EtwEventWriteFull - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTWMI_H
#if (PHNT_MODE != PHNT_MODE_KERNEL)

NTSYSAPI
ULONG
NTAPI
EtwEventWriteFull(
    _In_ REGHANDLE RegHandle,
    _In_ PCEVENT_DESCRIPTOR EventDescriptor,
    _In_ USHORT EventProperty,
    _In_opt_ LPCGUID ActivityId,
    _In_opt_ LPCGUID RelatedActivityId,
    _In_ ULONG UserDataCount,
    _In_reads_opt_(UserDataCount) PEVENT_DATA_DESCRIPTOR UserData
    );

#endif
#endif

View code on GitHub

This function is documented in Windows SDK.