Hi raid5atemyhomework,
On Tue, Jan 05 2021, raid5atemyhomework wrote:
What `install-zfs` does is that it installs the same
kernel-specific package in three different points:
* `kernel-loadable-modules`, because ZFS needs to get into the
kernel somehow.
* `packages`, because the kernel module is useless if you don't
have the userland tools to interact with the kernel module.
* `services`, because ZFS is well-documented outside of Guix as
automatically mounting its filesystems at bootup, but that
actually requires a bit of magic in the `init` system,
specifically you need to actually **load** the module, then
execute `zpool import -a -l` to have it scan for all filesystems
and mount those that need automounting.
Thus, an `install-zfs`, that is a *single* form that inserts the
correct bits in the correct ***three*** places, makes the
experience of adding ZFS to your `operating-system` easier
because there's less scope for error in actually adding the
package. You just add a single `install-zfs`, not add three
things (plus an extra `(define my-zfs (make-zfs-package
linux-libre-5.4))` before your form).
In principle, I think this should all be handled by a service.
Services have a number of extension points where they can impact
the operating system being declared, by extending other services.
For example, adding a package into the global profile is done by
extending profile-service-type (which you can find in
gnu/services.scm). Adding a shepherd service to manage a process
is done by extending shepherd-root-service-type (in
gnu/services/shepherd.scm).
This is how many services work. As an example, sddm-service-type
extends services to: (a) start a process on the running system,
(b) put files in /etc, (c) install some pam services, (d) add an
account on the system, and (e) install packages in the global
profile.
As far as I can tell, the only thing missing for a
zfs-service-type to do what you want is that services can't
currently add new kernel modules (although they can load them via
kernel-module-loader-service-type). I may have missed a mechanism
for this, though. If we added the ability to do this, then it
should be possible to add zfs support by adding a single (service
zfs-service-type) to your services list.
The approach of using services in this way has some advantages
which are outlined in a blog post from 2015[1]. For me the most
compelling advantage is that an zfs-service-type is more
restricted in what it can do, and must be more explicit. An
install-zfs procedure has free-reign over the entire
operating-system definition that it gets passed, which makes it
harder to reason about the composition of such procedures.
Carlo
[1]: https://guix.gnu.org/blog/2015/service-composition-in-guixsd/
