linux-kernel - Re: [RESEND] [PATCH] VFS: make file->f

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Message-ID: <20081008051630.GQ25780@parisc-linux.org>
Date:	Tue, 7 Oct 2008 23:16:31 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Hisashi Hifumi <hifumi.hisashi@....ntt.co.jp>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	torvalds@...ux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Theodore Ts'o <tytso@....edu>
Subject: Re: [RESEND] [PATCH] VFS: make file->f_pos access atomic on 32bit arch

On Wed, Oct 08, 2008 at 01:48:10PM +0900, Hisashi Hifumi wrote:
> Simultaneous access by two or more writer can corrupt file content,
> so this case needs some locks(flock or fcntl) to preserve synchronization
> of file content. This is responsibility of user-space application.
> But file->f_pos race issue can occur even if multiple threads just read 
> simultaneously. I think this is not responsibility of user-space application. 
> To avoid this currently, an application needs some locks to protect file offset
> even if it just read a file. So I think f_pos race should be fixed.

Why is this application not using pread() / pwrite() to use thread-local
file pointers?

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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