llama-cpp.service: add support for --models-dir flag (#477593)

nixos/modules/services/misc/llama-cpp.nix

@@ -19,9 +19,17 @@ in
       package = lib.mkPackageOption pkgs "llama-cpp" { };
 
       model = lib.mkOption {
-        type = lib.types.path;
+        type = lib.types.nullOr lib.types.path;
         example = "/models/mistral-instruct-7b/ggml-model-q4_0.gguf";
         description = "Model path.";
+        default = null;
+      };
+
+      modelsDir = lib.mkOption {
+        type = lib.types.nullOr lib.types.path;
+        example = "/models/";
+        description = "Models directory.";
+        default = null;
       };
 
       extraFlags = lib.mkOption {
@@ -61,7 +69,6 @@ in
   };
 
   config = lib.mkIf cfg.enable {
-
     systemd.services.llama-cpp = {
       description = "LLaMA C++ server";
       after = [ "network.target" ];
@@ -70,7 +77,25 @@ in
       serviceConfig = {
         Type = "idle";
         KillSignal = "SIGINT";
-        ExecStart = "${cfg.package}/bin/llama-server --log-disable --host ${cfg.host} --port ${toString cfg.port} -m ${cfg.model} ${utils.escapeSystemdExecArgs cfg.extraFlags}";
+        ExecStart =
+          let
+            args = [
+              "--host"
+              cfg.host
+              "--port"
+              (toString cfg.port)
+            ]
+            ++ lib.optionals (cfg.model != null) [
+              "-m"
+              cfg.model
+            ]
+            ++ lib.optionals (cfg.modelsDir != null) [
+              "--models-dir"
+              cfg.modelsDir
+            ]
+            ++ cfg.extraFlags;
+          in
+          "${cfg.package}/bin/llama-server ${utils.escapeSystemdExecArgs args}";
         Restart = "on-failure";
         RestartSec = 300;