If I remember correctly, the reasoning for the GPL module stuff was/is, that if kernel modules integrate deeply with the kernel, they fall under gpl. So the GPL flag is basically a guideline of what kernel developers believe is safe to use from non gpl-compatible modules
But from what I can see, marking the "save SIMD registers" function as GPL is a blatant lie by a kernel developer that wanted to spite certain modules.
Saving and restoring registers is an astoundingly generic function. If you list all the kernel exports and sort by how much they make your work derivative, it should be near the very bottom.
You are not supposed to use FP/SSE in kernel mode.
It was always frowned upon:
> In other words: it's still very much a special case, and if the question was "can I just use FP in the kernel" then the answer is still a resounding NO, since other architectures may not support it AT ALL.
> Linus Torvalds, 2003
and these specific functions, that were marked as GPL were already deprecated for well over a decade.
> You are not supposed to use FP/SSE in kernel mode.
> It was always frowned upon
Whether it's frowned upon is a completely different issue from whether it intertwines your data so deeply with the kernel that it makes your code a derivative work subject to the GPL license. Which it doesn't.
> if the question was "can I just use FP in the kernel" then the answer is still a resounding NO, since other architectures may not support it AT ALL.
It's not actually using floating point, it's using faster instructions for integer math, and it has a perfectly viable fallback for architectures that don't have those instructions. But why use the slower version when there's no real reason to?
> and these specific functions, that were marked as GPL were already deprecated for well over a decade.
But the GPL export is still there, isn't it? It's not that functionality is being removed, it's that functionality is being shifted to only have a GPL export with no license-based justification for doing so.
So what meets the criteria of being a "special case" and what doesn't? One of the examples that Linus gives is RAID checksumming. How come RAID checksumming is a special case but ZFS checksumming isn't? I don't think it has anything to do with the nature of the usage, the only problem is that the user is ZFS.
RAID checksuming is in the kernel, and when Linus says jump, the RAID folks ask back how high.
He is not going to beg people outside kernel, whether he is allowed to change something that may break their module. On the contrary, they must live with any breackage that is thrown at them.
Again, that symbol was deprecated for well over a decade. How long does it take to be allowed to remove it?
Sometimes in life we do things even though we are not explicitly obligated to do them. Nobody is asking for ZFS to get explicitly maintained support in the Linux kernel. They are simply asking for this one small inconsequential change to be reverted just this one time, since it would literally be no harm to the kernel developers to do so, and it would provide substantial benefits to any user wanting to use ZFS. Furthermore the amount of time that kernel developers have spent arguing in favour of this change has been significantly greater than the time it would have taken to just revert it.
> Again, that symbol was deprecated for well over a decade.
But not the GPL equivalent of the symbol. That symbol is not deprecated.
This is the commonly recited argument but I don't believe it was ever proven to be legally necessary. Furthermore, even if it was, it's not clear what level of integration is "too deep". So in practice, it's just a way for kernel developers to add political restrictions as they see fit.
Proven legally necessary, as in, a court ever telling anyone in that situation to stop doing it. Or even to start doing it in the first place. There's just no legal justification behind it whatsoever.
One can interpret this as something legally significant, or an embarrassing private anecdote, or nothing substantial at all, maybe even just talk. However, I'd give them the benefit of the doubt. Not the least since they could be the ones against Oracle's legal dept...
What he is referring to is the use of the GPL export restriction to strong-arm companies into releasing their code as GPL. It's nothing to do with a legal requirement, he is just an open source licensing hardhead. See: https://lwn.net/Articles/603145/
