Re: [RFC] vtunerc - virtual DVB device driver

From: HoP <jpetrous@gmail.com>
To: Mauro Carvalho Chehab <mchehab@redhat.com>
Cc: Andreas Oberritter <obi@linuxtv.org>,
	Linux Media Mailing List <linux-media@vger.kernel.org>
Subject: Re: [RFC] vtunerc - virtual DVB device driver
Date: Wed, 22 Jun 2011 14:37:30 +0200	[thread overview]
Message-ID: <BANLkTimpVu+Hz0j+WUmSAsyON4u=W3cr+g@mail.gmail.com> (raw)
In-Reply-To: <4E01DD57.3080508@redhat.com>

2011/6/22 Mauro Carvalho Chehab <mchehab@redhat.com>:
> Em 21-06-2011 14:38, HoP escreveu:
>> 2011/6/21 Mauro Carvalho Chehab <mchehab@redhat.com>:
>>> Em 21-06-2011 12:09, Andreas Oberritter escreveu:
>>>> On 06/21/2011 04:35 PM, Mauro Carvalho Chehab wrote:
>>>>> Em 21-06-2011 11:15, Andreas Oberritter escreveu:
>>>>>> On 06/21/2011 03:44 PM, Devin Heitmueller wrote:
>>>>>>> On Tue, Jun 21, 2011 at 7:04 AM, Andreas Oberritter <obi@linuxtv.org> wrote:
>>>>>>>> Mauro and Devin, I think you're missing the point. This is not about
>>>>>>>> creating drivers in userspace. This is not about open or closed source.
>>>>>>>> The "vtuner" interface, as implemented for the Dreambox, is used to
>>>>>>>> access remote tuners: Put x tuners into y boxes and access them from
>>>>>>>> another box as if they were local. It's used in conjunction with further
>>>>>>>> software to receive the transport stream over a network connection.
>>>>>>>> Honza's code does the same thing.
>>>>>>>
>>>>>>> I'm not missing the point at all.  I realize exactly what Honza is
>>>>>>> trying to accomplish (and from a purely technical standpoint, it's not
>>>>>>> a bad approach) - but I'm talking about the effects of such a driver
>>>>>>> being introduced which changes the kernel/userland licensing boundary
>>>>>>> and has very real implications with how the in-kernel code is
>>>>>>> accessed.
>>>>>>>
>>>>>>>> You don't need it in order to create closed source drivers. You can
>>>>>>>> already create closed kernel drivers now. Also, you can create tuner
>>>>>>>> drivers in userspace using the i2c-dev interface. If you like to connect
>>>>>>>> a userspace driver to a DVB API device node, you can distribute a small
>>>>>>>> (open or closed) wrapper with it. So what are you arguing about?
>>>>>>>> Everything you're feared of can already be done since virtually forever.
>>>>>>>
>>>>>>> I disagree.  There is currently no API which allows applications to
>>>>>>> issue tuning requests into the DVB core, and have those requests
>>>>>>> proxied back out to userland where an application can then use i2c-dev
>>>>>>> to tune the actual device.  Meaning if somebody wants to write a
>>>>>>> closed source userland application which controls the tuner, he/she
>>>>>>> can do that (while not conforming to the DVB API).  But if if he wants
>>>>>>> to reuse the GPL licensed DVB core, he has to replace the entire DVB
>>>>>>> core.
>>>>>>>
>>>>>>> The introduction of this patch makes it trivial for a third party to
>>>>>>> provide closed-source userland support for tuners while reusing all
>>>>>>> the existing GPL driver code that makes up the framework.
>>>>>>>
>>>>>>> I used to work for a vendor that makes tuners, and they do a bunch of
>>>>>>> Linux work.  And that work has resulted in a bunch of open source
>>>>>>> drivers.  I can tell you though that *every* conversation I've had
>>>>>>> regarding a new driver goes something like this:
>>>>>>>
>>>>>>> ===
>>>>>>> "Devin, we need to support tuner X under Linux."
>>>>>>>
>>>>>>> "Great!  I'll be happy to write a new GPL driver for the
>>>>>>> tuner/demodulator/whatever for that device"
>>>>>>>
>>>>>>> "But to save time/money, we just want to reuse the Windows driver code
>>>>>>> (or reference code from the vendor)."
>>>>>>>
>>>>>>> "Ok.  Well, what is the licensing for that code?  Is it GPL compatible?"
>>>>>>>
>>>>>>> "Not currently.  So can we just make our driver closed source?"
>>>>>>>
>>>>>>> "Well, you can't reuse any of the existing DVB core functionality or
>>>>>>> any of the other GPL drivers (tuners, bridges, demods), so you would
>>>>>>> have rewrite all that from scratch."
>>>>>>>
>>>>>>> "Oh, that would be a ton of work.   Can we maybe write some userland
>>>>>>> stuff that controls the demodulator which we can keep closed source?
>>>>>>> Since it's not in the kernel, the GPL won't apply".
>>>>>>>
>>>>>>> "Well, you can't really do that because there is no way for the DVB
>>>>>>> core to call back out to userland when the application makes the
>>>>>>> tuning request to the DVB core."
>>>>>>>
>>>>>>> "Oh, ok then.  I guess we'll have to talk to the vendor and get them
>>>>>>> to give us the reference driver code under the GPL."
>>>>>>> ===
>>>>>>>
>>>>>>> I can tell you without a doubt that if this driver were present in the
>>>>>>> kernel, that going forward that vendor would have *zero* interest in
>>>>>>> doing any GPL driver work.  Why would they?  Why give away the code
>>>>>>> which could potentially help their competitors if they can keep it
>>>>>>> safe and protected while still being able to reuse everybody else's
>>>>>>> contributions?
>>>>>>>
>>>>>>> Companies don't contribute GPL code out of "good will".  They do it
>>>>>>> because they are compelled to by licenses or because there is no
>>>>>>> economically viable alternative.
>>>>>>>
>>>>>>> Mauro, ultimately it is your decision as the maintainer which drivers
>>>>>>> get accepted in to the kernel.  I can tell you though that this will
>>>>>>> be a very bad thing for the driver ecosystem as a whole - it will
>>>>>>> essentially make it trivial for vendors (some of which who are doing
>>>>>>> GPL work now) to provide solutions that reuse the GPL'd DVB core
>>>>>>> without having to make any of their stuff open source.
>>>>>>>
>>>>>>> Anyway, I said in my last email that would be my last email on the
>>>>>>> topic.  I guess I lied.
>>>>>>
>>>>>> Yes, and you did lie to your vendor, too, as you did not mention the
>>>>>> possibilities to create
>>>>>> 1.) closed source modules derived from existing vendor drivers while
>>>>>> still being able to use other drivers (c.f. EXPORT_SYMBOL vs.
>>>>>> EXPORT_SYMBOL_GPL).
>>>>>
>>>>> AFAIK, the legal issues on writing a closed source driver using EXPORT_SYMBOL
>>>>> are not proofed legally in any court. While EXPORT_SYMBOL_GPL explicitly
>>>>> adds a restriction, not using it doesn't necessarily mean that the symbol
>>>>> can be used by a closed source driver.
>>>>>
>>>>> If you take a look at Kernel's COPYING file, the only exception to GPL license
>>>>> allowed there is:
>>>>>
>>>>>       NOTE! This copyright does *not* cover user programs that use kernel
>>>>>       services by normal system calls - this is merely considered normal use
>>>>>       of the kernel, and does *not* fall under the heading of "derived work".
>>>>>
>>>>> IANAL, but, as EXPORT_SYMBOL is not a "normal system call", my understanding is that
>>>>> it is also covered by GPL.
>>>>
>>>> Of course. But as you should know, the GPL only covers derived work.
>>>> Whether or not a driver is a derived work of the kernel can only be
>>>> decided individually. It is my understanding that a Windows driver
>>>> ported to Linux is unlikely to be a derived work of Linux.
>>>>
>>>>> I was told that several lawyers defend the idea that all software inside the
>>>>> kernel tree is covered by GPL, even the aggregated ones. That was the rationale
>>>>> used to split the firmware packages from the kernel itself.
>>>>
>>>> However, I wasn't referring to the kernel tree at all.
>>>>
>>>>>> 2.) a simple wrapper that calls userspace, therefore not having to open
>>>>>> up any "secrets" at all.
>>>>>
>>>>> A wrapper for a closed source driver is illegal, as it is trying to circumvent
>>>>> the GPL license.
>>>>
>>>> Is it? First, you are not a lawyer. Second, a wrapper is unlikely to be
>>>> illegal by its pure existence and a wrapper does usually not try to do
>>>> anything by itself. Third, you can implement a wrapper using normal
>>>> system calls (read, write, mmap, ioctl ...). That's what vtuner does,
>>>> too, to accomplish a totally different goal. Do you think vtuner is
>>>> illegal? I would be very surprised if it was. It perfectly matches the
>>>> license exception cited above. And even without the exception, a closed
>>>> driver in userspace would only very unlikely be a derived work of the
>>>> kernel.
>>>
>>> I think we're diverging from the subject. Most of those discussions are
>>> interesting on some lawyers forum, not here.
>>>
>>> My view about this subject is that vtuner can't give any additional permissions
>>> to the kernel GPL'd code, as vtuner were not made by the Kernel Copyright owners,
>>> nor were approved by them. So, the extra permission at the COPYING clause
>>> from kernel doesn't apply here, while the code is not merged into the Kernel.
>>>
>>> So, while it should be legal to use vtuner with a GPL'd client application,
>>> using it by a closed source application violates GPL.
>>>
>>> My understanding is that an addition of a code that exposes the internal
>>> DVB core API to userspace like that will require that all dvb developers
>>> that have copyright rights at the dvb core should explicitly ack with such
>>> change, otherwise adding such code will violate the original license.
>>>
>>> On the other hand, if vtunerc won't act as a proxy to userspace, it should
>>> probably be ok.
>>
>> Are you serious? Why there is not same violation on NFS? Or even beter
>> example NBD (network block device)? It sits in kernel for ages and nobody
>> cares. It looks for me like you should send some patch for removal such
>> "weak" places in kernel which allow to violate GPL.
>>
>> Do you really think that it is possible (in real, no in threory) to create
>> any networked subsystem for sharing anything over net the way
>> when it is not exposed (somehow) to the userspace? How will be
>> such system managable? Why there is usually companion daemon
>> there, which is responsible for managing connections etc?
>>
>> I think it is very evident you want find the way how to get yours word
>> back and return to your original position = such code is not acceptable.
>> Even if you still are not able to give anything clear.
>>
>> If I understand your last few mails, you won't accept such driver, isn't it?
>
> You got wrong. You can't change someone's else license without their acks.

That I understand very well. I never want to force anybody to change
his licence.

I simply don't believe you that it is necessary. Why the same was not needed
with USBIP driver? If you check theirs nice big picture on
http://usbip.sourceforge.net/
you see that it is exactly same technology like vtunerc, but for USB subsystem.
Why such driver exists at all?

And I'm sure I can find more examples inside kernel tree. What about NBD
(http://nbd.sourceforge.net)? Do you want find me more examples?

> It is as simple as that. Getting everybody's ack is not that hard, if they
> accept that what you're doing is the right thing. We've got everybody's
> ack in the past to change the licensing for videodev2.h for example, to allow
> using the V4L2 API under BSD license (just the license API was changed, not the
> code itself).
>
>>> If people have different understandings, then we'll likely need to ask some
>>> support from Open source lawyers about this subject.
>>
>> My very little opinion is that waving GPL is way to the hell. Nobody told me
>> why similar technologies, in different kernel parts are acceptable,
>> but not here.
>
> If you want to do the networking code at userspace, why do you need a kernel
> driver after all? The proper solution is to write an userspace library for that,
> and either enclose such library inside the applications, or use LD_PRELOAD to
> bind the library to handle the open/close/ioctl glibc calls. libv4l does that.
> As it proofed to be a good library, now almost all V4L applications are using
> it.

LD_PELOAD is out of bussiness for normal work. It is technique for development
and/or debugging. Library would be possible, but then you kill main advantage
- totally independece of changes inside userland DVB applications.

And about networking in userspace - do you know other way then using
userspace daemon for management of connections and other control
jobs? Can you describe me how to do it w/o userspace application (daemon).
Why all are using it? Check networking filesystems.

I hope you can learn me how to do it correct way. I'm open for any
discussion. But no talks like "it breaks GPL" without any evident
argument from you.

/Honza