请帮我解释一下这个DispatchRead例程

NTSTATUS DispatchRead (
IN PDEVICE_OBJECT pDevObj,
IN PIRP pIrp ) {


NTSTATUS status = STATUS_SUCCESS;
PVOID userBuffer; //DebugView 输出 userBuffer 是一个字符串 PVOID 是什么数据类型?
ULONG xferSize;
// The stack location contains the user buffer info
PIO_STACK_LOCATION pIrpStack =
IoGetCurrentIrpStackLocation( pIrp );
// Dig out the Device Extension from the Device object
PDEVICE_EXTENSION pDevExt = (PDEVICE_EXTENSION)
pDevObj->DeviceExtension;
// Determine the length of the request
xferSize = pIrpStack->Parameters.Read.Length;
// Obtain user buffer pointer
userBuffer = pIrp->AssociatedIrp.SystemBuffer;

// Don't transfer more than the user's request
xferSize = (xferSize < pDevExt->deviceBufferSize) ?
xferSize : pDevExt->deviceBufferSize;
// Now copy the pool buffer into user space
// 把需要的读数据copy到 useBuffer 中
RtlCopyMemory( userBuffer, pDevExt->deviceBuffer,
xferSize );//这样拷贝到内存中,API调用该例程,如何得到数据? userBuffer是一个指针码?在这里如果用pIrp->AssociatedIrp.SystemBuffer 代替userBuffer 可以?
#ifdef DEBUGMSG
     DbgPrint( "\n*******************\n");
          DbgPrint( "%d", pDevExt->deviceBufferSize);
  DbgPrint( "%s", pDevExt->deviceBuffer);
 DbgPrint( "\n*******************\n");
#endif
// Free the temporary pool buffer
ExFreePool( pDevExt->deviceBuffer );// 释放内存 读出之后就释放出来
pDevExt->deviceBuffer = NULL;
pDevExt->deviceBufferSize = 0;

// Now complete the IRP
pIrp->IoStatus.Status = status;
pIrp->IoStatus.Information = xferSize; // bytes xfered
IoCompleteRequest( pIrp, IO_NO_INCREMENT );
return status;
}

//DebugView 输出 userBuffer 是一个字符串 PVOID 是什么数据类型?
是PVOID  “void *”的意思
RtlCopyMemory( userBuffer, pDevExt->deviceBuffer,
xferSize );//这样拷贝到内存中,API调用该例程,如何得到数据? userBuffer是一个指针码?在这里如果用pIrp->AssociatedIrp.SystemBuffer 代替userBuffer 可以?
对,userBuffer是一个指针
pIrp->AssociatedIrp.SystemBuffer 和userBuffer ，具体看使用什么方式