[jahewson]

Given that it requires HyperV it’s running in a manner similar to a VM. That doesn’t require linking and any I/O occurs via the normal channels (CPU interrupts, serial console, etc).

This is similar to how running a userland application on Linux doesn’t require the application to be GPL’d because it’s not directly linked to the kernel. While it interacts with the kernel it is not derived from it.

[_wmd]

This is fairly classic engineer thinking and what I was referring to in my comment below.. you can wrap a GPL library in its own program, put that program on a separate VM on a separate physical host in a separate physical building, talk to it only over a network interface and your program's resulting interaction with it might still be construed as linking.

Similarly, your program might statically link against a GPL'd library, but only pass bulk data through a programming interface in a coarse manner, and the result may not be considered linking. The FSF FAQ even explicitly addresses this case.

GPL leaves these kinds of mechanisms blurry and ill-defined (I presume intentionally), it's just that as engineers we are commonly only taught how violations manifest in the usual case.

[billziss]

I think I agree with your overall understanding. It would be interesting to learn what FSF's position is regarding WSL2.