FSF: Interpreting, enforcing and changing the GNU GPL, as applied to combining Linux and ZFS

Richard Stallman looks at the GPL andhow it is incompatible with the CDDL (Common Development and DistributionLicense), which is the license used by ZFS. "Likewise, the copyright holders of ZFS (the version that is actually used) can give permission to use it under the GNU GPL, version 2 or later, in addition to any other license. This would make it possible to combine that version with Linux without violating the license of Linux. This would be the ideal resolution and we urge the copyright holders of ZFS to do so.Some copyright holders choose not to enforce their licenses in specific situations. That enables users to operate as if permission were granted. However, this does not alter the meaning of the GNU GPL, and does not cause uses that the GPL disallows to either suddenly or slowly become permitted by the GPL. Such acquiescence is not the case in regard to linking Linux and ZFS; indeed, some Linux copyright holders have said they consider this copyright infringement. We have explained above the reasons why that is so."