Extend tcmu dev_config to support optional device ID

Signed-off-by: Xun Chen <xunchen@hust.edu.cn>

Author: Xun Chen

pkg/snapshot/storage.go

@@ -275,6 +275,31 @@ func IsErofsFilesystem(path string) bool {
 	return binary.LittleEndian.Uint32(byte4) == 0xe0f5e1e2
 }
 
+// IsExperimentalEnabled checks whether the experimental.enable field is true in the config file.
+func IsExperimentalEnabled(configPath string) (bool, error) {
+	// Read the configuration file
+	data, err := os.ReadFile(configPath)
+	if err != nil {
+		return false, fmt.Errorf("failed to read config file %s: %w", configPath, err)
+	}
+
+	// Define a struct to match the JSON structure
+	type Config struct {
+		Experimental struct {
+			Enable bool `json:"enable"`
+		} `json:"experimental"`
+	}
+
+	// Parse the JSON data
+	var config Config
+	if err := json.Unmarshal(data, &config); err != nil {
+		return false, fmt.Errorf("failed to parse config file %s: %w", configPath, err)
+	}
+
+	// Return the value of experimental.enable
+	return config.Experimental.Enable, nil
+}
+
 func AttachDevice(ctx context.Context, params *AttachDeviceParams) (devName string, e error) {
 
 	devName = ""
@@ -299,8 +324,19 @@ func AttachDevice(ctx context.Context, params *AttachDeviceParams) (devName stri
 		}
 	}()
 
-	if err = os.WriteFile(path.Join(targetPath, "control"), ([]byte)(fmt.Sprintf("dev_config=overlaybd/%s", configPath)), 0666); err != nil {
-		return devName, fmt.Errorf("failed to write target dev_config for %s: dev_config=overlaybd/%s: %w", targetPath, configPath, err)
+	enabled, err := IsExperimentalEnabled("/etc/overlaybd-snapshotter/config.json")
+	if err != nil {
+		return devName, fmt.Errorf("failed to check experimental flag: %w", err)
+	}
+	log.G(ctx).Infof("experimental enabled: %t", enabled)
+	if enabled {
+		if err = os.WriteFile(path.Join(targetPath, "control"), ([]byte)(fmt.Sprintf("dev_config=overlaybd/%s;%s", configPath, snID)), 0666); err != nil {
+			return devName, fmt.Errorf("failed to write target dev_config for %s: dev_config=overlaybd/%s;%s: %w", targetPath, configPath, snID, err)
+		}
+	} else {
+		if err = os.WriteFile(path.Join(targetPath, "control"), ([]byte)(fmt.Sprintf("dev_config=overlaybd/%s", configPath)), 0666); err != nil {
+			return devName, fmt.Errorf("failed to write target dev_config for %s: dev_config=overlaybd/%s: %w", targetPath, configPath, err)
+		}
 	}
 
 	err = os.WriteFile(path.Join(targetPath, "control"), ([]byte)(fmt.Sprintf("max_data_area_mb=%d", obdMaxDataAreaMB)), 0666)

script/config.json

@@ -6,5 +6,8 @@
     "runtimeType": "containerd",
     "logReportCaller": false,
     "autoRemoveDev": false,
-    "mirrorRegistry": []
+    "mirrorRegistry": [],
+    "experimental": {
+        "enable": true
+    }
 }