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

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Date:	Mon, 8 Jan 2007 21:24:57 +0100 (MET)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	Shaya Potter <spotter@...columbia.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@....cs.sunysb.edu>,
	Erez Zadok <ezk@...sunysb.edu>
Subject: Re: [PATCH 01/24] Unionfs: Documentation


On Jan 8 2007 14:43, Shaya Potter 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?  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?

(Blunt counter-example: Modifying the underlying filesystem of
an NFS import does not break. But I agree with Shaya.)

Well it was suggested to make /a/b and /c/d read-only while the
union is mounted, using a ro bind mount, what about it? (To
catch unwanted tampering with the lowlevels)

	-`J'
-- 
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