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<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>
<!--============================================================-->
<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>linuxPackagesFor</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 $i | tail -n 1) \
| perl -e 'while (<>) { if (/(href|HREF)="([^"]*.bz2)"/) { print "$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
|