+
+    /* Register complete function */
+    if (H5ESregister_complete_func(H5ES_NONE, NULL, NULL) < 0)
+        TEST_ERROR;
+
+    /* Close */
+    if (H5ESclose(H5ES_NONE) < 0)
+        TEST_ERROR;
+
+    PASSED();
+    return 0;
+
+error:
+    return 1;
+}
+
+/*-------------------------------------------------------------------------
  * Function:    main
  *
  * Purpose:     Tests event sets
@@ -118,6 +183,7 @@ main(void)
 
     /* Tests */
     nerrors += test_es_create();
+    nerrors += test_es_none();
 
     /* Cleanup */
     h5_cleanup(FILENAME, fapl_id);
diff --git a/test/filter_plugin1_dsets.c b/test/filter_plugin1_dsets.c
index 5d6c1ef..2b1e4d2 100644
--- a/test/filter_plugin1_dsets.c
+++ b/test/filter_plugin1_dsets.c
@@ -17,7 +17,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 
-#include "H5PLextern.h"
+#include "hdf5dev.h"
 
 #define FILTER1_ID 257
 
diff --git a/test/filter_plugin2_dsets.c b/test/filter_plugin2_dsets.c
index d2011d4..0bef1a0 100644
--- a/test/filter_plugin2_dsets.c
+++ b/test/filter_plugin2_dsets.c
@@ -17,7 +17,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 
-#include "H5PLextern.h"
+#include "hdf5dev.h"
 
 #define FILTER2_ID 258
 #define MULTIPLIER 3
diff --git a/test/filter_plugin3_dsets.c b/test/filter_plugin3_dsets.c
index 618ce06..b9b3b82 100644
--- a/test/filter_plugin3_dsets.c
+++ b/test/filter_plugin3_dsets.c
@@ -18,7 +18,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 
-#include "H5PLextern.h"
+#include "hdf5dev.h"
 
 #define FILTER3_ID 259
 
diff --git a/test/filter_plugin4_groups.c b/test/filter_plugin4_groups.c
index 630dcd6..589347c 100644
--- a/test/filter_plugin4_groups.c
+++ b/test/filter_plugin4_groups.c
@@ -18,7 +18,7 @@
 #include <stdio.h>
 #include <string.h>
 
-#include "H5PLextern.h"
+#include "hdf5dev.h"
 
 #define FILTER4_ID   260
 #define SUFFIX_LEN   8
diff --git a/test/h5test.h b/test/h5test.h
index 0d7dade..f5c9608 100644
--- a/test/h5test.h
+++ b/test/h5test.h
@@ -22,9 +22,10 @@
 
 /*
  * Include required headers.  This file tests internal library functions,
- * so we include the private headers here.
+ * so we include the private headers here, along with developer routines.
  */
 #include "hdf5.h"
+#include "hdf5dev.h"
 #include "H5private.h"
 #include "H5Eprivate.h"
 
diff --git a/test/links.c b/test/links.c
index b2d0d9a..f022783 100644
--- a/test/links.c
+++ b/test/links.c
@@ -3507,6 +3507,7 @@ done:
             case H5I_ERROR_MSG:
             case H5I_ERROR_STACK:
             case H5I_SPACE_SEL_ITER:
+            case H5I_EVENTSET:
             case H5I_NTYPES:
             default:
                 return FAIL;
@@ -3597,6 +3598,7 @@ done:
             case H5I_ERROR_MSG:
             case H5I_ERROR_STACK:
             case H5I_SPACE_SEL_ITER:
+            case H5I_EVENTSET:
             case H5I_NTYPES:
             default:
                 return FAIL;
@@ -13785,6 +13787,7 @@ done:
             case H5I_ERROR_MSG:
             case H5I_ERROR_STACK:
             case H5I_SPACE_SEL_ITER:
+            case H5I_EVENTSET:
             case H5I_NTYPES:
             default:
                 return FAIL;
@@ -13876,6 +13879,7 @@ done:
             case H5I_ERROR_MSG:
             case H5I_ERROR_STACK:
             case H5I_SPACE_SEL_ITER:
+            case H5I_EVENTSET:
             case H5I_NTYPES:
             default:
                 return FAIL;
@@ -16683,7 +16687,7 @@ obj_exists(hid_t fapl, hbool_t new_format)
         FAIL_STACK_ERROR
 
     /* Hard links */
-    /* Verify that H5Oexists_by_name() fails for non-existent link in root group */
+    /* Verify that H5Oexists_by_name() returns false for non-existent link in root group */
     H5E_BEGIN_TRY
     {
         status = H5Oexists_by_name(fid, "foo", H5P_DEFAULT);
@@ -16702,7 +16706,7 @@ obj_exists(hid_t fapl, hbool_t new_format)
     if (TRUE != H5Oexists_by_name(fid, "group", H5P_DEFAULT))
         TEST_ERROR
 
-    /* Verify that H5Oexists_by_name() fails for non-existent link in non-root group */
+    /* Verify that H5Oexists_by_name() returns false for non-existent object in non-root group */
     H5E_BEGIN_TRY
     {
         status = H5Oexists_by_name(fid, "group/foo", H5P_DEFAULT);
diff --git a/test/null_vol_connector.c b/test/null_vol_connector.c
index b574a8e..7a1de6c 100644
--- a/test/null_vol_connector.c
+++ b/test/null_vol_connector.c
@@ -19,7 +19,7 @@
 #include "hdf5.h"
 
 /* For HDF5 plugin functionality */
-#include "H5PLextern.h"
+#include "hdf5dev.h"
 
 /* This connector's header */
 #include "null_vol_connector.h"
diff --git a/test/tfile.c b/test/tfile.c
index 6a52392..62f3c73 100644
--- a/test/tfile.c
+++ b/test/tfile.c
@@ -1452,6 +1452,7 @@ test_obj_count_and_id(hid_t fid1, hid_t fid2, hid_t did, hid_t gid1, hid_t gid2,
                     case H5I_ERROR_MSG:
                     case H5I_ERROR_STACK:
                     case H5I_SPACE_SEL_ITER:
+                    case H5I_EVENTSET:
                     case H5I_NTYPES:
                     default:
                         ERROR("H5Fget_obj_ids");
diff --git a/test/trefstr.c b/test/trefstr.c
index a3f568a..d0575ab 100644
--- a/test/trefstr.c
+++ b/test/trefstr.c
@@ -186,7 +186,7 @@ test_refstr_cmp(void)
     H5RS_str_t *rs1; /* Ref-counted string created */
     H5RS_str_t *rs2; /* Ref-counted string created */
     int         cmp; /* Comparison value */
-    ssize_t     len; /* Length of string */
+    size_t      len; /* Length of string */
     herr_t      ret; /* Generic return value */
 
     /* Output message about test being performed */
diff --git a/test/vol.c b/test/vol.c
index d975243..c7586d5 100644
--- a/test/vol.c
+++ b/test/vol.c
@@ -20,6 +20,12 @@
 
 /* Headers needed */
 #include "h5test.h"
+#include "H5Iprivate.h" /* IDs                                  */
+#define H5T_FRIEND      /* Suppress error about including H5Tpkg    */
+#include "H5Tpkg.h"     /* Datatypes                            */
+#define H5VL_FRIEND     /* Suppress error about including H5VLpkg    */
+#define H5VL_TESTING
+#include "H5VLpkg.h" /* Virtual Object Layer                 */
 
 /* Filename */
 const char *FILENAME[] = {"native_vol_test", NULL};
@@ -35,6 +41,136 @@ const char *FILENAME[] = {"native_vol_test", NULL};
 
 #define N_ELEMENTS 10
 
+/* A VOL class struct to verify registering optional operations */
+static int    reg_opt_curr_op_val;
+static herr_t reg_opt_op_optional(void *obj, H5VL_optional_args_t *args, hid_t dxpl_id, void **req);
+static herr_t reg_opt_link_optional(void *obj, const H5VL_loc_params_t *loc_params,
+                                    H5VL_optional_args_t *args, hid_t dxpl_id, void **req);
+static herr_t reg_opt_datatype_get(void *obj, H5VL_datatype_get_args_t *args, hid_t dxpl_id, void **req);
+#define REG_OPT_VOL_NAME  "reg_opt"
+#define REG_OPT_VOL_VALUE ((H5VL_class_value_t)502)
+static const H5VL_class_t reg_opt_vol_g = {
+    H5VL_VERSION,      /* VOL class struct version */
+    REG_OPT_VOL_VALUE, /* value        */
+    REG_OPT_VOL_NAME,  /* name         */
+    0,                 /* version      */
+    0,                 /* capability flags */
+    NULL,              /* initialize   */
+    NULL,              /* terminate    */
+    {
+        /* info_cls */
+        (size_t)0, /* size    */
+        NULL,      /* copy    */
+        NULL,      /* compare */
+        NULL,      /* free    */
+        NULL,      /* to_str  */
+        NULL,      /* from_str */
+    },
+    {
+        /* wrap_cls */
+        NULL, /* get_object   */
+        NULL, /* get_wrap_ctx */
+        NULL, /* wrap_object  */
+        NULL, /* unwrap_object */
+        NULL, /* free_wrap_ctx */
+    },
+    {
+        /* attribute_cls */
+        NULL,                /* create       */
+        NULL,                /* open         */
+        NULL,                /* read         */
+        NULL,                /* write        */
+        NULL,                /* get          */
+        NULL,                /* specific     */
+        reg_opt_op_optional, /* optional     */
+        NULL                 /* close        */
+    },
+    {
+        /* dataset_cls */
+        NULL,                /* create       */
+        NULL,                /* open         */
+        NULL,                /* read         */
+        NULL,                /* write        */
+        NULL,                /* get          */
+        NULL,                /* specific     */
+        reg_opt_op_optional, /* optional     */
+        NULL                 /* close        */
+    },
+    {
+        /* datatype_cls */
+        NULL,                 /* commit       */
+        NULL,                 /* open         */
+        reg_opt_datatype_get, /* get          */
+        NULL,                 /* specific     */
+        reg_opt_op_optional,  /* optional     */
+        NULL                  /* close        */
+    },
+    {
+        /* file_cls */
+        NULL,                /* create       */
+        NULL,                /* open         */
+        NULL,                /* get          */
+        NULL,                /* specific     */
+        reg_opt_op_optional, /* optional     */
+        NULL                 /* close        */
+    },
+    {
+        /* group_cls */
+        NULL,                /* create       */
+        NULL,                /* open         */
+        NULL,                /* get          */
+        NULL,                /* specific     */
+        reg_opt_op_optional, /* optional     */
+        NULL                 /* close        */
+    },
+    {
+        /* link_cls */
+        NULL,                 /* create       */
+        NULL,                 /* copy         */
+        NULL,                 /* move         */
+        NULL,                 /* get          */
+        NULL,                 /* specific     */
+        reg_opt_link_optional /* optional     */
+    },
+    {
+        /* object_cls */
+        NULL,                 /* open         */
+        NULL,                 /* copy         */
+        NULL,                 /* get          */
+        NULL,                 /* specific     */
+        reg_opt_link_optional /* optional     */
+    },
+    {
+        /* introspect_cls */
+        NULL, /* get_conn_cls */
+        NULL, /* get_cap_flags */
+        NULL, /* opt_query    */
+    },
+    {
+        /* request_cls */
+        NULL, /* wait         */
+        NULL, /* notify       */
+        NULL, /* cancel       */
+        NULL, /* specific     */
+        NULL, /* optional     */
+        NULL  /* free         */
+    },
+    {
+        /* blob_cls */
+        NULL, /* put          */
+        NULL, /* get          */
+        NULL, /* specific     */
+        NULL  /* optional     */
+    },
+    {
+        /* token_cls */
+        NULL, /* cmp              */
+        NULL, /* to_str           */
+        NULL  /* from_str         */
+    },
+    NULL /* optional     */
+};
+
 #define FAKE_VOL_NAME  "fake"
 #define FAKE_VOL_VALUE ((H5VL_class_value_t)501)
 
@@ -90,6 +226,136 @@ static const H5VL_class_t fake_vol_g = {
     },
     {
         /* datatype_cls */
+        NULL,                 /* commit       */
+        NULL,                 /* open         */
+        reg_opt_datatype_get, /* get          */
+        NULL,                 /* specific     */
+        NULL,                 /* optional     */
+        NULL                  /* close        */
+    },
+    {
+        /* file_cls */
+        NULL, /* create       */
+        NULL, /* open         */
+        NULL, /* get          */
+        NULL, /* specific     */
+        NULL, /* optional     */
+        NULL  /* close        */
+    },
+    {
+        /* group_cls */
+        NULL, /* create       */
+        NULL, /* open         */
+        NULL, /* get          */
+        NULL, /* specific     */
+        NULL, /* optional     */
+        NULL  /* close        */
+    },
+    {
+        /* link_cls */
+        NULL, /* create       */
+        NULL, /* copy         */
+        NULL, /* move         */
+        NULL, /* get          */
+        NULL, /* specific     */
+        NULL  /* optional     */
+    },
+    {
+        /* object_cls */
+        NULL, /* open         */
+        NULL, /* copy         */
+        NULL, /* get          */
+        NULL, /* specific     */
+        NULL  /* optional     */
+    },
+    {
+        /* introspect_cls */
+        NULL, /* get_conn_cls */
+        NULL, /* get_cap_flags */
+        NULL, /* opt_query    */
+    },
+    {
+        /* request_cls */
+        NULL, /* wait         */
+        NULL, /* notify       */
+        NULL, /* cancel       */
+        NULL, /* specific     */
+        NULL, /* optional     */
+        NULL  /* free         */
+    },
+    {
+        /* blob_cls */
+        NULL, /* put          */
+        NULL, /* get          */
+        NULL, /* specific     */
+        NULL  /* optional     */
+    },
+    {
+        /* token_cls */
+        NULL, /* cmp              */
+        NULL, /* to_str           */
+        NULL  /* from_str         */
+    },
+    NULL /* optional     */
+};
+
+static herr_t fake_async_get_cap_flags(const void *info, unsigned *cap_flags);
+
+#define FAKE_ASYNC_VOL_NAME  "fake_async"
+#define FAKE_ASYNC_VOL_VALUE ((H5VL_class_value_t)503)
+
+/* A VOL class struct that describes a VOL class with no
+ * functionality except to set the async capability flag.
+ */
+static const H5VL_class_t fake_async_vol_g = {
+    H5VL_VERSION,         /* VOL class struct version */
+    FAKE_ASYNC_VOL_VALUE, /* value        */
+    FAKE_ASYNC_VOL_NAME,  /* name         */
+    0,                    /* connector version */
+    H5VL_CAP_FLAG_ASYNC,  /* capability flags */
+    NULL,                 /* initialize   */
+    NULL,                 /* terminate    */
+    {
+        /* info_cls */
+        (size_t)0, /* size    */
+        NULL,      /* copy    */
+        NULL,      /* compare */
+        NULL,      /* free    */
+        NULL,      /* to_str  */
+        NULL,      /* from_str */
+    },
+    {
+        /* wrap_cls */
+        NULL, /* get_object   */
+        NULL, /* get_wrap_ctx */
+        NULL, /* wrap_object  */
+        NULL, /* unwrap_object */
+        NULL, /* free_wrap_ctx */
+    },
+    {
+        /* attribute_cls */
+        NULL, /* create       */
+        NULL, /* open         */
+        NULL, /* read         */
+        NULL, /* write        */
+        NULL, /* get          */
+        NULL, /* specific     */
+        NULL, /* optional     */
+        NULL  /* close        */
+    },
+    {
+        /* dataset_cls */
+        NULL, /* create       */
+        NULL, /* open         */
+        NULL, /* read         */
+        NULL, /* write        */
+        NULL, /* get          */
+        NULL, /* specific     */
+        NULL, /* optional     */
+        NULL  /* close        */
+    },
+    {
+        /* datatype_cls */
         NULL, /* commit       */
         NULL, /* open         */
         NULL, /* get          */
@@ -134,8 +400,9 @@ static const H5VL_class_t fake_vol_g = {
     },
     {
         /* introspect_cls */
-        NULL, /* get_conn_cls */
-        NULL, /* opt_query    */
+        NULL,                     /* get_conn_cls */
+        fake_async_get_cap_flags, /* get_cap_flags */
+        NULL,                     /* opt_query    */
     },
     {
         /* request_cls */
@@ -163,6 +430,146 @@ static const H5VL_class_t fake_vol_g = {
 };
 
 /*-------------------------------------------------------------------------
+ * Function:    reg_opt_op_optional_verify
+ *
+ * Purpose:     Common verification routine for dynamic optional operations
+ *
+ * Return:      Success:    0
+ *              Failure:    -1
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+reg_opt_op_optional_verify(void *obj, H5VL_optional_args_t *args)
+{
+    int *o = (int *)obj;
+    int *op_args;
+
+    /* Check for receiving correct operation value */
+    if (args->op_type != reg_opt_curr_op_val)
+        return -1;
+
+    /* Check that the object is correct */
+    if ((-1) != *o)
+        return -1;
+
+    /* Update the object, with the operation value */
+    *o = args->op_type;
+
+    /* Check that the argument is correct */
+    op_args = args->args;
+    if (NULL == op_args)
+        return -1;
+    if ((-1) != *op_args)
+        return -1;
+
+    /* Update the argument return parameter */
+    *op_args = args->op_type;
+
+    return 0;
+} /* end reg_opt_op_optional_verify() */
+
+/*-------------------------------------------------------------------------
+ * Function:    reg_opt_op_optional
+ *
+ * Purpose:     Common callback to perform a connector-specific operation
+ *              on an object
+ *
+ * Return:      Success:    0
+ *              Failure:    -1
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+reg_opt_op_optional(void *obj, H5VL_optional_args_t *args, hid_t H5_ATTR_UNUSED dxpl_id,
+                    void H5_ATTR_UNUSED **req)
+{
+    /* Invoke the common value verification routine */
+    return reg_opt_op_optional_verify(obj, args);
+} /* end reg_opt_op_optional() */
+
+/*-------------------------------------------------------------------------
+ * Function:    reg_opt_link_optional
+ *
+ * Purpose:     Callback to perform a connector-specific operation
+ *              on a link
+ *
+ * Return:      Success:    0
+ *              Failure:    -1
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+reg_opt_link_optional(void *obj, const H5VL_loc_params_t *loc_params, H5VL_optional_args_t *args,
+                      hid_t H5_ATTR_UNUSED dxpl_id, void H5_ATTR_UNUSED **req)
+{
+    /* Check for receiving correct loc_params info */
+    if (loc_params->type != H5VL_OBJECT_BY_NAME)
+        return -1;
+    if (loc_params->obj_type != H5I_GROUP)
+        return -1;
+    if (HDstrcmp(loc_params->loc_data.loc_by_name.name, ".") != 0)
+        return -1;
+    if (loc_params->loc_data.loc_by_name.lapl_id != H5P_LINK_ACCESS_DEFAULT)
+        return -1;
+
+    /* Invoke the common value verification routine */
+    return reg_opt_op_optional_verify(obj, args);
+} /* end reg_opt_link_optional() */
+
+/*-------------------------------------------------------------------------
+ * Function:    reg_opt_datatype_get
+ *
+ * Purpose:     Handles the datatype get callback
+ *
+ * Note:        This is _strictly_ a testing fixture to support the
+ *              exercise_reg_opt_oper() testing routine.  It fakes just
+ *              enough of the named datatype VOL callback for the
+ *              H5VL_register_using_vol_id() call in that test routine to
+ *              succeed.
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+reg_opt_datatype_get(void H5_ATTR_UNUSED *obj, H5VL_datatype_get_args_t *args, hid_t H5_ATTR_UNUSED dxpl_id,
+                     void H5_ATTR_UNUSED **req)
+{
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    if (H5VL_DATATYPE_GET_BINARY_SIZE == args->op_type) {
+        if (H5Tencode(H5T_NATIVE_INT, NULL, args->args.get_binary_size.size) < 0)
+            ret_value = FAIL;
+    } /* end if */
+    else if (H5VL_DATATYPE_GET_BINARY == args->op_type) {
+        if (H5Tencode(H5T_NATIVE_INT, args->args.get_binary.buf, &args->args.get_binary.buf_size) < 0)
+            ret_value = FAIL;
+    } /* end if */
+    else
+        ret_value = FAIL;
+
+    return ret_value;
+} /* end reg_opt_datatype_get() */
+
+/*-------------------------------------------------------------------------
+ * Function:    fake_async_get_cap_flags
+ *
+ * Purpose:     Return the capability flags for the 'fake async' connector
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+fake_async_get_cap_flags(const void H5_ATTR_UNUSED *info, unsigned *cap_flags)
+{
+    *cap_flags = fake_async_vol_g.cap_flags;
+
+    return SUCCEED;
+} /* end fake_async_get_cap_flags() */
+
+/*-------------------------------------------------------------------------
  * Function:    test_vol_registration()
  *
  * Purpose:     Tests if we can load, register, and close a simple
@@ -1176,6 +1583,519 @@ error:
 
 } /* end test_basic_datatype_operation() */
 
+typedef herr_t (*reg_opt_obj_oper_t)(const char *app_file, const char *app_func, unsigned app_line,
+                                     hid_t obj_id, H5VL_optional_args_t *args, hid_t dxpl_id, hid_t es_id);
+typedef herr_t (*reg_opt_link_oper_t)(const char *app_file, const char *app_func, unsigned app_line,
+                                      hid_t obj_id, const char *name, hid_t lapl_id,
+                                      H5VL_optional_args_t *args, hid_t dxpl_id, hid_t es_id);
+typedef union {
+    reg_opt_obj_oper_t  obj_op;
+    reg_opt_link_oper_t link_op;
+} reg_opt_oper_t;
+
+/*-------------------------------------------------------------------------
+ * Function:    exercise_reg_opt_oper()
+ *
+ * Purpose:     Exercise a particular optional operation for a type.
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+exercise_reg_opt_oper(hid_t fake_vol_id, hid_t reg_opt_vol_id, H5VL_subclass_t subcls,
+                      const char *subcls_name, H5I_type_t id_type, reg_opt_oper_t reg_opt_op)
+{
+    char                 op_name[256]; /* Operation name to register */
+    hid_t                obj_id = H5I_INVALID_HID;
+    H5VL_object_t *      vol_obj;
+    H5VL_optional_args_t vol_cb_args;
+    int                  fake_obj, fake_arg;
+    int                  op_val = -1, op_val2 = -1;
+    int                  find_op_val;
+    herr_t               ret = SUCCEED;
+
+    /* Test registering optional operation */
+    HDsnprintf(op_name, sizeof(op_name), "%s-op1", subcls_name);
+    if (H5VLregister_opt_operation(subcls, op_name, &op_val) < 0)
+        TEST_ERROR;
+
+    /* Verify that the reserved amount of optional operations is obeyed */
+    /* (The first optional operation registered should be at the lower limit) */
+    if (op_val != H5VL_RESERVED_NATIVE_OPTIONAL)
+        TEST_ERROR;
+
+    /* Look up 1st registered optional operation */
+    find_op_val = 0;
+    if (H5VLfind_opt_operation(subcls, op_name, &find_op_val) < 0)
+        TEST_ERROR;
+
+    /* Verify that the operation was looked up successfully */
+    if (op_val != find_op_val)
+        TEST_ERROR;
+
+    /* Test registering second optional operation */
+    HDsnprintf(op_name, sizeof(op_name), "%s-op2", subcls_name);
+    if (H5VLregister_opt_operation(subcls, op_name, &op_val2) < 0)
+        TEST_ERROR;
+
+    /* Verify that the reserved amount of optional operations is obeyed */
+    /* (The 2nd optional operation registered should be at the lower limit + 1) */
+    if (op_val2 != (H5VL_RESERVED_NATIVE_OPTIONAL + 1))
+        TEST_ERROR;
+
+    /* Look up 2nd registered optional operation */
+    find_op_val = 0;
+    if (H5VLfind_opt_operation(subcls, op_name, &find_op_val) < 0)
+        TEST_ERROR;
+
+    /* Verify that the operation was looked up successfully */
+    if (op_val2 != find_op_val)
+        TEST_ERROR;
+
+    /* Push a new API context on the stack */
+    /* (Necessary for the named datatype construction routines) */
+    if (H5VL_SUBCLS_DATATYPE == subcls)
+        H5CX_push();
+
+    /* Create fake object on fake VOL connector */
+    if (H5I_INVALID_HID == (obj_id = H5VL_register_using_vol_id(id_type, &fake_obj, fake_vol_id, TRUE)))
+        TEST_ERROR;
+
+    /* Pop the API context off the stack */
+    if (H5VL_SUBCLS_DATATYPE == subcls)
+        H5CX_pop(FALSE);
+
+    /* Attempt to issue operation on fake VOL connector */
+    fake_obj            = -1;
+    fake_arg            = -1;
+    vol_cb_args.op_type = op_val;
+    vol_cb_args.args    = &fake_arg;
+    H5E_BEGIN_TRY
+    {
+        if (H5VL_SUBCLS_LINK == subcls || H5VL_SUBCLS_OBJECT == subcls)
+            ret = (*reg_opt_op.link_op)(__FILE__, __func__, __LINE__, obj_id, ".", H5P_DEFAULT, &vol_cb_args,
+                                        H5P_DEFAULT, H5ES_NONE);
+        else
+            ret = (*reg_opt_op.obj_op)(__FILE__, __func__, __LINE__, obj_id, &vol_cb_args, H5P_DEFAULT,
+                                       H5ES_NONE);
+    }
+    H5E_END_TRY;
+    if (FAIL != ret)
+        FAIL_PUTS_ERROR("should not be able to perform an optional operation with a NULL callback");
+    if ((-1) != fake_obj)
+        FAIL_PUTS_ERROR("'fake_obj' changed during failed operation?");
+    if ((-1) != fake_arg)
+        FAIL_PUTS_ERROR("'fake_arg' changed during failed operation?");
+
+    /* Named datatypes must be destroyed differently */
+    if (H5VL_SUBCLS_DATATYPE == subcls) {
+        H5T_t *dt;
+
+        /* Destroy fake datatype object */
+        if (NULL == (dt = H5I_remove(obj_id)))
+            TEST_ERROR;
+        if (H5VL_free_object(dt->vol_obj) < 0)
+            TEST_ERROR;
+        dt->vol_obj = NULL;
+        if (H5T_close(dt) < 0)
+            TEST_ERROR;
+    } /* end if */
+    else {
+        /* Destroy fake object */
+        if (NULL == (vol_obj = H5I_remove(obj_id)))
+            TEST_ERROR;
+        if (H5VL_free_object(vol_obj) < 0)
+            TEST_ERROR;
+    } /* end else */
+
+    /* Push a new API context on the stack */
+    /* (Necessary for the named datatype construction routines) */
+    if (H5VL_SUBCLS_DATATYPE == subcls)
+        H5CX_push();
+
+    /* Create fake object on reg_opt VOL connector */
+    if (H5I_INVALID_HID == (obj_id = H5VL_register_using_vol_id(id_type, &fake_obj, reg_opt_vol_id, TRUE)))
+        TEST_ERROR;
+
+    /* Pop the API context off the stack */
+    if (H5VL_SUBCLS_DATATYPE == subcls)
+        H5CX_pop(FALSE);
+
+    /* Issue first operation */
+    fake_obj            = -1;
+    fake_arg            = -1;
+    reg_opt_curr_op_val = op_val;
+    vol_cb_args.op_type = op_val;
+    vol_cb_args.args    = &fake_arg;
+    if (H5VL_SUBCLS_LINK == subcls || H5VL_SUBCLS_OBJECT == subcls)
+        ret = (*reg_opt_op.link_op)(__FILE__, __func__, __LINE__, obj_id, ".", H5P_DEFAULT, &vol_cb_args,
+                                    H5P_DEFAULT, H5ES_NONE);
+    else
+        ret =
+            (*reg_opt_op.obj_op)(__FILE__, __func__, __LINE__, obj_id, &vol_cb_args, H5P_DEFAULT, H5ES_NONE);
+    if (ret < 0)
+        TEST_ERROR;
+
+    /* Verify that fake object & argument were modified correctly */
+    if (op_val != fake_obj)
+        FAIL_PUTS_ERROR("'fake_obj' not updated");
+    if (op_val != fake_arg)
+        FAIL_PUTS_ERROR("'fake_arg' not updated");
+
+    /* Issue second operation */
+    fake_obj            = -1;
+    fake_arg            = -1;
+    reg_opt_curr_op_val = op_val2;
+    vol_cb_args.op_type = op_val2;
+    vol_cb_args.args    = &fake_arg;
+    if (H5VL_SUBCLS_LINK == subcls || H5VL_SUBCLS_OBJECT == subcls)
+        ret = (*reg_opt_op.link_op)(__FILE__, __func__, __LINE__, obj_id, ".", H5P_DEFAULT, &vol_cb_args,
+                                    H5P_DEFAULT, H5ES_NONE);
+    else
+        ret =
+            (*reg_opt_op.obj_op)(__FILE__, __func__, __LINE__, obj_id, &vol_cb_args, H5P_DEFAULT, H5ES_NONE);
+    if (ret < 0)
+        TEST_ERROR;
+
+    /* Verify that fake object & argument were modified correctly */
+    if (op_val2 != fake_obj)
+        FAIL_PUTS_ERROR("'fake_obj' not updated");
+    if (op_val2 != fake_arg)
+        FAIL_PUTS_ERROR("'fake_arg' not updated");
+
+    /* Named datatypes must be destroyed differently */
+    if (H5VL_SUBCLS_DATATYPE == subcls) {
+        H5T_t *dt;
+
+        /* Destroy fake datatype object */
+        if (NULL == (dt = H5I_remove(obj_id)))
+            TEST_ERROR;
+        if (H5VL_free_object(dt->vol_obj) < 0)
+            TEST_ERROR;
+        dt->vol_obj = NULL;
+        if (H5T_close(dt) < 0)
+            TEST_ERROR;
+    } /* end if */
+    else {
+        /* Destroy fake object */
+        if (NULL == (vol_obj = H5I_remove(obj_id)))
+            TEST_ERROR;
+        if (H5VL_free_object(vol_obj) < 0)
+            TEST_ERROR;
+    } /* end else */
+
+    /* Unregister 2nd registered optional operation */
+    if (H5VLunregister_opt_operation(subcls, op_name) < 0)
+        TEST_ERROR;
+
+    return SUCCEED;
+
+error:
+    return FAIL;
+} /* end exercise_reg_opt_oper() */
+
+/*-------------------------------------------------------------------------
+ * Function:    test_register_opt_operation()
+ *
+ * Purpose:     Tests if we can load, register, and close a simple
+ *              VOL connector.
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+test_register_opt_operation(void)
+{
+    hid_t fake_vol_id    = H5I_INVALID_HID;
+    hid_t reg_opt_vol_id = H5I_INVALID_HID;
+    struct {
+        H5VL_subclass_t subcls;
+        const char *    subcls_name;
+        H5I_type_t      id_type;
+        reg_opt_oper_t  reg_opt_op;
+    } test_params[] = {{H5VL_SUBCLS_ATTR, "attr", H5I_ATTR, {.obj_op = H5VLattr_optional_op}},
+                       {H5VL_SUBCLS_DATASET, "dataset", H5I_DATASET, {.obj_op = H5VLdataset_optional_op}},
+                       {H5VL_SUBCLS_DATATYPE, "datatype", H5I_DATATYPE, {.obj_op = H5VLdatatype_optional_op}},
+                       {H5VL_SUBCLS_FILE, "file", H5I_FILE, {.obj_op = H5VLfile_optional_op}},
+                       {H5VL_SUBCLS_GROUP, "group", H5I_GROUP, {.obj_op = H5VLgroup_optional_op}},
+                       {H5VL_SUBCLS_LINK, "link", H5I_GROUP, {.link_op = H5VLlink_optional_op}},
+                       {H5VL_SUBCLS_OBJECT, "object", H5I_GROUP, {.link_op = H5VLobject_optional_op}}};
+    int      op_val = -1;
+    unsigned u;
+    herr_t   ret = SUCCEED;
+
+    TESTING("dynamically registering optional operations");
+
+    /* Register the VOL connectors for testing */
+    if ((fake_vol_id = H5VLregister_connector(&fake_vol_g, H5P_DEFAULT)) < 0)
+        TEST_ERROR;
+    if ((reg_opt_vol_id = H5VLregister_connector(&reg_opt_vol_g, H5P_DEFAULT)) < 0)
+        TEST_ERROR;
+
+    /* Test registering invalid optional VOL subclass operations */
+    H5E_BEGIN_TRY
+    {
+        ret = H5VLregister_opt_operation(H5VL_SUBCLS_NONE, "fail", &op_val);
+    }
+    H5E_END_TRY;
+    if (FAIL != ret)
+        FAIL_PUTS_ERROR("should not be able to register an optional operation for the 'NONE' VOL subclass");
+    if ((-1) != op_val)
+        FAIL_PUTS_ERROR("'op_val' changed during failed operation?");
+    H5E_BEGIN_TRY
+    {
+        ret = H5VLregister_opt_operation(H5VL_SUBCLS_INFO, "fail2", &op_val);
+    }
+    H5E_END_TRY;
+    if (FAIL != ret)
+        FAIL_PUTS_ERROR("should not be able to register an optional operation for the 'INFO' VOL subclass");
+    if ((-1) != op_val)
+        FAIL_PUTS_ERROR("'op_val' changed during failed operation?");
+    H5E_BEGIN_TRY
+    {
+        ret = H5VLregister_opt_operation(H5VL_SUBCLS_WRAP, "fail3", &op_val);
+    }
+    H5E_END_TRY;
+    if (FAIL != ret)
+        FAIL_PUTS_ERROR("should not be able to register an optional operation for the 'WRAP' VOL subclass");
+    if ((-1) != op_val)
+        FAIL_PUTS_ERROR("'op_val' changed during failed operation?");
+    H5E_BEGIN_TRY
+    {
+        ret = H5VLregister_opt_operation(H5VL_SUBCLS_BLOB, "fail4", &op_val);
+    }
+    H5E_END_TRY;
+    if (FAIL != ret)
+        FAIL_PUTS_ERROR("should not be able to register an optional operation for the 'BLOB' VOL subclass");
+    if ((-1) != op_val)
+        FAIL_PUTS_ERROR("'op_val' changed during failed operation?");
+    H5E_BEGIN_TRY
+    {
+        ret = H5VLregister_opt_operation(H5VL_SUBCLS_TOKEN, "fail5", &op_val);
+    }
+    H5E_END_TRY;
+    if (FAIL != ret)
+        FAIL_PUTS_ERROR("should not be able to register an optional operation for the 'TOKEN' VOL subclass");
+    if ((-1) != op_val)
+        FAIL_PUTS_ERROR("'op_val' changed during failed operation?");
+
+    /* Test registering valid optional VOL subclass operation with NULL op_val ptr*/
+    H5E_BEGIN_TRY
+    {
+        ret = H5VLregister_opt_operation(H5VL_SUBCLS_FILE, "fail6", NULL);
+    }
+    H5E_END_TRY;
+    if (FAIL != ret)
+        FAIL_PUTS_ERROR("should not be able to register an optional operation with a NULL 'op_val'");
+
+    /* Try finding a non-existent optional VOL subclass operation */
+    H5E_BEGIN_TRY
+    {
+        ret = H5VLfind_opt_operation(H5VL_SUBCLS_DATASET, "fail", &op_val);
+    }
+    H5E_END_TRY;
+    if (FAIL != ret)
+        FAIL_PUTS_ERROR("should not be able to find a non-existent optional operation");
+
+    /* Try unregistering a non-existent optional VOL subclass operation */
+    H5E_BEGIN_TRY
+    {
+        ret = H5VLunregister_opt_operation(H5VL_SUBCLS_DATASET, "fail");
+    }
+    H5E_END_TRY;
+    if (FAIL != ret)
+        FAIL_PUTS_ERROR("should not be able to unregister a non-existent optional operation");
+
+    /* Optional operations on requests are supported (but difficult to test further) */
+    if (H5VLregister_opt_operation(H5VL_SUBCLS_REQUEST, "req_op", &op_val) < 0)
+        TEST_ERROR;
+
+    /* Register & test calling optional operations for each valid VOL subclass */
+    /* (Table-driven, with test_params array) */
+    for (u = 0; u < NELMTS(test_params); u++)
+        /* Exercise appropriate callback, for each VOL subclass */
+        if (exercise_reg_opt_oper(fake_vol_id, reg_opt_vol_id, test_params[u].subcls,
+                                  test_params[u].subcls_name, test_params[u].id_type,
+                                  test_params[u].reg_opt_op) < 0)
+            TEST_ERROR;
+
+    /* Unregister the VOL connectors */
+    if (H5VLunregister_connector(fake_vol_id) < 0)
+        TEST_ERROR;
+    if (H5VLunregister_connector(reg_opt_vol_id) < 0)
+        TEST_ERROR;
+
+    PASSED();
+
+    return SUCCEED;
+
+error:
+    H5E_BEGIN_TRY
+    {
+        H5VLunregister_connector(fake_vol_id);
+        H5VLunregister_connector(reg_opt_vol_id);
+    }
+    H5E_END_TRY;
+
+    return FAIL;
+} /* end test_register_opt_operation() */
+
+/*-------------------------------------------------------------------------
+ * Function:    test_async_vol_props()
+ *
+ * Purpose:     Test properties related to asynchronous VOL connector operation
+ *
+ * Note:        Overrides the HDF5_VOL_CONNECTOR environment variable, to
+ *              provide stable testing environment.
+ *
+ * Return:      SUCCEED/FAIL
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+test_async_vol_props(void)
+{
+    hid_t                    fapl_id = H5I_INVALID_HID;
+    hid_t                    vol_id  = H5I_INVALID_HID;
+    H5VL_pass_through_info_t passthru_info;
+    unsigned                 cap_flags    = 0;
+    char *                   conn_env_str = NULL;
+
+    TESTING("Async VOL props");
+
+    /* Retrieve the file access property for testing */
+    fapl_id = h5_fileaccess();
+
+    /* Test 'capability flags' property */
+
+    /* Test query w/NULL for cap_flags parameter */
+    if (H5Pget_vol_cap_flags(fapl_id, NULL) < 0)
+        FAIL_STACK_ERROR;
+
+    /* Override possible environment variable & re-initialize default VOL connector */
+    conn_env_str = HDgetenv("HDF5_VOL_CONNECTOR");
+    if (conn_env_str) {
+        if (NULL == (conn_env_str = HDstrdup(conn_env_str)))
+            TEST_ERROR
+        if (HDunsetenv("HDF5_VOL_CONNECTOR") < 0)
+            TEST_ERROR
+        if (H5VL__reparse_def_vol_conn_variable_test() < 0)
+            TEST_ERROR
+    } /* end if */
+
+    /* Test query w/default VOL, which should indicate no async, since native connector
+     * doesn't support async.
+     */
+    if (H5Pget_vol_cap_flags(fapl_id, &cap_flags) < 0)
+        FAIL_STACK_ERROR;
+    if ((cap_flags & H5VL_CAP_FLAG_ASYNC) > 0)
+        TEST_ERROR
+    if ((cap_flags & H5VL_CAP_FLAG_NATIVE_FILES) == 0)
+        TEST_ERROR
+
+    /* Close FAPL */
+    if (H5Pclose(fapl_id) < 0)
+        FAIL_STACK_ERROR;
+
+    /* Register a fake VOL connector that sets the async capability flag */
+    if ((vol_id = H5VLregister_connector(&fake_async_vol_g, H5P_DEFAULT)) < 0)
+        FAIL_STACK_ERROR;
+
+    /* Set environment variable to use 'fake async' connector & re-init default connector */
+    if (HDsetenv("HDF5_VOL_CONNECTOR", "fake_async", TRUE) < 0)
+        TEST_ERROR
+    if (H5VL__reparse_def_vol_conn_variable_test() < 0)
+        TEST_ERROR
+
+    /* Retrieve the file access property again */
+    fapl_id = h5_fileaccess();
+
+    /* Test query w/fake async VOL, which should succeed */
+    cap_flags = 0;
+    if (H5Pget_vol_cap_flags(fapl_id, &cap_flags) < 0)
+        FAIL_STACK_ERROR;
+    if ((cap_flags & H5VL_CAP_FLAG_ASYNC) == 0)
+        TEST_ERROR
+    if ((cap_flags & H5VL_CAP_FLAG_NATIVE_FILES) > 0)
+        TEST_ERROR
+
+    /* Reset environment variable & re-init default connector */
+    if (HDunsetenv("HDF5_VOL_CONNECTOR") < 0)
+        TEST_ERROR
+    if (H5VL__reparse_def_vol_conn_variable_test() < 0)
+        TEST_ERROR
+
+    /* Close FAPL */
+    if (H5Pclose(fapl_id) < 0)
+        FAIL_STACK_ERROR;
+
+    /* Retrieve the file access property again */
+    fapl_id = h5_fileaccess();
+
+    /* Set the VOL connector for the FAPL to the fake async connector */
+    if (H5Pset_vol(fapl_id, vol_id, NULL) < 0)
+        FAIL_STACK_ERROR;
+
+    /* Test query w/fake async VOL, which should succeed */
+    cap_flags = 0;
+    if (H5Pget_vol_cap_flags(fapl_id, &cap_flags) < 0)
+        FAIL_STACK_ERROR;
+    if ((cap_flags & H5VL_CAP_FLAG_ASYNC) == 0)
+        TEST_ERROR
+    if ((cap_flags & H5VL_CAP_FLAG_NATIVE_FILES) > 0)
+        TEST_ERROR
+
+    /* Stack the [internal] passthrough VOL connector on top of the fake async connector */
+    passthru_info.under_vol_id   = vol_id;
+    passthru_info.under_vol_info = NULL;
+    if (H5Pset_vol(fapl_id, H5VL_PASSTHRU, &passthru_info) < 0)
+        FAIL_STACK_ERROR;
+
+    /* Test query w/passthru -> fake async VOL, which should succeed */
+    cap_flags = 0;
+    if (H5Pget_vol_cap_flags(fapl_id, &cap_flags) < 0)
+        FAIL_STACK_ERROR;
+    if ((cap_flags & H5VL_CAP_FLAG_ASYNC) == 0)
+        TEST_ERROR
+    if ((cap_flags & H5VL_CAP_FLAG_NATIVE_FILES) > 0)
+        TEST_ERROR
+
+    /* Unregister the fake async VOL ID */
+    if (H5VLunregister_connector(vol_id) < 0)
+        TEST_ERROR;
+
+    /* Close FAPL */
+    if (H5Pclose(fapl_id) < 0)
+        FAIL_STACK_ERROR;
+
+    /* Restore environment variable, if there was one */
+    if (conn_env_str) {
+        if (HDsetenv("HDF5_VOL_CONNECTOR", conn_env_str, TRUE) < 0)
+            TEST_ERROR
+        HDfree(conn_env_str);
+
+        if (H5VL__reparse_def_vol_conn_variable_test() < 0)
+            TEST_ERROR
+    } /* end if */
+
+    PASSED();
+
+    return SUCCEED;
+
+error:
+    H5E_BEGIN_TRY
+    {
+        H5Pclose(fapl_id);
+        H5VLunregister_connector(vol_id);
+    }
+    H5E_END_TRY;
+    HDfree(conn_env_str);
+
+    return FAIL;
+} /* end test_async_vol_props() */
+
 /*-------------------------------------------------------------------------
  * Function:    main
  *
@@ -1201,6 +2121,7 @@ main(void)
     HDputs("Testing basic Virtual Object Layer (VOL) functionality.");
 
     nerrors += test_vol_registration() < 0 ? 1 : 0;
+    nerrors += test_register_opt_operation() < 0 ? 1 : 0;
     nerrors += test_native_vol_init() < 0 ? 1 : 0;
     nerrors += test_basic_file_operation(env_h5_drvr) < 0 ? 1 : 0;
     nerrors += test_basic_group_operation() < 0 ? 1 : 0;
@@ -1209,6 +2130,7 @@ main(void)
     nerrors += test_basic_object_operation() < 0 ? 1 : 0;
     nerrors += test_basic_link_operation() < 0 ? 1 : 0;
     nerrors += test_basic_datatype_operation() < 0 ? 1 : 0;
+    nerrors += test_async_vol_props() < 0 ? 1 : 0;
 
     if (nerrors) {
         HDprintf("***** %d Virtual Object Layer TEST%s FAILED! *****\n", nerrors, nerrors > 1 ? "S" : "");