Package: ftp.debian.org Severity: normal blktap was replaced by blktap2 <https://wiki.xen.org/wiki/Blktap2> in current versions of Xen. It hasn't been possible to build a kernel module with this package since Linux 4.12 (#874751), over a year ago. The related userspace code (blktap package) was also broken by glibc changes around the same time.
Ben.