如何在Kmemory中读取数据

DS3.0创建的驱动 Read()中:
KMemory Mem(I.Mdl());
ULONG dwTotalSize = I.ReadSize(CURRENT);
ULONG dwMaxSize = m_Endpoint2IN.MaximumTransferSize();

PURB pUrb = m_Endpoint2IN.BuildBulkTransfer( Mem,
dwTotalSize,
TRUE,
NULL,
TRUE
);  
status = m_Endpoint2IN.SubmitUrb(pUrb, NULL, NULL,TIME_OUT_PERIOD);
如果我现在就直接想读取得到的数据,该如何?
试着PULONG pBuffer = (PULONG) Mem.MapToSystemSpace();
pBuffer中也没有数据,似乎只是一些地址