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Linux kernel head Linus Torvalds has warned engineers against adding a module for the ZFS filesystem that was designed by Sun Microsystems – and now owned by Oracle – due to licensing issues.

As reported by Phoronix, Torvalds has warned kernel developers against using ZFS on Linux, an implementation of OpenZFS, and refuses to merge any ZFS code until Oracle changes the open-source license it uses.

ZFS has long been licensed under Sun's Common Development and Distribution License (CDDL) as opposed to the Linux kernel, which is licensed under GNU General Public License (GPL).

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Torvalds aired his opinion on the matter in response to a developer who argued that a recent kernel change "broke an important third-party module: ZFS".

The Linux kernel creator says he refuses to merge the ZFS module into the kernel because he can't risk a lawsuit from "litigious" Oracle – which is still trying to sue Google for copyright violations over its use of Java APIs in Android – and Torvalds won't do so until Oracle founder Larry Ellison signs off on its use in the Linux kernel.

"If somebody adds a kernel module like ZFS, they are on their own. I can't maintain it and I cannot be bound by other people's kernel changes," explained Torvalds.

"And honestly, there is no way I can merge any of the ZFS efforts until I get an official letter from Oracle that is signed by their main legal counsel or preferably by Larry Ellison himself that says that yes, it's OK to do so and treat the end result as GPL'd," Torvalds continued.

"Other people think it can be OK to merge ZFS code into the kernel and that the module interface makes it OK, and that's their decision. But considering Oracle's litigious nature, and the questions over licensing, there's no way I can feel safe in ever doing so."

The licensing problem is explained on an FAQ from the developers of ZFS on Linux.

"While both are free open-source licenses they are restrictive licenses. The combination of them causes problems because it prevents using pieces of code exclusively available under one license with pieces of code exclusively available under the other in the same binary," the ZFS developers write.

"In the case of the kernel, this prevents us from distributing ZFS on Linux as part of the kernel binary. However, there is nothing in either license that prevents distributing it in the form of a binary module or in the form of source code."

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Torvalds addressed this issue too in his response and dismissed the idea of a proposed 'ZFS shim layer' to address problems combining two projects with different licenses, particularly due to Oracle's Java API copyright lawsuit.

"And I'm not at all interested in some 'ZFS shim layer' thing either that some people seem to think would isolate the two projects. That adds no value to our side, and given Oracle's interface copyright suits (see Java), I don't think it's any real licensing win either," he explained.

His final words on the matter: "Don't use ZFS. It's that simple. It was always more of a buzzword than anything else, I feel, and the licensing issues just make it a non-starter for me."

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