linux-kernel - Re: [RFC] What are the goals for the architecture of an in-kernel IR system?

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Date:	Tue, 30 Mar 2010 13:01:38 +0200
From:	David Härdeman <david@...deman.nu>
To:	Mauro Carvalho Chehab <mchehab@...hat.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jon Smirl <jonsmirl@...il.com>, Pavel Machek <pavel@....cz>,
	Krzysztof Halasa <khc@...waw.pl>,
	hermann pitton <hermann-pitton@...or.de>,
	Christoph Bartelmus <lirc@...telmus.de>, awalls@...ix.net,
	j@...nau.net, jarod@...hat.com, jarod@...sonet.com,
	kraxel@...hat.com, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	superm1@...ntu.com
Subject: Re: [RFC] What are the goals for the architecture of an in-kernel
 IR system?

On Sun, Mar 28, 2010 at 09:51:17PM -0300, Mauro Carvalho Chehab wrote:
> 
> I spoke too soon... removing the index causes a problem at the read ioctl: there's no way
> to retrieve just the non-sparsed values.
> 
> There's one solution that would allow both read/write and compat to work nicely,
> but the API would become somewhat asymmetrical:
> 
> At get (EVIOCGKEYCODEBIG):
> 	use index/len as input and keycode/scancode as output;
> 
> At set (EVIOCSKEYCODEBIG):
> 	use scancode/keycode/len as input (and, optionally, index as output).
> 

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

> Having it asymmetrical doesn't sound good, but, on the other hand, 
> using index for
> the set function also doesn't seem good, as the driver may reorder the 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 
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...)

-- 
David Härdeman
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