Fix container Id detection from cgroup as "12:rdma:/" is possible

plugin.go

@@ -168,17 +168,24 @@ func getContainerId() (string, error) {
 	defer file.Close()
 
 	scanner := bufio.NewScanner(file)
-	if !scanner.Scan() {
-		return "", errors.New("cgroup is empty")
+	for scanner.Scan() {
+		// The file name is the container identifier
+		// Example: 12:rdma:/docker/a33940bf95ec6c57b6d79a3edfa784a1364ce840fb92c9a7f3951b9f7b0ccccb/docker/330d9b057fdd54b224cd38daf370524f7e8c567ccf95f33a2388f02c0b854982
+		line := scanner.Text()
+		pathOffset := strings.LastIndex(line, ":")
+		if pathOffset == -1 {
+			continue
+		}
+
+		cgroup := line[pathOffset + 1:]
+
+		result := path.Base(cgroup)
+		if result == "." || result == "/" {
+			continue
+		}
+
+		return result, nil
 	}
 
-	// The file name is the container identifier
-	// Example: 12:rdma:/docker/a33940bf95ec6c57b6d79a3edfa784a1364ce840fb92c9a7f3951b9f7b0ccccb/docker/330d9b057fdd54b224cd38daf370524f7e8c567ccf95f33a2388f02c0b854982
-	cgroup := scanner.Text()
-	result := path.Base(cgroup)
-	if result == "." {
-		return "", errors.New("cgroup is unexpected")
-	}
-
-	return result, nil
+	return "", errors.New("no suitable cgroup entry found")
 }