Merge pull request #250316 from helsinki-systems/feat/stc-improve-mount-units

nixos/switch-to-configuration: Improve mount unit handling

1 files changed, 19 insertions, 5 deletions

diff --git a/nixos/modules/system/activation/switch-to-configuration.pl b/nixos/modules/system/activation/switch-to-configuration.pl
index 04d90968c4c12..8bd450d7343b2 100755
--- a/nixos/modules/system/activation/switch-to-configuration.pl
+++ b/nixos/modules/system/activation/switch-to-configuration.pl
@@ -313,7 +313,8 @@ sub unrecord_unit {
 # needs to be restarted or reloaded. If the units differ, the service
 # is restarted unless the only difference is `X-Reload-Triggers` in the
 # `Unit` section. If this is the only modification, the unit is reloaded
-# instead of restarted.
+# instead of restarted. If the only difference is `Options` in the
+# `[Mount]` section, the unit is reloaded rather than restarted.
 # Returns:
 # - 0 if the units are equal
 # - 1 if the units are different and a restart action is required
@@ -390,6 +391,11 @@ sub compare_units { ## no critic(Subroutines::ProhibitExcessComplexity)
                         next;
                     }
                 }
+                # If this is a mount unit, check if it was only `Options`
+                if ($section_name eq "Mount" and $ini_key eq "Options") {
+                    $ret = 2;
+                    next;
+                }
                 return 1;
             }
         }
@@ -440,10 +446,18 @@ sub handle_modified_unit { ## no critic(Subroutines::ProhibitManyArgs, Subroutin
         # properties (resource limits and inotify watches)
         # seem to get applied on daemon-reload.
     } elsif ($unit =~ /\.mount$/msx) {
-        # Reload the changed mount unit to force a remount.
-        # FIXME: only reload when Options= changed, restart otherwise
-        $units_to_reload->{$unit} = 1;
-        record_unit($reload_list_file, $unit);
+        # Just restart the unit. We wouldn't have gotten into this subroutine
+        # if only `Options` was changed, in which case the unit would be reloaded.
+        # The only exception is / and /nix because it's very unlikely we can safely
+        # unmount them so we reload them instead. This means that we may not get
+        # all changes into the running system but it's better than crashing it.
+        if ($unit eq "-.mount" or $unit eq "nix.mount") {
+            $units_to_reload->{$unit} = 1;
+            record_unit($reload_list_file, $unit);
+        } else {
+            $units_to_restart->{$unit} = 1;
+            record_unit($restart_list_file, $unit);
+        }
     } elsif ($unit =~ /\.socket$/msx) {
         # FIXME: do something?
         # Attempt to fix this: https://github.com/NixOS/nixpkgs/pull/141192