FSCTL_GET_COMPRESSION IOCTL (winioctl.h)
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
);
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.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows XP [desktop apps only] |
| Minimum supported server | Windows Server 2003 [desktop apps only] |
| Header | winioctl.h (include Windows.h) |