microvm host is stable (for now)

- per-system default.nix now inherits the source tree via `src` (this
allows modules to be optionally imported from `modules/opt/`)
- adds a default config for microvm hosts
  - enables systemd-networkd by default
  - allows passing in vms
  - binds vm nix-store to host nix-store
  - allows merging systemd jounals
- adds microvms to palatine-hill

Signed-off-by: ahuston-0 <aliceghuston@gmail.com>

modules/microvm-host.nix

@@ -1,33 +0,0 @@
-{
-  config,
-  lib,
-  inputs,
-  ...
-}:
-let
-  cfg = config.rad-dev.microvm-host;
-  inherit (inputs.microvm.nixosModules) microvm;
-in
-{
-  # imports = [microvm.host];
-  options.rad-dev.microvm-host = {
-    enable = lib.mkEnableOption "microvm-host";
-  };
-  config = lib.mkIf cfg.enable {
-    networking.useNetworkd = true;
-    # microvm.shares = [
-    #   {
-    #     tag = "ro-store";
-    #     source = "/nix/store";
-    #     mountPoint = "/nix/.ro-store";
-    #   }
-    # ];
-    #     systemd.tmpfiles.rules = map (vmHost:
-    #   let
-    #     machineId = lib.addresses.machineId.${vmHost};
-    #   in
-    #     # creates a symlink of each MicroVM's journal under the host's /var/log/journal
-    #     "L+ /var/log/journal/${machineId} - - - - /var/lib/microvms/${vmHost}/journal/${machineId}"
-    # ) (builtins.attrNames lib.addresses.machineId);
-  };
-}

modules/opt/default.nix

@@ -0,0 +1,5 @@
+{ ... }:
+
+{
+
+}

modules/opt/microvm-host.nix

@@ -0,0 +1,41 @@
+{
+  config,
+  lib,
+  inputs,
+  ...
+}:
+let
+  cfg = config.rad-dev.microvm-host;
+  microvm = inputs.microvm.nixosModules;
+in
+{
+  imports = [ microvm.host ];
+  options.rad-dev.microvm-host = {
+    vms = lib.mkOption {
+      type = lib.types.attrset;
+      default = { };
+      description = "A list of VMs to construct on the host";
+    };
+  };
+  config = {
+    networking.useNetworkd = true;
+    microvm.vms = cfg.vms;
+    microvm.shares = [
+      {
+        tag = "ro-store";
+        source = "/nix/store";
+        mountPoint = "/nix/.ro-store";
+      }
+    ];
+
+    # TODO: deprecate this once we have syslog forwarders
+    systemd.tmpfiles.rules = map (
+      vmHost:
+      let
+        machineId = lib.addresses.machineId.${vmHost};
+      in
+      # creates a symlink of each MicroVM's journal under the host's /var/log/journal
+      "L+ /var/log/journal/${machineId} - - - - /var/lib/microvms/${vmHost}/journal/${machineId}"
+    ) (builtins.attrNames lib.addresses.machineId);
+  };
+}