From mboxrd@z Thu Jan  1 00:00:00 1970
From: Glauber Costa <glommer@parallels.com>
Subject: Re: [PATCH 4/4] parse options in the vfs level
Date: Tue, 2 Aug 2011 11:43:37 -0300
Message-ID: <4E380D19.7030307@parallels.com>
References: <1311947059-17209-1-git-send-email-glommer@parallels.com> <1311947059-17209-5-git-send-email-glommer@parallels.com> <20110731013456.GM5404@dastard> <4E37F5C6.8060908@parallels.com> <20110802141806.GL2203@ZenIV.linux.org.uk>
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Cc: Dave Chinner <david@fromorbit.com>, <linux-kernel@vger.kernel.org>,
	<linux-fsdevel@vger.kernel.org>,
	<containers@lists.linux-foundation.org>,
	Pavel Emelyanov <xemul@parallels.com>,
	Hugh Dickins <hughd@google.com>,
	Nick Piggin <npiggin@kernel.dk>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Rik van Riel <riel@redhat.com>,
	Dave Hansen <dave@linux.vnet.ibm.com>,
	James Bottomley <JBottomley@parallels.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
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On 08/02/2011 11:18 AM, Al Viro wrote:
> On Tue, Aug 02, 2011 at 10:04:06AM -0300, Glauber Costa wrote:
>
>> I am not sure either, but I still believe my proposal is superior to
>> write-to-a-file specifically. Writing to a file, be it in proc, sys,
>> or wherever, leaves a window of opportunity open between mounting a
>> filesystem and limiting its caches. Doing it on mount is atomic.
>>
>> Effectively, I see this limit as a property of a particular instance
>> of a mounted filesystem. Since all properties of a filesystem are
>> specified during mount, this becomes a natural extension.
>
> The trouble is, dentry tree is fundamentally a property of superblock.
> It's shared between *all* instances of that fs in all mount trees...

And how is it different from any fs-specific options, like the ones extX 
have, for instance ? Many of them seem to operate on a superblock.

If you mount a superblock somewhere, you can tweak specifics about its 
operation. If you mount it somewhere else, the assumption is you know 
what you're doing.