linux-kernel - Re: [PATCH] sony_pi: Remove the BKL from sonypi_misc

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Message-Id: <200910221550.05524.arnd@arndb.de>
Date:	Thu, 22 Oct 2009 15:50:04 +0200
From:	Arnd Bergmann <arndbergmann@...glemail.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Arnd Bergmann <arndbergmann@...glemail.com>,
	John Kacur <jkacur@...hat.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] sony_pi: Remove the BKL from sonypi_misc_open

On Thursday 22 October 2009, Christoph Hellwig wrote:

> The right (although quite complicated) thing is to return -ESPIPE from
> vfs_llseek if no ->llseek method is present, or even better also
> disallowing pread/pwrite by default.  It'll need a quite substantial
> audit and is best done by different types of inodes - S_IFIFO is easy,
> SIFDIR at least has very few instances, S_IFREG usually wants a real
> llseek (generic_file_llseek in most cases) and directories also need
> a llseek method that takes i_mutex so it protects against namespace
> operations.

Is it safe to assume that file_operations without a read() or write()
method also don't need llseek?

There are over 200 instances of file_operations that have a no read,
write or lseek operations and we can easily detect that in vfs_llseek,
calling no_llseek by default.

Testing for S_IFREG will not work well for debugfs, which is probably
a large number of the cases that do not want an llseek method.

	Arnd <><
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