NtCopyFileChunk - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTRTL_H
#if (PHNT_VERSION >= PHNT_WIN11)

NTSYSCALLAPI
NTSTATUS
NTAPI
NtCopyFileChunk(
    _In_ HANDLE SourceHandle,
    _In_ HANDLE DestinationHandle,
    _In_opt_ HANDLE EventHandle,
    _Out_ PIO_STATUS_BLOCK IoStatusBlock,
    _In_ ULONG Length,
    _In_ PLARGE_INTEGER SourceOffset,
    _In_ PLARGE_INTEGER DestOffset,
    _In_opt_ PULONG SourceKey,
    _In_opt_ PULONG DestKey,
    _In_ ULONG Flags
    );

#endif
#endif

View code on GitHub
#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwCopyFileChunk(
    _In_ HANDLE SourceHandle,
    _In_ HANDLE DestinationHandle,
    _In_opt_ HANDLE EventHandle,
    _Out_ PIO_STATUS_BLOCK IoStatusBlock,
    _In_ ULONG Length,
    _In_ PLARGE_INTEGER SourceOffset,
    _In_ PLARGE_INTEGER DestOffset,
    _In_opt_ PULONG SourceKey,
    _In_opt_ PULONG DestKey,
    _In_ ULONG Flags
    );

#endif

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This function is documented in Windows Driver Kit.