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[Xen-users] Re: Xen and gnu gpl



Mark Williamson wrote:
Disclaimer: I am not a lawyer ;-)

That is true however it is only the case when the new work is a "derived work" of the old code. So if I add some extra features for the Linux Kernel, which is GPL-licensed, I have to distribute my new enhanced kernel under the terms of the GPL. Typically the patch you produced will be GPL-licensed too since it will be inspired heavily by the existing code and therefore considered a "derived work".
On the other hand, userspace apps running *on* the Linux kernel are not *part* 
of it and are not typically considered derived works.  For this reason you can 
write closed-source apps for the Linux kernel (for instance).  Many companies 
do this and it's generally agreed to be OK.  Creating closed-source *drivers* 
is more of a grey area.
The main answer is the same as above: XenServer adds management functionality 
on top of Xen and some extra drivers but if they are not a *derived work* of 
Xen itself then they don't have to be under the GPL.  They're just apps that 
happen to be running on top of Xen.
A second possible answer, although I think it is less of an issue in this 
case, is that if Citrix/XenSource own the copyright on some GPL-licensed code 
in Xen they would be within their rights to *also* sell closed-source software 
derived from this.  I'm not aware of them doing this but it is allowed to do 
this with GPL software *if and only if* you are the copyright holder.
Im not an lawyer either but I think this has nothing to do with "derived 
work" and/or kernel vs. userspace but rather with the second answer: the 
fact that Citrix owns Xen and releases it (kind of) using different 
licenses, for a more detailed explanation see: 
http://en.wikipedia.org/wiki/Dual-licensing


Best regards,
   Christian


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