linux-kernel - Re: [PATCH 01/24] Unionfs: Documentation

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Message-ID: <20070110212744.GD12654@atrey.karlin.mff.cuni.cz>
Date:	Wed, 10 Jan 2007 22:27:45 +0100
From:	Jan Kara <jack@...e.cz>
To:	Erez Zadok <ezk@...sunysb.edu>
Cc:	Andrew Morton <akpm@...l.org>,
	Josef 'Jeff' Sipek <jsipek@...sunysb.edu>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	hch@...radead.org, viro@....linux.org.uk, torvalds@...l.org,
	mhalcrow@...ibm.com, David Quigley <dquigley@...sunysb.edu>
Subject: Re: [PATCH 01/24] Unionfs: Documentation

> In message <20070110161215.GB12654@...ey.karlin.mff.cuni.cz>, Jan Kara writes:
> > > In message <20070109122644.GB1260@...ey.karlin.mff.cuni.cz>, Jan Kara writes:
> [...]
> > > Jan, all of it is duable: we can downgrade the f/s to readonly, grab various
> > > locks, search through various lists looking for open fd's and such, then
> > > decide if to allow the mount or not.  And hopefully all of that can be done
> > > in a non-racy manner.  But it feels just rather hacky and ugly to me.  If
> > > this community will endorse such a solution, we'll be happy to develop it.
> > > But right now my impression is that if we posted such patches today, some
> > > people will have to wipe the vomit off of their monitors... :-)
> >   I see :). To me it just sounds as if you want to do remount-read-only
> > for source filesystems, which is operation we support perfectly fine,
> > and after that create union mount. But I agree you cannot do quite that
> > since you need to have write access later from your union mount. So
> > maybe it's not so easy as I thought.
> >   On the other hand, there was some effort to support read-only bind-mounts of
> > read-write filesystems (there were even some patches floating around but
> > I don't think they got merged) and that should be even closer to what
> > you'd need...
> 
> I didn't know about those patches, but yes, they do sound useful.  I'm
> curious who needed such functionality before and why.  If someone can point
> me to those patches, we can look into using them for Unionfs.  Thanks.
  Dave Hansen writes them. One of recent submissions starts for example at
http://openvz.org/pipermail/devel/2006-December/002543.html.

									Honza

-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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