Update README, clarify licensing situation

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

10 files changed, 516 insertions, 23 deletions

diff --git a/COPYING.md b/COPYING.md
new file mode 100644
index 0000000..1185ad5
--- /dev/null
+++ b/COPYING.md
@@ -0,0 +1,44 @@
+# License of squashfs-tools-ng
+
+The `libsquashfs` library is released under the terms and conditions of the
+**GNU Lesser General Public License version 3 or later**. This applies to
+all source code in the directories `lib/sqfs`, `lib/util`, `include/sqfs`
+and `include/util`.
+
+The rest of squashfs-tools-ng is released under the terms and conditions of
+the **GNU General Public License version 3 or later**.
+
+Copies of the licenses are included in `licenses/LGPLv3.txt` and
+`licenses/GPLv3.txt` respectively.
+
+The original source code of squashfs-tools-ng has been written by David
+Oberhollenzer in 2019. Additional contributions have been added since the
+initial release which makes some parts of the package subject to the copyright
+of the respective authors. Appropriate copyright notices and SPDX identifiers
+are included in the source code files.
+
+Although the existing squashfs-tools and the Linux kernel implementation have
+been used for testing, the source code in this package is neither based on,
+nor derived from either of them.
+
+# Binary Packages with 3rd Party Libraries
+
+If this file is included in a binary release package, additional 3rd party
+libraries may be included, which are subject to the copyright of their
+respective authors and the terms and conditions of their respective liceses.
+
+The following may be included:
+
+ - The LZO compression library. Copyright Markus F.X.J. Oberhumer. This is
+   released under the terms and conditions of the GNU General Public License
+   version 2. A copy of the license is included in `licenses/GPLv2.txt`.
+ - The LZ4 compression library. Copyright Yann Collet. This is released under a
+   2 clause BSD style license, included in `licenses/LZ4.txt`.
+ - The XZ utils liblzma library is released into the public domain. An excerpt
+   from the `COPYING` file of its source code archive is included
+   in `licenses/xz.txt`.
+ - The zlib compression library. Copyright Jean-loup Gailly and Mark Adler.
+   This is released under the terms and conditions of the zlib license,
+   included in `licenses/zlib.txt`
+ - The zstd compression library. Copyright Facebook, Inc. All rights reserved.
+   This is released under a BSD style license, included in `licenses/zstd.txt`.
diff --git a/Makefile.am b/Makefile.am
index 379a949..4a865ed 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -16,8 +16,7 @@ dist_man1_MANS =
 check_PROGRAMS =
 pkgconfig_DATA =
 
-EXTRA_DIST = autogen.sh LICENSE-gpl.txt LICENSE-lgpl.txt README.md CHANGELOG.md
-EXTRA_DIST += mkwinbins.sh
+EXTRA_DIST = autogen.sh README.md CHANGELOG.md COPYING.md mkwinbins.sh licenses
 TESTS =
 
 include lib/sqfs/Makemodule.am
diff --git a/README.md b/README.md
index 67c1127..f4c3d1b 100644
--- a/README.md
+++ b/README.md
@@ -45,12 +45,30 @@ together with the existing tools:
  - `sqfsdiff` can compare the contents of two SquashFS images.
 
 
-Most of the actual logic of those tools is implemented in the `libsquashfs.so`
+Most of the actual logic of those tools is implemented in the `libsquashfs`
 library that (by default) gets installed on the system along with its header
-files, allowing 3rd party applications to use it (e.g. for embedding SqushFS
+files, allowing 3rd party applications to use it (e.g. for embedding SquashFS
 inside a custom container format without having to implement the SquashFS
 part).
 
+# Pre-built Windows binary Packages
+
+Pre-compiled binary packages for Windows are available here:
+
+https://infraroot.at/pub/squashfs/windows
+
+Those packages contain the binaries for the tools, the SquashFS library
+and pre-compiled dependency libraries (zlib, zstd, lzo, lzma, lz4).
+
+The binary package does not contain any source code. See below on how to obtain
+and compile the source for squashfs-tools-ng. The corresponding source code
+from which the 3rd party libraries have been built is also available for
+download at the above location.
+
+The headers and import libraries to build applications that use libsquashfs are
+included. For convenience, the pre-compiled, 3rd party dependency libraries
+also come with headers and import libraries.
+
 # Getting and Building the Source Code
 
 Official release tarballs can be obtained here:
@@ -76,6 +94,12 @@ If Doxygen is available, a reference manual can be built as follows:
 
 	make doxygen-doc
 
+The pre-compiled binary packages for Windows are built using a helper script
+that uses a MinGW cross toolchain to build squashfs-tools-ng and any of the
+required dependencies:
+
+	./mkwinbins.sh
+
 ## Structure of the Source Code
 
 The main functionality of the package is split up into a number libraries.
@@ -118,6 +142,24 @@ their choice of license, the code in the `lib/sqfs` and `lib/util`
 sub-directories is licensed under the LGPLv3, in contrast to the rest of this
 package.
 
+## A Note on LZO Support
+
+The SquashFS format supports compression using LZO. The `liblzo2` library
+itself is released under the GNU GPL, version 2.
+
+To make the `libsquashfs` library available as an LGPL library, it *cannot* be
+linked against `liblzo2`, neither statically nor dynamically.
+
+This legal problem has been solved using the following technical measure:
+
+ - `libsquashfs`, as of right now, does not support LZO compression.
+ - The `libcommon` helper library has an implementation of an `liblzo2` based
+   compressor. This library and the tools that use it are released under
+   the GPL.
+
+This way, the tools themselves *do* support LZO compression seamlessly, while
+the `libsquashfs` library does not.
+
 ## Further Information
 
 A documentation of the SquashFS on-disk format can be found here:
@@ -126,22 +168,4 @@ https://dr-emann.github.io/squashfs/
 
 # Copyright & License
 
-The code of the `libsquashfs` library is released under the terms and
-conditions of the GNU Lesser General Public License version 3 or later. The
-file `LICENSE-lgpl.txt` contains a copy of the license. Since the license is
-based on the General Public License version 3 and makes references to it
-instead of duplicating text, a copy of the GPL version 3 is also provided
-by the file `LICENSE-gpl.txt`.
-
-The rest of the software in this package is released under the terms and
-conditions of the GNU General Public License version 3 or later. The
-file `LICENSE-gpl.txt` contains a copy of the license.
-
-The original source code in this package has been written by David
-Oberhollenzer in 2019. Additional contributions have been added since the
-initial release which makes some parts of the package subject to the copyright
-of the respective authors.
-
-Although the existing squashfs-tools and the Linux kernel implementation have
-been used for testing, the source code in this package is neither based on,
-nor derived from either of them.
+See [COPYING.md](COPYING.md) for copyright and licensing information.
diff --git a/licenses/GPLv2.txt b/licenses/GPLv2.txt
new file mode 100644
index 0000000..d159169
--- /dev/null
+++ b/licenses/GPLv2.txt
@@ -0,0 +1,339 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
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diff --git a/LICENSE-gpl.txt b/licenses/GPLv3.txt
index f288702..f288702 100644
--- a/LICENSE-gpl.txt
+++ b/licenses/GPLv3.txt
diff --git a/LICENSE-lgpl.txt b/licenses/LGPLv3.txt
index 0a04128..0a04128 100644
--- a/LICENSE-lgpl.txt
+++ b/licenses/LGPLv3.txt
diff --git a/licenses/LZ4.txt b/licenses/LZ4.txt
new file mode 100644
index 0000000..74c2cdd
--- /dev/null
+++ b/licenses/LZ4.txt
@@ -0,0 +1,24 @@
+LZ4 Library
+Copyright (c) 2011-2016, Yann Collet
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright notice, this
+  list of conditions and the following disclaimer in the documentation and/or
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+
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diff --git a/licenses/xz.txt b/licenses/xz.txt
new file mode 100644
index 0000000..99c125d
--- /dev/null
+++ b/licenses/xz.txt
@@ -0,0 +1,17 @@
+liblzma is in the public domain.
+
+You can do whatever you want with the files that have been put into
+the public domain. If you find public domain legally problematic,
+take the previous sentence as a license grant. If you still find
+the lack of copyright legally problematic, you have too many
+lawyers.
+
+As usual, this software is provided "as is", without any warranty.
+
+If you copy significant amounts of public domain code from XZ Utils
+into your project, acknowledging this somewhere in your software is
+polite (especially if it is proprietary, non-free software), but
+naturally it is not legally required. Here is an example of a good
+notice to put into "about box" or into documentation:
+
+    This software includes code from XZ Utils <https://tukaani.org/xz/>.
diff --git a/licenses/zlib.txt b/licenses/zlib.txt
new file mode 100644
index 0000000..51c2378
--- /dev/null
+++ b/licenses/zlib.txt
@@ -0,0 +1,20 @@
+ (C) 1995-2017 Jean-loup Gailly and Mark Adler
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+
+  Jean-loup Gailly        Mark Adler
+  jloup@gzip.org          madler@alumni.caltech.edu
diff --git a/licenses/zstd.txt b/licenses/zstd.txt
new file mode 100644
index 0000000..3eb46a1
--- /dev/null
+++ b/licenses/zstd.txt
@@ -0,0 +1,26 @@
+Copyright (c) 2016-present, Facebook, Inc. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+ * Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+ * Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+ * Neither the name Facebook nor the names of its contributors may be used to
+   endorse or promote products derived from this software without specific
+   prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.