nixos/switch-to-configuration: Never unmount / or /nix

Also adds a huge test for fstab handling

1 files changed, 14 insertions, 4 deletions

diff --git a/nixos/modules/system/activation/switch-to-configuration.pl b/nixos/modules/system/activation/switch-to-configuration.pl
index 95308d5da946..e05f89bb0fb4 100755
--- a/nixos/modules/system/activation/switch-to-configuration.pl
+++ b/nixos/modules/system/activation/switch-to-configuration.pl
@@ -661,10 +661,20 @@ foreach my $mount_point (keys(%{$cur_fss})) {
         # Filesystem entry disappeared, so unmount it.
         $units_to_stop{$unit} = 1;
     } elsif ($cur->{fsType} ne $new->{fsType} || $cur->{device} ne $new->{device}) {
-        # Filesystem type or device changed, so unmount and mount it.
-        $units_to_stop{$unit} = 1;
-        $units_to_start{$unit} = 1;
-        record_unit($start_list_file, $unit);
+        if ($mount_point eq '/' or $mount_point eq '/nix') {
+            if ($cur->{options} ne $new->{options}) {
+                # Mount options changed, so remount it.
+                $units_to_reload{$unit} = 1;
+                record_unit($reload_list_file, $unit);
+            } else {
+                # Don't unmount / or /nix if the device changed
+                $units_to_skip{$unit} = 1;
+            }
+        } else {
+            # Filesystem type or device changed, so unmount and mount it.
+            $units_to_restart{$unit} = 1;
+            record_unit($restart_list_file, $unit);
+        }
     } elsif ($cur->{options} ne $new->{options}) {
         # Mount options changes, so remount it.
         $units_to_reload{$unit} = 1;