Reflink

bcachefs supports reflink, similarly to other filesystems with the same feature. cp –reflink will create a copy that shares the underlying storage. Reading from that file will become slightly slower - the extent pointing to that data is moved to the reflink btree (with a refcount added) and in the extents btree we leave a key that points to the indirect extent in the reflink btree, meaning that we now have to do two btree lookups to read from that data instead of just one.