[resf]

Stupid question: can the glue code not be licensed under both GPL and CCDL?

Clearly ZFS is not a derivative work of Linux and Linux is not a derivative work of ZFS. Only the glue code is in violation (because it derives from both).

[cryptonector]

I'm not sure this is true. It's certainly possible to construct an API/ABI such that one could build the glue, or even dispense with it, without having to use any part of ZFS or the kernel to build the other or the glue. I'm not saying that's been done. But it could be done. Indeed, that's what FUSE is, for example, and that's what NDIS does, for another.

To determine whether there is glue here that violates the GPL would require looking at the particulars. Said glue might be licensed under the GPL, and might export the sorts of interfaces that Illumos does, thus allowing the ZFS module to link without reference to either the glue or the kernel! Then how could such glue be said to violate the GPL? It couldn't! Nor could ZFS be said to be violating the GPL in that case.

I don't think you can avoid an escape hatch for the GPL in the kernel without disallowing dynamic loading or modifying the GPL to have harsher terms. But recall that the GPL, and/or much software distributed under the GPL, is designed to have escape hatches: so you can run proprietary software using standard interfaces, for example (i.e., user-land code is not required to be GPLed just because it runs on a GPLed kernel, though a kernel could require it, it's just that _Linux_ doesn't).

It seems here you can't have your cake and eat it too.