Remove $NIX_BUILD_HOOK and $NIX_CURRENT_LOAD
This is to simplify remote build configuration. These environment variables predate nix.conf. The build hook now has a sensible default (namely build-remote). The current load is kept in the Nix state directory now.
This commit is contained in:
Eelco Dolstra
parent
ca9f589a93
commit
d7653dfc6d
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@ -22,10 +22,7 @@ will call whenever it wants to build a derivation. The build hook
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will perform it in the usual way if possible, or it can accept it, in
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which case it is responsible for somehow getting the inputs of the
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build to another machine, doing the build there, and getting the
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results back. The details of the build hook protocol are described in
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the documentation of the <link
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linkend="envar-build-hook"><envar>NIX_BUILD_HOOK</envar>
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variable</link>.</para>
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results back.</para>
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<example xml:id='ex-remote-systems'><title>Remote machine configuration:
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<filename>remote-systems.conf</filename></title>
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@ -103,14 +100,6 @@ requiredSystemFeatures = [ "kvm" ];
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</orderedlist>
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You should also set up the environment variable
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<envar>NIX_CURRENT_LOAD</envar> to point at a directory (e.g.,
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<filename>/var/run/nix/current-load</filename>) that
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<filename>build-remote</filename> uses to remember how many builds
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it is currently executing remotely. It doesn't look at the actual
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load on the remote machine, so if you have multiple instances of Nix
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running, they should use the same <envar>NIX_CURRENT_LOAD</envar>
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file. Maybe in the future <filename>build-remote</filename> will
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look at the actual remote load.</para>
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</para>
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</chapter>
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@ -148,139 +148,6 @@ $ mount -o bind /mnt/otherdisk/nix /nix</screen>
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</varlistentry>
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<varlistentry xml:id="envar-build-hook"><term><envar>NIX_BUILD_HOOK</envar></term>
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<listitem>
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<para>Specifies the location of the <emphasis>build hook</emphasis>,
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which is a program (typically some script) that Nix will call
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whenever it wants to build a derivation. This is used to implement
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distributed builds<phrase condition="manual"> (see <xref
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linkend="chap-distributed-builds" />)</phrase>.</para>
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<!--
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The protocol by
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which the calling Nix process and the build hook communicate is as
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follows.
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<para>The build hook is called with the following command-line
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arguments:
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<orderedlist>
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<listitem><para>A boolean value <literal>0</literal> or
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<literal>1</literal> specifying whether Nix can locally execute
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more builds, as per the <link
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linkend="opt-max-jobs"><option>- -max-jobs</option> option</link>.
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The purpose of this argument is to allow the hook to not have to
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maintain bookkeeping for the local machine.</para></listitem>
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<listitem><para>The Nix platform identifier for the local machine
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(e.g., <literal>i686-linux</literal>).</para></listitem>
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<listitem><para>The Nix platform identifier for the derivation,
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i.e., its <link linkend="attr-system"><varname>system</varname>
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attribute</link>.</para></listitem>
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<listitem><para>The store path of the derivation.</para></listitem>
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</orderedlist>
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</para>
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<para>On the basis of this information, and whatever persistent
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state the build hook keeps about other machines and their current
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load, it has to decide what to do with the build. It should print
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out on standard error one of the following responses (terminated by
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a newline, <literal>"\n"</literal>):
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<variablelist>
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<varlistentry><term><literal># decline</literal></term>
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<listitem><para>The build hook is not willing or able to perform
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the build; the calling Nix process should do the build itself,
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if possible.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal># postpone</literal></term>
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<listitem><para>The build hook cannot perform the build now, but
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can do so in the future (e.g., because all available build slots
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on remote machines are in use). The calling Nix process should
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postpone this build until at least one currently running build
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has terminated.</para></listitem>
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</varlistentry>
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<varlistentry><term><literal># accept</literal></term>
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<listitem><para>The build hook has accepted the
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build.</para></listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>After sending <literal># accept</literal>, the hook should
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read one line from standard input, which will be the string
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<literal>okay</literal>. It can then proceed with the build.
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Before sending <literal>okay</literal>, Nix will store in the hook’s
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current directory a number of text files that contain information
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about the derivation:
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<variablelist>
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<varlistentry><term><filename>inputs</filename></term>
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<listitem><para>The set of store paths that are inputs to the
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build process (one per line). These have to be copied
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<emphasis>to</emphasis> the remote machine (in addition to the
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store derivation itself).</para></listitem>
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</varlistentry>
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<varlistentry><term><filename>outputs</filename></term>
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<listitem><para>The set of store paths that are outputs of the
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derivation (one per line). These have to be copied
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<emphasis>from</emphasis> the remote machine if the build
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succeeds.</para></listitem>
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</varlistentry>
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<varlistentry><term><filename>references</filename></term>
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<listitem><para>The reference graph of the inputs, in the format
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accepted by the command <command>nix-store
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- -register-validity</command>. It is necessary to run this
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command on the remote machine after copying the inputs to inform
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Nix on the remote machine that the inputs are valid
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paths.</para></listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>The hook should copy the inputs to the remote machine,
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register the validity of the inputs, perform the remote build, and
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copy the outputs back to the local machine. An exit code other than
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<literal>0</literal> indicates that the hook has failed. An exit
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code equal to 100 means that the remote build failed (as opposed to,
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e.g., a network error).</para>
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-->
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</listitem>
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</varlistentry>
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<varlistentry xml:id="envar-remote"><term><envar>NIX_REMOTE</envar></term>
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<listitem><para>This variable should be set to
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@ -140,7 +140,9 @@ int main (int argc, char * * argv)
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settings.buildTimeout = std::stoll(argv[3]);
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verbosity = (Verbosity) std::stoll(argv[4]);
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currentLoad = getEnv("NIX_CURRENT_LOAD", "/run/nix/current-load");
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/* It would be more appropriate to use $XDG_RUNTIME_DIR, since
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that gets cleared on reboot, but it wouldn't work on OS X. */
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currentLoad = settings.nixStateDir + "/current-load";
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std::shared_ptr<Store> sshStore;
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AutoCloseFD bestSlotLock;
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@ -583,11 +583,7 @@ struct HookInstance
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HookInstance::HookInstance()
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{
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debug("starting build hook");
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Path buildHook = getEnv("NIX_BUILD_HOOK");
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if (string(buildHook, 0, 1) != "/") buildHook = settings.nixLibexecDir + "/nix/" + buildHook;
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buildHook = canonPath(buildHook);
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debug("starting build hook ‘%s’", settings.buildHook);
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/* Create a pipe to get the output of the child. */
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fromHook.create();
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@ -621,9 +617,9 @@ HookInstance::HookInstance()
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std::to_string(verbosity)
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};
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execv(buildHook.c_str(), stringsToCharPtrs(args).data());
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execv(settings.buildHook.get().c_str(), stringsToCharPtrs(args).data());
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throw SysError(format("executing ‘%1%’") % buildHook);
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throw SysError("executing ‘%s’", settings.buildHook);
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});
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pid.setSeparatePG(true);
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@ -1569,7 +1565,7 @@ void DerivationGoal::buildDone()
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HookReply DerivationGoal::tryBuildHook()
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{
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if (!settings.useBuildHook || getEnv("NIX_BUILD_HOOK") == "" || !useDerivation) return rpDecline;
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if (!settings.useBuildHook || !useDerivation) return rpDecline;
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if (!worker.hook)
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worker.hook = std::make_unique<HookInstance>();
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@ -127,6 +127,9 @@ public:
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Setting<bool> useBuildHook{this, true, "remote-builds",
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"Whether to use build hooks (for distributed builds)."};
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PathSetting buildHook{this, true, nixLibexecDir + "/nix/build-remote", "build-hook",
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"The path of the helper program that executes builds to remote machines."};
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Setting<off_t> reservedSize{this, 8 * 1024 * 1024, "gc-reserved-space",
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"Amount of reserved disk space for the garbage collector."};
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@ -43,7 +43,6 @@ in
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{ config, pkgs, ... }:
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{ nix.maxJobs = 0; # force remote building
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nix.distributedBuilds = true;
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nix.envVars = pkgs.lib.mkAfter { NIX_BUILD_HOOK = "${nix}/libexec/nix/build-remote"; };
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nix.buildMachines =
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[ { hostName = "slave1";
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sshUser = "root";
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