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Win32 API reference (ni-winioctl-fsctl_get_compression)

FSCTL_GET_COMPRESSION IOCTL

Description

Retrieves the current compression state of a file or directory on a volume whose file system supports per-stream compression.

To perform this operation, call the DeviceIoControl function with the following parameters.

BOOL DeviceIoControl(
  (HANDLE) hDevice,             // handle to file
  FSCTL_GET_COMPRESSION,        // dwIoControlCode
  NULL,                         // lpInBuffer
  0,                            // nInBufferSize
  (LPVOID) lpOutBuffer,         // output buffer
  (DWORD) nOutBufferSize,       // size of output buffer
  (LPDWORD) lpBytesReturned,    // number of bytes returned
  (LPOVERLAPPED) lpOverlapped   // OVERLAPPED structure
);

Parameters

Input buffer

Input buffer length

Output buffer

Output buffer length

Input/output buffer

Input/output buffer length

Status block

Irp->IoStatus.Status is set to STATUS_SUCCESS if the request is successful.

Otherwise, Status to the appropriate error condition as a NTSTATUS code.

For more information, see NTSTATUS Values.

Remarks

The LZNT1 compression algorithm is the only compression algorithm implemented.

COMPRESSION_FORMAT_DEFAULT is not a compression state so it is not included in the table under the lpOutBuffer parameter. This value is only used with the FSCTL_SET_COMPRESSION control code.

If the file system of the volume containing the specified file or directory does not support per-file or per-directory compression, the operation fails.

You can set the compression state of a file or directory by using the FSCTL_SET_COMPRESSION control code. You can also compress or uncompress a file using this control code.

You can retrieve the compression attribute of a file or directory by calling the GetFileAttributes function. The compression attribute indicates whether a file or directory is compressed. The compression state indicates whether a file or directory is compressed, and, if it is, the format of the compressed data.

In Windows 8 and Windows Server 2012, this code is supported by the following technologies.

Technology	Supported
Server Message Block (SMB) 3.0 protocol	Yes
SMB 3.0 Transparent Failover (TFO)	No
SMB 3.0 with Scale-out File Shares (SO)	No
Cluster Shared Volume File System (CsvFS)	Yes
Resilient File System (ReFS)	No

SMB 3.0 Transparent Failover and Scale-Out do not support NTFS compressed files. The FSCTL call is not blocked, but unsupported.

FSCTL_GET_COMPRESSION - NtDoc