btrfs subvolume create /var/lib/libvirt/images/
chown libvirt-qemu:kvm images
chattr +C /var/lib/libvirt/images

create root subvolume

mount /dev/sda1 /tmp/btrfs
btrfs subvolume set-default 5 /tmp/btrfs
cd /tmp/btrfs
btrfs subvolume create @

add “ rootflags=subvol=@ ” to grub kernel options

if update-grub fail check this