Permissive open-source licenses (MIT, BSD, etc.) are GPL-compatible. But I think the question here is more one of motivation: was a decision made for reason X which had the side-effect of making DTrace's license incompatible with Linux, or was the choice of license made specifically to cause that effect? There appear to be conflicting accounts from people who were at Sun at the time.
> Permissive open-source licenses (MIT, BSD, etc.) are GPL-compatible.
I guess I have a problem characterizing them that way since the traffic is going to be purely one-way. The GPL code can't be used by the projects with more permissive licenses without some kind of dual licensing, can it?
It depends on what level of compatibility we're looking at. It's true that MIT-licensed code can migrate to a GPL codebase but not vice-versa. But a different kind of compatibility (what I was thinking of) is whether you can maintain separate and separately-licensed codebases and legally distribute the combined binary. If DTrace were MIT and the Linux kernel were GPL, you could legally link them and distribute the result, so in that sense they'd be "compatible". Which isn't the case if you have a CDDL and a GPL codebase.
