keeping the GPL out of userspace? Nope...

Posted Apr 1, 2011 1:21 UTC (Fri) by rahulsundaram (subscriber, #21946) [Link]

Posted Apr 5, 2011 2:06 UTC (Tue) by cmccabe (guest, #60281) [Link]

Posted May 31, 2011 12:22 UTC (Tue) by Trelane (subscriber, #56877) [Link]

If a program released under the GPL uses plug-ins, what are the requirements for the licenses of a plug-in?

It depends on how the program invokes its plug-ins. If the program uses fork and exec to invoke plug-ins, then the plug-ins are separate programs, so the license for the main program makes no requirements for them.

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, which must be treated as an extension of both the main program and the plug-ins. This means the plug-ins must be released under the GPL or a GPL-compatible free software license, and that the terms of the GPL must be followed when those plug-ins are distributed.

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.

Can I release a non-free program that's designed to load a GPL-covered plug-in?

It depends on how the program invokes its plug-ins. For instance, if the program uses only simple fork and exec to invoke and communicate with plug-ins, then the plug-ins are separate programs, so the license of the plug-in makes no requirements about the main program.

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, which must be treated as an extension of both the main program and the plug-ins. In order to use the GPL-covered plug-ins, the main program must be released under the GPL or a GPL-compatible free software license, and that the terms of the GPL must be followed when the main program is distributed for use with these plug-ins.

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.

Using shared memory to communicate with complex data structures is pretty much equivalent to dynamic linking.

See also the question I am writing free software that uses a non-free library.

What is the difference between an “aggregate” and other kinds of “modified versions”?

An “aggregate” consists of a number of separate programs, distributed together on the same CD-ROM or other media. The GPL permits you to create and distribute an aggregate, even when the licenses of the other software are non-free or GPL-incompatible. The only condition is that you cannot release the aggregate under a license that prohibits users from exercising rights that each program's individual license would grant them.

Where's the line between two separate programs, and one program with two parts? This is a legal question, which ultimately judges will decide. We believe that a proper criterion depends both on the mechanism of communication (exec, pipes, rpc, function calls within a shared address space, etc.) and the semantics of the communication (what kinds of information are interchanged).

If the modules are included in the same executable file, they are definitely combined in one program. If modules are designed to run linked together in a shared address space, that almost surely means combining them into one program.

By contrast, pipes, sockets and command-line arguments are communication mechanisms normally used between two separate programs. So when they are used for communication, the modules normally are separate programs. But if the semantics of the communication are intimate enough, exchanging complex internal data structures, that too could be a basis to consider the two parts as combined into a larger program.