+++ src/app/virtualbox/src/VBox/Frontends/VBoxBFE/VBoxBFE.cpp
@@ -158,6 +160,7 @@
 static bool        g_fReleaseLog = true; /**< Set if we should open the release. */
        const char *g_pszProgressString;
        unsigned    g_uProgressPercent = ~0U;
+static bool        g_fOverlay= false;
 
 
 /**
@@ -715,6 +718,8 @@
             g_fCSAM = false;
 #endif /* VBOXSDL_ADVANCED_OPTIONS */
         /* just show the help screen */
+        else if (strcmp(pszArg, "-overlay") == 0)
+            g_fOverlay = true;
         else
         {
             SyntaxError("unrecognized argument '%s'\n", pszArg);
@@ -1532,7 +1550,7 @@
         rc = CFGMR3InsertNode(pLunL0,   "AttachedDriver", &pDrv);                   UPDATE_RC();
         rc = CFGMR3InsertString(pDrv,   "Driver",         "VD");                    UPDATE_RC();
         rc = CFGMR3InsertNode(pDrv,     "Config",         &pCfg);                   UPDATE_RC();
-        rc = CFGMR3InsertString(pCfg,   "Path",           g_pszHdaFile);            UPDATE_RC();
+        rc = CFGMR3InsertString(pCfg,   "Type",           "HardDisk");              UPDATE_RC();
 
         if (g_fHdaSpf)
         {
@@ -1541,13 +1559,23 @@
         else
         {
             char *pcExt = RTPathExt(g_pszHdaFile);
-            if ((pcExt) && (!strcmp(pcExt, ".vdi")))
+            if ((pcExt) && (!strcmp(pcExt, ".vdi") && !g_fOverlay))
             {
                 rc = CFGMR3InsertString(pCfg, "Format",       "VDI");               UPDATE_RC();
+                rc = CFGMR3InsertString(pCfg, "Path",         g_pszHdaFile);            UPDATE_RC();
             }
             else
             {
-                rc = CFGMR3InsertString(pCfg, "Format",       "VMDK");              UPDATE_RC();
+                /*
+                 * Use the overlay.vdi file to store differential changes.
+                 * Leave the VMDK file passed as argument unchanged.
+                 */
+                PCFGMNODE pParent = 0;
+                rc = CFGMR3InsertString(pCfg, "Format", "VDI");              UPDATE_RC();
+                rc = CFGMR3InsertString(pCfg, "Path",   "/ram/overlay.vdi");      UPDATE_RC();
+                rc = CFGMR3InsertNode(pCfg,   "Parent", &pParent);            UPDATE_RC();
+                rc = CFGMR3InsertString(pParent, "Format", "VDI");           UPDATE_RC();
+                rc = CFGMR3InsertString(pParent, "Path",   g_pszHdaFile);     UPDATE_RC();
             }
         }
     }