freebsd stable - Jun 2007 - unionfs through whole / with upper layer on remote NFS directory

Hi all,

can you advise me if it is real and realizable what I plan ?

Here it is, I have installed fbsd-6-stable pc with the last unionfs
diff-19 patch and
have a recompiled kernel with this new unionfs implementation and I
would like this:

- /dev/ad0s1a on CF card is read-only permanently
- mdconfig is forbiden to create var and tmp ramdisks in rc.conf
- to my custom directory for example /unionfs is mounted remote NFS
directory
with read-write rights and with no_all_squash or no_root_squash and sync
options etc.

- the upper layer of unionfs should be on this remote NFS directory
- the lower layer of unionfs should be the whole mount point / the whole
CF card with ro

When I tried to start this command, new error message appeared and I do
not know what to do with this probably because I do something wrong.

The mount_unionfs utility attaches directory above uniondir in such a way
that the contents of both directory trees remain visible.  By default,
directory becomes the upper layer and uniondir becomes the lower layer.

So directory is /unionfs
and lower layer is the whole /

# mount -t unionfs /unionfs /
mount_unionfs: /unionfs (/unionfs) and / (/) are not distinct paths

the second try:

# mount -t unionfs /unionfs /dev/ad0s1a like with cd-rom
mount: /dev/ad0s1a: not a directory

but with /var it is okay
# mount -t unionfs /unionfs /var

# mount
/dev/ad0s1a on / (ufs, NFS exported, local)
devfs on /dev (devfs, local)
/dev/ad0s2a on /free (ufs, local, soft-updates)
procfs on /proc (procfs, local)
<above>:/unionfs on /var (unionfs, local)
NFS:/home/buffer on /unionfs (nfs)


It seems that lower layer could not be the whole / or /dev/ad0s1a, doesn?t it ?

Bye

Dan