Fixes issue with null struct columns in ORC reader

cpp/src/io/orc/orc.h

@@ -539,10 +539,7 @@ class OrcDecompressor {
 };
 
 /**
- * @brief Stores orc id for each column and its adjacent number of children
- * in case of struct or number of children in case of list column.
- * If list column has struct column, then all child columns of that struct are treated as child
- * column of list.
+ * @brief Stores orc id for each column and number of children in that column.
  *
  * @code{.pseudo}
  * Consider following data where a struct has two members and a list column
@@ -559,11 +556,18 @@ class OrcDecompressor {
  *
  */
 struct orc_column_meta {
-  // orc_column_meta(uint32_t _id, uint32_t _num_children) : id(_id), num_children(_num_children){};
   uint32_t id;            // orc id for the column
   uint32_t num_children;  // number of children at the same level of nesting in case of struct
 };
 
+/**
+ * @brief Stores column's validity map and null count
+ */
+struct column_validity_info {
+  uint32_t* valid_map_base;
+  uint32_t null_count;
+};
+
 /**
  * @brief A helper class for ORC file metadata. Provides some additional
  * convenience methods for initializing and accessing metadata.

cpp/src/io/orc/orc_gpu.h

@@ -24,6 +24,7 @@
 #include <cudf/utilities/span.hpp>
 #include <io/statistics/statistics.cuh>
 #include <io/utilities/column_buffer.hpp>
+#include "orc.h"
 #include "orc_common.h"
 
 #include <rmm/cuda_stream_view.hpp>
@@ -85,6 +86,14 @@ struct DictionaryEntry {
  */
 constexpr int orc_decimal2float64_scale = 0x80;
 
+/**
+ * Struct to store parent column mask and null count
+ */
+struct ParentColumnData {
+  uint32_t* valid_map_base;
+  uint32_t null_count;
+};
+
 /**
  * @brief Struct to describe per stripe's column information
  */
@@ -109,6 +118,7 @@ struct ColumnDesc {
   uint8_t dtype_len;      // data type length (for types that can be mapped to different sizes)
   int32_t decimal_scale;  // number of fractional decimal digits for decimal type
   int32_t ts_clock_rate;  // output timestamp clock frequency (0=default, 1000=ms, 1000000000=ns)
+  column_validity_info parent_validity_info;  // consists of parent column valid_map and null count
 };
 
 /**