rootfs: Build using the image-builder

modules/system-types.nix

@@ -34,14 +34,18 @@ let
       }
       {
         name = "system";
-        # Equivalent to:
-        #  → nix-build nixos -I nixos-config=system-image.nix -A config.system.build.sdImage
-        path = ((import (pkgs.path + "/nixos")) { configuration = ../system-image.nix; }).config.system.build.sdImage;
+        path = config.system.build.rootfs;
       }
     ];
   };
 in
 {
+  imports = [
+    ../systems/rootfs.nix
+    # FIXME: factor out installation device profile.
+    <nixpkgs/nixos/modules/profiles/installation-device.nix>
+  ];
+
   options.mobile = {
     system.type = mkOption {
       type = types.enum (lib.attrNames build_types);

systems/rootfs.nix

@@ -0,0 +1,83 @@
+# This builds a rootfs image (ext4) from the current configuration.
+{ config, lib, pkgs, ... }:
+
+{
+  boot.loader.grub.enable = false;
+  boot.loader.generic-extlinux-compatible.enable = false;
+
+  system.build.rootfs =
+    pkgs.imageBuilder.fileSystem.makeExt4 {
+      name = "NIXOS_SYSTEM";
+      partitionID = "44444444-4444-4444-8888-888888888888";
+      populateCommands =
+      let
+        closureInfo = pkgs.buildPackages.closureInfo { rootPaths = config.system.build.toplevel; };
+      in
+      ''
+        mkdir -p ./nix/store
+        echo "Copying system closure..."
+        while IFS= read -r path; do
+          echo "  Copying $path"
+          cp -prf "$path" ./nix/store
+        done < "${closureInfo}/store-paths"
+        echo "Done copying system closure..."
+        cp -v ${closureInfo}/registration ./nix-path-registration
+      '';
+      # FIXME : fixup the partition autoexpand.
+      extraPadding = pkgs.imageBuilder.size.MiB 500;
+    }
+  ;
+
+  # FIXME: this is not a rootfs!
+  system.build.diskImage = 
+    pkgs.imageBuilder.diskImage.makeMBR {
+      name = "mobile-nixos";
+      diskID = "01234567";
+      partitions = [
+        # FIXME : initrd how?
+        config.system.build.rootfs
+      ];
+    }
+  ;
+
+  #pkgs.runCommandNoCC "mobile-nixos-rootfs" {} ''
+  #  echo "${config.system.build.toplevel}" > $out
+  #'';
+
+  boot.postBootCommands = ''
+    # On the first boot do some maintenance tasks
+    if [ -f /nix-path-registration ]; then
+      ${""
+      # TODO : optionally resize NIXOS_SYSTEM, depending on the target.
+      # # Figure out device names for the boot device and root filesystem.
+      # rootPart=$(readlink -f /dev/disk/by-label/NIXOS_SYSTEM)
+      # bootDevice=$(lsblk -npo PKNAME $rootPart)
+
+      # # Resize the root partition and the filesystem to fit the disk
+      # echo ",+," | sfdisk -N2 --no-reread $bootDevice
+      # ${pkgs.parted}/bin/partprobe
+      # ${pkgs.e2fsprogs}/bin/resize2fs $rootPart
+      }
+
+      # Register the contents of the initial Nix store
+      ${config.nix.package.out}/bin/nix-store --load-db < /nix-path-registration
+
+      # nixos-rebuild also requires a "system" profile and an /etc/NIXOS tag.
+      touch /etc/NIXOS
+      ${config.nix.package.out}/bin/nix-env -p /nix/var/nix/profiles/system --set /run/current-system
+
+      # Prevents this from running on later boots.
+      rm -f /nix-path-registration
+    fi
+  '';
+
+  fileSystems = {
+    "/" = {
+      # Expected to be installed as `system` partition on android-like.
+      # Thus the name.
+      # TODO: move into the android system type.
+      device = "/dev/disk/by-label/NIXOS_SYSTEM";
+      fsType = "ext4";
+    };
+  };
+}