Index: uspace/srv/vfs/vfs_ops.c
===================================================================
--- uspace/srv/vfs/vfs_ops.c	(revision c544c5d07c2bd7b5301e09b4a820744b9010991c)
+++ uspace/srv/vfs/vfs_ops.c	(revision 11c2ae5a15f0dfff238ade7d0f2e9f969de56b0b)
@@ -72,6 +72,9 @@
 	dev_handle_t dev_handle;
 	vfs_node_t *mp_node = NULL;
+	ipc_callid_t callid;
+	ipc_call_t data;
 	int rc;
 	int phone;
+	size_t size;
 
 	/*
@@ -86,7 +89,4 @@
 	 * carry mount options in the future.
 	 */
-
-	ipc_callid_t callid;
-	size_t size;
 
 	/*
@@ -116,4 +116,15 @@
 	
 	/*
+	 * Wait for IPC_M_PING so that we can return an error if we don't know
+	 * fs_name.
+	 */
+	callid = async_get_call(&data);
+	if (IPC_GET_METHOD(data) != IPC_M_PING) {
+		ipc_answer_0(callid, ENOTSUP);
+		ipc_answer_0(rid, ENOTSUP);
+		return;
+	}
+
+	/*
 	 * Check if we know a file system with the same name as is in fs_name.
 	 * This will also give us its file system handle.
@@ -121,7 +132,11 @@
 	fs_handle_t fs_handle = fs_name_to_handle(fs_name, true);
 	if (!fs_handle) {
+		ipc_answer_0(callid, ENOENT);
 		ipc_answer_0(rid, ENOENT);
 		return;
 	}
+
+	/* Acknowledge that we know fs_name. */
+	ipc_answer_0(callid, EOK);
 
 	/* Now, we want the client to send us the mount point. */