Created attachment 1738054 [details]
snapshot booting patch

Description of problem:
Installing new kernels under the following setup do not get the right path to the kernel:
btrfs as file system
boot as part of root instead of separate partition
snapper configured so the default subvolume of the btrfs is the current root/snapshot
in /etc/default/grub having:
SUSE_BTRFS_SNAPSHOT_BOOTING=true

Version-Release number of selected component (if applicable):
grub2-common-2.04-31.fc33.noarch


How reproducible:
install a new kernel and the path in the generated bls will have a path relative to the root subvolume instead of the default one


Steps to Reproduce:
1. Install a system as described above
2. Install a new kernel

Actual results:
For example, after installing kernel 5.9.12-200
/boot/loader/entries/xxx-5.9.12-200.fc33.x86_64.conf:
linux /root/boot/vmlinuz-5.9.12-200.fc33.x86_64
initrd /root/boot/initramfs-5.9.12-200.fc33.x86_64.img


Expected results:
It should have generated
linux /boot/vmlinuz-5.9.12-200.fc33.x86_64
initrd /boot/initramfs-5.9.12-200.fc33.x86_64.img



Additional info:
/etc/grub.d/10_linux (grub2-tools) seems to be able to handle it. The issue is in /usr/lib/kernel/install.d/20-grub.install (grub2-common). After reviewing how 10_linux works attached patch seems to fix the issue. Note that the check is overly cautious and checks that the FS is actually btrfs and not only the SUSE_BTRFS_SNAPSHOT_BOOTING flag. Since the GRUB_FS variable is not available it is currently expanded