From de128feaccaf9751d7092d83f7dcc488f51a4dda Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Janne=20He=C3=9F?= <janne@hess.ooo>
Date: Sun, 10 Oct 2021 17:58:06 +0200
Subject: [PATCH] nixos/switch-to-configuration: Ignore slice units

---
 .../activation/switch-to-configuration.pl     |  4 +--
 nixos/tests/switch-test.nix                   | 34 +++++++++++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/nixos/modules/system/activation/switch-to-configuration.pl b/nixos/modules/system/activation/switch-to-configuration.pl
index 58453dddc602..d5b7f0c07300 100644
--- a/nixos/modules/system/activation/switch-to-configuration.pl
+++ b/nixos/modules/system/activation/switch-to-configuration.pl
@@ -152,7 +152,7 @@ sub fingerprintUnit {
 sub handleModifiedUnit {
     my ($unit, $baseName, $newUnitFile, $activePrev, $unitsToStop, $unitsToStart, $unitsToReload, $unitsToRestart, $unitsToSkip) = @_;
 
-    if ($unit eq "sysinit.target" || $unit eq "basic.target" || $unit eq "multi-user.target" || $unit eq "graphical.target") {
+    if ($unit eq "sysinit.target" || $unit eq "basic.target" || $unit eq "multi-user.target" || $unit eq "graphical.target" || $unit =~ /\.slice$/) {
         # Do nothing.  These cannot be restarted directly.
         # Slices and Paths don't have to be restarted since
         # properties (resource limits and inotify watches)
@@ -161,7 +161,7 @@ sub handleModifiedUnit {
         # Reload the changed mount unit to force a remount.
         $unitsToReload->{$unit} = 1;
         recordUnit($reloadListFile, $unit);
-    } elsif ($unit =~ /\.slice$/ || $unit =~ /\.path$/) {
+    } elsif ($unit =~ /\.path$/) {
         # FIXME: do something?
     } else {
         my $unitInfo = parseUnit($newUnitFile);
diff --git a/nixos/tests/switch-test.nix b/nixos/tests/switch-test.nix
index 76a9ef6f624e..1acccbd17540 100644
--- a/nixos/tests/switch-test.nix
+++ b/nixos/tests/switch-test.nix
@@ -107,6 +107,8 @@ import ./make-test-python.nix ({ pkgs, ...} : {
             };
           };
         };
+
+        # The same system but with an activation script that restarts all services
         restart-and-reload-by-activation-script.configuration = {
           imports = [ config.specialisation.service-and-socket.configuration ];
           system.activationScripts.restart-and-reload-test = {
@@ -128,6 +130,25 @@ import ./make-test-python.nix ({ pkgs, ...} : {
             '';
           };
         };
+
+        # A system with a slice
+        with-slice.configuration = {
+          systemd.slices.testslice.sliceConfig.MemoryMax = "1"; # don't allow memory allocation
+          systemd.services.testservice = {
+            serviceConfig = {
+              Type = "oneshot";
+              RemainAfterExit = true;
+              ExecStart = "${pkgs.coreutils}/bin/true";
+              Slice = "testslice.slice";
+            };
+          };
+        };
+
+        # The same system but the slice allows to allocate memory
+        with-slice-non-crashing.configuration = {
+          imports = [ config.specialisation.with-slice.configuration ];
+          systemd.slices.testslice.sliceConfig.MemoryMax = lib.mkForce null;
+        };
       };
     };
     other = { ... }: {
@@ -263,5 +284,18 @@ import ./make-test-python.nix ({ pkgs, ...} : {
         assert_contains(out, "would restart the following units: simple-restart-service.service\n")
         assert_contains(out, "\nwould start the following units: simple-service.service")
 
+    # This test ensures that changes to slice configuration get applied.
+    # We test this by having a slice that allows no memory allocation at
+    # all and starting a service within it. If the service crashes, the slice
+    # is applied and if we modify the slice to allow memory allocation, the
+    # service should successfully start.
+    with subtest("slices"):
+        machine.succeed("echo 0 > /proc/sys/vm/panic_on_oom")  # allow OOMing
+        out = switch_to_specialisation("with-slice")
+        machine.fail("systemctl start testservice.service")
+        out = switch_to_specialisation("with-slice-non-crashing")
+        machine.succeed("systemctl start testservice.service")
+        machine.succeed("echo 1 > /proc/sys/vm/panic_on_oom")  # disallow OOMing
+
   '';
 })