[Libguestfs] [PATCH nbdkit 0/9] [mainly for discussion and early review] Implement extents.

I want to post this but mainly for discussion and early review. It's not safe for these patches to all go upstream yet (because not all filters have been checked/adjusted), but if any patches were to go upstream then probably 1 & 2 only are safe. File, VDDK, memory and data plugins all work, although I have only done minimal testing on them. The current tests, such as they are, all pass. We probably do need more testing of the extents feature specifically. I have only tested against qemu (3.1.0) not against any other clients (if any exist that support this feature?) For reference the original plan which I'm working to is here: https://www.redhat.com/archives/libguestfs/2019-March/msg00017.html https://www.redhat.com/archives/libguestfs/2019-March/msg00021.html Rich.