nixos/systemd: Add reloadTriggers to services

4 files changed, 41 insertions, 0 deletions

diff --git a/nixos/doc/manual/from_md/release-notes/rl-2205.section.xml b/nixos/doc/manual/from_md/release-notes/rl-2205.section.xml
index 04bb7ec12d3..811702f5e52 100644
--- a/nixos/doc/manual/from_md/release-notes/rl-2205.section.xml
+++ b/nixos/doc/manual/from_md/release-notes/rl-2205.section.xml
@@ -42,6 +42,14 @@
           upgrade notes</link>.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          systemd services can now set
+          <link linkend="opt-systemd.services">systemd.services.&lt;name&gt;.reloadTriggers</link>
+          instead of <literal>reloadIfChanged</literal> for a more
+          granular distinction between reloads and restarts.
+        </para>
+      </listitem>
     </itemizedlist>
   </section>
   <section xml:id="sec-release-22.05-new-services">
@@ -550,6 +558,15 @@
               honors <literal>restartIfChanged</literal> and
               <literal>reloadIfChanged</literal> of the units.
             </para>
+            <itemizedlist spacing="compact">
+              <listitem>
+                <para>
+                  Preferring to reload instead of restarting can still
+                  be achieved using
+                  <literal>/run/nixos/activation-reload-list</literal>.
+                </para>
+              </listitem>
+            </itemizedlist>
           </listitem>
           <listitem>
             <para>
diff --git a/nixos/doc/manual/release-notes/rl-2205.section.md b/nixos/doc/manual/release-notes/rl-2205.section.md
index a2e8038ae1f..fca37420977 100644
--- a/nixos/doc/manual/release-notes/rl-2205.section.md
+++ b/nixos/doc/manual/release-notes/rl-2205.section.md
@@ -17,6 +17,8 @@ In addition to numerous new and upgraded packages, this release has the followin
   Migrations may take a while, see the [changelog](https://docs.mattermost.com/install/self-managed-changelog.html#release-v6-3-extended-support-release)
   and [important upgrade notes](https://docs.mattermost.com/upgrade/important-upgrade-notes.html).
 
+- systemd services can now set [systemd.services.\<name\>.reloadTriggers](#opt-systemd.services) instead of `reloadIfChanged` for a more granular distinction between reloads and restarts.
+
 ## New Services {#sec-release-22.05-new-services}
 
 - [aesmd](https://github.com/intel/linux-sgx#install-the-intelr-sgx-psw), the Intel SGX Architectural Enclave Service Manager. Available as [services.aesmd](#opt-services.aesmd.enable).
@@ -179,6 +181,7 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - `switch-to-configuration` (the script that is run when running `nixos-rebuild switch` for example) has been reworked
     * The interface that allows activation scripts to restart units has been streamlined. Restarting and reloading is now done by a single file `/run/nixos/activation-restart-list` that honors `restartIfChanged` and `reloadIfChanged` of the units.
+        * Preferring to reload instead of restarting can still be achieved using `/run/nixos/activation-reload-list`.
     * The script now uses a proper ini-file parser to parse systemd units. Some values are now only searched in one section instead of in the entire unit. This is only relevant for units that don't use the NixOS systemd moule.
         * `RefuseManualStop`, `X-OnlyManualStart`, `X-StopOnRemoval`, `X-StopOnReconfiguration` are only searched in the `[Unit]` section
         * `X-ReloadIfChanged`, `X-RestartIfChanged`, `X-StopIfChanged` are only searched in the `[Service]` section
diff --git a/nixos/lib/systemd-unit-options.nix b/nixos/lib/systemd-unit-options.nix
index 520f2e982a2..8029ba0e3f6 100644
--- a/nixos/lib/systemd-unit-options.nix
+++ b/nixos/lib/systemd-unit-options.nix
@@ -201,6 +201,17 @@ in rec {
       '';
     };
 
+    reloadTriggers = mkOption {
+      default = [];
+      type = types.listOf unitOption;
+      description = ''
+        An arbitrary list of items such as derivations.  If any item
+        in the list changes between reconfigurations, the service will
+        be reloaded.  If anything but a reload trigger changes in the
+        unit file, the unit will be restarted instead.
+      '';
+    };
+
     onFailure = mkOption {
       default = [];
       type = types.listOf unitNameType;
@@ -338,6 +349,11 @@ in rec {
         configuration switch if its definition has changed.  If
         enabled, the value of <option>restartIfChanged</option> is
         ignored.
+
+        This option should not be used anymore in favor of
+        <option>reloadTriggers</option> which allows more granular
+        control of when a service is reloaded and when a service
+        is restarted.
       '';
     };
 
diff --git a/nixos/modules/system/boot/systemd.nix b/nixos/modules/system/boot/systemd.nix
index 9dcf9eb769f..1f2dd618698 100644
--- a/nixos/modules/system/boot/systemd.nix
+++ b/nixos/modules/system/boot/systemd.nix
@@ -243,6 +243,8 @@ let
           { Requisite = toString config.requisite; }
         // optionalAttrs (config.restartTriggers != [])
           { X-Restart-Triggers = toString config.restartTriggers; }
+        // optionalAttrs (config.reloadTriggers != [])
+          { X-Reload-Triggers = toString config.reloadTriggers; }
         // optionalAttrs (config.description != "") {
           Description = config.description; }
         // optionalAttrs (config.documentation != []) {
@@ -917,6 +919,9 @@ in
               (optional hasDeprecated
                 "Service '${name}.service' uses the attribute 'StartLimitInterval' in the Service section, which is deprecated. See https://github.com/NixOS/nixpkgs/issues/45786."
               )
+              (optional (service.reloadIfChanged && service.reloadTriggers != [])
+                "Service '${name}.service' has both 'reloadIfChanged' and 'reloadTriggers' set. This is probably not what you want, because 'reloadTriggers' behave the same whay as 'restartTriggers' if 'reloadIfChanged' is set."
+              )
             ]
         )
         cfg.services