struct IO_RESOURCE_DESCRIPTOR

typedef struct _IO_RESOURCE_DESCRIPTOR
{
     UCHAR Option;
     UCHAR Type;
     UCHAR ShareDisposition;
     UCHAR Spare1;
     WORD Flags;
     WORD Spare2;
     ULONG u;
} IO_RESOURCE_DESCRIPTOR, *PIO_RESOURCE_DESCRIPTOR;

Windows Vista Kernel Structures