Merge pull request #2876 from vchoi-hdfgroup/2my_feature_select_io_tconvfeature/select_io_tconv

2my feature select io tconv

9 files changed, 345 insertions, 32 deletions

diff --git a/src/H5CX.c b/src/H5CX.c
index e5595b7..1243cdf 100644
--- a/src/H5CX.c
+++ b/src/H5CX.c
@@ -305,6 +305,11 @@ typedef struct H5CX_t {
     hbool_t no_selection_io_cause_set;   /* Whether reason for not performing selection I/O is set */
     hbool_t no_selection_io_cause_valid; /* Whether reason for not performing selection I/O is valid */
 
+    uint32_t
+            actual_selection_io_mode; /* Actual selection I/O mode used (H5D_ACTUAL_SELECTION_IO_MODE_NAME) */
+    hbool_t actual_selection_io_mode_set;   /* Whether actual selection I/O mode is set */
+    hbool_t actual_selection_io_mode_valid; /* Whether actual selection I/O mode is valid */
+
     /* Cached LCPL properties */
     H5T_cset_t encoding;                 /* Link name character encoding */
     hbool_t    encoding_valid;           /* Whether link name character encoding is valid */
@@ -386,6 +391,8 @@ typedef struct H5CX_dxpl_cache_t {
     H5D_selection_io_mode_t selection_io_mode;     /* Selection I/O mode (H5D_XFER_SELECTION_IO_MODE_NAME) */
     uint32_t                no_selection_io_cause; /* Reasons for not performing selection I/O
                                                             (H5D_XFER_NO_SELECTION_IO_CAUSE_NAME) */
+    uint32_t actual_selection_io_mode;             /* Actual selection I/O mode
+                                                         (H5D_XFER_ACTUAL_SELECTION_IO_MODE_NAME) */
     hbool_t modify_write_buf;                      /* Whether the library can modify write buffers */
 } H5CX_dxpl_cache_t;
 
@@ -576,13 +583,18 @@ H5CX_init(void)
 
     /* Get the selection I/O mode */
     if (H5P_get(dx_plist, H5D_XFER_SELECTION_IO_MODE_NAME, &H5CX_def_dxpl_cache.selection_io_mode) < 0)
-        HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve parallel transfer method")
+        HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve selection I/O mode")
 
     /* Get the local & global reasons for breaking selection I/O values */
     if (H5P_get(dx_plist, H5D_XFER_NO_SELECTION_IO_CAUSE_NAME, &H5CX_def_dxpl_cache.no_selection_io_cause) <
         0)
         HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve cause for no selection I/O")
 
+    /* Get the actual selection I/O mode */
+    if (H5P_get(dx_plist, H5D_XFER_ACTUAL_SELECTION_IO_MODE_NAME,
+                &H5CX_def_dxpl_cache.actual_selection_io_mode) < 0)
+        HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve actual selection I/O mode")
+
     /* Get the modify write buffer property */
     if (H5P_get(dx_plist, H5D_XFER_MODIFY_WRITE_BUF_NAME, &H5CX_def_dxpl_cache.modify_write_buf) < 0)
         HGOTO_ERROR(H5E_CONTEXT, H5E_CANTGET, FAIL, "Can't retrieve modify write buffer property")
@@ -2658,6 +2670,43 @@ done:
 } /* end H5CX_get_no_selection_io_cause() */
 
 /*-------------------------------------------------------------------------
+ * Function:    H5CX_get_no_selection_io_cause
+ *
+ * Purpose:     Retrieves the cause for not performing selection I/O
+ *              for the current API call context.
+ *
+ * Return:      Non-negative on success / Negative on failure
+ *
+ * Programmer:  Vailin Choi
+ *              April 15, 2023
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5CX_get_actual_selection_io_mode(uint32_t *actual_selection_io_mode)
+{
+    H5CX_node_t **head      = NULL;    /* Pointer to head of API context list */
+    herr_t        ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI(FAIL)
+
+    /* Sanity check */
+    HDassert(actual_selection_io_mode);
+    head = H5CX_get_my_context(); /* Get the pointer to the head of the API context, for this thread */
+    HDassert(head && *head);
+    HDassert(H5P_DEFAULT != (*head)->ctx.dxpl_id);
+
+    H5CX_RETRIEVE_PROP_VALID_SET(dxpl, H5P_DATASET_XFER_DEFAULT, H5D_XFER_ACTUAL_SELECTION_IO_MODE_NAME,
+                                 actual_selection_io_mode)
+
+    /* Get the value */
+    *actual_selection_io_mode = (*head)->ctx.actual_selection_io_mode;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5CX_get_actual_selection_io_mode() */
+
+/*-------------------------------------------------------------------------
  * Function:    H5CX_get_modify_write_buf
  *
  * Purpose:     Retrieves the modify write buffer property for the current API call context.
@@ -3702,7 +3751,42 @@ H5CX_set_no_selection_io_cause(uint32_t no_selection_io_cause)
     } /* end if */
 
     FUNC_LEAVE_NOAPI_VOID
-} /* end H5CX_set_no_selectiion_io_cause() */
+} /* end H5CX_set_no_selection_io_cause() */
+
+/*-------------------------------------------------------------------------
+ * Function:    H5CX_set_actual_selecction_io_mode
+ *
+ * Purpose:     Sets the actual selection I/O mode for the current API
+ *              call context.
+ *
+ * Return:      <none>
+ *
+ * Programmer:  Vailin Choi
+ *              April 15, 2023
+ *
+ *-------------------------------------------------------------------------
+ */
+void
+H5CX_set_actual_selection_io_mode(uint32_t actual_selection_io_mode)
+{
+    H5CX_node_t **head = NULL; /* Pointer to head of API context list */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOERR
+
+    /* Sanity checks */
+    head = H5CX_get_my_context(); /* Get the pointer to the head of the API context, for this thread */
+    HDassert(head && *head);
+    HDassert((*head)->ctx.dxpl_id != H5P_DEFAULT);
+
+    /* If we're using the default DXPL, don't modify it */
+    if ((*head)->ctx.dxpl_id != H5P_DATASET_XFER_DEFAULT) {
+        /* Cache the value for later, marking it to set in DXPL when context popped */
+        (*head)->ctx.actual_selection_io_mode     = actual_selection_io_mode;
+        (*head)->ctx.actual_selection_io_mode_set = TRUE;
+    } /* end if */
+
+    FUNC_LEAVE_NOAPI_VOID
+} /* end H5CX_set_actual_selection_io_mode() */
 
 /*-------------------------------------------------------------------------
  * Function:    H5CX_get_ohdr_flags
@@ -3766,6 +3850,7 @@ H5CX__pop_common(hbool_t update_dxpl_props)
     /* Check for cached DXPL properties to return to application */
     if (update_dxpl_props) {
         H5CX_SET_PROP(H5D_XFER_NO_SELECTION_IO_CAUSE_NAME, no_selection_io_cause)
+        H5CX_SET_PROP(H5D_XFER_ACTUAL_SELECTION_IO_MODE_NAME, actual_selection_io_mode)
 #ifdef H5_HAVE_PARALLEL
         H5CX_SET_PROP(H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_NAME, mpio_actual_chunk_opt)
         H5CX_SET_PROP(H5D_MPIO_ACTUAL_IO_MODE_NAME, mpio_actual_io_mode)
diff --git a/src/H5CXprivate.h b/src/H5CXprivate.h
index f0bec20..885d6a6 100644
--- a/src/H5CXprivate.h
+++ b/src/H5CXprivate.h
@@ -117,6 +117,7 @@ H5_DLL herr_t H5CX_get_vlen_alloc_info(H5T_vlen_alloc_info_t *vl_alloc_info);
 H5_DLL herr_t H5CX_get_dt_conv_cb(H5T_conv_cb_t *cb_struct);
 H5_DLL herr_t H5CX_get_selection_io_mode(H5D_selection_io_mode_t *selection_io_mode);
 H5_DLL herr_t H5CX_get_no_selection_io_cause(uint32_t *no_selection_io_cause);
+H5_DLL herr_t H5CX_get_actual_selection_io_mode(uint32_t *actual_selection_io_mode);
 H5_DLL herr_t H5CX_get_modify_write_buf(hbool_t *modify_write_buf);
 
 /* "Getter" routines for LCPL properties cached in API context */
@@ -163,6 +164,7 @@ H5_DLL herr_t H5CX_init(void);
 /* "Setter" routines for cached DXPL properties that must be returned to application */
 
 H5_DLL void H5CX_set_no_selection_io_cause(uint32_t no_selection_io_cause);
+H5_DLL void H5CX_set_actual_selection_io_mode(uint32_t actual_selection_io_mode);
 
 #ifdef H5_HAVE_PARALLEL
 H5_DLL void H5CX_set_mpio_actual_chunk_opt(H5D_mpio_actual_chunk_opt_mode_t chunk_opt);
diff --git a/src/H5Dprivate.h b/src/H5Dprivate.h
index 8265ac2..285529c 100644
--- a/src/H5Dprivate.h
+++ b/src/H5Dprivate.h
@@ -78,15 +78,16 @@
 #define H5D_MPIO_LOCAL_NO_COLLECTIVE_CAUSE_NAME                                                              \
     "local_no_collective_cause" /* cause of broken collective I/O in each process */
 #define H5D_MPIO_GLOBAL_NO_COLLECTIVE_CAUSE_NAME                                                             \
-    "global_no_collective_cause"                         /* cause of broken collective I/O in all processes */
-#define H5D_XFER_EDC_NAME                   "err_detect" /* EDC */
-#define H5D_XFER_FILTER_CB_NAME             "filter_cb"  /* Filter callback function */
-#define H5D_XFER_CONV_CB_NAME               "type_conv_cb"          /* Type conversion callback function */
-#define H5D_XFER_XFORM_NAME                 "data_transform"        /* Data transform */
-#define H5D_XFER_DSET_IO_SEL_NAME           "dset_io_selection"     /* Dataset I/O selection */
-#define H5D_XFER_SELECTION_IO_MODE_NAME     "selection_io_mode"     /* Selection I/O mode */
-#define H5D_XFER_NO_SELECTION_IO_CAUSE_NAME "no_selection_io_cause" /* Cause for no selection I/O */
-#define H5D_XFER_MODIFY_WRITE_BUF_NAME      "modify_write_buf"      /* Modify write buffers */
+    "global_no_collective_cause" /* cause of broken collective I/O in all processes */
+#define H5D_XFER_EDC_NAME                      "err_detect"            /* EDC */
+#define H5D_XFER_FILTER_CB_NAME                "filter_cb"             /* Filter callback function */
+#define H5D_XFER_CONV_CB_NAME                  "type_conv_cb"          /* Type conversion callback function */
+#define H5D_XFER_XFORM_NAME                    "data_transform"        /* Data transform */
+#define H5D_XFER_DSET_IO_SEL_NAME              "dset_io_selection"     /* Dataset I/O selection */
+#define H5D_XFER_SELECTION_IO_MODE_NAME        "selection_io_mode"     /* Selection I/O mode */
+#define H5D_XFER_NO_SELECTION_IO_CAUSE_NAME    "no_selection_io_cause" /* Cause for no selection I/O */
+#define H5D_XFER_ACTUAL_SELECTION_IO_MODE_NAME "actual_selection_io_mode" /* Actual selection I/O mode */
+#define H5D_XFER_MODIFY_WRITE_BUF_NAME         "modify_write_buf"         /* Modify write buffers */
 #ifdef H5_HAVE_INSTRUMENTED_LIBRARY
 /* Collective chunk instrumentation properties */
 #define H5D_XFER_COLL_CHUNK_LINK_HARD_NAME        "coll_chunk_link_hard"
diff --git a/src/H5FDint.c b/src/H5FDint.c
index 6d90aae..bc23ba2 100644
--- a/src/H5FDint.c
+++ b/src/H5FDint.c
@@ -457,10 +457,16 @@ H5FD_read_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addrs
 
     /* if the underlying VFD supports vector read, make the call */
     if (file->cls->read_vector) {
+        uint32_t actual_selection_io_mode;
 
         if ((file->cls->read_vector)(file, dxpl_id, count, types, addrs, sizes, bufs) < 0)
 
             HGOTO_ERROR(H5E_VFL, H5E_READERROR, FAIL, "driver read vector request failed")
+
+        /* Set actual selection I/O mode */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_VECTOR_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
     else {
 
@@ -470,6 +476,7 @@ H5FD_read_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addrs
         extend_sizes = FALSE;
         extend_types = FALSE;
         uint32_t no_selection_io_cause;
+        uint32_t actual_selection_io_mode;
 
         for (i = 0; i < count; i++) {
 
@@ -511,6 +518,11 @@ H5FD_read_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addrs
         H5CX_get_no_selection_io_cause(&no_selection_io_cause);
         no_selection_io_cause |= H5D_SEL_IO_NO_VECTOR_OR_SELECTION_IO_CB;
         H5CX_set_no_selection_io_cause(no_selection_io_cause);
+
+        /* Set actual selection I/O mode */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_SCALAR_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
 
 done:
@@ -665,9 +677,16 @@ H5FD_write_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addr
     /* if the underlying VFD supports vector write, make the call */
     if (file->cls->write_vector) {
 
+        uint32_t actual_selection_io_mode;
+
         if ((file->cls->write_vector)(file, dxpl_id, count, types, addrs, sizes, bufs) < 0)
 
             HGOTO_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "driver write vector request failed")
+
+        /* Set actual selection I/O */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_VECTOR_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
     else {
         /* otherwise, implement the vector write as a sequence of regular
@@ -676,6 +695,7 @@ H5FD_write_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addr
         extend_sizes = FALSE;
         extend_types = FALSE;
         uint32_t no_selection_io_cause;
+        uint32_t actual_selection_io_mode;
 
         for (i = 0; i < count; i++) {
 
@@ -717,6 +737,11 @@ H5FD_write_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addr
         H5CX_get_no_selection_io_cause(&no_selection_io_cause);
         no_selection_io_cause |= H5D_SEL_IO_NO_VECTOR_OR_SELECTION_IO_CB;
         H5CX_set_no_selection_io_cause(no_selection_io_cause);
+
+        /* Set actual selection I/O */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_SCALAR_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
 
 done:
@@ -998,18 +1023,31 @@ H5FD__read_selection_translate(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, uin
 
     /* Issue vector read call if appropriate */
     if (use_vector) {
+        uint32_t actual_selection_io_mode;
+
         H5_CHECK_OVERFLOW(vec_arr_nused, size_t, uint32_t)
         if ((file->cls->read_vector)(file, dxpl_id, (uint32_t)vec_arr_nused, types, addrs, sizes, vec_bufs) <
             0)
             HGOTO_ERROR(H5E_VFL, H5E_READERROR, FAIL, "driver read vector request failed")
+
+        /* Set actual selection I/O */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_VECTOR_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
     else {
         uint32_t no_selection_io_cause;
+        uint32_t actual_selection_io_mode;
 
         /* Add H5D_SEL_IO_NO_VECTOR_OR_SELECTION_IO_CB to no selection I/O cause */
         H5CX_get_no_selection_io_cause(&no_selection_io_cause);
         no_selection_io_cause |= H5D_SEL_IO_NO_VECTOR_OR_SELECTION_IO_CB;
         H5CX_set_no_selection_io_cause(no_selection_io_cause);
+
+        /* Set actual selection I/O */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_SCALAR_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
 
 done:
@@ -1165,6 +1203,8 @@ H5FD_read_selection(H5FD_t *file, H5FD_mem_t type, uint32_t count, H5S_t **mem_s
 
     /* if the underlying VFD supports selection read, make the call */
     if (file->cls->read_selection) {
+        uint32_t actual_selection_io_mode;
+
         /* Allocate array of space IDs if necessary, otherwise use local
          * buffers */
         if (count > sizeof(mem_space_ids_local) / sizeof(mem_space_ids_local[0])) {
@@ -1190,6 +1230,11 @@ H5FD_read_selection(H5FD_t *file, H5FD_mem_t type, uint32_t count, H5S_t **mem_s
         if ((file->cls->read_selection)(file, type, dxpl_id, count, mem_space_ids, file_space_ids, offsets,
                                         element_sizes, bufs) < 0)
             HGOTO_ERROR(H5E_VFL, H5E_READERROR, FAIL, "driver read selection request failed")
+
+        /* Set actual selection I/O */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_SELECTION_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
     else
         /* Otherwise, implement the selection read as a sequence of regular
@@ -1329,9 +1374,16 @@ H5FD_read_selection_id(H5FD_t *file, H5FD_mem_t type, uint32_t count, hid_t mem_
 
     /* if the underlying VFD supports selection read, make the call */
     if (file->cls->read_selection) {
+        uint32_t actual_selection_io_mode;
+
         if ((file->cls->read_selection)(file, type, dxpl_id, count, mem_space_ids, file_space_ids, offsets,
                                         element_sizes, bufs) < 0)
             HGOTO_ERROR(H5E_VFL, H5E_READERROR, FAIL, "driver read selection request failed")
+
+        /* Set actual selection I/O */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_SELECTION_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
     else {
         /* Otherwise, implement the selection read as a sequence of regular
@@ -1645,18 +1697,31 @@ H5FD__write_selection_translate(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, ui
 
     /* Issue vector write call if appropriate */
     if (use_vector) {
+        uint32_t actual_selection_io_mode;
+
         H5_CHECK_OVERFLOW(vec_arr_nused, size_t, uint32_t)
         if ((file->cls->write_vector)(file, dxpl_id, (uint32_t)vec_arr_nused, types, addrs, sizes, vec_bufs) <
             0)
             HGOTO_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "driver write vector request failed")
+
+        /* Set actual selection I/O */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_VECTOR_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
     else {
         uint32_t no_selection_io_cause;
+        uint32_t actual_selection_io_mode;
 
         /* Add H5D_SEL_IO_NO_VECTOR_OR_SELECTION_IO_CB to no selection I/O cause */
         H5CX_get_no_selection_io_cause(&no_selection_io_cause);
         no_selection_io_cause |= H5D_SEL_IO_NO_VECTOR_OR_SELECTION_IO_CB;
         H5CX_set_no_selection_io_cause(no_selection_io_cause);
+
+        /* Set actual selection I/O */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_SCALAR_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
 
 done:
@@ -1804,6 +1869,8 @@ H5FD_write_selection(H5FD_t *file, H5FD_mem_t type, uint32_t count, H5S_t **mem_
 
     /* if the underlying VFD supports selection write, make the call */
     if (file->cls->write_selection) {
+        uint32_t actual_selection_io_mode;
+
         /* Allocate array of space IDs if necessary, otherwise use local
          * buffers */
         if (count > sizeof(mem_space_ids_local) / sizeof(mem_space_ids_local[0])) {
@@ -1829,6 +1896,11 @@ H5FD_write_selection(H5FD_t *file, H5FD_mem_t type, uint32_t count, H5S_t **mem_
         if ((file->cls->write_selection)(file, type, dxpl_id, count, mem_space_ids, file_space_ids, offsets,
                                          element_sizes, bufs) < 0)
             HGOTO_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "driver write selection request failed")
+
+        /* Set actual selection I/O */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_SELECTION_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
     else
         /* Otherwise, implement the selection write as a sequence of regular
@@ -1959,9 +2031,16 @@ H5FD_write_selection_id(H5FD_t *file, H5FD_mem_t type, uint32_t count, hid_t mem
 
     /* if the underlying VFD supports selection write, make the call */
     if (file->cls->write_selection) {
+        uint32_t actual_selection_io_mode;
+
         if ((file->cls->write_selection)(file, type, dxpl_id, count, mem_space_ids, file_space_ids, offsets,
                                          element_sizes, bufs) < 0)
             HGOTO_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "driver write selection request failed")
+
+        /* Set actual selection I/O mode */
+        H5CX_get_actual_selection_io_mode(&actual_selection_io_mode);
+        actual_selection_io_mode |= H5D_SELECTION_IO;
+        H5CX_set_actual_selection_io_mode(actual_selection_io_mode);
     }
     else {
         /* Otherwise, implement the selection write as a sequence of regular
diff --git a/src/H5Pdxpl.c b/src/H5Pdxpl.c
index 6eef558..fd63a66 100644
--- a/src/H5Pdxpl.c
+++ b/src/H5Pdxpl.c
@@ -176,6 +176,9 @@
 /* Definitions for cause of no selection I/O property */
 #define H5D_XFER_NO_SELECTION_IO_CAUSE_SIZE sizeof(uint32_t)
 #define H5D_XFER_NO_SELECTION_IO_CAUSE_DEF  0
+/* Definitions for actual selection I/O mode property */
+#define H5D_XFER_ACTUAL_SELECTION_IO_MODE_SIZE sizeof(uint32_t)
+#define H5D_XFER_ACTUAL_SELECTION_IO_MODE_DEF  0
 /* Definitions for modify write buffer property */
 #define H5D_XFER_MODIFY_WRITE_BUF_SIZE sizeof(hbool_t)
 #define H5D_XFER_MODIFY_WRITE_BUF_DEF  FALSE
@@ -296,7 +299,8 @@ static const H5S_t *H5D_def_dset_io_sel_g =
     H5D_XFER_DSET_IO_SEL_DEF; /* Default value for dataset I/O selection */
 static const H5D_selection_io_mode_t H5D_def_selection_io_mode_g     = H5D_XFER_SELECTION_IO_MODE_DEF;
 static const uint32_t                H5D_def_no_selection_io_cause_g = H5D_XFER_NO_SELECTION_IO_CAUSE_DEF;
-static const hbool_t                 H5D_def_modify_write_buf_g      = H5D_XFER_MODIFY_WRITE_BUF_DEF;
+static const uint32_t H5D_def_actual_selection_io_mode_g             = H5D_XFER_ACTUAL_SELECTION_IO_MODE_DEF;
+static const hbool_t  H5D_def_modify_write_buf_g                     = H5D_XFER_MODIFY_WRITE_BUF_DEF;
 
 /*-------------------------------------------------------------------------
  * Function:    H5P__dxfr_reg_prop
@@ -473,6 +477,13 @@ H5P__dxfr_reg_prop(H5P_genclass_t *pclass)
                            NULL) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
 
+    /* Register the actual selection I/O mode property */
+    /* (Note: this property should not have an encode/decode callback) */
+    if (H5P__register_real(pclass, H5D_XFER_ACTUAL_SELECTION_IO_MODE_NAME,
+                           H5D_XFER_ACTUAL_SELECTION_IO_MODE_SIZE, &H5D_def_actual_selection_io_mode_g, NULL,
+                           NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
+
     /* Register the modify write buffer property */
     if (H5P__register_real(pclass, H5D_XFER_MODIFY_WRITE_BUF_NAME, H5D_XFER_MODIFY_WRITE_BUF_SIZE,
                            &H5D_def_modify_write_buf_g, NULL, NULL, NULL, H5D_XFER_MODIFY_WRITE_BUF_ENC,
@@ -2562,7 +2573,7 @@ H5Pget_selection_io(hid_t plist_id, H5D_selection_io_mode_t *selection_io_mode /
     herr_t          ret_value = SUCCEED; /* Return value */
 
     FUNC_ENTER_API(FAIL)
-    H5TRACE2("e", "i*DC", plist_id, selection_io_mode);
+    H5TRACE2("e", "ix", plist_id, selection_io_mode);
 
     /* Check arguments */
     if (NULL == (plist = H5P_object_verify(plist_id, H5P_DATASET_XFER)))
@@ -2611,6 +2622,39 @@ done:
 } /* end H5Pget_no_selection_io_cause() */
 
 /*-------------------------------------------------------------------------
+ * Function:	H5Pget_actual_selection_io_mode
+ *
+ * Purpose:	    Retrieves actual selection I/O mode
+ *
+ * Return:	    Non-negative on success/Negative on failure
+ *
+ * Programmer:	Vailin Choi
+ *              April 27, 2023
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pget_actual_selection_io_mode(hid_t plist_id, uint32_t *actual_selection_io_mode /*out*/)
+{
+    H5P_genplist_t *plist;
+    herr_t          ret_value = SUCCEED; /* return value */
+
+    FUNC_ENTER_API(FAIL)
+    H5TRACE2("e", "ix", plist_id, actual_selection_io_mode);
+
+    /* Get the plist structure */
+    if (NULL == (plist = H5P_object_verify(plist_id, H5P_DATASET_XFER)))
+        HGOTO_ERROR(H5E_ID, H5E_BADID, FAIL, "can't find object for ID")
+
+    /* Return values */
+    if (actual_selection_io_mode)
+        if (H5P_get(plist, H5D_XFER_ACTUAL_SELECTION_IO_MODE_NAME, actual_selection_io_mode) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "unable to get actual_selection_io_mode value")
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pget_actual_selection_io_mode() */
+
+/*-------------------------------------------------------------------------
  * Function:    H5P__dxfr_modify_write_buf_enc
  *
  * Purpose:     Callback routine which is called whenever the modify write
diff --git a/src/H5Ppublic.h b/src/H5Ppublic.h
index a08119d..518b147 100644
--- a/src/H5Ppublic.h
+++ b/src/H5Ppublic.h
@@ -423,6 +423,11 @@ typedef enum H5D_selection_io_mode_t {
 } H5D_selection_io_mode_t;
 //! <!--[H5D_selection_io_mode_t_snip] -->
 
+/* Actual selection I/O modes for H5Pget_actual_selection_io_mode() property */
+#define H5D_SCALAR_IO    0x1 /* Scalar (or legacy MPIO) I/O was performed */
+#define H5D_VECTOR_IO    0x2 /* Vector I/O was performed */
+#define H5D_SELECTION_IO 0x4 /* Selection I/O was performed */
+
 /********************/
 /* Public Variables */
 /********************/
@@ -8398,6 +8403,56 @@ H5_DLL herr_t H5Pget_selection_io(hid_t plist_id, H5D_selection_io_mode_t *selec
 H5_DLL herr_t H5Pget_no_selection_io_cause(hid_t plist_id, uint32_t *no_selection_io_cause);
 
 /**
+ * \ingroup DXPL
+ *
+ * \brief Retrieves the type(s) of I/O that HDF5 actually performed on
+ *        last I/O call (not necessarily the type requested)
+ *
+ * \dxpl_id{plist_id}
+ * \param[out] actual_selection_io_mode A bitwise set value indicating the
+ *                                      type(s) of I/O performed
+ * \return \herr_t
+ *
+ * \par Motivation:
+ *      A user can request selection I/O to be performed via a data transfer
+ *      property list (DXPL).  This can be used to enable collective I/O with
+ *      type conversion, or with custom VFDs that support vector or selection
+ *      I/O.  However, there are conditions that can cause HDF5 to forgo
+ *      selection or vector I/O and perform legacy (scalar) I/O instead.
+ *      This function allows the user to determine which type or types of
+ *      I/O were actually performed.
+ *
+ * \details H5Pget_actual_selection_io_mode() allows the user to determine which
+ *          type(s) of I/O were actually performed during the last I/O operation
+ *          which used \p plist_id.  This property is set after all I/O is
+ *          completed; if I/O fails, it will not be set.
+ *
+ *          H5Pget_no_selection_io_cause() can be used to determine the reason
+ *          why selection or vector I/O was not performed.
+ *
+ *          Valid values returned in \p actual_selection_io_mode are listed
+ *          as follows.
+ *
+ *          - #H5D_SCALAR_IO
+ *          Scalar (or legacy MPIO) I/O was performed
+ *          - #H5D_VECTOR_IO
+ *          Vector I/O was performed
+ *          - #H5D_SELECTION_IO
+ *          Selection I/O was performed
+ *
+ *          Be aware that this function will include the types of all I/O that
+ *          were performed during this operation, including any metadata
+ *          operations that may be incidental to the requested I/O. To make sure
+ *          this function is only capturing raw data I/O, one can temporarily
+ *          disable metadata cache evictions by calling H5Fset_mdc_config() with
+ *          evictions_enabled set to false.
+ *
+ * \since 1.14.2
+ *
+ */
+H5_DLL herr_t H5Pget_actual_selection_io_mode(hid_t plist_id, uint32_t *actual_selection_io_mode);
+
+/**
  *
  * \ingroup DXPL
  *
diff --git a/test/select_io_dset.c b/test/select_io_dset.c
index 9a1de06..a84c40d 100644
--- a/test/select_io_dset.c
+++ b/test/select_io_dset.c
@@ -106,6 +106,21 @@ typedef enum {
 #define TEST_TCONV_BUF_TOO_SMALL               0x100
 #define TEST_IN_PLACE_TCONV                    0x200
 
+static herr_t
+check_actual_selection_io_mode(hid_t dxpl, uint32_t sel_io_mode_expected)
+{
+    uint32_t actual_sel_io_mode;
+
+    if (H5Pget_actual_selection_io_mode(dxpl, &actual_sel_io_mode) < 0)
+        FAIL_STACK_ERROR;
+    if (actual_sel_io_mode != sel_io_mode_expected)
+        TEST_ERROR;
+
+    return SUCCEED;
+error:
+    return FAIL;
+}
+
 /*
  *  Case 1: single dataset read/write, no type conversion (null case)
  *  --create dataset with H5T_NATIVE_INT
@@ -127,7 +142,8 @@ test_no_type_conv(hid_t fid, unsigned chunked, unsigned dtrans, unsigned mwbuf)
     int         trans_wbuf[DSET_SELECT_DIM];
     int         rbuf[DSET_SELECT_DIM];
     char        dset_name[DSET_NAME_LEN];
-    const char *expr = "2*x";
+    const char *expr                  = "2*x";
+    uint32_t    no_selection_io_cause = 0;
 
     /* Create 1d data space */
     dims[0] = DSET_SELECT_DIM;
@@ -256,17 +272,18 @@ error:
 static herr_t
 test_no_size_change_no_bkg(hid_t fid, unsigned chunked, unsigned mwbuf)
 {
-    int     i;
-    hid_t   did  = H5I_INVALID_HID;
-    hid_t   sid  = H5I_INVALID_HID;
-    hid_t   dcpl = H5I_INVALID_HID;
-    hid_t   dxpl = H5I_INVALID_HID;
-    hsize_t dims[1];
-    hsize_t cdims[1];
-    char   *wbuf     = NULL;
-    char   *wbuf_bak = NULL;
-    char   *rbuf     = NULL;
-    char    dset_name[DSET_NAME_LEN];
+    int      i;
+    hid_t    did  = H5I_INVALID_HID;
+    hid_t    sid  = H5I_INVALID_HID;
+    hid_t    dcpl = H5I_INVALID_HID;
+    hid_t    dxpl = H5I_INVALID_HID;
+    hsize_t  dims[1];
+    hsize_t  cdims[1];
+    char    *wbuf     = NULL;
+    char    *wbuf_bak = NULL;
+    char    *rbuf     = NULL;
+    char     dset_name[DSET_NAME_LEN];
+    uint32_t no_selection_io_cause = 0;
 
     if ((wbuf = (char *)HDmalloc((size_t)(4 * DSET_SELECT_DIM))) == NULL)
         FAIL_STACK_ERROR;
@@ -417,7 +434,8 @@ test_larger_mem_type_no_bkg(hid_t fid, unsigned chunked, unsigned dtrans, unsign
     long        trans_wbuf[DSET_SELECT_DIM];
     long long   rbuf[DSET_SELECT_DIM];
     char        dset_name[DSET_NAME_LEN];
-    const char *expr = "5 * (10 - x)";
+    const char *expr                  = "5 * (10 - x)";
+    uint32_t    no_selection_io_cause = 0;
 
     /* Create 1d data space */
     dims[0] = DSET_SELECT_DIM;
@@ -559,7 +577,8 @@ test_smaller_mem_type_no_bkg(hid_t fid, unsigned chunked, unsigned dtrans, unsig
     short       trans_wbuf[DSET_SELECT_DIM];
     short       rbuf[DSET_SELECT_DIM];
     char        dset_name[DSET_NAME_LEN];
-    const char *expr = "2 * (10 + x)";
+    const char *expr                  = "2 * (10 + x)";
+    uint32_t    no_selection_io_cause = 0;
 
     /* Create 1d data space */
     dims[0] = DSET_SELECT_DIM;
@@ -1060,6 +1079,7 @@ test_multi_dsets_no_bkg(hid_t fid, unsigned chunked, unsigned dtrans, unsigned m
     const void *wbufs[MULTI_NUM_DSETS];
     void       *rbufs[MULTI_NUM_DSETS];
     const char *expr = "2*x";
+    uint32_t    no_selection_io_cause;
 
     ndsets = MAX(MULTI_MIN_DSETS, MULTI_NUM_DSETS);
 
@@ -2886,9 +2906,6 @@ test_no_selection_io_cause_mode(const char *filename, hid_t fapl, uint32_t test_
     if ((fid = H5Fcreate(filename, H5F_ACC_TRUNC, fcpl, fapl)) < 0)
         FAIL_STACK_ERROR;
 
-    /* If default mode, 1st write will trigger cb, 2nd write will trigger sieve */
-    /* If on mode, will trigger nothing because the on mode path is different */
-    /* Need 2 writes */
     if (test_mode & TEST_CONTIGUOUS_SIEVE_BUFFER) {
         no_selection_io_cause_write_expected |= H5D_SEL_IO_CONTIGUOUS_SIEVE_BUFFER;
         no_selection_io_cause_read_expected |= H5D_SEL_IO_CONTIGUOUS_SIEVE_BUFFER;
diff --git a/testpar/CMakeLists.txt b/testpar/CMakeLists.txt
index fb66e76..3a44fca 100644
--- a/testpar/CMakeLists.txt
+++ b/testpar/CMakeLists.txt
@@ -8,7 +8,6 @@ project (HDF5_TEST_PAR C)
 set (testphdf5_SOURCES
     ${HDF5_TEST_PAR_SOURCE_DIR}/testphdf5.c
     ${HDF5_TEST_PAR_SOURCE_DIR}/t_dset.c
-    ${HDF5_TEST_PAR_SOURCE_DIR}/t_select_io_dset.c
     ${HDF5_TEST_PAR_SOURCE_DIR}/t_file.c
     ${HDF5_TEST_PAR_SOURCE_DIR}/t_file_image.c
     ${HDF5_TEST_PAR_SOURCE_DIR}/t_mdset.c
diff --git a/testpar/t_select_io_dset.c b/testpar/t_select_io_dset.c
index 10b29e4..cda5620 100644
--- a/testpar/t_select_io_dset.c
+++ b/testpar/t_select_io_dset.c
@@ -154,7 +154,7 @@ set_dxpl(hid_t dxpl, H5D_selection_io_mode_t select_io_mode, H5FD_mpio_xfer_t mp
 } /* set_dxpl() */
 
 /*
- * Helper routine to check actual I/O mode on a dxpl
+ * Helper routine to check actual parallel I/O mode on a dxpl
  */
 static void
 check_io_mode(hid_t dxpl, unsigned chunked)
@@ -182,6 +182,20 @@ check_io_mode(hid_t dxpl, unsigned chunked)
 } /* check_io_mode() */
 
 /*
+ * Helper routine to check actual selection I/O mode on a dxpl
+ */
+static void
+check_actual_selection_io_mode(hid_t dxpl, uint32_t sel_io_mode_expected)
+{
+    uint32_t actual_sel_io_mode;
+
+    if (H5Pget_actual_selection_io_mode(dxpl, &actual_sel_io_mode) < 0)
+        P_TEST_ERROR;
+    if (actual_sel_io_mode != sel_io_mode_expected)
+        P_TEST_ERROR;
+}
+
+/*
  *  Case 1: single dataset read/write, no type conversion (null case)
  */
 static void
@@ -280,6 +294,7 @@ test_no_type_conv(hid_t fid, unsigned chunked, unsigned dtrans, unsigned mwbuf)
         HDmemcpy(wbuf, wbuf_bak, sizeof(wbuf));
 
     check_io_mode(dxpl, chunked);
+    check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
     /* Read data from the dataset (if dtrans, without data transform set in dxpl) */
     if (H5Dread(did, H5T_NATIVE_INT, mspace_id, fspace_id, ntrans_dxpl, rbuf) < 0)
@@ -426,6 +441,7 @@ test_no_size_change_no_bkg(hid_t fid, unsigned chunked, unsigned mwbuf)
         HDmemcpy(wbuf, wbuf_bak, (size_t)(4 * DSET_SELECT_DIM));
 
     check_io_mode(dxpl, chunked);
+    check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
     /* Read the data from the dataset with little endian */
     if (H5Dread(did, H5T_STD_I32LE, mspace_id, fspace_id, dxpl, rbuf) < 0)
@@ -578,6 +594,7 @@ test_larger_mem_type_no_bkg(hid_t fid, unsigned chunked, unsigned dtrans, unsign
         HDmemcpy(wbuf, wbuf_bak, sizeof(wbuf));
 
     check_io_mode(dxpl, chunked);
+    check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
     /* Read data from the dataset (if dtrans, without data transform set in dxpl) */
     if (H5Dread(did, H5T_NATIVE_LLONG, mspace_id, fspace_id, ntrans_dxpl, rbuf) < 0)
@@ -727,6 +744,7 @@ test_smaller_mem_type_no_bkg(hid_t fid, unsigned chunked, unsigned dtrans, unsig
         HDmemcpy(wbuf, wbuf_bak, sizeof(wbuf));
 
     check_io_mode(dxpl, chunked);
+    check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
     /* Read data from the dataset (if dtrans, without data transform set in dxpl) */
     if (H5Dread(did, H5T_NATIVE_SHORT, mspace_id, fspace_id, ntrans_dxpl, rbuf) < 0)
@@ -918,6 +936,7 @@ test_cmpd_with_bkg(hid_t fid, unsigned chunked, unsigned mwbuf)
         HDmemcpy(s1_wbuf, s1_wbuf_bak, sizeof(s1_t) * DSET_SELECT_DIM);
 
     check_io_mode(dxpl, chunked);
+    check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
     /* Read all the data from the dataset */
     HDmemset(s1_rbuf, 0, sizeof(s1_t) * DSET_SELECT_DIM);
@@ -1224,6 +1243,7 @@ test_type_conv_sel_empty(hid_t fid, unsigned chunked, unsigned dtrans, unsigned
         HDmemcpy(lwbuf, lwbuf_bak, sizeof(lwbuf));
 
     check_io_mode(dxpl, chunked);
+    check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
     /* Read the data from the dataset: type conversion int-->long */
     /* If dtrans, without data transform set in dxpl */
@@ -1552,6 +1572,7 @@ test_multi_dsets_no_bkg(hid_t fid, unsigned chunked, unsigned dtrans, unsigned m
         HDmemcpy(total_wbuf, total_wbuf_bak, ndsets * DSET_SELECT_DIM * sizeof(int));
 
     check_io_mode(dxpl, chunked);
+    check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
     /* Read data from the dataset (if dtrans, without data transform set in dxpl) */
     if (H5Dread_multi(ndsets, dset_dids, mem_tids, mem_sids, file_sids, ntrans_dxpl, rbufs) < 0)
@@ -1856,6 +1877,7 @@ test_multi_dsets_cmpd_with_bkg(hid_t fid, unsigned chunked, unsigned mwbuf)
         HDmemcpy(total_wbuf, total_wbuf_bak, buf_size);
 
     check_io_mode(dxpl, chunked);
+    check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
     if (H5Dread_multi(ndsets, dset_dids, mem_tids, mem_sids, file_sids, dxpl, rbufs) < 0)
         P_TEST_ERROR;
@@ -2297,6 +2319,7 @@ test_multi_dsets_size_change_no_bkg(hid_t fid, unsigned chunked, unsigned mwbuf)
         HDmemcpy(total_wbuf, total_wbuf_bak, buf_size);
 
     check_io_mode(dxpl, chunked);
+    check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
     /* Read data from the dataset */
     if (H5Dread_multi(ndsets, dset_dids, mem_tids, mem_sids, file_sids, dxpl, rbufs) < 0)
@@ -2766,6 +2789,7 @@ test_multi_dsets_conv_sel_empty(hid_t fid, unsigned chunked, unsigned dtrans, un
         HDmemcpy(total_wbuf, total_wbuf_bak, buf_size);
 
     check_io_mode(dxpl, chunked);
+    check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
     /* Initialize buffer indices */
     for (i = 0; i < (int)ndsets; i++) {
@@ -3243,6 +3267,7 @@ test_multi_dsets_all(int niter, hid_t fid, unsigned chunked, unsigned mwbuf)
                 P_TEST_ERROR;
 
             check_io_mode(dxpl, chunked);
+            check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
 
             /* Verify result read */
             /* for i ndsets */
@@ -3418,6 +3443,8 @@ test_no_selection_io_cause_mode(const char *filename, hid_t fapl, uint32_t test_
     if ((dxpl = H5Pcreate(H5P_DATASET_XFER)) < 0)
         P_TEST_ERROR;
 
+    set_dxpl(dxpl, H5D_SELECTION_IO_MODE_ON, H5FD_MPIO_COLLECTIVE, H5FD_MPIO_COLLECTIVE_IO, false);
+
     if ((fid = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl)) < 0)
         P_TEST_ERROR;
 
@@ -3482,6 +3509,10 @@ test_no_selection_io_cause_mode(const char *filename, hid_t fapl, uint32_t test_
     if (H5Dwrite(did, tid, H5S_ALL, H5S_ALL, dxpl, wbuf) < 0)
         P_TEST_ERROR;
 
+    if (!(test_mode & TEST_DISABLE_BY_API || test_mode & TEST_NOT_CONTIGUOUS_OR_CHUNKED_DATASET ||
+          ((test_mode & TEST_TCONV_BUF_TOO_SMALL) && !(test_mode & TEST_IN_PLACE_TCONV))))
+        check_actual_selection_io_mode(dxpl, H5D_VECTOR_IO);
+
     if (H5Pget_no_selection_io_cause(dxpl, &no_selection_io_cause_write) < 0)
         P_TEST_ERROR;