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-rw-r--r--doc/manual/builtins.xml2
-rw-r--r--doc/manual/release-notes.xml23
-rw-r--r--doc/manual/writing-nix-expressions.xml239
3 files changed, 250 insertions, 14 deletions
diff --git a/doc/manual/builtins.xml b/doc/manual/builtins.xml
index 1ce40a607..b6c886199 100644
--- a/doc/manual/builtins.xml
+++ b/doc/manual/builtins.xml
@@ -17,7 +17,7 @@ functions and values. For instance, <function>derivation</function>
is also available as <function>builtins.derivation</function>.</para>
-<variablelist >
+<variablelist>
<varlistentry><term><function>abort</function> <replaceable>s</replaceable></term>
diff --git a/doc/manual/release-notes.xml b/doc/manual/release-notes.xml
index 46c540b87..727a3e4a6 100644
--- a/doc/manual/release-notes.xml
+++ b/doc/manual/release-notes.xml
@@ -38,9 +38,13 @@
paths.</para></listitem>
- <listitem><para>TODO: <varname>allowedReferences</varname> for
- checking the set of references in the output of a
- derivation.</para></listitem>
+ <listitem><para>Derivations can specify the new special attribute
+ <varname>allowedReferences</varname> to enforce that the references
+ in the output of a derivation are a subset of a declared set of
+ paths. For example, if <varname>allowedReferences</varname> is an
+ empty list, then the output must not have any references. This is
+ used in NixOS to check that generated files such as initial ramdisks
+ for booting Linux don’t have any dependencies.</para></listitem>
<listitem><para>TODO: semantic cleanups of string concatenation
@@ -54,8 +58,11 @@
<command>nix-store --register-validity</command>.</para></listitem>
- <listitem><para>TODO: magic <varname>exportReferencesGraph</varname>
- attribute.</para></listitem>
+ <listitem><para>The new attribute
+ <varname>exportReferencesGraph</varname> allows builders access to
+ the references graph of their inputs. This is used in NixOS for
+ tasks such as generating ISO-9660 images that contain a Nix store
+ populated with the closure of certain paths.</para></listitem>
<listitem><para>TODO: option <option>--max-silent-time</option>,
@@ -109,8 +116,10 @@
disambiguation (<command>nix-env -qaA</command>).</para></listitem>
- <listitem><para>TODO: substitutes table is gone, registering
- substitutes is now much faster.</para></listitem>
+ <listitem><para>The substitutes table has been removed from the
+ database. This makes operations such as <command>nix-pull</command>
+ and <command>nix-channel --update</command>
+ <emphasis>much</emphasis> faster.</para></listitem>
<listitem><para><command>nix-prefetch-url</command> now has a
diff --git a/doc/manual/writing-nix-expressions.xml b/doc/manual/writing-nix-expressions.xml
index c4bc35cc7..5fa9e423d 100644
--- a/doc/manual/writing-nix-expressions.xml
+++ b/doc/manual/writing-nix-expressions.xml
@@ -607,7 +607,7 @@ language.</para>
<simplesect><title>Simple values</title>
-<para>Nix has the following basic datatypes:
+<para>Nix has the following basic data types:
<itemizedlist>
@@ -679,7 +679,7 @@ configureFlags = "
instance, <filename>builder.sh</filename> is not a
path<footnote><para>It's parsed as an expression that selects the
attribute <varname>sh</varname> from the variable
- <varname>builder</varname>.</para></footnote>. If the filename is
+ <varname>builder</varname>.</para></footnote>. If the file name is
relative, i.e., if it does not begin with a slash, it is made
absolute at parse time relative to the directory of the Nix
expression that contained it. For instance, if a Nix expression in
@@ -701,7 +701,7 @@ configureFlags = "
<simplesect><title>Lists</title>
<para>Lists are formed by enclosing a whitespace-separated list of
-values between square bracktes. For example,
+values between square brackets. For example,
<programlisting>
[ 123 ./foo.nix "abc" (f {x=y;}) ]</programlisting>
@@ -927,7 +927,7 @@ evaluates to <literal>["foobar" "foobla" "fooabc"]</literal>.</para>
if <replaceable>e1</replaceable> then <replaceable>e2</replaceable> else <replaceable>e3</replaceable></programlisting>
where <replaceable>e1</replaceable> is an expression that should
-evaluate to a boolean value (<literal>true</literal> or
+evaluate to a Boolean value (<literal>true</literal> or
<literal>false</literal>).</para>
</simplesect>
@@ -942,7 +942,7 @@ on or between features and dependencies hold. They look like this:
assert <replaceable>e1</replaceable>; <replaceable>e2</replaceable></programlisting>
where <replaceable>e1</replaceable> is an expression that should
-evaluate to a boolean value. If it evaluates to
+evaluate to a Boolean value. If it evaluates to
<literal>true</literal>, <replaceable>e2</replaceable> is returned;
otherwise expression evaluation is aborted and a backtrace is printed.</para>
@@ -1234,7 +1234,7 @@ set, the attributes of which specify the inputs of the build.</para>
</para></listitem>
- <listitem><para>The optional argument <varname>args</varname>
+ <listitem><para>The optional attribute <varname>args</varname>
specifies command-line arguments to be passed to the builder. It
should be a list.</para></listitem>
@@ -1337,6 +1337,233 @@ command-line argument. See <xref linkend='sec-standard-environment'
</para>
+
+<section><title>Advanced attributes</title>
+
+<para>Derivations can declare some infrequently used optional
+attributes.</para>
+
+<variablelist>
+
+ <varlistentry><term><varname>allowedReferences</varname></term>
+
+ <listitem><para>The optional attribute
+ <varname>allowedReferences</varname> specifies a list of legal
+ references (dependencies) of the output of the builder. For
+ example,
+
+<programlisting>
+allowedReferences = [];
+</programlisting>
+
+ enforces that the output of a derivation cannot have any runtime
+ dependencies on its inputs. This is used in NixOS to check that
+ generated files such as initial ramdisks for booting Linux don’t
+ have accidental dependencies on other paths in the Nix
+ store.</para></listitem>
+
+ </varlistentry>
+
+
+ <varlistentry><term><varname>exportReferencesGraph</varname></term>
+
+ <listitem><para>This attribute allows builders access to the
+ references graph of their inputs. The attribute is a list of
+ inputs in the Nix store whose references graph the builder needs
+ to know. The value of this attribute should be a list of pairs
+ <literal>[<replaceable>name1</replaceable>
+ <replaceable>path1</replaceable> <replaceable>name2</replaceable>
+ <replaceable>path2</replaceable>
+ <replaceable>...</replaceable>]</literal>. The references graph
+ of each <replaceable>pathN</replaceable> will be stored in a text
+ file <replaceable>nameN</replaceable> in the temporary build
+ directory. The text files have the format used by
+ <command>nix-store --register-validity</command> (with the deriver
+ fields left empty). For example, when the following derivation is
+ built:
+
+<programlisting>
+derivation {
+ ...
+ exportReferencesGraph = ["libfoo-graph" libfoo];
+};
+</programlisting>
+
+ the references graph of <literal>libfoo</literal> is placed in the
+ file <filename>libfoo-graph</filename> in the temporary build
+ directory.</para>
+
+ <para><varname>exportReferencesGraph</varname> is useful for
+ builders that want to do something with the closure of a store
+ path. Examples include the builders in NixOS that generate the
+ initial ramdisk for booting Linux (a <command>cpio</command>
+ archive containing the closure of the boot script) and the
+ ISO-9660 image for the installation CD (which is populated with a
+ Nix store containing the closure of a bootable NixOS
+ configuration).</para></listitem>
+
+ </varlistentry>
+
+
+ <varlistentry xml:id="fixed-output-drvs">
+ <term><varname>outputHash</varname></term>
+ <term><varname>outputHashAlgo</varname></term>
+ <term><varname>outputHashMode</varname></term>
+
+ <listitem><para>These attributes declare that the derivation is a
+ so-called <emphasis>fixed-output derivation</emphasis>, which
+ means that a cryptographic hash of the output is already known in
+ advance. When the build of a fixed-output derivation finishes,
+ Nix computes the cryptographic hash of the output and compares it
+ to the hash declared with these attributes. If there is a
+ mismatch, the build fails.</para>
+
+ <para>The rationale for fixed-output derivations is derivations
+ such as those produced by the <function>fetchurl</function>
+ function. This function downloads a file from a given URL. To
+ ensure that the downloaded file has not been modified, the caller
+ must also specify a cryptographic hash of the file. For example,
+
+<programlisting>
+fetchurl {
+ url = http://ftp.gnu.org/pub/gnu/hello/hello-2.1.1.tar.gz;
+ md5 = "70c9ccf9fac07f762c24f2df2290784d";
+}
+</programlisting>
+
+ It sometimes happens that the URL of the file changes, e.g.,
+ because servers are reorganised or no longer available. We then
+ must update the call to <function>fetchurl</function>, e.g.,
+
+<programlisting>
+fetchurl {
+ url = ftp://ftp.nluug.nl/pub/gnu/hello/hello-2.1.1.tar.gz;
+ md5 = "70c9ccf9fac07f762c24f2df2290784d";
+}
+</programlisting>
+
+ If a <function>fetchurl</function> derivation was treated like a
+ normal derivation, the output paths of the derivation and
+ <emphasis>all derivations depending on it</emphasis> would change.
+ For instance, if we were to change the URL of the Glibc source
+ distribution in Nixpkgs (a package on which almost all other
+ packages depend) massive rebuilds would be needed. This is
+ unfortunate for a change which we know cannot have a real effect
+ as it propagates upwards through the dependency graph.</para>
+
+ <para>For fixed-output derivations, on the other hand, the name of
+ the output path only depends on the <varname>outputHash*</varname>
+ and <varname>name</varname> attributes, while all other attributes
+ are ignored for the purpose of computing the output path. (The
+ <varname>name</varname> attribute is included because it is part
+ of the path.)</para>
+
+ <para>As an example, here is the (simplified) Nix expression for
+ <varname>fetchurl</varname>:
+
+<programlisting>
+{stdenv, curl}: # The <command>curl</command> program is used for downloading.
+
+{url, md5}:
+
+stdenv.mkDerivation {
+ name = baseNameOf (toString url);
+ builder = ./builder.sh;
+ buildInputs = [curl];
+
+ # This is a fixed-output derivation; the output must be a regular
+ # file with MD5 hash <varname>md5</varname>.
+ outputHashMode = "flat";
+ outputHashAlgo = "md5";
+ outputHash = md5;
+
+ inherit url;
+}
+</programlisting>
+
+ </para>
+
+ <para>The <varname>outputHashAlgo</varname> attribute specifies
+ the hash algorithm used to compute the hash. It can currently be
+ <literal>"md5"</literal>, <literal>"sha1"</literal> or
+ <literal>"sha256"</literal>.</para>
+
+ <para>The <varname>outputHashMode</varname> attribute determines
+ how the hash is computed. It must be one of the following two
+ values:
+
+ <variablelist>
+
+ <varlistentry><term><literal>"flat"</literal></term>
+
+ <listitem><para>The output must be a non-executable regular
+ file. If it isn’t, the build fails. The hash is simply
+ computed over the contents of that file (so it’s equal to what
+ Unix commands like <command>md5sum</command> or
+ <command>sha1sum</command> produce).</para>
+
+ <para>This is the default.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><literal>"recursive"</literal></term>
+
+ <listitem><para>The hash is computed over the NAR archive dump
+ of the output (i.e., the result of <link
+ linkend="refsec-nix-store-dump"><command>nix-store
+ --dump</command></link>). In this case, the output can be
+ anything, including a directory tree.</para></listitem>
+
+ </varlistentry>
+
+ </variablelist>
+
+ </para>
+
+ <para>The <varname>outputHash</varname> attribute, finally, must
+ be a string containing the hash in either hexadecimal or base-32
+ notation. (See the <link
+ linkend="sec-nix-hash"><command>nix-hash</command> command</link>
+ for information about converting to and from base-32
+ notation.)</para></listitem>
+
+ </varlistentry>
+
+
+ <varlistentry><term><varname>impureEnvVars</varname></term>
+
+ <listitem><para>This attribute allows you to specify a list of
+ environment variables that should be passed from the environment
+ of the calling user to the builder. Usually, the environment is
+ cleared completely when the builder is executed, but with this
+ attribute you can allow specific environment variables to be
+ passed unmodified. For example, <function>fetchurl</function> in
+ Nixpkgs has the line
+
+<programlisting>
+impureEnvVars = ["http_proxy" "https_proxy" <replaceable>...</replaceable>];
+</programlisting>
+
+ to make it use the proxy server configuration specified by the
+ user in the environment variables <envar>http_proxy</envar> and
+ friends.</para>
+
+ <para>This attribute is only allowed in <link
+ linkend="fixed-output-drvs">fixed-output derivations</link>, where
+ impurities such as these are okay since (the hash of) the output
+ is known in advance. It is ignored for all other
+ derivations.</para></listitem>
+
+ </varlistentry>
+
+
+
+
+</variablelist>
+
+</section>
+
+
</section>
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