请问有关内存映射的问题？

请问用DDk编程中，内存映射是什么意思？以下代码什么意思
NTSTATUS
MapMemoryToUserSpace(
    IN ULONG pmbar,
IN ULONG length,
    IN INTERFACE_TYPE itype,
IN ULONG bno,
    OUT PVOID *umapaddr
    )
{
    NTSTATUS          status;
    UNICODE_STRING    phyUnicodeString;
    OBJECT_ATTRIBUTES objattr;
    HANDLE            PMHandle  = NULL;
    PVOID             PMSection = NULL;
    ULONG             AddressSpace = 0L;
    PHYSICAL_ADDRESS  BusAddress;
    PHYSICAL_ADDRESS  pMapAdrBase;
    PHYSICAL_ADDRESS  pMapAdrEnd;
    PHYSICAL_ADDRESS  viewBase;
    PHYSICAL_ADDRESS  mappedLength;
    BOOLEAN           transBaseAddr;
    BOOLEAN           transEndAddr;

    // Create a physical address long integer
BusAddress.HighPart = 0x0;
BusAddress.LowPart  = (ULONG) pmbar;  

    // Create the name
    RtlInitUnicodeString( &phyUnicodeString,
             L"\\Device\\PhysicalMemory" );

    // Initialize the data so we can find the object
    InitializeObjectAttributes( &objattr, &phyUnicodeString,
               OBJ_CASE_INSENSITIVE, (HANDLE) NULL,
               (PSECURITY_DESCRIPTOR) NULL );

    // Open a handle to the oject and check its status
    status = ZwOpenSection( &PMHandle, SECTION_ALL_ACCESS, &objattr );

    if (!NT_SUCCESS(status))
    {
   KdPrint(("PCI2040: ZwOpenSection failed\n"));
   return status;
    }

    // Get a pointer to this object
    status = ObReferenceObjectByHandle( PMHandle, SECTION_ALL_ACCESS,
                   (POBJECT_TYPE) NULL, KernelMode,
                   &PMSection,
                                        (POBJECT_HANDLE_INFORMATION) NULL );
    if (!NT_SUCCESS(status))
    {
   KdPrint(("PCI2040: ObReferenceObjectByHandle failed\n"));
        ZwClose(PMHandle);
   return status;
    }

    // Initialize the physical addresses that will be translated
    KdPrint (("PCI2040: HalTranslateBusAddress Start Interface = %d, bno = %d, Bar = 0x%X\n", itype, bno, BusAddress.LowPart ));
    // Translate the physical addresses.
AddressSpace = 0L;
    if( !HalTranslateBusAddress( itype, bno, BusAddress, &AddressSpace, &pMapAdrBase ))
{
     KdPrint (("PCI2040: HalTranslatephysicalAddress start failed\n"));
        ZwClose(PMHandle);
   return STATUS_UNSUCCESSFUL;
}

    BusAddress = RtlLargeIntegerAdd( BusAddress,
                RtlConvertUlongToLargeInteger(length) );

    KdPrint (("PCI2040: HalTranslateBusAddress Emd Interface = %d, bno = %d, Bar = 0x%X\n", itype, bno, BusAddress.LowPart ));
AddressSpace = 0L;
    if( !HalTranslateBusAddress( itype, bno, BusAddress, &AddressSpace, &pMapAdrEnd ))
{
     KdPrint (("PCI2040: HalTranslatephysicalAddress end failed\n"));
        ZwClose(PMHandle);
   return STATUS_UNSUCCESSFUL;
}


    // Calculate the length of the memory to be mapped
    mappedLength = RtlLargeIntegerSubtract( pMapAdrEnd, pMapAdrBase );
    length = mappedLength.LowPart;

// Map the section
viewBase  = pMapAdrBase;
*umapaddr = NULL;
status = ZwMapViewOfSection( PMHandle, (HANDLE) -1, umapaddr, 0L,
                length, &viewBase, &length, ViewShare,
                0, PAGE_READWRITE | PAGE_NOCACHE );
if (!NT_SUCCESS(status))
{
   KdPrint(("PCI2040: ZwMapViewOfSection failed\n"));
        ZwClose(PMHandle);
        return status;
}
*umapaddr = (PVOID) (((ULONG) *umapaddr) +
((ULONG) pMapAdrBase.LowPart -
 (ULONG) viewBase.LowPart));
KdPrint(("PCI2040: ZwMapViewOfSection succeeded, returning 0x%X\n", *umapaddr));
    return STATUS_SUCCESS;
}

这段代码是将一段内存（也有可能是某块卡上的RAM或寄存器）映射到用户空间，可以在应用模式来访问这段内存。

老兄,前段时间我也为内存映射烦了一阵子,不过我的是ISA的,现在搞通了,还得多谢Arthur Tu和冷老大的帮忙.但你的贴上好像是PCI的,我就不大懂了,有空多问问老大们,他们有办法...