linux-kernel - Re: O_DIRECT question

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Message-ID: <45AB6F69.6030004@aitel.hist.no>
Date:	Mon, 15 Jan 2007 13:11:21 +0100
From:	Helge Hafting <helge.hafting@...el.hist.no>
To:	Michael Tokarev <mjt@....msk.ru>
CC:	Chris Mason <chris.mason@...cle.com>,
	Linus Torvalds <torvalds@...l.org>,
	dean gaudet <dean@...tic.org>, Viktor <vvp01@...ox.ru>,
	Aubrey <aubreylee@...il.com>, Hua Zhong <hzhong@...il.com>,
	Hugh Dickins <hugh@...itas.com>, linux-kernel@...r.kernel.org,
	hch@...radead.org, kenneth.w.chen@...el.com, akpm@...l.org
Subject: Re: O_DIRECT question

Michael Tokarev wrote:
> Chris Mason wrote:
> []
>   
>> I recently spent some time trying to integrate O_DIRECT locking with
>> page cache locking.  The basic theory is that instead of using
>> semaphores for solving O_DIRECT vs buffered races, you put something
>> into the radix tree (I call it a placeholder) to keep the page cache
>> users out, and lock any existing pages that are present.
>>     
>
> But seriously - what about just disallowing non-O_DIRECT opens together
> with O_DIRECT ones ?
>   
Please do not create a new local DOS attack.
I open some important file, say /etc/resolv.conf
with O_DIRECT and just sit on the open handle.
Now nobody else can open that file because
it is "busy" with O_DIRECT ?

Helge Hafting
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