Comment 3 for bug 1662107

I am the upstream maintainer of this module.
The compilation problem has been fixed as of version 2.2.6.
https://github.com/akiradeveloper/dm-writeboost/commit/08b96fcad9d223aa80f9ac76ddb677e056066b48
I recommend all users to upgrade to the latest version immediately because some other important fixes are included since 2.1.1.

By the way, I will release 2.2.7 or 2.3.0 soon. Keep watching.