private void Read(uint physicalBlockIndex, uint blockIndex)
{
if (m_currentPhysicalBlock == physicalBlockIndex)
{
return;
}
Flush();
if (blockIndex >= m_subFile.DataBlockCount)
{
uint additionalBlocks = blockIndex - m_subFile.DataBlockCount + 1;
Memory.Clear(m_memory.Address, m_blockSize);
m_header.AllocateFreeBlocks(additionalBlocks);
m_subFile.DataBlockCount += additionalBlocks;
}
else
{
ReadBlockCount++;
m_stream.Position = physicalBlockIndex * m_blockSize;
int bytesRead = m_stream.Read(m_buffer, 0, m_blockSize);
if (bytesRead < m_buffer.Length)
{
Array.Clear(m_buffer, bytesRead, m_buffer.Length - bytesRead);
}
Marshal.Copy(m_buffer, 0, m_memory.Address, m_buffer.Length);
}
//I don't need to verify any of the footer data since I've written it all correctly.
m_currentPhysicalBlock = physicalBlockIndex;
m_currentBlockIndex = blockIndex;
}
/// <summary>
/// Makes a shadow copy of the indirect index passed to this function. If the block does not exists, it creates it.
/// </summary>
/// <param name="sourceBlockAddress">The block to be copied</param>
/// <param name="indexValue">the index value that goes in the footer of the file.</param>
/// <param name="blockType">Gets the expected block type</param>
/// <param name="remoteAddressOffset">the offset of the remote address that needs to be updated.</param>
/// <param name="remoteBlockAddress">the value of the remote address.</param>
/// <returns>Returns true if the block had to be shadowed, false if it did not change</returns>
private bool ShadowCopyIndexIndirect(ref uint sourceBlockAddress, uint indexValue, BlockType blockType, int remoteAddressOffset, uint remoteBlockAddress)
{
uint indexIndirectBlock;
//Make a copy of the index block referenced
//if the block does not exist, create it.
if (sourceBlockAddress == 0)
{
DiskIoSession buffer = m_ioSessions.SourceIndex;
indexIndirectBlock = m_fileHeaderBlock.AllocateFreeBlocks(1);
m_subFileHeader.TotalBlockCount++;
buffer.WriteToNewBlock(indexIndirectBlock, blockType, indexValue);
Memory.Clear(buffer.Pointer, buffer.Length);
WriteIndexIndirectBlock(buffer.Pointer, remoteAddressOffset, remoteBlockAddress);
sourceBlockAddress = indexIndirectBlock;
return(true);
}
//if the data page is an old page, allocate space to create a new copy
else if (sourceBlockAddress <= m_lastReadOnlyBlock)
{
indexIndirectBlock = m_fileHeaderBlock.AllocateFreeBlocks(1);
m_subFileHeader.TotalBlockCount++;
ReadThenWriteIndexIndirectBlock(sourceBlockAddress, indexIndirectBlock, indexValue, blockType, remoteAddressOffset, remoteBlockAddress);
sourceBlockAddress = indexIndirectBlock;
return(true);
}
//The page has already been copied, use the existing address.
else
{
ReadThenWriteIndexIndirectBlock(sourceBlockAddress, sourceBlockAddress, indexValue, blockType, remoteAddressOffset, remoteBlockAddress);
return(false);
}
}
