vfs-module linense

Matt Seitz mseitz at yahoo.com
Mon Mar 4 14:40:15 GMT 2002

>Date: Wed, 27 Feb 2002 18:03:47 +0200
>From: Alexander Bokovoy <a.bokovoy at sam-solutions.net>
>Subject: Re: vfs-module lincense

>On Wed, Feb 27, 2002 at 09:14:00AM -0600, Esh, Andrew wrote:
>>    How does that [the GPL] apply to VFS modules that are dynamically linked,

>Please look at http://www.fsf.org/licenses/gpl-faq.html#GPLAndPlugins for
>detailed description why VFS modules for Samba must be under GPL-compatible

This is a very timely discussion.  It appears there is currently a court case
arging the very question of whether the GPL covers dynamically linked plug-ins
(see http://www.oreillynet.com/cs/weblog/view/wlg/1168 among oters).

While the FSF certainly claims that the GPL covers dynamically linked plug-ins,
not everyone agrees.  The GPL does not explicitly address the issue of
plug-ins.  The GPL says:

"These requirements apply to the modified work as a whole.  If
identifiable sections of that work are not derived from the Program,
and can be reasonably considered independent and separate works in
themselves, then this License, and its terms, do not apply to those
sections when you distribute them as separate works.  But when you
distribute the same sections as part of a whole which is a work based
on the Program, the distribution of the whole must be on the terms of
this License, whose permissions for other licensees extend to the
entire whole, and thus to each and every part regardless of who wrote it."

So the question is whether the plug-in is a derived work or a separate work. 
This is especially important if one is distributing just the plug-in.  If the
plug-in is an independent work, not a derived work, and the plug-in is
distributed independently, then the GPL is moot.  One does not need permission
from anyone to distribute a work that is not derived from anyone else's work.

The FSF's GPL FAQ is the FSF's interpretation of copyright law and the GPL. 
The FAQ says:

"If the program dynamically links plug-ins, and they make function calls to
each other and share data structures, we believe they form a single program, so
plug-ins must be treated as extensions to the main program.  This means they
must be released under the GPL or a GPL-compatible free software license.  If
the program dynamically links plug-ins, but the communication between them is
limited to invoking the `main' function of the plug-in with some options and
waiting for it to return, that is a borderline case."  

Note the use of "we believe" and "borderline case".  In other words, the FSF
believes that the GPL covers (most) dynamically linked plug-ins, but that this
is not a certainty.  One can very reasonably argue that a plug-in that does not
contain any of the calling program's code is a separate work, and therefore not
subject to the GPL license.  

As the author of the GPL, the FSF's interpretation should carry significant
weight.  But just as one should not blindly accept Microsoft's interpretation
of the GPL (see http://news.com.com/2100-1001-268889.html), one should also not
blindly accept the FSF's interpretation of a derived work under copyright law. 
Ultimately it will be up to the courts to decide whether a plug-in is a derived
work or an independent work.

Matt Seitz

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