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To: current@freebsd.org
Reply-To: graphix@iastate.edu
Subject: translucent filesystem (was union mounts)
Date: Sun, 20 Oct 1996 14:14:12 CDT
From: Kent Vander Velden <graphix@iastate.edu>
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  (After asking this question yesterday I received message saying that
my use of terms was incorrect.  Here is my question again, corrected.)

  After searching the mail list archives I have a bad feeling that that
translucent filesystems do not work but hoped that perhaps they where
fixed in current.

  To make certain that I do not misunderstand the way in which a
translucent filesystem is supposed to work I do:

mount -t union -o -b /usr/src /original/usr/src

  I would like to be able to modify code that exists in /usr/src and as
I modify it (at least the first time) have it copied to
/original/usr/src.  All new additions in /original/usr/src exist only in
/original/usr/src.  All of the files that are in /usr/src appear in
/original/usr/src.  /usr/src should never be altered unless the files
are referenced via /usr/src.

  What happens is that a directory listing of /original/usr/src
displays only the files that where created in /original/usr/src and not
those in /usr/src.  If I access a file that should exist in
/original/usr/src/ because of the mount, the file does exist.  If I
access a directory that should exist there, a new directory is created.

  The code that is in /usr/src/sys/miscfs/unionfs/ suggest that I should
replace certain files in /usr/src/lib/libc/gen/ but the suggested
replacements do not compile (perhaps fixable... did not look that
closely at the errors).

  If I compile a current kernel with the null and union filesystems
staticly linked the system will die on startup with a page fault.  At
the moment I am using a union mount with the lkm module.

  Do translucent filesystems work or do I misunderstand the use of them?
>From the sound of the mount_union man page this should do exactly what
I want.

  Thanks.

---
Kent Vander Velden
graphix@iastate.edu