220 lines
8.6 KiB
Org Mode
220 lines
8.6 KiB
Org Mode
-*- mode: org; coding: utf-8; -*-
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#+TITLE: Hacking GNU Guix and Its Incredible Distro
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Copyright © 2012, 2013 Ludovic Courtès <ludo@gnu.org>
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Copying and distribution of this file, with or without modification,
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are permitted in any medium without royalty provided the copyright
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notice and this notice are preserved.
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* Running Guix before it is installed
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Command-line tools can be used even if you have not run "make install".
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To do that, prefix each command with ‘./pre-inst-env’, as in:
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./pre-inst-env guix build --help
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Similarly, for a Guile session using the Guix modules:
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./pre-inst-env guile -c '(use-modules (guix utils)) (pk (%current-system))'
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The ‘pre-inst-env’ script sets up all the environment variables
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necessary to support this.
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* The Perfect Setup
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The Perfect Setup to hack on Guix is basically the perfect setup used
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for Guile hacking (info "(guile) Using Guile in Emacs"). First, you
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need more than an editor, you need [[http://www.gnu.org/software/emacs][Emacs]], empowered by the wonderful
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[[http://nongnu.org/geiser/][Geiser]].
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Geiser allows for interactive and incremental development from within
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Emacs: code compilation and evaluation from within buffers, access to
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on-line documentation (docstrings), context-sensitive completion, M-. to
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jump to an object definition, a REPL to try out your code, and more.
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To actually edit the code, Emacs already has a neat Scheme mode. But in
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addition to that, you must not miss [[http://www.emacswiki.org/emacs/ParEdit][Paredit]]. It provides facilities to
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directly operate on the syntax tree, such as raising an s-expression or
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wrapping it, swallowing or rejecting the following s-expression, etc.
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* Packaging Guidelines
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The GNU distribution is about respecting the freedom of users. Consequently,
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it contains only free software as defined at
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http://www.gnu.org/philosophy/free-sw.html .
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In addition, we follow the [[http://www.gnu.org/distros/free-system-distribution-guidelines.html][free software distribution guidelines]]. Among other
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things, this means that the distribution tries hard not to steer users towards
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obtaining information about non-free software.
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* Adding new packages
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Package recipes in Guix look like this:
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#+BEGIN_SRC scheme
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(package
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(name "nettle")
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(version "2.5")
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(source
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(origin
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(method url-fetch)
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(uri (string-append "mirror://gnu/nettle/nettle-"
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version ".tar.gz"))
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(sha256
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(base32
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"0wicr7amx01l03rm0pzgr1qvw3f9blaw17vjsy1301dh13ll58aa"))))
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(build-system gnu-build-system)
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(inputs `(("m4" ,m4)))
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(propagated-inputs `(("gmp" ,gmp)))
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(home-page
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"http://www.lysator.liu.se/~nisse/nettle/")
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(synopsis "GNU Nettle, a cryptographic library")
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(description
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"Nettle is a cryptographic library...")
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(license gpl2+))
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#+END_SRC
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Such a recipe can be written by hand, and then tested by running
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‘./pre-inst-env guix build nettle’.
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When writing the recipe, the base32-encoded SHA256 hash of the source
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code tarball, which can be seen in the example above, can be obtained by
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running:
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guix download http://ftp.gnu.org/gnu/nettle/nettle-2.5.tar.gz
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Alternatively, it is possible to semi-automatically import recipes from
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the [[http://nixos.org/nixpkgs/][Nixpkgs]] software distribution using this command:
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guix import /path/to/nixpkgs/checkout nettle
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The command automatically fetches and converts to Guix the “Nix
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expression” of Nettle.
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* Submitting Patches
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Development is done using the Git distributed version control system. Thus,
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access to the repository is not strictly necessary. We welcome contributions
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in the form of patches as produced by ‘git format-patch’ sent to
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bug-guix@gnu.org. Please write commit logs in the [[http://www.gnu.org/prep/standards/html_node/Change-Logs.html#Change-Logs][GNU ChangeLog format]].
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As you become a regular contributor, you may find it convenient to have write
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access to the repository (see below.)
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* Commit Access
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For frequent contributors, having write access to the repository is
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convenient. When you deem it necessary, feel free to ask for it on the
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mailing list. When you get commit access, please make sure to follow the
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policy below (discussions of the policy can take place on bug-guix@gnu.org.)
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Non-trivial patches should always be posted to bug-guix@gnu.org (trivial
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patches include fixing typos, etc.)
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For patches that just add a new package, and a simple one, it’s OK to commit,
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if you’re confident (which means you successfully built it in a chroot setup.)
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Likewise for package upgrades. We have a mailing list for commit
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notifications (guix-commits@gnu.org), so people can notice. Before pushing
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your changes, make sure to run ‘git pull --rebase’.
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For anything else, please post to bug-guix@gnu.org and leave time for a
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review, without committing anything. If you didn’t receive any reply
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after two weeks, and if you’re confident, it’s OK to commit.
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That last part is subject to being adjusted, allowing individuals to commit
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directly on non-controversial changes on parts they’re familiar with.
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* Porting the Guix distro on a new platform
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** Introduction
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Unlike Make or similar build tools, Guix requires absolutely /all/ the
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dependencies of a build process to be specified.
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For a user-land software distribution, that means that the process that
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builds GCC (then used to build all other programs) must itself be
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specified; and the process to build the C library to build that GCC; and
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the process to build the GCC to build that library; and... See the
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problem? Chicken-and-egg.
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To break that cycle, the distro starts from a set of pre-built
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binaries–usually referred to as “bootstrap binaries.” These include
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statically-linked versions of Guile, GCC, Coreutils, Grep, sed,
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etc., and the GNU C Library.
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This section describes how to build those bootstrap binaries when
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porting to a new platform.
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** When the platform is supported by Nixpkgs
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In that case, the easiest thing is to bootstrap the distro using
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binaries from Nixpkgs.
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To do that, you need to comment out the definitions of
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‘%bootstrap-guile’ and ‘%bootstrap-inputs’ in gnu/packages/bootstrap.scm
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to force the use of Nixpkgs derivations. For instance, when porting to
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‘i686-linux’, you should redefine these variables along these lines:
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#+BEGIN_SRC scheme
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(define %bootstrap-guile
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(nixpkgs-derivation "guile" "i686-linux"))
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(define %bootstrap-inputs
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(compile-time-value
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`(("libc" ,(nixpkgs-derivation "glibc" "i686-linux"))
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,@(map (lambda (name)
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(list name (nixpkgs-derivation name "i686-linux")))
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'("gnutar" "gzip" "bzip2" "xz" "patch"
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"coreutils" "gnused" "gnugrep" "bash"
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"gawk" ; used by `config.status'
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"gcc" "binutils")))))
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#+END_SRC
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That should allow the distro to be bootstrapped.
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Then, the tarballs containing the initial binaries of Guile, Coreutils,
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GCC, libc, etc. need to be built. To that end, run the following
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commands:
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#+BEGIN_SRC sh
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./pre-inst-env guix build -K \
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-e '(@ (gnu packages make-bootstrap) %bootstrap-tarballs)' \
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--system=i686-linux
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#+END_SRC
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These should build tarballs containing statically-linked tools usable on
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that system.
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In the source tree, you need to install binaries for ‘mkdir’, ‘bash’,
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‘tar’, and ‘xz’ under ‘gnu/packages/bootstrap/i686-linux’. These
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binaries can be extracted from the static-binaries tarball built above.
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A rule for ‘gnu/packages/bootstrap/i686-linux/guile-2.0.7.tar.xz’
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needs to be added in ‘Makefile.am’, with the appropriate hexadecimal
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vrepresentation of its SHA256 hash.
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You may then revert your changes to ‘bootstrap.scm’. For the variables
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‘%bootstrap-coreutils&co’, ‘%bootstrap-binutils’, ‘%bootstrap-glibc’,
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and ‘%bootstrap-gcc’, the expected SHA256 of the corresponding tarballs
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for ‘i686-linux’ (built above) must be added.
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This should be enough to bootstrap the distro without resorting to
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Nixpkgs.
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** When the platform is *not* supported by Nixpkgs
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In that case, the bootstrap binaries should be built using whatever
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tools are available on the target platform. That is, the tarballs and
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binaries show above must first be built manually, using the available
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tools.
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They should have the same properties as those built by the Guix recipes
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shown above. For example, all the binaries (except for glibc) must be
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statically-linked; the bootstrap Guile must be relocatable (see patch in
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the Guix distro); the static-binaries tarball must contain the same
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programs (Coreutils, Grep, sed, Awk, etc.); and so on.
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