<chapter xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xml:id="chap-package-notes">

<title>Package Notes</title>

<para>This chapter contains information about how to use and maintain
the Nix expressions for a number of specific packages, such as the
Linux kernel or X.org.</para>


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<section xml:id="sec-linux-kernel">

<title>Linux kernel</title>

<para>The Nix expressions to build the Linux kernel are in <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/os-specific/linux/kernel"><filename>pkgs/os-specific/linux/kernel</filename></link>.</para>

<para>The function that builds the kernel has an argument
<varname>kernelPatches</varname> which should be a list of
<literal>{name, patch, extraConfig}</literal> attribute sets, where
<varname>name</varname> is the name of the patch (which is included in
the kernel’s <varname>meta.description</varname> attribute),
<varname>patch</varname> is the patch itself (possibly compressed),
and <varname>extraConfig</varname> (optional) is a string specifying
extra options to be concatenated to the kernel configuration file
(<filename>.config</filename>).</para>

<para>The kernel derivation exports an attribute
<varname>features</varname> specifying whether optional functionality
is or isn’t enabled.  This is used in NixOS to implement
kernel-specific behaviour.  For instance, if the kernel has the
<varname>iwlwifi</varname> feature (i.e. has built-in support for
Intel wireless chipsets), then NixOS doesn’t have to build the
external <varname>iwlwifi</varname> package:

<programlisting>
modulesTree = [kernel]
  ++ pkgs.lib.optional (!kernel.features ? iwlwifi) kernelPackages.iwlwifi
  ++ ...;
</programlisting>

</para>

<para>How to add a new (major) version of the Linux kernel to Nixpkgs:

<orderedlist>

  <listitem>
    <para>Copy the old Nix expression
    (e.g. <filename>linux-2.6.21.nix</filename>) to the new one
    (e.g. <filename>linux-2.6.22.nix</filename>) and update it.</para>
  </listitem>

  <listitem>
    <para>Add the new kernel to <filename>all-packages.nix</filename>
    (e.g., create an attribute
    <varname>kernel_2_6_22</varname>).</para>
  </listitem>

  <listitem>
    <para>Now we’re going to update the kernel configuration.  First
    unpack the kernel.  Then for each supported platform
    (<literal>i686</literal>, <literal>x86_64</literal>,
    <literal>uml</literal>) do the following:

      <orderedlist>

        <listitem>
          <para>Make an copy from the old
          config (e.g. <filename>config-2.6.21-i686-smp</filename>) to
          the new one
          (e.g. <filename>config-2.6.22-i686-smp</filename>).</para>
        </listitem>

        <listitem>
          <para>Copy the config file for this platform
          (e.g. <filename>config-2.6.22-i686-smp</filename>) to
          <filename>.config</filename> in the kernel source tree.
          </para>
        </listitem>

        <listitem>
          <para>Run <literal>make oldconfig
          ARCH=<replaceable>{i386,x86_64,um}</replaceable></literal>
          and answer all questions.  (For the uml configuration, also
          add <literal>SHELL=bash</literal>.)  Make sure to keep the
          configuration consistent between platforms (i.e. don’t
          enable some feature on <literal>i686</literal> and disable
          it on <literal>x86_64</literal>).
          </para>
        </listitem>

        <listitem>
          <para>If needed you can also run <literal>make
          menuconfig</literal>:

            <screen>
$ nix-env -i ncurses
$ export NIX_CFLAGS_LINK=-lncurses
$ make menuconfig ARCH=<replaceable>arch</replaceable></screen>
          
          </para>
        </listitem>

        <listitem>
          <para>Copy <filename>.config</filename> over the new config
          file (e.g. <filename>config-2.6.22-i686-smp</filename>).</para>
        </listitem>

      </orderedlist>
    
    </para>
    
  </listitem>

  <listitem>
    <para>Test building the kernel: <literal>nix-build -A
    kernel_2_6_22</literal>.  If it compiles, ship it!  For extra
    credit, try booting NixOS with it.</para>
  </listitem>

  <listitem>
    <para>It may be that the new kernel requires updating the external
    kernel modules and kernel-dependent packages listed in the
    <varname>kernelPackagesFor</varname> function in
    <filename>all-packages.nix</filename> (such as the NVIDIA drivers,
    AUFS, etc.).  If the updated packages aren’t backwards compatible
    with older kernels, you may need to keep the older versions
    around.</para>
  </listitem>

</orderedlist>

</para>

</section>


<!--============================================================-->

<section xml:id="sec-xorg">

<title>X.org</title>

<para>The Nix expressions for the X.org packages reside in
<filename>pkgs/servers/x11/xorg/default.nix</filename>.  This file is
automatically generated from lists of tarballs in an X.org release.
As such it should not be modified directly; rather, you should modify
the lists, the generator script or the file
<filename>pkgs/servers/x11/xorg/overrides.nix</filename>, in which you
can override or add to the derivations produced by the
generator.</para>

<para>The generator is invoked as follows:

<screen>
$ cd pkgs/servers/x11/xorg
$ cat tarballs-7.5.list extra.list old.list \
  | perl ./generate-expr-from-tarballs.pl
</screen>

For each of the tarballs in the <filename>.list</filename> files, the
script downloads it, unpacks it, and searches its
<filename>configure.ac</filename> and <filename>*.pc.in</filename>
files for dependencies.  This information is used to generate
<filename>default.nix</filename>.  The generator caches downloaded
tarballs between runs.  Pay close attention to the <literal>NOT FOUND:
<replaceable>name</replaceable></literal> messages at the end of the
run, since they may indicate missing dependencies.  (Some might be
optional dependencies, however.)</para>

<para>A file like <filename>tarballs-7.5.list</filename> contains all
tarballs in a X.org release.  It can be generated like this:

<screen>
$ export i="mirror://xorg/X11R7.4/src/everything/"
$ cat $(PRINT_PATH=1 nix-prefetch-url $i | tail -n 1) \
  | perl -e 'while (&lt;>) { if (/(href|HREF)="([^"]*.bz2)"/) { print "$ENV{'i'}$2\n"; }; }' \
  | sort > tarballs-7.4.list
</screen>

<filename>extra.list</filename> contains libraries that aren’t part of
X.org proper, but are closely related to it, such as
<literal>libxcb</literal>.  <filename>old.list</filename> contains
some packages that were removed from X.org, but are still needed by
some people or by other packages (such as
<varname>imake</varname>).</para>

<para>If the expression for a package requires derivation attributes
that the generator cannot figure out automatically (say,
<varname>patches</varname> or a <varname>postInstall</varname> hook),
you should modify
<filename>pkgs/servers/x11/xorg/overrides.nix</filename>.</para>

</section>



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<!--
<section>
  <title>Gnome</title>
  <para>* Expression is auto-generated</para>
  <para>* How to update</para>
</section>
-->


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<!--
<section>
  <title>GCC</title>
  <para>…</para>
</section>
-->

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<section xml:id="sec-eclipse">

  <title>Eclipse</title>

  <para>
    The Nix expressions related to the Eclipse platform and IDE are in
    <link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/editors/eclipse"><filename>pkgs/applications/editors/eclipse</filename></link>.
  </para>

  <para>
    Nixpkgs provides a number of packages that will install Eclipse in
    its various forms, these range from the bare-bones Eclipse
    Platform to the more fully featured Eclipse SDK or Scala-IDE
    packages and multiple version are often available. It is possible
    to list available Eclipse packages by issuing the command:

<screen>
$ nix-env -f '&lt;nixpkgs&gt;' -qaP -A eclipses --description
</screen>

    Once an Eclipse variant is installed it can be run using the
    <command>eclipse</command> command, as expected. From within
    Eclipse it is then possible to install plugins in the usual manner
    by either manually specifying an Eclipse update site or by
    installing the Marketplace Client plugin and using it to discover
    and install other plugins. This installation method provides an
    Eclipse installation that closely resemble a manually installed
    Eclipse.
  </para>

  <para>
    If you prefer to install plugins in a more declarative manner then
    Nixpkgs also offer a number of Eclipse plugins that can be
    installed in an <emphasis>Eclipse environment</emphasis>. This
    type of environment is created using the function
    <varname>eclipseWithPlugins</varname> found inside the
    <varname>nixpkgs.eclipses</varname> attribute set. This function
    takes as argument <literal>{ eclipse, plugins ? [], jvmArgs ? []
    }</literal> where <varname>eclipse</varname> is a one of the
    Eclipse packages described above, <varname>plugins</varname> is a
    list of plugin derivations, and <varname>jvmArgs</varname> is a
    list of arguments given to the JVM running the Eclipse. For
    example, say you wish to install the latest Eclipse Platform with
    the popular Eclipse Color Theme plugin and also allow Eclipse to
    use more RAM. You could then add

<screen>
packageOverrides = pkgs: {
  myEclipse = with pkgs.eclipses; eclipseWithPlugins {
    eclipse = eclipse-platform;
    jvmArgs = [ "-Xmx2048m" ];
    plugins = [ plugins.color-theme ];
  };
}
</screen>

    to your Nixpkgs configuration
    (<filename>~/.nixpkgs/config.nix</filename>) and install it by
    running <command>nix-env -f '&lt;nixpkgs&gt;' -iA
    myEclipse</command> and afterward run Eclipse as usual. It is
    possible to find out which plugins are available for installation
    using <varname>eclipseWithPlugins</varname> by running

<screen>
$ nix-env -f '&lt;nixpkgs&gt;' -qaP -A eclipses.plugins --description
</screen>
  </para>

  <para>
    If there is a need to install plugins that are not available in
    Nixpkgs then it may be possible to define these plugins outside
    Nixpkgs using the <varname>buildEclipseUpdateSite</varname> and
    <varname>buildEclipsePlugin</varname> functions found in the
    <varname>nixpkgs.eclipses.plugins</varname> attribute set. Use the
    <varname>buildEclipseUpdateSite</varname> function to install a
    plugin distributed as an Eclipse update site. This function takes
    <literal>{ name, src }</literal> as argument where
    <literal>src</literal> indicates the Eclipse update site archive.
    All Eclipse features and plugins within the downloaded update site
    will be installed. When an update site archive is not available
    then the <varname>buildEclipsePlugin</varname> function can be
    used to install a plugin that consists of a pair of feature and
    plugin JARs. This function takes an argument <literal>{ name,
    srcFeature, srcPlugin }</literal> where
    <literal>srcFeature</literal> and <literal>srcPlugin</literal> are
    the feature and plugin JARs, respectively.
  </para>

  <para>
    Expanding the previous example with two plugins using the above
    functions we have
<screen>
packageOverrides = pkgs: {
  myEclipse = with pkgs.eclipses; eclipseWithPlugins {
    eclipse = eclipse-platform;
    jvmArgs = [ "-Xmx2048m" ];
    plugins = [
      plugins.color-theme
      (plugins.buildEclipsePlugin {
        name = "myplugin1-1.0";
        srcFeature = fetchurl {
          url = "http://…/features/myplugin1.jar";
          sha256 = "123…";
        };
        srcPlugin = fetchurl {
          url = "http://…/plugins/myplugin1.jar";
          sha256 = "123…";
        };
      });
      (plugins.buildEclipseUpdateSite {
        name = "myplugin2-1.0";
        src = fetchurl {
          stripRoot = false;
          url = "http://…/myplugin2.zip";
          sha256 = "123…";
        };
      });
    ];
  };
}
</screen>
  </para>

</section>

<section xml:id="sec-elm">

<title>Elm</title>

<para>
The Nix expressions for Elm reside in
<filename>pkgs/development/compilers/elm</filename>. They are generated
automatically by <command>update-elm.rb</command> script. One should
specify versions of Elm packages inside the script, clear the
<filename>packages</filename> directory and run the script from inside it.
<literal>elm-reactor</literal> is special because it also has Elm package
dependencies. The process is not automated very much for now -- you should
get the <literal>elm-reactor</literal> source tree (e.g. with
<command>nix-shell</command>) and run <command>elm2nix.rb</command> inside
it. Place the resulting <filename>package.nix</filename> file into
<filename>packages/elm-reactor-elm.nix</filename>.
</para>

</section>

</chapter>
