typedef struct _PCIE_DEVICE_ID
{
     WORD VendorID;
     WORD DeviceID;
     ULONG ClassCode: 24;
     ULONG FunctionNumber: 8;
     ULONG DeviceNumber: 8;
     ULONG Segment: 16;
     ULONG PrimaryBusNumber: 8;
     ULONG SecondaryBusNumber: 8;
     ULONG Reserved1: 2;
     ULONG SlotNumber: 14;
     ULONG Reserved2: 8;
} PCIE_DEVICE_ID, *PPCIE_DEVICE_ID;

Windows Vista Kernel Structures