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Date: Tue, 12 May 2009 16:22:21 +1000
From: Paul Mackerras <paulus@samba.org>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@elte.hu>,
       Corey Ashford <cjashfor@linux.vnet.ibm.com>,
       linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 3/5] perf_counter: rework ioctl()s
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References: <20090508165219.469818319@chello.nl>
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Peter Zijlstra writes:

> Hmm, are you saying that the 3rd argument to unlocked_ioctl is actually
> (void __user *) instead of unsigned long?

He's saying (correctly) that using _IOR or _IOW implies that the ioctl
is going to read or write the memory location pointed to by the 3rd
argument to unlocked_ioctl.  If the 3rd argument is just a number, not
an address, I believe you should use _IO.

Paul.