pkgs.writeErofsLayers,profiles/ch-runner: MVE

$ nix-build -A examples.dummy.config.debug.closure.erofs.list | xargs
cat | xargs du -h
749M    /nix/store/bzfv5x6lycq6hzhjv6d6vlk1q8fdg9di-base0.erofs
24M     /nix/store/hp41jfq36y0mmjrzqilyh3jfsvqic3kb-nixos.erofs

$ nix run -f . examples.dummy.config.uvms.cloud-hypervisor.runner
...
<<< Welcome to NixOS 25.11pre-git (x86_64) - ttyS0 >>>

nixos login:

The definition of the `pkgs` fixpoint was moved to pkgs/default.nix.
For that, dirToAttrs was moved to lib/, imported ad hoc

profiles/ch-runner.nix

@@ -0,0 +1,114 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+# It is not the intent to stick to the microvm.nix-like static interface,
+# but we shall begin by reproducing at least some of their work.
+
+let
+  cfg = config.uvms.cloud-hypervisor;
+  inherit (config.debug.closure.erofs) layers;
+in
+{
+  options = {
+    uvms.cloud-hypervisor.enable = lib.mkEnableOption "Configure guest (e.g. fileSystems)";
+    uvms.cloud-hypervisor.runner = lib.mkOption {
+      type = lib.types.package;
+      description = "A naive script for running this system in cloud-hypervisor";
+    };
+    uvms.cloud-hypervisor.extraArgv = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+    };
+    uvms.cloud-hypervisor.argv = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+    };
+    uvms.cloud-hypervisor.extraCmdline = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [ ];
+    };
+    uvms.cloud-hypervisor.cmdline = lib.mkOption {
+      type = lib.types.listOf lib.types.str;
+      default = [
+        "earlyprintk=ttyS0"
+        "console=ttyS0"
+        "reboot=t"
+        "panic=-1"
+        "init=${config.system.build.toplevel}/init"
+      ]
+      ++ config.boot.kernelParams
+      ++ config.uvms.cloud-hypervisor.extraCmdline;
+    };
+  };
+  config = lib.mkMerge [
+    {
+      uvms.cloud-hypervisor.argv = lib.mkBefore (
+        [
+          (lib.getExe pkgs.cloud-hypervisor)
+          "--cmdline=${lib.concatStringsSep " " cfg.cmdline}"
+          "--kernel=${config.boot.kernelPackages.kernel}/${pkgs.stdenv.hostPlatform.linux-kernel.target}"
+          "--initramfs=${config.system.build.initialRamdisk}/${config.system.boot.loader.initrdFile}"
+          "--vsock=cid=4,socket=CONNECT.sock"
+          "--api-socket=ch.sock"
+          "--serial=tty"
+          "--console=null"
+          "--watchdog"
+          "--seccomp=true"
+        ]
+        ++ cfg.extraArgv
+      );
+      uvms.cloud-hypervisor.runner = pkgs.writeShellScriptBin "run-${config.networking.hostName}" ''
+        set -euo pipefail
+        GUESTNAME=${config.networking.hostName}
+        args=(
+        ${lib.concatMapStringsSep "\n" lib.escapeShellArg cfg.argv}
+        )
+        mkdir -p "$HOME/uvms/$GUESTNAME"
+        cd "$HOME/uvms/$GUESTNAME"
+        cleanup() {
+            rm "$HOME/uvms/$GUESTNAME"/{ch,CONNECT}.sock
+        }
+        exec -a "uuvm/$GUESTNAME" "''${args[@]}"
+      '';
+    }
+    (lib.mkIf cfg.enable {
+      boot.initrd.availableKernelModules = [
+        "erofs"
+        "overlay"
+        "virtio_mmio"
+        "virtio_pci"
+        "virtio_blk"
+        # "9pnet_virtio"
+        # "9p"
+        "virtiofs"
+      ];
+      boot.initrd.systemd.enable = true;
+      fileSystems = {
+        "/nix/store" = {
+          fsType = "overlay";
+          overlay.lowerdir = map (img: "/nix/.ro-stores/${toString img.seq}") layers;
+          neededForBoot = true;
+        };
+      }
+      // lib.listToAttrs (
+        map (
+          img:
+          lib.nameValuePair "/nix/.ro-stores/${toString img.seq}" {
+            device = "/dev/disk/by-label/${img.label}";
+            neededForBoot = true;
+            options = [ "x-systemd.device-timeout=5" ];
+          }
+        ) layers
+      );
+      uvms.cloud-hypervisor.argv = [
+        "--memory=size=1536M,hotplug_size=1536M,hotplugged_size=512M,hotplug_method=virtio-mem,mergeable=on,shared=on"
+        "--cpus=boot=4"
+        "--disk"
+      ]
+      ++ map (img: "path=${img},readonly=true,id=${toString img.label}") layers;
+    })
+  ];
+}