Calculate verity hash tree.

Calculate verity hash tree in FilesystemVerifierAction based on configs
specified in protobuf, and write it to target partition before reading
from those blocks.

A new error code kVerityCalculationError was added to report error if
it fails.

Bug: 28171891
Test: update_engine_unittests

Change-Id: I492885a0655bf51043902f578720fffd87e6a3cf
diff --git a/payload_consumer/verity_writer_interface.h b/payload_consumer/verity_writer_interface.h
new file mode 100644
index 0000000..a3ecef3
--- /dev/null
+++ b/payload_consumer/verity_writer_interface.h
@@ -0,0 +1,53 @@
+//
+// Copyright (C) 2018 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 UPDATE_ENGINE_PAYLOAD_CONSUMER_VERITY_WRITER_INTERFACE_H_
+#define UPDATE_ENGINE_PAYLOAD_CONSUMER_VERITY_WRITER_INTERFACE_H_
+
+#include <cstdint>
+#include <memory>
+
+#include <base/macros.h>
+
+#include "update_engine/payload_consumer/install_plan.h"
+
+namespace chromeos_update_engine {
+
+class VerityWriterInterface {
+ public:
+  virtual ~VerityWriterInterface() = default;
+
+  virtual bool Init(const InstallPlan::Partition& partition) = 0;
+  // Update partition data at [offset : offset + size) stored in |buffer|.
+  // Data not in |hash_tree_data_extent| or |fec_data_extent| is ignored.
+  // Will write verity data to the target partition once all the necessary
+  // blocks has passed.
+  virtual bool Update(uint64_t offset, const uint8_t* buffer, size_t size) = 0;
+
+ protected:
+  VerityWriterInterface() = default;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(VerityWriterInterface);
+};
+
+namespace verity_writer {
+std::unique_ptr<VerityWriterInterface> CreateVerityWriter();
+}
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_PAYLOAD_CONSUMER_VERITY_WRITER_INTERFACE_H_