tool/create: take guest config into account

core/internal/build.nix

@@ -26,6 +26,7 @@ mkIf cfg.enable {
       mkdir -p $out/boot
       ln -sT ${config.system.build.toplevel}/init $out/boot/init
       cp ${closureInfo}/registration $out/boot/nix-path-registration
+    ln -s ${pkgs.writeText "miniguest-config.json" (builtins.toJSON cfg)} $out/miniguest-config.json
     ${lib.optionalString (cfg.guestType == "qemu")
     "cp -P ${config.system.build.toplevel}/{kernel,initrd} -t $out"
     }

tool/common.hpp

@@ -17,6 +17,7 @@
  */
 
 #include <filesystem>
+#include <nlohmann/json.hpp>
 #include <optional>
 
 namespace miniguest {
@@ -48,4 +49,26 @@ private:
 
 void completeGuestName(size_t, std::string_view prefix);
 
+enum class GuestType { qemu, lxc };
+NLOHMANN_JSON_SERIALIZE_ENUM(GuestType, {
+                                            {GuestType::qemu, "qemu"},
+                                            {GuestType::lxc, "lxc"},
+                                        })
+
+enum class QemuFsType { _9p, virtiofs };
+NLOHMANN_JSON_SERIALIZE_ENUM(QemuFsType, {
+                                             {QemuFsType::_9p, "9p"},
+                                             {QemuFsType::virtiofs, "virtiofs"},
+                                         })
+
+struct GuestConfig final {
+  GuestType guest_type;
+  QemuFsType qemu_fs_type;
+};
+
+inline void from_json(const nlohmann::json &j, GuestConfig &cfg) {
+  j.at("guestType").get_to(cfg.guest_type);
+  j.at("qemu").at("fsType").get_to(cfg.qemu_fs_type);
+}
+
 } // namespace miniguest

tool/create.cpp

@@ -49,6 +49,16 @@ struct CmdCreate : virtual EvalCommand, virtual MixProfile {
 	-t, --hypervisor: hypervisor to configure. Can be one of: 'libvirt' and 'lxc' (default: 'libvirt'))"";
   }
 
+  GuestConfig load_config() {
+    auto path =
+        fs::path("/etc/miniguests") / guest_name / "miniguest-config.json";
+    try {
+      return nlohmann::json::parse(readFile(path)).get<GuestConfig>();
+    } catch (SysError &err) { logWarning(err.info()); }
+    warn("metadata unavailable: falling back to defaults");
+    return {};
+  }
+
   void display_command(Strings cmd) const {
     std::cout << "# Create " << guest_name << " using:" << std::endl;
     for (auto &line : cmd)
@@ -56,24 +66,28 @@ struct CmdCreate : virtual EvalCommand, virtual MixProfile {
     std::cout << std::endl;
   }
 
-  void display_command_libvirt() const {
+  void display_command_libvirt(const GuestConfig &cfg) const {
+    auto virtiofs = cfg.qemu_fs_type == QemuFsType::virtiofs;
+    std::string memorybacking =
+        virtiofs ? " --memorybacking=access.mode=shared" : "";
+    std::string fsArgs =
+        virtiofs ? "driver.type=virtiofs" : "readonly=yes,accessmode=squash";
     Strings cmd{
         "virt-install -n " + guest_name,
         "--connect qemu:///system",
         "--os-variant nixos-unstable",
-        "--memory 1536",
+        "--memory 1536" + memorybacking,
         "--disk none",
         "--import",
         "--boot kernel=/etc/miniguests/" + guest_name +
             "/kernel,initrd=/etc/miniguests/" + guest_name + "/initrd",
-        "--filesystem /nix/store/,nix-store,readonly=yes,accessmode=squash",
-        "--filesystem /etc/miniguests/" + guest_name +
-            "/boot/,boot,readonly=yes,accessmode=squash",
+        "--filesystem /nix/store/,nix-store," + fsArgs,
+        "--filesystem /etc/miniguests/" + guest_name + "/boot/,boot," + fsArgs,
     };
     display_command(cmd);
   }
 
-  void display_command_lxc() const {
+  void display_command_lxc(const GuestConfig &cfg) const {
     Strings cmd = {
         "lxc-create " + guest_name,
         "-f extra-config",
@@ -89,7 +103,7 @@ struct CmdCreate : virtual EvalCommand, virtual MixProfile {
   }
 
   struct HypervisorData {
-    void (CmdCreate::*display_commmand)() const;
+    void (CmdCreate::*display_commmand)(const GuestConfig &cfg) const;
   };
 
   static const std::map<std::string, HypervisorData> hypervisors;
@@ -119,13 +133,15 @@ struct CmdCreate : virtual EvalCommand, virtual MixProfile {
   }
 
   void run(ref<Store> store) override {
+    auto cfg = load_config();
+
     if (!hypervisor)
-      hypervisor = "libvirt";
+      hypervisor = cfg.guest_type == GuestType::lxc ? "lxc" : "libvirt";
 
     if (auto it = hypervisors.find(*hypervisor); it != hypervisors.end()) {
-      (this->*it->second.display_commmand)();
+      (this->*it->second.display_commmand)(cfg);
     } else
-      throw Error(2, "unknown hypervisor type");
+      throw Error(2, "unknown hypervisor type: " + *hypervisor);
   }
 
   virtual ~CmdCreate() = default;