Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Tue, 18 Dec 2001 15:03:28 -0600

Korhonen Timo wrote:
> 
> Trying to figure out what can and what can not be done under different
> types of licenses gives me a headache. It would be nice if somebody
> clarified the license issues concerning various software components
> that are used together with Epics (no, I am NOT volunteering to do
> this!)

I Am Not A Lawyer (IANAL), This Is Not Legal Advice (TINLA).

Each site that is making software available to the EPICS community and the
general public will almost certainly need to discuss this with their legal
department to discover what your lab's requirements are.  I've been
following the EPICS and Open Source licensing issues closely, and I'll
explain what I personally think the situation is for labs who have signed
an EPICS agreement and how this interacts with the GPL.  I may be
completely mistaken though, don't rely on the contents of this message!

1. The agreement that each lab signed with LANL gives labs the right to
use and modify EPICS, but not to distribute it to anyone else in either
source code or binary form.

2. One of the key features of the GNU General Public License is that it
does not permit the distribution of software linked to non-system
libraries that are distributed under different licensing terms.  The EPICS
Channel Access library falls into that non-system category, thus it can't
be used in a GPL application.

3. Note however that the GPL only controls the making of copies of
licensed software, it can't control how you use a legally-obtained copy. 
Thus it *may* be legal to write and use programs that combine GPL code
with proprietary code, but you would need to be *extremely* careful what
you actually distribute to other people (no binaries, nor source code that
might have been contaminated by GPL source code).

4. It *is* possible to license a program with the GPL that uses EPICS
software, but the author must include an exception in the license allowing
it to be linked with the relevant EPICS libraries (there is a section in
the GPL FAQ at
http://www.fsf.org/copyleft/gpl-faq.html#WritingFSWithNFLibs explaining
how to add exceptions like this).  However you can only do this if you
wrote the *whole* application yourself or you get permission to add this
exception from all other authors.  You can't include any "standard GPL"
licensed code in such an application, nor link with any other GPL
libraries unless they also have the exact same exceptions in their
licenses (even using dynamic linking needs you to include some information
in your binaries from the GPL header files).

5. That "however" in point 4 above means that (as far as I can see) it
would not be legal to develop an EPICS display manager that used the Qt
widget set unless you first paid for a Qt Professional Edition license,
which doesn't hold you to the terms of the GPL.  According to the
www.trolltech.com website you have to get that license at the start of
your development too, you can't develop non-free software using the Qt
Free Edition.

6. The Gnome libraries are distributed under the LGPL, which does permit
linking with non-free software, so a Gnome-based display manager could be
written and distributed perfectly legally.  There are also other free C++
widget sets available that may have compatible licenses.

Sorry if I've made your headache worse Timo, and unfortunately it
currently doesn't look like we're going to be able to make it any easier
in the near future either.  We discovered recently that EPICS has been
ruled by the Department of Commerce to be subject to EAR99 export
regulations, which makes it impossible to put EPICS base on a public
website or license it as Open Source unless that ruling is changed - we'll
say more about this in the New Year.

- Andrew
-- 
Perfection is reached, not when there is no longer anything to add,
but when there is no longer anything to take away.
- Antoine de Saint-Exupery

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System