关于device_object里的device_extension的问题

DDK文档里的描述为：
PVOID DeviceExtension
Points to the device extension. The structure and contents of the device extension are driver-defined. The size is driver-determined, specified in the driver's call to IoCreateDevice. Most driver routines that process IRPs are given a pointer to the device object so the device extension is usually every driver's primary global storage area and frequently a driver's only global storage area for objects, resources, and any state the driver maintains about the I/O requests it handles.
也就是驱动开发者可以根据所开发的设备具体定义相关的device extension成员
请问自定义的这些成员如何初始化？
比如有一个pci9054的驱动里device extension的定义为：
typedef struct _DEVICE_EXTENSION
{
    PDEVICE_OBJECT        pDeviceObject;            // device object this extension belongs to
    PDEVICE_OBJECT        pLowerDeviceObject;        // next lower driver in same stack
    PDEVICE_OBJECT        pPhysicalDeviceObject;    // the PDO

    IO_REMOVE_LOCK        RemoveLock;                // removal control locking structure

    UNICODE_STRING        InterfaceName;            // interface name

    DEVICE_POWER_STATE    DevicePower;            // current device power state
    SYSTEM_POWER_STATE    SystemPower;            // current system power state

    PULONG IdleCount;                            // address of idle counter from idle detection registration
    DEVICE_CAPABILITIES DeviceCaps;                // copy of most recent device capabilities

    LONG Handles;                                // # open handles

    // Interrupt handling variables
    ULONG                InterruptSource;
    PKINTERRUPT            pInterruptObject;        // address of interrupt object
    
    LIST_ENTRY          InterruptEventList;
    KSPIN_LOCK          InterruptEventListLock;

    PUCHAR                PortBase;                // I/O port base address
    ULONG                PortCount;                
    // TODO add additional per-device declarations
    BOOLEAN                bMappedPort;            // true if we mapped port addr in StartDevice
    BOOLEAN                bBusy;                    // true if device busy with a request
    BOOLEAN                bStalledForPower;        // power management has stalled IRP queue

    //ʼþ¶ÔÏóÖ¸Õë
    PKEVENT                pWaitEvent;
    BOOLEAN                bSetWaitEvent;

    PKEVENT                pWaitEvent2;
    BOOLEAN                bSetWaitEvent2;



    //PCI9054ÄÚ²¿¼Ä´æÆ÷Ó³ÉäµÄÄÚ´æ×ÊÔ´
    ULONG                *LocalRegisterMemBase;                
    PHYSICAL_ADDRESS    LocalRegisterPhysicalMemBase;
    ULONG                LocalRegisterMemCount;
    //×Ô¶¨ÒåÄÚ´æ×ÊÔ´
    ULONG                *PdcMemBase0;
    PHYSICAL_ADDRESS    PdcPhysicalMemBase0;
    ULONG                PdcMemCount0;

    KSPIN_LOCK          HardwareAccessLock;

    signed long            UsageCount;                //The pending I/O Count
    BOOLEAN                bStopping;                //
    KEVENT                StoppingEvent;            // Set when all pending I/O complete

    BOOLEAN                GotResource;            //

    NTSTATUS            TransmitIrpStatus;

    //Power Defines
    DEVICE_POWER_STATE  PowerState;

    //DMA
     // DMA access information
    DMA_CHANNEL_INFO    DmaInfo[NUMBER_OF_DMA_CHANNELS];
    KSPIN_LOCK          DmaChannelLock;

    // Doorbell storage
    ULONG                IntraDoorbellValue;

} DEVICE_EXTENSION, *PDEVICE_EXTENSION;

可是这些元素都是在哪初始化的？在驱动程序里的addevice或iocreatedevice等例程里没有看到初始化操作啊
可是后面有一些例程直接用到device extension里的值！
比如那个ULONG                *LocalRegisterMemBase;  
应该是定义为PCI BAR0里的值的，可是木有定义啊，直接使用有木有
难道是系统自动赋值的吗？可是是自己定义的device extension啊

求解答！！！

done