GPL Violations Related to Combining ZFS and Linux

February 25, 2016 by Bradley M. Kuhn and Karen M. Sandler

GPL Violations Related to Combining ZFS and Linux

This post discusses an atypical GPL violation. Unlike most GPL violations
Conservancy faces, in this case, a third-party entity holds a magic wand that
can instantly resolve the situation. Oracle is the primary copyright holder
of ZFS, and, despite nearly eight years (going back to the days of Sun’s
control of the code) of the anti-license-proliferation community’s urging,
Oracle continues to license their code under their own, GPL-incompatible
license. While this violation has many facets, and Oracle did not themselves
violate GPL in this specific case, they hold the keys to this particular
kingdom and they forbid the Linux community to enter. While there are
complexities that we must address, in this context, Oracle could make
everyone’s life easier by waving their magic relicensing wand. Nevertheless,
until they do, since GPL-incompatible licenses are the root of all GPL
violations, combinations of GPL’d code with Oracle’s GPL-incompatible code
yield GPL violations, such as the ongoing violation by Canonical, Ltd.

The Basic Facts

Sun released the Z File System (ZFS) code
under the Common Development
and Distribution License, version 1 (CDDLv1)
as part of OpenSolaris. Sun
was ultimately acquired by Oracle. Community members, mostly acting
non-commercially, have improved ZFS and adapted it to function with Linux,
but unfortunately, CDDLv1 is incompatible with GPLv2, so distribution of
binaries is not permitted (see below for details). Many community members
have been frustrated for years that Oracle didn’t simply relicense the code
under a GPLv2-compatible license.

The situation escalated last week
because Canonical,
Ltd. announced their plans to commercially distribute, in Ubuntu 16.04, a
binary distribution of ZFS as a Linux kernel module
, which adapts ZFS
natively for Linux. Conservancy contacted Canonical to inform them of their
GPL violation, and Canonical encouraged us to speak publicly. We’re glad to
do so to clarify the differing views on this issue. As you’ll read below,
Conservancy disagrees with Canonical’s decision, and Conservancy hopes to
continue dialogue with Canonical regarding their violation. We do not give
up on friendly resolution of a GPL violation easily and are glad Canonical
seeks to transparently discuss both sides of this issue in public.

Summary of our Conclusion

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. We have
written this statement to answer, from the point of view of many key Linux
copyright holders, the community questions that we’ve seen on this

Specifically, we provide our detailed analysis of the incompatibility
between CDDLv1 and GPLv2 — and its potential impact on the trajectory
of free software development — below. However, our conclusion is simple: Conservancy and the Linux copyright
holders in the GPL Compliance Project for
Linux Developers
believe that distribution of ZFS binaries is a GPL
violation and infringes Linux’s copyright. We are also concerned that it may
infringe Oracle’s copyrights in ZFS. As such, we again ask Oracle to respect
community norms against license proliferation and simply relicense its
copyrights in ZFS under a GPLv2-compatible license.

GPL Incompatibility

The license of Linux, the GNU General Public License, version 2 (GPLv2), is
conceptually known as a strong copyleft
license. A strong copyleft license extends software freedom policies as far
as copyright law allows. As such, GPLv2 requires that, when combinations
and/or derivatives are made under copyright law with GPLv2’d works, the
license of the resulting combination and/or derivative is also GPLv2.

The Free Software Foundation (FSF)
has long
discussed the question of licenses incompatible with the GPL
, pointing
out that:

In order to combine two programs (or substantial parts of them) into a
larger work, you need to have permission to use both programs in this
way. If the two programs’ licenses permit this, they are compatible. If
there is no way to satisfy both licenses at once, they are incompatible.

License compatibility is not merely a question for Free Software
licenses. We can analyze any two copyright licenses and consider whether
they are compatible.

In the proprietary software world, rarely are two licenses ever
compatible. You can’t, by default, license a copy of Oracle’s database, and
then make a combination with Apple’s iOS. To do so, you would need to
negotiate (and pay for) a special license from both Apple and Oracle to make
that combination.

Furthermore, with proprietary software, there is a practical problem
somewhat unrelated to the legal permission: you must procure (again, likely
for a rather expensive fee) a copy of the source code for Apple’s and
Oracle’s proprietary software to have the practical ability to make the

Since the GPL, and all copyleft licenses, are fundamentally copyright
licenses, the analysis is similar. However,
GPL requires that all software distributions include complete corresponding
source code to any binaries, so the practical problem never presents itself.
Nevertheless, when you wish to combine GPL’d software with some other
software and distribute the resulting combination, both the copyright holders
of the GPL’d software and the copyright holders of the other software must
provide a license that allows distribution of the combination.

Most prefer to discuss the issue of combining truly proprietary,
no-source-available copyrighted material with GPL’d software, as it creates the most
stark practical contrast, and is the most offensive fact pattern.
Proprietary software gives the users no freedom to even examine, let alone
modify, rebuild, and reinstall the software. The proprietary license doesn’t
allow nor even give the practical ability to redistribute source code, and
the GPL mandates source distribution when binary distribution occurs. The
incompatibility is intuitively obvious. Few consider the fact that
proprietary software licensing is just one (rather egregious) example of a
GPL-incompatible license.

In that context, we can imagine licenses that are GPL-incompatible, but do
give some interesting permissions to users. An example is
source-code-available systems that prohibit commercial distribution and
forbid modification to the source code. The GPL has terms that permit
modification and allow commercial distribution of GPL’d software, and as
such, even though source code is available for non-commercial, non-modifiable
software, the license is nonetheless GPL-incompatible.

Finally, we can consider the most subtle class of GPL-incompatibility, in
which we find ZFS’s license,
the Common
Development and Distribution License, version 1 (CDDLv1)
. The CDDLv1 is
considered both
a Free
and an Open
license, and is a weak copyleft license. Nevertheless, neither
CDDLv1 nor GPLv2 permits combination of copyrighted material under the
other license.

To understand this non-intuitive incompatibility, we can analyze in
detail the requirements of both licenses. First, GPLv2 requires:

[§2](b) You must cause any work that you distribute … that in
whole or in part contains or is derived from the Program or any
part thereof, to be licensed as a whole … under the terms of this

[§]3. You may copy and distribute the Program (or a work based on it,
under Section 2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also…

a) Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of Sections
1 and 2 above…

[§]6. …You may not impose any further
restrictions on the recipients’ exercise of the rights granted herein.

According to these provisions of GPLv2, if you create a binary work that
incorporates components from the GPLv2’d program, you must provide the
complete corresponding source for that entire work with the binary, and the
terms of the GPLv2 apply to that source. If the sources as a whole cannot be
outbound-licensed under GPLv2, you have no permission under copyright law to
distribute the binary work, since GPLv2 didn’t grant you that permission.

GPLv2-compatible licenses do not contradict the requirements of GPLv2, which is
what makes them compatible. For example, highly permissive licenses like
the ISC
allow imposition of additional licensing requirements (even
proprietary ones), and so combining ISC-licensed source and GPLv2’d
source into a binary work is permitted; compliance with GPLv2 is possible
when distributing binaries based on the combined sources.

CDDLv1, however, contains various provisions that are incompatible with
that outcome. Specifically, CDDLv1 requires (emphasis ours):

[§]3.1 … Any Covered Software that You distribute or otherwise make available in
Executable form must also be made available in Source Code form and that
Source Code form must be distributed only under the terms of this
. …

[§] 3.4 … You may not offer or impose any terms on any Covered
Software in Source Code form that alters or restricts the applicable
version of this License

CDDLv1 is a weak copyleft license in that it allows you create a binary work with
components under different terms (see CDDLv1§3.6). However, as seen
in the text above, with regard to the specific copyrighted material already
under CDDLv1, that material must remain only licensed under the terms of
the CDDLv1. Furthermore, when redistributing the source code, you cannot
alter the terms of the license on that copyrighted material.

GPLv2, as shown above, requires that you alter those terms for the source
code — namely, as a strong copyleft, the terms of GPLv2 apply to the
entire complete corresponding source for any binary work. Furthermore,
downstream users need permission to make GPLv2’d modifications to that
source. This creates a contradiction; you cannot simultaneously satisfy
that obligation of GPLv2 and also avoid alter[ing] the terms of
CDDLv1-licensed source. Thus, the licenses are incompatible, and
redistributing a binary work incorporating CDDLv1’d and GPLv2’d copyrighted
portions constitutes copyright infringement in both directions. (In
addition to this big incompatibility, there are also other smaller
incompatibilities throughout CDDLv1.)

We believe Sun was aware when drafting CDDLv1 of
the incompatibilities; in fact, our research into its history indicates the
GPLv2-incompatibility was Sun’s design choice. At the time, Sun’s apparent
goal was to draw developers away from GNU and Linux development into
Solaris. Not only did Sun not want code from GNU and Linux in Solaris,
more importantly, Sun did not want technological advantages from Solaris’ kernel to
appear in Linux.

Much has changed in the seven and a half years since CDDLv1’s publication
and promulgation. OpenSolaris has been discontinued; CDDLv1 codebases
never became an active area of Free Software development like GNU and
Linux. Oracle could now easily indicate that combination of ZFS with Linux
into binary works is permitted, (e.g., as the overwhelming majority
copyright holder0, Oracle
could make
a decree like the one University of California did to fix a similar
). Until Oracle takes an action like that, it remains a
license violation of both CDDLv1 and GPLv2 to distribute
binary works that combine together and/or derive from both GPLv2 and CDDLv1

What Constitutes a Combined/Derivative Work?

Once license incompatibility is established, the
remaining question is solely whether or not combining ZFS with Linux creates
a combined and/or derivative work under copyright law (which then would, in
turn, trigger the GPLv2 obligations on the ZFS code).

Conservancy has helped put similar questions (still
pending) before a Court,
in Hellwig’s
VMware case
Conservancy currently funds.
In fact, the same questions come up with all sorts of GPL-incompatible Linux
modules and reuses of Linux code.

Courts have not spoken specifically on this question; precedents that
exist are not perfectly on-topic. Citing an opinion of a lawyer is
often not helpful in this context, because lawyers advise clients, and
argue zealously for their clients’ views. When Courts are unclear on a
matter, it generates disputes, and only Courts (or possibly new
legislation) can ultimately resolve those disputes.

Nevertheless, our lawyers have analyzed these situations with
the assistance of our license compliance and software forensics staff for
many years, and we have yet to encounter a Linux module that — when
distributed in binary form — did not, in our view, yield combined
work with Linux. The FSF, stewards of the GPL,
have stated
many times over the past decades that they believe there is no legal
distinction between dynamic and static
linking of a C program
and we agree. Accordingly, the analysis is quite
obvious to us1: if ZFS were
statically linked with Linux and shipped as a single work, few would argue
it was not a “work based on the Program” under GPLv2. And, if
we believe there is no legal difference when we change that linking from
static to dynamic, we conclude easily that binary distribution of ZFS plus
Linux — even with ZFS in a .ko file — constitutes distribution
of a combined work, which we name Linux+ZFS.

Canonical has found some lawyers who disagree — a minority position, from our understanding of community norms. But Canonical’s
public position on the matter contributes to license uncertainty, and
opponents of Free Software may use this as an opportunity to marginalize
copyleft enforcement generally. Canonical can resolve the situation by
ceasing the infringing distribution, but Oracle can also unilaterally resolve
this trivially with a simple relicense of ZFS to a GPL-compatible license.

Thus, all parties currently stand at an impasse. Conservancy (as a Linux
copyright holder ourselves), along with the members of our coalition in the
GPL Compliance Project for Linux Developers, all agree that Canonical and
others infringe Linux copyrights when they distribute zfs.ko. Canonical’s
lawyers disagree. Oracle refuses to relicense their ZFS copyrights under a
GPL-compatible license.

Ultimately, various Courts in the world will have to rule on the more
general question of Linux combinations. Conservancy is committed to
working towards achieving clarity on these questions in the long term. That work began in earnest last year with the
VMware lawsuit, and our work in this area will continue indefinitely,
as resources permit. We must do so, because, too
often, companies are complacent about compliance. While we and other
community-driven organizations have historically avoided lawsuits at any cost
in the past, the absence of litigation on these questions caused many
companies to treat the GPL as a weaker copyleft than it actually is.

Why Conservancy Does Not Use Litigation Immediately

As discussed in our
, Conservancy, while willing to litigate, uses
litigation only as a last resort. Compliance actions are primarily
education and assistance processes to aid those who are not following the
We completely
exhaust every other diplomatic option
for compliance before seeking
resolution from the Courts.

“Almost There” is More Painful Than Proprietary

Conservancy and our GPL Compliance Project for Linux Developers are quite
sympathetic to the feeling of “almost there” that exists with ZFS
for Linux. CDDL is a Free Software license, but sadly a
GPL-incompatible one. Like a partial fix for a problematic bug, a
GPL-incompatible Free Software license feels like a solution that’s
“oh-so-close”. Everyone wants to try to tweak
that incomplete solution into a full one. We hope this explanation helps
bring clarity that the seemingly “almost there” of
combining CDDL’d and GPL’d code is a mirage. The community must seek
together a better solution.

Oracle holds the better solution in their hands; like waving a magic wand,
they can take any of a myriad of actions to communicate permission to
relicense ZFS under GPL. Conservancy encourages Free Software enthusiasts
and for-profit companies alike to lobby Oracle to relicense their ZFS
copyrights. While this change by Oracle cannot resolve Canonical’s
violation, Oracle’s relicensing would create a path for Canonical that
might ultimately yield a compliant binary distribution of Linux+ZFS. As
such, we’ve asked Canonical to commit to lobbying Oracle for this

Is The Analysis Different With Source-Only Distribution?

We cannot close discussion without considering one final unique aspect to
this situation. CDDLv1 does allow for free redistribution of ZFS source
code. We can also therefore consider the requirements when distributing
Linux and ZFS in source code form only.

Pure distribution of source with no binaries is undeniably
different. When distributing source code and no binaries,
requirements in those sections of GPLv2 and CDDLv1 that cover modification
and/or binary (or “Executable”, as CDDLv1 calls it)
distribution do not activate. Therefore, the analysis is simpler, and we
find no specific clause in either license that prohibits
source-only redistribution of Linux and ZFS, even on the same distribution

Nevertheless, there may be arguments for contributory and/or indirect
copyright infringement in many jurisdictions. We present no specific
analysis ourselves on the efficacy of a contributory infringement claim
regarding source-only distributions of ZFS and Linux. However, in our GPL
litigation experience, we have noticed that judges are savvy at sniffing
out attempts to circumvent legal requirements, and they are skeptical about
attempts to exploit loopholes. Furthermore, we cannot predict Oracle’s
view — given its past willingness to enforce copyleft licenses, and
Oracle’s recent attempts to adjudicate the limits of copyright in Court.
Downstream users should consider carefully before engaging in even
source-only distribution.

We note
that Debian’s
decision to place source-only ZFS in a relegated area of their archive
called contrib
, is an innovative solution. Debian
fortunately had a long-standing policy that contrib was
specifically designed for source code that, while licensed under an
acceptable license
for Debian’s
Free Software Guidelines
, also has a default use that can cause
licensing problems for downstream Debian users. Therefore, Debian
communicates clearly to their users that this code is problematic by
keeping it out of their main archive. Furthermore, Debian
does not distribute any binary form of zfs.ko.

(Full disclosure: Conservancy has a services agreement with Debian in
which Conservancy occasionally gives its opinions, in a non-legal capacity,
to Debian on topics of Free Software licensing, and gave Debian advice on
this matter under that agreement. Conservancy is not Debian’s legal

Do Not Rely On This Document As Legal Advice

You cannot and should not rely on this document as legal
advice. Our lawyers, in conjunction with our GPL compliance and software
forensics experts, have analyzed the Linux+ZFS that Canonical includes in
their Ubuntu 16.04 prereleases. Conservancy has determined, with the advice
of both inside and outside law firm legal counsel, that the binary
distribution constitutes a derivative and/or combined work of ZFS and Linux
together, and therefore violates the GPL, as explained above. We also know
from Canonical’s
blog post
that they have found other lawyers to give them contradictory
advice. Such situations are common on groundbreaking legal issues, and,
after all, copyleft is perhaps the most novel legal construction for
copyright in its history. Lawyers and their clients who oppose copyleft will
attempt to limit copyleft’s scope (with litigation, FUD, and moxie), and
those of us who use copyleft as a tool for software freedom will
diametrically seek to uphold its scope to achieve the license drafter’s and
licensors’ intended broad impact for software freedom.

Indeed, Conservancy believes this situation is one battle in a larger
proxy war by those who seek to limit the scope of strong copyleft generally.
Yet, the GPL not only benefits charitable community organizations like
Conservancy, but also for-profit companies, since GPL ensures your
competitors cannot circumvent the license and gain an unfair advantage. We
therefore urge charities, trade associations and companies who care about
Linux to stand with us in opposition of GPL violations like this one.

More work might be
required to relicense all modern ZFS code, since others have contributed, but
we expect that those contributors would gladly relicense in the same manner
if Oracle does first.

More discussion on
these issues can be found in this
section of Copyleft and the GNU General Public License: A Comprehensive
Tutorial and Guide
, which is part
of, a project co-sponsored by
the FSF and Software Freedom Conservancy.

Posted by Bradley M. Kuhn and Karen M. Sandler on February 25, 2016. Please email any comments on this entry to

Tags: GPL

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