Mounting FS read-only for specific user (or root)

[Andrew Bradford]

Hi all,

I'm trying to set up a mounted filesystem that is read-write for root, 
but read-only for anyone else.  It will be mounted as a backup 
directory, so files listed in that directory will be owned by current 
users on the system but can't be writeable, regardless of the file 
permissions.

Example
<normal filesystems mounted from hd1>
hd2 mounted rw in /root/backup-rw
hd2 mounted ro in /backups

Only root should be able to write to anything under /root/backup-rw/ 
even though normal users will own files in that directory.  Normal users 
should be able to read anything that permissions allow in /backups so 
that they can restore files from the backup.

I was planning on using the nullfs fs type to achieve the second 
mountpoint for the fs.

Is this possible?

Thanks,

Andrew