求助自写虚拟磁盘 回应MOUNTMGR的IOCTL_MOUNTDEV_QUERY_DEVICE_NAME

自写虚拟磁盘 回应MOUNTMGR的IOCTL_MOUNTDEV_QUERY_DEVICE_NAME 但是MOUNTMGR并不给予足够长BUFFER为什么？
代码如下
case IOCTL_MOUNTDEV_QUERY_DEVICE_NAME:
{
PMOUNTDEV_NAME mountName = Irp->AssociatedIrp.SystemBuffer;
ULONG Retlength = 0;
WCHAR tmp[256] = {0};
UNICODE_STRING ntUnicodeString;

if (irpSp->Parameters.DeviceIoControl.OutputBufferLength < sizeof(MOUNTDEV_NAME))
return DouboxRequestComplete(DeviceObject, Irp, STATUS_BUFFER_OVERFLOW, sizeof (MOUNTDEV_NAME));


G_SptDynamicFunction.sptSnwprintf(
tmp,
256,
L"\\DosDevices\\%wc:",
volumeDeviceExtension->driveLetter);
RtlInitUnicodeString (&ntUnicodeString, tmp);

mountName->NameLength = ntUnicodeString.Length;
Retlength = ntUnicodeString.Length + sizeof(USHORT);

if (irpSp->Parameters.DeviceIoControl.OutputBufferLength < Retlength)
{
return DouboxRequestComplete(DeviceObject, Irp, STATUS_BUFFER_OVERFLOW, sizeof (MOUNTDEV_NAME));
}
RtlCopyMemory ((PCHAR)mountName->Name,ntUnicodeString.Buffer, ntUnicodeString.Length);


return DouboxRequestComplete(DeviceObject, Irp, STATUS_SUCCESS, Retlength);
}


每次给予的OUTBUFFER长度都是4

飘过