v3 posted here:
https://www.redhat.com/archives/libguestfs/2019-July/msg00200.html
v4:
- The first patch in the v3 series was just a trivial doc whitespace
fix so I pushed it.
- There's a new patch using the nbdkit-retry-filter. This is not
actually upstream in nbdkit but we know enough about how it will
work.
- Rebased against master and reran the tests.
Rich.