Add new API function H5Pget_actual_select_io_mode() (#2974)

This function allows the user to determine if the library performed selection I/O, vector I/O, or scalar (legacy) I/O during the last HDF5 operation performed with the provided DXPL. Expanded existing tests to check this functionality.

7 files changed, 362 insertions, 46 deletions

diff --git a/src/H5CX.c b/src/H5CX.c
index b3b2fca..c46c58a 100644
--- a/src/H5CX.c
+++ b/src/H5CX.c
@@ -299,6 +299,11 @@ typedef struct H5CX_t {
     bool no_selection_io_cause_set; /* Whether reason for not performing selection I/O is set */
     bool 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 */
     bool       encoding_valid;           /* Whether link name character encoding is valid */
@@ -380,6 +385,8 @@ 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) */
     bool modify_write_buf;                         /* Whether the library can modify write buffers */
 } H5CX_dxpl_cache_t;
 
@@ -571,13 +578,18 @@ 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");
@@ -2515,6 +2527,47 @@ done:
 } /* end H5CX_get_no_selection_io_cause() */
 
 /*-------------------------------------------------------------------------
+ * Function:    H5CX_get_actual_selection_io_mode
+ *
+ * Purpose:     Retrieves the actual I/O mode (scalar, vector, and/or selection) for the current API call
+ *context.
+ *
+ * Return:      Non-negative on success / Negative on failure
+ *
+ *-------------------------------------------------------------------------
+ */
+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 */
+    assert(actual_selection_io_mode);
+    head = H5CX_get_my_context(); /* Get the pointer to the head of the API context, for this thread */
+    assert(head && *head);
+    assert(H5P_DEFAULT != (*head)->ctx.dxpl_id);
+
+    /* This property is a special case - we want to wipe out any previous setting.  Copy the default setting
+     * if it has not been set yet. */
+    if ((*head)->ctx.dxpl_id != H5P_DATASET_XFER_DEFAULT && !(*head)->ctx.actual_selection_io_mode_set &&
+        !(*head)->ctx.actual_selection_io_mode_valid) {
+        (*head)->ctx.actual_selection_io_mode     = H5CX_def_dxpl_cache.actual_selection_io_mode;
+        (*head)->ctx.actual_selection_io_mode_set = true;
+    }
+    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.
@@ -3443,7 +3496,7 @@ done:
 #endif /* H5_HAVE_PARALLEL */
 
 /*-------------------------------------------------------------------------
- * Function:    H5CX_set_no_selecction_io_cause
+ * Function:    H5CX_set_no_selection_io_cause
  *
  * Purpose:     Sets the reason for not performing selection I/O for
  *              the current API call context.
@@ -3472,7 +3525,39 @@ 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_selection_io_mode
+ *
+ * Purpose:     Sets the actual selection I/O mode for the current API
+ *              call context.
+ *
+ * Return:      <none>
+ *
+ *-------------------------------------------------------------------------
+ */
+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 */
+    assert(head && *head);
+    assert((*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;
+    }
+
+    FUNC_LEAVE_NOAPI_VOID
+} /* end H5CX_set_actual_selection_io_mode() */
 
 /*-------------------------------------------------------------------------
  * Function:    H5CX_get_ohdr_flags
@@ -3529,7 +3614,17 @@ H5CX__pop_common(bool update_dxpl_props)
 
     /* Check for cached DXPL properties to return to application */
     if (update_dxpl_props) {
+        /* actual_selection_io_mode is a special case - we always want to set it in the property list even if
+         * it was never set by the library, in that case it indicates no I/O was performed and we don't want
+         * to leave the (possibly incorrect) old value in the property list, so set from the default property
+         * list */
+        if ((*head)->ctx.dxpl_id != H5P_DATASET_XFER_DEFAULT && !(*head)->ctx.actual_selection_io_mode_set) {
+            (*head)->ctx.actual_selection_io_mode     = H5CX_def_dxpl_cache.actual_selection_io_mode;
+            (*head)->ctx.actual_selection_io_mode_set = true;
+        }
+
         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 aa6883b..76812ee 100644
--- a/src/H5CXprivate.h
+++ b/src/H5CXprivate.h
@@ -116,6 +116,7 @@ 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(bool *modify_write_buf);
 
 /* "Getter" routines for LCPL properties cached in API context */
@@ -162,6 +163,7 @@ 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 118c6cd..fa8b077 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 082b602..5d3a802 100644
--- a/src/H5FDint.c
+++ b/src/H5FDint.c
@@ -212,8 +212,9 @@ done:
 herr_t
 H5FD_read(H5FD_t *file, H5FD_mem_t type, haddr_t addr, size_t size, void *buf /*out*/)
 {
-    hid_t  dxpl_id   = H5I_INVALID_HID; /* DXPL for operation */
-    herr_t ret_value = SUCCEED;         /* Return value */
+    hid_t    dxpl_id = H5I_INVALID_HID; /* DXPL for operation */
+    uint32_t actual_selection_io_mode;
+    herr_t   ret_value = SUCCEED; /* Return value */
 
     FUNC_ENTER_NOAPI(FAIL)
 
@@ -257,6 +258,13 @@ H5FD_read(H5FD_t *file, H5FD_mem_t type, haddr_t addr, size_t size, void *buf /*
     if ((file->cls->read)(file, type, dxpl_id, addr + file->base_addr, size, buf) < 0)
         HGOTO_ERROR(H5E_VFL, H5E_READERROR, FAIL, "driver read request failed");
 
+    /* Set actual selection I/O, if this is a raw data operation */
+    if (type == H5FD_MEM_DRAW) {
+        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:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5FD_read() */
@@ -273,9 +281,10 @@ done:
 herr_t
 H5FD_write(H5FD_t *file, H5FD_mem_t type, haddr_t addr, size_t size, const void *buf)
 {
-    hid_t   dxpl_id;                 /* DXPL for operation */
-    haddr_t eoa       = HADDR_UNDEF; /* EOA for file */
-    herr_t  ret_value = SUCCEED;     /* Return value */
+    hid_t    dxpl_id;           /* DXPL for operation */
+    haddr_t  eoa = HADDR_UNDEF; /* EOA for file */
+    uint32_t actual_selection_io_mode;
+    herr_t   ret_value = SUCCEED; /* Return value */
 
     FUNC_ENTER_NOAPI(FAIL)
 
@@ -308,6 +317,13 @@ H5FD_write(H5FD_t *file, H5FD_mem_t type, haddr_t addr, size_t size, const void
     if ((file->cls->write)(file, type, dxpl_id, addr + file->base_addr, size, buf) < 0)
         HGOTO_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "driver write request failed");
 
+    /* Set actual selection I/O, if this is a raw data operation */
+    if (type == H5FD_MEM_DRAW) {
+        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:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5FD_write() */
@@ -360,6 +376,7 @@ H5FD_read_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addrs
     size_t     size      = 0;
     H5FD_mem_t type      = H5FD_MEM_DEFAULT;
     hid_t      dxpl_id   = H5I_INVALID_HID; /* DXPL for operation */
+    hbool_t    is_raw    = FALSE;           /* Does this include raw data */
     herr_t     ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_NOAPI(FAIL)
@@ -441,6 +458,10 @@ H5FD_read_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addrs
                 else {
 
                     type = types[i];
+
+                    /* Check for raw data operation */
+                    if (type == H5FD_MEM_DRAW)
+                        is_raw = TRUE;
                 }
             }
 
@@ -455,13 +476,27 @@ H5FD_read_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addrs
                             (unsigned long long)eoa);
         }
     }
+    else
+        /* We must still check if this is a raw data read */
+        for (i = 0; i < count && types[i] != H5FD_MEM_NOLIST; i++)
+            if (types[i] == H5FD_MEM_DRAW) {
+                is_raw = true;
+                break;
+            }
 
     /* if the underlying VFD supports vector read, make the call */
     if (file->cls->read_vector) {
-
         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, if this is a raw data operation */
+        if (is_raw) {
+            uint32_t actual_selection_io_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 {
 
@@ -471,6 +506,7 @@ 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++) {
 
@@ -512,6 +548,13 @@ 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, if this is a raw data operation */
+        if (is_raw) {
+            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:
@@ -575,6 +618,7 @@ H5FD_write_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addr
     H5FD_mem_t type = H5FD_MEM_DEFAULT;
     hid_t      dxpl_id;                 /* DXPL for operation */
     haddr_t    eoa       = HADDR_UNDEF; /* EOA for file */
+    hbool_t    is_raw    = FALSE;       /* Does this include raw data */
     herr_t     ret_value = SUCCEED;     /* Return value */
 
     FUNC_ENTER_NOAPI(FAIL)
@@ -646,6 +690,10 @@ H5FD_write_vector(H5FD_t *file, uint32_t count, H5FD_mem_t types[], haddr_t addr
             else {
 
                 type = types[i];
+
+                /* Check for raw data operation */
+                if (type == H5FD_MEM_DRAW)
+                    is_raw = true;
             }
         }
 
@@ -663,10 +711,17 @@ 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) {
-
         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 mode, if this is a raw data operation */
+        if (is_raw) {
+            uint32_t actual_selection_io_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 {
         /* otherwise, implement the vector write as a sequence of regular
@@ -675,6 +730,7 @@ 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++) {
 
@@ -716,6 +772,13 @@ 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 mode, if this is a raw data operation */
+        if (is_raw) {
+            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:
@@ -996,18 +1059,35 @@ H5FD__read_selection_translate(uint32_t skip_vector_cb, H5FD_t *file, H5FD_mem_t
 
     /* 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, if this is a raw data operation */
+        if (type == H5FD_MEM_DRAW && count > 0) {
+            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 {
+    else if (count > 0) {
         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, if this is a raw data operation */
+        if (type == H5FD_MEM_DRAW) {
+            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:
@@ -1161,6 +1241,8 @@ 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])) {
@@ -1186,6 +1268,13 @@ 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, if this is a raw data operation */
+        if (type == H5FD_MEM_DRAW) {
+            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
@@ -1337,9 +1426,18 @@ H5FD_read_selection_id(uint32_t skip_cb, H5FD_t *file, H5FD_mem_t type, uint32_t
 
     /* if the underlying VFD supports selection read, make the call */
     if (!skip_selection_cb && 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, if this is a raw data operation */
+        if (type == H5FD_MEM_DRAW) {
+            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
@@ -1653,18 +1751,35 @@ H5FD__write_selection_translate(uint32_t skip_vector_cb, H5FD_t *file, H5FD_mem_
 
     /* 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, if this is a raw data operation */
+        if (type == H5FD_MEM_DRAW && count > 0) {
+            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 {
+    else if (count > 0) {
         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, if this is a raw data operation */
+        if (type == H5FD_MEM_DRAW) {
+            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:
@@ -1810,6 +1925,8 @@ 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])) {
@@ -1835,6 +1952,13 @@ 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, if this is a raw data operation */
+        if (type == H5FD_MEM_DRAW) {
+            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
@@ -1979,9 +2103,18 @@ H5FD_write_selection_id(uint32_t skip_cb, H5FD_t *file, H5FD_mem_t type, uint32_
 
     /* if the underlying VFD supports selection write, make the call */
     if (!skip_selection_cb && 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, if this is a raw data operation */
+        if (type == H5FD_MEM_DRAW) {
+            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/H5M.c b/src/H5M.c
index e2fd202..f59e02f 100644
--- a/src/H5M.c
+++ b/src/H5M.c
@@ -893,9 +893,6 @@ H5Mget_count(hid_t map_id, hsize_t *count /*out*/, hid_t dxpl_id)
     else if (true != H5P_isa_class(dxpl_id, H5P_DATASET_XFER))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not xfer parms");
 
-    /* Set DXPL for operation */
-    H5CX_set_dxpl(dxpl_id);
-
     /* Set up VOL callback arguments */
     map_args.get.get_type             = H5VL_MAP_GET_COUNT;
     map_args.get.args.get_count.count = 0;
@@ -952,9 +949,6 @@ H5M__put_api_common(hid_t map_id, hid_t key_mem_type_id, const void *key, hid_t
     else if (true != H5P_isa_class(dxpl_id, H5P_DATASET_XFER))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not xfer parms");
 
-    /* Set DXPL for operation */
-    H5CX_set_dxpl(dxpl_id);
-
     /* Set up VOL callback arguments */
     map_args.put.key_mem_type_id   = key_mem_type_id;
     map_args.put.key               = key;
@@ -1087,9 +1081,6 @@ H5M__get_api_common(hid_t map_id, hid_t key_mem_type_id, const void *key, hid_t
     else if (true != H5P_isa_class(dxpl_id, H5P_DATASET_XFER))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not xfer parms");
 
-    /* Set DXPL for operation */
-    H5CX_set_dxpl(dxpl_id);
-
     /* Set up VOL callback arguments */
     map_args.get_val.key_mem_type_id   = key_mem_type_id;
     map_args.get_val.key               = key;
@@ -1225,9 +1216,6 @@ H5Mexists(hid_t map_id, hid_t key_mem_type_id, const void *key, hbool_t *exists,
     else if (true != H5P_isa_class(dxpl_id, H5P_DATASET_XFER))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not xfer parms");
 
-    /* Set DXPL for operation */
-    H5CX_set_dxpl(dxpl_id);
-
     /* Set up VOL callback arguments */
     map_args.exists.key_mem_type_id = key_mem_type_id;
     map_args.exists.key             = key;
@@ -1305,9 +1293,6 @@ H5Miterate(hid_t map_id, hsize_t *idx, hid_t key_mem_type_id, H5M_iterate_t op,
     else if (true != H5P_isa_class(dxpl_id, H5P_DATASET_XFER))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not xfer parms");
 
-    /* Set DXPL for operation */
-    H5CX_set_dxpl(dxpl_id);
-
     /* Set up VOL callback arguments */
     map_args.specific.specific_type                    = H5VL_MAP_ITER;
     map_args.specific.args.iterate.loc_params.type     = H5VL_OBJECT_BY_SELF;
@@ -1394,9 +1379,6 @@ H5Miterate_by_name(hid_t loc_id, const char *map_name, hsize_t *idx, hid_t key_m
     else if (true != H5P_isa_class(dxpl_id, H5P_DATASET_XFER))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not xfer parms");
 
-    /* Set DXPL for operation */
-    H5CX_set_dxpl(dxpl_id);
-
     /* Set up VOL callback arguments */
     map_args.specific.specific_type                                        = H5VL_MAP_ITER;
     map_args.specific.args.iterate.loc_params.type                         = H5VL_OBJECT_BY_NAME;
@@ -1462,9 +1444,6 @@ H5Mdelete(hid_t map_id, hid_t key_mem_type_id, const void *key, hid_t dxpl_id)
     else if (true != H5P_isa_class(dxpl_id, H5P_DATASET_XFER))
         HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not xfer parms");
 
-    /* Set DXPL for operation */
-    H5CX_set_dxpl(dxpl_id);
-
     /* Set up VOL callback arguments */
     map_args.specific.specific_type                = H5VL_MAP_DELETE;
     map_args.specific.args.del.loc_params.type     = H5VL_OBJECT_BY_SELF;
diff --git a/src/H5Pdxpl.c b/src/H5Pdxpl.c
index b6130f5..9adb2d6 100644
--- a/src/H5Pdxpl.c
+++ b/src/H5Pdxpl.c
@@ -175,6 +175,9 @@
 /* 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(bool)
 #define H5D_XFER_MODIFY_WRITE_BUF_DEF  false
@@ -295,7 +298,8 @@ 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 bool                    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 bool     H5D_def_modify_write_buf_g                     = H5D_XFER_MODIFY_WRITE_BUF_DEF;
 
 /*-------------------------------------------------------------------------
  * Function:    H5P__dxfr_reg_prop
@@ -470,6 +474,13 @@ 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,
@@ -2457,6 +2468,39 @@ 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 a58d97f..d822925 100644
--- a/src/H5Ppublic.h
+++ b/src/H5Ppublic.h
@@ -420,6 +420,13 @@ typedef enum H5D_selection_io_mode_t {
 } H5D_selection_io_mode_t;
 //! <!--[H5D_selection_io_mode_t_snip] -->
 
+/**
+ * Causes for H5Pget_actual_selection_io_mode() property
+ */
+#define H5D_SCALAR_IO    (0x0001u) /**< Scalar (or legacy MPIO) I/O was performed */
+#define H5D_VECTOR_IO    (0x0002u) /**< Vector I/O was performed */
+#define H5D_SELECTION_IO (0x0004u) /**< Selection I/O was performed */
+
 /********************/
 /* Public Variables */
 /********************/
@@ -5811,7 +5818,7 @@ H5_DLL int H5Pget_external_count(hid_t plist_id);
  * \note H5Pget_fill_time() is designed to work in coordination with the
  *       dataset fill value and dataset storage allocation time properties,
  *       retrieved with the functions H5Pget_fill_value() and
- *       H5Pget_alloc_time().
+ *       H5Pget_alloc_time().type == H5FD_MEM_DRAW
  *
  * \since 1.6.0
  *
@@ -8300,6 +8307,61 @@ 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 raw data
+ *        during the last I/O call
+ *
+ * \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 on raw data 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 bitflags 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
+ *
+ *          0 or more of these can be present in \p actual_selection_io_mode in
+ *          a bitwise fashion, since a single operation can trigger multiple
+ *          instances of I/O, possibly with different types.  A value of \p 0
+ *          indicates no raw data I/O was performed during the operation.
+ *
+ *          Be aware that this function will only include raw data I/O performed
+ *          to/from disk as part of the last I/O operation.  Any metadata
+ *          I/O, including attribute and compact dataset I/O, is disregarded.
+ *          It is also possible that data was cached in the dataset chunk cache
+ *          or sieve buffer, which may prevent I/O from hitting the disk, and
+ *          thereby prevent it from being counted by this function.
+ *
+ * \since 1.14.3
+ *
+ */
+H5_DLL herr_t H5Pget_actual_selection_io_mode(hid_t plist_id, uint32_t *actual_selection_io_mode);
+
+/**
  *
  * \ingroup DXPL
  *