systemd: use sd-switch

This makes the systemd module use the sd-switch application to perform
the unit switch during a generation activation.

Since the closure of sd-switch is relatively lightweight we
unconditionally pull it in as a dependency. We simultaneously remove
the `systemd.user.startServices` option and perform the switch action
automatically.

PR #1388

1 files changed, 20 insertions, 13 deletions

diff --git a/modules/systemd.nix b/modules/systemd.nix
index dcb1a29570d..5acfabc7469 100644
--- a/modules/systemd.nix
+++ b/modules/systemd.nix
@@ -54,8 +54,6 @@ let
   buildServices = style: serviceCfgs:
     concatLists (mapAttrsToList (buildService style) serviceCfgs);
 
-  servicesStartTimeoutMs = builtins.toString cfg.servicesStartTimeoutMs;
-
   unitType = unitKind: with types;
     let
       primitive = either bool (either int str);
@@ -152,9 +150,11 @@ in
         example = unitExample "Path";
       };
 
+      # Keep for a while for backwards compatibility.
       startServices = mkOption {
         default = false;
         type = types.bool;
+        visible = false;
         description = ''
           Start all services that are wanted by active targets.
           Additionally, stop obsolete services from the previous
@@ -164,10 +164,10 @@ in
 
       servicesStartTimeoutMs = mkOption {
         default = 0;
-        type = types.int;
+        type = types.ints.unsigned;
         description = ''
-          How long to wait for started services to fail until their
-          start is considered successful.
+          How long to wait for started services to fail until their start is
+          considered successful. The value 0 indicates no timeout.
         '';
       };
 
@@ -203,6 +203,10 @@ in
               "Must use Linux for modules that require systemd: " + names;
         }
       ];
+
+      warnings = mkIf cfg.startServices [
+        "The option 'systemd.user.startServices' is obsolete and can be removed."
+      ];
     }
 
     # If we run under a Linux system we assume that systemd is
@@ -230,13 +234,17 @@ in
       # set it ourselves in that case.
       home.activation.reloadSystemD = hm.dag.entryAfter ["linkGeneration"] (
         let
-          autoReloadCmd = ''
-            ${pkgs.ruby}/bin/ruby ${./systemd-activate.rb} \
-              "''${oldGenPath=}" "$newGenPath" "${servicesStartTimeoutMs}"
-          '';
+          timeoutArg =
+            if cfg.servicesStartTimeoutMs != 0 then
+              "--timeout " + toString cfg.servicesStartTimeoutMs
+            else
+              "";
 
-          legacyReloadCmd = ''
-            bash ${./systemd-activate.sh} "''${oldGenPath=}" "$newGenPath"
+          sdSwitchCmd = ''
+            ${pkgs.sd-switch}/bin/sd-switch \
+              ''${DRY_RUN:+--dry-run} $VERBOSE_ARG ${timeoutArg} \
+              ''${oldGenPath:+--old-units $oldGenPath/home-files/.config/systemd/user} \
+              --new-units $newGenPath/home-files/.config/systemd/user
           '';
 
           ensureRuntimeDir = "XDG_RUNTIME_DIR=\${XDG_RUNTIME_DIR:-/run/user/$(id -u)}";
@@ -254,8 +262,7 @@ in
               fi
 
               ${ensureRuntimeDir} \
-              PATH=${dirOf cfg.systemctlPath}:$PATH \
-                ${if cfg.startServices then autoReloadCmd else legacyReloadCmd}
+                ${sdSwitchCmd}
             else
               echo "User systemd daemon not running. Skipping reload."
             fi