Fix model serialization with external data in current directory (micr…

…osoft#17311)

When original model has external data in current directory, saving the
optimized model will raise File not found exception during looking for
external data file under root directory "/". This fix will look under
current directory for this case.

I manually tested an extra case and it is working: Original model with
external data in root directory ("/"), and save optimized to current
directory.

BTW, there is another bug found: when
"session.optimized_model_external_initializers_min_size_in_bytes" is set
a large value, some tensor is still pointed to the original external
data file. Add a TODO in unit test for this bug. Possible solution: load
external data into memory before saving model.

onnxruntime/core/framework/tensorprotoutils.cc

@@ -1492,7 +1492,7 @@ Status UnpackInitializerData(const onnx::TensorProto& initializer,
   if (initializer.data_location() == TensorProto_DataLocation_EXTERNAL) {
     ORT_RETURN_IF_ERROR(ReadExternalDataForTensor(
         initializer,
-        model_path.IsEmpty() ? nullptr : model_path.ParentPath().ToPathString().c_str(),
+        (model_path.IsEmpty() || model_path.ParentPath().IsEmpty()) ? nullptr : model_path.ParentPath().ToPathString().c_str(),
         unpacked_tensor));
     return Status::OK();
   }

onnxruntime/test/python/onnxruntime_test_python.py

@@ -179,6 +179,62 @@ def test_model_serialization_with_original_external_initializers_to_directory(se
             else:
                 raise onnxruntime_error
 
+    def test_model_serialization_with_original_external_initializers_to_current_directory(self):
+        optimized_model_filepath = "model_opt_with_ext_data_1.onnx"
+        external_initializers_file = "model_opt_with_ext_data_1.bin"
+        optimized_model_filepath_2 = "model_opt_with_ext_data_2.onnx"
+        external_initializers_file_2 = "model_opt_with_ext_data_2.bin"
+
+        so = onnxrt.SessionOptions()
+        so.log_severity_level = 1
+        so.logid = "TestModelSerializationWithOriginalExternalInitializersToCurrentDirectory"
+        so.optimized_model_filepath = optimized_model_filepath
+
+        so.add_session_config_entry(
+            "session.optimized_model_external_initializers_file_name", external_initializers_file
+        )
+
+        # TODO(anyone): Set this to 100 will cause test error since some tensor below the threshold
+        # still refers to the original external data file. We shall fix this issue so that the
+        # optimized model only refers to one external data file.
+        so.add_session_config_entry("session.optimized_model_external_initializers_min_size_in_bytes", "10")
+        session1 = onnxrt.InferenceSession(
+            get_name("model_with_orig_ext_data.onnx"), sess_options=so, providers=["CPUExecutionProvider"]
+        )
+        del session1
+        self.assertTrue(os.path.isfile(optimized_model_filepath))
+        self.assertTrue(os.path.isfile(external_initializers_file))
+
+        so2 = onnxrt.SessionOptions()
+        so2.log_severity_level = 1
+        so2.logid = "TestModelSerializationWithExternalInitializersInCurrentDirectory"
+        so2.optimized_model_filepath = optimized_model_filepath_2
+        so2.add_session_config_entry(
+            "session.optimized_model_external_initializers_file_name", external_initializers_file_2
+        )
+        so2.add_session_config_entry("session.optimized_model_external_initializers_min_size_in_bytes", "10")
+
+        # verify that we can load the optimized model with external data in current directory and save
+        # optimized model with external data to current directory.
+        session2 = onnxrt.InferenceSession(
+            optimized_model_filepath, sess_options=so2, providers=["CPUExecutionProvider"]
+        )
+        del session2
+        self.assertTrue(os.path.isfile(optimized_model_filepath_2))
+        self.assertTrue(os.path.isfile(external_initializers_file_2))
+
+        # Remove model 1 to make sure optimized model 2 can be loaded independently from model 1
+        os.remove(optimized_model_filepath)
+        os.remove(external_initializers_file)
+
+        session3 = onnxrt.InferenceSession(
+            optimized_model_filepath_2, sess_options=onnxrt.SessionOptions(), providers=["CPUExecutionProvider"]
+        )
+        del session3
+
+        os.remove(optimized_model_filepath_2)
+        os.remove(external_initializers_file_2)
+
     def test_get_providers(self):
         self.assertTrue("CPUExecutionProvider" in onnxrt.get_available_providers())
         # get_all_providers() returns the default EP order from highest to lowest.