NtOpenKeyTransactedEx - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTREGAPI_H
#if (PHNT_VERSION >= PHNT_WIN7)

/**
 * Opens an existing registry key in a transaction with extended options.
 * 
 * @param[out] KeyHandle A pointer to a handle that receives the key handle.
 * @param[in] DesiredAccess The access mask that specifies the desired access rights.
 * @param[in] ObjectAttributes A pointer to an OBJECT_ATTRIBUTES structure that specifies the object attributes.
 * @param[in] OpenOptions The options to use when opening the key.
 * @param[in] TransactionHandle A handle to the transaction.
 * @return NTSTATUS Successful or errant status.
 */
NTSYSCALLAPI
NTSTATUS
NTAPI
NtOpenKeyTransactedEx(
    _Out_ PHANDLE KeyHandle,
    _In_ ACCESS_MASK DesiredAccess,
    _In_ POBJECT_ATTRIBUTES ObjectAttributes,
    _In_ ULONG OpenOptions,
    _In_ HANDLE TransactionHandle
    );

#endif
#endif

View code on GitHub
#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwOpenKeyTransactedEx(
    _Out_ PHANDLE KeyHandle,
    _In_ ACCESS_MASK DesiredAccess,
    _In_ POBJECT_ATTRIBUTES ObjectAttributes,
    _In_ ULONG OpenOptions,
    _In_ HANDLE TransactionHandle
    );

#endif

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This function is documented in Windows Driver Kit.