payload_consumer/mount_history.cc

//
// 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.
//

#include "update_engine/payload_consumer/mount_history.h"

#include <inttypes.h>

#include <string>
#include <vector>

#include <base/logging.h>
#include <base/time/time.h>

#include "update_engine/common/utils.h"

namespace chromeos_update_engine {
void LogMountHistory(const FileDescriptorPtr blockdevice_fd) {
  static constexpr ssize_t kBlockSize = 4096;

  if (blockdevice_fd == nullptr) {
    return;
  }

  brillo::Blob block0_buffer(kBlockSize);
  ssize_t bytes_read;

  if (!utils::PReadAll(
          blockdevice_fd, block0_buffer.data(), kBlockSize, 0, &bytes_read)) {
    LOG(WARNING) << "PReadAll failed";
    return;
  }

  if (bytes_read != kBlockSize) {
    LOG(WARNING) << "Could not read an entire block";
    return;
  }

  // https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout
  // Super block starts from block 0, offset 0x400
  //   0x2C: len32 Mount time
  //   0x30: len32 Write time
  //   0x34: len16 Number of mounts since the last fsck
  //   0x38: len16 Magic signature 0xEF53

  time_t mount_time =
      *reinterpret_cast<uint32_t*>(&block0_buffer[0x400 + 0x2C]);
  uint16_t mount_count =
      *reinterpret_cast<uint16_t*>(&block0_buffer[0x400 + 0x34]);
  uint16_t magic = *reinterpret_cast<uint16_t*>(&block0_buffer[0x400 + 0x38]);

  if (magic == 0xEF53) {
    if (mount_count > 0) {
      LOG(WARNING) << "Device was remounted R/W " << mount_count << " times. "
                   << "Last remount happened on "
                   << base::Time::FromTimeT(mount_time) << ".";
    }
  }
}
}  // namespace chromeos_update_engine