nix-builder disko

AGENTS.md

@@ -653,7 +653,8 @@ A host registry may use a specification like this:
 
 The current role assignment is intentional: nix-example is the development VM;
 ops is the remote-access VM with host-specific static networking;
-internal-app-01 is the container server VM; and installer builds the minimal
+internal-app-01 is the container server VM; nix-builder is the remote Nix build
+VM with dedicated build and store disks; and installer builds the minimal
 installation ISO without Home Manager. x1g9 is a full NixOS desktop with niri,
 labwc, ly, the shared Linux desktop applications, and the personal workload.
 x1g13 is the secure NixOS development and personal ThinkPad, with the same
@@ -692,6 +693,10 @@ configuration fragments. For example:
 
 ```text
 hosts/
+├── nix-builder/
+│   ├── disko.nix
+│   ├── hardware-configuration.nix
+│   └── nixos.nix
 ├── installer/
 │   └── nixos.nix
 ├── internal-app-01/
@@ -721,12 +726,15 @@ hosts/
 ```
 
 `hosts/x1g9/nixos.nix` explicitly loads `hardware-configuration.nix` with the
-normal top-level Nix module `imports`. `hosts/x1g13/nixos.nix` loads its
-generated hardware configuration and host-local `disko.nix` the same way. Do
-not confuse these host imports with the prohibition on top-level `imports` in
-unit configuration fragments. `hosts/galleria/disko.nix` manages only the two
-dedicated NixOS partitions by PARTUUID and deliberately excludes the Windows
-disk, Windows partitions, and the Windows EFI System Partition.
+normal top-level Nix module `imports`. `hosts/nix-builder/nixos.nix` and
+`hosts/x1g13/nixos.nix` load their generated hardware configuration and
+host-local `disko.nix` the same way. The nix-builder Disko definition mounts its
+existing VM filesystems by stable QEMU SCSI IDs and does not take destructive
+ownership of them. Do not confuse these host imports with the prohibition on
+top-level `imports` in unit configuration fragments. `hosts/galleria/disko.nix`
+manages only the two dedicated NixOS partitions by PARTUUID and deliberately
+excludes the Windows disk, Windows partitions, and the Windows EFI System
+Partition.
 
 Derive the system class from the host's `system`:
 

hosts/nix-builder/disko.nix

@@ -0,0 +1,66 @@
+_:
+let
+  osDisk = "/dev/disk/by-id/scsi-0QEMU_QEMU_HARDDISK_drive-scsi0";
+in
+{
+  disko.enableConfig = true;
+
+  # The VM disks already contain live filesystems. Model each existing
+  # filesystem without giving Disko ownership of their partitioning or data.
+  disko.devices.disk = {
+    boot = {
+      type = "disk";
+      device = "${osDisk}-part1";
+      destroy = false;
+
+      content = {
+        type = "filesystem";
+        format = "vfat";
+        mountpoint = "/boot";
+        mountOptions = [ "umask=0077" ];
+      };
+    };
+
+    root = {
+      type = "disk";
+      device = "${osDisk}-part2";
+      destroy = false;
+
+      content = {
+        type = "filesystem";
+        format = "ext4";
+        mountpoint = "/";
+      };
+    };
+
+    nix-build = {
+      type = "disk";
+      device = "/dev/disk/by-id/scsi-0QEMU_QEMU_HARDDISK_drive-scsi1";
+      destroy = false;
+
+      content = {
+        type = "filesystem";
+        format = "ext4";
+        mountpoint = "/var/lib/nix-build";
+        mountOptions = [ "noatime" ];
+      };
+    };
+
+    nix-store = {
+      type = "disk";
+      device = "/dev/disk/by-id/scsi-0QEMU_QEMU_HARDDISK_drive-scsi2";
+      destroy = false;
+
+      content = {
+        type = "filesystem";
+        format = "ext4";
+        mountpoint = "/nix/store";
+        mountOptions = [ "noatime" ];
+      };
+    };
+  };
+
+  fileSystems."/nix/store".neededForBoot = true;
+  nix.settings.build-dir = "/var/lib/nix-build";
+  services.fstrim.enable = true;
+}

hosts/nix-builder/filesystem.nix

@@ -1,25 +0,0 @@
-{
-  fileSystems."/nix/store" = {
-    device = "/dev/disk/by-label/nix-store";
-    fsType = "ext4";
-
-    options = [
-      "noatime"
-    ];
-
-    neededForBoot = true;
-  };
-
-  fileSystems."/var/lib/nix-build" = {
-    device = "/dev/disk/by-label/nix-build";
-    fsType = "ext4";
-
-    options = [
-      "noatime"
-    ];
-  };
-
-  nix.settings.build-dir = "/var/lib/nix-build";
-
-  services.fstrim.enable = true;
-}

hosts/nix-builder/hardware-configuration.nix

@@ -20,20 +20,6 @@
   boot.kernelModules = [ ];
   boot.extraModulePackages = [ ];
 
-  fileSystems."/" = {
-    device = "/dev/disk/by-uuid/49fc2e1c-7909-41cc-ac78-55b4d9a01e62";
-    fsType = "ext4";
-  };
-
-  fileSystems."/boot" = {
-    device = "/dev/disk/by-uuid/40D4-ABBE";
-    fsType = "vfat";
-    options = [
-      "fmask=0077"
-      "dmask=0077"
-    ];
-  };
-
   swapDevices = [ ];
 
   nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";

hosts/nix-builder/nixos.nix

@@ -1,6 +1,6 @@
 {
   imports = [
-    ./filesystem.nix
+    ./disko.nix
     ./hardware-configuration.nix
   ];
 }