/usr/share/man/man8/btrfs-zero-log.8.gz is in btrfs-progs 4.7.3-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/man/man8/btrfs-rescue.8.gz
/usr/share/man/man8/btrfs-rescue.8.gz