linux-ext4 - Re: Can one file system be R/W mounted multiple times in Linux?

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Message-ID: <20150112130058.GM20899@x2.net.home>
Date:	Mon, 12 Jan 2015 14:00:58 +0100
From:	Karel Zak <kzak@...hat.com>
To:	Lukáš Czerner <lczerner@...hat.com>
Cc:	Stefan Hajnoczi <stefanha@...hat.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Dexuan Cui <decui@...rosoft.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"'linux-ext4'" <linux-ext4@...r.kernel.org>
Subject: Re: Can one file system be R/W mounted multiple times in Linux?

On Fri, Jan 09, 2015 at 04:52:11PM +0100, Lukáš Czerner wrote:
> Now the question is, whether 'mount' can be a bit smarter than that
> and just mount the already existing block device instead of creating
> new one ? Karel ?

Well, the question is how smart is too smart :-) And Al is right, problem
is in races.

Anyway, I'd like to avoid complex FS specific code in mount(8). IMHO
it's FS driver responsibility to avoid (or support) FS sharing between
more block devices.

BTW, for ext4 you can enable ETX4_FEATURE_INCOMPAT_MMP to protect
against multi-mount.

    Karel

-- 
 Karel Zak  <kzak@...hat.com>
 http://karelzak.blogspot.com
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