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Overview

System compression, also known as "Compact OS", is a Windows feature that allows rarely modified files to be compressed using the XPRESS or LZX compression formats. It is not built directly into NTFS but rather is implemented using reparse points. This feature appeared in Windows 10 and it appears that many Windows 10 systems have been using it by default.

This repository contains a plugin which enables the NTFS-3G FUSE driver to transparently read from system-compressed files. It must be built against NTFS-3G version 2017.3.23 or later, since that was the first stable version to include support for reparse point plugins.

Currently, only reading is supported. Compressing an existing file may be done by using the "compact" utility on Windows, with one of the options below ("xpress4k" is the weakest and fastest, "lzx" is the strongest and slowest):

/exe:xpress4k
/exe:xpress8k
/exe:xpress16k
/exe:lzx

Installation

First, either download and extract the latest release tarball from https://github.com/ebiggers/ntfs-3g-system-compression/releases, or clone the git repository. If you're building from the git repository, you'll need to generate the configure script by running autoreconf -i. This requires autoconf, automake, libtool, and pkg-config.

The plugin can then be built by running ./configure && make. The build system must be able to find the NTFS-3G library and headers as well as the FUSE headers. Depending on the operating system, this may require that the "ntfs-3g-dev" and "libfuse-dev" (or similarly named) packages be installed. pkg-config must also be installed.

After compiling, run make install to install the plugin to the NTFS-3G plugin directory, which will be a subdirectory "ntfs-3g" of the system library directory ($libdir). An example full path to the installed plugin is /usr/lib/ntfs-3g/ntfs-plugin-80000017.so. It may differ slightly on different platforms. make install will create the plugin directory if it does not already exist.

Implementation note

The XPRESS and LZX compression formats used in system-compressed files are identical to the formats used in Windows Imaging (WIM) archives. Therefore, for the system compression plugin I borrowed the XPRESS and LZX decompressors I had already written for the wimlib project (https://wimlib.net/). I made some slight modifications for integration purposes, and I relicensed the files that used the LGPLv3+ license to GPLv2+ for compatibility with NTFS-3G's license.

Notices

The NTFS-3G system compression plugin was written by Eric Biggers, with contributions from Jean-Pierre André. You can contact the author at ebiggers3@gmail.com.

This software may be redistributed and/or modified under the terms of the GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version. There is NO WARRANY, to the extent permitted by law. See the COPYING file for details.