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Linux and Open Source

Steven J. Vaughan-Nichols & Paula Rooney

When open source licenses collide

By | June 9, 2010, 6:40am PDT

Summary: ZFS must be offered under Sun’s CDDL. Linux, of course, is licensed under the GPL. You can’t combine the two.

With so much diversity within open source, it was inevitable that, one day, a great open source project would be ruined by license incompatibility.

So it is with ZFS for Linux.

It’s an attempt to port the file system of Open Solaris into a version of Linux, and was created by the good people at the Lawrence Livermore Lab.

The problem, as Brian Behlendorf noted at Github, is that the licenses are incompatible. ZFS must be offered under Sun’s CDDL. Linux, of course, is licensed under the GPL. You can’t combine the two.

It would be like, as the late Richard Pryor noted in one of his best monologues, trying to mix regular milk with low-fat. It would explode.

There are some kludgy work-arounds, Behlendorf noted. You can implement ZFS in a user space with FUSE, making it a derived work. Or you can modify and build it separately from the Linux, then build the combination yourself. But this is very hard.

The work was done before the Oracle-Sun merger, and was originally meant for the Lustre project. It was part of a technology Sun acquired in 2007. The usual solution in cases like this is to dual-license the code. The CDDL is based on the Mozilla license, and I have yet to see a problem like this involving Firefox.

Behlendorf says Oracle was contacted about the incompatibility but his group has not had any luck on the license issue, which led to the decision to move the problem to a public forum.

That decision, in turn, just adds more public pressure on Oracle.  They publicly stated a desire to cooperate with open source in the run-up to the Sun merger. Few believed them at the time.

The skeptics appear to have been right. Which means open source advocates who supported the merger, as well as Oracle, may have some explaining to do.

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Dana Blankenhorn has been a business journalist for 30 years, a tech freelancer since 1983.

Disclosure

Dana Blankenhorn

Dana Blankenhorn has been a journalist, writer and part-time futurist for over 30 years.

At the present moment I run only a personal blog in addition to my ZDNet open source blog.

DanaBlankenhorn.Com has the subtitle The War Against Oil. In the past I have used it to write about political history, e-commerce, personal matters, some ideas related to open source, and The World of Always On, which is the idea of using sensors, motes and RFID to turn WiFi links into platforms for applications which live in the air.

My IRA account at Schwab holds a few tech shares, most notably some Intel and Applied Materials, but there are no open source companies in it. I don’t even own any CBS stock.

Biography

Dana Blankenhorn

Dana Blankenhorn has been a business journalist for nearly 25 years and has covered the online world professionally since 1985. He founded the Interactive Age Daily for CMP Media, and has written for the Chicago Tribune, Advertising Age's "NetMarketing" supplement, and dozens of other publications over the years.

Talkback Most Recent of 13 Talkback(s)

  • ZFS is a moot issue ...
    All of the features of ZFS and more are being built into btrfs which is licensed under the GPL. btrfs is nearly production ready with some distros launching it within months from now. Oracle owns both ZFS and btrfs, btrfs will be the Linux product and ZFS will be used for non-Linux applications. In the end, btrfs will be the newer and more robust filesystem.
    ZDNet Gravatar
    George Mitchell
    9th Jun 2010
  • Perhaps, but not the point
    Glad to see that there is a workaround in this particular case, but the larger issue still remains. What should be the best way to proceed when license issues prevent technical progress? This isn't a case of proprietary versus open source, but rather, where legal maneuvering in an attempt to keep two products "open" have prevented technical progress.

    That isn't supposed to happen with open source projects. Quite the opposite, actually. The entire purpose of copyleft is to ensure that the very best open technology can be examined, built upon, and shared.

    I would be very curious as to hear where the incomparabilities arise. Is it due to the inflexibility of the GPL? And should the Linux kernel consider moving to another, less restrictive license, such as the LGPL? Or even a BSD style license?
    ZDNet Gravatar
    Rob Oakes
    9th Jun 2010
  • RE: When open source licenses collide
    @Rob Oakes My understanding of the ZFS problem is that the GPL specifically prohibits directly interfacing with software that is under a MORE restrictive license than the GPL itself. Arms length applications are OK, but inclusion in the kernel (which is required with filesystems) is NOT OK. Thus, when Sun chose to license ZFS under the CDDL, that sealed the door to inclusion in the Linux kernel.

    There have been attempts in the past to modify the licensing of the Linux kernel itself. The problem is that the Linux kernel includes software copyrighted by literally hundreds if not thousands of individual developers. To make any change in how it is licensed would require written agreement from every one of those developers in order to pass legal muster. That is NOT going to happen. It would be far easier for Oracle to modify the license of ZFS, but that would not be so easy either for precisely the same reason. And if any developer is deceased, one has to get permission from ALL of the heirs. Its a very big deal. So it is much easier to go around the problem.

    By the way, this is not just an issue with open source, it is also a major issue with proprietary software as well. Even the OWNERS of a given proprietary software can not change the licensing without agreement from every last stakeholder. It has to do with copyright law, not with whether something is closed source or open source. Copyright law governs both open and closed source licenses.
    ZDNet Gravatar
    George Mitchell
    9th Jun 2010
  • RE: When open source licenses collide
    The Brian Behlendorf working on ZFS Linux support for LLNL is *not* the same as the Brian Behlendorf (writing this comment now) pictured above, who's doing much more Open Source advising than coding these days. I love the geek cred he's giving our name!
    ZDNet Gravatar
    brianbehlendorf
    9th Jun 2010
  • RE: When open source licenses collide
    @brianbehlendorf That's an easy mistake to make. I'll take out the other Brian's picture. Got one for me?
    ZDNet Gravatar
    DanaBlankenhorn
    9th Jun 2010
  • GPL seems to be more the issue
    I don't like people describing the GPL as less restrictive. To me it seems to be more restrictive. Other systems under what I consider to be less restrictive licenses (BSD) do not have issues incorporating ZFS. Why not complain to Linus and the Linux community about re-licensing Linux under a less restrictive license? Why must the onus be on Sun/Oracle?
    ZDNet Gravatar
    dbsoft
    9th Jun 2010
  • Re: ZFS on Linux
    @dbsoft Certainly if Linux users really wanted ZFS that bad, they could complain. But none of the Linux users that I know, and I know a lot of them, really care. Linux currently supports more file systems (29) than BSD (15) as far as I know. How many file systems do the major OS's like Windows, Mac, and even Solaris support? I am a long time user of Linux and I really don't care about ZFS with btrfs on the way. btrfs, unlike ZFS, will be pretty much custom designed for Linux and will thus provide everything that ZFS provides and more with near perfect interface to the Linux kernel since it is being built for Linux from the ground up. BSD can have ZFS, I'll be happy to wait a few more months for btrfs.
    ZDNet Gravatar
    George Mitchell
    10th Jun 2010
  • BTRFS lacks Disk Encryption
    ZFS will soon have disk encryption thanks to the work of Darren Moffat. This will make it more feasible to use on laptops. BTFRS doesn't have any plans for this. Currently with OpenSolaris there is a workaround for disk encryption for laptops. http://blogs.sun.com/darren/entry/encrypting_zfs_pools_using_lofi
    ZDNet Gravatar
    Felix Derzhinsky
    11th Jun 2010
  • ZDNet Gravatar
    Felix Derzhinsky
    11th Jun 2010
  • Disk encryption ...
    ZFS needs a disk encryption feature because Solaris does not have OS support for disk encryption. Linux DOES have OS support for disk encryption and thus can provide it externally to the file system itself. However, there are some reports out there indicating that integrated disk encryption is eventually being considered for btrfs. I suspect that is unlikely to happen because btrfs is being designed exclusively for use on Linux and as such, will be designed to benefit from those global capabilities already built into the Linux kernel and architecture. In fact, many of the features to be provided by btrfs are actually provided externally to the FS itself which is fine as long as the final product appears seamless to the user. The major drawback will be that it will be nearly impossible to implement btrfs on any other OS than Linux. But it will make btrfs development faster and less expensive than doing a standalone FS like ZFS. So just because a chart says that ZFS has a feature and btrfs doesn't may not take into account the fact that Linux may be able to provide that feature globally as it currently does for ext4 which btrfs is scheduled to replace. Personally, I don't care how they do it. I have never had any problem with Linux file systems. I have had one major mechanical failure of a disk drive which has been my only data loss in ten years, and even in that case, only a handful of files were lost on a rather large drive. I have used hardware RAID ever since that happened and am looking forward to using btrfs on top of hardware RAID.
    ZDNet Gravatar
    George Mitchell
    11th Jun 2010
  • zfs list
    "All of the features of ZFS and more are being built into btrfs"
    That is not even possible, since ZFS is not just a filesystem but includes volume management as well.

    "am looking forward to using btrfs on top of hardware RAID"
    That is a very flimsy arrangement compared to end-to-end checksums and redundancy on ZFS.

    As for the license discussion, this is a current topic on the ZFS mailing list, since a new ZFS porting project has recently been announced there.
    ZDNet Gravatar
    qu1j0t3
    11th Jun 2010
  • RE: When open source licenses collide
    @qu1j0t3 According to an article on H-Open by Dr Oliver Diedrich: "With its integrated volume management, checksums for data integrity,Copy on Write and snapshots, Btrfs offers a range of features unrivalled by any of the Linux file systems currently in production use."

    I see both volume management and checksums on the list.

    Further down in the same article: "RAID functionality is an integral feature (only RAID-0, RAID-1 and RAID-10 are currently available, however). Devices can be added and removed during operation. What's still missing is RAID-5 and RAID-6 with one or two redundant disks."

    So data redundancy is built in as well.

    Also: "The file system can be up-sized or down-sized as well as de-fragmented during operation."

    So btrfs also features built in defragmentation. Perhaps you can tell me about how ZFS handles fragmentation?

    The reality is that because of the constraints of IP law, attempting to relicense ANY major piece of software is a VERY big deal. That is probably why Oracle is putting all of their effort into getting btrfs out the door.

    To see how big a deal btrfs is in terms of the future, I suggest anyone interested do a search on Coherent Remote File System. Oracle is placing some major bets on this technology which is going to eclipse ZFS guaranteed.
    ZDNet Gravatar
    George Mitchell
    11th Jun 2010
  • RE: When open source licenses collide
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    ZDNet Gravatar
    efsane
    25th Apr

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