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Date: Mon, 30 Nov 2009 08:23:05 -0500
Message-ID: <9e4733910911300523y69b66963t36db6d52def6679d@mail.gmail.com>
Subject: Re: [RFC] What are the goals for the architecture of an in-kernel IR 
	system?
From: Jon Smirl <jonsmirl@gmail.com>
To: Andy Walls <awalls@radix.net>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>, Ray Lee <ray-lk@madrabbit.org>,
       Maxim Levitsky <maximlevitsky@gmail.com>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, Krzysztof Halasa <khc@pm.waw.pl>,
       Christoph Bartelmus <lirc@bartelmus.de>, dmitry.torokhov@gmail.com,
       j@jannau.net, jarod@redhat.com, jarod@wilsonet.com,
       linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
       linux-media@vger.kernel.org, stefanr@s5r6.in-berlin.de,
       superm1@ubuntu.com
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On Mon, Nov 30, 2009 at 7:57 AM, Andy Walls <awalls@radix.net> wrote:
> I suppose my best answer to that is question back to you: Why does udev
> run in userspace versus a kernel thread?

Because udev is a scripting system. I've always said that the
scripting piece of IR belongs in user space. IR scripting should be
optional, none of the systems I work on need it.

This is the event flow being built...

device timing data
 -- send timing data to user space
 -- do protocol decode (40K code)
 -- send decoded data back to kernel
other devices that decode in HW add events here
 -- send decoded data to user space
 -- map to keys (30K code)
 -- send keys back to kernel
apps listen for keys
 -- send keys back to user space
 -- user space apps act on key (possibly run scripts)

I'd like to see...

device timing data
-- user space can inject timing data from user space drivers
do protocol decode (40K code)
other devices that decode in HW add events here
-- user space can inject decoded data from user space drivers
map to keys (30K code)
apps listen for keys
 -- send keys back to user space
 -- user space apps act on key (possibly run scripts)


>
> My personal thoughts on why user space is more flexible:
>
> 1. You have all of *NIX available to you to use as tools to achieve your
> requirements.
>
> 2. You are not constrained to use C.
>
> 3. You can link in libraries with functions that are not available in
> the kernel. ?(udev has libudev IIRC to handle complexities)
>
> 4. Reading a configuration file or other file from the filesystem is
> trivial - file access from usespace is easy.
>
> 5. You don't have to be concerned about the running context (am I
> allowed to sleep here or not?).
>
>
>
>
>
>
>> A kernelspace input device driver can start working since boot time.
>> On the other hand, an userspace device driver will be available only
>> after mounting the filesystems and starting the deamons
>> (e. g. after running inittab).
>>
>> So, you cannot catch a key that would be affecting the boot
>> (for example to ask the kernel to run a different runlevel or entering
>> on some administrative mode).
>
> Right. ?That's another requirement that makes sense, if we're talking
> about systems that don't have any other keyboard handy to the user.
>
> So are we optimizing for the embedded/STB and HTPC with no keyboard use
> case, or the desktop or HTPC with a keyboard for maintencance?
>
>
> Regards,
> Andy
>
>
> --
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>


-- 
Jon Smirl
jonsmirl@gmail.com
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