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

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Message-ID: <20091015162926.25a99cab@lxorguk.ukuu.org.uk>
Date:	Thu, 15 Oct 2009 16:29:26 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Arnd Bergmann <arndbergmann@...glemail.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jeff Dike <jdike@...toit.com>
Subject: Re: [patch 6/7] um: Convert mmapper to unlocked_ioctl

On Thu, 15 Oct 2009 15:00:34 +0200
Arnd Bergmann <arndbergmann@...glemail.com> wrote:

> 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.

That is wrong.

SuS requires an unknown ioctl code returns -ENOTTY. If the code is
currently remapping it to EINVAL then it wants fixing.
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