The VFS union mount patches require some changes to util-linux and
e2fsprogs to support the union mount option and the ext2 whiteout
feature flag.  We are not submitting them for formal review at this
time, but the patches are below for quick reference.  They are also
available in git repos linked to from the Union Mount HOWTO page:

http://valerieaurora.org/union/

-VAL

From: Valerie Aurora Henson <vaurora@redhat.com>
Date: Sat, 21 Mar 2009 20:56:57 -0700
Subject: [PATCH 1/1] union mount patches from:

ftp://ftp.suse.com/pub/people/jblunck/union-mount/util-linux-2.13-union_mount.diff
---
 mount/mount.c           |    5 +++++
 mount/mount_constants.h |    3 +++
 2 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/mount/mount.c b/mount/mount.c
index 9cbc466..9bf766b 100644
--- a/mount/mount.c
+++ b/mount/mount.c
@@ -138,6 +138,7 @@ static const struct opt_map opt_map[] = {
   { "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 */
@@ -1638,6 +1639,7 @@ static struct option longopts[] = {
 	{ "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 }
 };
@@ -1929,6 +1931,9 @@ main(int argc, char *argv[]) {
 		case 143:
 			mounttype = (MS_UNBINDABLE | MS_REC);
 			break;
+		case 145: /* union */
+			mounttype = MS_UNION;
+			break;
 
 		case '?':
 		default:
diff --git a/mount/mount_constants.h b/mount/mount_constants.h
index dc3ca27..fb4c663 100644
--- a/mount/mount_constants.h
+++ b/mount/mount_constants.h
@@ -39,6 +39,9 @@ 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