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

Sun Jan 31 22:44:40 EST 2010

I believe Benoit's already put forth one (and the only ?) concern : to
prevent forks of eigen.

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.

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
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> Fax: +61 2 9351 7474
> URL: http://www.acfr.usyd.edu.au/
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