Adding code. Closes #0.

include/internal/filesystem.h

@@ -0,0 +1,38 @@
+// Copyright 2017 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// An interface for the filesystem that allows mocking the filesystem in
+// unittests.
+#ifndef THIRD_PARTY_CPU_FEATURES_INCLUDE_INTERNAL_FILESYSTEM_H_
+#define THIRD_PARTY_CPU_FEATURES_INCLUDE_INTERNAL_FILESYSTEM_H_
+
+#include <stddef.h>
+#include <stdint.h>
+#include "cpu_features_macros.h"
+
+START_CPP_NAMESPACE
+
+// Same as linux "open(filename, O_RDONLY)", retries automatically on EINTR.
+int OpenFile(const char* filename);
+
+// Same as linux "read(file_descriptor, buffer, buffer_size)", retries
+// automatically on EINTR.
+int ReadFile(int file_descriptor, void* buffer, size_t buffer_size);
+
+// Same as linux "close(file_descriptor)".
+void CloseFile(int file_descriptor);
+
+END_CPP_NAMESPACE
+
+#endif  // THIRD_PARTY_CPU_FEATURES_INCLUDE_INTERNAL_FILESYSTEM_H_