ZFS on Guix

[raid5atemyhomework]

Hi guix-developers,

I'm trying to get ZFS working on a test VM running Guix System.

Attempting to do a simple `guix install zfs` does not work, as I reported in 
https://issues.guix.gnu.org/45401 , ZFS 0.8.5 is only up to kernel 5.9 but 
latest guix has kernel 5.10.

I created a procedure to modify the base `zfs` package and compile it for a 
different Linux kernel:

```scheme
(define (make-zfs-package kernel)
  (package
    (inherit zfs)
    (name (string-append "zfs-for-"
                         (package-name kernel)
                         "-"
                         (package-version kernel)
                         "-version"))
    (arguments
      (cons* #:linux kernel (package-arguments zfs)))))
```

Then in my system configuration `.scm`, I selected a specific Linux and had its 
module added to the boot and had it loaded in a Shepherd service:

```scheme
(define system-kernel linux-libre-5.4)
(define system-zfs (make-zfs-package system-kernel))

;; ...

(operating-system
  (kernel system-kernel)
  (kernel-loadable-modules (list (list system-zfs "module")))
  ;; ...
  (packages
    (cons* system-zfs
           ; ...
           %base-packages))
  ;; ...

  (services
    (cons* (service kernel-module-loader-service-type
                    '("zfs"))
           ; ...
           %base-services))
  ;; ...
  )
```

As I documented here: https://issues.guix.gnu.org/45592#1

Now ZFS is loaded at boot (`lsmod | grep zfs` shows ZFS loaded), and `zfs 
version` and `zpool list` don't error out.

However, when I created some extra space in the QEMU image and created a 
partition `vda3`, I get an error in `zpool create tank vda3`.
The error is `cannot mount 'tank': Input/output error`.

I've also tried adding a new device to the QEMU boot as well, also the same 
occurs.

Looking at a partition editor, the partition does get formatted as zfs, it just 
won't mount.



Has anyone ever managed to get ZFS working on Guix?  Any tips?  Is it enough to 
`modprobe` it in a system service or does it have to somehow be added to the 
Linux command line?  Maybe it only works on even older Linux-libre versions 
than 5.4?

Thanks
raid5atemyhomework