From 4d59ace14f96db0b45fc3bef1d9b9e91325b0a2c Mon Sep 17 00:00:00 2001
From: WilliButz <willibutz@posteo.de>
Date: Tue, 27 Feb 2024 13:29:23 +0100
Subject: [PATCH] nixos/systemd-repart: add assertion for partition label
 length

The maximum length for a GPT label supported by systemd is 36
characters. When a repart definition contains a label that is longer
than the supported maximum length, it is ignored by systemd-repart and
a log message is produced.

The new assertion makes this obvious to the user at evaluation time,
allowing them to either drop the property entirely or choose a supported
label within the length limit instead.
---
 nixos/modules/system/boot/systemd/repart.nix | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/system/boot/systemd/repart.nix b/nixos/modules/system/boot/systemd/repart.nix
index 3be744acd0b3..6cc387cb6f43 100644
--- a/nixos/modules/system/boot/systemd/repart.nix
+++ b/nixos/modules/system/boot/systemd/repart.nix
@@ -10,6 +10,20 @@ let
     "repart.d"
     format
     (lib.mapAttrs (_n: v: { Partition = v; }) cfg.partitions);
+
+  partitionAssertions = lib.mapAttrsToList (fileName: definition:
+    let
+      maxLabelLength = 36; # GPT_LABEL_MAX defined in systemd's gpt.h
+      labelLength = builtins.stringLength definition.Label;
+    in
+    {
+      assertion = definition ? Label -> maxLabelLength >= 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}.
+      '';
+    }
+  ) cfg.partitions;
 in
 {
   options = {
@@ -81,7 +95,7 @@ in
           'boot.initrd.systemd.repart.enable' requires 'boot.initrd.systemd.enable' to be enabled.
         '';
       }
-    ];
+    ] ++ partitionAssertions;
 
     # systemd-repart uses loopback devices for partition creation
     boot.initrd.availableKernelModules = lib.optional initrdCfg.enable "loop";