From 1ffa946beb073737752983fc68a5c3ad12c1e45e Mon Sep 17 00:00:00 2001 From: P. J. McDermott Date: Wed, 30 May 2012 02:13:54 -0400 Subject: Remove full task descriptions from "dev". --- (limited to 'dev.html') diff --git a/dev.html b/dev.html index 54082f0..37fd1e6 100755 --- a/dev.html +++ b/dev.html @@ -37,53 +37,17 @@

All packages are cross-built using a toolchain consisting of kernel headers, GNU Binutils, GCC, and a standard C/C++ library. The cortexa8-linux-eglibc port, for example, is currently built using Linux-libre 3.2.7, GMP 5.0.2, MPFR 3.1.0, MPC 0.9, Binutils 2.22, GCC 4.6.2, and EGLIBC 2.15.

This operating system currently supports the following programming languages: C (ISO/IEC 9899 as implemented by GCC), C++ (ISO/IEC 14882 as implemented by GCC), UNIX shell command language (POSIX.1-2008 XCU), and microprocessor assembly languages (with syntax and directives as implemented in GNU as). Support for more languages (e.g. Perl and Python) will come as their respective interpreters and compilers are packaged; this may take time as these programs usually have many build-time and run-time dependencies and some of these programs cannot easily be cross-built.

Remaining Tasks

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The following is an overview of development projects that need to be done before the operating system can be considered ready for production use.

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Boot Sequencing

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Currently, service init scripts are provided by the monolithic initscripts binary package. These init scripts are executed in the lexicographic order of the symbolic links matching /etc/rc.d/S* that target them. The names of these symbolic links are currently hardcoded in the build makefile of the basefiles source package. This monolithic packaging and hardcoding of link names is a temporary and poor technical solution that doesn't scale with the number and selection of services that can be installed on a system. Init scripts should instead be provided by the packages that provide the relevant system services. The order in which init scripts are executed should be determined by dynamic boot sequencing based on inter-service dependency metadata.

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This boot sequencing can be done when the system boots or after a new system service is installed. For reference, NetBSD uses a program called "rcorder" to determine a boot sequence at boot time. Many GNU/Linux distributions follow (to some degree) the Linux Standard Base (LSB) specification, which defines "Comment Conventions" for dependency metadata and a method for installing sequentially-named symbolic links. Conforming implementations perform boot sequencing at the time of service installation. Because boot sequencing at boot time can slow down system booting, it is better to perform boot sequencing at install time.

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Thus, generally speaking, the solution to be adopted in this system is to make packages that provide system services also include the necessary init scripts (installed in /etc/init.d), to include inter-service dependency metadata in init scripts, and to use a tool at the time of service package installation to generate sequentially-named symoblic links in /etc/rc.d.

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An obvious boot sequencing tool is "insserv" maintained by Werner Fink and used by Debian and openSUSE. However, this C program (in compliance with the LSB) assumes the use of runlevels. This operating system uses the init daemon of BusyBox, which doesn't support runlevels. Therefore, we'll need to either modify insserv to work without runlevels or write our own tool for installing symbolic links to init scripts.

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Additionally, we need to decide how completely we'll conform, if at all, with the LSB in this area.

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Multiarch

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Multiarch refers to the ability to install and use packages built for non-native architectures. It is currently being documented and implemented in Debian and Ubuntu. Multiarch is useful for this distribution because it makes cross compiling easy (see "Package Cross Building Tool" and "Multiarch Cross Toolchain Packages" below).

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Simply speaking, there are six aspects of a multiarch implementation:

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In summary, there is much design work to be done, opkg and opkhelper must be modified to support multiarch, and certain packages will need to be built to handle multiarch library paths. Of course Debian is a great reference implementation, but there still remains much original work to be done.

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Installation Bootstrap Tool

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A tool similar to debootstrap of Debian needs to be written to bootstrap the installation of a basic system. It can be used for building packages (see "Package Cross Building Tool" below) or installing the operating system on hardware targets.

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Basically, the tool would fetch from the package archive the index of packages, determine which packages need to be installed, download each package, and unpack each package. Since the package manager may not be available, the tool must handle dependency resolution and package unpacking on its own.

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We can't use debootstrap, since the formats of our binary packages and package archives differ slightly from those of Debian. But we can model our tool after debootstrap or even just fork debootstrap.

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Package Cross Building Tool

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A tool similar to pbuilder and sbuild of Debian needs to be written to build packages within a chroot environment containing a base system installed by the installation bootstrap tool. It needs to support cross building of packages using multiarch cross toolchains.

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Multiarch Cross Toolchain Packages

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Needed are packages of toolchain components (e.g. GCC and EGLIBC) that use multiarch library paths.

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There is currently a Google Summer of Code 2012 project to develop such packages for Debian.

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There are a number of development projects that remain to be done.

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Boot Sequencing
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A flexible method of determining the order in which init scripts should be executed.
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Multiarch
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The ability to install and use packages built for non-native architectures.
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Installation Bootstrap Tool
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A tool to bootstrap the installation of a basic system.
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Package Cross Building Tool +
A tool to build packages within a chroot environment
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Multiarch Cross Toolchain Packages
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Packages of toolchain components that use multiarch library paths.
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