flake: create generator for aarch64 sdcard image

hosts/caramel/default.nix

@@ -1,4 +1,4 @@
-{ config, inputs, modules, overlays, pkgs, ... }: {
+{ config, inputs, modules, modulesPath, overlays, pkgs, ... }: {
   networking.hostName = "caramel";
   system.stateVersion = "21.11";
   time.timeZone = "Asia/Phnom_Penh";
@@ -12,6 +12,7 @@
   };
   imports =
     (with modules.system; [
+      "${builtins.toString modulesPath}/installer/sd-card/sd-image-aarch64.nix"
       inputs.home-manager-porcupine.nixosModule
 
       base
@@ -23,15 +24,16 @@
 
       ./filesystem.nix
       ./kernel.nix
+      ./image.nix
       ./networking.nix
       ./packages.nix
 
       ../../users/hana
     ]) ++
     (with modules.services; [
-      nginx
-      postgres
-      synapse
+#       nginx
+#       postgres
+#       synapse
       tmptsync
       unbound
       vaultwarden

hosts/caramel/filesystem.nix

@@ -1,4 +1,4 @@
-{ config, ... }:
+{ config, lib, ... }:
 let
   bind = src: {
     depends = [ "/persist" ];
@@ -9,16 +9,31 @@ let
   };
 in {
   fileSystems = {
-    "/" = {
+    "/" = lib.mkForce {
       device = "rootfs";
       fsType = "tmpfs";
-      options = [ "defaults" "size=2G" "mode=755" ];
+      options = [ "defaults" "size=1G" "mode=755" ];
     };
 
-    "/nix" = {
+    # "/nix" = {
+    #   device = "overlayfs";
+    #   fsType = "overlay";
+    #   options = [
+    #     "lowerdir=/mnt/image/nix"
+    #     "upperdir=/persist/nix-overlay"
+    #     "workdir=/persist/.overlaytmp"
+    #   ];
+    #   noCheck = true;
+    #   depends = [ "/mnt/image" "/persist" ];
+    # };
+
+    "/nix" = (bind "/mnt/image/nix") // { depends = [ "/mnt/image" ]; };
+
+    "/mnt/image" = {
       device = "/dev/disk/by-label/NIXOS_SD";
       fsType = "ext4";
       options = [ "defaults" "noatime" ];
+      neededForBoot = true;
     };
 
     "/persist" = {
@@ -31,6 +46,6 @@ in {
     "/var/persist" = bind "/persist";
     "/var/lib/acme" = bind "/persist/acme";
     "/var/log/journal" = bind "/persist/journal";
-    "/boot" = (bind "/nix/persist/boot") // { depends = [ "/nix" ]; };
+    "/boot" = (bind "/mnt/image/boot") // { depends = [ "/mnt/image" ]; };
   };
 }

hosts/caramel/image.nix

@@ -0,0 +1,29 @@
+{ config, lib, pkgs, ... }: {
+  sdImage.expandOnBoot = false;
+  boot.postBootCommands = ''
+    # On the first boot do some maintenance tasks
+    if [ -f /mnt/image/nix-path-registration ]; then
+      set -euo pipefail
+      set -x
+      # Figure out device names for the boot device and root filesystem.
+      rootPart=$(${pkgs.util-linux}/bin/findmnt -n -o SOURCE /mnt/image)
+      bootDevice=$(lsblk -npo PKNAME $rootPart)
+      partNum=$(lsblk -npo MAJ:MIN $rootPart | ${pkgs.gawk}/bin/awk -F: '{print $2}')
+
+      # Resize the root partition and the filesystem to fit the disk
+      echo ",+," | sfdisk -N$partNum --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 < /mnt/image/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 /mnt/image/nix-path-registration
+    fi
+  '';
+}

hosts/caramel/kernel.nix

@@ -1,11 +1,15 @@
-{ config, inputs, pkgs, ... }: {
+{ config, inputs, lib, pkgs, ... }: {
   imports = [
     inputs.nixos-hardware.nixosModules.raspberry-pi-4
   ];
   hardware.raspberry-pi."4".fkms-3d.enable = true;
 
-  boot.kernel.sysctl = {
-    "kernel.core_pattern" = "|/bin/false";
-    "kernel.sysrq" = 1;
+  boot = {
+    initrd.kernelModules = [ "overlay" ];
+    supportedFilesystems = lib.mkForce [ "btrfs" "vfat" ];
+    kernel.sysctl = {
+      "kernel.core_pattern" = "|/bin/false";
+      "kernel.sysrq" = 1;
+    };
   };
 }