324 lines
12 KiB
XML
324 lines
12 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
|
|
<!DOCTYPE chapter [
|
|
<!ENTITY ndash "–"> <!-- @vcunat likes to use this one ;-) -->
|
|
]>
|
|
<chapter xmlns="http://docbook.org/ns/docbook"
|
|
xmlns:xlink="http://www.w3.org/1999/xlink"
|
|
xml:id="chap-multiple-output">
|
|
<title>Multiple-output packages</title>
|
|
<section xml:id="sec-multiple-outputs-introduction">
|
|
<title>Introduction</title>
|
|
|
|
<para>
|
|
The Nix language allows a derivation to produce multiple outputs, which is
|
|
similar to what is utilized by other Linux distribution packaging systems.
|
|
The outputs reside in separate nix store paths, so they can be mostly
|
|
handled independently of each other, including passing to build inputs,
|
|
garbage collection or binary substitution. The exception is that building
|
|
from source always produces all the outputs.
|
|
</para>
|
|
|
|
<para>
|
|
The main motivation is to save disk space by reducing runtime closure sizes;
|
|
consequently also sizes of substituted binaries get reduced. Splitting can
|
|
be used to have more granular runtime dependencies, for example the typical
|
|
reduction is to split away development-only files, as those are typically
|
|
not needed during runtime. As a result, closure sizes of many packages can
|
|
get reduced to a half or even much less.
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
The reduction effects could be instead achieved by building the parts in
|
|
completely separate derivations. That would often additionally reduce
|
|
build-time closures, but it tends to be much harder to write such
|
|
derivations, as build systems typically assume all parts are being built at
|
|
once. This compromise approach of single source package producing multiple
|
|
binary packages is also utilized often by rpm and deb.
|
|
</para>
|
|
</note>
|
|
</section>
|
|
<section xml:id="sec-multiple-outputs-installing">
|
|
<title>Installing a split package</title>
|
|
|
|
<para>
|
|
When installing a package via <varname>systemPackages</varname> or
|
|
<command>nix-env</command> you have several options:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
You can install particular outputs explicitly, as each is available in the
|
|
Nix language as an attribute of the package. The
|
|
<varname>outputs</varname> attribute contains a list of output names.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
You can let it use the default outputs. These are handled by
|
|
<varname>meta.outputsToInstall</varname> attribute that contains a list of
|
|
output names.
|
|
</para>
|
|
<para>
|
|
TODO: more about tweaking the attribute, etc.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
NixOS provides configuration option
|
|
<varname>environment.extraOutputsToInstall</varname> that allows adding
|
|
extra outputs of <varname>environment.systemPackages</varname> atop the
|
|
default ones. It's mainly meant for documentation and debug symbols, and
|
|
it's also modified by specific options.
|
|
</para>
|
|
<note>
|
|
<para>
|
|
At this moment there is no similar configurability for packages installed
|
|
by <command>nix-env</command>. You can still use approach from
|
|
<xref linkend="sec-modify-via-packageOverrides" /> to override
|
|
<varname>meta.outputsToInstall</varname> attributes, but that's a rather
|
|
inconvenient way.
|
|
</para>
|
|
</note>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
<section xml:id="sec-multiple-outputs-using-split-packages">
|
|
<title>Using a split package</title>
|
|
|
|
<para>
|
|
In the Nix language the individual outputs can be reached explicitly as
|
|
attributes, e.g. <varname>coreutils.info</varname>, but the typical case is
|
|
just using packages as build inputs.
|
|
</para>
|
|
|
|
<para>
|
|
When a multiple-output derivation gets into a build input of another
|
|
derivation, the <varname>dev</varname> output is added if it exists,
|
|
otherwise the first output is added. In addition to that,
|
|
<varname>propagatedBuildOutputs</varname> of that package which by default
|
|
contain <varname>$outputBin</varname> and <varname>$outputLib</varname> are
|
|
also added. (See <xref linkend="multiple-output-file-type-groups" />.)
|
|
</para>
|
|
</section>
|
|
<section xml:id="sec-multiple-outputs-">
|
|
<title>Writing a split derivation</title>
|
|
|
|
<para>
|
|
Here you find how to write a derivation that produces multiple outputs.
|
|
</para>
|
|
|
|
<para>
|
|
In nixpkgs there is a framework supporting multiple-output derivations. It
|
|
tries to cover most cases by default behavior. You can find the source
|
|
separated in
|
|
<<filename>nixpkgs/pkgs/build-support/setup-hooks/multiple-outputs.sh</filename>>;
|
|
it's relatively well-readable. The whole machinery is triggered by defining
|
|
the <varname>outputs</varname> attribute to contain the list of desired
|
|
output names (strings).
|
|
</para>
|
|
|
|
<programlisting>outputs = [ "bin" "dev" "out" "doc" ];</programlisting>
|
|
|
|
<para>
|
|
Often such a single line is enough. For each output an equally named
|
|
environment variable is passed to the builder and contains the path in nix
|
|
store for that output. Typically you also want to have the main
|
|
<varname>out</varname> output, as it catches any files that didn't get
|
|
elsewhere.
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
There is a special handling of the <varname>debug</varname> output,
|
|
described at <xref linkend="stdenv-separateDebugInfo" />.
|
|
</para>
|
|
</note>
|
|
|
|
<section xml:id="multiple-output-file-binaries-first-convention">
|
|
<title><quote>Binaries first</quote></title>
|
|
|
|
<para>
|
|
A commonly adopted convention in <literal>nixpkgs</literal> is that
|
|
executables provided by the package are contained within its first output.
|
|
This convention allows the dependent packages to reference the executables
|
|
provided by packages in a uniform manner. For instance, provided with the
|
|
knowledge that the <literal>perl</literal> package contains a
|
|
<literal>perl</literal> executable it can be referenced as
|
|
<literal>${pkgs.perl}/bin/perl</literal> within a Nix derivation that needs
|
|
to execute a Perl script.
|
|
</para>
|
|
|
|
<para>
|
|
The <literal>glibc</literal> package is a deliberate single exception to
|
|
the <quote>binaries first</quote> convention. The <literal>glibc</literal>
|
|
has <literal>libs</literal> as its first output allowing the libraries
|
|
provided by <literal>glibc</literal> to be referenced directly (e.g.
|
|
<literal>${stdenv.glibc}/lib/ld-linux-x86-64.so.2</literal>). The
|
|
executables provided by <literal>glibc</literal> can be accessed via its
|
|
<literal>bin</literal> attribute (e.g.
|
|
<literal>${stdenv.glibc.bin}/bin/ldd</literal>).
|
|
</para>
|
|
|
|
<para>
|
|
The reason for why <literal>glibc</literal> deviates from the convention is
|
|
because referencing a library provided by <literal>glibc</literal> is a
|
|
very common operation among Nix packages. For instance, third-party
|
|
executables packaged by Nix are typically patched and relinked with the
|
|
relevant version of <literal>glibc</literal> libraries from Nix packages
|
|
(please see the documentation on
|
|
<link xlink:href="https://nixos.org/patchelf.html">patchelf</link> for more
|
|
details).
|
|
</para>
|
|
</section>
|
|
|
|
<section xml:id="multiple-output-file-type-groups">
|
|
<title>File type groups</title>
|
|
|
|
<para>
|
|
The support code currently recognizes some particular kinds of outputs and
|
|
either instructs the build system of the package to put files into their
|
|
desired outputs or it moves the files during the fixup phase. Each group of
|
|
file types has an <varname>outputFoo</varname> variable specifying the
|
|
output name where they should go. If that variable isn't defined by the
|
|
derivation writer, it is guessed – a default output name is defined,
|
|
falling back to other possibilities if the output isn't defined.
|
|
</para>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>
|
|
<varname> $outputDev</varname>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
is for development-only files. These include C(++) headers, pkg-config,
|
|
cmake and aclocal files. They go to <varname>dev</varname> or
|
|
<varname>out</varname> by default.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname> $outputBin</varname>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
is meant for user-facing binaries, typically residing in bin/. They go
|
|
to <varname>bin</varname> or <varname>out</varname> by default.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname> $outputLib</varname>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
is meant for libraries, typically residing in <filename>lib/</filename>
|
|
and <filename>libexec/</filename>. They go to <varname>lib</varname> or
|
|
<varname>out</varname> by default.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname> $outputDoc</varname>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
is for user documentation, typically residing in
|
|
<filename>share/doc/</filename>. It goes to <varname>doc</varname> or
|
|
<varname>out</varname> by default.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname> $outputDevdoc</varname>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
is for <emphasis>developer</emphasis> documentation. Currently we count
|
|
gtk-doc and devhelp books in there. It goes to <varname>devdoc</varname>
|
|
or is removed (!) by default. This is because e.g. gtk-doc tends to be
|
|
rather large and completely unused by nixpkgs users.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname> $outputMan</varname>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
is for man pages (except for section 3). They go to
|
|
<varname>man</varname> or <varname>$outputBin</varname> by default.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname> $outputDevman</varname>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
is for section 3 man pages. They go to <varname>devman</varname> or
|
|
<varname>$outputMan</varname> by default.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
<varname> $outputInfo</varname>
|
|
</term>
|
|
<listitem>
|
|
<para>
|
|
is for info pages. They go to <varname>info</varname> or
|
|
<varname>$outputBin</varname> by default.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</section>
|
|
|
|
<section xml:id="sec-multiple-outputs-caveats">
|
|
<title>Common caveats</title>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
Some configure scripts don't like some of the parameters passed by
|
|
default by the framework, e.g. <literal>--docdir=/foo/bar</literal>. You
|
|
can disable this by setting <literal>setOutputFlags = false;</literal>.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
The outputs of a single derivation can retain references to each other,
|
|
but note that circular references are not allowed. (And each
|
|
strongly-connected component would act as a single output anyway.)
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Most of split packages contain their core functionality in libraries.
|
|
These libraries tend to refer to various kind of data that typically gets
|
|
into <varname>out</varname>, e.g. locale strings, so there is often no
|
|
advantage in separating the libraries into <varname>lib</varname>, as
|
|
keeping them in <varname>out</varname> is easier.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Some packages have hidden assumptions on install paths, which complicates
|
|
splitting.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
</section>
|
|
<!--Writing a split derivation-->
|
|
</chapter>
|