Prefer XBOOTLDR to ESP when installing unified kernel images.

[VasilisMylonas]

When installing unified kernel images images (uefi=yes) dracut currently searches /efi, /boot/efi and /boot to determine where the ESP is mounted. I suggest that the install location be instead queried by bootctl -x in order to also support a possible XBOOTLDR partition.

[jpetazzo]

I just ran into this :)

I'm using Unified Kernel Images. (My end goal is to encrypt my rootfs with LUKS and store the key in the machine's TPM. For that, I need to use SecureBoot to protect the boot chain, and I understand that UKI is a good way to achieve that.)

The machine is a dual boot machine, and Windows has created a 100 MB ESP partition. I have therefore created a separate XBOOTLDR partition. They are respectively mounted on /efi and /boot.

It looks like dracut systematically installs UEFI images to the ESP partition (if it detects that /efi is a mountpoint, it will install to /efi instead of /boot):

https://github.com/dracutdevs/dracut/blob/master/dracut.sh#L1125

That's problematic if the ESP partition is too small, because Unified Kernel Images tend to be pretty big, especially when adding e.g. a recovery image too.

I've tried to move the image (from /efi/EFI/Linux to /boot/EFI/Linux) and it seems to boot fine; but perhaps that's specific to the bootloader that I'm using (systemd-boot). I don't know if that would still work with other bootloaders; perhaps that's why dracut puts the UEFI images in the ESP partition.

This is my first time using dracut; so perhaps I'm doing something wrong - I'm happy to hear what others think before trying to suggest a PR. :)

[aafeijoo-suse]

@jpetazzo Thanks for your detailed use case, it makes sense to try to fix this.