Configure ZFS filesystems after install

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It’s generally a good idea to avoid activation scripts when possible. Activation is run at very sensitive times, and when things go wrong in activation they cause huge problems. I would probably have created systemd services to handle this. Something like:

{ pkgs, lib, config, utils, ... }: {
  systemd.services."zfs-create-${utils.escapeSystemdPath dataset}" = {
    unitConfig.DefaultDependencies = false;
    requiredBy = [ "local-fs.target" ];
    before = [ "local-fs.target" ];
    after = [ "zfs-import-${pool}.service" "zfs-mount.service" ];
    unitConfig.ConditionPathIsMountPoint = "!${mountpoint}";
    script = ''
      ${config.boot.zfs.package}/bin/zfs create -o mountpoint=${mountpoint} -o recordsize=8k -p ${dataset}
      chmod 700 ${mountpoint}
    '';
  };
}

I did some systemd trickery with ConditionPathIsMountPoint. By ordering after zfs-mount.service, I’ve ensured that any existing datasets are already mounted, then ConditionPathIsMountPoint (with the negation !) causes this service to be skipped if this dataset already exists and is therefore mounted.

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