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https://gitlab.com/libvirt/libvirt.git
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147 lines
6.7 KiB
HTML
147 lines
6.7 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml">
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<body>
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<h1>Project Strategy</h1>
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<p>
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This document attempts to outline the libvirt project strategy for
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the near future. Think of this as a high level vision or to-do list
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setting the direction for the project and its developers to take.
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</p>
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<h2>Language consolidation</h2>
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<p>
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At time of writing libvirt uses the following languages:
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</p>
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<dl>
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<dt>C</dt>
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<dd>The core libvirt library, daemons, and helper tools are all written
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in the C language.</dd>
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<dt>Python</dt>
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<dd>Various supporting build/test scripts are written in Python, with
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compatibility for Python 2 and 3.</dd>
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<dt>Perl</dt>
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<dd>Various supporting build/test scripts are written in Perl. It is
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also used for many syntax-check inline rules</dd>
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<dt>Shell</dt>
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<dd><code>configure</code>, generated by autoconf, is a shell script.
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Shell is also used for some simple build/test scripts. At runtime
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libvirt avoids shell except when using SSH tunnels to a remote
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host</dd>
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<dt>XSLT</dt>
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<dd>The website uses XSLT for its templating system. The API
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documentation is also autogenerated from an XML description
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using XSLT</dd>
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<dt>HTML</dt>
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<dd>The website documentation is all written in plain HTML. Some HTML
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is also auto-generated for API documentation</dd>
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<dt>M4</dt>
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<dd>The autoconf <code>configure</code> script uses a large number of
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M4 macros to generate its content</dd>
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<dt>make</dt>
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<dd>The core build system uses the traditional GNU make recipes</dd>
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<dt>automake</dt>
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<dd>The make recipes use automake's language extensions which are
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then turned into regular make rules</dd>
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<dt>awk/sed</dt>
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<dd>A number of the syntax-check inline rules involve use of awk/sed
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scripts</dd>
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<dt>POD</dt>
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<dd>The command line manual pages are typically written in Perl's POD
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format, and converted to troff</dd>
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</dl>
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<p>
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The wide range of languages used present a knowledge burden for
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developers involved in libvirt, especially when there are multiple
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languages all used in the same problem spaces. This is most notable
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in the build system which uses a combination of shell, M4, make,
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automake, awk, sed, Perl and Python, with debugging requiring
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understanding of the interactions between many languages. The
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popularity of Perl has declined, while Python has become
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more popular. This directly influences the amount and quality of
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contributions that can be expected for programs written in the
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respective languages.
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</p>
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<p>
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The C language has served libvirt well over the years, but its age shows
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giving rise to limitations which negatively impact the project in terms
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of code quality, reliability, and efficiency of development. Most notably
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its lack of memory safety means that many code bugs become trivially
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exploitable security flaws or denial of service. The lack of a high
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level portable runtime results in a lot of effort being spent to
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ensure cross platform portability. The modern languages Rust and Go
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provide viable options for low level systems programming, in a way that
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is not practical with other common languages such as Python and Java.
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There is thus a desire to make use of either Rust or Go, or a combination
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of both, to incrementally replace existing use of C, and also for
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greenfield development.
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</p>
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<p>
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With this in mind the libvirt project has set a vision for language
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usage in the future:
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</p>
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<dl>
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<dt>C</dt>
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<dd>Large parts of the core libvirt library, daemons, and helper tools
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will continue to make use in the C language. Integration of other
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languages will be an incremental, targetted process where they can
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bring the greatest benefit.</dd>
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<dt>Rust / Go</dt>
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<dd>Parts of the core libvirt library, daemons and helper tools are to
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leverage Rust or Go or both to replace C.</dd>
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<dt>Meson</dt>
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<dd>The core build system is to be written in Meson.</dd>
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<dt>Python</dt>
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<dd>Various supporting build/test scripts are written in Python 3
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compatible mode only.</dd>
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<dt>reStructuredText</dt>
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<dd>The website and command man pages are to be written in RST, using
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Sphinx as the engine to convert to end user formats like HTML, troff,
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etc</dd>
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</dl>
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<p>
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Some notable points from the above. Whether the core library / daemons
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will use Rust or Go internally is still to be decided based on more
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detailed evaluation to identify the best fit. The need to link and embed
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this functionality in other processes has complex interactions both at a
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technical and non-technical level. For standalone helper tools, either
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language is viable, but there are fewer concerns around interactions with
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other in-process code from 3rd parties. Thus a different decision may be
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made for daemons/libraries vs tools. Any rewrite proposed for existing
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functionality will have to weigh up the benefits of the new code,
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against the risk of introducing regressions with respect to the previous
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code.
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</p>
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<p>
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The Meson build system is written in Python 3. This directly informs the
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choice of Python 3 as the language for all supporting build scripts,
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re-inforcing the other benefits of Python over Perl, Shell, M4,
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automake, etc. There is no intention to support Python 2 given Meson's
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requirement for Python 3.
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</p>
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<p>
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Using the RST format for documentation allows for the use of XSLT to be
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eliminated from the build process. RST and the Sphinx toolkit are widely
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used, as seen by the huge repository of content on
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<a href="https://readthedocs.org/">Read The Docs</a>.
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The ability to embed raw HTML in the RST docs will greatly facilitate its
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adoption, avoiding the need for a big bang conversion of existing content.
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Given the desire to eliminate Perl usage, replacing the use of POD
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documentation for manual pages is an obvious followup task. RST is the
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obvious choice to achieve alignment with the website, allowing the man
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pages to be easily published online with other docs. It is further
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anticipated that the current API docs generator which uses XSLT to
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convert the XML API description would be converted to something which
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generates RST using Python instead of XSLT.
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</p>
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</body>
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</html>
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