/// <summary>
/// Read the contents of this FAT from the given device at the given offset.
/// </summary>
/// <exception cref="IOException">IOException on read error</exception>
private void Read()
{
var data = new byte[sectorCount * sectorSize];
device.Read(offset, new MemoryStream(data));
for (var i = 0; i < entries.Length; i++)
{
entries[i] = fatType.ReadEntry(data, i);
}
}
public static BootSector Read(IBlockDevice device)
{
var b = new byte[512];
var bb = new MemoryStream(b);
device.Read(0, bb);
bb.Position = 510;
if (bb.ReadByte() != 0x55)
{
throw new IOException(
"missing boot sector signature");
}
bb.Position = 511;
if (bb.ReadByte() != 0xaa)
{
throw new IOException(
"missing boot sector signature");
}
bb.Position = SECTORS_PER_CLUSTER_OFFSET;
var sectorsPerCluster = (byte)bb.ReadByte();
if (sectorsPerCluster <= 0)
{
throw new IOException(
"suspicious sectors per cluster count " + sectorsPerCluster);
}
var rootDirEntriesB = new byte[2];
bb.Position = Fat16BootSector.ROOT_DIR_ENTRIES_OFFSET;
bb.Read(rootDirEntriesB, 0, 2);
if (!BitConverter.IsLittleEndian)
{
Array.Reverse(rootDirEntriesB, 0, 2);
}
int rootDirEntries = BitConverter.ToUInt16(rootDirEntriesB, 0);
var rootDirSectors = ((rootDirEntries * 32) +
(device.GetSectorSize() - 1)) / device.GetSectorSize();
var total16B = new byte[2];
bb.Position = TOTAL_SECTORS_16_OFFSET;
bb.Read(total16B, 0, 2);
if (!BitConverter.IsLittleEndian)
{
Array.Reverse(total16B, 0, 2);
}
int total16 = BitConverter.ToUInt16(total16B, 0);
var total32B = new byte[4];
bb.Position = TOTAL_SECTORS_32_OFFSET;
bb.Read(total32B, 0, 4);
if (!BitConverter.IsLittleEndian)
{
Array.Reverse(total32B, 0, 4);
}
long total32 = BitConverter.ToUInt32(total32B, 0);
var totalSectors = total16 == 0 ? total32 : total16;
var fatSz16B = new byte[2];
bb.Position = Fat16BootSector.SECTORS_PER_FAT_OFFSET;
bb.Read(fatSz16B, 0, 2);
if (!BitConverter.IsLittleEndian)
{
Array.Reverse(fatSz16B, 0, 2);
}
int fatSz16 = BitConverter.ToUInt16(fatSz16B, 0);
var fatSz32B = new byte[4];
bb.Position = Fat32BootSector.SECTORS_PER_FAT_OFFSET;
bb.Read(fatSz32B, 0, 4);
if (!BitConverter.IsLittleEndian)
{
Array.Reverse(fatSz32B, 0, 4);
}
long fatSz32 = BitConverter.ToUInt32(fatSz32B, 0);
var fatSz = fatSz16 == 0 ? fatSz32 : fatSz16;
var reservedSectorsB = new byte[2];
bb.Position = RESERVED_SECTORS_OFFSET;
bb.Read(reservedSectorsB, 0, 2);
if (!BitConverter.IsLittleEndian)
{
Array.Reverse(reservedSectorsB, 0, 2);
}
int reservedSectors = BitConverter.ToUInt16(reservedSectorsB, 0);
bb.Position = FAT_COUNT_OFFSET;
var fatCount = bb.ReadByte();
var dataSectors = totalSectors - (reservedSectors +
(fatCount * fatSz) + rootDirSectors);
var clusterCount = dataSectors / sectorsPerCluster;
var result =
(clusterCount > Fat16BootSector.MAX_FAT16_CLUSTERS) ?
(BootSector) new Fat32BootSector(device) : (BootSector) new Fat16BootSector(device);
result.Read();
return(result);
}
/// <summary>
/// Reads the contents of this <see cref="Sector"/> from the device into
/// internal buffer and resets the "dirty" state.
/// </summary>
/// <exception cref="IOException">IOException on read error</exception>
/// <seealso cref="IsDirty"/>
protected void Read()
{
Buffer.Position = 0;
device.Read(offset, Buffer);
dirty = false;
}
protected override void Read(MemoryStream data)
{
device.Read(deviceOffset, data);
}
