linux-kernel - Re: [patch 6/7] um: Convert mmapper to unlocked

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Date:	Thu, 15 Oct 2009 15:00:34 +0200
From:	Arnd Bergmann <arndbergmann@...glemail.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	ALan Cox <alan@...rguk.ukuu.org.uk>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jeff Dike <jdike@...toit.com>
Subject: Re: [patch 6/7] um: Convert mmapper to unlocked_ioctl

On Thursday 15 October 2009, Thomas Gleixner wrote:
> The ioctl is empty and needs no serialization. We might remove it
> completely but that would change the return value from -ENOIOCTLCMD to
> -ENOTTY.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Jeff Dike <jdike@...toit.com>

This one is tricky if you want to get it right according to the
book. ENOIOCTLCMD is never a valid return code for user space,
but sys_ioctl passes it down anyway.

However, returning -ENOIOCTLCMD from an *unlocked_ioctl* function
automatically gets turned into -EINVAL. It does this to allow
the same functions to be used for unlocked_ioctl and compat_ioctl.
In effect, this patch is functionally identical to removing the
ioctl function, which I think is what should be done here.

	Arnd <><
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