Ubuntu and ZFS: Possibly Illegal, Definitely Exciting

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The project originally known as the Zettabyte File System was born the same year that Windows XP began shipping. Conceived and originally written by Bill Moore, Jeff Bonwick and Matthew Ahrens among others, it was a true next generation project – designed for needs that could not be imagined at the time. It was a filesystem built for the future.

Fifteen years later, it’s the future. Though it’s a teenager now, ZFS’s features remain attractive enough that Canonical – the company behind the Ubuntu distribution – wants to ship ZFS as a default. Which wouldn’t seem terribly controversial as it’s an open source project, except for the issue of its licensing.

Questions about open source licensing, once common, have thankfully subsided in recent years as projects have tended to coalesce around standard, understood models – project (e.g. GPL), file (e.g. MPL) or permissive (e.g. Apache). The steady rise in share of the latter category has further throttled licensing controversy, as permissive licenses impose few if any restrictions on the consumption of open source, so potential complications are minimized.

ZFS, and the original OpenSolaris codebase it was included with, were not permissively licensed, however. When Sun made its Solaris codebase available for the first time in 2005, it was offered under the CDDL (Common Development and Distribution License), an MPL (Mozilla Public License) derivative previously written by Sun and later approved by the OSI. Why this license was selected for Solaris remains a matter of some debate, but one of the plausible explanations centered around questions of compatibility with the GPL – or lackthereof.

At the time of its release, and indeed still to this day as examples like ZFS suggest, Solaris was technically differentiated from the far more popular Linux, offering features that were unavailable on operating system alternatives. For this reason, the theory went, Sun chose the CDDL at least in part to avoid its operating system being strip-mined, with its best features poached and ported to Linux specifically.

Whether this was actually the intent or whether the license was selected entirely on its merits, the perceived incompatibility between the licenses (verbal permission from Sun’s CEO notwithstanding) – along with healthy doses of antagonism and NIH between the communities – kept Solaris’ most distinctive features out of Linux codebases. There were experimental ports in the early days, and the quality of these has progressed over the years and been made available as on-demand packages, but no major Linux distributions have ever shipped CDDL-licensed features by default.

That may change soon, however. In February, Canonical announced its intent to include ZFS in its next Long Term Support version, 16.04. This prompted a wide range of reactions.

Many Linux users, who have eyed ZFS’ distinctive featureset with envy, were excited by the prospect of having official, theoretically legitimate access to the technology in a mainstream distribution. Even some of the original Solaris authors were enthusiastic about the move. Observers with an interest in licensing issues, however, were left with questions, principally: aren’t these two licenses incompatible? That had, after all, been the prevailing assumption for over a decade.

The answer is, perhaps unsurprisingly, not clear. Canonical, for its part, was unequivocal, saying:

We at Canonical have conducted a legal review, including discussion with the industry’s leading software freedom legal counsel, of the licenses that apply to the Linux kernel and to ZFS.

And in doing so, we have concluded that we are acting within the rights granted and in compliance with their terms of both of those licenses. Others have independently achieved the same conclusion.

The Software Freedom Conservancy, for its part, was equally straightforward:

We are sympathetic to Canonical’s frustration in this desire to easily support more features for their users. However, as set out below, we have concluded that their distribution of zfs.ko violates the GPL.

If those contradictory opinions weren’t confusing enough, the Software Freedom Law Center’s position is dependent on a specific interpretation of the intent of the GPL:

Canonical, in its Ubuntu distribution, has chosen to provide kernel and module binaries bundling ZFS with the kernel, while providing the source tree in full, with the relevant ZFS filesystem code in files licensed as required by CDDL.

If there exists a consensus among the licensing copyright holders to prefer the literal meaning to the equity of the license, the copyright holders can, at their discretion, object to the distribution of such combinations

The one thing that seems certain here, then, is that very little is certain about Canonical’s decision to ship ZFS by default.

The evidence suggests that Canonical either believes its legal position is defensible, that none of the actors would be interested or willing to pursue litigation on the matter, or both. As stated elsewhere, this is if nothing else a testament to the quality of the original ZFS engineering. The fact that on evidence, Canonical perceives the benefits to outweigh the potential overhead of this fifteen year old technology is remarkable.

But if there are questions for Canonical, there are for their users as well. Not about the technology, for the most part: it has withstood impressive amounts of technical scrutiny, and remains in demand. But as much as it would be nice for questions of its licensing to give way before its attractive features, it will be surprising if conservative enterprises consider Ubuntu ZFS a viable option.

If ZFS were a technology less fundamental than a filesystem, reactions might be less binary. As valuable as DTrace is, for example, it is optional for a system in a way that a filesystem is not. With technology like filesystems or databases, however, enterprises will build the risk of having to migrate into their estimates of support costs, making it problematic economically. Even if we assume the legal risks to end users of the ZFS version distributed with Ubuntu to be negligible, concerns about support will persist.

According to the SFLC, for example, the remedy for an objection from “licensing copyright holders” would be for distributors to “cease distributing such combinations.” End users could certainly roll their own versions of the distribution including ZFS, and Canonical would not be under legal restriction from supporting the software, but it’s difficult to imagine conservative buyers being willing to invest long term in a platform that their support vendor may not legally distribute. Oracle could, as has been pointed out, remove the uncertainty surrounding ZFS by relicensing the asset, but the chances of this occurring are near zero.

The uncertainty around the legality of shipping ZFS notwithstanding, this announcement is likely to be a net win for both Canonical and Ubuntu. If we assume that the SFLC’s analysis is correct, the company’s economic downside is relatively limited as long as it complies promptly to objections from copyright holders. Even in such a scenario, meanwhile, developers are reminded at least that ZFS is an available option for the distribution, regardless of whether the distribution’s sponsor is able to provide it directly. It’s also worth noting that the majority of Ubuntu in usage today is commercially unsupported, and therefore unlikely to be particularly concerned with questions of commercial support. If you browse various developer threads on the ZFS announcement, in fact, you’ll find notable developers from high profile web properties who are already using Ubuntu and ZFS in production.

Providing developers with interesting and innovative tools – which most certainly describes ZFS – is in general an approach we recommend. While this announcement is not without its share of controversy, then, and may not be significant ultimately in the commercial sense, it’s exciting news for a lot of developers. As one developer put it in a Slack message to me, “i’d really like native zfs.”

One way or another, they’ll be getting it soon.

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