[Libguestfs] [PATCH 0/9] Add filters to nbdkit.

The first three patches are identical to: https://www.redhat.com/archives/libguestfs/2018-January/msg00079.html "[PATCH nbdkit v2 0/3] Refactor plugin_* functions into a backend" The rest of the patches add filters using the new filter API previously described here: https://www.redhat.com/archives/libguestfs/2018-January/msg00073.html This needs a lot more testing -- and tests -- and I also want to write a couple of more complicated filters to prove the point that the API allows different plugin methods to be called from a single filter method. However the two included filters (delay and offset) do appear to work well. Rich.