'edonr' and 'skein' zpool features are not supported for root pools even though UEFI is a thing

[locdtm]

Exhibit A:

https://github.com/zfsonlinux/zfs/blob/376994828fd3753aba75d492859727ca76f6a293/module/zfs/zfs_ioctl.c#L3991-L4004

Exhibit B:

https://github.com/zfsonlinux/zfs/blob/376994828fd3753aba75d492859727ca76f6a293/lib/libzfs/libzfs_dataset.c#L1593-L1598

(3769948 is the current master.)

As for the rationale, @skiselkov stated the following in https://www.listbox.com/member/archive/post_content.html?post_id=20131007080502:B04DC60C-2F48-11E3-9198-9C9438B0F59B&address=000:

No, this is to cover the ERANGE return from zfs_ioctl.c:3784 where we
check to make sure nobody enables any salted checksums on a root pool,
since GRUB doesn't have support for that feature. Bootloader support on
FreeBSD might differ, though.

On UEFI systems, GRUB is not even used. Prohibiting the setting and use of specific flags is, in this configuration, rather unnecessary.

#6202 notes the same: disallowing zpool features is not warranted when GRUB is not used, which is a configuration that has worked for several years now.

[bunder2015]

While EFI stub booting is a thing, most people who use EFI still use it to boot grub, which doesn't support several feature flags. illumos (to the best of my knowledge) doesn't support EFI either. I don't know the complete status of the grub they use. (I'm a doofus, they use freebsd btx now.) It might be possible their grub btx can't boot all-flag pools as well.

[sylveon]

What about users of systemd-boot, which on UEFI systems just boots the EFI stub? EDIT: Even if it does not (not completely sure about that fact), the Arch Wiki's recommended way of installing root on ZFS uses systemd-boot and the bootfs flag.

[bunder2015]

Unfortunately the linux ecosystem is so diverse, I don't think we would find a solution that suits everybody's needs.

[sylveon]

What about the possibility to enable those features (and others) on bootfs pools with a clear warning about the possibility to break some bootloaders?

[bunder2015]

Its probably doable, but I think a better idea would be to add it behind a -f option to zfs set so people don't arbitrarily change it by mistake. I'm not a dev and it would probably need to get approval across all the platforms before implementing. Sounds like something worthy of the mailing lists.