unionfs 5.4
Jeremie Le Hen
jeremie at le-hen.org
Thu Mar 10 04:05:54 PST 2005
> And if unionfs panic the system on 5.4 too, I think it can't be STABLE
> at all.
>
> BTW, from man mount_nullfs:
>
> BUGS
> THIS FILE SYSTEM TYPE IS NOT YET FULLY SUPPORTED (READ: IT DOESN'T WORK)
> AND USING IT MAY, IN FACT, DESTROY DATA ON YOUR SYSTEM. USE AT
> YOUR OWN RISK. BEWARE OF DOG. SLIPPERY WHEN WET.
>
> So you can't suggest to use nullfs instead of unionfs, because "is
> well-documented to be broken".
FYI, this is an email I just sent in reply to David Schultz on -hackers at .
%%%
Date: Thu, 10 Mar 2005 12:38:43 +0100
From: Jeremie Le Hen <jeremie at le-hen.org>
To: David Schultz <das at FreeBSD.ORG>
Cc: freebsd-fs at FreeBSD.ORG
Cc: Mikhail Teterin <mi+mx at aldan.algebra.com>
Cc: hackers at FreeBSD.ORG
Hi David,
> Nullfs works better than unionfs. Unionfs worked well in 4.X.
> Despite numerous minor bugs such as being unable to cope with
> FIFOs, several people have reported using it quite successfully on
> production systems. However, unionfs no longer works quite as
> well in 5.X or -CURRENT. There are several reasons for this:
>
> 1. Nobody seems to have both the time and interest to maintain it.
>
> 2. Developers can't be expected to prevent regressions in
> something that's unsupported.
>
> 3. There are a couple of people who always respond to questions
> about unionfs with comments along the lines of:
> ``It's broken, so we won't help you. Go away and don't tell
> us if you find any bugs.''
>
> There's some pretty low-hanging fruit in terms of nits to fix.
> See the PR database if you're interested in helping, and don't let
> anyone scare you away. ;-)
>
> > What about the `union' option to regular mounts? Is that safe to use?
>
> Last I checked, it was very broken, but I'm not sure.
A little time ago, phk@ asked for people to submit regression tests for
virtual filesystem like this [1]. AFAIK, nobody submitted even one test
so far. This could be a good starting point to have unionfs work
correctly again. However, I think FreeBSD VFS gurus should first spread
some ideas and clues about tests to do. I guess indeed there are very
tricky ones that most common mortals wouldn't even suspect.
Regards,
[1] http://lists.freebsd.org/pipermail/freebsd-current/2005-January/045743.html
--
Jeremie Le Hen
< jeremie at le-hen dot org >< ttz at chchile dot org >
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