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Date: Tue, 7 Dec 2010 08:51:01 -0800
From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Kay Sievers <kay.sievers@vrfy.org>, Henrik Rydberg <rydberg@euromail.se>,
        Jiri Kosina <jkosina@suse.cz>, linux-input@vger.kernel.org,
        linux-kernel@vger.kernel.org, Ping Cheng <pingc@wacom.com>,
        Chris Bagwell <chris@cnpbagwell.com>
Subject: Re: [RFC][PATCH] input: Introduce device information ioctl
Message-ID: <20101207165101.GB25344@core.coreip.homeip.net>
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 <AANLkTimnSsfCG0WtDpa-qEu3N1uMOeo+CzzZ8wsaZN1v@mail.gmail.com>
 <201012071340.26244.arnd@arndb.de>
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On Tue, Dec 07, 2010 at 01:40:26PM +0100, Arnd Bergmann wrote:
> On Tuesday 07 December 2010, Kay Sievers wrote:
> > On Tue, Dec 7, 2010 at 10:16, Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:
> > > Hi Henrik,
> > >
> > > On Tue, Dec 07, 2010 at 08:25:26AM +0100, Henrik Rydberg wrote:
> > >> Today, userspace sets up an input device based on the data it emits.
> > >> This is not always enough; a tablet and a touchscreen may emit exactly
> > >> the same data, for instance, but the former should be set up with a
> > >> pointer whereas the latter does not need to. Recently, a new type of
> > >> touchpad has emerged where the buttons are under the pad, which changes
> > >> handling logic without changing the emitted data. This patch introduces
> > >> a new ioctl, EVIOCGDEVINFO, which allows userspace to extract information
> > >> about the device resulting in proper setup.
> > >
> > > If we agree that the new ioctl is suitable we'llalso need to wireit up
> > > through sysfs. Also, can we keep all definitions to INPUT_ namespace?
> > 
> > Please don't add new ioctls which are not extensible. The ioctl should
> > carry the length or the version of the structure it asks for, so it
> > can be extended in the future. Sysfs should be good enough for such
> > interface though.
> 
> Please never add any ioctls that have a version or length field!
> 
> Ideally ioctls should have only scalar arguments, not structures,
> so I'd recommend splitting it into two, so you can read type and
> capability parameters separately.

Yes, I think it is a good idea to turn it into 2 scalar ioctls.

-- 
Dmitry
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