nixos/systemd: enable systemd-pstore.service

As described in issue #81138, the Install section of upstream units is
currently ignored, so we make it part of the sysinit.target manually.

nixos/doc/manual/release-notes/rl-2105.xml

@@ -1035,6 +1035,12 @@ environment.systemPackages = [
      </programlisting>
     </para>
    </listitem>
+   <listitem>
+    <para>
+     The newly enabled <literal>systemd-pstore.service</literal> now automatically evacuates crashdumps and panic logs from the persistent storage to <literal>/var/lib/systemd/pstore</literal>.
+     This prevents NVRAM from filling up, which ensures the latest diagnostic data is always stored and alleviates problems with writing new boot configurations.
+    </para>
+   </listitem>
   </itemizedlist>
  </section>
 </section>

nixos/modules/profiles/installation-device.nix

@@ -99,5 +99,13 @@ with lib;
     # because we have the firewall enabled. This makes installs from the
     # console less cumbersome if the machine has a public IP.
     networking.firewall.logRefusedConnections = mkDefault false;
+
+    # Prevent installation media from evacuating persistent storage, as their
+    # var directory is not persistent and it would thus result in deletion of
+    # those entries.
+    environment.etc."systemd/pstore.conf".text = ''
+      [PStore]
+      Unlink=no
+    '';
   };
 }

nixos/modules/system/boot/systemd.nix

@@ -90,6 +90,7 @@ let
       "systemd-fsck@.service"
       "systemd-fsck-root.service"
       "systemd-remount-fs.service"
+      "systemd-pstore.service"
       "local-fs.target"
       "local-fs-pre.target"
       "remote-fs.target"
@@ -1183,6 +1184,7 @@ in
     systemd.targets.remote-fs.unitConfig.X-StopOnReconfiguration = true;
     systemd.targets.network-online.wantedBy = [ "multi-user.target" ];
     systemd.services.systemd-importd.environment = proxy_env;
+    systemd.services.systemd-pstore.wantedBy = [ "sysinit.target" ]; # see #81138
 
     # Don't bother with certain units in containers.
     systemd.services.systemd-remount-fs.unitConfig.ConditionVirtualization = "!container";