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