System::getJsonFilesOnUsbStick(): return list of JSON files for configured

directory under mount path.

common/src/System.cpp

@@ -332,6 +332,27 @@ QString System::getUSBMountPath(QString const &dirPathUnderMountPath) {
     return "";
 }
 
+QStringList System::getJsonFilesOnUsbStick(QString const &mountPath) {
+    QStringList jsonFiles;
+
+    // /media/sda2/etc/psa_config
+    QString const &dirPath = QDir::cleanPath(mountPath + QDir::separator() + "etc" + QDir::separator() + "psa_config");
+    QDir d(dirPath);
+    if (d.exists()) {
+        QDirIterator it(dirPath, QStringList() << "*.json", QDir::Files, QDirIterator::NoIteratorFlags);
+        while (it.hasNext()) {
+            QString const &jsonFile = it.next();
+            QFileInfo fi(jsonFile);
+            if (System::allowedJsonFiles.contains(fi.fileName())) {
+                jsonFiles << jsonFile;
+            } else {
+                qCritical() << "Warning:" << fi.fileName() << "unknown";
+            }
+        }
+    }
+
+    return jsonFiles;
+}
 
 /********************************************************************************
  * static function to check if a mounted sd-card is writable.