the current status of nullfs, unionfs
ezk at cs.sunysb.edu
Thu Mar 10 10:45:37 PST 2005
In message <76f962c6050310092461fc850 at mail.gmail.com>, Lou Kamenov writes:
> On Thu, 10 Mar 2005 09:19:10 -0500, Michael W. Lucas
> <mwlucas at blackhelicopters.org> wrote:
> > On Thu, Mar 10, 2005 at 12:38:43PM +0100, Jeremie Le Hen wrote:
> > But the mere existence of even a basic regression test would be a
> > start and would encourage people to not hose things further.
> > Folks, don't let the fact that you're not a guru stop you from taking
> > a kiddie step and submitting a basic test!
> I do use unionfs on daily basis. Mostly to union $home/bin directories and
> such. For the last 1.5y I had it crash only 2 times. Of course trying
> to unmount /bin
> will turn into hell. I've used it successfully with pdumpfs from ports
> to restore
> old filespace view. I surely think that a stable unionfs will be a
> good thing (tm).
> Erez's unionfs has the same problem, the case there is that you wont be
> able to unmount it at all. (At least last time I tried with 1.0.3)
You should NEVER be allowed to unmount an underlying file system of a
stackable file system, if it's busy or in use, no more than you can remove a
/dev/sda drive while ffs is mounted on it. Our approach in the Linux
unionfs is to prevent users from shooting themselves too much in the
However, our unionfs does provide mechanisms such that read-only or non-busy
file system branches in the union, *can* indeed be removed safely.
Generally we can support arbitrary insertions and removals of branches
anywhere in the (fan-out) union; however, we found out that most of our
unionfs users rarely want or need that.
BTW, the latest version of our linux unionfs is 1.0.9. There has been a lot
of work done on our unionfs recently, and it was deemed stable enough that
several LiveCD distros, including the just-released Knoppix 3.8, are using
> Problem or not it could be easily solved with simple heuristics.
> Building a filespace
> with unioning shouldnt really be that hard.
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