file system with no gratuitous writes?

[Steven Bellovin <smb%cs.columbia.edu@localhost>]

I'm building a compact flash-based system for a Soekris box.  I'd like to set 
it up so that there are no write operations that are not specifically initiated 
by the administrator.  That is, if I modify a configuration file, of course 
that should be flushed to disk; however, I don't want writes at any other time, 
such as rewriting the superblock every 30 seconds.  Is there some way I can do 
it?

In an older instance of this system, the disk was mounted read-only; I'd mount 
it read-write to updated it, flush the buffer cache, then remount it read-only. 
 On 5.0 and later, however (and as has been discussed ad nauseum), that is no 
longer supported.  The next possibility is to have some way to mount the file 
system so there are no such writes.  Specifying noatime will certainly help -- 
but is that enough?  (Log files and such use tmpfs, so they're not a problem.)  
I've also thought about mounting /var/db as a FAT file system -- would that do 
the trick?  Any other suggestions?

                --Steve Bellovin, http://www.cs.columbia.edu/~smb