650 lines
27 KiB
TeX
650 lines
27 KiB
TeX
%% $Id: proposal.tex,v 1.2 2004/02/29 20:00:47 michel-schinz Exp $
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%% TODO
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%% - clean up permissions mess
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\documentclass[a4paper,12pt]{article}
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\usepackage[latin1]{inputenc}
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\usepackage{a4wide, palatino, url, hyperref}
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\newcommand{\file}{\begingroup \urlstyle{tt}\Url}
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\newcommand{\envvar}[1]{\texttt{#1}}
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\newcommand{\cloption}[1]{\texttt{#1}}
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\newcommand{\package}[1]{\texttt{#1}}
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\newcommand{\layout}[1]{\texttt{#1}}
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\newcommand{\location}[1]{\texttt{#1}}
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\newcommand{\ident}[1]{\texttt{#1}}
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\newcommand{\define}[3]{%
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\noindent%
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(\texttt{#1} \textit{#2})\hfill\textit{(#3)}\\[0.5em]%
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}
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\newcommand{\definep}[2]{\define{#1}{#2}{procedure}}
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\newcommand{\defines}[2]{\define{#1}{#2}{syntax}}
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\newcommand{\param}[1]{\emph{#1}}
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\newenvironment{rationale}%
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{\begin{quotation}\noindent\textbf{Rationale}}%
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{\end{quotation}}
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\newenvironment{example}%
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{\begin{quotation}\noindent\textbf{Example}}%
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{\end{quotation}}
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\begin{document}
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\title{A proposal for scsh packages}
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\author{Michel Schinz}
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\maketitle
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\section{Introduction}
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\label{sec:introduction}
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The aim of the following proposal is to define a standard for the
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packaging, distribution, installation, use and removal of libraries
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for scsh. Such packaged libraries are called \emph{scsh packages} or
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simply \emph{packages} below.
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This proposal attempts to cover both libraries containing only Scheme
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code and libraries containing additional C code. It does not try to
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cover applications written in scsh, which are currently considered to
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be outside of its scope.
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\subsection{Package identification and naming}
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Packages are identified by a globally-unique name. This name should
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start with an ASCII letter (a-z or A-Z) and should consist only of
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ASCII letters, digits or underscore characters `\verb|_|'. Package
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names are case-sensitive, but there should not be two packages with
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names which differ only by their capitalisation.
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\begin{rationale}
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This restriction on package names ensures that they can be used to
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name directories on current operating systems.
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\end{rationale}
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Several versions of a given package can exist. A version is identified
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by a sequence of non-negative integers. Versions are ordered
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lexicographically.
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A version has a printed representation which is obtained by separating
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(the printed representation of) its components by dots. For example,
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the printed representation of a version composed of the integer 1
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followed by the integer 2 is the string \texttt{1.2}. Below, versions
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are usually represented using their printed representation for
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simplicity, but it is important to keep in mind that versions are
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sequences of integers, not strings.
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A specific version of a package is therefore identified by a name and
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a version. The \emph{full name} of a version of a package is obtained
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by concatenating:
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\begin{itemize}
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\item the name of the package,
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\item a hyphen `\texttt{-}',
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\item the printed representation of the version.
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\end{itemize}
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In what follows, the term \emph{package} is often used to designate a
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specific version of a package, but this should be clear from the
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context.
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\section{Distributing packages}
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Packages are distributed in \texttt{tar} archives, which can
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optionally be compressed by \texttt{gzip} or \texttt{bzip2}. The name
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of the archive is composed by appending:
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\begin{itemize}
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\item the full name of the package,
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\item the string \texttt{.tar} indicating that it's a \texttt{tar}
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archive,
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\item either the string \texttt{.gz} if the archive is compressed
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using \texttt{gzip}, or the string \texttt{.bz2} if the archive is
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compressed using \texttt{bzip2}, or nothing if the archive is not
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compressed.
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\end{itemize}
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\subsection{Archive contents}
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The archive is organised so that it contains one top-level directory
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whose name is the full name of the package. This directory is called
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the \emph{package unpacking directory}. All the files belonging to the
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package are stored below it.
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The unpacking directory contains at least the following files:
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\begin{description}
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\item[\file{install-pkg}] a script performing the installation of the
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package,
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\item[\file{README}] a textual file containing a short description of
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the package,
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\item[\file{COPYING}] a textual file containing the license of the
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package.
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\end{description}
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\section{Downloading and installing packages}
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A package can be installed on a target machine by downloading its
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archive, expanding it and finally running the installation script
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located in the unpacking directory.
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\subsection{Layouts}
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The installation script installs files according to some given
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\emph{layout}. A layout maps abstract \emph{locations} to concrete
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directories on the target machine. For example, a layout could map the
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abstract location \location{doc}, where documentation is stored, to
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the directory \file{/usr/local/share/doc/my_package}.
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Currently, the following abstract locations are defined:
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\begin{description}
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\item[\location{base}] The ``base'' location of a package, where the
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package loading script \file{load.scm} resides.
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\item[\location{active}] Location containing a symbolic link, with the
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same name as the package (excluding the version), pointing to the
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base location of the package. This link is used to designate the
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\emph{active} version of a package\,---\,the one to load when a
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package is requested by giving only its name, without an explicit
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version.
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\item[\location{scheme}] Location containing all Scheme code. If the
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package comes with some examples showing its usage, they are put in
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a sub-directory called \file{examples} of this location.
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\item[\location{lib}] Location containing platform-dependent files,
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like shared libraries. This location contains one sub-directory per
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platform for which packages have been installed, and nothing else.
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\item[\location{doc}] Location containing all the package
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documentation. This location contains one or more sub-directories,
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one per format in which the documentation is available. The contents
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of these sub-directories is standardised as follows, to make it easy
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for users to find the document they need:
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\begin{description}
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\item[\file{html}] Directory containing the HTML documentation of
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the package, if any; this directory should at least contain one
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file called \file{index.html} serving as an entry point to the
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documentation.
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\item[\file{pdf}] Directory containing the PDF documentation of the
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package, if any; this directory should contain at least one file
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called \file{<package_name>.pdf} where \file{<package_name>} is
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the name of the package.
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\item[\file{ps}] Directory containing the PostScript documentation
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of the package, if any; this directory should contain at least one
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file called \file{<package_name>.ps} where \file{<package_name>}
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is the name of the package.
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\item[\file{text}] Directory containing the raw textual
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documentation of the package, if any.
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\end{description}
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\item[\location{misc-shared}] Location containing miscellaneous data
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which does not belong to any directory above, and which is
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platform-independant.
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\end{description}
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The directories to which a layout maps these abstract locations are
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not absolute directories, but rather relative ones. They are relative
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to a \emph{prefix}, specified at installation time using the
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\cloption{--prefix} option, as explained in section
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\ref{sec:inst-proc}.
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\begin{example}
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Let's imagine that a user is installing version 1.2 of a package
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called \package{foo}. This package contains a file called
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\file{COPYING} which has to be installed in sub-directory
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\file{license} of the \location{doc} location. If the user chooses
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to use the default layout, which maps \location{doc} to directory
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\file{<package_full_name>/doc} (see <20>~\ref{sec:scsh-layout}), and
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specifies \file{/usr/local/share/scsh/modules} as a prefix, then the
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\file{COPYING} file will end up in:
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\[
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\underbrace{\mathtt{/usr/local/share/scsh/modules/}}_{1}%
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\underbrace{\mathtt{foo-1.2/doc/}}_{2}%
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\underbrace{\mathtt{license/COPYING}}_{3}
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\]
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Part 1 is the prefix, part 2 is the layout's mapping for the
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\location{doc} location, and part 3 is the file name relative to the
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location.
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\end{example}
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\subsubsection{Predefined layouts}
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\label{sec:predefined-layouts}
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Every installation script comes with a set of predefined layouts which
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serve different aims. They are described below.
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\paragraph{The \layout{scsh} layout}
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\label{sec:scsh-layout}
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The \layout{scsh} layout is the default layout. It maps all locations
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to sub-directories of a single directory, called the package
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installation directory, which contains nothing but the files of the
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package being installed. Its name is simply the full name of the
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package in question, and it resides in the \file{prefix} directory.
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The \layout{scsh} layout maps locations as given in the following
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table, where \file{<package_full_name>} stands for the full name of
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the package:
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\begin{center}
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\begin{tabular}{|l|l|}
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\hline
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\textbf{Location} & \textbf{Directory (relative to prefix)}\\
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\hline
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\location{base} & \file{<package_full_name>} \\
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\location{active} & \file{.} \\
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\location{scheme} & \file{<package_full_name>/scheme} \\
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\location{lib} & \file{<package_full_name>/lib} \\
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\location{doc} & \file{<package_full_name>/doc} \\
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\location{misc-shared} & \file{<package_full_name>} \\
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\hline
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\end{tabular}
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\end{center}
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This layout is well suited for installations performed without the
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assistance of an additional package manager, because it makes many
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common operations easy. For example, finding to which package a file
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belongs is trivial, as is the removal of an installed package.
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\paragraph{The \layout{fhs} layout}
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\label{sec:fhs-layout}
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The \layout{fhs} layout maps locations according to the File Hierarchy
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Standard (FHS, see \href{http://www.pathname.com/fhs/}%
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{http://www.pathname.com/fhs/}), as follows:
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\begin{center}
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\begin{tabular}{|l|l|}
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\hline
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\textbf{Location} & \textbf{Directory (relative to prefix)}\\
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\hline
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\layout{base} & \file{share/scsh/modules/<package_full_name>} \\
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\layout{active} & \file{share/scsh/modules} \\
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\layout{scheme} & \file{share/scsh/modules/<package_full_name>/scheme} \\
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\layout{lib} & \file{lib/scsh/modules/<package_full_name>} \\
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\layout{doc} & \file{share/doc/<package_full_name>} \\
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\layout{misc-shared} & \file{share/scsh/modules/<package_full_name>} \\
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\hline
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\end{tabular}
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\end{center}
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The main advantage of this layout is that it adheres to the FHS
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standard, and is therefore compatible with several packaging policies,
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like \href{http://www.debian.org/}{Debian}'s,
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\href{http://fink.sourceforge.net/}{Fink}'s and others. Its main
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drawback is that files belonging to a given package are scattered, and
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therefore hard to find when removing or upgrading a package. Its use
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should therefore be considered only if third-party tools are available
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to track files belonging to a package.
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%% \subsection{File permissions}
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%% TODO
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\subsection{Installation procedure}
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\label{sec:inst-proc}
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Packages are installed using the \file{install-pkg} script located in
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the package archive. This script must be given the name of the prefix
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using the \cloption{--prefix} option. It also accepts the following
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options:
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\begin{center}
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\begin{tabular}{lp{.6\textwidth}}
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\cloption{--layout} name & Specifies the layout to use (see <20>~\ref{sec:predefined-layouts}). \\
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\cloption{--verbose} & Print messages about what is being done. \\
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\cloption{--dry-run} & Print what actions would be performed to install the package, but do not perform them. \\
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\cloption{--inactive} & Do not activate package after installing it. \\
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\cloption{--non-shared-only} & Only install platform-dependent files, if any. \\
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\cloption{--force} & Overwrite existing files during installation. \\
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\cloption{--no-user-defaults} & Don't read user defaults in \file{.scsh-pkg-defaults} (see <20>~\ref{sec:user-preferences}). \\
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\end{tabular}
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\end{center}
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\subsubsection{User preferences}
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\label{sec:user-preferences}
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Users can store default values for the options passed to the
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installation script by storing them in a file called
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\file{.scsh-pkg-defaults.scm} residing in their home directory. This
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file must contain exactly one Scheme expression whose value is an
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association list. The keys of this list, which must be symbols,
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identify options and the values specify the default value for these
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options. The contents of this file is implicitely quasi-quoted.
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The values stored in this file override the default values of the
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options, but they are in turn overriden by the values specified on the
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command line of the installation script. Furthermore, it is possible
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to ask for this file to be completely ignored by passing the
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\cloption{--no-user-defaults} option to the installation script.
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\begin{example}
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A \file{.scsh-pkg-defaults} file containing the following:
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\begin{verbatim}
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;; Default values for scsh packages installation
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((layout . "fhs")
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(prefix . "/usr/local/share/scsh/modules")
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(verbose . #t))
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\end{verbatim}
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specifies default values for the \cloption{--layout},
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\cloption{--prefix} and \cloption{--verbose} options.
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\end{example}
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%% \subsection{Creating images}
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%% TODO (my current idea is to add support to install-lib to easily
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%% create an image containing the package being installed, and maybe some
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%% structures opened. Then, at install time, users could say that they
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%% want an image to be created, and the install script would do that).
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\section{Using packages}
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To use a package, its \emph{loading script} must be loaded in
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Scheme~48's exec package. The loading script for a package is a file
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written in the Scheme 48 exec language, whose name is \file{load.scm}
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and which resides in the \location{base} location.
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To load this file, one typically uses scsh's \cloption{-lel} option
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along with a properly defined \envvar{SCSH\_LIB\_DIRS} environment
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variable.
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Scsh has a list of directories, called the library directories, in
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which it looks for files to load when the options \cloption{-ll} or
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\cloption{-lel} are used. This list can be given a default value
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during scsh's configuration, and this value can be overridden by
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setting the environment variable \envvar{SCSH\_LIB\_DIRS} before running
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scsh.
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In order for scsh to find the package loading scripts, one must make
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sure that scsh's library search path contains the names of all
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\location{active} locations which containing packages.
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The names of these directories should not end with a slash `\verb|/|',
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as this forces scsh to search them recursively. This could
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\emph{drastically} slow down scsh when looking for packages.
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\begin{example}
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Let's imagine a machine on which the system administrator installs
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scsh packages according to the \layout{fhs} layout in prefix
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directory \file{/usr/local}. The \location{active} location for
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these packages corresponds to the directory
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\file{/usr/local/share/scsh/modules}, according to section
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\ref{sec:fhs-layout}.
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Let's also imagine that there is a user called \texttt{john} on this
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machine, who installs additional scsh packages for himself in his
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home directory, using \file{/home/john/scsh-packages} as a prefix.
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To ease their management, he uses the \layout{scsh} layout. The
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\location{active} location for these packages corresponds to the
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directory \file{/home/john/scsh-packages}, according to section
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\ref{sec:scsh-layout}.
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In order to be able to use scsh packages installed both by the
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administrator and by himself, user \texttt{john} needs to put both
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active directories in his \envvar{SCSH\_LIB\_DIRS} environment
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variable. The value of this variable will therefore be:
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\begin{small}
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\begin{verbatim}
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"/usr/local/share/scsh/modules" "/home/john/scsh-packages"
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\end{verbatim}
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\end{small}
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Now, in order to use packages \package{foo} and \package{bar} in one
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of his script, user \texttt{john} just needs to load their loading
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script using the \cloption{-lel} option when invoking scsh, as
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follows:
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\begin{verbatim}
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-lel foo/load.scm -lel bar/load.scm
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\end{verbatim}
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\end{example}
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\section{Authoring packages}
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Once the Scheme and/or C code for a package has been written, the last
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step in turning it into a standard package as defined by this proposal
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is to write the installation script.
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This script could be written fully by the package author, but in order
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to simplify this task a small scsh installation framework is provided.
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This framework is composed of several files which are meant to be
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included in the package archive. These files are:
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\begin{description}
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\item[\file{install-pkg}] A trivial \texttt{sh} script which launches
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scsh on the main function of the installation library, passing it
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all the arguments given by the user.
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\item[\file{install-lib.scm}] The code for the installation library,
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whose public interface is documented below.
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\item[\file{install-lib-module.scm}] Scheme 48 interface and structure
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definitions for the installation library.
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\end{description}
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As explained above, when the \file{install-pkg} script is invoked, it
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launches scsh on the main function of the installation library, which
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does the following:
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\begin{enumerate}
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\item parse the command line arguments (e.g the \cloption{--prefix}
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option),
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\item load the package definition file, a (Scheme) file called
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\file{pkg-def.scm}, which is supplied by the package author and
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which contains one or several package definition statements, and
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\item install the packages which were defined in the previous step.
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\end{enumerate}
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Most package definition files should contain a single package
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definition, but the ability to define several packages in one file can
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sometimes be useful.
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The main job of the package author is therefore to write the package
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definition file, \file{pkg-def.scm}. This file is mostly composed of a
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package definition statement, which specifies the name, version and
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installation code for the package. The package definition statement is
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expressed using the \ident{define-package} form, documented in the
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next section.
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\subsection{Installation library}
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\label{sec:install-library}
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\subsubsection{Package definition}
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\defines{define-package}{name version extension body ...}%
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Define a package to be installed. \param{Name} (a string) is the
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package name, \param{version} (a list of integers) is its version,
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\param{extensions} is a list of extensions (see below), and
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\param{body} is the list of statements to be evaluated in order to
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install the package.
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The installation statements typically use functions of the
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installation library in order to install files in their target
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location. The available functions are presented below.
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\param{Extensions} is currently used only to specify additional
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command-line arguments, but in the future it could serve other
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purposes. It consists in a list of lists, each one starting with a
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symbol identifying the extension, followed by extension-specific
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parameters.
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\begin{description}
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\item[options] enables the script to define additional command-line
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||
options. It accepts nine parameters in total, with the last three
|
||
being optional. The description of these parameters follows, in the
|
||
order in which they should appear:
|
||
\begin{description}
|
||
\item[\param{name}] (a symbol) is the name of the option, without
|
||
the initial double hyphen (\verb|--|),
|
||
\item[\param{help-text}] (a string) describes the option for the
|
||
user,
|
||
\item[\param{arg-help-text}] (a string) describes the option's
|
||
argument (if any) for the user,
|
||
\item[\param{required-arg?}] (a boolean) says whether this option
|
||
requires an argument or not,
|
||
\item[\param{optional-arg?}] (a boolean) says whether this option's
|
||
argument can be omitted or not,
|
||
\item[\param{default}] (anything) is the default value for the
|
||
option,
|
||
\item[\param{parser}] (a function from string to anything) parses
|
||
the option, i.e. turns its string representation into its internal
|
||
value,
|
||
\item[\param{unparser}] (a function from anything to string) turns
|
||
the internal representation of the option into a string,
|
||
\item[\param{transformer}] is a function taking the current value of
|
||
the option, the value given by the user and returning its new
|
||
value.
|
||
\end{description}
|
||
By default, \param{parser} and \param{unparser} are the identity
|
||
function, and \param{transformer} is a function which takes two
|
||
arguments and returns the second (i.e. the current value of the
|
||
option is simply replaced by the one given).
|
||
\end{description}
|
||
|
||
\subsubsection{Content installation}
|
||
|
||
\definep{install-file}{file location [target-dir]}%
|
||
Install the given \param{file} in the sub-directory \param{target-dir}
|
||
(which must be a relative directory) of the given \param{location}.
|
||
\param{Target-dir} is \file{.} by default.
|
||
|
||
If the directory in which the file is about to be installed does not
|
||
exist, it is created along with all its parents, as needed. If
|
||
\param{file} is a string, then the installed file will have the same
|
||
name as the original one. If \param{file} is a pair, then its first element
|
||
specifies the name of the source file, and its second element the name
|
||
it will have once installed. The second element must be a simple file
|
||
name, without any directory part.
|
||
|
||
\vspace{1em}
|
||
\definep{install-files}{file-list location [target-dir]}%
|
||
Like \ident{install-file} but for several files, which are specified
|
||
as a list. Each element in the list can be either a simple string or a
|
||
pair, as explained above.
|
||
|
||
\vspace{1em}
|
||
\definep{install-directory}{directory location [target-dir]}%
|
||
Install the given \param{directory} and all its contents, including
|
||
sub-directories, in sub-directory \param{target-dir} of
|
||
\param{location}. This is similar to what \param{install-file} does,
|
||
but for complete hierarchies.
|
||
|
||
Notice that \param{directory} will be installed as a sub-directory of
|
||
\param{target-dir}.
|
||
|
||
\vspace{1em}
|
||
\definep{install-directories}{dir-list location [target-dir]}%
|
||
Install several directories in one go.
|
||
|
||
\vspace{1em}
|
||
\definep{install-directory-contents}{directory location [target-dir]}%
|
||
Install the contents of the given \param{directory} in sub-directory
|
||
\param{target} of \param{location}.
|
||
|
||
\vspace{1em}
|
||
\definep{install-string}{string location [target-dir]}%
|
||
Install the contents of \param{string} in sub-directory
|
||
\param{target-dir} of \param{location}.
|
||
|
||
\subsubsection{Queries}
|
||
|
||
\definep{get-directory}{location install?}%
|
||
Get the absolute name of the directory to which the current layout
|
||
maps the abstract \param{location}. If \param{install?} is true, the
|
||
directory is the one valid during installation; If it is false, the
|
||
directory is the one valid after installation, that is when the
|
||
package is later used.
|
||
|
||
The distinction between installation-time and usage-time directories
|
||
is necessary to support staged installation, as performed by package
|
||
managers like Debian's APT.
|
||
|
||
\vspace{1em}
|
||
\definep{get-option-value}{option}%
|
||
Return the value of the given command-line \param{option} (a symbol).
|
||
This can be used to get the value of predefined options (like
|
||
\cloption{--dry-run}) or package-specific options.
|
||
|
||
\subsubsection{Load script generation}
|
||
|
||
\definep{with-output-to-load-script*}{thunk}%
|
||
Evaluate \param{thunk} with the current output opened on the loading
|
||
script of the current package. If this script was already existing,
|
||
its previous contents is deleted.
|
||
|
||
\vspace{1em}
|
||
\defines{with-output-to-load-script}{body ...}%
|
||
Syntactic sugar for \ident{with-output-to-load-script*}.
|
||
|
||
\vspace{1em}
|
||
\definep{write-to-load-script}{s-expression}%
|
||
Pretty-print the \param{s-expression} to the loading script of the
|
||
current package. If this script was already existing, its previous
|
||
contents is deleted.
|
||
|
||
\begin{example}
|
||
A typical package definition file for a simple package called
|
||
\package{pkg} whose version is 1.2 could look like this:
|
||
\begin{verbatim}
|
||
(define-package "pkg" (1 2) ()
|
||
(install-file "load.scm" 'base)
|
||
(install-directory-contents "scheme" 'scheme)
|
||
(install-file ("LICENSE" . "COPYING") 'doc)
|
||
(install-directory-contents "doc" 'doc))
|
||
\end{verbatim}
|
||
|
||
With such a definition, invoking the installation script with
|
||
\file{/usr/local/} as prefix and \layout{fhs} as layout has the
|
||
following effects:
|
||
\begin{enumerate}
|
||
\item The base directory \file{/usr/local/share/scsh/modules/pkg-1.2}
|
||
is created and file \file{load.scm} is copied to it.
|
||
\item All the contents of the directory called \file{scheme} is copied
|
||
to directory \file{/usr/local/share/scsh/modules/pkg-1.2/scheme}
|
||
which is created before, if needed.
|
||
\item File \file{LICENSE} is copied to directory
|
||
\file{/usr/local/share/doc/pkg-1.2/} with name \file{COPYING}.
|
||
\item All the contents of the directory called \file{doc} is copied to
|
||
directory \file{/usr/local/share/doc/pkg-1.2/}
|
||
\item The package is activated by creating a symbolic link with name
|
||
\file{/usr/local/share/scsh/modules/pkg} pointing to
|
||
\file{./pkg-1.2}
|
||
\end{enumerate}
|
||
\end{example}
|
||
|
||
\subsection{Packages containing C code (for shared libraries)}
|
||
|
||
Packages containing C code are more challenging to write, since all
|
||
the problems related to C's portability and incompatibilities between
|
||
the APIs of the various platforms have to be accounted for.
|
||
Fortunately, the GNU Autoconf system simplifies the management of
|
||
these problems, and authors of scsh packages containing C code are
|
||
strongly encouraged to use it.
|
||
|
||
%% Integrating Autoconf into the installation procedure should not be a
|
||
%% major problem thanks to scsh's ability to run separate programs.
|
||
|
||
\section{Packaging packages}
|
||
|
||
Most important Unix systems today have one (or several) package
|
||
management systems which ease the installation of packages on a
|
||
system. In order to avoid confusion between these packages and the
|
||
scsh packages discussed above, they will be called \emph{system
|
||
packages} in what follows.
|
||
|
||
It makes perfect sense to provide system packages for scsh packages.
|
||
System packages should as much as possible try to use the standard
|
||
installation script described above to install scsh packages. This
|
||
script currently provides some support for staged installations, which
|
||
are required by several packaging systems.
|
||
|
||
This support is provided through an additional option,
|
||
\cloption{--dest-dir}, which specifies the root directory in which to
|
||
install files. The files will then have to be moved from this location
|
||
to their final location by the system packaging tools.
|
||
|
||
(The \cloption{--dest-dir} option plays the same role as the
|
||
\envvar{DESTDIR} variable which is typically given to \texttt{make
|
||
install}, for makefiles which support staging directories).
|
||
|
||
%% \section{Glossary}
|
||
%% TODO define the following terms
|
||
%% Version
|
||
%% Target machine
|
||
%% Package
|
||
%% (Package) unpacking directory
|
||
%% Layout
|
||
%% (Abstract) location
|
||
%% Package loading script
|
||
|
||
\end{document} |