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, 03 Dec 2011 19:17:21 +0100
From:	Andreas Oberritter <obi@...uxtv.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	VDR User <user.vdr@...il.com>, 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 03.12.2011 18:42, Alan Cox 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?

Yes.

>> 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.

USB tuners may be removed anytime during any ioctl, too. Handling such
error cases is therefore already a requirement, at least for
hotplug-capable software.

> 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.

It's certainly not suitable for every possible use case in the world.
For many, however, I think it's the optimal solution.

Regards,
Andreas
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