He states: "having been developed totally independently of Linux: they literally were developed before Linux even existed, by people who had zero knowledge of Linux. That tends to strengthen the argument that they clearly aren't derived."
He does continue to say that he believe it would be "hard to argue that any new driver or filesystem was developed without any thought of Linux", although in the specific case of ZFS (as opposed to, say, nvidia.ko), I think there would be a strong argument that the ZFS module was originally written in whole as a non-derived work.
(Obviously, Linus is not the only stakeholder here, and even his own opinion may have changed since then. Still, it's not a new conversation and the community hasn't been too ruffled by the status quo for the past 13 years)
For those of us that can read source code there are a couple of strong indications that the Linux copyright holders still believe that Linux kernel modules may not necessarily constitute derivative works:
1. Every Linux kernel module can tell the kernel what license regulates its use, using the MODULE_LICENSE() macro. The Linux kernel keeps track of which modules are under GPLv2 (and a few other compatible licenses). When a module under a presumably "proprietary" license is loaded the kernel will mark itself as "tainted". (It could just as well refuse to load the module, but it doesn't.)
2. There are two macros used to export Linux kernel symbols: EXPORT_SYMBOL and EXPORT_SYMBOL_GPL. The former will make the symbol available to all kernel modules, while the latter makes it available only to GPL-licensed kernel modules. The clear purpose and motivation is that a kernel module that needs access to a symbol exported with EXPORT_SYMBOL_GPL must be a derivative work, while a kernel module that only depends on symbols exported with EXPORT_SYMBOL is not necessarily a derivate work.
Also, IANAL, but from a purely legal perspective I think it would be difficult to get a court to agree that a user space program that talks to the Linux kernel through system calls is never a derivative work, while a kernel module (even one that accesses only symbols exported with EXPORT_SYMBOL) is always a derivative work. The system call versus dynamic loaded module distinction is simply not very relevant from a purely legal perspective.
What this kind of analysis, which is very common, misses is this: there's potentially two "works" that need talking about here, not just one.
One work is the module, considered in isolation. Is that a derivative of the kernel? Possibly, but that's a reasonably high bar to clear. If it's not, distributing the module by itself can be done entirely without reference to the Linux kernel's license.
The other potential work though is the module-and-Linux-kernel (and possibly many other bits too), delivered as one combined work. Is that a separate work as per copyright law? If so, is that work a derivative (of both the kernel and the module)? This is a much lower bar, and means that the combined work can only be distributed in accordance with the licenses of both the kernel and the module.
> What this kind of analysis, which is very common, misses is this: there's potentially two "works" that need talking about here, not just one.
I agree this is only one side of the analysis (does zfs.ko fall under the Linux kernel GPLv2?), but that's also the only question that the OP can credibly address (because SFC is a copyright holder in Linux, not in ZFS).
> The other potential work though is the module-and-Linux-kernel (and possibly many other bits too), delivered as one combined work. Is that a separate work as per copyright law? If so, is that work a derivative (of both the kernel and the module)? This is a much lower bar, and means that the combined work can only be distributed in accordance with the licenses of both the kernel and the module.
That line of reasoning would upend pretty much all open source licensing as we know it. E.g., paragraph 9 of the OSI's Open Source Definition [1] clearly states that "The license must not place restrictions on other software that is distributed along with the licensed software." The fact that the OSI has accepted the GPLv2 [2] as an open source license implies that they (for one) do not agree.
There's clearly a continuum between two independent programs distributed on the same DVD through to a pre-linked static binary combining two pieces of code together.
I believe the OSI point is aiming towards the first part of that continuum (and of course the GPL itself specifically disclaims "mere aggregation"). The line here is somewhat fuzzy, but for example if you were selling NAS boxes based on linux-on-ZFS, it seems to me that it would be hard to explain that away as "mere aggregation", since the essential functionality of the product relies on both those parts working together.
SFC isn't a copyright holder of Linux. They are just giving their opinion.
Also, as far as combined work, the OSD is not talking about that, but what the GPL calls "mere aggregation". The GPL is quite clear that "mere aggregation" is not under the scope of the GPL, thus OSD consider the GPL to be open source. A module linked to Linux and distributed along with Linux, however, is no longer "mere aggregation", but distributed as a single work.
> license is loaded the kernel will mark itself as "tainted". (It could just as well refuse to load the module, but it doesn't.)
Why, because they used the word "tainted"? I kind of thought that always meant to be used a flag for "this user loaded some random binary in the kernel and now complains there is bug ". So developers look at the debug output and see "oh, well, it is tained, so, we won't waste time on this, you are on your own" kind of stuff. Which is reasonable.
As you said, if they didn't want it to work with non-GPL modules, they could have prevented loading. Unless you think they setup a honeypot of sorts -- "We'll trick them, then sue them!".
I kind of thought that always meant to be used a flag for "this user loaded some random binary in the kernel and now complains there is bug ". So developers look at the debug output and see "oh, well, it is tained, so, we won't waste time on this, you are on your own" kind of stuff. Which is reasonable.
I think it's useful to look at it as that if the kernel is flagged as tainted, it means it's in a state that can't be properly debugged, independent of the exact reason.
This could be because there's a opaque blob loaded that makes debugging difficult, if not impossible.
It could also be because the license of the code that was loaded (even if it isn't an opaque blob) means that even if someone did figure out the problem, they couldn't necessarily get their changes committed upstream (or might have a hard time of it) and then they'd have wasted that time debugging something that legally can't be debugged by anyone or anyone can't use the results of the debugging (the fix), which are freedoms the GPL is designed to protect. There's a lot of bugs to work on, and it's meaningful to consider code that is licensed in a way that is not strictly GPL compatible as lower priority than code that is GPL.
ZFS was designed and implemented by a team at Sun led by Jeff Bonwick, Bill Moore[106] and Matthew Ahrens. It was announced on September 14, 2004,[107] but development started in 2001.[108] Source code for ZFS was integrated into the main trunk of Solaris development on October 31, 2005[28] and released as part of build 27 of OpenSolaris on November 16, 2005
In 2003, Linus could not have known about ZFS without some insight knowledge, nor if the people developing it had any knowledge about linux. It also contradict the claim that CDDL was choose for the explicit purpose to prevent ZFS being used on Linux and competing with Solaris.
So:
"having been developed totally (not) independently of Linux: they literally were developed (after) Linux even existed, by people who had (full) knowledge of Linux. That tends to strengthen the argument that...?"
The developers knew of Linux but did not necessarily design with any intention of a port or plans in regard to the Linux VFS or kernel design. When it was a Solaris kernel feature, it was clearly not derived from Linux.
The modifications to make this driver to run on Linux caused a derivative work its original source (Solaris) and maybe of Linux itself. The 2003 thread implies that in such a case these modifications may not be derivative of Linux. That some kernel developers feel that the headers are factual and thus not copyrightable.
One could legally blackbox recreate the necessary header files and guarantee that their kernel module was not a derivative binary, so I believe that creating a proprietary kernel module should be legal in principal.
On the matter of linking, the FSF claims that dynamic linking can violate the license, but this is constituted under their understanding of a "derived work". Yet, the US code[1] clarifies that new copies and "adaptations" of a work do not constitute an infringement when created as an essential step in the utilization of the computer program[2]. The term "adaptation" is not defined but because this section is notwithstanding the author's "exclusive right... to prepare derivative works" implies that "adaptations" and "derivative works"[3] are not equal. This would strengthen a position stating that no derivative works are created by simply running, linking, or loading applications.
He states: "having been developed totally independently of Linux: they literally were developed before Linux even existed, by people who had zero knowledge of Linux. That tends to strengthen the argument that they clearly aren't derived."
He does continue to say that he believe it would be "hard to argue that any new driver or filesystem was developed without any thought of Linux", although in the specific case of ZFS (as opposed to, say, nvidia.ko), I think there would be a strong argument that the ZFS module was originally written in whole as a non-derived work.
(Obviously, Linus is not the only stakeholder here, and even his own opinion may have changed since then. Still, it's not a new conversation and the community hasn't been too ruffled by the status quo for the past 13 years)