diff -ur util-linux-2.17.2/mount/mount.c util-linux-2.17.2.mod/mount/mount.c
--- util-linux-2.17.2/mount/mount.c	2011-01-14 23:29:43.000000000 +0100
+++ util-linux-2.17.2.mod/mount/mount.c	2011-01-14 23:42:31.000000000 +0100
@@ -149,6 +149,7 @@
   { "sync",	0, 0, MS_SYNCHRONOUS},	/* synchronous I/O */
   { "async",	0, 1, MS_SYNCHRONOUS},	/* asynchronous I/O */
   { "dirsync",	0, 0, MS_DIRSYNC},	/* synchronous directory modifications */
+  { "union",	0, 0, MS_UNION  },	/* Union mount */
   { "remount",  0, 0, MS_REMOUNT},      /* Alter flags of mounted FS */
   { "bind",	0, 0, MS_BIND   },	/* Remount part of tree elsewhere */
   { "rbind",	0, 0, MS_BIND|MS_REC }, /* Idem, plus mounted subtrees */
@@ -1446,6 +1447,8 @@
     case EBUSY:
       if (flags & MS_REMOUNT) {
 	error (_("mount: %s is busy"), node);
+      } else if (flags & MS_UNION) {
+	error (_("mount: %s is not read-only"), node);
       } else if (!strcmp(types, "proc") && !strcmp(node, "/proc")) {
 	/* heuristic: if /proc/version exists, then probably proc is mounted */
 	if (stat ("/proc/version", &statbuf))   /* proc mounted? */
@@ -1491,6 +1494,8 @@
 
       if (flags & MS_REMOUNT) {
 	error (_("mount: %s not mounted already, or bad option"), node);
+      } else if (flags & MS_UNION) {
+	error (_("mount: file system on %s doesn't support whiteouts"), spec);
       } else {
 	error (_("mount: wrong fs type, bad option, bad superblock on %s,\n"
 	       "       missing codepage or helper program, or other error"),
@@ -1585,10 +1590,13 @@
     case EACCES:  /* pre-linux 1.1.38, 1.1.41 and later */
     case EROFS:   /* linux 1.1.38 and later */
     { char *bd = (loop ? "" : _("block device "));
-      if (ro || (flags & MS_RDONLY)) {
-          error (_("mount: cannot mount %s%s read-only"),
+      if (flags & MS_UNION) {
+	  error (_("mount: %s%s is read-only"), bd, spec);
+	  break;
+      } else if (ro || (flags & MS_RDONLY)) {
+	  error (_("mount: cannot mount %s%s read-only"),
 		 bd, spec);
-          break;
+	  break;
       } else if (readwrite) {
 	  error (_("mount: %s%s is write-protected but explicit `-w' flag given"),
 		 bd, spec);
@@ -1950,6 +1958,7 @@
 	{ "make-rprivate", 0, 0, 142 },
 	{ "make-runbindable", 0, 0, 143 },
 	{ "no-canonicalize", 0, 0, 144 },
+	{ "union", 0, 0, 145 },
 	{ "internal-only", 0, 0, 'i' },
 	{ NULL, 0, 0, 0 }
 };
@@ -2079,7 +2088,7 @@
 
 static void
 print_version(int rc) {
-	printf(	"mount from %s (with "
+	printf(	"mount from %s (with union "
 #ifdef HAVE_LIBBLKID
 		"libblkid"
 #else
@@ -2249,6 +2258,9 @@
 		case 144:
 			nocanonicalize = 1;
 			break;
+		case 145: /* union */
+			mounttype = MS_UNION;
+			break;
 		case '?':
 		default:
 			usage (stderr, EX_USAGE);
diff -ur util-linux-2.17.2/mount/mount_constants.h util-linux-2.17.2.mod/mount/mount_constants.h
--- util-linux-2.17.2/mount/mount_constants.h	2010-02-04 12:53:56.000000000 +0100
+++ util-linux-2.17.2.mod/mount/mount_constants.h	2010-09-29 17:10:37.000000000 +0200
@@ -22,6 +22,25 @@
 #ifndef MS_DIRSYNC
 #define MS_DIRSYNC	128	/* Directory modifications are synchronous */
 #endif
+#ifndef MS_ACTION_MASK
+#define	MS_ACTION_MASK	0x380
+/* Remount, but new filesystem may be different from old. Atomic
+   (i.e. there is no interval when nothing is mounted at the mountpoint).
+   If new fs differs from the old one and old is busy - -EBUSY. */
+#define	MS_REPLACE	0x080	/* 128 */
+/* After, Before: as soon as we get unions these will add a new member
+   in the end or beginning of the chain. Fail if there is a stack
+   on the mountpoint. */
+#define	MS_AFTER	0x100	/* 256 */
+#define	MS_BEFORE	0x180
+/* Over: if nothing mounted on a mountpoint - same as if none of these
+flags had been set; if we have a union with more than one element - fail;
+if we have a stack or plain mount - mount atop of it, forming a stack. */
+#define	MS_OVER		0x200	/* 512 */
+#endif
+#ifndef MS_UNION
+#define MS_UNION	0x100	/* 256: Mount on top of a union */
+#endif
 #ifndef MS_NOATIME
 #define MS_NOATIME	0x400	/* 1024: Do not update access times. */
 #endif