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Date: Thu, 29 Jul 2004 14:02:11 -0700
From: Andrew Morton <akpm@osdl.org>
To: Michael Hunold <hunold@convergence.de>
Cc: js@convergence.de, viro@parcelfarce.linux.theplanet.co.uk,
       linux-kernel@vger.kernel.org
Subject: Re: 2.6.8-rc2-mm1
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Michael Hunold <hunold@convergence.de> wrote:
>
> > This is a hack introduced by someone years ago. The "pointer" is
> > actually an integer argument, e.g. in include/linux/dvb/audio.h:
> > 
> > #define AUDIO_SET_MUTE             _IO('o', 6)
> > 
> > actually takes an integer argument (!0 mute, 0 unmute), so one can write
> > 
> > 	if (ioctl(fd, AUDIO_SET_MUTE, 1) == -1)
> > 		perror("mute");
> > 
> > It is unusual (maybe even wrong?), but we cannot change it without
> > losing binary API compatibility. However, I see that sparse might
> > flag this as a possible bug :-(
> 
> Is this convenient trick considered harmful?
> Or is it a creative way of using ioctls?
> 
> We're currently using this stuff in the overhauled DVB v4 API, too. So 
> before we finally establish the DVB v4 API, I'd like to know if this is 
> a no-no.

It's a no-no.  Please define the interface to be as typesafe and as
__user-correct as possible.