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:	Tue, 06 Dec 2011 11:10:47 -0200
From:	Mauro Carvalho Chehab <mchehab@...hat.com>
To:	Andreas Oberritter <obi@...uxtv.org>
CC:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, HoP <jpetrous@...il.com>,
	Florian Fainelli <f.fainelli@...il.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 06-12-2011 10:01, Andreas Oberritter wrote:
> On 06.12.2011 12:18, Mark Brown wrote:
>> On Mon, Dec 05, 2011 at 10:20:03PM +0100, Andreas Oberritter wrote:
>>> On 05.12.2011 21:55, Alan Cox wrote:
>>>> The USB case is quite different because your latency is very tightly
>>>> bounded, your dead device state is rigidly defined, and your loss of
>>>> device is accurately and immediately signalled.
>>
>>>> Quite different.
>>
>>> How can usbip work if networking and usb are so different and what's so
>>> different between vtunerc and usbip, that made it possible to put usbip
>>> into drivers/staging?
>>
>> USB-IP is a hack that will only work well on a tightly bounded set of
>> networks - if you run it over a lightly loaded local network it can
>> work adequately.  This starts to break down as you vary the network
>> configuration.
>
> I see. So it has problems that vtunerc doesn't have.

The vtunerc has the same issues. High latency (due to high loads,  high
latency links or whatever) affects it badly, and may cause application
breakages if if the device is opened are using O_NONBLOCK mode [1].

Regards,
Mauro.

[1] Btw, if some DVB ioctl currently waits in O_NONBLOCK, this is a POSIX
violation that needs to be fixed.
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