Index: Makefile
==================================================================
--- Makefile
+++ Makefile
@@ -74,11 +74,13 @@
 	echo 'if {[catch { eval $$::env(XVFS_TEST_LOAD_COMMANDS); source $(XVFS_ROOT_MOUNTPOINT)example/main.tcl }]} { puts stderr $$::errorInfo; exit 1 }; exit 0' > __test__.tcl
 	@export XVFS_ROOT_MOUNTPOINT; export XVFS_TEST_LOAD_COMMANDS; for XVFS_TEST_LOAD_COMMANDS in \
 		'load ./example-standalone$(LIB_SUFFIX) Xvfs_example' \
 		'load -global ./xvfs$(LIB_SUFFIX); load ./example-client$(LIB_SUFFIX) Xvfs_example' \
 		'load ./xvfs$(LIB_SUFFIX); load ./example-flexible$(LIB_SUFFIX) Xvfs_example' \
-		'load ./example-flexible$(LIB_SUFFIX) Xvfs_example'; do \
+		'load ./example-flexible$(LIB_SUFFIX) Xvfs_example' \
+		'load ./xvfs$(LIB_SUFFIX); load ./example-standalone$(LIB_SUFFIX) Xvfs_example' \
+		'load ./example-standalone$(LIB_SUFFIX) Xvfs_example; load ./xvfs$(LIB_SUFFIX)'; do \
 			echo "[$${XVFS_TEST_LOAD_COMMANDS}] $(GDB) $(TCLSH) __test__.tcl $(TCL_TEST_ARGS)"; \
 			$(GDB) $(TCLSH) __test__.tcl $(TCL_TEST_ARGS) || exit 1; \
 	done
 	rm -f __test__.tcl
 

Index: xvfs-core.c
==================================================================
--- xvfs-core.c
+++ xvfs-core.c
@@ -25,10 +25,12 @@
 #define XVFS_INTERNAL_SERVER_MAGIC "\xD4\xF3\x05\x96\x25\xCF\xAF\xFE"
 #define XVFS_INTERNAL_SERVER_MAGIC_LEN 8
 
 struct xvfs_tclfs_server_info {
 	char magic[XVFS_INTERNAL_SERVER_MAGIC_LEN];
+	int protocolVersion;
+	const char *rootMountpoint;
 	int (*registerProc)(Tcl_Interp *interp, struct Xvfs_FSInfo *fsInfo);
 };
 #endif /* XVFS_MODE_FLEXIBLE || XVFS_MODE_SERVER */
 
 #if defined(XVFS_MODE_SERVER) || defined(XVFS_MODE_STANDALONE) || defined(XVFS_MODE_FLEXIBLE)
@@ -980,12 +982,29 @@
 	/*
 	 * XXX:TODO: What is the chance that the handler for //xvfs:/ hold
 	 * client data smaller than XVFS_INTERNAL_SERVER_MAGIC_LEN ?
 	 */
 	if (memcmp(fsHandlerData->magic, XVFS_INTERNAL_SERVER_MAGIC, sizeof(fsHandlerData->magic)) == 0) {
-		XVFS_DEBUG_PUTS("Found a server handler");
-		xvfs_register = fsHandlerData->registerProc;
+		/*
+		 * Refuse to talk to the in-core implementation if it is a lower
+		 * version.
+		 */
+		XVFS_DEBUG_PUTS("Found a server handler, checking for compatible version");
+		if (fsHandlerData->protocolVersion >= XVFS_PROTOCOL_VERSION) {
+			XVFS_DEBUG_PUTS("Found a server handler with a compatible version, checking for compatible root");
+			if (strcmp(XVFS_ROOT_MOUNTPOINT, fsHandlerData->rootMountpoint) == 0) {
+				XVFS_DEBUG_PUTS("Found a server handler with a compatible version and checking for compatible root");
+
+				xvfs_register = fsHandlerData->registerProc;
+			}
+		}
+	}
+
+	if (xvfs_register == &xvfs_standalone_register) {
+		XVFS_DEBUG_PUTS("Using xvfs_standalone_register");
+	} else {
+		XVFS_DEBUG_PUTS("Using Xvfs_Register from Xvfs Server Core");
 	}
 
 	XVFS_DEBUG_LEAVE;
 
 	return(xvfs_register(interp, fsInfo));
@@ -995,11 +1014,11 @@
 #if defined(XVFS_MODE_SERVER)
 static Tcl_Filesystem xvfs_tclfs_dispatch_fs;
 static Tcl_HashTable xvfs_tclfs_dispatch_map;
 static struct xvfs_tclfs_server_info xvfs_tclfs_dispatch_fsdata;
 
-static int xvfs_tclfs_dispatch_pathInFS(Tcl_Obj *path, ClientData *dataPtr) {
+static int xvfs_tclfs_dispatch_pathInXVFS(Tcl_Obj *path) {
 	const char *pathStr, *rootStr;
 	int pathLen, rootLen;
 
 	XVFS_DEBUG_ENTER;
 
@@ -1045,11 +1064,11 @@
 
 	XVFS_DEBUG_ENTER;
 
 	path = xvfs_absolutePath(path);
 
-	if (xvfs_tclfs_dispatch_pathInFS(path, NULL) != TCL_OK) {
+	if (xvfs_tclfs_dispatch_pathInXVFS(path) != TCL_OK) {
 		Tcl_DecrRefCount(path);
 
 		XVFS_DEBUG_LEAVE;
 
 		return(NULL);
@@ -1093,10 +1112,21 @@
 	 * a warning about it not being used.
 	 */
 	xvfs_tclfs_pathInFilesystem(NULL, NULL, NULL);
 	return(NULL);
 }
+
+static int xvfs_tclfs_dispatch_pathInFS(Tcl_Obj *path, ClientData *dataPtr) {
+	struct xvfs_tclfs_instance_info *instanceInfo;
+
+	instanceInfo = xvfs_tclfs_dispatch_pathToInfo(path);
+	if (!instanceInfo) {
+		return(-1);
+	}
+
+	return(TCL_OK);
+}
 
 static int xvfs_tclfs_dispatch_stat(Tcl_Obj *path, Tcl_StatBuf *statBuf) {
 	struct xvfs_tclfs_instance_info *instanceInfo;
 
 	instanceInfo = xvfs_tclfs_dispatch_pathToInfo(path);
@@ -1194,11 +1224,13 @@
 	xvfs_tclfs_dispatch_fs.loadFileProc               = NULL;
 	xvfs_tclfs_dispatch_fs.getCwdProc                 = NULL;
 	xvfs_tclfs_dispatch_fs.chdirProc                  = NULL;
 
 	memcpy(xvfs_tclfs_dispatch_fsdata.magic, XVFS_INTERNAL_SERVER_MAGIC, XVFS_INTERNAL_SERVER_MAGIC_LEN);
-	xvfs_tclfs_dispatch_fsdata.registerProc = Xvfs_Register;
+	xvfs_tclfs_dispatch_fsdata.registerProc    = Xvfs_Register;
+	xvfs_tclfs_dispatch_fsdata.protocolVersion = XVFS_PROTOCOL_VERSION;
+	xvfs_tclfs_dispatch_fsdata.rootMountpoint  = XVFS_ROOT_MOUNTPOINT;
 
 	tclRet = Tcl_FSRegister((ClientData) &xvfs_tclfs_dispatch_fsdata, &xvfs_tclfs_dispatch_fs);
 	if (tclRet != TCL_OK) {
 		if (interp) {
 			Tcl_SetResult(interp, "Tcl_FSRegister() failed", NULL);