Linux chief developer Linus Torvalds has again given a clear refusal to include the ZFS file system in the Linux kernel. In a mailing list discussion, he advises Linux users: “Don’t use ZFS.” He said he would not include any ZFS code in the kernel until he personally received an official letter from the Oracle attorneys – or better yet – from CEO Larry Ellison, who approved a ZFS implementation under the kernel’s GPLv2 license. ZFS was developed by Sun for Solaris and later released as open source. It now belongs to the database giant Oracle.
The file system, which is very popular among other Unix operating systems, never got a native Linux version for licensing reasons. Torvald’s stance on this topic has long been known, but the ZFS discussions flare up again and again. Last after the kernel developers had removed an interface a year ago that was used by a ZFS module used by many users.
Minefield under license
It is extremely unlikely that Linux developers will get direct permission from Oracle to latch ZFS directly into the kernel under the GPL. In his mailing list entry, Torvalds refers to “Oracle’s complaint-friendly corporate culture” and the ongoing legal dispute with Google regarding Java implementation in Android and the associated complications for kernel interfaces. The developers fear that a ZFS module directly in the Linux kernel could result in Oracle suing them for license violations because this module would then interact directly with GPLv2 code. The ZFS source code is licensed under the CDDL (Common Development and Distribution License), which some open source license experts consider to be incompatible with the GPL.
It is still controversial whether the two licenses are actually incompatible and this would lead to legal problems. Open source license experts were already arguing about this question in 2016, when Ubuntu included the zfsonlinux module in its distribution. On the one hand, the software Feedom Law Center (SFLC) argued that CDDL and GPLv2 could be combined under certain circumstances. This is opposed to the opinion of the Freedom Conservancy software, which sees significant legal problems in this combination. The question is still not fully resolved, although there are probably more experts who have come up with the arguments of conservancy.
Torvalds doesn’t want to take any chances
In the end such a question can probably only be decided in court and Torvald’s statements make it clear that the Linux developers do not want to take such a risk. In the past, many of his co-developers strengthened his back again and again – first of all Torvald’s right hand Greg Kroah-Hartman, the maintainer of the stable branch of the kernel. According to Kroah-Hartman’s past statements, ZFS is simply not worth exposing itself to the risk of Oracle’s lawsuit. Mainly because other file systems are gradually taking over more functionality from ZFS.
Torvald’s recent comments also hit a similar notch. So it looks like the hopes of some users on ZFS in the Linux kernel continue to be disappointed.