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diff --git a/src/inode2filename/inode_result.h b/src/inode2filename/inode_result.h
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+++ b/src/inode2filename/inode_result.h
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+// Copyright (C) 2019 The Android Open Source Project
+//
+// 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.
+
+#ifndef IORAP_SRC_INODE2FILENAME_INODE_RESULT_H_
+#define IORAP_SRC_INODE2FILENAME_INODE_RESULT_H_
+
+#include "common/expected.h"
+#include "inode2filename/inode.h"
+#include "inode2filename/inode_result.h"
+#include "inode2filename/system_call.h"
+
+#include <rxcpp/rx.hpp>
+
+#include <memory>
+#include <optional>
+#include <string>
+#include <vector>
+namespace iorap::inode2filename {
+
+// Tuple of (Inode -> (Filename|Errno))
+struct InodeResult {
+  // We set this error when all root directories have been searched and
+  // yet we still could not find a corresponding filename for the inode under search.
+  static constexpr int kCouldNotFindFilename = ENOKEY;
+
+  // An initial inode->filename mapping was found, but subsequent verification for it failed.
+  static constexpr int kVerificationFailed = EKEYEXPIRED;
+
+  // There is always an inode, but sometimes we may fail to resolve the filename.
+  Inode inode;
+  // Value: Contains the filename (with a root directory as a prefix).
+  // Error: Contains the errno, usually one of the above, otherwise some system error.
+  iorap::expected<std::string /*filename*/, int /*errno*/> data;
+
+  static InodeResult makeSuccess(Inode inode, std::string filename) {
+    return InodeResult{inode, std::move(filename)};
+  }
+
+  static InodeResult makeFailure(Inode inode, int err_no) {
+    return InodeResult{inode, iorap::unexpected{err_no}};
+  }
+
+  constexpr explicit operator bool() const {
+    return data.has_value();
+  }
+
+  constexpr bool operator==(const InodeResult& other) const {
+    if (inode == other.inode) {
+      if (data && other.data) {
+        return *data == *other.data;
+      } else if (!data && !other.data) {
+        return data.error() == other.data.error();
+      }
+      // TODO: operator== for expected
+    }
+    return false;
+  }
+
+  constexpr bool operator!=(const InodeResult& other) const {
+    return !(*this == other);
+  }
+
+  // Returns a human-readable error message, or 'nullopt' if there was no error.
+  std::optional<std::string_view> ErrorMessage() const;
+};
+
+std::ostream& operator<<(std::ostream& os, const InodeResult& result);
+
+}  // namespace iorap::inode2filename
+
+#endif  // IORAP_SRC_INODE2FILENAME_INODE_RESULT_H_
+\ No newline at end of file