[bug#45692] [PATCH v3 0/3] New patch series for Even Better ZFS Support on Guix

[raid5atemyhomework via Guix-patches via <guix-patches@gnu.org>]

This is a new patch series, please completely forget the previous patch series.

Notable differences are:

* ZFS automounted datasets are mounted before `user-processes` instead of `file-systems`, since there is strong objection to modifying `file-systems` so it can be extended to allow ZFS automounted datasets to be mounted before `file-systems`.  This prevents easy `/home` on ZFS (though see the added documentation in 3/3 for a workaround).
* The old `kernel-loadable-module-service-type` is renamed to `linux-loadable-module-service-type`, despite the corresponding `operating-system` field being named `kernel-loadable-modules`, and the loader service type being named `kernel-module-loader-service-type` :rolleyes:.
* There is a new `linux-builder-service-type`, which can be extended with a function to modify its `linux-builder-configuration`.  The `linux-loadable-module-service-type` extends this base service.  I think this design patttern should be more extensively used in Guix; currently services are only extensible via one field of their configuration, this pattern allows creating multiple service types for each extensible field of the configuration.  In this particular case, the `kernel` of the `linux-builder-service-type` can be extended (by adding/removing `configure` or `make` flags, or added `inputs`) independently of the list of loadable modules using this design pattern.
* Auto-scrub and auto-snapshot is now supported, with additional fields in `zfs-configuration` to support it.
* The auto-mounting Shepherd service has been renamed `zfs-auto-mount` (previously `zfs-automount`).
* Documentation includes a list of things that are currently not (fully) supported.

Personally I'm not particularly motivated to push this anymore.  I have a frankenstein's `configuration.scm` that gets me the bits of ZFS functionality that I absolutely need, with the rest something I'm just living without, and while it would be *nice* to have *some* out-of-the-box support for ZFS (or at least make it easy to get a box to get support for ZFS out of), I personally don't need it at this point.

Patch 1/3 corresponds to the original Patch 1/4.  Patch 2/3 has no corresponding patch in the original patch set, but is the same patch as https://issues.guix.gnu.org/47134 which nobody is looking at, as usual.  Patch 3/3 corresponds to the original Patch 4/4.

The original Patch 2/4 has been removed since it's what makes `/home` on ZFS work by making `file-systems` extensible.  The original Patch 3/4 was already merged.

This patch series is minimally tested compared to the previous patch series; I have homework to store on my ZFS pool and should really stop fooling around with the operating system.  I have this patch series running in a VM with a ZFS pool.  Auto-scrub is not tested, though auto-snapshot looks working.  Auto-mounting works as with previous patch series.  Encrypted and compressed filesystems are untested but I don't expect it to be significantly regressed compared to the previous patch series.

More work can be done for ZFS support.  But I think the current set gives a workable ZFS support; further work can be done piecemeal afterwards.  The documentation includes notes for anyone who feels motivated enough to keep improving the ZFS support.

Thanks
raid5atemyhomework