RtlGetCompressionWorkSpaceSize function (ntifs.h)

Article
09/28/2023

The RtlGetCompressionWorkSpaceSize function is used to determine the correct size of the WorkSpace buffer for the RtlCompressBuffer and RtlDecompressFragment functions.

Syntax

NT_RTL_COMPRESS_API NTSTATUS RtlGetCompressionWorkSpaceSize(
  [in]  USHORT CompressionFormatAndEngine,
  [out] PULONG CompressBufferWorkSpaceSize,
  [out] PULONG CompressFragmentWorkSpaceSize
);

Parameters

[in] CompressionFormatAndEngine

Bitmask specifying the compression format and engine type. This parameter must be set to a valid bitwise OR combination of one format type and one engine type. For example, COMPRESSION_FORMAT_LZNT1 | COMPRESSION_ENGINE_STANDARD.

The meanings of these, and other related values, are as follows:

Value	Meaning
COMPRESSION_FORMAT_NONE	Not supported by this function.
COMPRESSION_FORMAT_DEFAULT	Not supported by this function.
COMPRESSION_FORMAT_LZNT1	The function will perform LZ compression.
COMPRESSION_FORMAT_XPRESS	The function will perform Xpress compression.
COMPRESSION_FORMAT_XPRESS_HUFF	The function will perform Xpress Huffman compression.
COMPRESSION_ENGINE_STANDARD	The UncompressedBuffer buffer is compressed using an algorithm that provides a balance between data compression and performance. This value cannot be used with COMPRESSION_ENGINE_MAXIMUM.
COMPRESSION_ENGINE_MAXIMUM	The UncompressedBuffer buffer is compressed using an algorithm that provides maximum data compression but with relatively slower performance. This value cannot be used with COMPRESSION_ENGINE_STANDARD.
COMPRESSION_ENGINE_HIBER	Not supported by this function.

[out] CompressBufferWorkSpaceSize

A pointer to a caller-allocated buffer receiving the size, in bytes, required to compress a buffer. This value is used to determine the correct size of RtlCompressBuffer's WorkSpace buffer.

[out] CompressFragmentWorkSpaceSize

A pointer to a caller-allocated buffer receiving the size, in bytes, required to decompress a compressed buffer to a fragment. This value is used to determine the correct size of RtlDecompressFragment's WorkSpace buffer. Note that the RtlCompressFragment function does not currently exist.

Return value

RtlGetCompressionWorkSpaceSizereturns an appropriate error status, such as one of the following:

Return code	Description
STATUS_SUCCESS	The required buffer sizes, in bytes, were successfully returned.
STATUS_INVALID_PARAMETER	An invalid compression format was specified via the CompressionFormatAndEngine parameter. If CompressionFormatAndEngine is either COMPRESSION_FORMAT_NONE or COMPRESSION_FORMAT_DEFAULT (but not both), this value is returned.
STATUS_UNSUPPORTED_COMPRESSION	An invalid compression format was specified via the CompressionFormatAndEngine parameter. If CompressionFormatAndEngine is not one of the following, STATUS_UNSUPPORTED_COMPRESSION is returned: COMPRESSION_FORMAT_LZNT1, COMPRESSION_FORMAT_XPRESS, COMPRESSION_FORMAT_XPRESS_HUF
STATUS_NOT_SUPPORTED	An invalid compression engine was specified via the CompressionFormatAndEngine parameter. If CompressionFormatAndEngine is not COMPRESSION_ENGINE_STANDARD or COMPRESSION_ENGINE_MAXIMUM (but not both), this value is returned.

Remarks

The RtlCompressBuffer and RtlDecompressFragmentfunctions require an appropriately sized work space buffer to compress and decompress successfully. To determine the correct work space buffer size, in bytes, call the RtlGetCompressionWorkSpaceSize function.

As an example, the WorkSpace parameter of the RtlCompressBuffer function must point to an adequately sized work space buffer. The CompressBufferWorkSpaceSize parameter of the RtlGetCompressionWorkSpaceSize provides this size.

To compress an uncompressed buffer, use the RtlCompressBuffer function.

To decompress a compressed buffer, use the RtlDecompressBuffer function.

To decompress only a portion of a compressed buffer (that is, a "fragment" of the buffer), use the RtlDecompressFragment function.

Requirements

Requirement	Value
Minimum supported client	Windows XP
Target Platform	Universal
Header	ntifs.h (include Fltkernel.h, Ntifs.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe
IRQL	<= APC_LEVEL