linux-kernel - Re: [RFC] vtunerc: virtual DVB device - is it ok to NACK driver because of worrying about possible misusage?

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Date:	Sat, 3 Dec 2011 12:48:13 -0500
From:	Devin Heitmueller <dheitmueller@...nellabs.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	VDR User <user.vdr@...il.com>,
	Andreas Oberritter <obi@...uxtv.org>, HoP <jpetrous@...il.com>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] vtunerc: virtual DVB device - is it ok to NACK driver
 because of worrying about possible misusage?

On Sat, Dec 3, 2011 at 12:42 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> On Sat, 3 Dec 2011 09:21:23 -0800
> VDR User <user.vdr@...il.com> wrote:
>
>> On Sat, Dec 3, 2011 at 8:13 AM, Andreas Oberritter <obi@...uxtv.org> wrote:
>> > You could certainly build a library to reach a different goal. The goal
>> > of vtuner is to access remote tuners with any existing program
>> > implementing the DVB API.
>>
>> So you could finally use VDR as a server/client setup using vtuner,
>> right? With full OSD, timer, etc? Yes, I'm aware that streamdev
>> exists. It was horrible when I tried it last (a long time ago) and I
>> understand it's gotten better. But it's not a suitable replacement for
>> a real server/client setup. It sounds like using vtuner, this would
>> finally be possible and since Klaus has no intention of ever
>> modernizing VDR into server/client (that I'm aware of), it's also the
>> only suitable option as well.
>
> I would expect it to still suck. One of the problems you have with trying
> to pretend things are not networked is that you fake asynchronous events
> synchronously, you can't properly cover error cases and as a result you
> get things like ioctls that hang for two minutes or fail in bogus and
> bizarre ways. If you loop via userspace you've also got to deal with
> deadlocks and all sorts of horrible cornercases like the user space
> daemon dying.
>
> There is a reason properly working client/server code looks different -
> it's not a trivial transformation and faking it kernel side won't be any
> better than faking it in user space - it may well even be a worse fake.
>
> Alan

This whole notion of creating fake kernel devices to represent
networked tuners feels like a hack.  If applications want to access
networked tuners, adding support for RTP/RTSP or incorporating
libhdhomerun (LGPL) is a fairly straightforward exercise.  In fact,
many applications already have incorporated support for one of these
two approaches.  The fact that app maintainers have been
unwilling/uninterested to do such doesn't feel like it should be an
excuse for hacking this functionality into the kernel.

Devin

-- 
Devin J. Heitmueller - Kernel Labs
http://www.kernellabs.com
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