Specify root dataset as KCL argument to ZBM, so I can add menuentry to rEFInd

[nybblr]

I have a dual boot setup of Ubuntu and Fedora. Both run off of one ZFS pool. I successfully have both booting:

1. Boots into rEFInd, which has a menu entry for ZBM
2. Booting into ZBM, from there I can select one of two bootable datasets (mountpoint=/)

I'm trying to add two more dedicated menu entries to rEFInd so I don't always have to click through ZBM. Here's my refind.conf:

menuentry "Fedora" {
    icon /EFI/refind/themes/refind-theme-regular/icons/128-48/os_fedora.png
    loader /EFI/ZBM/VMLINUZ.EFI
    options "root=ZFS=rpool/ROOT/fedora_hunk3r ro quiet loglevel=0 zbm.skip"
}

menuentry "Ubuntu" {
    icon /EFI/refind/themes/refind-theme-regular/icons/128-48/os_ubuntu.png
    loader /EFI/ZBM/VMLINUZ.EFI
    options "root=ZFS=rpool/ROOT/ubuntu_frpkgs ro quiet loglevel=0 zbm.skip"
}

menuentry "ZBM" {
    icon /EFI/refind/themes/refind-theme-regular/icons/128-48/os_linux.png
    loader /EFI/ZBM/VMLINUZ.EFI
    options "ro quiet loglevel=0 zbm.show"
}

Right now, the root= argument doesn't do anything. My hope was to tell ZBM which dataset to boot from (hence zbm.skip). But it instead just uses the default bootfs as specified for the pool.

Is there currently a way to accomplish this?

[zdykstra]

There isn't a way to pass that in to ZFSBootMenu currently. It could potentially be added in, but there'd need to be some pretty careful work done to make it play nicely with the rest of the setup/import code.

[nybblr]

Thanks @zdykstra, is there perhaps a different way to tackle this that comes to mind? (With current feature set).

[zdykstra]

We're going to add in the zbm.bootfs argument that will accomplish what you want. It'll be part of an up-coming release. The only other way to do it with the current feature set is to use multiple pools, and have zbm.prefer pick which pool to use, which then causes ZFSBootMenu to prefer the bootfs value on that pool.

I'll tag you on the PR so that you can test the EFI that CI/CD builds for us as part of the PR process, if you're interested.

[nybblr]

Great, happy to test the bootfs PR when that's underway!

RE multiple pools, the one pool has already taken over two drives (mirrored) and I learned the hard way you can't shrink a pool. Not ready to install a third drive haha.

[zdykstra]

@nybblr if you're feeling brave, please grab one of the CI/CD artifacts from #741 at https://github.com/zbm-dev/zfsbootmenu/actions/runs/14483289003?pr=741 and give them a shot. ZFSBootMenu now accepts zbm.bootfs as a parameter that will override whatever is currently set on the pool. Let me know if you have any issues with it.

[zdykstra]

Followup - use the EFI from https://github.com/zbm-dev/zfsbootmenu/actions/runs/14500772072?pr=741 . zbm.prefer has been extended to allow you to specify a dataset; that will be used in place of the bootfs value set on the pool.

[nybblr]

@zdykstra I'll take this for a spin soon! I love the zbm.prefer approach.

[zdykstra]

Any luck with testing this?

[nybblr]

Sorry for the radio silence! In between upgrading OSes and breaking a ton of stuff, haven't been comfortable fiddling with the bootloader yet.