linux-kernel - Re: [PATCH 1/2] BKL: Remove BKL from default

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Message-ID: <20091118175540.GR21750@bolzano.suse.de>
Date:	Wed, 18 Nov 2009 18:55:40 +0100
From:	Jan Blunck <jblunck@...e.de>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Jamie Lokier <jamie@...reable.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-fsdevel@...r.kernel.org,
	Linux-Kernel Mailinglist <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, jkacur@...hat.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Hellwig <hch@...radead.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 1/2] BKL: Remove BKL from default_llseek()

On Wed, Nov 18, Oliver Neukum wrote:

> Am Mittwoch, 18. November 2009 18:27:30 schrieb Jamie Lokier:
> > > No. Your logic is flawed
> > > 
> > > The BKL is protected something here - it protects the change of offset
> > > with respect to other BKL users within drivers. The question is what if
> > > anything in any other driver code depends upon the BKL and uses it to
> > > protect f_pos. Probably very little if anything but a grep for f_pos
> > > through the drivers might not be a bad idea before assuming this. Very
> > > few touch f_pos except in their own llseek method.
> > 
> > Of course, drivers shouldn't be using f_pos outside their llseek
> > method, as they should all behave the same with pread/pwrite as with
> > llseek+read/write.
> 
> Might not a driver update f_pos after read/write?

Actually the VFS is doing that for you in read/write syscall. So anything you
change in your driver gets corrected (or overwritten anyway).

Regards,
	Jan

-- 
Jan Blunck <jblunck@...e.de>
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