Use systemd service templates

[Zocker1999NET]

Hey, thanks for this great documentation. However I have an idea to further improve it:

You stated one could use multiple ExecStart= lines to control, which drive's keys should be loaded on boot. You can use systemd templates instead of them. I think this may be easier to manage & debug in the long run.

To use them, you need to:

• append an @ at the end of the service's file name like zfs-load-key@.service
• use ExecStart=/usr/bin/zfs load-key %i
• optionally use Description=Load encryption keys for %i
• select which keys you want to load by enabling the services as required: systemctl enable zfs-load-key@my-dataset.service

This supports multiple instances but then uses one instance / service per dataset. If some import fails, systemd will easily indicate which failed to load. All while maintaining a single main configuration file which doesn't need to be edited to enable another dataset.

And if someone wants to import all, one still can use systemctl enable zfs-load-key@-a.service as systemd will then eventually call zfs load-key -a.