typedef struct _RTL_TRACE_SEGMENT
{
     ULONG Magic;
     PRTL_TRACE_DATABASE Database;
     PRTL_TRACE_SEGMENT NextSegment;
     ULONG TotalSize;
     CHAR * SegmentStart;
     CHAR * SegmentEnd;
     CHAR * SegmentFree;
} RTL_TRACE_SEGMENT, *PRTL_TRACE_SEGMENT;

Windows Vista Kernel Structures