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From: David =?iso-8859-1?Q?H=E4rdeman?= <david@hardeman.nu>
Subject: Re: [RFC] What are the goals for the architecture of an in-kernel
 IR system?
Date: Tue, 30 Mar 2010 13:01:38 +0200
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To: Mauro Carvalho Chehab <mchehab@redhat.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>, Jon Smirl <jonsmirl@gmail.com>, Pavel Machek <pavel@ucw.cz>, Krzysztof Halasa <khc@pm.waw.pl>, hermann pitton <hermann-pitton@arcor.de>, Christoph Bartelmus <lirc@bartelmus.de>, awalls@radix.net, j@jannau.net, jarod@redhat.com, jarod@wilsonet.com, kraxel@redhat.com, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, superm1@ubuntu.com
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On Sun, Mar 28, 2010 at 09:51:17PM -0300, Mauro Carvalho Chehab wrote:
>=20
> I spoke too soon... removing the index causes a problem at the read i=
octl: there's no way
> to retrieve just the non-sparsed values.
>=20
> There's one solution that would allow both read/write and compat to w=
ork nicely,
> but the API would become somewhat asymmetrical:
>=20
> At get (EVIOCGKEYCODEBIG):
> 	use index/len as input and keycode/scancode as output;
>=20
> At set (EVIOCSKEYCODEBIG):
> 	use scancode/keycode/len as input (and, optionally, index as output)=
=2E
>=20

This was exactly the approach I had in mind when I suggested using=20
indexes.

> Having it asymmetrical doesn't sound good, but, on the other hand,=20
> using index for
> the set function also doesn't seem good, as the driver may reorder th=
e entries after
> setting, for example to work with a binary tree or with hashes.

I don't think the assymetry is really a problem. As I see it, there are=
=20
basically two user cases:

1) Userspace wants scancode X to generate keypress Y
   (In which case userspace doesn't care one iota what the index is)

2) Userspace wants to get the current keytable from the kernel
   (In which case a loop with an index from 0 to n is appropriate)

and, possibly:

3) Userspace wants to know what keycode (if any) scancode X generates
   (In which case approach 2 will work just as well, but this usecase
    seems a bit contrived anyway...)

--=20
David H=E4rdeman