#ifndef _NTRTL_H
#if (PHNT_VERSION >= PHNT_REDSTONE4)
NTSYSAPI
NTSTATUS
NTAPI
RtlQueryRegistryValueWithFallback(
_In_opt_ HANDLE PrimaryHandle,
_In_opt_ HANDLE FallbackHandle,
_In_ PUNICODE_STRING ValueName,
_In_ ULONG ValueLength,
_Out_opt_ PULONG ValueType,
_Out_writes_bytes_to_(ValueLength, *ResultLength) PVOID ValueData,
_Out_range_(<= , ValueLength) PULONG ResultLength
);
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This function is documented in Windows Driver Kit.