linux-kernel - Re: O_DIRECT question

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Message-ID: <Pine.LNX.4.58.0701172319570.2544@be1.lrz>
Date:	Wed, 17 Jan 2007 23:36:10 +0100 (CET)
From:	Bodo Eggert <7eggert@....de>
To:	Arjan van de Ven <arjan@...radead.org>
cc:	7eggert@....de, Helge Hafting <helge.hafting@...el.hist.no>,
	Michael Tokarev <mjt@....msk.ru>,
	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

On Tue, 16 Jan 2007, Arjan van de Ven wrote:
> On Tue, 2007-01-16 at 21:26 +0100, Bodo Eggert wrote:
> > Helge Hafting <helge.hafting@...el.hist.no> wrote:
> > > Michael Tokarev wrote:

> > >> 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 ?
> > 
> > Suspend O_DIRECT access while non-O_DIRECT-fds are open, fdatasync on close?
> 
> .. then any user can impact the operation, performance and reliability
> of the database application of another user... sounds like plugging one
> hole by making a bigger hole ;)

Don't allow other users to access your raw database files then, and if
backup kicks in, pausing the database would DTRT for integrety of the
backup. For other applications, paused O_DIRECT may very well be a
problem, but I can't think of one right now.

-- 
Logic: The art of being wrong with confidence... 
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