Restrict access for non-GPL symbols. This is legally nonsense.
It isn't meant to make sense legally. It's a way to stick it to creators of non-GPL code technically, by making your work unavailable for their use. Like if you threw a party and admitted only people who had never written a non-GPL piece of kernel code.
I've never been entirely sure what's to stop those people from simply putting a MODULE_LICENSE("GPL") in their non-GPL code. Either it's the hope that that line of code legally effects a copyright license or it's reliance on the author's honor.
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