Guix,

After adding (specification->package+output "zfs:module") to my 
system packages, it's still missing from current-system:

  $ guix system reconfigure …

  $ ls /run/current-system/profile/lib/modules/
  5.4.0-pf7-4-ed26-M88

That's my horrible custom Linux fork/version/abomination. 
Apologies.  The ZFS package simply compiles against Guix's default 
linux-libre-5.4.20-gnu package.

After editing the zfs package to install everything into the main 
:out output:

  $ guix system reconfigure …

  $ ls /run/current-system/profile/lib/modules/
  5.4.0-pf7-4-ed26-M88  5.4.20-gnu

  $ ls 
  /run/current-system/profile/lib/modules/5.4.20-gnu/extra/zfs/
  zfs.ko

Kind regards,

T G-R