src/virtualization/bin/vmm/device/qcow.h

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef SRC_VIRTUALIZATION_BIN_VMM_DEVICE_QCOW_H_
#define SRC_VIRTUALIZATION_BIN_VMM_DEVICE_QCOW_H_

#include <endian.h>

#include "src/virtualization/bin/vmm/device/block_dispatcher.h"

// Each QCOW file starts with this magic value "QFI\xfb".
static constexpr uint32_t kQcowMagic = 0x514649fb;

// The top bits in a table entry have special significance. The remaining bits
// identify the target. For L1 table entries this is physical offset of the L2
// table. For L2 table entries, this is the physical offset of the cluster.
static constexpr uint64_t kTableEntryCopiedBit = 1ul << 63;
static constexpr uint64_t kTableEntryCompressedBit = 1ul << 62;
static constexpr uint64_t kTableOffsetMask = ~(kTableEntryCopiedBit | kTableEntryCompressedBit);

struct BigToHostEndianTraits {
  static uint16_t Convert(uint16_t val) { return be16toh(val); }
  static uint32_t Convert(uint32_t val) { return be32toh(val); }
  static uint64_t Convert(uint64_t val) { return be64toh(val); }
};

struct HostToBigEndianTraits {
  static uint16_t Convert(uint16_t val) { return htobe16(val); }
  static uint32_t Convert(uint32_t val) { return htobe32(val); }
  static uint64_t Convert(uint64_t val) { return htobe64(val); }
};

struct QcowHeader {
  uint32_t magic;
  uint32_t version;
  uint64_t backing_file_offset;
  uint32_t backing_file_size;
  uint32_t cluster_bits;
  uint64_t size;
  uint32_t crypt_method;
  uint32_t l1_size;
  uint64_t l1_table_offset;
  uint64_t refcount_table_offset;
  uint32_t refcount_table_clusters;
  uint32_t nb_snapshots;
  uint64_t snapshots_offset;

  // Only present on version 3+
  uint64_t incompatible_features;
  uint64_t compatible_features;
  uint64_t autoclear_features;
  uint32_t refcount_order;
  uint32_t header_length;

  uint32_t cluster_size() const { return 1u << cluster_bits; }

  // Return a new header that has been converted from host-endian to big-endian.
  QcowHeader HostToBigEndian() const { return ByteSwap<HostToBigEndianTraits>(); }

  // Return a new header that has been converted from big-endian to host-endian.
  QcowHeader BigToHostEndian() const { return ByteSwap<BigToHostEndianTraits>(); }

 private:
  // Byte-swaps the members of the header using the desired scheme.
  template <typename ByteOrderTraits>
  QcowHeader ByteSwap() const {
    return QcowHeader{
        .magic = ByteOrderTraits::Convert(magic),
        .version = ByteOrderTraits::Convert(version),
        .backing_file_offset = ByteOrderTraits::Convert(backing_file_offset),
        .backing_file_size = ByteOrderTraits::Convert(backing_file_size),
        .cluster_bits = ByteOrderTraits::Convert(cluster_bits),
        .size = ByteOrderTraits::Convert(size),
        .crypt_method = ByteOrderTraits::Convert(crypt_method),
        .l1_size = ByteOrderTraits::Convert(l1_size),
        .l1_table_offset = ByteOrderTraits::Convert(l1_table_offset),
        .refcount_table_offset = ByteOrderTraits::Convert(refcount_table_offset),
        .refcount_table_clusters = ByteOrderTraits::Convert(refcount_table_clusters),
        .nb_snapshots = ByteOrderTraits::Convert(nb_snapshots),
        .snapshots_offset = ByteOrderTraits::Convert(snapshots_offset),
        .incompatible_features = ByteOrderTraits::Convert(incompatible_features),
        .compatible_features = ByteOrderTraits::Convert(compatible_features),
        .autoclear_features = ByteOrderTraits::Convert(autoclear_features),
        .refcount_order = ByteOrderTraits::Convert(refcount_order),
        .header_length = ByteOrderTraits::Convert(header_length),
    };
  }
} __PACKED;

class QcowFile {
 public:
  QcowFile();
  ~QcowFile();

  QcowFile(const QcowFile&) = delete;
  QcowFile& operator=(const QcowFile&) = delete;
  QcowFile(QcowFile&& other) = delete;
  QcowFile& operator=(QcowFile&& other) = delete;

  const QcowHeader& header() const { return header_; }

  // The size (in bytes) of the virtual disk exposed by this QCOW file.
  size_t size() const { return header_.size; }

  // The number of bytes in a single cluster.
  //
  // This will be the unit used for all block allocations (both data and meta-
  // data blocks).
  size_t cluster_size() const { return 1u << header_.cluster_bits; }

  // Load the file header and verifiy the image is a valid QCOW file.
  void Load(BlockDispatcher* disp, BlockDispatcher::Callback callback);

  // Read |size| bytes at |off| from within the file.
  //
  // It is not an error for a read to cross an unmapped cluster. The section of
  // |data| for the unmapped cluster will be left unmodified.
  void ReadAt(BlockDispatcher* disp, void* data, uint64_t size, uint64_t off,
              BlockDispatcher::Callback callback);

 private:
  QcowHeader header_;

  class LookupTable;
  std::unique_ptr<LookupTable> lookup_table_;

  void LoadLookupTable(BlockDispatcher* disp, BlockDispatcher::Callback callback);
};

#endif  // SRC_VIRTUALIZATION_BIN_VMM_DEVICE_QCOW_H_