Grub won't boot to zfs after system rebuild.

[RyukaZou]

System information

Type	Version/Name
Distribution Name	Gentoo Linux
Distribution Version	17.1
Kernel Version	5.15.52
Architecture	X64
OpenZFS Version	2.1.4-r1

Describe the problem you're observing

When installing gentoo with GRUB that has libzfs enable via a chrooted environment and reboot into such works as expected.

If the system is rebuild immediately after set up with emerge -e @world and perform grub-mkconfig -o /boot/grub/grub.cfg then reboot will fail to boot into system.

Describe how to reproduce the problem

1. Instell gentoo follow Fearedbliss's guide.(https://wiki.gentoo.org/wiki/User:Fearedbliss/Installing_Gentoo_Linux_On_ZFS)
2. Immediately rebuild system with emerge -e @world after out of chroot and reboot into the installation.
3. After rebuild is done perfrom grub-mkconfig -o /boot/grub/grub.cfg.

Include any warning/errors/backtraces from the system logs

Message: filesystem 'rpool/' cannot be mounted, unable to open the dataset 

Possible fix solution

zfsonlinux/grub#22 (comment)

https://wiki.archlinux.org/title/Install_Arch_Linux_on_ZFS#bug:_broken_root_pool_detection

[RyukaZou]

This problem cost by missing hostid, after zgenhostid -o /etc/hostid solved problem. Close issue.