- mount allows loopback devices to be mounted
  more than once to the same mount point

--- util-linux-2.13-pre6/mount/fstab.h.twiceloop	2006-09-15 08:50:46.000000000 +0200
+++ util-linux-2.13-pre6/mount/fstab.h	2006-09-15 08:51:10.000000000 +0200
@@ -2,6 +2,7 @@
 int mtab_is_writable(void);
 int mtab_does_not_exist(void);
 int is_mounted_once(const char *name);
+int is_mounted_same_loopfile(const char *loopfile, const char *dir);
 
 struct mntentchn {
 	struct mntentchn *nxt, *prev;
--- util-linux-2.13-pre6/mount/mount.c.twiceloop	2006-09-15 08:50:23.000000000 +0200
+++ util-linux-2.13-pre6/mount/mount.c	2006-09-15 08:50:24.000000000 +0200
@@ -671,7 +671,7 @@
 
 static int
 loop_check(const char **spec, const char **type, int *flags,
-	   int *loop, const char **loopdev, const char **loopfile) {
+	   int *loop, const char **loopdev, const char **loopfile, const char *dir) {
   int looptype;
   unsigned long long offset;
 
@@ -709,6 +709,11 @@
     } else {
       int loopro = (*flags & MS_RDONLY);
 
+      if (is_mounted_same_loopfile(*loopfile, dir)) {
+	error(_("mount: %s already mounted on %s"), *loopfile, dir);
+	return EX_FAIL;
+      }
+      
       if (!*loopdev || !**loopdev)
 	*loopdev = find_unused_loop_device();
       if (!*loopdev)
@@ -856,7 +861,7 @@
        * stale assignments of files to loop devices. Nasty when used for
        * encryption.
        */
-      res = loop_check(&spec, &types, &flags, &loop, &loopdev, &loopfile);
+      res = loop_check(&spec, &types, &flags, &loop, &loopdev, &loopfile, node);
       if (res)
 	  goto out;
   }
--- util-linux-2.13-pre6/mount/fstab.c.twiceloop	2006-09-15 08:50:23.000000000 +0200
+++ util-linux-2.13-pre6/mount/fstab.c	2006-09-15 08:50:24.000000000 +0200
@@ -254,6 +254,27 @@
 	return (ct == 1);
 }
 
+/*
+ * Given the loop file LOOPFILE, and the mount point DIR, check that
+ * same file is already mounted on same directory 
+ *
+ * Don't forget there's 
+ *   /path/loopfile /path/dir loop=/dev/loop0
+ * in mtab for loop devices.
+ */
+int
+is_mounted_same_loopfile(const char *loopfile, const char *dir) {
+	struct mntentchn *mc, *mc0;
+	int ct = 0;
+
+	mc0 = mtab_head();
+	for (mc = mc0->prev; mc && mc != mc0; mc = mc->prev)
+		if (streq(mc->m.mnt_fsname, loopfile) && 
+		    streq(mc->m.mnt_dir, dir))
+			ct++;
+	return (ct == 1);
+}
+
 /* Given the name FILE, try to find the option "loop=FILE" in mtab.  */ 
 struct mntentchn *
 getmntoptfile (const char *file) {