deviceiocontrol 和磁盘大小问题
我正在使用 C# 和 pinvoke 来读取/写入原始 SD 卡。我需要使用deviceiocontrol获取总容量：
[StructLayout(LayoutKind.Sequential)]
public struct DISK_GEOMETRY
{
public long Cylinders;
public int MediaType;
public int TracksPerCylinder;
public int SectorsPerTrack;
public int BytesPerSector;
public long DiskSize
{
get
{
return Cylinders * (long)TracksPerCylinder * (long)SectorsPerTrack * (long)BytesPerSector;
}
}
}
...
uint dummy;
DISK_GEOMETRY diskGeo = new DISK_GEOMETRY();
DeviceIoControl(safeHandle, EIOControlCode.DiskGetDriveGeometry, IntPtr.Zero, 0,
ref diskGeo, (uint)Marshal.SizeOf(typeof(DISK_GEOMETRY)), out dummy, IntPtr.Zero);
this.sectorSize = diskGeo.BytesPerSector;
this.bufferSize = this.sectorSize * 16384;
this.diskSize = diskGeo.DiskSize;
对于1 GiB的sd卡，diskGeo.DiskSize是1011709440。为什么？
I am using C# and pinvoke to read/write a raw sd card. I need to get the total capacity with deviceiocontrol:
[StructLayout(LayoutKind.Sequential)]
public struct DISK_GEOMETRY
{
public long Cylinders;
public int MediaType;
public int TracksPerCylinder;
public int SectorsPerTrack;
public int BytesPerSector;
public long DiskSize
{
get
{
return Cylinders * (long)TracksPerCylinder * (long)SectorsPerTrack * (long)BytesPerSector;
}
}
}
...
uint dummy;
DISK_GEOMETRY diskGeo = new DISK_GEOMETRY();
DeviceIoControl(safeHandle, EIOControlCode.DiskGetDriveGeometry, IntPtr.Zero, 0,
ref diskGeo, (uint)Marshal.SizeOf(typeof(DISK_GEOMETRY)), out dummy, IntPtr.Zero);
this.sectorSize = diskGeo.BytesPerSector;
this.bufferSize = this.sectorSize * 16384;
this.diskSize = diskGeo.DiskSize;
With a sd card of 1 GiB, the diskGeo.DiskSize is 1011709440. Why?
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那是大约。 965MB，这是可用分区的实际大小。丢失的 59MB 是一个开销分区，其中包含 SD 版权保护机制等内容。根据文件格式（FAT16、FAT32 等），文件分配表等也可能会丢失空间。
That's approx. 965MB which is the actual size of the useable partition. The lost 59MB is an overhead partition which contains things like the SD Copyright Protection Mechanism. Also space may be lost to the file allocation table etc. depending on the file format (FAT16, FAT32, etc.)