linux-kernel - Re: Union mount and lockdep design issues

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Message-ID: <87liw24ijo.fsf@tucsk.pomaz.szeredi.hu>
Date:	Wed, 13 Jul 2011 11:49:15 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Michal Suchanek <hramrach@...trum.cz>
Cc:	Ian Kent <ikent@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	David Howells <dhowells@...hat.com>,
	Ric Wheeler <rwheeler@...hat.com>,
	Alexander Viro <aviro@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>
Subject: Re: Union mount and lockdep design issues

Michal Suchanek <hramrach@...trum.cz> writes:

> You can still do
>
> mount --bind /lower1 /lower2/lower1
> mount --bind /lower2 /lower1/lower2
>
> Which is technically not against usage guidelines, unlike mount --bind
> /upper /lower1/upper

Overlayfs will take the directory you specify as upperdir and lowerdir
and will clone those mounts internally.

This means that any present or future submounts are ignored and the
mount containting those directories may be moved or umounted and
overlayfs will still function.

None of the bind mounts above will have any effect on an overlayfs that
uses /lower[12] and /upper.

> If crossing mount boundaries is forbidden try with symlinks or hardlinks.

I'm not sure what you mean here.

Thanks,
Miklos
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