Merge pull request #302590 from nikstur/repart-image-label-length

nixos/image/repart: assert maximum label length

nixos/lib/systemd-lib.nix

···
       )}
     '';
 
+  # The maximum number of characters allowed in a GPT partition label. This
+  # limit is specified by UEFI and enforced by systemd-repart.
+  # Corresponds to GPT_LABEL_MAX from systemd's gpt.h.
+  GPTMaxLabelLength = 36;
+
 }

nixos/modules/image/repart.nix

···
 let
   cfg = config.image.repart;
 
+  inherit (utils.systemdUtils.lib) GPTMaxLabelLength;
+
   partitionOptions = {
     options = {
       storePaths = lib.mkOption {
···
   };
 
   config = {
+
+    assertions = lib.mapAttrsToList (fileName: partitionConfig:
+      let
+        inherit (partitionConfig) repartConfig;
+        labelLength = builtins.stringLength repartConfig.Label;
+      in
+      {
+        assertion = repartConfig ? Label -> GPTMaxLabelLength >= labelLength;
+        message = ''
+          The partition label '${repartConfig.Label}'
+          defined for '${fileName}' is ${toString labelLength} characters long,
+          but the maximum label length supported by UEFI is ${toString
+          GPTMaxLabelLength}.
+        '';
+      }
+    ) cfg.partitions;
+
+    warnings = lib.filter (v: v != null) (lib.mapAttrsToList (fileName: partitionConfig:
+      let
+        inherit (partitionConfig) repartConfig;
+        suggestedMaxLabelLength = GPTMaxLabelLength - 2;
+        labelLength = builtins.stringLength repartConfig.Label;
+      in
+        if (repartConfig ? Label && labelLength >= suggestedMaxLabelLength) then ''
+          The partition label '${repartConfig.Label}'
+          defined for '${fileName}' is ${toString labelLength} characters long.
+          The suggested maximum label length is ${toString
+          suggestedMaxLabelLength}.
+
+          If you use sytemd-sysupdate style A/B updates, this might
+          not leave enough space to increment the version number included in
+          the label in a future release. For example, if your label is
+          ${toString GPTMaxLabelLength} characters long (the maximum enforced by UEFI) and
+          you're at version 9, you cannot increment this to 10.
+        '' else null
+    ) cfg.partitions);
 
     image.repart =
       let

nixos/modules/system/boot/systemd/repart.nix

···
 
   partitionAssertions = lib.mapAttrsToList (fileName: definition:
     let
-      maxLabelLength = 36; # GPT_LABEL_MAX defined in systemd's gpt.h
+      inherit (utils.systemdUtils.lib) GPTMaxLabelLength;
       labelLength = builtins.stringLength definition.Label;
     in
     {
-      assertion = definition ? Label -> maxLabelLength >= labelLength;
+      assertion = definition ? Label -> GPTMaxLabelLength >= labelLength;
       message = ''
         The partition label '${definition.Label}' defined for '${fileName}' is ${toString labelLength}
-        characters long, but the maximum label length supported by systemd is ${toString maxLabelLength}.
+        characters long, but the maximum label length supported by systemd is ${toString GPTMaxLabelLength}.
       '';
     }
   ) cfg.partitions;