Information to packagers of XZ Utils
====================================
0. Preface
1. Package naming
2. Package description
3. License
4. configure options
4.1. Static vs. dynamic linking of liblzma
4.2. Optimizing xzdec and lzmadec
5. Additional documentation
6. Extra files
7. Installing XZ Utils and LZMA Utils in parallel
8. Example
0. Preface
----------
This document is meant for people who create and maintain XZ Utils
packages for operating system distributions. The focus is on GNU/Linux
systems, but most things apply to other systems too.
While the standard "configure && make DESTDIR=$PKG install" should
give a pretty good package, there are some details which packagers
may want to tweak.
Packagers should also read the INSTALL file.
1. Package naming
-----------------
The preferred name for the XZ Utils package is "xz", because that's
the name of the upstream tarball. Naturally you may have good reasons
to use some other name; I won't get angry about it. ;-) It's just nice
to be able to point people to the correct package name without asking
what distro they have.
If your distro policy is to split things into small pieces, here is
one suggestion:
xz xz, xzdec, scripts (xzdiff, xzgrep, etc.), docs
xz-lzma lzma, unlzma, lzcat, lzgrep etc. symlinks and
lzmadec binary for compatibility with LZMA Utils
liblzma liblzma.so.*
liblzma-devel liblzma.so, liblzma.a, API headers
2. Package description
----------------------
Here is a suggestion which you may use as the package description.
If you can use only one-line description, pick only the first line.
Naturally, feel free to use some other description if you find it
better, and maybe send it to me too.
Library and command line tools for XZ and LZMA compressed files
XZ Utils provide a general purpose data compression library
and command line tools. The native file format is the .xz
format, but also the legacy .lzma format is supported. The .xz
format supports multiple compression algorithms, of which LZMA2
is currently the primary algorithm. With typical files, XZ Utils
create about 30 % smaller files than gzip.
If you are splitting XZ Utils into multiple packages, here are some
suggestions for package descriptions:
xz:
Command line tools for XZ and LZMA compressed files
This package includes the xz compression tool and other command
line tools from XZ Utils. xz has command line syntax similar to
that of gzip. The native file format is the .xz format, but also
the legacy .lzma format is supported. The .xz format supports
multiple compression algorithms, of which LZMA2 is currently the
primary algorithm. With typical files, XZ Utils create about 30 %
smaller files than gzip.
Note that this package doesn't include the files needed for
LZMA Utils 4.32.x compatibility. Install also the xz-lzma
package to make XZ Utils emulate LZMA Utils 4.32.x.
xz-lzma:
LZMA Utils emulation with XZ Utils
This package includes executables and symlinks to make
XZ Utils emulate lzma, unlzma, lzcat, and other command
line tools found from the legacy LZMA Utils 4.32.x package.
liblzma:
Library for XZ and LZMA compressed files
liblzma is a general purpose data compression library with
an API similar to that of zlib. liblzma supports multiple
algorithms, of which LZMA2 is currently the primary algorithm.
The native file format is .xz, but also the legacy .lzma
format and raw streams (no headers at all) are supported.
This package includes the shared library.
liblzma-devel:
Library for XZ and LZMA compressed files
This package includes the API headers, static library, and
other development files related to liblzma.
3. License
----------
If the package manager supports a license field, you probably should
put GPLv2+ there (GNU GPL v2 or later). The interesting parts of
XZ Utils are in the public domain, but some less important files
ending up into the binary package are under GPLv2+. So it is simplest
to just say GPLv2+ if you cannot specify "public domain and GPLv2+".
If you split XZ Utils into multiple packages as described earlier
in this file, liblzma and liblzma-dev packages will contain only
public domain code (from XZ Utils at least; compiler or linker may
add some third-party code, which may be copyrighted).
4. configure options
--------------------
Unless you are building a package for a distribution that is meant
only for embedded systems, don't use the following configure options:
--enable-debug
--enable-encoders (*)
--enable-decoders
--enable-match-finders
--enable-checks
--enable-small (*)
--disable-threads (*)
(*) These are OK when building xzdec and lzmadec as explained later.
You may use --enable-werror but be careful with it since it may break
the build due to some useless warning when the build environment
changes (like CPU architecture or compiler version).
4.1. Static vs. dynamic linking of liblzma
The default is to link the most important command line tools against
static liblzma, and the less important tools against shared liblzma.
This can be changed by passing --enable-dynamic to configure, or by
not building static libraries at all by passing --disable-static
to configure. It is mildly recommended that you use the default, but
the configure options make it easy to do otherwise if the distro policy
so requires.
On 32-bit x86, linking against static liblzma can give a minor
speed improvement. Static libraries on x86 are usually compiled as
position-dependent code (non-PIC) and shared libraries are built as
position-independent code (PIC). PIC wastes one register, which can
make the code slightly slower compared to a non-PIC version. (Note
that this doesn't apply to x86-64.)
Linking against static liblzma avoids a dependency on liblzma shared
library, and makes it slightly easier to copy the command line tools
between systems (e.g. quick 'n' dirty emergency recovery of some
files). It also allows putting the command line tools to /bin while
leaving liblzma to /usr/lib (assuming that your distribution uses
such a file system hierarchy), if no other file in /bin would require
liblzma.
If you don't want to distribute static libraries but you still
want to link the command line tools against static liblzma, it is
probably easiest to build both static and shared liblzma, but after
"make DESTDIR=$PKG install" remove liblzma.a and modify liblzma.la
to not contain a reference to liblzma.a.
4.2. Optimizing xzdec and lzmadec
xzdec and lzmadec are intended to be relatively small instead of
optimizing for the best speed. Thus, it is a good idea to build
xzdec and lzmadec separately:
- Only decoder code is needed, so you can speed up the build
slightly by passing --disable-encoders to configure. This
shouldn't affect the final size of the executables though,
because the linker is able to omit the encoder code anyway.
- xzdec and lzmadec will never use multithreading capabilities of
liblzma. You can avoid dependency on libpthread by passing
--disable-threads to configure.
- There are and will be no translated messages for xzdec and
lzmadec, so it is fine to pass also --disable-nls to configure.
- To select somewhat size-optimized variant of some things in
liblzma, pass --enable-small to configure.
- Tell the compiler to optimize for size instead of speed.
E.g. with GCC, put -Os into CFLAGS.
5. Additional documentation
---------------------------
"make install" copies some additional documentation to $docdir
(--docdir in configure). These a copy of the GNU GPL v2, which can
be replaced with a symlink if your distro ships with shared copies
of the common license texts.
6. Extra files
--------------
The "extra" directory contains some small extra tools or other files.
The exact set of extra files can vary between XZ Utils releases. The
extra files have only limited use or they are too dangerous to be
put directly to $bindir (7z2lzma.sh is a good example, since it can
silently create corrupt output if certain conditions are not met).
If you feel like it, you may copy the extra directory under the doc
directory (e.g. /usr/share/doc/xz/extra). Maybe some people will find
them useful. However, most people needing these tools probably are
able to find them from the source package too.
The "debug" directory contains some tools that are useful only when
hacking on XZ Utils. Don't package these tools.
7. Installing XZ Utils and LZMA Utils in parallel
-------------------------------------------------
XZ Utils and LZMA Utils 4.32.x can be installed in parallel by
omitting the compatibility symlinks (lzma, unlzma, lzcat, lzgrep etc.)
from the XZ Utils package. It's probably a good idea to still package
the symlinks into a separate package so that users may choose if they
want to use XZ Utils or LZMA Utils for handling .lzma files.
8. Example
----------
Here is an example for i686 GNU/Linux that
- links xz against static liblzma;
- includes only shared liblzma in the final package;
- links xzdec and lzmadec against static liblzma while
avoiding libpthread dependency.
PKG=/tmp/xz-pkg
tar xf xz-x.y.z.tar.gz
cd xz-x.y.z
./configure \
--prefix=/usr \
--sysconfdir=/etc \
CFLAGS='-march=i686 -O2'
make
make DESTDIR=$PKG install-strip
rm -f $PKG/usr/lib/lib*.a
sed -i "s/^old_library=.*$/old_library=''/" $PKG/usr/lib/lib*.la
make clean
./configure \
--prefix=/usr \
--sysconfdir=/etc \
--disable-shared \
--disable-nls \
--disable-encoders \
--enable-small \
--disable-threads \
CFLAGS='-march=i686 -Os'
make -C src/liblzma
make -C src/xzdec
make -C src/xzdec DESTDIR=$PKG install-strip
cp -a extra $PKG/usr/share/doc/xz
