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