linux-kernel - Re: [RFC] Remove or convert empty ioctls ?

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Date:	Thu, 15 Oct 2009 08:12:44 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [RFC] Remove or convert empty ioctls ?

On 10/15/2009 05:20 AM, Thomas Gleixner wrote:
> Hi,
>
> while looking into pushing down BKL to ioctls I noticed that we have a
> lot of ioctls which simply return -EINVAL or some other fancy error
> code.
>
> The question is whether we should convert them to unlocked_ioctl or
> simply remove them and let the sys_ioctl code return the default
> -ENOTTY error code.
>
> One could argue that this is a user visible change, but OTOH there is
> no particular value of EINVAL or any other weird error code when it
> just says: there is no ioctl for this fd.

It seems like a mistake to generalize a rule out of this, especially if 
it leads to error return values changing unexpectedly in years-old code.

"no particular value" is highly subjective, and I think unprovable, 
without an exhaustive survey of userland programs interacting with 
kernel drivers.  Userland programs often interact with a -class- of 
drivers, expecting predictable behavior from a DoThisThing ioctl, with 
EINVAL or "other weird error code" returned intentionally.

Changing the return codes seems quite unwise.

	Jeff

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