ring_buffer_manager.h

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/*
 * Copyright (C) 2024 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.
 */
 
#pragma once
 
#include <atomic>
#include <map>
 
#include "cuttlefish/common/libs/fs/shared_fd.h"
#include "cuttlefish/common/libs/utils/result.h"
 
namespace cuttlefish {
 
// This header is allocated / placed at start of IPC ringbuffer. Intention of
// elements here is to allow to compute the valid read/write address for
// current frame from an external process.
struct DisplayRingBufferHeader {
  volatile std::uint32_t display_width_;
  volatile std::uint32_t display_height_;
  volatile std::uint32_t bpp_;
  std::atomic<std::uint32_t> last_valid_frame_index_;
 
  void set(std::uint32_t w, std::uint32_t h, std::uint32_t bpp,
           std::uint32_t index);
};
 
class DisplayRingBuffer {
 public:
  ~DisplayRingBuffer();
  static Result<std::unique_ptr<DisplayRingBuffer>> Create(
      const std::string& name, int size);
  // Allowing optional in the case the buffer doesn't yet exist.
  static std::optional<std::unique_ptr<DisplayRingBuffer>> ShmemGet(
      const std::string& name, int size);
 
  void* GetAddress();
 
  std::uint8_t* WriteNextFrame(std::uint8_t* frame_data, int size);
  std::uint8_t* CurrentFrame();
  std::uint8_t* ComputeFrameAddressForIndex(std::uint32_t index);
 
 private:
  DisplayRingBuffer(void* addr, std::string name, bool owned, ScopedMMap shm);
 
  DisplayRingBufferHeader* header_;
  void* addr_;
  std::string name_;
  bool owned_;
  ScopedMMap shm_;
};
 
class DisplayRingBufferManager {
 public:
  DisplayRingBufferManager(int vm_index, std::string group_uuid);
  Result<void> CreateLocalDisplayBuffer(int vm_index, int display_index,
                                        int display_width, int display_height);
  std::uint8_t* WriteFrame(int vm_index, int display_index,
                           std::uint8_t* frame_data, int size);
  std::uint8_t* ReadFrame(int vm_index, int display_index, int frame_width,
                          int frame_height);
 
 private:
  std::string MakeLayerName(int display_index, int vm_index = -1);
  int local_group_index_;  // Index of the current process in the cluster of VMs
  std::string group_uuid_;  // Unique identifier for entire VM cluster
  // All IPC buffers are cached here for speed, to prevent OS from
  // continually remapping RAM every read/write request.
  std::map<std::pair<int, int>, std::unique_ptr<DisplayRingBuffer>>
      display_buffer_cache_;
};
 
}  // namespace cuttlefish