Subject: Re: device busy upon mount
To: Zafer Aydogan <>
From: Antti Kantee <>
List: tech-kern
Date: 09/11/2007 21:05:56
On Tue Sep 11 2007 at 19:32:57 +0200, Zafer Aydogan wrote:
> > Ah, ok, I found the problem.  The real problem, I guess, is that device
> > nodes on layered file systems don't appear to really work.
> >
> > When a layered vnode is initialized, it has a special specinfo structure
> > allocated for it.  The specmountpoint field, which is causing EBUSY
> > to be returned, is uninitialized memory (deadbeef on a debug kernel),
> > so this is clearly wrong.  If I initialize it to NULL to allow mount to
> > proceed, I get a panic at unmount for dangling buffers.
> >
> > Another point is that layered vnodes don't appear to be considered
> > aliases, although I think they should; at least in the sense that they
> > should share specinfo with all the other nodes in the stack.
> >
> > All this needs a bit more than my next 5min timeslice.  For now the best
> > solution is to not null-mount /dev and e.g. mount a second tmpfs for it.
> >
> Excellent. Not null mounting /dev solved all problems.
> I will release a new version with this fix and send a patch to xtraeme.

Cool!  Please file a PR about the layerfs problem.  I don't have time
to deal with the issue in the coming days.

Antti Kantee <>                     Of course he runs NetBSD                
    "la qualité la plus indispensable du cuisinier est l'exactitude"