A minimal statically linked 'btrfs device scan' replacement for busybox based initramfs builds.
btrfs-progs has too many dependencies to be easily statically compiled.
Example initramfs script usage:
echo "Waiting for devices..."
sleep 1
echo "Registering BTRFS block devices"
echo "Root partition candidates:" /dev/sd[a-f]2
/bin/btrfs-register /dev/sd[a-f]2
...then proceed to mount the root filesystem.