linux-kernel - Re: [patch] fs: remove local variable copy of f

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Date:	Fri, 2 May 2008 16:41:00 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Matti Linnanvuori <mattilinnanvuori@...oo.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] fs: remove local variable copy of f_pos to enable
	thread-safe updates

On Fri, May 02, 2008 at 08:33:50AM -0700, Matti Linnanvuori wrote:

> File systems can be written so that implementations of read, lseek etc.
> acquire a lock before using *pos, which precludes races. That was the
> idea behind my patch. So, my patch does not necessarily cause races.
> read instances can be racy in Linux now because there is no lock to
> serialize read etc. system calls.

Oh, yes it does - current tree guarantees that variable passed to ->read()
will not change under it, so any code that relied on that got broken.

And no, modifying every driver's ->read() is not going to be fun - it's
not just filesystems.
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