https://btrfs.wiki.kernel.org/index.php/FAQ#Does_grub_support_btrfs.3F
Does anyone know if this is still a problem on Btrfs if grubenv has xattr +C set? In which case it should be possible to overwrite and there's no csums that are invalidated. I kinda wonder if in 2018 it's specious for, effectively out of tree code, to be making modifications to the file system, outside of the file system. -- Chris Murphy
