[Xen-users] Re: Xen and gnu gpl

[Christian Tramnitz <chris.ace@xxxxxxx>]

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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