RtlGetPersistedStateLocation - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTRTL_H
#if (PHNT_VERSION >= PHNT_REDSTONE3)

// private
NTSYSAPI
NTSTATUS
NTAPI
RtlGetPersistedStateLocation(
    _In_ PCWSTR SourceID,
    _In_opt_ PCWSTR CustomValue,
    _In_opt_ PCWSTR DefaultPath,
    _In_ STATE_LOCATION_TYPE StateLocationType,
    _Out_writes_bytes_to_opt_(BufferLengthIn, *BufferLengthOut) PWCHAR TargetPath,
    _In_ ULONG BufferLengthIn,
    _Out_opt_ PULONG BufferLengthOut
    );

#endif
#endif

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This function is documented in Windows Driver Kit.