[vtk-developers] Scope of VTK and it's potential as a common research language

Mon Feb 1 08:38:03 EST 2010

2010/1/31 Karthik Krishnan <karthik.krishnan at kitware.com>:
> I believe Benoit's already put forth one (and the only ?) concern : to
> prevent forks of eigen.

Indeed, that's the main reason: we don't want to allow _proprietary_
forks of eigen. Different open source projects are in different
situations, allowing them different licenses. Eigen is a
volunteer-only project, so developer motivation is subtle and is our
only asset, and Eigen developers have stated that their motivation
would be affected if our license allowed proprietary forks.

> It would be great then if a BSD like license can be adopted with
> explicit clauses such as these.. but that's entirely upto the eigen
> folks.

Yes, that would be nice. In our case, as I explained, such a "BSD +
preventing proprietary forks" would be equivalent to the LGPL, but
that would allow us to do without our long FAQ. I could attempt to
write such a license, but that's not reasonable as I'm not a lawyer.

Benoit

>
> On Mon, Feb 1, 2010 at 8:24 AM, Andrew Maclean
> <andrew.amaclean at gmail.com> wrote:
>> Jacob,
>>   In an attempt to move along a very interesting discussion, I would
>> like to get to the point:
>>
>>   Would you be happy to use a BSD like license the same as VTK? It
>> seems to me that this will nicely remove all the complexities raised
>> in the previous discussion.
>>
>> Is there a specific reason for preferring LGPL?
>>
>> Regards
>>   Andrew
>>
>>
>>
>> On Mon, Feb 1, 2010 at 6:55 AM, Benoit Jacob <jacob.benoit.1 at gmail.com> wrote:
>>> 2010/1/31 Benoit Jacob <jacob.benoit.1 at gmail.com>:
>>>> 2010/1/31 Berk Geveci <berk.geveci at kitware.com>:
>>>>> I don't agree. Here are two sections:
>>>>>
>>>>> 0. Additional Definitions.
>>>>>
>>>>> ...
>>>>>
>>>>> A “Combined Work” is a work produced by combining or linking an
>>>>> Application with the Library. The particular version of the Library
>>>>> with which the Combined Work was made is also called the “Linked
>>>>> Version”.
>>>>>
>>>>> ...
>>>>>
>>>>> 4. Combined Works.
>>>>>
>>>>> You may convey a Combined Work under terms of your choice that, taken
>>>>> together, effectively do not restrict modification of the portions of
>>>>> the Library contained in the Combined Work and reverse engineering for
>>>>> debugging such modifications, if you also do each of the following:
>>>>>
>>>>> ...
>>>>>
>>>>>
>>>>> I read these together to conclude that a binary that is compiled from
>>>>> any code that includes Eigen is "Combined Work" (a work produced by
>>>>> combining through the inclusion of templates). If that is the case, 4
>>>>> would apply and hence the reverse engineering clause. It would be
>>>>> against the spirit of LGPL to grant templated libraries less
>>>>> protection than compiled libraries so why would they leave such a
>>>>> loophole?
>>>>
>>>> Section 3 only talks about using material from header files. It never
>>>> says that this material is assumed to be used by #include'ing it.
>>>>
>>>> If VTK uses Eigen headers code, and then application X uses VTK, then
>>>> the only Eigen code that application X uses is code from Eigen's
>>>> header files. Actually, all Eigen code is located in header files. So
>>>> Section 3 still fully applies.
>>>>
>>>> One might wonder the extent to which that might be used to abuse the
>>>> LGPL by claiming that arbitrary files are header files. In the case of
>>>> Eigen, it's very simple: all our internal source file have the ".h"
>>>> extension and all our documentation tells to use Eigen by #including
>>>> files, not linking to anything.
>>>
>>> ...and perhaps most conclusively, these files are inherently header
>>> files at the level of their contents, for example, they have include
>>> guards, and they define templates without instantiating them which
>>> would be a NOP if they weren't headers.
>>>
>>> Benoit
>>>
>>>>
>>>> As to why this "loophole", I believe that's simply because there's no
>>>> way around it if the FSF wanted the LGPL to be applicable at all to
>>>> libraries that have nontrivial code in header files, which includes
>>>> most C++ libraries including Qt (think QVector). The reason why
>>>> there's no way around it is that #including is in essence similar to
>>>> static linking, and doesn't have a runtime analogue.
>>>>
>>>> Benoit
>>>>
>>>>
>>>>
>>>>>
>>>>> Of course, the copyright holders of Eigen are free to write an
>>>>> addendum to the license that explicitly states (4) does not apply.
>>>>>
>>>>> My vote is to keep Eigen out of core VTK. I wouldn't have any problem
>>>>> with releasing an application that brings together VTK and Eigen (and
>>>>> Qt for that matter) because I don't see any issues with LGPL's
>>>>> requirements but I don't think many of VTK's users that develop
>>>>> proprietary apps would share my opinion. We have worked very hard to
>>>>> keep VTK's license free of complications and the value Eigen adds is
>>>>> not worth wasting all of that effort.
>>>>>
>>>>> -berk
>>>>>
>>>>>
>>>>> On Sun, Jan 31, 2010 at 11:14 AM, Benoit Jacob <jacob.benoit.1 at gmail.com> wrote:
>>>>>> 2010/1/31 Berk Geveci <berk.geveci at kitware.com>:
>>>>>>> Hi Benoit,
>>>>>>>
>>>>>>> That's great! The only clause that still gives me pause is the
>>>>>>> following from section 4:
>>>>>>
>>>>>> Section 4 doesn't apply at all to Eigen ;) see my previous e-mail.
>>>>>>
>>>>>> So if this is your only concern then I am very optimistic :)
>>>>>>
>>>>>> Benoit
>>>>>>
>>>>>>>
>>>>>>> "You may convey a Combined Work under terms of your choice that, taken
>>>>>>> together, effectively do not restrict modification of the portions of
>>>>>>> the Library contained in the Combined Work and reverse engineering for
>>>>>>> debugging such modifications ..."
>>>>>>>
>>>>>>> I am guessing that this applies to Eigen and it allows anyone the
>>>>>>> right to reverse engineer a proprietary application for the purpose of
>>>>>>> debugging Eigen. Am I right? If that is the case, this would be a
>>>>>>> concern because this section does not impose a clear limitation on
>>>>>>> what reverse engineering means. To track a particular bug in Eigen,
>>>>>>> which is intertwined with the original code, you may need access to
>>>>>>> some top-secret-data-structure that the developers do not intend to
>>>>>>> release. I would expect that this would be unacceptable to some of the
>>>>>>> users of VTK.
>>>>>>>
>>>>>>> Sorry for making this complicated but such is life when mixing
>>>>>>> open-source with proprietary app development.
>>>>>>>
>>>>>>> -berk
>>>>>>>
>>>>>>> On Sun, Jan 31, 2010 at 12:36 AM, Benoit Jacob <jacob.benoit.1 at gmail.com> wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> [Re-sending now that I am subscribed to the list which is subscribers-only]
>>>>>>>>
>>>>>>>> I'm one of the developers of Eigen. Reading your e-mails and your
>>>>>>>> concerns, I updated a bit the FAQ, see especially:
>>>>>>>> http://eigen.tuxfamily.org/index.php?title=Licensing_FAQ#How_about_static_linking.3F_2
>>>>>>>>
>>>>>>>> Let me summarize things a little (just elaborating on what Marcus said).
>>>>>>>>
>>>>>>>> Executive Summary:
>>>>>>>>
>>>>>>>> The LGPL version 3 is fully applicable to template libraries and there
>>>>>>>> simply is no issue at all with static linking, not even if VTK uses
>>>>>>>> Eigen and then some application links statically to VTK.
>>>>>>>>
>>>>>>>> Explanation:
>>>>>>>>
>>>>>>>> First of all, the old LGPL version 2.1 did indeed have lots of issues
>>>>>>>> with template libraries. That's why we don't use it for Eigen.
>>>>>>>>
>>>>>>>> The LGPL version 3 provides 3 different ways in why LGPL-licensed
>>>>>>>> libraries may be used: these are Sections 3, 4, and 5.
>>>>>>>>
>>>>>>>> In the case of Eigen, the only of these sections that you have to read
>>>>>>>> is Section 3. It covers the case of template libraries. Eigen is to be
>>>>>>>> used entirely under Section 3.
>>>>>>>>
>>>>>>>> Section 3 is very simple, it's essentially the same thing as a
>>>>>>>> 2-clause BSD license. That doesn't mean that LGPL=BSD, because there
>>>>>>>> still is the fact that the LGPL prevents proprietary forks of Eigen
>>>>>>>> itself.
>>>>>>>>
>>>>>>>> I would now like to address this concern:
>>>>>>>>
>>>>>>>>>> I disagree with this not being an issue. Adopting something licensed
>>>>>>>>>> under LGPL as a
>>>>>>>>>> core library in VTK is a bad idea since it would preclude anyone
>>>>>>>>>> building a statically
>>>>>>>>>> linked application using VTK - unless they were distributing all of
>>>>>>>>>> the components
>>>>>>>>>> required to relink.
>>>>>>>>
>>>>>>>> The "issues with statically linking to LGPL libraries" refer to
>>>>>>>> Section 4, specifically 4.d.1. As I said, Section 4 simply doesn't
>>>>>>>> apply to Eigen. The confusion comes from the fact that most LGPL
>>>>>>>> libraries are used under Section 4 (e.g. Qt is) but Eigen is just a
>>>>>>>> special case as it is a pure headers-only library with nothing to link
>>>>>>>> to. Thus Eigen is used entirely under Section 3, thus bypassing
>>>>>>>> Section 4 entirely, thus bypassing the issues with static linking in
>>>>>>>> particular. Subsequently, it just doesn't matter that VTK is a binary
>>>>>>>> library and not a headers-only library, because Section 4 just never
>>>>>>>> was used in the first place.
>>>>>>>>
>>>>>>>> More details and explanations in the FAQ that Marcus already linked to:
>>>>>>>> http://eigen.tuxfamily.org/index.php?title=Licensing_FAQ
>>>>>>>>
>>>>>>>> I hope that this addresses your concerns and am available if you need
>>>>>>>> more explanations, or disagree with mine!
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Benoit
>>>>>>>> _______________________________________________
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>>>>>>>>
>>>>>>>
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>>>>>>
>>>>>
>>>>
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>>
>>
>>
>> --
>> ___________________________________________
>> Andrew J. P. Maclean
>> Centre for Autonomous Systems
>> The Rose Street Building J04
>> The University of Sydney  2006  NSW
>> AUSTRALIA
>> Ph: +61 2 9351 3283
>> Fax: +61 2 9351 7474
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