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

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Message-Id: <20070108131957.cbaf6736.akpm@osdl.org>
Date:	Mon, 8 Jan 2007 13:19:57 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Shaya Potter <spotter@...columbia.edu>
Cc:	"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@....cs.sunysb.edu>,
	Erez Zadok <ezk@...sunysb.edu>
Subject: Re: [PATCH 01/24] Unionfs: Documentation

On Mon, 8 Jan 2007 14:43:39 -0500 (EST)
Shaya Potter <spotter@...columbia.edu> wrote:

> On Mon, 8 Jan 2007, Andrew Morton wrote:
> 
> > On Sun,  7 Jan 2007 23:12:53 -0500
> > "Josef 'Jeff' Sipek" <jsipek@...sunysb.edu> wrote:
> >
> >> +Modifying a Unionfs branch directly, while the union is mounted, is
> >> +currently unsupported.
> >
> > Does this mean that if I have /a/b/ and /c/d/ unionised under /mnt/union, I
> > am not allowed to alter anything under /a/b/ and /c/d/?  That I may only
> > alter stuff under /mnt/union?
> >
> > If so, that sounds like a significant limitation.
> 
> haven't we been through this?

If it's not in the changelog or the documentation, it doesn't exist.  It's
useful for the developers to keep track of obvious and frequently-asked
questions such as this and to address them completely in the changelog
and/or documentation.  Otherwise things just come around again and again,
as we see here.

>  It's the same thing as modifying a block 
> device while a file system is using it.  Now, when unionfs gets confused, 
> it shouldn't oops, but would one expect ext3 to allow one to modify its 
> backing store while its using it?

There's no such problem with bind mounts.  It's surprising to see such a
restriction with union mounts.

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