/usr/lib/x86_64-linux-gnu/libbtrfs.so is in btrfs-tools 3.17-1.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libbtrfs.so.0.1
/usr/lib/x86_64-linux-gnu/libbtrfs.so.0.1