typedef struct _WMI_BUFFER_HEADER
{
     union
     {
          WNODE_HEADER Wnode;
          struct
          {
               ULONG BufferSize;
               ULONG SavedOffset;
               ULONG CurrentOffset;
               LONG ReferenceCount;
               union
               {
                    LARGE_INTEGER TimeStamp;
                    LARGE_INTEGER StartPerfClock;
               };
               INT64 SequenceNumber;
               ULONG Spare0;
               ULONG Spare1;
               ETW_BUFFER_CONTEXT ClientContext;
               union
               {
                    ETW_BUFFER_STATE State;
                    ULONG Flags;
               };
               ULONG Offset;
               WORD BufferFlag;
               WORD BufferType;
               union
               {
                    ULONG Padding1[4];
                    LARGE_INTEGER StartTime;
                    LIST_ENTRY Entry;
                    SINGLE_LIST_ENTRY SlistEntry;
                    PWMI_BUFFER_HEADER NextBuffer;
               };
               SINGLE_LIST_ENTRY GlobalEntry;
} WMI_BUFFER_HEADER, *PWMI_BUFFER_HEADER;

Windows Vista Kernel Structures