EtwEventUnregister - 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
//EtwEventRegister(
//    _In_ LPCGUID ProviderId,
//    _In_opt_ PENABLECALLBACK EnableCallback,
//    _In_opt_ PVOID CallbackContext,
//    _Out_ PREGHANDLE RegHandle
//    );

NTSYSAPI
ULONG
NTAPI
EtwEventUnregister(
    _In_ REGHANDLE RegHandle
    );

#endif
#endif

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This function is documented in Windows SDK.