PatOS is born!

modules/filesystems.nix

@@ -0,0 +1,44 @@
+{ config, ... }: {
+
+  zramSwap = {
+    enable = true;
+    algorithm = "zstd";
+    memoryPercent = 20;
+  };
+
+  fileSystems = {
+    "/" = {
+      fsType = "tmpfs";
+      options = [
+        "size=20%"
+      ];
+    };
+
+    "/var" =
+      let
+        partConf = config.image.repart.partitions."var".repartConfig;
+      in
+      {
+        device = "/dev/disk/by-partuuid/${partConf.UUID}";
+        fsType = partConf.Format;
+      };
+
+    "/boot" =
+      let
+        partConf = config.image.repart.partitions."esp".repartConfig;
+      in
+      {
+        device = "/dev/disk/by-partuuid/${partConf.UUID}";
+        fsType = partConf.Format;
+      };
+
+    "/nix/store" =
+      let
+        partConf = config.image.repart.partitions."store".repartConfig;
+      in
+      {
+        device = "/dev/disk/by-partlabel/${partConf.Label}";
+        fsType = partConf.Format;
+      };
+  };
+}

modules/generic.nix

@@ -0,0 +1,41 @@
+{ pkgs, config, ... }: {
+
+  boot.uki.name = "patos";
+  boot.kernelParams = [ "console=ttyS0" ];
+
+  system.nixos.release = "2024-09";
+  system.nixos.codeName = "Finn";
+
+  system.nixos.distroId = "patos";
+  system.nixos.distroName = "PatOS";
+  system.image.version = "0.0.1"; # FIXME: Use epoch version.
+
+  # Make the current system version visible in the prompt.
+  programs.bash.promptInit = ''
+    export PS1="\u@\h (version ${config.system.image.version}) $ "
+  '';
+
+  # Not compatible with system.etc.overlay.enable yet.
+  # users.mutableUsers = false;
+
+  services.getty.autologinUser = "root";
+
+  boot.initrd.systemd.enable = true;
+
+  # Don't accumulate crap.
+  boot.tmp.cleanOnBoot = true;
+  services.journald.extraConfig = ''
+    SystemMaxUse=10M
+  '';
+
+  # Debugging
+  environment.systemPackages = with pkgs; [
+    parted
+    (runCommand "systemd-sysupdate" { } ''
+      mkdir -p $out/bin
+      ln -s ${config.systemd.package}/lib/systemd/systemd-sysupdate $out/bin
+    '')
+  ];
+
+  system.stateVersion = "24.11";
+}

modules/minimize.nix

@@ -0,0 +1,19 @@
+{ modulesPath, ... }: {
+  imports = [
+    "${modulesPath}/profiles/minimal.nix"
+  ];
+
+  boot.loader.grub.enable = false;
+
+  system.switch.enable = false;
+  nix.enable = false;
+
+  system.etc.overlay.enable = true;
+  systemd.sysusers.enable = true;
+
+  system.disableInstallerTools = true;
+  programs.less.lessopen = null;
+  programs.command-not-found.enable = false;
+  boot.enableContainers = false;
+  environment.defaultPackages = [ ];
+}

modules/network.nix

@@ -0,0 +1,11 @@
+{ config, ... }: {
+  networking = {
+    useNetworkd = true;
+
+    # Easy debugging.
+    firewall.enable = false;
+  };
+
+  # Faster boot.
+  systemd.network.wait-online.enable = false;
+}

modules/partitions.nix

@@ -0,0 +1,85 @@
+{ config, pkgs, lib, modulesPath, ... }: {
+
+  imports = [
+    "${modulesPath}/image/repart.nix"
+  ];
+
+  image.repart =
+    let
+      efiArch = pkgs.stdenv.hostPlatform.efiArch;
+    in
+    {
+      name = config.boot.uki.name;
+      split = true;
+
+      partitions = {
+        "esp" = {
+          contents = {
+            "/EFI/BOOT/BOOT${lib.toUpper efiArch}.EFI".source =
+              "${pkgs.systemd}/lib/systemd/boot/efi/systemd-boot${efiArch}.efi";
+
+            "/EFI/Linux/${config.system.boot.loader.ukiFile}".source =
+              "${config.system.build.uki}/${config.system.boot.loader.ukiFile}";
+
+            # systemd-boot configuration
+            "/loader/loader.conf".source = (pkgs.writeText "$out" ''
+              timeout 3
+            '');
+          };
+          repartConfig = {
+            Type = "esp";
+            UUID = "c12a7328-f81f-11d2-ba4b-00a0c93ec93b"; # Well known
+            Format = "vfat";
+            SizeMinBytes = "256M";
+            SplitName = "-";
+          };
+        };
+        "store" = {
+          storePaths = [ config.system.build.toplevel ];
+          stripNixStorePrefix = true;
+          repartConfig = {
+            Type = "linux-generic";
+            Label = "store_${config.system.image.version}";
+            Format = "squashfs";
+            Minimize = "off";
+            ReadOnly = "yes";
+
+            SizeMinBytes = "1G";
+            SizeMaxBytes = "1G";
+            SplitName = "store";
+          };
+        };
+
+        # Placeholder for the second installed Nix store.
+        "store-empty" = {
+          repartConfig = {
+            Type = "linux-generic";
+            Label = "_empty";
+            Minimize = "off";
+            SizeMinBytes = "1G";
+            SizeMaxBytes = "1G";
+            SplitName = "-";
+          };
+        };
+
+        # Persistent storage
+        "var" = {
+          repartConfig = {
+            Type = "var";
+            UUID = "4d21b016-b534-45c2-a9fb-5c16e091fd2d"; # Well known
+            Format = "xfs";
+            Label = "nixos-persistent";
+            Minimize = "off";
+
+            # Has to be large enough to hold update files.
+            SizeMinBytes = "2G";
+            SizeMaxBytes = "2G";
+            SplitName = "-";
+
+            # Wiping this gives us a clean state.
+            FactoryReset = "yes";
+          };
+        };
+      };
+    };
+}

modules/system_overrides.nix

@@ -0,0 +1,5 @@
+{ lib, options, ... }: {
+  # This fields is immutable by default, but can be overridden.
+  options.system.nixos.codeName = lib.mkOption { readOnly = false; };
+  options.system.nixos.release = lib.mkOption { readOnly = false; };
+}

modules/sysupdate.nix

@@ -0,0 +1,63 @@
+{ config, ... }: {
+  systemd.sysupdate = {
+    enable = true;
+
+    transfers = {
+      "10-uki" = {
+        Source = {
+          MatchPattern = [
+            "${config.boot.uki.name}_@v.efi.xz"
+          ];
+
+          # We could fetch updates from the network as well:
+          #
+          # Path = "https://download.example.com/";
+          # Type = "url-file";
+          Path = "/var/updates/";
+          Type = "regular-file";
+        };
+        Target = {
+          InstancesMax = 2;
+          MatchPattern = [
+            "${config.boot.uki.name}_@v.efi"
+          ];
+
+          Mode = "0444";
+          Path = "/EFI/Linux";
+          PathRelativeTo = "boot";
+
+          Type = "regular-file";
+        };
+        Transfer = {
+          ProtectVersion = "%A";
+        };
+      };
+
+      "20-store" = {
+        Source = {
+          MatchPattern = [
+            "store_@v.img.xz"
+          ];
+          # Path = "https://download.example.com/";
+          # Type = "url-file";
+          Path = "/var/updates/";
+          Type = "regular-file";
+        };
+
+        Target = {
+          InstancesMax = 2;
+
+          # This doesn't work, because / is a tmpfs and the heuristic is not that smart.
+          #
+          # Path = "auto";
+          Path = "/dev/sda";
+
+          MatchPattern = "store_@v";
+
+          Type = "partition";
+          ReadOnly = "yes";
+        };
+      };
+    };
+  };
+}