RtlGetCompressionWorkSpaceSize function

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(
  USHORT CompressionFormatAndEngine,
  PULONG CompressBufferWorkSpaceSize,
  PULONG CompressFragmentWorkSpaceSize
);

Parameters

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.

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.

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_HUFF
  • COMPRESSION_FORMAT_NONE (in this case, STATUS_INVALID_PARAMETER is returned)
  • COMPRESSION_FORMAT_DEFAULT (in this case, STATUS_INVALID_PARAMETER is returned)
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

   
Windows version Available in Windows XP and all later versions of Windows operating systems.
Target Platform Universal
Header ntifs.h (include Fltkernel.h, Ntifs.h)
Library NtosKrnl.lib
DLL NtosKrnl.exe
IRQL "<= APC_LEVEL"

See Also

FILE_COMPRESSION_INFORMATION

RtlCompressBuffer

RtlDecompressBuffer

RtlDecompressFragment